Abstract:This paper presents a microgrid composed of photovoltaic (PV) array‐battery energy storage (BES) and a diesel generator (DG) set. A bidirectional DC–DC converter (BDDC) is used to integrate the BES to the DC link of the voltage source converter. The BDDC controls the voltage at the DC link to the output voltage of the maximum power point tracking (MPPT) controller, thereby PV array always operates at its maximum power point (MPP). Another function of the BDDC is to block the second‐order harmonic from the BES, when the microgrid is feeding with unequal loads in the three phases. The magnitude of DG set terminal voltages is regulated by an electronic automatic voltage regulator (AVR) that controls the excitation to the synchronous generator. A fast, accurate and oscillations‐less modified variable step size least mean square based adaptive control is used here for improving the power quality. The main features of this microgrid topology are the operation of the PV array at its MPP in all operating scenarios, regulation of DG set voltages, harmonics elimination, balancing of DG set currents and reactive power compensation for the unity power factor operation.
Abstract:In this study, a proportionate power sharing among the parallel inverters operating in an islanded microgrid is achieved using droop and virtual inductance control. The same droop coefficients are used to achieve the frequency regulation as well. The frequency changes which are inevitable in droop control are measured and used to emulate the behaviour of damping and inertia to the DC link voltage using hybrid energy storage system consisting of battery and supercapacitor units. The proposed DC link voltage regulator restores the DC link voltage quickly by providing power corresponding to the rate of change of frequency and frequency deviation. This reduces the impact of voltage variations on the DC-load and keeps modulation index within the linear range for voltage source inverter. The design aspects of DC link voltage regulator, damping and inertia constants, selection of battery and supercapacitor units based on rating of the DC link voltage are discussed. The proposed decentralised droop control and DC link voltage restoration methods are validated through detailed simulation and experimental studies.
Abstract: This study presents the control of distribution static compensator (DSTATCOM) using band-dependent variable step size (BD-VSS) individual weighting factor with sign error based adaptive filter for power quality improvement in a weak distribution grid. Here, the proposed algorithm is used for estimation of fundamental active weight components from the distorted load currents in order to generate the reference grid currents to mitigate the grid currents power quality issues. This new control algorithm is proposed for fast and accurate estimation of active weight components with low steady-state error, without dynamic oscillation at fast convergence speed. Moreover, the frequency locked loop-double self-tuning second-order generalised integrator based voltage filter is used to extract the positive sequence voltages of the distorted grid voltages for estimating the harmonics, and noise-free voltage unit templates. Therefore, the DSTATCOM with the proposed control algorithm is capable of mitigating the harmonic currents, providing reactive power compensation and operating at unity power factor in a weak distribution grid. Test results demonstrate the viability and robustness of the proposed control algorithm under balanced and unbalanced non-linear load conditions.
Abstract:The incorporation of ancillary services on dis-tributed generators (DGs) at utility level has imposed severalchallenges on the existing distribution networks. To address oneof such problem, this paper discusses the impact of ancillaryservices, mainly the voltage ride through (VRT) capability andactive power curtailment control (APCC) of DGs on their anti-islanding protection scheme (AIPS). In this study, different typesof load models (viz. ZIP, induction motor (IM) and compositeloads) have been considered and non-detection zone (NDZ)characteristics are obtained for a modified IEEE 1547/ UL 1741test system for analyzing the problem. Further demonstrationof this issue has been carried out by conducting time domainsimulations in PSCAD/EMTDC platform on modified IEEE 1547and CIGRE low voltage benchmark test system having compositeloads at each of the load buses. Finally, an appropriate mitigationframework has been proposed by incorporating a hybrid island-ing detection technique to enable simultaneous implementation ofVRT, APCC and AIPS in DGs. The online implementation of theproposed framework is realized in MATLAB/Simulink platformand real-time simulations are performed in OPAL-RT (OP5600)test bed on the modified IEEE 1547/ UL 1741 test system forvalidating its efficacy.
Abstract:The relative share of renewable energy, specifically the solar photovoltaic (PV), is increasing exponentially in the world electric energy sector. This is a cumulative result of reduction in the cost of solar panels, improvement in the panel efficiency, and advancement in the associated power electronics. Among different types of PV plants, installation of small-scale rooftop PV is growing rapidly due to direct end-user benefits and lucrative governmental incentives. There are various standards developed in regards to grid integration of PVs and other distributed generations (DGs). Different power converter topologies are developed to interface the PV panel with the utility grid. To keep up with the stringent regulations imposed by the standards, various control strategies and grid synchronization methods have been developed. This review article amalgamates and summarizes all of the aforementioned aspects of a grid-integrated PV system including various standards, power stage architectures, grid synchronization methods, operation under extreme events, and control methodologies, pertaining to small-scale PV plants. This article will help freshman researchers to gain some familiarity with the topic and introduce them to some of the key issues encountered in this field.
Abstract:A solar photovoltaic (PV)-battery energy storage-based microgrid with a multifunctional voltage source converter(VSC) is presented in this article. The maximum power extractionfrom a PV array, reactive power compensation, harmonics mit-igation, balancing of grid currents and seamless transition fromgrid connected (GC) mode to standalone (SA) mode and vice versa,are performed in this system. Whenever the grid fails, this systemoperates in SA mode automatically, thereby without causing anyinterruption in supplying the load. Similarly, it automatically shiftsto the GC mode, when the grid is restored. The VSC functions incurrent control for GC mode, and it operates in voltage controlfor SA mode of operation. This system is capable of extracting themaximum power from the solar PV array irrespective it is operatingin the GC mode or SA mode. The charging and discharging of thebattery are controlled by using a bidirectional dc–dc converter. Itregulates the dc-link voltage to the maximum power point voltageof the PV array. If the absence of the battery is detected, thenthe control is automatically shifted to VSC for performing theextraction of the maximum power of the PV array.
Abstract:The presence of phasor measurements in ac systems provides a range of protection techniques based on sequence components and phase comparison to discriminate the fault. However, the absence of phasor measurements in dc system reduces the available alternatives for fault detection. In addition, the presence of low fault tolerant converters, large range of fault impedance and varying grid conditions demands sensitive and selective protection schemes. In this regard, several recent works have suggested a communication-based primary protection due to its high sensitivity to faults. However, with a failure in the communication network, the primary protection will also fail to detect a fault. This paper proposes a backup scheme to isolate the faulty section, even in the case of a communication failure. In the literature, overcurrent- and undervoltage-based backup protection schemes are suggested along with unit primary protection. In the presence of low fault tolerant converters and variable fault resistances, the traditional backup schemes may not work well. This paper proposes a new fault detection method for backup schemes, which utilizes only the locally measured current signal, and uses both derivative and integral characteristics of current to ascertain the occurrence of a fault. The proposed method is capable of detecting the fault accurately and within the required time. The performance of the proposed scheme has been assessed on a � 600 V TN-S grounded dc microgrid under various conditions using hardware-in-loop simulations on real-time digital simulator.
Abstract:Switched-mode power converters are used to interface equipments andconsumer electronic devices over a wide range of power levels. The switch technology ofany power converter is a signature of its power rating. The article discusses differentpower electronic switch technologies used in modern power supply implementation andevaluates their impact in the system design. From the design prospective, power loss ismore important than efficiency. It can be established that as power level of converter goesup, it is indispensable to have higher efficiency due to thermal design considerations.A trend between the switching frequency and its efficiency with respect to the powerrating of the converter has been inculcated in the article.
Abstract:In this paper, the effect of jamming in free space optical (FSO) link, is evaluated by deriving closed-form expressions of the bit error rate (BER) and outage probability (OP) for single-input single-output (SISO) and multiple-input single-output (MISO) FSO systems. The effects of partial-band jamming and broadband jamming over the error performance of the considered FSO systems are also analyzed. The jammer behaves as a random noise source, following the negative exponential distribution-due to the atmospheric turbulence. Therefore, in the presence of jammer, the error performance of FSO systems is governed by the additive negative exponential noise. It is shown by a rigorous analysis that a MISO FSO system can significantly mitigate the effect of jamming. Specifically, we consider a 2×1 FSO system for analysis, and demonstrate the improvement in BER and OP performance an FSO system can gain by using an additional spatial dimension, in the presence of a random jammer. The mitigation of jamming, due to implementation of arbitrary transmit apertures, is also verified through simulation results; which lies in complete agreement with the analytical results. Also, the error performance under the jamming effect is studied numerically over the Gamma-Gamma fading channel incorporated with pointing error effect.
Abstract:Synchronous reference frame (SRF) control strategy for solar photovoltaic (SPV) sources is widely used to delivermaximum power to the grid. However, poor inertia support just after a disturbance and improper phase angle tracking inpresence of the harmonics and system unbalance are noticed when the conventional phase-locked loop (PLL) based SRFcontrol structure is used. In this study, an inertia enhancement method for inverter interfaced SPV sources is proposed, whichadjusts only the PLL parameters with a notch filter (NF) in the SRF controller. NF in PLL is used due to its disturbance rejectionpotential and accurate phase angle tracking, even during system unbalance. The dynamic equation of pseudo induced voltage(PIV) vector with respect to the point of common coupling is derived. The kinematic equation of the PIV angle vector correlatesinertia contribution and inverter terminal voltage. The impact of the change in PLL parameters on inertia enhancement isanalyzed by validating the proposed technique on a test system in the real-time digital simulator. The frequency response by theproposed method has been compared with two state-of-art methods to prove the superiority of the proposed approach inenhancing the inertia of the SPV source in a microgrid.
Abstract:Point wind velocity measurement given by nacelle-top mounted sensor may not be same as effective wind velocity, which strikes the wind turbine rotor blades. This article proposes a new method for the computation of effective wind velocity by inverting the turbine's aerodynamic model after estimating the turbine torque and its rotor speed. Nonlinear control theory-based sliding mode observers are used to estimate the wind turbine generator induced speed emfs, rotor speed, and aerodynamic torque imparted to generator shaft. While satisfying the Lyapunov inequality condition, design aspects of sliding mode observers are discussed in detail. The performance of the proposed wind velocity estimation method is evaluated by using permanent magnet synchronous generator-based wind turbine emulator in laboratory. Simulation and experimental studies confirm that the estimated wind velocity under different wind profile conditions is accurate and can be used in various control algorithms in wind energy conversion systems.
Abstract: Utility-interfaced power electronic systems use a grid synchronizing framework, known as phase locked-loop and need transformation of sinusoidal signals to rotating dq reference frame, for control purpose. The voltage or current signal parameters including instantaneous fundamental frequency, phase angle, amplitude need to be captured in presence of harmonics, noise and DC offset. This work proposes an adaptive estimation scheme for the same, using recursive least squares with time-varying covariance gains. Proposed adaptation of gain presents faster transient response and noise-tolerant steady-state response, achieving optimal trade-off between the two. Covariance resetting mechanism is presented for better dynamic profile during step-changes in the signal. The scheme for single phase signal transformation is extended for transforming three phase unbalanced sinusoids to decoupled double synchronous reference frame. Stability analysis, design guidelines and discrete-time realization of proposed methods is provided for reproducibility. Theoretical deductions of proposed method are supported with several comparative test cases simulated in MATLAB/Simulink as well as the experimental results.
Abstract: This article proposes an optimal charging and dis-charging schedule for a hybrid photovoltaic-battery system con-nected in the premises of a residential customer. The schedulingstrategy is formulated to minimize the electricity bill of the cus-tomer. The proposed scheme uses the data obtained from short-term load, weather, and solar forecasting. A time-of-use tariffscheme is considered to be implemented by the utility. The proposedmethod is tested on real residential load and solar generationscenario. The test results verify that the implementation of theoptimal battery scheduling algorithm can significantly increase thenet saving in the electricity bill of the customer.
Abstract:System inertia plays a vital role in controlling theangular stability of the system during a disturbance. Due toincreased penetration of power electronic interfaced sources, suchas Solar Photovoltaic (SPV) source, the overall system inertiareduces and varies depending on their operating conditions. Inthis paper, an approach for online inertia estimation in thepower system network with SPV sources is proposed, using thesynchronized measurements from Phasor Measurement Units(PMUs). An equivalent swing equation is used to emulate thenetwork dynamics. A relationship between the inertia constantand the roots of this equation is determined. In order tonumerically obtain the roots, the Estimation of Signal Parametervia Rotational Invariance Techniques (ESPRIT) method is firstused to find the modes present in the frequency signal. A newformulation is proposed to extract an equivalent mode from allthe obtained modes. Also, to avoid phase step error, Rate OfChange Of Frequency (ROCOF) is estimated from the equivalentmode of the frequency signal. Results obtained for the39busNew England system for various test cases, using Real-TimeDigital Simulator (RTDS), prove the efficacy and superiorityof the proposed approach over the existing approaches in theliterature.
