Journal Articles
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Item Protection schemes for a battery energy storage system based microgrid(Elsevier Ltd, 2022) Joshua, A.M.; Vittal, K.P.This paper evaluates directional and adaptive overcurrent protection schemes in microgrids. A microgrid supported by a centralised Battery Energy Storage System (BESS) is chosen for the study. The stringent PQ controller of BESS will not allow it to dissipate into a fault, during its charging mode, causing the conventional directional schemes to mal-operate. A direction estimation scheme using magnitude and angle of superimposed positive sequence impedance is proposed to address this issue in BESS. Further, two fault detection techniques are proposed for BESS integrated feeders. The Main Protection Unit (MPU) detects an internal fault when there is a mismatch in the direction of relays at either end of a feeder. The second scheme uses adaptive overcurrent relay settings. Since the fault current is limited with PQ control, the pickup current is calculated dynamically with this control. Whereas a fixed pickup current is chosen, when the BESS inverter is voltage controlled. Simulations have been carried out using MATLAB/SIMULINK software. The proposed schemes work well for bidirectional power flows and in grid connected and standalone modes of microgrid operation. © 2021Item Incremental transient power-based protection scheme for a DC microgrid(Springer Science and Business Media Deutschland GmbH, 2022) Joshua, A.M.; Vittal, K.P.A key step in the realisation of DC microgrids is the development of robust protection schemes. Bidirectional power flow in ring-type configurations makes protection design too complicated. This paper presents an algorithm for selective fault location and isolation of faulty parts in the transient stage itself. At the onset of a fault, the proposed scheme computes incremental transient power (Δ P) from initial changes in voltage and current. The sign of Δ P captured by different IEDs is compared to determine the fault location. Though the scheme is designed for the unit protection of feeders, it is also capable of locating and isolating external faults accurately. A backup scheme using local measurements is provided, in case of communication failure. The schemes are simulated using extensive simulations in MATLAB/SIMULINK platform. The results confirm that the proposed protection design operates within a few milliseconds and is highly selective and stable. © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.Item Superimposed current based differential protection scheme for AC microgrid feeders(Elsevier Ltd, 2023) Joshua, A.M.; Vittal, K.P.Legacy protection schemes face numerous challenges with the emergence of microgrids. Due to the complex controls, the fault responses in microgrids differ from conventional behaviour and vary with the operation mode. In this paper, a differential protection scheme based on fundamental frequency superimposed current phasors is proposed for microgrid feeders. The phasors are extracted using dq components instead of conventional Fourier algorithms. The performance of proposed method is tested for different fault scenarios by carrying out simulations in MATLAB/SIMULINK software. The results confirm that internal faults are detected in a few milliseconds. At the same time, the scheme remains insensitive to external faults with CT saturation and other system disturbances. The proposed scheme is unaffected by the microgrid mode of operation, direction of power flow and DG type. © 2023 Elsevier LtdItem Passive Islanding Detection Scheme Based on Instantaneous Voltage and Current for a Multi-DG Microgrid(Institute of Electrical and Electronics Engineers Inc., 2024) Pinto, J.A.; Vittal, K.P.; Manjunatha Sharma, K.M.The electricity grid has been transforming since its inception. The increase in carbon emissions and scarcity of fossil fuels has led to using renewable energy sources for power generation. In recent times, microgrids have been gaining popularity, as they can connect to the grid or disconnect from the grid to supply power to the local loads during grid failure and calamities. The presence or absence of the utility grid is crucial to the overall operation of the microgrid. This paper focuses on early islanding detection by considering the instantaneous values of phase voltage and line currents. In the proposed method, the relative position of voltage and current signals are monitored, and a coincidence index keeps track of any change in their relative positions. During the grid-connected operation, the coincidence index remains low. However, when the grid is disconnected, the coincidence index rises. Islanding is detected when the coincidence index crosses a fixed threshold. MATLAB/Simulink-based simulation studies were carried out on the IEEE 13 bus system to check the effectiveness of the proposed Instantaneous Islanding Detection technique during normal operation, faults, switching of loads, and switching of Distributed Generators. It was found that the proposed scheme could detect islanding in less than one-fourth of the cycle and has a low non-detection zone. Also, during the evaluation, the proposed instantaneous islanding detection technique identified islanding much earlier than existing methods. © 2024 The Authors.