Papers Published/Accepted in Conference Proceedings
This paper presents a multi-objective framework for the optimal scheduling of Electric Vehicles (EVs) to satisfy the interests of multiple stakeholders, such as EV owner/aggregator and the Distribution System Operator (DSO). Optimal scheduling refers to smart charging and Vehicle-to-Grid (V2G) discharging operations of EV. The modelling of stochastic nature of arrival, departure, and the distance travelled by the EV is taken into account with appropriate Probability Distribution Funtions (PDFs). The proposed formulation considers the perspectives of the aggregator and the DSO, which are minimization of net cost of charging of EVs and the power loss in the system to improve the performance of the system, respectively. A multi-objective function is formulated using normalized linear weighted sum approach, to optimize both the objectives simultaneously. The Particle Swarm Optimization (PSO) is implemented to find out the optimal scheduling of charging and discharging of EVs. The competence of the proposed methodology is tested by implementing it on the IEEE 33-bus test feeder. The analysis is carried out for the residential and commercial loads with the consideration of different Time-of-Use (TOU) tariffs. The results show that the scheduling operation of EV, obtained by implementing proposed methodology, leads to significant reduction in the net cost of charging borne by the owner/aggregator and decrement in the network power loss.
This work proposes a multi-objective optimization formulation to solve the Conservation Voltage Reduction (CVR) problem for three-phase unbalanced active distribution systems. CVR is a tool deployed for reducing power consumption by exploiting the voltage dependency of loads. Here, the node voltage magnitudes are kept near to its lower limits, as a strategy. Voltage Regulators (VRs), Capacitor Banks (CBs), On- Load Tap Changers (OLTCs), and reactive power output from smart inverters are used to achieve this objective. Along with minimizing the load demand, minimization of the losses is also considered as an objective. Since many of the devices are operated separately across each phase, the grid suffers from increased voltage unbalances. This issue is handled by choosing Voltage Unbalance Factors (VUFs) at all nodes as constraints. Minimization of unbalance current flow in the substation transformer is also added as an objective in the optimization problem to reduce associated ill-effects. The optimization problem solved using Multi-Objective Particle Swarm Optimization (MOPSO), is tested on modified IEEE 13-bus and 34-bus systems. Obtained results show a reduction in losses and demand while ensuring acceptable voltage profiles throughout the feeders. Results show that the load profile and the R/X ratio of the lines profoundly influence the effectiveness of CVR.
The adoption of Electric Vehicles (eV) as an alternate and sustainable replacement to the existing natural-resource powered vehicles paves the way to realize the vision for a cleaner and greener environment. Electric-Rickshaw (also known as e-Rickshaws) are a common mode of transportation in Indian traffic ecosystem and are mainly used for last mile connectivity. This article explores the feasibility of using Battery-Swap Technology as the charging mechanism for e-Rickshaws. The challenges associated with the technology, policy considerations and its economic impact have been presented in the paper. The promise shown by the suggested technology has been presented with reference to few case studies.
Power Hardware In Loop (PHIL) methodology enables the flexible and risk-free testing of physical equipment. In these simulations, part of the system is simulated in a Real-Time (RT) simulator, and another part is the actual hardware. A communication module is essential to exchange signals between the RT simulator and the hardware side. Conventionally, copper wires are used as the communication link. However, they suffer from various disadvantages such as no isolation, presence of ground loop, and high EMI, etc. To mitigate these shortcomings, a fiber optics communication module is developed to interface the RTDS and the power amplifier. The design, implementation, fabrication, and verification of the fiber optics communication module is the subject of this paper. The design leads to a full-duplex, galvanically isolated communication module with a large bandwidth and transmission delay of 2.3 μs. The experimental results verifying the performance of the communication module are also reported.
