Line Fault Analysis and Diagnosis of Three-wire Bipolar DC Microgrid Equipped by Voltage Balancer

In a three-wire bipolar DC microgrid with voltage balancers (VBs), the fault characteristics and propagation mechanisms remain unclear due to the complex grid structure and line coupling relationships, which seriously threaten the safety of power electronic equipment and system stability. In this paper, based on the design of the voltage balance strategy and grounding scheme, the fault characteristics in three-wire bipolar DC microgrids are revealed through equivalent circuit modeling and simulation analysis. The effective fault feature variables for fast diagnosis of line faults are determined. Furthermore, a fast fault diagnosis scheme based on single-node faults current is proposed to detect line faults by setting threshold values for derivatives of positive and negative (P &N) currents of the VBs, and classify faults accurately by comparing the absolute values. The proposed diagnosis method uses few sensors and doesn't require communication links between nodes, which provides a new way to protect bipolar DC microgrids with complex wiring structure. The availability of proposed scheme is estimated with MATLAB/Simulink.