US-India CollAborative For Smart DiStribution System WIth STorage

Publications

Papers Published/Accepted in Refereed Journals

Abstract:The presence of phasor measurements in ac systems provides a range of protection techniques based on sequence components and phase comparison to discriminate the fault. However, the absence of phasor measurements in dc system reduces the available alternatives for fault detection. In addition, the presence of low fault tolerant converters, large range of fault impedance and varying grid conditions demands sensitive and selective protection schemes. In this regard, several recent works have suggested a communication-based primary protection due to its high sensitivity to faults. However, with a failure in the communication network, the primary protection will also fail to detect a fault. This paper proposes a backup scheme to isolate the faulty section, even in the case of a communication failure. In the literature, overcurrent- and undervoltage-based backup protection schemes are suggested along with unit primary protection. In the presence of low fault tolerant converters and variable fault resistances, the traditional backup schemes may not work well. This paper proposes a new fault detection method for backup schemes, which utilizes only the locally measured current signal, and uses both derivative and integral characteristics of current to ascertain the occurrence of a fault. The proposed method is capable of detecting the fault accurately and within the required time. The performance of the proposed scheme has been assessed on a ± 600 V TN-S grounded dc microgrid under various conditions using hardware-in-loop simulations on real-time digital simulator.

Abstract: In this paper, we study the physical layer secrecy performance of a hybrid satellite and free-space optical (FSO) cooperative system. The satellite links are assumed to follow the shadowed-Rician fading distribution, and the channel of the terrestrial link between the relay and destination is assumed to experience the gamma–gamma fading. For the FSO communications, the effects of different types of detection techniques (i.e., heterodyne detection and intensity modulation with direct detection) as well as the pointing error are considered. We derive exact analytical expressions for the average secrecy capacity and secrecy outage probability (SOP) for both cases of amplify-and-forward (AF) and decodeand- forward (DF) relaying. The asymptotic analysis for the SOP is also conducted to provide more insights on the impact of FSO and satellite channels on secrecy performance. It is found that with the AF with fixed gain scheme, the secrecy diversity order of the investigated system is only dependent on the channel characteristics of the FSO link and the FSO detection type, whereas the secrecy diversity is zero when the relay node employs DF or AF with variable-gain schemes.

Abstract:This paper deals with the design and stability analysis of a DC microgrid with battery-supercapacitor energy storage system under variable supercapacitor operating voltage. The conventional design method reported in the literature considers the rated supercapacitor voltage in the modeling and design of controllers. However, the supercapacitor unit can discharge as low as 10% of its rated voltage due to self discharge. It is observed that the conventional method of controller design can potentially make the system unstable or introduce ringing in the DC link voltage at low supercapacitor voltage. In this work, the sensitivity of DC microgrid stability with respect to supercapacitor voltage variation is analyzed, an optimal supercapacitor voltage to be considered in the design is calculated and a design method is proposed to ensure the stability of DC microgrid in all operating modes. The stability of the DC microgrid with controllers designed using the proposed method is evaluated with digital simulation and experimental studies.

Abstract:This paper deals with the protection of critical loads from voltage-related power quality issues using a dynamic voltage restorer (DVR). A generalized control algorithm based on instantaneous space phasor and dual P -Q theory has been proposed to generate the instantaneous reference voltages to compensate the load voltages with direct power flow control. The proposed algorithm adapts energy-optimized series voltage compensation, which results in a reduction of energy storage requirement. The proposed DVR control scheme can support the load from voltage-related power quality issues irrespective of the load current profile. Each leg of the three-phase three-leg split capacitor inverter is used to inject series compensation voltage in respective phases of the system. Model-based computer simulation studies and real-time experimental results validate the effectiveness of the proposed control algorithm.

Abstract: With increased integration of wind energy systems, an accurate wind speed forecasting technique is a must for the reliable and secure operation of the power network. Statistical methods such as Auto-Regressive Integrated Moving Average (ARIMA) and hybrid methods such as Wavelet Transform (WT) based ARIMA (WT-ARIMA) model have been the popular techniques in recent times for short-term and very short-term forecasting of wind speed. However, the contribution of the forecasting error due to different decomposed time series on the resultant wind speed forecasting error has yet not been analyzed. This paper, thus explores this shortcoming of the ARIMA and WT-ARIMA models in forecasting of wind speed and proposes a new Repeated WT based ARIMA (RWT-ARIMA) model, which has improved accuracy for very short-term wind speed forecasting. A comparison of the proposed RWT-ARIMA model with the benchmark persistence model for very short-term wind speed forecasting, ARIMA model and WT-ARIMA model has been done for various time-scales of forecasting such as 1min, 3min, 5min, 7min and 10min. This comparison proves the superiority of the proposed RWT-ARIMA model over other models in very short-term wind speed forecasting.

