Coordinated Suppression Method of Fault Current for DC Grid with Novel Dissipative Resistors Topology

A DC grid based on half-bridge modular multilevel converters (HB-MMC) is a feasible means to realize the friendly grid connection of renewable energy. To solve problems such as the high cost and technical difficulty of DC circuit breakers (DCCB), a coordinated control method for fault current suppression of DC grid connecting wind power is proposed. The key influencing factors of DC fault current are revealed by fault characteristics analysis, and an adaptive current-limiting control method for MMC is proposed, whose parameter selection principles are designed to ensure the safe operation of equipment while achieving effective suppression of fault current. In addition, a novel configuration method of dissipative resistors with the current-limiting function is proposed, which can solve the problem of surplus power in the DC grid and reduce the current stress of converter valves. Based on this, a coordination scheme of dissipative resistors, the adaptive current-limiting control method, and DCCBs are proposed to block fault current, effectively reducing the manufacturing difficulty and cost of DCCB. Finally, a four-terminal DC grid simulation model is built based on the RTLAB OP5600 real-time digital simulation platform, and the effectiveness and feasibility of the proposed methods are verified.