Adaptive Protection Scheme for Low-Voltage DC-Bus Microgrid Systems

Abstract

This thesis has presented an adaptive protection method for LVDC microgrid. The suggested protection methodology for fault recognition and separation that based on differential protection concept consists of segment controller able to sense abnormal currents and fast switches able to separate the segment that includes the fault to avoid the complete system shutdown. A ring bus type for microgrid system with segment controller and freewheeling path has been suggested. Hence, the idea of this methodology has been confirmed by simulation using MATLAB/Simulink. L-G and L-L faults have been simulated and it is observed that the current of the fault in L-L is much higher than in L-G fault. In addition, after adding grounding resistance the fault current decreases by large value and the disturbances in the AC load voltage are almost nonexistent. Moreover, the snubber circuit has an important role for protecting the bidirectional solid-state switches against the overvoltage during turnoff because of the line inductance and the high rate of change in current. These reasons may cause a huge damage in solid-state switches in the microgrid.