Abstract: Quick fault detection and isolation of faulty section are desired in DC microgrid due to the presence of power electronic converters and low cable impedances. Owing to need of fast disconnection, limited time and data are available for online fault distance estimation. Some of the existing techniques consider source capacitors connected at only one end of the cable; therefore, assume that the fault current is contributed by only one end of the cable. This may not be true in the case of multi-source DC microgrids, where fault current would be supplied from both the ends. Further, existing communication-based techniques require either data synchronisation or fast communication network. To address these issues, this study proposes an online fault location method for multi-source DC microgrid without using communication. The mathematical model of faulted cable section connected to sources at both the ends is derived. This model is used along with the measurements to determine the fault distance. The model consistency with the measurements is quantified using the confidence level based on the residual analysis. A ring-type multi-source DC microgrid system is considered and simulated on real-time digital simulator to demonstrate the effectiveness of the proposed algorithm.

Abstract:The AC-DC distribution systems have recently gained huge popularity due to advancements in power converters, high penetration of renewable energy resources and wide usages of DC loads. However, load flow in such systems is a challenging task due to non linear characteristics of power converters. This paper presents a novel load flow algorithm for AC-DC distribution systems, utilizing the concept of graph theory and matrix algebra. Four developed matrices, loads beyond branch matrix [LB], path impedance matrix [PI], path drop matrix [PD], slack bus to other buses drop matrix [SBOBD] and simple matrix operations are utilized to obtain load flow solutions. These matrices reveal the network topology and relevant information about the behaviour of AC-DC distribution network during load flow studies. In contrast with traditional load flow methods for HVDC systems, the proposed technique does not require any lower upper (LU) decomposition, matrix inversion and forward-backward substitution of Jacobian matrix. Because of the aforementioned reasons, the developed technique is computationally efficient. The proposed method has been tested using several case studies of AC-DC distribution network which includes different operating modes of various power converters. Results show feasibility and authenticity of the proposed method.

Abstract:This paper proposes a centralized control strategy for power management of hybrid microgrid connected to the grid using a parallel combination of grid side converters (GSCs). An improved version of instantaneous symmetrical component theory (ISCT) is developed and is used for the control of parallel operated GSCs, which results in reduced sensor requirement, control complexity, and communication bandwidth. In addition, a simple power management algorithm is developed to test the efficacy of the proposed parallel grid side converter control strategy for all the microgrid modes considering state of charge (SOC) limits of hybrid energy storage system (HESS), load changes, and renewable power variations. In the proposed system, a better dc link voltage regulation is achieved and usage of supercapacitor reduces the current stresses on the battery. With the proposed control strategy, the essential features of grid side converters like power quality, power injection, bidirectional power flow and proportional power sharing are achieved. The effectiveness of the developed control strategy for the proposed system is tested using MATLAB based simulink environment and validated experimentally using a laboratory prototype.

Abstract: Home energy management systems (HEMS) encourage participation of residential consumers into the demand response programs. This paper proposes a robust-CVaR (Conditional Value at Risk) optimization approach for day ahead HEMS to reduce the effect of risk of real time exposure to energy price and solar power generation uncertainties. Initially the CVaR method is integrated with the Two-point Estimation (2PE) analysis to approximate the solar power, modelled as Beta probability distribution function, in low computation effort compared to conventional Monte Carlo Simulation (MCS) based CVaR approach. Then the optimization constraints are revised to their robust counterparts by accounting a certain amount of uncertainty in the energy prices from their nominal values. Unlike previous literatures, the optimization problem is developed to minimize the risk value of the energy cost. Again to maximize the life of the plug in electric vehicle (PEV) a pseudo cost function for the PEV battery degradation is proposed. The entire optimization portfolio is developed as a mixed integer linear programming (MILP) for its easy execution. Simulation is demonstrated on a smart home, designed as an AC-DC microgrid (MG), having practical appliance data sets, to prove the efficacy of the proposed method.