As businesses grow, trust among participating stakeholders assumes prime importance. The transparency and efficiency in the transactions that occur in these businesses are equally valuable as the profits. Digitization of the economy helps ease-out the conduct of business; however, the increase in vulnerability to cyber-attacks is also on the rise. Blockchain technology revolutionizes the way digital transactions can occur and holds much promise in securing the flow of information that primarily drives them. Such a distributed ledger framework allows the traceability of a transaction through its immutable chain of blocks. Each block registers a time-stamped information set, verified by all the stakeholders involved in the business. These sets of features and much more make the blockchain technology an immensely powerful force to bring in transparency, efficiency, and trust in various industries. The paper’s primary focus is given the features that empower a blockchain to facilitate various tasks securely, efficiently, and smoothly in a power sector. It also gives impressions of pilot projects in India with blockchain applications in different sectors. Glimpses of a prototype developed by the authors for managing the trading of rooftop solar energy among a set of consumers have been provided as one of the applications in power distribution.
The penetration of distributed generations (DGs) in the existing power distribution system imposes severe challenges to the existing protection schemes. The direction and magnitude of fault current vary significantly with microgrid operating conditions, which may affect the coordination among protective relays and lead to protection system failure. This paper proposes an optimal relay coordination scheme based upon the chaotic cuckoo search (CCS) algorithm. The current setting of the directional overcurrent relays (DOCRs) is updated with the operating condition of the microgrid, which results in minimum possible operating time. The CCS algorithm is implemented on a standard IEC 61850 microgrid to obtain the optimal time multiplier setting (TMS) in grid-connected (GC) and islanding modes. The impact of DGs on the proposed scheme is studied by implementing the CCS technique to IEC 61850 distribution network without DGs. The performance comparision of the CCS based method with existing relay coordination schemes is carried out. The extensive test results carried out in the microgrid integrated with inverter and induction-based DGs indicate the potential of the presented CCS based relay coordination technique for developing a reliable protection measure for microgrids.
With the increased penetration of power electronics based distributed energy resources (DERs), its control and automation in traditional grid gives rise to more complex operation of power system. It is difficult to realize such a multidisciplinary power system using a single real-time simulator. Co-simulation is a versatile technique to split the large system models into multiple subsystems and components. In case of limited capability of a single simulator, these components can be modeled in more than one simulators and can be solved in parallel. The technique is also useful to interconnect simulators of different make which utilizes propriety software tools. In this paper, a co-simulation based testbed is developed, which can facilitate a platform for validation of various power engineering algorithms. Two different make of real time simulators, Typhoon Hardware-In-Loop (HIL) and Real Time Digital Simulator (RTDS) have been interfaced using peer-to-peer and VILLASnode based UDP/IP socket communication. In this work, an Ideal Transformer model (ITM) based approach is utilized to couple the simulators where the information is exchanged using the dynamic phasors. An illustrative testbed of CIGRE low voltage distribution system is developed using both types of communication methods and the results are compared in terms of latency, jitter and round trip time. In addition, the effects of packet loss, data corruption and duplication on system transient are also presented in this paper. The results demonstrate the capability of the testbed to evaluate the controllers for microgrid, DERs and protective devices in the distribution network at different levels of deployment.
In this paper, a frequency measurement based Instantaneous Frequency Relay (IFR) is proposed for quick real-time islanding detection of Distributed Generators (DGs). The proposed IFR has reduced detection time and improved performance compared to conventional frequency relay. The later has an inherent 50ms minimum time delay. The proposed IFR can issue an instantaneous trip signal in event of occurrence of islanding to the circuit breaker during its operation but restrains during transient conditions. It is designed to have a pickup time in the range of 1 – 5 cycles to avoid any maloperation during switching transients. A Savitzky-Golay (SG) filter is used here to remove unwanted noise from signals while preserving the transient present in the signal. Further, IFR is flexible in operation as it can be easily re-tuned for both 50Hz and 60Hz system frequencies. Test results from Real-Time Digital Simulator (RTDS) indicate that the proposed IFR is quick in operation and has an accurate performance for several test conditions.
In this paper, a modified leaky-least mean square (MLLMS) control strategy for remotely located microgrid includes solar photovoltaic (PV), battery storage (BS) and diesel generator (DG) set is developed to provide continuous supply to remote locations. The storage battery is integrated at the DC link with the help of a bidirectional buck-boost converter (BDC). It functions as a buck converter during the charging of the battery. Whereas it operates as a boost converter when it discharges power. Moreover, the BDC fixes PV maximum power point (MPP) voltage at the DC link; thereby, peak power is harvested. Here, a synchronous generator based DG set is connected at the point of common interphase (PCI) to provide the load demand. It feeds linear or nonlinear loads. The linear and nonlinear loads demand reactive power and harmonics; thus, the voltage source converter (VSC) that integrates the energy sources at the PCI is controlled to compensate for power quality (PQ) issues.
