Adaptive Protection Scheme for Microgrid With Multiple Point of Common Couplings

Abstract

Frequent changes in operating conditions of microgrid affect the coordination of directional overcurrent relays (DOCRs). This article proposes an adaptive protection scheme to handle DOCRs coordination problem in microgrid having multiple point of common couplings. The proposed scheme consists of two blocks: offline and online. In offline, settings of DOCRs are calculated for most important operating conditions (grid connected and islanded modes) and stored in corresponding DOCRs. The online task is performed based on local and global decision approaches. The local decision approach ensures significant less burden on microgrid central controller. Also, the proposed scheme does not cause any catastrophic conditions in microgrid when a fault occurs during critical situations. Then, coordination problem is formulated as constrained nonlinear programming problem and solved using a symbiotic organism search algorithm. The effectiveness of the proposed scheme is examined on 7-bus and IEEE 33-bus microgrids during various operating conditions. Furthermore, simulation results are validated on hardware-in-loop test bed using real-time digital simulator, numerical relays, and CMS-356 (voltage and current amplifier). From simulation and hardware results, it is noticed that proposed scheme is able to provide an adequate protection to microgrids during various operating conditions, various types of bolted faults, and high-impedance faults.