Abstract: Real-time visualisation of large power systems, by tracking the system states, is a challenging task as it involves processing a large measurement set to obtain the system states. This study proposes a hierarchical parallel dynamic estimation algorithm to estimate the states of a large-scale interconnected power system. The power system is decomposed into smaller subsystems, which is processed in parallel to obtain a reduced order state estimate. This information is then transmitted to the central processor, which collates the individual reduced order estimates to obtain the global estimates. Each processor uses state matrix of smaller dimension, thereby reducing the computational burden. The low-level processors utilise only a fraction of the global measurements in the proposed approach, and there is no need for any information exchange from the central processor to the low level processors, which helps in reducing the communication requirements. Moreover, detection of anomalies can also be carried out at the local processors without the need for any separate bad data detection at the central processor. IEEE 30- and 118-bus systems are used as test beds to study the proposed approach.

Abstract: With the rapid proliferation of the advanced metering infrastructure, the smart grid is evolving towards increased customer participation. It is now possible for a utility to influence the customer demand profile via demand side management techniques such as real-time pricing and incentives. Energy storage devices play a critical role in this context, and must be optimally utilized. For instance, the peak power demands can be shaved by charging (discharging) the batteries during periods of low (high) demand. This paper considers the problem of optimal battery usage under real-time and non-stationary prices. The problem is formulated as a finite-horizon optimization problem, and solved via an online stochastic algorithm that is provably near-optimal. The proposed approach gives rise to a class of algorithms that utilize the battery state-of-charge to make usage decisions in real-time. The proposed algorithms are simple to implement, provably convergent for a wide class of nonstationary prices, easy to modify for a variety of use cases, and outperform the state-of-the-art techniques, such as those based on the theory of Markov decision processes or Lyapunov optimization. The robustness and flexibility of the proposed algorithms is tested extensively via numerical studies in MATLAB and real time digital simulator (RTDS).

Papers Published/Accepted in Conference Proceedings

Abstract:

Abstract:

Abstract:

Abstract:

Abstract:

Abstract:

Abstract:

Abstract:

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:

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 area.

Abstract:

Abstract:

Abstract:

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 efficacy.

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:

Abstract:

Abstract:

Abstract:A solar photovoltaic (PV) - battery energy storage (BES) involved microgrid system is presented in this paper. It contains a bidirectional DC-DC converter (BDDC), which is responsible for extracting the maximum power output from the PV array by regulating the DC link voltage to the maximum power point (MPP) voltage of the PV array. Whenever, the PV array is not delivering any power then the control of the BDDC is automatically shifted to regulate the DC link voltage to a constant DC voltage. Thus the BDDC regulates the DC link voltage to desired voltage in the presence of BES in the microgrid. Whenever the BES is disconnected from the microgrid then the voltage source converter (VSC) functions regulation of the DC link voltage to desired value, so this enhances the reliability of the system. The neutral current compensation is performed by the zig-zag transformer. The VSC performs different functions such as mitigation of harmonics, reactive power, balancing of grid currents and the regulation of the DC link voltage in the absence of BES. The system behavior is analysed under different operating conditions in the laboratory on a system prototype.

Abstract:Recent developments in the power converter technology and the need for better power quality/reliability, have necessitated the integration of AC and DC grids. The realization of AC-DC distribution network has become more rational with the increase in renewable generations and DC electronic loads. There are numerous technical advantages of using DC power in conjunction with AC power in distribution systems. But for widespread utilization of AC-DC distribution network, the economic impact of aforementioned technology on the affiliated customers needs to be inspected. Distribution use of system (DUoS) charges is an eminent means for scrutinizing the economics related to an AC-DC distribution system in transferring power to its associated users. This article presents a MW+MVAr-Miles methodology for DUoS charges calculation. The proposed network pricing mechanism reward the users working at better power factors and efficiently utilizing the network, while forfeiting those who don’t. As a result, the proposed pricing model encourages users to act in a manner for the betterment of the system condition. The aforesaid analysis will enables to realize the economic benefits or detriments of an AC-DC distribution system in distributing power to customers.

Abstract: A solar photovoltaic (PV) - battery energy storage (BES) based microgrid with multifunctional voltage source converter (VSC) is presented in this paper. The maximum power extraction from a PV array, reactive power compensation, harmonics mitigation, balancing of grid currents and seamless transition from grid connected (GC) mode to standalone (SA) mode and vice versa, are performed in this system. Whenever, the grid fails, this system operates in SA mode automatically thereby without causing any interruption in supplying the load. Similarly, it automatically shifts to the GC mode when the grid is restored. The VSC functions in current control mode (CCM) for GC mode and it operates in voltage control mode (VCM) for SA mode of operation. This system is capable of extracting the maximum power from the solar PV array irrespective it is operating in the GC mode or in SA mode of operation. The charging and discharging of the battery, are controlled by employing a bidirectional DC-DC converter (BDDC). It regulates the DC link voltage to the maximum power point (MPP) voltage of the PV array. If the absence of battery is detected, then the control is automatically shifted to VSC for performing the extraction of maximum power of PV array.

