A Novel Protection Coordination Strategy for Zonal DC Microgrids

In this paper, an inverse time-current curve (ITCC) based optimal coordination strategy is proposed for a zonal DC Microgrid system. First, the solid state circuit breakers (SSCBs) are optimally coordinated during overload, short circuit, and instantaneous conditions. Subsequently, the ITCCs for each of these conditions are plotted. The coordination time intervals (CTI) between primary and backup SSCBs are incorporated to accomplish better selectivity. The CTI during the turn-off operation is selected by considering the conduction time interval of the metal-oxide varistor (MOV) into account. The operation speed of the proposed scheme is improved by using a distance-based backup protection scheme (DBBPS) and a probe power unit (PPU) in the second step. The proposed DBBPS-included ITCC scheme greatly minimizes system damage, lowers the energy absorbed by SSCBs, considerably reduces the energy spent by faults, and subsequently improves the safety of operators and the stability of the zonal DC Microgrid. In addition to highly reliable operation, the proposed coordination scheme eliminates the need for communication lines between SSCBs. The proposed coordination strategy is simulated using MATLAB/Simulink platform, and the experimental validation is assessed using real-time digital simulator (RTDS) and dSPACE 1104 controller. It can be validated from the results that the proposed strategy can quickly isolate defective sections and restore healthy sections in order to improve the system's reliability.