Abstract:Recent transformations in the electrical distribution network include formation of microgrids and large deployment of Renewable Energy Sources (RESs), particularly Solar Photo Voltaic (SPV) and wind plants. Due to intermittency of the power outputs of these sources, maintaining continuity and reliability of supply becomes more challenging, which can be addressed through deployment of storage systems. The Battery Energy Storage System (BESS) is the most popular choice at present in the distribution systems and microgrids. It is important to decide optimal placement and sizing of BESS in order to reduce the power losses and large voltage deviation in the system, while maintaining the continuity of supply and power quality. This work presents the optimal planning of the BESS in a residential area microgrid pilot inside IITK campus, mimicking typical semi- urban distribution in India, as part of joint Indo-US project ‘UI-ASSIST’. It has been formulated as an optimization problem having objective function to minimize the total network real power loss and voltage deviation at each node, subject to various physical and operating constraints. DigSilent is used to simulate different operating conditions and perform load flows. An analytic approach is used to minimize the objective function. The results are further validated on the simulation model of microgrid pilot under various operating conditions using Real Time Digital Simulator (RTDS).
In addition to high conversion efficiency, low cost and compact size are also desirable for the wide-scale adoption of multilevel Photovoltaic (PV) inverters. Generally, the multilevel PV inverters employ a large number of power semiconductor devices, most of which are not ground referenced. The cost and size of PV inverters is expected to increase due to isolated power supplies for gate drivers of high side devices. A Bootstrapped gate driver supply eliminates the need for isolated power supplies by introducing relatively low cost and low size components, such as resistors, diodes, and capacitors. This paper proposes a methodology to design a bootstrapped gate driver power supply for multilevel PV inverters. The proposed approach is generic and applicable to a wide range of popularly known multilevel inverter topologies. The design guidelines and component sizing constraints for the proposed methodology are also presented. The proposed approach is also demonstrated for a single phase transformerless multilevel PV inverter. Its operation is validated by experimental studies.
This paper presents an islanded microgrid comprised of solar energy conversion (SEC), a battery energy storage (BES) and a diesel generator (DG) set with an efficient control strategy. This configuration aims at the maximum utilization of solar energy and the economical usage of other sources. The maximum utilization of solar energy is achieved by harvesting the photovoltaic (PV) array maximum power. The DG set is controlled to operate only when the PV array together BES can’t support the load power. Thus this configuration mitigates the discontinuity in supplying the load demand. A weighted zero-attracting leaky least mean square (WZA-LLMS) adaptive control provides solutions for power quality issues such as reactive power, harmonics and power unbalance in three phases etc. The MATLAB/Simulink platform is used for the modeling and simulation of the microgrid system.
The off-grid village electrification is made viable by utilizing the full potential offered by renewable energy sources (RESs). Integrating more than one resource i.e. wind and solar, offers self-sufficiency of power due to their complementary nature. The intermittency issues raised by RESs are overcome by using a battery as the storage. The battery reduces the uncertainty during demand rise, power deficiency and overloading with its faster response than diesel generators and micro-turbines. This work deals with the wind energy/solar photovoltaic (PV)/battery energy storage (BES) operating in coordinated manner to meet the high power residential loads at village scale. For the required speed regulation of a wind turbine driven generator, the traditional proportional integral (PI) controller is replaced by evolution inspired biogeography based optimization control (BBO) based PI controller. The relevant issues identified by a use of fixed gain PI controller such as, unsuitable regulation due to incorrect tuning are addressed by the use of BBO tuned speed controller providing fine-tuning of the weighting factors. Whereas, in the voltage control, the performance degradation issue of PI controller while dealing with AC quantities, is dealt with adaptive proportional resonant (PR) controller along with disturbance observer based phase locked loop (DO-PLL). The DO control filters the load current component and improves the power quality at point of common coupling (PCC). The battery is deployed through a bidirectional converter, acts as a residential storage for backing up the power firming RESs production. Performance improvement obtained from a laboratory developed test setup verifies the microgrid effectiveness at RESs generation variability and load changes.