Abstract: This paper develops a robust control strategy forvoltage regulation of customer-end AC loads, where the lowvoltage multi-terminal DC network has been used for powerdistribution purpose. The control law for load-end DC-ACconverter is synthesized by Lyapunov’s direct method usingbackstepping design process. The resultant control action issimply obtained by linear combination of states and referenceset-points, and do not add extra dynamics into the systemavoiding complexity. The proposed method does not require loadcurrent measurement. Simulation studies in MATLAB/Simulinkshow better dynamic performance compared to conventional PIcontrollers. The experimental results from a laboratory-scaleprototype demonstrate robustness of proposed controller againstvariations in type and amount of load profile as well as DCvoltage.
Abstract: In this article, the presented work proposes a power management scheme in a dc microgrid by utilizing integrated device level control designs. Dynamics of nondispatchable energy sources, energy storage systems, and critical loads while synthesizing the control scheme are extensively studied. The presented work focuses on the integrated operation of local converter controls and power control unit during load fluctuations, environmental changes, accidental islanding, state of charge (SOC) breach, etc., without any time-critical information sharing. Low bandwidth communication (LBC) assisted control actions are enabled only in response to specific events such as battery management system (BMS) operation in autonomy, onset of peak hours, and load shedding. This article examines small signal analysis of individual interfacing converters to conduct eigenvalue studies of the closed-loop control systems. Successful control transitions are achieved in real-time digital simulator to validate the proposed management strategy under various system conditions. Hardware-in-the-loop setup validates the implement-ability of the control strategy in dc microgrids.
Abstract:In this paper, the groundwork on jamming effect and its alleviation mechanismsin free space optical (FSO) communication are studied over Gamma-Gamma (GG) fadingchannels along with the pointing error (PE) effects. A closed-form expression of the biterror rate (BER) is evaluated analytically for a single-input single-output (SISO) FSO systemin the presence of jammer. The worst case jamming condition for maximization of erroris calculated numerically. The jammer channel is considered to be GG distributed. Beingthe most dominating noise, the jamming signal is acted as the only noise source in theconsidered FSO set-up. Therefore, this study is performed over additive GG noise channel.The error performances are investigated for different atmospheric turbulence (AT) regimes(weak to strong) and for different PE parameters of jamming noise. Moreover, to combatthe jamming effect, a multiple-input single-output (MISO) FSO system is considered. Aclosed-form expression of the BER of the multiple transmit channels over the GG noiseis analytically calculated. The analytical results for both SISO and MISO FSO systems areverified with the help of the simulation results obtained by MATLAB software. It is establishedthat MISO FSO performs better than SISO FSO system in terms of BER performance underthe influence of jamming noise. Furthermore, many important observations are made uponthe BER performances for different AT and PE parameters for SISO and MISO FSO systems.
Abstract:This article elucidates a real-time energy management strategy for a smart residential apartment building having nonidentical occupants at the dwelling units (DUs). The aim of the present article is to design a distributed energy management algorithm, which can optimize the real-time demand of the entire building against abruptly updated rooftop solar generation and real-time price (RTP) of energy. The proposed energy management strategy differentiates among the DUs by considering a new parameter named load criticality level, which is defined as the value imposed by the DU residents to their power consumption. The optimization portfolio is developed as a novel bilevel, stochastic, multiobjective optimization problem where the maximization of utility of the consumed power is considered simultaneously with the cost minimization. To this end, a virtual energy trading platform is designed in this article between central building management system and the DUs, where they interact with each other by following the directives of single-leader multifollower Stackelberg game. The solution strategy is proposed as a Lyapunov optimization, which needs only the current values of the uncertain parameters, such as load variation, renewable generation, and energy price, and do not require any knowledge about their probabilistic variation, to eliminate the complexities regarding time average stochastic equations. Strenuous simulation on real-time data of four DUs, it is proved that the proposed framework can track the abrupt change in RTP and solar generation efficiently. Comparing with two benchmark methods viz. centralized process and greedy algorithm, the superiority of the designed energy management portfolio is established.
Abstract: In this work, the authors consider the communication network of a power substation, where multiple intelligent electronic devices (IEDs) transmit their delay sensitive control and monitoring messages to a common receiver over a wireless network; in the presence of a broadband jammer, which is capable of jamming multiple channels simultaneously. The objective of the IEDs is to successfully transmit their messages within a specified time, whereas the jammer wants to obstruct IED's transmission. A novel utility function is designed for the players, that addresses the time-critical nature of communication. Due to the conflicting interest of the IEDs and the jammer, they model the interaction between them as a repeated Bayesian zero-sum game, which also addresses the repeated interaction among the IEDs and the jammer, and the unavailability of exact information about the jammer. The equilibrium strategies for both the scenarios of perfect and imperfect monitoring are derived and verified through simulation results. Further, the performance of the proposed game model in various scenarios is thoroughly compared in the result section. Finally, the efficacy of the proposed defence strategies is tested in a practical communication network of a power substation under jamming, which is simulated in Optimised Network Engineering Tool (OPNET).
Abstract:This paper deals with the design and stability analysis
of a DC microgrid with battery-supercapacitor energy storage
system under variable supercapacitor operating voltage. The
conventional design method reported in the literature considers
the rated supercapacitor voltage in the modeling and design of
controllers. However, the supercapacitor unit can discharge as
low as 10% of its rated voltage due to self discharge. It is observed
that the conventional method of controller design can potentially
make the system unstable or introduce ringing in the DC link
voltage at low supercapacitor voltage. In this work, the sensitivity
of DC microgrid stability with respect to supercapacitor voltage
variation is analyzed, an optimal supercapacitor voltage to be
considered in the design is calculated and a design method is
proposed to ensure the stability of DC microgrid in all operating
modes. The stability of the DC microgrid with controllers
designed using the proposed method is evaluated with digital
simulation and experimental studies.
Abstract:This paper proposes a centralized control strategy
for power management of hybrid microgrid connected to the
grid using a parallel combination of grid side converters (GSCs).
An improved version of instantaneous symmetrical component
theory (ISCT) is developed and is used for the control of parallel
operated GSCs, which results in reduced sensor requirement,
control complexity, and communication bandwidth. In addition,
a simple power management algorithm is developed to test the
efficacy of the proposed parallel grid side converter control
strategy for all the microgrid modes considering state of charge
(SOC) limits of hybrid energy storage system (HESS), load
changes, and renewable power variations. In the proposed system,
a better dc link voltage regulation is achieved and usage of
supercapacitor reduces the current stresses on the battery. With
the proposed control strategy, the essential features of grid
side converters like power quality, power injection, bidirectional
power flow and proportional power sharing are achieved. The
effectiveness of the developed control strategy for the proposed
system is tested using MATLAB based simulink environment and
validated experimentally using a laboratory prototype.
Abstract:The AC-DC distribution systems have recently gained huge popularity due to advancements in power converters, high penetration of renewable energy resources and wide usages of DC loads. However, load flow in such systems is a challenging task due to non linear characteristics of power converters. This paper presents a novel load flow algorithm for AC-DC distribution systems, utilizing the concept of graph theory and matrix algebra. Four developed matrices, loads beyond branch matrix [LB], path impedance matrix [PI], path drop matrix [PD], slack bus to other buses drop matrix [SBOBD] and simple matrix operations are utilized to obtain load flow solutions. These matrices reveal the network topology and relevant information about the behaviour of AC-DC distribution network during load flow studies. In contrast with traditional load flow methods for HVDC systems, the proposed technique does not require any lower upper (LU) decomposition, matrix inversion and forward-backward substitution of Jacobian matrix. Because of the aforementioned reasons, the developed technique is computationally efficient. The proposed method has been tested using several case studies of AC-DC distribution network which includes different operating modes of various power converters. Results show feasibility and authenticity of the proposed method.
Abstract: Home energy management systems (HEMS) encourage
participation of residential consumers into the demand response
programs. This paper proposes a robust-CVaR (Conditional Value at
Risk) optimization approach for day ahead HEMS to reduce the effect
of risk of real time exposure to energy price and solar power
generation uncertainties. Initially the CVaR method is integrated
with the Two-point Estimation (2PE) analysis to approximate the
solar power, modelled as Beta probability distribution function, in
low computation effort compared to conventional Monte Carlo
Simulation (MCS) based CVaR approach. Then the optimization
constraints are revised to their robust counterparts by accounting a
certain amount of uncertainty in the energy prices from their nominal
values. Unlike previous literatures, the optimization problem is
developed to minimize the risk value of the energy cost. Again to
maximize the life of the plug in electric vehicle (PEV) a pseudo cost
function for the PEV battery degradation is proposed. The entire
optimization portfolio is developed as a mixed integer linear
programming (MILP) for its easy execution. Simulation is
demonstrated on a smart home, designed as an AC-DC microgrid
(MG), having practical appliance data sets, to prove the efficacy of the
Abstract: In this paper, we study the physical layer secrecy performance of a hybrid satellite
and free-space optical (FSO) cooperative system. The satellite links are assumed to follow
the shadowed-Rician fading distribution, and the channel of the terrestrial link between
the relay and destination is assumed to experience the gamma–gamma fading. For the
FSO communications, the effects of different types of detection techniques (i.e., heterodyne
detection and intensity modulation with direct detection) as well as the pointing error are
considered. We derive exact analytical expressions for the average secrecy capacity and
secrecy outage probability (SOP) for both cases of amplify-and-forward (AF) and decodeand-
forward (DF) relaying. The asymptotic analysis for the SOP is also conducted to provide
more insights on the impact of FSO and satellite channels on secrecy performance. It is
found that with the AF with fixed gain scheme, the secrecy diversity order of the investigated
system is only dependent on the channel characteristics of the FSO link and the FSO
detection type, whereas the secrecy diversity is zero when the relay node employs DF or
AF with variable-gain schemes.
With increased integration of wind energy systems, an accurate wind speed forecasting technique is a must for the reliable and secure operation of the power network. Statistical methods such as Auto-Regressive Integrated Moving Average (ARIMA) and hybrid methods such as Wavelet Transform (WT) based ARIMA (WT-ARIMA) model have been the popular techniques in recent times for short-term and very short-term forecasting of wind speed. However, the contribution of the forecasting error due to different decomposed time series on the resultant wind speed forecasting error has yet not been analyzed. This paper, thus explores this shortcoming of the ARIMA and WT-ARIMA models in forecasting of wind speed and proposes a new Repeated WT based ARIMA (RWT-ARIMA) model, which has improved accuracy for very short-term wind speed forecasting. A comparison of the proposed RWT-ARIMA model with the benchmark persistence model for very short-term wind speed forecasting, ARIMA model and WT-ARIMA model has been done for various time-scales of forecasting such as 1min, 3min, 5min, 7min and 10min. This comparison proves the superiority of the proposed RWT-ARIMA model over other models in very short-term wind speed forecasting.
With the rapid proliferation of the advanced metering infrastructure, the smart grid is evolving towards increased
customer participation. It is now possible for a utility to influence the customer demand profile via
demand side management techniques such as real-time pricing and incentives. Energy storage devices play a
critical role in this context, and must be optimally utilized. For instance, the peak power demands can be shaved
by charging (discharging) the batteries during periods of low (high) demand. This paper considers the problem
of optimal battery usage under real-time and non-stationary prices. The problem is formulated as a finite-horizon
optimization problem, and solved via an online stochastic algorithm that is provably near-optimal. The proposed
approach gives rise to a class of algorithms that utilize the battery state-of-charge to make usage decisions in
real-time. The proposed algorithms are simple to implement, provably convergent for a wide class of nonstationary
prices, easy to modify for a variety of use cases, and outperform the state-of-the-art techniques, such
as those based on the theory of Markov decision processes or Lyapunov optimization. The robustness and
flexibility of the proposed algorithms is tested extensively via numerical studies in MATLAB and real time digital
Abstract: Quick fault detection and isolation of faulty section are desired in DC microgrid due to the presence of power
electronic converters and low cable impedances. Owing to need of fast disconnection, limited time and data are available for
online fault distance estimation. Some of the existing techniques consider source capacitors connected at only one end of the
cable; therefore, assume that the fault current is contributed by only one end of the cable. This may not be true in the case of
multi-source DC microgrids, where fault current would be supplied from both the ends. Further, existing communication-based
techniques require either data synchronisation or fast communication network. To address these issues, this study proposes an
online fault location method for multi-source DC microgrid without using communication. The mathematical model of faulted
cable section connected to sources at both the ends is derived. This model is used along with the measurements to determine
the fault distance. The model consistency with the measurements is quantified using the confidence level based on the residual
analysis. A ring-type multi-source DC microgrid system is considered and simulated on real-time digital simulator to demonstrate
the effectiveness of the proposed algorithm.