Abstract:This paper demonstrates a solar photovoltaic (PV)- battery energy storage (BES) based microgrid system with multifunctional voltage source converter (VSC). It dealts with maximum power extraction from a PV array, reactive power compensation, harmonics elimination and seamless transition from the grid connected mode (GCM) to standalone mode (SAM) and vice versa. The maximum power extraction from a PV array, is achieved by using a DC-DC converter. A bidirectional DC-DC converter (BDDC) is used for regulating the DC link voltage. Whenever the BES is not connected then the VSC performs the regulation of the DC link voltage. The system behavior is studied on a prototype of the microgrid system under various operating conditions.

Abstract:The participation of solar photovoltaic (PV) in the world energy sector is increasing expeditiously, as a cumulative result of a reduction in the cost of solar panel, improvement in panel efficiency, and advancement in associated power electronics. Among different types of PV plants, installation of small-scale rooftop PV are growing rapidly due to direct end-user benefits and lucrative governmental schemes. There are various standards developed regarding grid integration of PVs and other distributed generations (DGs). Different power converter topologies are developed to interface the PV panel with the utility grid. To keep up with the stringent regulations imposed by the standards various control strategies, and grid synchronization methods have been developed. This review paper amalgamates and summarizes all the aforementioned aspects of a grid-integrated PV system. Various standards, power stage architectures, grid synchronization methods, and control methodologies pertaining to small-scale PV plants are discussed at length. This paper will act as a one-stop reference for practicing engineers and introduce the vast research in the field of solar PV integration to the new generation of researchers.

Abstract:Recent trends in renewable source integration and advancements in electric loads led to the emerging of local DC microgrids. However, due to majority of AC loads hybrid AC-DC microgrids are formed, incorporating feasible power converters as medium of power flow. Instead of conventional bidirectional AC-DC and DC-DC converters as interlinking converters in hybrid AC-DC microgrid, an open-end transformer based multilevel converter configuration is proposed as interlinking converter in this paper. The converter configuration includes two converters concatenated with primary of transformer, is a unique substitution for conventional multiple converters utilized. The salient features of the configuration include reduced control complexity, inherent isolation from AC grid, and able to provide inter-grid bidirectional power flow. A modified control scheme is proposed for precise power flow control in the system. Real time simulation of the proposed configuration of hybrid AC-DC microgrid is implemented in RSCAD/RTDS and experimented on a scaled hardware prototype. The outcomes depict the potency of control scheme in inter-grid power flow control.

Abstract:This paper proposes the application of a traditional dq controller to provide virtual inertia to the Solar PhotoVoltaic (SPV) based Distributed Generators (DGs) by adjusting its Phase Locked Loop (PLL) parameters. The relationship between the phase angle of inverter and power mismatch is derived in terms of the inertia constant. Based on this, an equivalent inertial constant expression is obtained. The proposed controller is tested for a SPV system connected to a grid represented by a Synchronous Generator (SG) which is double the rating of SPV system. Real Time Digital Simulator (RTDS) platform is used to investigate the effectiveness of the proposed scheme and its performance has been compared with a Virtual Synchronous Generator (VSG) scheme under load disturbances and bolted fault.

Abstract:Adaptive under frequency load-shedding schemes are gaining more attention, as power systems are being operated under increasingly stressed conditions. Synchrophasor devices are used in power system networks to monitor the system frequency and the rate of change of frequency (ROCOF) and hence can be utilized for adaptive load-shedding schemes. Since the synchrophasors utilize a global positioning system (GPS) to time synchronize their measurements, they are prone to time synchronization attack (TSA) by spoofing the GPS. This paper discusses the impact of TSA on synchrophasor assisted loadshedding schemes. WSCC 9-bus system is used as the test bed for the study.