This paper deals with a 3-phase 4-wire PV (Photovoltaic)-grid connected system feeding nonlinear and unbalanced loads. The four-leg VSC (Voltage Source Converter) is used to regulate the power flow between the source and load sand to mitigate the power quality (PQ) issues using modified variable step size diffusion normalized sign- error adaptive filtering control algorithm (VSS-DNSEA). The control algorithm is designed to extract the fundamental active current of the load current and to reduce PQ issues using 4-leg VSC as a distributed static compensator (DSTATCOM). A simple and efficient P&O (Perturb & Observe) MPPT (Maximum Power Point Tracking) algorithm is used to utilize the PV array to its maximum capacity and thus achieving effective dynamic and steady state performances. The THD (Total Harmonic Distortion) of the grid current in the system is well maintained within prescribed limits. The control of this system is validated using an experimental prototype and in simulation under different variations.
This paper presents a simple procedure to obtain a comprehensive set of non-isolated DC-DC converter topologies for the specified voltage gain expression. The proposed method utilizes the principle of inductor flux balance as a synthesis tool. The symmetries in the flux balance equations are identified and are used to obtain the complete set of unique converter topologies. The proposed method is applied to synthesize a comprehensive set quadratic boost topology. The total number of unique q-boost topologies is found to be eleven. The operation and feasibility of two novel topologies, identified by the proposed theory, are verified experimentally.
To replicate the harmonic behavior of a home load connected to a distribution grid, a Harmonic Tolerant Mock-Up-Load (HT-MuL) is presented in this paper. A comprehensive design methodology of HT-MuL considering various practical constraints such as switching frequency and the output voltage is developed. The HT-MuL is designed to work as a power sink. It can draw up to 19 th harmonic current from the distribution grid without violating the imposed constraints. A lab-scaled prototype of 110 V, 200 VA is made to validate the performance of HT-MuL with the designed parameters.
In this paper an adaptive least mean absolute third (LMAT) control for a 3-phase double stage solar photovoltaic (SPV) grid integrated system to improvise the quality of power. It consists of a DC-DC boost converter, a ripple filter, a VSC (Voltage source converter) and three phase loads. The VSC is coupled at DC-link for feeding SPV power into the utility grid with harmonics elimination of load currents and grid currents balancing. Here, the LMAT adaptive control technique is used to evaluate the fundamental weight of load current to provide the fast convergence. Here, for the solar PV generation, a feed-forward term is used to enhance the dynamic performance. Therefore, this adaptive LMAT control technique is tuned by a simple way. The harmonics in grid currents are shown under the IEEE-519 std.
Increasing environmental concerns have driven the adoption of clean energy sources at the local power system level. However, it is also the cost-economics that has led to the rise in bulk-power system-level participation of renewable energy sources like solar photovoltaic (PV). Distributed and decentralized energy systems have also emerged as an effective alternative to the centralized power system and many countries have announced target-driven policies to encourage the same. Rooftop solar PV is a popular form of distributed generation that has huge potential in facilitating local demand-supply balance and ensuring energy security. However, the true value of rooftop solar energy is not well discovered and enjoyed by both the consumers and the utilities and hence the rooftop solar PV penetration level has not risen significantly, particularly in India, which has an ambitious target of 40 GWp to be achieved by 2022. One of the possible ways to attract more consumer and utility interest in rooftop solar is to provide a fair degree of autonomy wherein the prosumers can sell their excess to their neighbors at prices determined competitively. Peer to peer (P2P) Energy Sharing is one such way of encouraging the same. However, efficient pricing mechanisms are required to enable such a framework along with effective and trust-based platforms to facilitate and manage the trading process. This paper discusses three of such pricing mechanisms - Mid-market rate, bill-sharing, and demand-supply ratio and benchmarks their performances against coalition game-theory based method which is best suited to model such a scenario. These have been compared on various performance indices for an institutional setup in India.
