Joydeep Mitra

Microgrid Protection Using Communication-Assisted Digital Relays

Microgrids have been proposed as a way of integrating large numbers of distributed renewable energy sources with distribution systems. One problem with microgrid implementation is designing a proper protection scheme. It has been shown that traditional protection schemes will not work successfully. In this paper a protection scheme using digital relays with a communication network is proposed for the protection of the microgrid system. The increased reliability of adding an additional line to form a loop structure is explored. Also a novel method for modeling high impedance faults is demonstrated to show how the protection scheme can protect against them. This protection scheme is simulated on a realistic distribution system containing a high penetration of inverter connected Distributed Generation (DG) sources operating as a microgrid. In all possible cases of operation the primary and secondary relays performed their intended functions including the detection of high impedance faults. This system is simulated using Matlab Simulinks SimPowerSystems toolbox to establish the claims made in this paper.

Composite system reliability evaluation using state space pruning

This paper presents a method of computing the reliability indices of a composite generation-transmission system by performing Monte Carlo simulation selectively on those regions of the state space where loss of load states are more likely to occur. These regions are isolated by performing state space decomposition to remove coherent acceptable subspaces. It is shown that this method results in a significant reduction in the number of sampled states, thereby reducing the computational effort required to compute the system and bus indices. The method assumes a DC flow model, and is tested using the IEEE Reliability Test System. The proposed method is not intended to replace existing variance reduction techniques; in fact, such techniques may be used in conjunction with the proposed method to further improve its efficiency.

Hybrid Transformer Model for Transient Simulation—Part I: Development and Parameters

A new topologically correct hybrid transformer model is developed for low and midfrequency transient simulations. Power transformers have a conceptually simple design, but behaviors can be very complex. The selection of the most suitable representation for a given behavior depends on the type of transformer to be simulated, the frequency range, and other factors, such as the internal design of the transformer and available parameters or design data. Here, a modular model suitable for frequencies up to 3-5 kHz is developed, utilizing a duality-based lumped-parameter saturable core, matrix descriptions of leakage and capacitive effects, and frequency-dependent coil resistance. Implementation and testing of this model was done for 15-kVA 208Delta-120Y 3-legged and 150-kVA 12,470Y-208Y 5-legged transformers. The basis and development of the model is presented, along with a discussion of necessary parameters and the approaches for obtaining them

Incorporating the DC load flow model in the decomposition-simulation method of multi-area reliability evaluation

This paper presents a computationally viable means of incorporating the DC load flow model in the decomposition-simulation method of multi-area reliability evaluation. The implementation described herein uses a multi-state generation model for each area, a cluster-based multi-area load model which accommodates load correlation between areas, a linear programming model with DC load flow constraints for determining the partitioning states in the decomposition phase, and a similar LP model for determining acceptability of sampled states in the simulation phase. Formulations have been described which enhance the speed and accuracy of the method. The implementation has been tested on 3-area, 4-area, and 5-area cases, and the results obtained have been compared with those produced by an explicit Monte-Carlo simulation. While the results obtained from both methods are similar, the method described has been shown to be considerably faster than explicit simulation.

Siting and sizing of distributed generation for optimal microgrid architecture

This paper presents a method for optimally siting and sizing distributed generation (DG) units in a microgrid. The optimization is based on stipulated reliability criteria. Power system planning based on reliability gives rise to efficient architectures which can meet the consumer requirements with minimum system upgrade. This paper develops a technique for determining the optimal location and sizes of DG units in a microgrid, given the network configuration and the heat and power requirements at various load points. The method is based on simulated annealing. Thermal output and utilization of combined heat and power (CHP) units are considered. The paper presents the development and implementation of the method, and demonstrates its application on a six bus test system.

Pruning and simulation for determination of frequency and duration indices of composite power systems

This paper introduces a method for computing the frequency and duration indices of a composite power system, using random Monte Carlo sampling selectively on those parts of the state space where failure states are more likely to occur. The implementation uses a DC flow model to represent network power flows. The method is tested using a modified form of the IEEE Reliability Test System and is shown to be significantly faster than conventional Monte Carlo simulation, while retaining the same level of accuracy.

Determination of Storage Required to Meet Reliability Guarantees on Island-Capable Microgrids With Intermittent Sources

It is well known that the presence of energy storage ameliorates the reliability challenges posed by intermittent sources. However, a quantitative assessment of the exact amount of storage required to meet a reliability target or guarantee in the presence of intermittent sources is not trivial. This paper describes a practical approach to achieving this. First, an analytical approach is developed for determining the amount of storage required to meet a reliability target at a specific load point. Then the method is extended to a more complex island-capable microgrid system where initial reliability assessment and final verification of reliability guarantee are performed using sequential Monte Carlo simulation. The necessary component and system models are developed and described, and a mock military base is used to demonstrate the method. The work reported was performed under a contract from Sandia National Laboratory to determine storage need in order to provide reliability guarantee on an island-capable military microgrid, but the approach applies as well to civilian systems, both islanded and grid-connected. A method for determining an optimal storage mix is also developed.

Reliability-Based Sizing of Backup Storage

This letter describes an analytical approach to determining the size, in terms of both power and energy capacity, of a backup storage unit in such a way as to meet a specified reliability target. The backup could be in the form of electrical energy storage or fuel storage. The proposed approach might benefit facilities that require high levels of reliability in their electric supply.

Hybrid Transformer Model for Transient Simulation—Part II: Laboratory Measurements and Benchmarking

The topological structure and basic approaches for parameter estimation for a new hybrid transformer model are presented in Part I of this two-paper set. Part II deals with the model benchmarking and also discusses additional methods for parameter estimation based on laboratory measurements. The simulation results confirm the validity of the model for the low- and medium-frequency range

Achieving the Smart Grid through customer-driven microgrids supported by energy storage

This paper describes some of the aspects of the Smart Grid Initiative in the US and purports its realization through an emerging paradigm in microgrids, i.e., the customer-driven microgrids. Special attention is paid to the increasing role played by energy storage elements. Some existing technologies of energy storage are revisited in the perspective of their utilization in customer-driven microgrids.