Current Limiting Protection Scheme for Multi-Terminal DC Grids Based on Transient Boundary Voltage

Multi-terminal DC grids based on voltage source converters (VSCs) are widely recognized as a feasible solution to cope with increasing electricity demand and high penetration of new renewable energy sources. The VSCs are vulnerable to DC line faults due to the high discharge current of DC-link capacitance. The high current would damage the insulation of DC cable, and subsequently destroy the anti-parallel diodes during freewheeling stage. In this paper, a current limiting protection scheme, which includes a current limiting circuit and a fault detection method based transient boundary voltage, for multi-terminal DC grids. The current limiting circuit is proposed to suppress the fault current within the interrupting capability of hybrid DC circuit breakers (HCB). The fault detection method is proposed to achieve fast and reliable fault detection of DC line. Comparisons with some conventional protection methods reveal the promising performance of proposed fault detection method. Simulation results of several cases have been verified the effectiveness of the proposed protection scheme, and indicate that the faulted DC line can be identified correctly and quickly, and the non-fault system is able to recover to normal operation immediately after fault clearance without power interruption.