In this paper, a three-phase four-wire (TPFW) standalone microgrid is presented for powering the electrical energy to the rural areas where the electric grid is not available. This microgrid is designed with a synchronous generator (SG) based diesel generator (DG) set, a photovoltaic (PV) array and a battery storage system (BSS). The BSS handles the intermittent variation of the PV array power as well as provides power to the load during the heavy load demand. The DG set feeds power to the nonlinear and unbalanced loads. Hence the voltage source converter (VSC) is controlled in such a manner that it provides the harmonics, reactive power as well as the compensation of unbalanced load. Thereby the power quality (PQ) at the DG set is improved. The main functional features of the microgrid, are extraction of maximum PV array output power, DG set terminal voltage regulation, unity power factor (UPF) operation of the DG set by compensating the reactive power, harmonics elimination, compensation of the unbalanced load and neutral current compensation etc.
Regulating bus voltage and system frequency within desired permissible limits in an islanded microgrid with Renewable Energy Sources (RESs) is a challenging task. Hence, an optimal day-ahead load scheduling for the islanded operation of a microgrid is proposed here, which caters to this issue. The loads in the microgrid are assumed to exhibit Demand Response (DR) characteristics. Load curtailment options are also used in the proposed approach to cater to generation deficit situations in the islanded microgrid. A novel multi-objective formulation is also proposed to ensure optimal day-ahead load scheduling and load curtailment by minimizing the cost of energy supplied and the voltage deviation at all buses throughout the day. The best-compromised solution obtained from the associated optimal Pareto front ensures optimal load schedule by keeping the bus voltages and system frequency within the desired limits. The test results obtained for the IEEE 33 bus distribution system prove the efficacy of the proposed formulation.
This article illustrates a real time centralized energy management process for a residential flat building under randomly updated energy price, rooftop solar generation and load demand at each flat. The residents at each flat are considered to be non-identical as far as their response towards respective power consumption are concerned, which is modelled as utility function of the flat occupants. The derived optimization problem is solved by utilizing Lyapunov optimization technique, which does not require the probabilistic estimation of the uncertain parameters but only their real time values. Convexity of the derived problem is validated to proof the existence of only one optimum result i.e. global minima. Proposed real time energy management process is implemented on a building having four flats. Superiority of the proposed strategy is established by comparing with another real time method named greedy algorithm.
Large integration of DC distributed energy resources and DC electrical loads into the existing AC distribution network are made possible with the deployment of power electronics converters. This transforms the conventional AC network to an AC/DC hybrid distribution network (HDN). However, intermittent renewable energy, uncertain market energy price and vulnerable load demand of consumers causes serious real time power imbalance situation. To address the above deficiency, this paper assesses the impact of real time demand control on AC/DC HDN by designing a multi-objective, non-linear, convex, real time energy management algorithm based on Lyapunov optimization technique, which works only by knowing the updated present data of the uncertain parameters rather than their probabilistic estimated values. Efficacy of the proposed methodology is evaluated by simulating case studies on modified IEEE 33 bus AC/DC HDN test case.
Unintentional Islanding Detection (UID) of Distributed Generators (DGs) in a microgrid through passive approaches is still an active area of the research as most of the existing passive approaches fail to detect UI in Non-Detection Zone (NDZ). Hence, this paper proposes a new passive technique for quick UID of multiple DGs, even in the case of zero power mismatch/ power balance, by the use of the Lissajous pattern. Point of Common Coupling (PCC) voltage and current phasors are estimated by Moving Window Discrete Fourier Transform (MWDFT). The Lissajous pattern and the associated parameters, such as slant angle, major and minor axes, are evaluated from these phasors. Based on these parameters, UI is detected. The proposed approach is tested as per the IEEE 1547 standard for different load quality factors in Real-Time Digital Simulator (RTDS). The obtained results prove the efficacy of the proposed Lissajous pattern-based UID, with detection time being less than 3 cycles for all simulated cases.