Abstract:This paper presents a new approach to physical relocation of photovoltaic (PV) modules in Totally Cross Tied (TCT) configuration of an array without altering the electrical connection. This proposed arrangement is a one time arrangement at the time of installation and this arrangement ensures for the enhancement of power generation of the PV array under partial shading conditions. In this arrangement, the shading effects are distributed over the entire array and hence reduce the multiple peaks in the power-voltage characteristics. The power generated by the proposed arrangement of a PV array is compared with the TCT configuration under different shading patterns. Also, the mismatch loss in the proposed configuration is compared with existing configurations under different shading patterns.

Abstract:In this paper, a Dynamic Voltage Restorer (DVR) control algorithm with battery management features are presented for the protection of sensitive and censorious loads. A simple DVR control scheme based on dual P-Q theory has been presented to obtain the instantaneous reference DVR voltages to compensate the load voltages. The proposed control scheme embraces energy optimized compensation, which results in a reduction of DC energy storage requirement. A DVR battery management scheme, as a part of this control strategy, has been introduced for better battery energy utilization. Each leg of the three-phase three-leg split capacitor inverter is used to inject series DVR compensation voltages explicitly in each phase of the three phase distribution power system. The effectiveness of the proposed control algorithm has been validated by using computer simulation studies.

Abstract: Distributed secondary controllers for dc microgrids have proven to be more effective and reliable as compared to decentralized and centralized controllers, respectively. The distributed secondary controller relies on information exchange between the distributed units. Conventionally, a full communication network topology is used, wherein all controllers communicate with each other. Recently, adoption of consensus control in DC microgrids have enabled achieving good performance using reduced communication network. This work aims at comparing the performance of the secondary controller with reduced and full communication topologies. It is shown that with proper tuning of gains, the secondary controller under reduced communication has similar performance as under full communication. The results are substantiated with numerical simulations using MATLAB/Simulink.

Abstract:The short term load forecasting plays a crucial role in optimal operation and scheduling of the generation resources in power system. In this work, Auto-Regressive Integrated Moving Average (ARIMA), Multiple Linear Regression (MLR), Recursive Partitioning and Regression Trees (RPART), Conditional Inference Trees (CTREE) with Bootstrap Aggregating (BAGGING), and Random Forest (RF) models have been tested and compared for short term load forecasting. These methods have been tested on a sample electricity load data of a residential area containing data sets for training and testing.

Abstract: Locating faults in meshed dc microgrids poses challenges due to low impedance offered by the dc network. In this paper, an on-line fault location scheme which can be implemented as an additional feature in a relay is proposed. The algorithm is developed to determine fault location based on voltage and current transients. Both line to line and monopole ground faults are analysed separately and algorithms are developed based on the rate of change of current. Direct short circuit faults are located using transient measurements captured locally, while communication based technique is utilized to locate the impedance faults. The developed fault location technique is also capable of estimating the fault resistance accurately. The algorithm is validated on a ±600 V meshed dc grid, for both the types of faults under wide range of fault impedance at different fault locations.

Abstract: Protection is an important factor affecting the viability of dc microgrids in future. Traditional ac protection methods are not directly applicable to the dc microgrids due to more extensive use of power electronic converters as compared to the ac systems. Behaviour of different converters during fault is not identical and depends on the converter topologies. Some converter topologies are capable of controlling its output current and hence reduce the risk of system failure. While other topologies are unable to limit the current and require external devices such as fuse, breakers to protect itself. Therefore, a detailed study of various power electronics converters response for different types of faults is desirable. In this paper, analysis of direct short circuit and monopole to ground fault are analysed for different converters. The fault current transient is characterised in terms of peak value and time to reach the peak current. The results are verified through simulations for different converter topologies using Real Time Digital Simulation (RTDS).

Doctoral and Masters Thesis acknowledging UI-ASSIST project

Anju Meghwani, Development of Efficient Fault Detection and Location Techniques for DC Microgrid Protection, Ph D Thesis, IIT Kanpur, February 2018.
Anmol Sharma, Design and Control of DC Microgrid with Energy Storage, M Tech Thesis, IIT Kanpur, May 2018.
Soumya Sahoo, Optimal Dispatch Scheduling for Residential Battery Storage with Solar Photovoltaics,MS(Research) Thesis, IIT Kanpur, November 2018
Rizwan Ahmed Khan,Short Term Load & Solar Forecasting and Optimal Distribution Energy Resource Planning ,MS(Research) Thesis, IIT Kanpur, November 2018
Sanjeev Pannala, Power Control Operation & Management using DC Micro-grid, PhD Thesis, IIT Roorkee, April 2019.




UI-ASSIST COLLABORATOR-India
UI-ASSIST COLLABORATOR-US