Abstract:This paper deals with the protection of critical
loads from voltage-related power quality issues using a
dynamic voltage restorer (DVR). A generalized control algorithm
based on instantaneous space phasor and dual P -Q
theory has been proposed to generate the instantaneous
reference voltages to compensate the load voltages with
direct power flow control. The proposed algorithm adapts
energy-optimized series voltage compensation, which results
in a reduction of energy storage requirement. The
proposed DVR control scheme can support the load from
voltage-related power quality issues irrespective of the load
current profile. Each leg of the three-phase three-leg split
capacitor inverter is used to inject series compensation voltage
in respective phases of the system. Model-based computer
simulation studies and real-time experimental results
validate the effectiveness of the proposed control algorithm.
Abstract: Real-time visualisation of large power systems, by tracking the system states, is a challenging task as it involves
processing a large measurement set to obtain the system states. This study proposes a hierarchical parallel dynamic estimation
algorithm to estimate the states of a large-scale interconnected power system. The power system is decomposed into smaller
subsystems, which is processed in parallel to obtain a reduced order state estimate. This information is then transmitted to the
central processor, which collates the individual reduced order estimates to obtain the global estimates. Each processor uses
state matrix of smaller dimension, thereby reducing the computational burden. The low-level processors utilise only a fraction of
the global measurements in the proposed approach, and there is no need for any information exchange from the central
processor to the low level processors, which helps in reducing the communication requirements. Moreover, detection of
anomalies can also be carried out at the local processors without the need for any separate bad data detection at the central
processor. IEEE 30- and 118-bus systems are used as test beds to study the proposed approach.
Papers Published/Accepted in Conference Proceedings
Abstract:Microgrid with hybrid renewable energy sources is a promising solution where the distribution network expansion is unfeasible or not economical. Integration of renewable energy sources provides energy security, substantial cost savings and reduction in greenhouse gas emissions, enabling nation to meet emission targets. Microgrid energy management is a challenging task for microgrid operator (MGO) for optimal energy utilization in microgrid with penetration of renewable energy sources, energy storage devices and demand response. In this paper, optimal energy dispatch strategy is established for grid connected and standalone microgrids integrated with photovoltaic (PV), wind turbine (WT), fuel cell (FC), micro turbine (MT), diesel generator (DG) and battery energy storage system (ESS). Techno-economic benefits are demonstrated for the hybrid power system. So far, microgrid energy management problem has been addressed with the aim of minimizing operating cost only. However, the issues of power losses and environment i.e., emission-related objectives need to be addressed for effective energy management of microgrid system. In this paper, microgrid energy management (MGEM) is formulated as mixed-integer linear programming and a new multi-objective solution is proposed for MGEM along with demand response program. Demand response is included in the optimization problem to demonstrate it’s impact on optimal energy dispatch and techno-commercial benefits. Fuzzy interface has been developed for optimal scheduling of ESS. Simulation results are obtained for the optimal capacity of PV, WT, DG, MT, FC, converter, BES, charging/discharging scheduling, state of charge of battery, power exchange with grid, annual net present cost, cost of energy, initial cost, operational cost, fuel cost and penalty of greenhouse gases emissions. The results show that CO2 emissions in standalone hybrid microgrid system is reduced by 51.60% compared to traditional system with grid only. Simulation results obtained with the proposed method is compared with various evolutionary algorithms to verify it’s effectiveness.
Abstract:System inertia plays a crucial role in maintaining transient stability in a Power System (PS) network during a disturbance. Increased penetration of Renewable Energy Sources (RESs) into the system, makes the system inertia a variable quantity. Hence, the estimation of the system inertia under such scenarios is becoming more pertinent. In this paper, an energy function based approach is proposed for online inertia estimation using measurements from Phasor Measurement Units (PMUs). The synchronous machine's swing equation is used to emulate the system dynamics. The Potential Energy (PE) at a bus is calculated from the PMU measurement. A novel analogy is established between the inertia constant and the rate of change of PE. Real-Time Digital Simulator (RTDS) is used to illustrate the performance of the proposed approach on the WSCC 9 bus system. The superiority of the proposed approach is investigated by comparing the results with an existing method in the literature.
Abstract:In this paper an effective current based inverter efficiency computation method for a hybrid microgrid system consisting of renewable energy sources and energy storage systems is proposed. Using the proposed inverter efficiency computation method, the efficiency curve of a single inverter is obtained. Then, particle swarm optimization is used to solve the loss minimization function of a parallel inverter setup. In this work, instantaneous symmetrical component theory and power management algorithm (PMA) are used for generating reference quantities for various power electronic converters. Once, the reference quantity for the parallel inverter setup is obtained, the reference quantity sharing among parallel inverters is determined by particle swarm optimization to achieve optimal conversion efficiency. Apart from energy savings analysis, power quality aspects such as harmonic mitigation, reactive power support and unity power factor are achieved. The proposed control strategy is simulated using a MATLAB based simulink environment only during excess mode of microgrid by taking PV variations into account.
Abstract:This paper describes the power management in DC microgrid system which consists of solar energy system, Wind Energy Conversion System and Composite Energy Storage System. Both the sources are operated in Maximum Power Point Tracking (MPPT) mode to extract maximum energy from the respective sources. The intermittent nature of solar/wind power makes the output power fluctuating. To make it reliably available, a composite energy storage system is used. In the proposed scheme, off-MPPT control and dump load scheme are compared. A simulation study is carried out in MATLAB/Simulink to validate the proposed Power Management Algorithm (PMA).
Abstract:The popularity of wind turbine generator (WTG) in the field of harnessing maximum renewable-based generation has promoted doubly-fed induction generator (DFIG) based WTG in the power sector. Nevertheless, DFIG-WTG is highly influenced by the grid disturbances which further affects its fault ride through capabilities. Majority research work is focused on the symmetrical fault analysis. However, the asymmetrical fault has more pernicious influences on the DFIG system. This paper compares both the symmetrical and asymmetrical fault effect on the DFIG-WTG and presents a clear distinction on their impact. Further, power hardware in loop (PHIL) investigation is carried out to support the theoretical analysis. The system considered here is a 2.2 kW rated DFIG-WTG hardware setup, is connected to the distribution network which is simulated in real time digital simulator (RTDS), via a power amplifier. The experimentation results imply that the asymmetrical fault has a fatal impact on the DFIG wind system. Henceforth, it requires to develop a cost-effective technique to improve its fault ride through.
Abstract:The work presented investigates the dynamics of a reverse droop current controller and a conventional droop voltage controller in a distributed cooperative secondary control environment operating with the consensus aided communication network for a 5-bus DC microgrid (MG). The microgrid system considered has multiple distributed energy resources (DER) i.e. photovoltaic array and battery connected to 4 buses while the last bus serves as an interconnection for a remote load terminal. This aids in bolstering the performance analysis of the aforementioned controllers under various operating scenarios like switching networks, delay, plug-n-play, etc. The current dynamics being faster than the voltage dynamics, a single current controller could be employed instead of voltage controller or a cascaded voltage-current controller for reducing system complexity and achieving faster convergence. A low voltage DC microgrid test-system (48 V) assuming (semi) dispatchable energy sources at its inputs catering to local and remote resistive & constant power loads is considered in the study to investigate and validate the controllers' transient responses.
Abstract:The rapid growth of renewable energy integration
in existing power system network will pose a serious threat to
the system inertia due to replacement of synchronous generators
with null inertial power electronic converters interfacing renewables to the power system. To overcome this the interlinking
power electronic converters (ILC) are operated as synchronous
generators synthesizing virtual inertia. This paper proposes a
decentralized virtual inertial control scheme for Hybrid Energy
Storage systems (HESS) and ILC of Hybrid AC-DC microgrids to
cumulatively operate as a synchronous generator. The proposed
control scheme utilizes the high power density storage device
such as ultra-capacitor integrated to DC side to operate as
rotor mass to synthesize virtual inertia demanded by the power
system and battery as a virtual governer to fulfill the steady state
power deficit during islanded and community connected mode
of operation. The proposed control scheme is validated through
power hardware in loop simulation of a hardware prototype.
Index Terms—Virtual Synchronous generator, Hybrid AC-DC
microgrid, Battery, Ultra-capacitor, Interlinking converter
Abstract:The coordinated power-sharing among multiple
energy storages utilizing decentralized control is a persistent issue
in DC microgrid. Instead of using centralized and distributed
control strategies, a novel decentralized control scheme which
enables effective power management among the multiple Hybrid
Energy Storage Systems (HESS) is proposed. The proposed
control scheme manages the power flow irrespective of dissimilar
line parameters and dissimilar power ratings of converters
interfacing energy sources to DC microgrid utilizing a model
reference adaptive control-based voltage drop estimation
technique to maintain the DC bus voltage and share the load
demand proportionally. The efficaciousness of the proposed
control scheme is validated through small-signal analysis and
real-time simulation for versatile load transients.
Abstract: As Isolated DC microgrids (IDCMG) rely on
renewable energy resources (RES) to reduce carbon emissions,
running cost, etc., the reliability become serious issue due to their
intermittency and uncertainty. Diesel generators (DG) are used as
prevalent alternatives to suppress this issue. However, they suffer
from startup delay, frequent switching, and uneven loading when
embedded with RES that results in increased maintenance and
carbon footprint. Besides, their fuel efficiency and emission
characteristic vary with loading since most of DGs are driven by
constant speed engines. Effective power management techniques
play crucial role in conquering above issues. Hence, an exhaustive
power management scheme (PMS) is proposed in this paper by
considering the hybrid energy storage system. Further, this
strategy includes the extreme scenarios like DG failure/scheduled
maintenance, low power generation and battery charge. This
paper considers AC bus coupled IDCMG as study system so that
it can enclose both AC and DC loads/buses simultaneously. This
makes system more comprehensive to resemble various practical
isolated DC grids behavior. Simulation of the system is explored in
real time digital simulator (RTDS) platform to show efficacy of
Abstract:Penetration of DC distributed energy resources (DERs) and development of different DC loads necessitate the integration of DC distribution networks with the existing AC networks by deploying power electronics converters. This paper designs a centralized mixed integer linear optimization portfolio for optimal operation of a grid tied AC/DC hybrid distribution network having DERs and voltage source converters (VSCs) by leveraging the benefit of load shifting process. Power flow equations due to the presence of VSCs are modelled in this article to achieve power balance in the network at lowest energy cost condition. Simulation process is carried out on a modified IEEE 33-bus AC/DC distribution network. The case study shows that energy cost is reduced significantly due to inclusion of the load shifting process.
Abstract:This paper deals with the enhanced comb-frequency locked loop control approach for grid integrated single stage solar photovoltaic (PV) system. The PV array is interfaced to the grid using a voltage source converter (VSC). An incremental conductance technique is utilized to extract the peak power of the PV array. This control approach mitigates the power quality problems and provides the operation of the system smooth and fast. The developed prototype of the PV system is tested at different type of grid disturbances like harmonic distortions, and load unbalances. Moreover, the capabilities of proposed control are found superior compared to other control techniques. Test results of the grid interfaced PV system is used to validate the control algorithm.
Abstract:This paper deals with a double stage photo voltaic (PV) system connected to the grid and nonlinear load. In this work, an improved performance of the grid tied system is presented by using the CMPN (Continuous Mixed p-Norm) adaptive filter based control algorithm. Over the last few years, adaptive filter algorithms like LMS (Least Mean Square) algorithm are widely used due to its easy implementation, but unfortunately generation of impulsive noise in LMS deteriorates overall system performance. On the other hand, few adaptive p-norm advanced adaptive filtering algorithm have come into existence and hereby, this proposed CMPN (Continuous Mixed p-Norm) adaptive-algorithm, has fast convergence capability and easily adapted to control the complex power electronics circuits. This proposed adaptive control algorithm is verified by MATLAB simulation as well as a prototype is used for experimental verification. With this adaptive controlled process, the overall performance of the system is satisfactorily improved.