Event detection and localization is at the heart of all automated system restoration processes. Localizing an event can help in alleviating the root cause behind such disturbances. During an event, the operating states of the power distribution network may undergo significant changes. These variations are more prominent in buses which are close to the source of the event. Thus, events in a distribution system can be localized by analyzing the changes in the system states. This paper proposes an event locator based on the results of a event triggered distribution network state estimator. The state estimation is performed using measurements from a limited number of micro phasor measurement units (µPMUs). An l1 regularization based state estimator is designed to estimate the change in system states, using limited number of µPMU measurements. The results of the state estimation process are further analyzed to locate any event. The algorithm is designed for active distribution networks with radial and meshed topologies. The proposed method is validated on a 13-node test distribution feeder simulated using OPAL-RT real-time simulator.
In this paper, the authors have attempted to address the problem of power sharing in networked hybrid AC/DC micro-grid clusters by utilising back-to-back converter. The hierarchical distributed cooperative control strategy is employed for both the AC and DC microgrid clusters (intra-microgrid control) and an inter-microgrid control strategy employing back-to-back converter for enabling power sharing among the clusters according to the required needs. The distributed secondary control for both the AC and DC MGs aid to reprimand the voltage drops due to presence of cable resistance and droop characteristics. It thus helps to achieve a regulated voltage at both the AC and DC PCC. Particularly in AC MG, it enhances the voltage and power quality. Further, it is worth noting that most of the consensus algorithms are asymptotically convergent and hence in order to achieve finite-time convergence, a modified consensus approach is used for the DC microgrid cluster. This is done to achieve faster consensus irrespective of the unforeseen disturbance / transients that may occur in the AC microgrid clusters. The distributed dynamic averaging consensus algorithm based on PI controllers (DAC-PI) is also investigated for robustness against physical and communication failures. With the proposed inter and intra-microgrid cluster control mechanism, power balance between three phase AC MGs and DC MG is illustrated in this work. This could be utilised as practical applications in stand-alone microgrids, marine power systems, more electric aircraft power systems and can be equipped with mode selection algorithms to enable connection to the utility thereby endowing flexibility and reliability to the network of microgrid clusters. Extensive simulations of test-cases are provided with MATLAB/Simpowersystems platform to elucidate the performance of the proposed control strategy and the hybrid infrastructure.
Relay-assisted cooperative free space optical (FSO) communication system is a powerful technique, which offers advantages like fading mitigation and significant gain in spatial diversity due to shorter transmission hops. Even so, it can be hampered by jamming activities which in turn degrade the overall system performance. In this paper, the effect of relay jamming in the decode-and-forward (DF) protocol based cooperative FSO communication system, is introduced and studied thoroughly. The probability density function (pdf) of a random variable containing mixture of the negative exponential and Gaussian random variables is derived. The error performance of the considered FSO system is analysed over this new kind of additive mixture noise for different probabilities of jamming. By utilizing the derived pdf, a closed-form expression of the average bit error rate (BER) of the DF FSO relaying is obtained. A comparison of the BER performance of maximum-likelihood (ML) detector and a derived threshold based detector is also provided. It is observed that the derived threshold based detector offers almost similar performance as that of the ML detector. A thorough numerical study is also provided by considering different pointing error parameters of jammer’s and user’s channels.
The renewable energy sources are operated at Maximum Power Point Tracking (MPPT) mode to extract maximum energy. The integration of renewable energy sources to the grid is a challenging task. During the integration of the renewable energy sources to the grid, the DC bus voltage should be regulated and maintained constant. As these sources are highly variable and unpredictable in nature, requires a storage devices to maintain the DC bus voltage constant. The designed controller stabilizes the DC bus voltage. The controller regulates the DC bus voltage with changes in wind velocity, solar irradiation and load. The system maintains the Point of Common Coupling (PCC) voltage under variable load condition. The grid voltage and currents harmonic distortion are within the acceptable limits. The system is tested in two modes using MATLAB-Simulink.
The renewable energy intermittency indicating generation unavailability and volatility in a microgrid need to be addressed with prime attention. Here, in this work, the operational reliability and generation adequacy are reinforced by integrating a battery as the energy storage to the variable speed wind power generation system (WPGS). The grid interconnection to the system and combined performance offer significant benefits of improved power quality (PQ), energy sufficiency and surety by managing the local load support. The control of the battery allows the generation of the grid reference current. The grid side power converter utilizes the maximum-likelihood estimator based adaptive filter for improving the PQ indices by addressing the prevailing concerns stemmed by nonlinear loads. The control has high tracking performance while dealing with the contingency event of load variation. The machine side power converter utilizes vector control for obtaining the switching pulses. A hardware prototype is developed and the test results acquired substantiate that the work carried out is effective, reliable and offer improved PQ indices.
