Influence of VSC Converter Station on Switching Overvoltage of LCC Converter Station in LCC-VSC Hybrid DC System

LCC-VSC hybrid DC system combines the advantages of LCC in transmitting large-capacity electric energy and VSC in power transmitting to weak AC power system without commutation failure, which makes the transmission form more flexible. A HVDC overvoltage calculation model of VSC converter station with LCC converter at the sending end and MMC converter at the receiving end is established in this paper. The principle of influence which is exerted by VSC converter station on LCC converter station is researched. The differences of Overvoltage of LCC converter station in hybrid DC System with blocking diode and not are compared and analyzed. The reason for larger overvoltage energy of LCC converter station is obtained. The necessity of blocking VSC station reverse DC voltage output is presented. The results show that the blocking diode plays an important role in limiting the overvoltage energy of LCC converter station in Hybrid DC system, which needs to be equipped in Hybrid DC system. After the blocking diode is installed, the insulation coordination of the LCC converter station at the transmission end can be the same as that of the conventional LCC HVDC transmission system.