Abstract:This paper presents a dual operational mode namely voltage control (VC) mode and current control (CC) mode of a microgrid that consisting of a photovoltaic (PV) array, battery energy storage (BES) and a diesel generator (DG) set. The functional features of this microgrid, are harmonics elimination, balancing of DG currents, reactive power compensation, DG set terminal voltage regulation and extraction of PV array maximum power etc. An automatic voltage regulator (AVR) is employed in the field circuit of a synchronous generator for controlling DG set terminal voltages. The voltage source converter (VSC) of the microgrid operates in VC modein standalone (SA) operation and in CC mode in DG operation. The DG set in this microgrid, is used as an auxiliary energy source, which generates power only during low battery state of charge (SOC) and lower solar irradiation where the PV power is lower than the load power. This operation of microgrid ensures continuous supply to the connected loads without any interruption. A bidirectional DC-DC converter (BDC) is used to integrate the BES at the DC link terminals. Thus the second order harmonic during the unbalanced load is not fed to the battery hence it enhances the life of the battery. Simulated responses of proposed microgrid, are studied by using MATLAB/Simulink toolbox. The experimental performance of proposed system is carried out on a hardware prototype developed in the laboratory.
Abstract: In an active distribution network with increasing penetration of Distributed generators (DGs), it is critical to model DGs and keep the model updated for analysis. However, the generator parameter provided by the manufacturer changes because of aging and errors. Modeling parameters are typically provided by manufacturers and routinely adjusted with offline field testing. With availability of the high resolution real time measurement data such as μ-PMUs, parameter can be estimated without taking generator offline. Model validation and calibration allows non-intrusive estimation of the parameters in distributed generators. This work aims at estimating the state and transient reactances of a distributed synchronous generator based combined heat and power generation unit connected to a medium voltage distribution network. The state and parameter estimation is performed on-line using phasor data collected by micro-phasor measurement unit (μ-PMU) connected at the terminals of the machine. A constrained least-squares algorithm is used in recursion to track the changes in the state and parameter of the synchronous generator. The parameters are estimated considering different switching and dynamic events like faults, islanding, and load/capacitor switching. Results show the superiority of the proposed approach.
Abstract:The number of Electric vehicles (EVs) in the transportation fleet of many countries is increasing rapidly to tackle rising air pollution levels. In terms of running costs and ability to support the utility power grid, electric mobility clearly standsout amongst the non-fossil fuel based transportation alternatives. Electric vehicles are distributed energy storage units that can act as energy sources to the local distribution network. Therefore, EVs can work in two modes that support bidirectional power flow: charging or discharging known as Grid to Vehicle (G2V) and Vehicle to Grid (V2G) modes respectively. In the V2G mode, EVs can help the grid by providing reactive power support and also mainly by discharging during peak load times to improve efficiency & reliability, provide V/f regulation, manage renewable energy intermittency and provide load balancing with Demand Side Management (DSM) as a set of possible ancillary services. The challenges associated with V2G system include life cycles lost and battery degradation, changes required in the grid infrastructure/equipment, energy losses and the huge investment cost involved. This paper gives an account of the advantages and disadvantages of V2G system for EV owners and grid operators.
Abstract:In a competitive electricity market, it is unpredictable to analyze the behavior of participants from the view-point of another participant. In this case, the market can be realized by solving the individual's problem collectively, known as Equilibrium Problem (EP). The paper proposes a mathematical technique, called complementarity modeling, to solve an EP. Nash Equilibrium (NE) point is calculated, which gives the best possible solution for every participating player who is solving an interlinked optimization problem. A Cournot duopoly model is considered to frame the EP with the objective of profit maximization. Results are derived at NE using complementarity modeling and validated by solving the problem graphically using a derivative method. EP is also solved for Cournot duopoly and oligopoly test models using commercial software.
Abstract:Traditionally, to ensure the power system security a list of critical contingencies is shortlisted for detailed analysis. The system operator of transmission system (TS) considers the distribution system (DS) as a fixed aggregated load at the point of connection bus. The load value indicates the power demand of DS from the grid. However, this demand is no longer fixed if the uncertainties associated with renewable distributed generation (DG) units is taken into consideration. Thus, any component outage which is not severe may become critical when there is an increase in power demand by DS due to unexpected change in weather conditions. Hence, to prevent missing out a potential alarm signal during such events, the critical contingency selection (CS) has to be made considering the impact of uncertain distributed generation in DS. This paper proposes the methodology for transmission contingency selection based on decoupled-coordinated AC load flow between different system operators. Numerical simulations are performed on a test system to show the changes in contingency ranking due to uncertain renewable DG units.
Abstract:A distribution transformer is an important asset whose failure causes huge financial loss to a utility and scarcity of power for end consumers. One of the prime causes for failure of Distribution Transformers (DTs) is overloading. A Battery Energy Storage System (BESS) can reduce the stress on a DT by discharging itself during peak demand periods. An effective energy management methodology for BESS at DT level has been presented in this paper. A novel method for battery charging & discharging is proposed based on real-time net power flow measurements from DT and from load-side, considering penetration of rooftop solar Photovoltaic (PV) power at consumer end. BESS will be charged and discharged during off peak and peak demand periods respectively. The designed BESS has a bi-directional converter and solar PV with boost converter that are connected at the DC-link of their respective individual three-phase converters. The control logic for battery charging/discharging is developed in such a way that the power flow from distribution transformer shall not exceed 80 % of its rated capacity. The charging is performed under two modes of operation. Current control mode charging is preferred till battery SoC is 80%. Subsequently, voltage control mode of charging is performed up to 95% SoC level. The modeling and simulation is carried out in MATLAB® and results are presented to showcase the effectiveness of proposed control logic for different modes of operation. The proposed methodology will be tested and validated on real-time HIL testing platform for pre-pilot implementation validation.
Abstract:In this paper, a Battery Energy Storage System (BESS) based solution has been proposed to reduce the fluctuations in the output power of large solar Photovoltaic (PV) parks. This will contribute to reduction in the frequency deviations of large power systems and moderating pressure on conventional power plants with the increasing penetration of solar power. Solar PV smoothening is one such application of BESS to moderate inherent intermittencies of solar PV power plants. Different methods adopted for smoothening of solar PV output could lead to arrival of different sizes of the batteries. Thus, assessment of various methods to smoothen PV output power and scope of smoothening becomes significant. A technique has been proposed and has been evaluated against different existing methods for comparing the performance. The results from the proposed technique have been found to be encouraging in terms of determining the battery life and size.
Abstract:—Demand response analysis in smart grid
deployment substantiated itself as an important research area
in recent few years. Two-way communication between utility
and users makes peak load reduction feasible by delaying the
operation of deferrable appliances. Flexible appliance
rescheduling is preferred to the users compared to traditional
load curtailment. Again, if users’ preferences are accounted
into appliance transferring process, then customers concede a
little discomfort to help the utility in peak reduction. This
paper presents a novel Utility-User Cooperative Algorithm
(UUCA) to lower total electricity cost and gross peak demand
while preserving users’ privacy and preferences. Main driving
force in UUCA to motivate the consumers is a new cost
function for their flexible appliances. As a result, utility will
experience low peak and due to electricity cost decrement,
users will get reduced bill. However, to maintain privacy, the
behaviors of one customer have not be revealed either to other
customers or to the central utility. To justify the effectiveness,
UUCA is executed separately on residential, commercial and
industrial customers of a distribution grid. Harmony search
optimization technique has proved itself superior compared to
other heuristic search techniques to prove efficacy of UUCA.
Abstract:This paper investigates the performance assessment of droop controlled converters in a low inertia, low voltage DC microgrid scenario. It employs a generalized DC distribution network consisting of both current-controlled and voltage-controlled voltage source converters and a mix of constant impedance, constant current and constant power loads. Since in large distribution networks, lack of inertia is the cause of instability, virtual impedance based methods and capacitor control techniques have been proposed. A RC-based droop control strategy is employed in this work in order to impart inertia to the system thereby improving the transient performance of the network. The converters considered are both grid-feeding and grid-forming in order to analyze the response in the presence of dissimilar electrical energy sources. The grid-feeding converters, both voltage and current-controlled, are interconnected via communication layer and are governed by the consensus laws for multi-agent systems. The networked control systems aids in achieving proper load current sharing and desired voltage regulation. This is essential for the operation of critical loads. The study presents a comparative assessment of the response of RC-droop and conventional droop in the varied microgrid conditions. The cyber-physical system is modeled in MATLAB/Simulink and tested against various operating situations and cyber adversities to test the efficacy of the control law.
Abstract:This paper deals with a power quality improvement through MRZA-LMM (Modified Reweighted Zero-Attracting Least Mean M-estimate) with IMTOGI (Improved Mixed Third-Order Generalized Integrator) based control algorithm for a grid tied PV (Photovoltaic) system. The proposed control technique is used to control the PV panel power and to deliver the good quality at the utility distribution grid. The proposed control strategy is divided into two parts (1) extraction of fundamental weight component from the distorted load current and (2) extracting the unit template from the unbalanced and distorted grid voltage. The first objective is achieved through proposed MRZA-LMM control. It has fast convergence speed with low steady state errors. The prime objective of the control is met by the IMTOGI technique to estimate the balanced and sinusoidal grid synchronizing signals. This good quality of grid synchronizing signals are helpful to connect the AC/DC converter to the grid and injects the solar DC power into the main grid. The proposed control algorithm is through experimental results at steady state and transient conditions.
Abstract:Hardware-in-Loop (HIL) based simulation improveseffectiveness of system simulation process by enabling interactionwith part of the physical components. Hybrid ac/dc microgridscomprise of both dc and ac distribution, and comprise of differentsources, loads and storage, interfaced to either bus. A criticalfactor related to successful microgrid implementation is man-agement of energy interaction amongst the different components.The control systems for each of the different elements need to becritically validated in such a configuration. This paper presentsthe use of Typhoon HIL as the validation tool for control systemsfor all the constituents within hybrid dc-ac microgrid. Themodelled Micro Grid consists of Distributed Energy Resources(DERs) such as a PV plant, Diesel Generator, Fuel Cell, WindFarm, Micro-turbines, Battery Energy Storage System (BESS)and Converters. The simulation of Bidirectional Converter, con-nected between ac and dc buses, and its operation has beenvalidated first using Matlab Simulink, and then compared toTyphoon HIL 402 based simulation.
Abstract:Microgrid mandates a highly accurate and reliable protection measure for safe and secure operation. Reliability of the protecting system becomes a serious concern when the microgrid operates with various types of DG units which includes synchronous, induction and inverter based DGs with different topology and modes of operation. This paper demonstrates an intelligent protection scheme using deep neural network (DNN) to perform the task of fault detection and classification. Fault currents retrieved at the relaying points are given to the proposed protection scheme to perform the desired task. The performance of the scheme is measured with wide variations in system parameters such as modes of operation and network topologies of the microgrid. The scheme is extensively tested on a large dataset even by varying types of inputs and different deep neural network structures. The test results and response time show that the proposed algorithm can be used in real time for protective measures of microgrid.
Abstract:Electric Vehicles (EVs) are becoming an integral part of the transportation fleet in many countries. They have substantially progressed to become a mainstream component of the smart electricity grid and are catalyzing changes in policies and regulations relating to power distribution systems. EVs represent distributed storage units whose load depends on the driving patterns and the battery charging characteristics. Random and uncontrolled EV charging has implications on both the network loading and the charging cost since time-based pricing is in effect for many utility companies. A well-managed charging system is thus important and must consider asset loading as well as time-varying tariff. This paper presents a regulated charging scheme that takes into account the charging cost which is reflective of both the transformer loading and the utility-level Time of Day (ToD) tariff. The task of finding a charging schedule that gives the least overall charging cost for the day has been formulated as an optimization problem for an actual distribution utility in India. The driving pattern was estimated based on a survey of EV owners plying in the utility license area. The results demonstrate how such a controlled charging scheme can save on the customers’ money and help the utility manage its load curve by ensuring that the distribution transformers serving the EVs are not overloaded.