This paper presents a dual layer least mean fourth adaptive filter based algorithm for the grid side converter (GSC) control of a wind turbine driven doubly fed induction generator (DFIG) to extract the active fundamental weights of both load and stator currents in grid connected mode. This is essentially eliminates the use of phase locked loop, abc to dq and dq to abc transformations in GSC control as compared to conventional synchronous reference frame based vector control. Moreover, a reduced sensor based control is incorporated in the rotor side converter (RSC) control of DFIG. In this, rotor currents are estimated in stationary reference frame from sensed stator currents and stator voltages. Therefore, in totality, it reduces two current sensors and results in lower cost and less complexity of the system. To qualify the system performance, simulations are carried out under linear and nonlinear loads, constant and varying wind speed, and nonlinear unbalanced loads. The total harmonic distortions of currents and voltages, are obtained as specified in the standard of the IEEE 519. Moreover, both the grid and DFIG stator are operated at unity power factor. Finally, the system steady state and dyamic performances, are verified on a prototype developed in the laboratory
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.
DC microgrid protection is a challenging task owing to its need for ultra-high-speed fault detection and isolation, which further makes fault location and system restoration even more challenging for limited data and time window. This paper, thus, proposes a Gaussian Process Regression (GPR) based fault location in DC microgrid using both supervised and semi-supervised learning modes. The proposed approach is also capable of estimating fault resistance. The data measured locally is sufficient to locate the fault accurately. Unlike other existing methods, the proposed approach does not require pre-processing of data, thereby decreasing the complexity and computational time involved in feature extraction. Also, the algorithm is independent of the DC microgrid operating condition. A test system is simulated in Real-Time Digital Simulator (RTDS), and the current measurements extracted are used in training and testing of GPR in MATLAB. The proposed method is tested for different test scenarios, such as high impedance fault (up to 10Ω), fault parameters, different sampling frequency, and noise levels. The obtained results prove the superiority of the proposed approach as compared to other existing approaches.
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.
This paper deals with an adaptive rotor side converter (RSC) control through linearization of rotor currents dynamics for wind turbine (WT) coupled doubly fed induction generator (DFIG). The WT coupled DFIG is interfaced to the grid. The control comprises of feedback control and unique state observer. The dynamics of rotor currents in synchronously rotating dq reference frame, are linearized to obtain the feedback control design. The unique state observer is designed to estimate the system unique states. Moreover, these states are established to include the disturbances due to sudden change in wind speeds, coupling terms between d and q axes and system nonlinearities. The adaptive RSC control is framed to effectively obtain unity power factor in the stator and also to acquire maximum power from the WT. In addition, the control of grid side converter is designed to regulate the DC link voltage and to compensate the unbalanced and nonlinear loads. The simulated performance of the system is presented for varying wind speeds and nonlinear unbalanced loads to show the effectiveness of the control algorithms. Moreover, a prototype is developed in the laboratory to validate its steady state and dynamic behaviors.
The interfacing of renewable energy sources (RESs) into power system through power electronic converters is being increased in microgrid. The control and integration of RESs require an accurate fundamental frequency positive sequence (FFPS) component extraction methods to enhance the disturbance rejection capability of SRF-PLL for various grid conditions. The extraction of FFPS components based on second order generalized integrator (SOGI), cascaded delayed signal cancellation (CDSC) and multiple delayed signal cancellation (MDSC) PLLs are reviewed and their extraction accuracy is evaluated for various grid conditions based on the quality of frequency in SRF-PLL. The performance comparison of these PLLs is presented based on the MATLAB simulation results.
