A Voltage-Boosting Submodules Based Modular Multilevel Converter With Temporary Energy Storage Ability for Fault Ride Through of Offshore Wind VSC-HVDC System

VSC-HVDC technology has broad application prospects in the field of long-distance and large-capacity offshore wind system, and it is of great significance to realize the fault ride through (FRT) of the system. Aiming at the problems of high cost of adding DC chopper and low reliability of actively reducing wind turbine power, the scheme of temporary improving MMC capacitor voltage to store energy to realize FRT is considered to have the advantages of low cost and high reliability. However, due to the limit of insulated gate bipolar transistor (IGBT) operating voltage, the existing method do not have strong fault ride through ability. To solve this problem, the voltage-utilization boosting circuit composed of gap and metal oxide varistor (MOV) is proposed to ensures the safe operation of the IGBT after capacitor voltage temporary rise. In addition, a fault ride through strategy based on the cooperation of wind turbine and the voltage-boosting submodules (SMs) based modular multilevel converter with temporary energy storage ability (VBS-MMC) is proposed in this paper. Through the organic combination of new nonlinear circuit and control strategy, the system FRT under various fault conditions is realized. Furthermore, a 3.3 kV welded IGBT experimental platform is built, and the results show that the SM temporary voltage-boosting method is feasible. Finally, the simulation results of ± 320 kV/400 MW VSC-HVDC system verify the FRT capability of VBS-MMC. And the cost and performance comparisons are analysis.