Abstract:Widespread adoption of Electric Vehicles (EVs) for light, medium, and heavy-duty applications has gained significant interest. Based on ownership and user preferences, light duty and local delivery medium-duty EVs are typically connected to grid distribution networks whereas larger medium duty and heavy-duty EVs are typically connected to distribution or even sub-transmission networks. Challenges with at-scale EVs and charging infrastructure supporting them include interoperability, distribution network upgrades, surge in demand charges, power quality issues, voltage stability, etc. Based on real-world data, steady-state and dynamic assessments of light-duty EV charging with a focus on DC Fast Charging (DCFC) for weak distribution grids is presented. Three main areas of contributions in this paper include - steady state and dynamic power quality measurements and assessments using real world data, transient assessments of light duty EV integration with weak distribution networks (IEEE 13 node feeder system) under grid-connected and microgrid modes, and formulation of an intelligent charging decision algorithm to enable an impact-minimal charging.
Abstract:Distributed generation sources having stochastic power-output characteristics, e.g. solar panels, are preferred to be used in conjunction with storage to improve the availability of the overall system. This paper proposes an Integrated Dual-DC Boost converter topology (IDDBC) as a single-stage power electronic interface for solar battery integration into a dc distribution system. In the present work, the characteristics of proposed topology has been analysed and control scheme for the same proposed. The design aspects for converter topology has been addressed in the paper. The behavior of the topology has been validated using simulation.
Abstract:A distributed secondary control based on consensus algorithm containing voltage synchronization and improvised optimizer modules is established along with a primary reverse droop controller to ameliorate the operation of shunt DC electric springs (DC-ES) in a typical DC microgrid cluster. These networked DC-ESs in the clusters,employed for voltage compensation and power balancing, are interconnected via a sparse communication layer. A low voltage DC microgrid is considered in this paper with boost converters for PV arrays emulating constant power sources, synchronous buck converters for DC-ESs and mix of resistance and constant power loads to assess the functioning of the proposed control philosophy for the DC-ES. The unified operation of compensating the DC bus voltage and simultaneously operating every DC spring at its own optimal operating point on the cost-generation characteristic curve aids to minimize the associated costs. In this work, the current contribution from each shunt compensator in the DC microgrid is correlated with its optimal operating point. To circumvent the case wherein any of the DC-ESs disregards its upper and lower boundaries, they are assumed to be graphically disconnected and the rest operate for achieving consensus in their respective incremental costs; provided the system incremental cost achieved via consensus is acceptable. With the aforementioned framework, the work presented herein investigates the operation of the radial DC network under physical and cyber adversities.
Abstract:The utilization factor of the power converter used for series part of unified power quality conditioner (UPQC) is very less due to least occurrence frequency of voltage related quality problems. To improve this factor, a conventional back-to-back converters are replaced with a dual output converters (nine-switch converter). A sliding mode control (SMC) scheme is recognized as robust controller with less sensitive to system parameter variation and load fluctuations. In this paper, SMC scheme is proposed to control the outputs of a nine-switch power quality conditioner such that they can track to their references. The reference quantities of the shunt compensator and series compensator are generated using modified instantaneous symmetrical components theory (ISCT) and in-phase compensation strategy respectively. Delayed signal cancellation (DSC) operator is used to extract fundamental positive sequence components of point of common coupling (PCC) voltages required for ISCT and also, to obtain phase angle of PCC voltages required for reference load voltage generation. The effectiveness of the proposed SMC system's performance is validated through simulation studies.
Abstract:The current work presented in this article proposes a
day ahead multi-objective optimization portfolio for a residential
microgrid or a home consisting of different domestic appliances
and rooftop solar panels associated with storage device. The
proposed framework aims to determine synergetic sourcestorage-load dispatch schedule by simultaneously minimizing the
electricity cost, ocular discomfort and thermal discomfort
experienced by the home occupants for the following day while
controlling switching of the discrete loads (like washing machine,
dryer etc.) and consumption of the continuous loads (like airconditioner, lights etc.). The entire optimization framework takes
the form of a mixed integer non-linear programming and the
solution technique is proposed using Genetic Algorithm. The
simulation is carried out on practical data set of a residential unit
to prove effectiveness of the designed method.
Abstract:The paper highlights the revived requirement of parameter estimation of the induction
machine. The data derived identification technique
is introduced to provide the approximate induction
machine model parameters. The active and reactive
power output of the induction machine at some known
condition is compared with active and reactive power
output of the induction machine simulated in realtime digital simulator environment at different values
of parameters at given operating conditions. Thus
a real-world optimization problem is formed and is
addressed by the mean-variance optimization scheme.
The results are platformed on the MATLAB-RTDS
environment which shares information via the TCP/IP
connection. The estimated parameters will help in providing increased reliability in designing the advanced
control scheme. The proposed methodology is tested
in single as well as double cage rotor winding type of
the induction motor and also in reduced voltage level
scenario for the validation of the technique.
Abstract:This paper proposes a fault detection scheme for microgrid based upon the angle of differential sequence impedance (ADSI). The fault detecting parameter ADSI is computed using positive sequence phasor of voltages and currents of both ends of the line. The IEEE C37.118.1 complied phasor measurement units (PMUs) are employed to fetch the voltage and current signals. The proposed scheme is tested on a medium voltage microgrid. The microgrid and the PMU are modeled in MATLAB/SIMULINK platform. The proposed relaying scheme is extensively tested for different fault types, fault at different line lengths and the fault with different DER penetration in islanding and grid-connected (GC) mode of operation. The ADSI based scheme is also tested for its response towards critical no-fault cases. The test results show that the ADSI index can detect faults in the microgrid with wide variation in fault cases and operating conditions within the desired response time.
Abstract:The variation in wind speed changes the output
power of Wind Energy Conversion System (WECS). In DC
microgrid, the WECS system connected to DC link through
DC-DC boost converter results in large variation in DC link
voltage. Maintaining the DC link voltage constant is a challenging
issue. Under wide variation of wind speed, the Composite
Energy Storage System (CESS) can stabilize the DC link voltage.
Similarly, during the gust period, the CESS maintains the DC link
voltage constant by supercapacitor absorbing transient energy
from the system. In this paper, a power management algorithm
for WECS based CESS is proposed. The power management
algorithm maintains the SoC limits of both supercapacitor and
battery. The simulation of the system carried out in MATLABSimulink to validate the results.
Abstract:Distribution transformers are one of the critical components of a distribution network involving huge capital investments and requiring special care to be ensured during their operation. Overloading of distribution transformers must be avoided beyond a certain threshold after which the capital-intensive process of their augmentation or replacement becomes inevitable. The cumulative peak demands of many distribution transformers contribute to the feeder peak and conditions of overloading lead to costly peak power purchases. Increasing penetration levels of distributed solar photovoltaic power on distribution transformers is also adding to the stress in the form of sudden variations in the net-load. Installation of battery energy storage systems at the secondary side of distribution transformers can provide a lot of techno-economic benefits in mitigating these conditions. This paper presents a two-stage approach for sizing such a system for one of the selected distribution transformers on an actual distribution feeder operational in Delhi, India. The intended application is overload management and peak shaving. The results of the preliminary sizing stage are rigorously tested against different sensitivity scenarios in terms of the number of continuous overloading instances in a year. In the advanced stage, the charge rate and the total amount of unmet energy are used as a feedback to fine tune the size so as to optimally meet the application.
Abstract:This paper deals with thepower quality improvement of a double stage solar PV (Photovoltaic)energy conversion system through anEIAF-PNLMS (Enhanced Individual Activation Factor Proportionate Normalized LeastMean Square)based control algorithm. This EIAF-PNLMS based algorithm uses thebenefit of thisscheme,which isused to improvethe filter coefficient. Therefore, the dynamic and steady state oscillations from the load fundamental current component is eliminated. The control algorithm gives the fast convergence, goodfrequency response, harmonics mitigation, andnoise cancellation. The UDDBC (Unidirectional DC-DC Boost Converter)is the bridge between the solar PV arrayand DC-link of the VSC(Voltage Source Converter). This UDDBC is to extract the peak power from the solar PV arrayand this UDDBC switching pattern is governedby adaptive P&O (Perturb and Observed) based MPPT(Maximum Power Point Tracking). This adaptive P&O based MPPT algorithm hasgood tracking capability and it has high immunityfrom therapidly solar irradiance perturbation.Here, FOIQGI (Fourth Order Improved Quadrature Generalized Integrator)based voltage filter,is used to mitigate the grid voltage distortions.Test results of the proposed solar interfaced grid system demonstrates satisfactory operationand effectiveness of control algorithm.
Abstract:In order to minimize the losses of the distribution network, solving the reconfiguration problem is a vitally established issue. Modification in the bus connection reduces the system loss and improves the bus voltages as well. Major intricacy for reconfiguring distribution system lies in the development of a convex optimization model constituting voltage-dependent loads. This paper models mixed integer second order conic program for Network Reconfiguration of a Distribution System (NRDS), where binary variables depict the branch connections between the buses. A ZIP load model composed of constant impedance, constant current, and constant power type loads, has been deployed for voltage-dependent load study. Proposed ZIP load model based NRDS has been tested on 33-bus, and 69-bus distribution system. Results are compared with the existing model given in literature incorporating only constant power loads that establishes the case for adaptation of the proposed model. Simulated results of constant power and voltage-dependent load model are also validated by performing load flow for evaluated branch connections.
Abstract:Conventionally, the power system security is ensuredthrough transmission system (TS) contingency analysis. The dis-tribution system (DS) is considered as a fixed aggregated load atthe point of connection bus where the quantum of load indicatesthe power demand of DS from the grid. However, this demand isno longer fixed with the proliferation of renewable energy baseddistributed generation (DG). The temporal variations associatedwith the power output of DGs eventually produces uncertaintyin the power drawn by a DS from the grid. Thus, any componentoutage which is not severe may become critical under the instanceof sudden increase in load (power demand by DS) and alters theresult of contingency analysis (CA). Hence, to prevent missing outalarm signals during such events, the system operators need tocommunicate with each other for performing security analysis. Inthis paper, a transmission contingency analysis method has beenproposed that considers the impact of active distribution networkwith exchange of limited data at the point of connection busbetween the system operators. To shorten the computation time,criteria for selecting the sensitive load buses is also proposed.Numerical simulations are performed on various test systems toshow the impact of uncertainty of renewable energy (RE) basedDGs on transmission line flows and bus voltages that can alterthe list of critical contingencies.
Abstract:Optimal day-ahead scheduling of batteries relies
on reliable day-ahead forecast of residential load profile,
solar insolation, and time-of-use tariff. However, actual values
may not be the same as the forecasted values due to various
factors like weather, cloud cover, consumer behaviour, etc. This
work aims at optimally scheduling the batteries installed in a
residence to minimize the cost of power consumption from the
grid and increasing the battery lifetime, while accounting for
the variations in the forecasted load profile, solar insolation
and time-of-use tariff. The proposed method uses short-term
forecasts and employs a sliding window technique to generate
optimal schedule on an hourly basis. The sliding window
technique helps in adjusting for the variations in the forecasts
used. Artificial bee colony (ABC) algorithm is used as the
optimization technique during each window. Effect of allowable
maximum depth-of-discharge, and sliding window size on the
optimized cost are also studied. The results are compared with
Abstract:This paper proposes a voltage regulation scheme for distribution networks using demand response. The problem is formulated as a linear objective function which minimizes the total cost to be paid by the utility. Tbe voltage regolation is designed as constraint in the optimization problem. The demand response algorithm considers the curtailment of non essential loads during peak load demand, when network bns voltages are hitting their Umits. Hence, demand response is nsed as a substitute for conventional voltage regolation scheme which uses multiple OLTCs and capacitor banks. In this work, demand response is nsed for voltage regulation by cnrtailing the minimum amount of non-essential loads. The algorithm is tested by aimulating dilferent operating scenario in the IEEE 33 bns distribution network.-->
Abstract:This paper deals with the implementation of a hybrid method for islanding detection of inverter interfaced distributed generators (DGs) in a distribution Network. The proposed algorithm requires injection of a low frequency sinusoidal disturbance signal (around 10-20 Hz) into the d-axis current control loop of the Distributed Generators (DGs). Thereafter, it utilizes two different features obtained from the superimposed component of d-axis voltage sensed at the point of common coupling (PCC) of the DGs for detecting unintentional islanding event. The decision logic that is made out of these two features enables faster detection of islanding events of DGs and also helps in accurately discriminating unintentional islanding from other kind of events such as load switching, sudden voltage sag at PCC and others. Numerous simulation studies are performed with generic UL 1741/IEEE 1547 anti-islanding test system developed on MATLAB/Simulink platform to validate the efficacy of the proposed algorithm.
