Analysis and Suppression of AC Faults in Receiving-End of Hybrid Cascaded Multi-Terminal HVDC

Hybrid Cascaded Multi-Terminal HVDC (HC-MTDC) combines the advantages of Line Commutated Converters (LCC) and Modular Multilevel Converters (MMC). However, the coupling between LCC and MMC on the AC/DC side also brings new challenges. Additionally, the transient recovery characteristics after receiving-end AC grid faults adversely affect the DC fault clearance capability. Therefore, this paper analyzes the impact and coupling effects of AC faults on the LCC side and MMC side when they occur at the receiving end. It explains the mechanism of DC overvoltage generation. A suppression strategy is proposed to reduce the risk of controllable surge arrester exceeding its energy limit in HC-MTDC. An electromechanical-electromagnetic transient hybrid simulation model is constructed to validate the correctness of the mechanism analysis in this paper and the effectiveness of the suppression strategy.