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:There is a substantial increase in the use of doubly fed induction generator (DFIG) based wind turbine in determining the frequency response. The frequency regulation capability of the DFIG has contributed to enhancing the system response at the time of frequency variations. The authors have proposed the coordinated frequency controller to achieve the following objectives: first to provide the transitory support to the system at the time of frequency event and second to maintain the deloading capability of the DFIG system depending on the wind speed and the deloading mechanism limitations. Further, the combination selection scheme based on the weighing factor is introduced that provides an apt strategy to manage various control scheme at the time of varying reserve power depending on wind power availability. The real-time digital simulator platform provides the simulation results that showcase the effectiveness of the proposed scheme in obtaining the frequency regulation with the help of the DFIG system.
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:Volt-VAR Optimization (VVO) is an essential tool which ensures acceptable node voltages in a distribution system while ensuring minimum operational losses. Recent relaxations of IEEE standard 1547, on the usage of smart inverters in distribution system as source of reactive power, has increased the flexibility in VVO. Smart Inverters can operate in various modes such as real power priority (P-Priority), reactive power priority (Q-Priority) or in Constant Power Factor (CPF) mode, when participating in VVO. They can also be operate in Volt-Watt Optimization (VWO) mode. This work investigates how loss in VVO is affected due to various modes of operation of smart inverters. Particle Swarm Intelligence (PSO) has been used to solve VVO and associated results have been obtained for the IEEE 13 bus unbalanced distribution system which consists of two Capacitor Banks (CBs), one Voltage Regulator (VR) and a smart inverter. These results suggest the selection of mode of operation of smart inverter based on practical considerations rather than operating it in the same mode throughout the day.
Abstract:Recently, False Data Injection Attack (FDIA) has gained much attention in the electrical research community, because of the adverse effects of FDIA on the day-to-day operation of smart grids. Recent literature provides various approaches to formulate the Attack Vector (AV), to misguide the DC state estimator as well as AC state estimator. However most approaches which formulate the AV for AC state estimator are iterative in nature. Hence, in this work, an approach for linearized AV formulation has been proposed to formulate stealth as well as semi-stealth FDIAs against the nonlinear AC state estimator. The proposed linearized attack vector formulation technique, will not only be able to deceive the bad data detection but shall also be able to formulate the AV in the least possible amount of time. A maximizing approach has also been proposed to maximize the effect of FDIA. The proposed approach has been tested on the IEEE 118 bus test system, under various loading conditions with varying degree of attack magnitudes, which prove the efficacy of the approach.
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.
The conventional multifunctional DSTATCOM has a compensation limitation as it cannot compensate deep voltage sag and swell. To overcome this, a new configuration of multifunctional DSTATCOM is proposed in this paper. The proposed system consists of a voltage source inverter (VSI) and battery-supercapacitor energy storage system which is connected to the DC link through DC/DC converters. The proposed multifunctional DSTATCOM has all the advantages of a conventional multifunctional DSTATCOM. Moreover, it can mitigate deep voltage sag, swell and interruption. The battery-supercapacitor energy storage system delivers power to the load during deep voltage sag, swell and interruption, known as uninterruptible power supply mode (UPS). Battery delivers average load power during UPS mode, while grid is disconnected from the system and supercapacitor delivers all the load fluctuating power. The supercapacitor also delivers the fluctuating power during normal operation. This helps to improve the DC link voltage dynamics during sudden changes in source voltage and load power. The performance of the proposed hybrid DSTATCOM with battery-supercapacitor energy storage system has been verified through simulation studies.
—Proper protection of microgrids (MGs) is a challenging task due to bidirectional power flow and changing network topology. Application of micro-phasor measurement units (𝜇PMUs) in MGs is gaining popularity in providing bettersystem observability. Protective device coordination in MGs is affected by the change in network topology and status of various distributed generations (DGs). The real-time measurements available from 𝜇PMUs can be used for providing better protection to the MGs. In this paper, an adaptive protection coordination scheme for AC MGs using 𝜇PMU based measurements and numerical directional overcurrent relays is proposed. The 𝜇PMU based measurements are used to estimate the existing network topology, power contributed from all the connected DGs, and the status of the point of common coupling. The proposed approach has been validated on a 7-bus AC MG derived from the IEEE 14-bus test system. The results obtained demonstrate the effectiveness of the proposed adaptive protection scheme.
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