Receiving-end AC fault ride-through method of hybrid HVDC transmission based on adaptive DC voltage reduction

The hybrid high -voltage direct current (HVdc) transmission that combines line -commutated converters (LCCs) at the sending end and modular multilevel converters (MMCs) at the receiving end is a promising choice for integrating bulk renewable power transmission. However, ac faults at the receiving -end MMC may result in output power limitation, and cause the overvoltage of MMC submodule (SM) capacitors and the dc line. Given the long distance of transmission lines and the relatively slow response from the sending LCC, traditional methods cannot ride through ac faults well. To solve this problem, this study proposes a fault ride -through (FRT) strategy by adaptively decreasing the dc voltage of the MMC to achieve a fast and adaptive power balance after the occurrence of an ac fault. It needs no modification of the LCC control structure. Based on the MMC topology with dc voltage adjustment capability, the controllers for dc voltage adjustment and FRT are designed. A simulation model of a 2500 MW/800 kV LCC-MMC hybrid HVdc transmission system is built. Simulation results show that the proposed method can maintain the SM capacitor and dc voltages and achieve FRT, and outperforms traditional methods.