RESEARCH ON THE DC FAULTS INMULTI-TERMINAL DC TRANSMISSIONSYSTEM BASED ON MMC

[摘要] Multi-Terminal Direct Current transmission system based on Modular Multilevel Converter（MMCMTDC） has great application prospects on power transmission away from load centre, renewable energy transmission, distributed power transmission and the multi-grid interconnection. A voltage margin control scheme is designed for MMC-MTDC system; and a detailed mechanism analysis of the monopole ground fault and bipolar short-circuit fault of the MMC-MTDC is carried out on the DC cable faults. Using PSCAD / EMTDC, a three-terminal DC transmission system is built to proof the effect of control and protection schemes for DC cable faults in MMC-MTDC system. The simulation results show that thanks to the control and protection schemes, the multi-terminal DC transmission system under the faults can achieve fast recovery based on quick DC switches after a system failure. Moreover, the power transmission requirements are well met, and the stability of the system is effectively improved.

[关键词] Modular Multilevel Converter (MMC);Multi-Terminal Direct Current (MTDC);DC Cable Fault;Coordinated Control;Control and Protection Schemes