Abstract:This paper elucidates a day ahead direct load control strategy for a smart residential apartment building (SRAB) comprising of multiple dwelling units (DUs) of non-identical functionalities. The objective of the current article is to design a distributed load management strategy for SRAB in multi-objective optimization platform by utilizing a virtual energy trading software platform between building load master controller (BLMC) and the DUs. The propounded optimization portfolio is developed as a multi-objective optimization problem where maximization of consumed power utility is simultaneously considered with the energy cost minimization objective. Interaction between BLMC and DUs is modelled as one-leader, N-followers Stackelberg Game, where the outcome of the game is proved to be at Stackelberg Equilibrium point. Stringent simulation is carried out on a real world data of four DUs to show efficacy of the proposed load control process.
Abstract:In free space optical (FSO) communication, jamming can cause inaccuracy in the received information. In this paper, we investigate the impact of jamming over atmospheric turbulence (AT) fading channels. To describe the AT, negative exponential (NE) and Gamma-Gamma (ΓΓ) fading channel models are considered. The effect of jamming is studied over a single-input single-output (SISO) FSO link. We introduce a theoretical framework to acquire a closed-form expression of the average bit error rate (ABER) under jamming-leading to an additive non-Gaussian noise channel. It is observed by thorough analysis that a 2 x 1 FSO system performs better than SISO FSO system in presence of jamming signal. It is realized that under jamming the performance of FSO link is dependent on different AT conditions. Furthermore, increasing number of transmit apertures allows FSO system to significantly overcome the effect of jamming, in order to obtain an improved ABER.
Abstract:The Indian electricity sector is undergoing a significant transition with increasing share of variable renewable energy (VRE) in the system. This, coupled with an annual increase in peak demand could put significant stress on the distribution network. The role of b attery energy storage systems (BESS) thus becomes im-portant for distribution network applications such as voltage regul ation and peak shaving. With high summer peaks, distribu-tion networks with high penetration of solar rooftop PV systems (SRPV) tend to have a low load factor. This has an impact on rate of loss-of -life of equipment, especially distribution transformers (DTs) and thus for such feeders, the non -reduction in augmenta-tion/replacement costs on these componentsoffsets the benefits of load reduction through SRPV. There are certain factors which affect the health/life of DTs (1) Overloading (2) Non-linear load ope ration (3) Poor maintenance are among the prominent ones. Overloading is a major cause of DT failure (failure rate in India is around 12 to 15 %) particularly in urban areas where the pop-ulation growth is high. The overloading of a DT can be prevented by deployment of BESS at its secondary side, thus preventing DTaugmentation. This study tries to eval uate the need for BESS at the distribution level to defer investments on DT augmentation and reduce DT failure while increasing the DT life. This applica-tion along with energy arbitrate could make BESS viable at the distribution level. A control logic developed for the battery moni-toring system along with detailed cost benefit analysis under var-ious scenarios has been reported in this study
Abstract:Quite notably, over the years, the Distributed Genera-tion (DG) concept has evolved and the role of Renewable Energy (RE) has become increasingly important in shaping the develop-ments. In the form of Distributed Energy Resources (DERs), RE sources also help in reducing burden on the utility by providing an alternative source which is most relevant for a distribution network. With increasing penetration of DERs at the distribu-tion-level, electricity distribution is rapidly transforming into a two-way business where consumers (as prosumers) are selling power back to the utility. All such interactions can be stream-lined in the form of Peer to Peer (P2P) trading of energy and a decentralized network between “peers” participating in a local energy market can be created thus transforming into a virtual power plant. If used properly, DERs at the distribution-end can not only reduce losses but can also help the utilities in managing demand more efficiently by engaging people who own these gen-erating assets. Blockchain serves the P2P framework well, creat-ing an efficient platform for energy trading between peers with-out any requirement of an intermediary. This paper presents a review of the existing major projects on P2P trading using DERs. The aim of this paper is to report different price bidding strate-gies and auction mechanisms employed to create a win-win ap-proach for both prosumers and consumers. Societal aspects and institutional development required for using Blockchain for P2P trading have also been discussed. In the end, a prototype model for P2P trading of rooftop solar energy, developed by the au-thors, is introduced.
Abstract:Identification of various power system events such
as fault and power swing is important for its reliable and
secure operation. Multiple sequential events may make the
event identification algorithm complex. By taking advantage of
The high reporting rate of Phasor Measurement Units (PMUs),
this paper proposes a method to identify the power system
events in the network. Synchronized voltage and current phasor
measurements are utilized along with the forecasting-aided state
estimator to extract the features of the event. The proposed
method can detect an invalid PMU data and can correct it to
avoid wrong identification of an event. The method is capable
of detecting events like fault and power swing. The proposed
event detection algorithm is validated on WSCC 9-bus system
using the Real Time Digital Simulator (RTDS).-->
Abstract: A novel moving window phaselet based approachhas been proposed in this paper for quick islanding detection(within5-10ms) in ADNs, even in the case of zero powermismatch/ power balance case. The Instantaneous Phase Angle(IPA) and magnitude of the PCC voltage have been extractedthrough a linearly moving window phaselet to generate two in-dices - Phaselet Angle Difference (PAD) and Phaselet MagnitudeDifference (PMD) at sub-cycle rate, which are critical parametersin quickly discriminating islanding from non-islanding events inADNs. These indices also offer the added advantage of quicklyclassifying the type of fault, in the events of faults in ADN.Real Time Digital Simulator (RTDS) based results prove theefficacy of the proposed phaselet based technique in accuratelyand dynamically estimating the phasors within sub-cycle intervaland quickly detecting islanding, even in power balance case withdifferent load quality factors as per standard.
Abstract: The swift spread of Distributed Generation (DG) across the Distribution System (DS) has imposed the need to study their impact on the entire power system. The current independently operating Transmission and Distribution (T&D) management systems are incompetent to appropriately reflect the effect of DS operating conditions at the transmission level. The diverse attributes of each T-D system have motivated to perform Optimal Power Flow (OPF) in a distributed fashion with communication of limited data. Thus, a Coordinated Optimal Power Flow (COPF) method for a coupled T-D system was proposed with the objective to minimize the total operational cost for T&D system. This paper proposes a Modified COPF (M-COPF) method that presents the significance of this concept in the presence of voltage-dependent loads in DS. The mathematical model formulated is capable of handling system operators with different objective functions. The viability of the proposed framework is validated by implementing it on the test system developed on real-time simulators (RTDS and OPAL-RT). The results obtained for various test cases through simulations substantiate the significance of proposed methodology.
Abstract:A distributed control paradigm based on reverse droop primary controller is established to formulate a control framework for the problem of achieving voltage regulation and proportionate load current sharing in a DC microgrid scenario. It utilizes the hierarchical control approach to form a cyber-physical interaction layer of the DC distribution system. The adjustment/correction factors for the DC voltage is generated by the secondary control layer wherein the voltage and current observers process the neighboring agents' dataset to effectively regulate the DC voltage. The proposed control achieves faster dynamics as compared to a conventional V-I droop controller thereby enabling improved transient and steady state dynamics. The controller is subjected to various test cases like plug-n-play capability, switched networks, remote and local load changes, resiliency to communication delays, etc. in order to investigate its robustness to disturbances and uncertainties. A low voltage DC microgrid test-bench with underlying buck converters with dispatchable energy source inputs is employed to validate the aforementioned features. The paper considers the functioning of the microgrid test-bench under various load dynamics such as constant power loads (CPLs) and resistive loads.
Abstract:A novel and efficient methodology for comprehensive fault detection and classification by using synchrophasor measurement based variations of a power system is proposed. Presently, Artificial Intelligence (AI) techniques have been used in power system protection owing to the greater degree of automation and robustness offered by AI. Evolutionary techniques like Genetic Algorithm (GA) are efficient optimization procedures mimicking the processes of biological evolution that have been shown to perform better than their gradient based counterparts in many problems. We propose a combined GA and Particle Swarm Optimization (PSO) approach to find the optimal features relevant to our fault detection process. As is evidenced by recent advances in multi-modal learning, it has been shown that this combined approach yields a more accurate feature optimization than that obtained by a single meta-heuristic. A systematic comparison of Artificial Neural Network (ANN) and Support Vector Machine (SVM) based methods for fault classification using the identified optimal features is presented. The proposed algorithm can be effectively used for real time fault detection and also for performing postmortem analysis on signals. We demonstrate its effectiveness by simulation results on real world data from the North American SynchroPhasor Initiative (NASPI) and signal variations from a test distribution system.
Abstract: A standalone solar photovoltaic (PV)- battery energy storage (BES)- diesel generator (DG) based microgrid system is presented in this paper. The BES is integrated directly to the DC link of the voltage source converter (VSC). This system functions PV array maximum power extraction along with improvement of power quality such as harmonics elimination, reactive power compensation and balancing of DG currents. The PV array is integrated to the DC link of the VSC through a DC-DC boost converter. An automatic voltage regulator (AVR) is used to regulate the output voltage of the DG to the desired value. The performance of the standalone hybrid microgrid is studied under various operating conditions in the laboratory environment.
Abstract: Industrial and critical infrastructure automation systems, integrated with Industrial Internet of things (IIoT) are becoming lucrative targets for cyber-attackers. Typically these are cyber-physical systems, with cyber components such as sensors, actuators, micro-controllers, programmable logic controllers, or distributed control systems, field-area network, wide-area network etc., overseen by supervisory control and data acquisition systems (SCADA). After the discovery of the Stuxnet in 2009, and multiple other instances of cyber-attacks such as on a German steel plant, Ukraine power distribution system, chemical plant etc., research on securing these systems from cyber-attacks have become very important. However, it is often not permissible to attack the real operational critical systems for vulnerability assessment or testing mitigation techniques. Therefore, virtual or real test beds are required. In this paper we focus on a lab-scale test bed for a 3 phase power distribution system under industrial PLC control, instrumented with relay, power meters, various field protocol switches, supervised by an industrial SCADA system. Main contributions of the paper are (i) case studies of vulnerability assessment of the industrial components of this test bed - components that are being widely deployed in real critical systems throughout the world. (ii) the exploits and their security implications, especially their effect on the physical functioning of the systems; and (iii) mitigation techniques we have deployed to defend against such attacks. We are working with the original equipment manufacturers to disclose these vulnerabilities and in deploying mitigation techniques. A library of exploits and payloads which can be used in similar industrial control systems is under preparation.
Abstract:This paper proposes an application of Indirect
Adaptive Control (IAC) philosophy for Power System (PS) inertia estimation. It only requires the frequency measurement
from the Phasor Measurement Unit (PMU) located at the bus
at which inertia is to be estimated. No other system data or
approximations are required, which is generally a necessity in
other inertia estimation techniques in the literature. In order
to implement the IAC philosophy for inertia estimation, swing
equation of the synchronous generator is to be rearranged
in a standard affine system form. Radial Basis Function
Network (RBFN) is used in IAC for swing equation emulation
while feedback linearization technique is used to generate
a control signal required to track the desired frequency
response. The parameters of the IAC structure are updated
online and no prior knowledge is required in this regard.
Real Time Digital Simulator (RTDS) based results on the
two area Prabha Kundur system prove the accuracy of the
proposed inertia estimation approach.
Abstract:One of the key challenges in an islanded microgrid
is fundamental and harmonic power sharing by the inverters in
proportion to their ratings. Emulating virtual impedance much
larger than the line impedance at the output of the inverters
ensures proportional sharing of harmonic currents at the cost
of increase in voltage harmonic distortion. This may violate
the voltage harmonic limits specified by IEEE 519 standard.
These limits are even more stringent when the loads are highly
voltage sensitive. A novel method is proposed in this work to
ensure proportional harmonic current sharing while maintaining
the harmonic voltage distortion within the limit. Increase in
harmonics in the output voltage due to high virtual impedance
is estimated and compensated. A low bandwidth communication
(LBC) is used to compensate the harmonic voltage which utilizes
only two bits per harmonic frequency. A detailed simulation study
is done in MATLAB-Simulink to validate the proposed technique.
Abstract:— A sudden surge in the demand and the global
warming has paved the way for the renewable energy sources
(RES) to take a lead in the generation of electricity across the
globe. Among the RES, Photovoltaics (PV) and wind energy
are playing a key role due to their abundant availability. The
Doubly fed Induction generator (DFIG) based wind system has
attracted research community and investors due to their
numerous advantages such as cost effectiveness. On the other
hand, the parallel research advancement in the area of DC
microgrid (DCMG) has gathered global attention in recent
days to improve the system efficiency. A significant effort has
been done by the research community to effectively integrate
DFIG wind system to the PV based DC microgrid to suit
isolated application. However, these research works were
restricted to a few kW hardware implementation only. In this
work, in order to visualize the impact of DFIG hardware
prototype on the MW rated DCMG, power hardware In Loop
(PHIL) based experimentation on prototype DFIG wind system
connected to DCMG which is simulated in the real time digital
simulator (RTDS) platform has been carried out. The
performance of the system is tested under varying conditions of
different loads and sources. The PHIL experimental results
indicate that the overall system is stable in spite of such
variations and hence opens door for further research in this
Abstract: Virtual synchronous generator control or synonymously referred as synchronverter control of converters which integrates renewable energy sources to the utility grid or microgrid is emerging as a suitable control where the response of a conventional synchronous generator is emulated, thereby improving system stability. In this paper, a three-phase synchronverter control with an inbuilt synchronization unit is proposed in order to eliminate the external phase-locked loop (PLL) unit. The inbuilt synchronization unit does not use any additional PI control or integral control unlike the PLL unit. Thus, the computation burden of the overall controller is reduced. In this work a grid-tied synchronverter with the proposed inbuilt synchronization unit is simulated with different initial frequency and initial phase difference conditions. Also, variable grid frequency during synchronization is simulated in order to verify the effectiveness of proposed synchronization control.
Abstract:Nacelle-top mounted anemometer gives wind velocity information pertaining to the surroundings of nacelle and this point wind velocity measurement may or may not be same as effective wind velocity which strikes the wind turbine rotor blades. In this paper, a new method for the computation of wind speed is proposed to avoid the presence of mechanical sensors like anemometer and speed encoders in the wind turbine control systems. Suitable sliding mode observers designed for the estimation of turbine rotor speed and aerodynamic torque. Effective wind velocity is computed by inverting the turbine's aerodynamic model after estimating the turbine torque and its rotor speed. Design criterion and inequality constraints are discussed in detail while satisfying the Lyapunov inequality condition. The simulation studies confirm that the computed wind speed under variable wind flow conditions is converging with true wind speed. This proposed method can be used for maximum power extraction and various control algorithms' implementations as well in wind energy conversion systems control applications.
Abstract: A phaselet approach for the real-time differential
protection of the series-shunt compensated transmission
line is proposed here. Phasors of the signal using phaslet
approach can be obtained at 0.4 sub cycle. The measured
input currents from both ends of the transmission line are fed
to the phasor estimation algorithm where both current signals
are reconstructed by using the phaselet approach. An index
namely, Moving Average Error (MAE) is calculated using the
errors between the actual and estimated current signals taken
from Current Transformers (CTs). The Rate Of Change Of
Mean Average Error (ROCOMAE) of both signals is calculated
and the difference of ROCOMAEs is taken, which is Trip
Decision Index (TDI) for the proposed method. The operation
of differential relay based on the TDI is investigated. For
validation, two area system with midpoint compensation along
with series compensation is also considered and simulated in
Real Time Digital Simulator (RTDS) platform. Different test
cases like internal fault, external fault, high impedance fault,
CT saturation and series-shunt compensation are generated to
test the efficacy of the proposed approach.
Abstract: The impact of Virtual Synchronous Generator
(VSG) parameters on the transient performance of Solar Photo-
Voltaic (SPV) based system has been analyzed in this paper. In
addition, the variations in Kinetic Energy (KE) and Potential
Energy (PE) components of a Structure Preserving Energy
Function (SPEF) for the system under consideration have also
been analyzed for the same purpose. In order to do this, state
space model of the SPV system with VSG controller has been
developed. SPEF has then been derived with this model for a
SPV source connected to a Synchronous Generator (SG) by a
cable with the nonlinear load. In order to analyze the transient
behavior of the system under 3 bolted fault and induction motor
switching, a nonlinear Runge-Kutta 4th order method is used for
numerical simulation. Results from Real Time Digital Simulator
(RTDS) show that the variations in KE and PE of SPEF can aid
in assessing the transient behavior of SPV based system.
Abstract: Voltage control is an important operational requirement
for efficient and reliable operation in distribution systems.
The accelerated proliferation of Solar Photo-Voltaics (SPV) in
distribution networks, has resulted in voltage fluctuations in the
distribution system. This is due to the high R/X ratio in Low
Voltage (LV) distribution network that leads to strong coupling
between active power and voltage. This paper thus proposes
coordinated control of voltage in LV distribution systems by On-
Load Tap Changer (OLTC) and Battery Energy Storage Systems
(BESS) so as to mitigate the issue of voltage rise/ drop. The
objectives are to operate the slow-acting OLTC in the presence
of fast-acting BESS and reduce the stress on battery charging/
discharging. This leads to increase in battery life and reduced
operation of OLTC, which helps in utility asset optimization in
terms of both the OLTC and BESS. In the proposed scheme,
OLTC tap operation is based on the weighted average of
the bus voltages. The feasibility of the proposed approach is
demonstrated on a modified IEEE 13 node distribution system
which is simulated in MATLAB/ Simulink. Simulation results
verify the proposed coordination voltage control scheme.
Abstract: With the flow of time there is a rapid addition of
distributed generation (DG) units in the distribution system (DS).
This transformation of DS from passive to active network has
made the examination of coupling between transmission and
distribution (T&D) systems more significant. Conventionally, the
load flow studies are performed individually for both transmission
system (TS) and DS, presuming the other system as an
equivalent. But to achieve a global solution for the entire power
system, a Coordinated Load Flow (CLF) method is required.
It will perform load flow in a distributed manner with a little
reciprocity of information at the common bus, in order to reduce
the computational complexities of solving large scale problems.
This will allow to analyze the impact of detailed modeling of DS
on global load flow solution which was otherwise neglected in
traditional methods. This paper firstly presents the methodology
to perform CLF. Further, the significance of CLF method is
proved especially in the presence of voltage dependent loads
in DS and its performance is compared with the solutions
of independent T&D load flows. Numerical simulations are
performed on various test cases and the results are validated
using Newton-Raphson load flow method with optimal multiplier.
Abstract:Due to the advancement of microgrids, the electrical
distribution network is transforming rapidly. The close proximity
of distributed generations, loads and widespread use of power
electronic converters have brought enormous flexibility and
controllability to the distribution system. The transient studies of
dc microgrid need more attention to ensure stable and reliable
operation of the converters. One of the important phenomena is
overloading of a source converter during a large load transient.
The source current may increase due to the large increase in load
connected to its proximity. Conventionally this issue is addressed
by using a static current limit, which protects the converters.
However, this leads to significant disturbances in the system,
especially when this converter recovers from saturation due to
other converters sharing the load. A suitable dynamic overcurrent
saturation technique, proposed in this paper is advantageous
over the existing constant current saturation method. This
paper shows a detailed procedure of determining the dynamic
current limit and its implementation in the controller in line with
the device manufacturers’ guidelines for the enhanced operating
condition in dc microgrid.
Abstract: Microgrid facilitates penetration of renewable
energy sources into the existing distribution systems to reduce
the overall carbon footprint of the globe by reducing the
dependency on the main grid. To justify the large deployment
of the microgrid concept, economic operation should be
guaranteed. But non-linearities present in the nature of
microgrid components and network make the scheduling
process complex. Again, non-linear solution strategies do not
guarantee global convergence. Therefore, efficient but linear
model for microgrid resource scheduling algorithms are
gaining interest in present time due to its simplicity and fast
computation. On the contrary, for peak demand management,
flexible load scheduling is a viable and easiest option to the
microgrid operators to minimize the customers’ dissatisfaction.
This article serves the aforementioned purposes by designing a
linear model for microgrid scheduling by implementing
demand side management strategies to manage flexible
appliances aiming for peak demand reduction. The strategy is
implemented on a practical Indian distribution system
consisting of commercial and residential loads to prove its
Abstract:The distribution network reconfiguration (DNR) is
mainly done by controlling the status of sectionalizing switches
and tie lines (switch ON or OFF). This operation can be carried
out with various objectives, and one of them is network loss
reduction, keeping the radial behavior of the network is intact.
Traditionally, DNR is done by assuming the voltages at various
feeders at nominal value (1 pu). But practically, each feeder
may be connected to different buses of the transmission system
(TS) defined as interfacing buses (IBs). And each of the IB
may have some value of voltage other than 1 pu. Thus, under
the condition when the tap regulators are locked and unable
to maintain secondary side voltage at nominal value, the basic
assumption fails. Hence, it is recommended to conduct DNR with
actual feeder voltages in order to get refined output. This paper
proposes an algorithm to perform feeder voltage dependent DNR
for loss reduction. It will perform the transmission system load
flow (TLF) and DNR in a sequential fashion, to present the
updated voltages for reconfiguration process. The aim is to find
a more appropriate configuration of the distribution network
(DN) when feeders are not at nominal voltage level. Numerical
simulations are executed on different test cases to validate the
relevance of the proposed algorithm.
Abstract:This paper presents a grid connected mode (GCM) and standalone mode (SAM) of the photovoltaic (PV) - battery based microgrid system. Whenever the grid fails, this system transfers from GCM to SAM without causing any interruption to the load supply. In the similar context, after the restoration of the grid, the system goes into GCM of operation. In the GCM, the voltage source converter (VSC) of microgrid, operates in current control mode (CCM) and in SAM, it operates in voltage control mode (VCM). A bidirectional DC-DC converter (BDDC), controls the charging and discharging of the battery in GCM and in SAM. In SAM, the BDDC performs the extraction of PV array maximum power by regulating the DC link voltage to the PV array maximum power point (MPP) voltage. In GCM, the VSC performs the extraction of PV array maximum power. The BDDC is used for interconnecting the solar PV array and the battery; hence the second order harmonic is not fed to the battery so the effective life of the battery is increased. The VSC performs the seamless transition from SAM to GCM and vice versa and it also performs multi-functions such as harmonics mitigation, balancing of grid currents and unity power factor (UPF) operation in GCM.
Abstract:Protean demand pattern with the rise in
environmental concerns are the driving factors towards
integration of renewable energy source (RES). Incorporation of
RES generation, lead to displacement of conventional generators
and hence causes a decline in the system inertia and Primary
Frequency Response (PFR) capability. Moreover, RES uncertain
characteristics would further dwindle in systems inherent inertia
and PFR capability. This arises concern for the system operator
to maintain reliability and security of the system particularly at
the time of contingency like largest generator outage or loss of
a large block of the load. This imbalances between generation
and load require an additional response for maintaining system
stability. In this regard, present work signifies the need of an
additional response from the Interruptible load (IL) in presence
of uncertain PV penetration. The uncertainty of the PV is
being handled by the ARIMA model. Present work introduces
a potential role of IL in day ahead stochastic unit commitment
(SUC) framework considering PV uncertainty. Case studies are
implemented on one area IEEE RTS 24 bus system considering
30% penetration level of PV. Simulation results would assess the
validation of role played by IL in enhancing system frequency
parameters under uncertain PV power
Abstract:Urbanization of the rural areas increases the
residential area load demand of the globe. Again, integration of
intermittent renewable energy generations and volatile habits
of the domestic users make the household demand profile as
unpredictable in nature. Therefore, control of the residential
loads is highly required to manage the increasing demand
efficiently and also to match the load variability with the
available generation to get lowest electricity cost. Advancement
in communication technology enables the chance of application
of demand response (DR) strategies in the modern smart grid
era. DR programs aims to diminish the overall peak
consumption of the domestic customers while meeting the
power balance constraint at each time interval. This study
presents an overview of the articles dealing with the
application of demand response analysis in the residential
Abstract:A solar photovoltaic (PV) - battery energy storage
(BES) involved microgrid system is presented in this paper. It
contains a bidirectional DC-DC converter (BDDC), which is
responsible for extracting the maximum power output from the
PV array by regulating the DC link voltage to the maximum
power point (MPP) voltage of the PV array. Whenever, the PV
array is not delivering any power then the control of the BDDC is
automatically shifted to regulate the DC link voltage to a constant
DC voltage. Thus the BDDC regulates the DC link voltage to
desired voltage in the presence of BES in the microgrid.
Whenever the BES is disconnected from the microgrid then the
voltage source converter (VSC) functions regulation of the DC
link voltage to desired value, so this enhances the reliability of the
system. The neutral current compensation is performed by the
zig-zag transformer. The VSC performs different functions such
as mitigation of harmonics, reactive power, balancing of grid
currents and the regulation of the DC link voltage in the absence
of BES. The system behavior is analysed under different
operating conditions in the laboratory on a system prototype.
Abstract:Recent developments in the power converter
technology and the need for better power quality/reliability, have
necessitated the integration of AC and DC grids. The realization
of AC-DC distribution network has become more rational with
the increase in renewable generations and DC electronic
loads. There are numerous technical advantages of using DC
power in conjunction with AC power in distribution systems. But
for widespread utilization of AC-DC distribution network, the
economic impact of aforementioned technology on the affiliated
customers needs to be inspected. Distribution use of system
(DUoS) charges is an eminent means for scrutinizing the
economics related to an AC-DC distribution system in
transferring power to its associated users. This article presents a
MW+MVAr-Miles methodology for DUoS charges calculation.
The proposed network pricing mechanism reward the users
working at better power factors and efficiently utilizing the
network, while forfeiting those who don’t. As a result, the
proposed pricing model encourages users to act in a manner for
the betterment of the system condition. The aforesaid analysis
will enables to realize the economic benefits or detriments of an
AC-DC distribution system in distributing power to customers.
Abstract: A solar photovoltaic (PV) - battery energy storage
(BES) based microgrid with multifunctional voltage source
converter (VSC) is presented in this paper. The maximum power
extraction from a PV array, reactive power compensation,
harmonics mitigation, balancing of grid currents and seamless
transition from grid connected (GC) mode to standalone (SA) mode
and vice versa, are performed in this system. Whenever, the grid
fails, this system operates in SA mode automatically thereby
without causing any interruption in supplying the load. Similarly, it
automatically shifts to the GC mode when the grid is restored. The
VSC functions in current control mode (CCM) for GC mode and it
operates in voltage control mode (VCM) for SA mode of operation.
This system is capable of extracting the maximum power from the
solar PV array irrespective it is operating in the GC mode or in SA
mode of operation. The charging and discharging of the battery, are
controlled by employing a bidirectional DC-DC converter (BDDC).
It regulates the DC link voltage to the maximum power point
(MPP) voltage of the PV array. If the absence of battery is detected,
then the control is automatically shifted to VSC for performing the
extraction of maximum power of PV array.
Abstract:This paper demonstrates a solar photovoltaic (PV)-
battery energy storage (BES) based microgrid system with
multifunctional voltage source converter (VSC). It dealts with
maximum power extraction from a PV array, reactive power
compensation, harmonics elimination and seamless transition from
the grid connected mode (GCM) to standalone mode (SAM) and
vice versa. The maximum power extraction from a PV array, is
achieved by using a DC-DC converter. A bidirectional DC-DC
converter (BDDC) is used for regulating the DC link voltage.
Whenever the BES is not connected then the VSC performs the
regulation of the DC link voltage. The system behavior is studied on
a prototype of the microgrid system under various operating
Abstract:The participation of solar photovoltaic (PV) in the world
energy sector is increasing expeditiously, as a cumulative result of a
reduction in the cost of solar panel, improvement in panel efficiency, and
advancement in associated power electronics. Among different types of
PV plants, installation of small-scale rooftop PV are growing rapidly due
to direct end-user benefits and lucrative governmental schemes. There
are various standards developed regarding grid integration of PVs and
other distributed generations (DGs). Different power converter
topologies are developed to interface the PV panel with the utility grid.
To keep up with the stringent regulations imposed by the standards
various control strategies, and grid synchronization methods have been
developed. This review paper amalgamates and summarizes all the
aforementioned aspects of a grid-integrated PV system. Various
standards, power stage architectures, grid synchronization methods, and
control methodologies pertaining to small-scale PV plants are discussed
at length. This paper will act as a one-stop reference for practicing
engineers and introduce the vast research in the field of solar PV
integration to the new generation of researchers.
Abstract:Recent trends in renewable source integration and
advancements in electric loads led to the emerging of local DC
microgrids. However, due to majority of AC loads hybrid AC-DC
microgrids are formed, incorporating feasible power converters
as medium of power flow. Instead of conventional bidirectional
AC-DC and DC-DC converters as interlinking converters
in hybrid AC-DC microgrid, an open-end transformer based
multilevel converter configuration is proposed as interlinking
converter in this paper. The converter configuration includes
two converters concatenated with primary of transformer, is a
unique substitution for conventional multiple converters utilized.
The salient features of the configuration include reduced control
complexity, inherent isolation from AC grid, and able to provide
inter-grid bidirectional power flow. A modified control scheme
is proposed for precise power flow control in the system. Real
time simulation of the proposed configuration of hybrid AC-DC
microgrid is implemented in RSCAD/RTDS and experimented on
a scaled hardware prototype. The outcomes depict the potency
of control scheme in inter-grid power flow control.
Abstract:This paper proposes the application of a traditional
dq controller to provide virtual inertia to the Solar PhotoVoltaic
(SPV) based Distributed Generators (DGs) by adjusting its Phase
Locked Loop (PLL) parameters. The relationship between the
phase angle of inverter and power mismatch is derived in terms of
the inertia constant. Based on this, an equivalent inertial constant
expression is obtained. The proposed controller is tested for a
SPV system connected to a grid represented by a Synchronous
Generator (SG) which is double the rating of SPV system. Real
Time Digital Simulator (RTDS) platform is used to investigate
the effectiveness of the proposed scheme and its performance has
been compared with a Virtual Synchronous Generator (VSG)
scheme under load disturbances and bolted fault.
Abstract:Adaptive under frequency load-shedding schemes
are gaining more attention, as power systems are being operated
under increasingly stressed conditions. Synchrophasor devices
are used in power system networks to monitor the system
frequency and the rate of change of frequency (ROCOF) and
hence can be utilized for adaptive load-shedding schemes. Since
the synchrophasors utilize a global positioning system (GPS) to
time synchronize their measurements, they are prone to time
synchronization attack (TSA) by spoofing the GPS. This paper
discusses the impact of TSA on synchrophasor assisted loadshedding
schemes. WSCC 9-bus system is used as the test bed
for the study.
Abstract:This paper presents a new approach to physical relocation of photovoltaic (PV) modules in Totally Cross Tied (TCT) configuration of an array without altering the electrical connection. This proposed arrangement is a one time arrangement at the time of installation and this arrangement ensures for the enhancement of power generation of the PV array under partial shading conditions. In this arrangement, the shading effects are distributed over the entire array and hence reduce the multiple peaks in the power-voltage characteristics. The power generated by the proposed arrangement of a PV array is compared with the TCT configuration under different shading patterns. Also, the mismatch loss in the proposed configuration is compared with existing configurations under different shading patterns.
Abstract:In this paper, a Dynamic Voltage Restorer (DVR)
control algorithm with battery management features are presented
for the protection of sensitive and censorious loads. A
simple DVR control scheme based on dual P-Q theory has been
presented to obtain the instantaneous reference DVR voltages
to compensate the load voltages. The proposed control scheme
embraces energy optimized compensation, which results in a
reduction of DC energy storage requirement. A DVR battery
management scheme, as a part of this control strategy, has been
introduced for better battery energy utilization. Each leg of the
three-phase three-leg split capacitor inverter is used to inject
series DVR compensation voltages explicitly in each phase of the
three phase distribution power system. The effectiveness of the
proposed control algorithm has been validated by using computer
Abstract: Distributed secondary controllers for dc microgrids
have proven to be more effective and reliable as compared
to decentralized and centralized controllers, respectively. The
distributed secondary controller relies on information exchange
between the distributed units. Conventionally, a full communication
network topology is used, wherein all controllers communicate
with each other. Recently, adoption of consensus control in
DC microgrids have enabled achieving good performance using
reduced communication network. This work aims at comparing
the performance of the secondary controller with reduced and
full communication topologies. It is shown that with proper
tuning of gains, the secondary controller under reduced communication
has similar performance as under full communication.
The results are substantiated with numerical simulations using
Abstract:The short term load forecasting plays a crucial role
in optimal operation and scheduling of the generation resources
in power system. In this work, Auto-Regressive Integrated
Moving Average (ARIMA), Multiple Linear Regression (MLR),
Recursive Partitioning and Regression Trees (RPART), Conditional
Inference Trees (CTREE) with Bootstrap Aggregating
(BAGGING), and Random Forest (RF) models have been tested
and compared for short term load forecasting. These methods
have been tested on a sample electricity load data of a residential
area containing data sets for training and testing.
Abstract: Locating faults in meshed dc microgrids poses challenges
due to low impedance offered by the dc network. In this
paper, an on-line fault location scheme which can be implemented
as an additional feature in a relay is proposed. The algorithm
is developed to determine fault location based on voltage and
current transients. Both line to line and monopole ground
faults are analysed separately and algorithms are developed
based on the rate of change of current. Direct short circuit
faults are located using transient measurements captured locally,
while communication based technique is utilized to locate the
impedance faults. The developed fault location technique is
also capable of estimating the fault resistance accurately. The
algorithm is validated on a ±600 V meshed dc grid, for both the
types of faults under wide range of fault impedance at different
Abstract: Protection is an important factor affecting the viability
of dc microgrids in future. Traditional ac protection methods
are not directly applicable to the dc microgrids due to more
extensive use of power electronic converters as compared to the
ac systems. Behaviour of different converters during fault is not
identical and depends on the converter topologies. Some converter
topologies are capable of controlling its output current and hence
reduce the risk of system failure. While other topologies are
unable to limit the current and require external devices such
as fuse, breakers to protect itself. Therefore, a detailed study
of various power electronics converters response for different
types of faults is desirable. In this paper, analysis of direct short
circuit and monopole to ground fault are analysed for different
converters. The fault current transient is characterised in terms
of peak value and time to reach the peak current. The results
are verified through simulations for different converter topologies
using Real Time Digital Simulation (RTDS).
Doctoral and Masters Thesis acknowledging UI-ASSIST project
Anju Meghwani,Development of Efficient Fault Detection and Location Techniques for DC Microgrid Protection, PhD Thesis, IIT Kanpur, February 2018.
Amrit Singh Bedi,Distributed and Online Learning with Stochastic Gradient Methods, PhD Thesis, IIT Kanpur, 2018.
Ankit Garg, Quantized Feedback Based Precoding For Mimo Systems, PhD Thesis, IIT Roorkee, 2018.
J.G.Sreenath, Distributed Forecasting-Aided Power System State Estimation in the Presence of Unreliable Communication, Multi-Rate Measurements, and Cyber-Attacks,PhD Thesis, IIT Kanpur,2019.
Sanjeev Pannala, Power Control Operation & Management using DC Micro-grid, PhD Thesis, IIT Roorkee, April 2019.
Krishna Murari Pandey, Distribution Load Flow Algorithm for AC-DC Micro Grid, IIT Roorkee, August 2019.
M V Gururaj,Performance investigation of a DFIG interfaced with a microgrid, PhD Thesis, IIT Roorkee, April 2020.
Anmol Sharma, Design and Control of DC Microgrid with Energy Storage, M Tech Thesis, IIT Kanpur, May 2018.
Soumya Sahoo, Optimal Dispatch Scheduling for Residential Battery Storage with Solar Photovoltaics,MS(Research) Thesis, IIT Kanpur, November 2018
Rizwan Ahmed Khan,Short Term Load & Solar Forecasting and Optimal Distribution Energy Resource Planning ,MS(Research) Thesis, IIT Kanpur, November 2018
Garvis Garg,Optimal Day-Ahead Load Scheduling in an Islanded Microgrid using Demand-Side Management”, M. Tech. Thesis, IIT Kanpur, Dec 2018.
Tanmay Tewari,Coordinated Control of OLTC and Energy Storage for Voltage Regulation in Distribution Network with High PV Penetration”, M. Tech. Thesis, IIT Kanpur, July 2019.
Sai Sowmya Nagam,Gaussian Process Regression based Fault Location in DC Microgrid, M. Tech. Thesis, IIT Kanpur, November 2019.
Sivam Kumar Srivastva,Fault Location Identification in Ungrounded DC microgrid, M. Tech. Thesis, IIT Kanpur, June 2020.
Ankit Bhatt,Topology and parameter estimation in distribution grids using terminal measurements, M. Tech. Thesis, IIT Kanpur, June 2020.
Rajneesh Yadav,Droop Characteristics based Secondary Controller for Islanded DC Microgrid with Improved Voltage Regulation, Load Sharing and Line Loss, M. Tech. Thesis, IIT Kanpur, June 2020.