Fault current limiting method based on virtual impedance for hybrid high‐voltage direct current with cascaded MMC inverters

Abstract

The hybrid high-voltage direct current (HVDC) with cascaded multi-infeed MMC inverters is proposed in recent years, and it will be put into reality in near future. But the commutation failure of the line-commutated converter (LCC) inverter will make the whole HVDC system to be blocked because the DC fault current could reach beyond the safety region of the MMC inverter. To solve such problem, this letter proposes a novel fault current limiting method based on the LCC control strategy, namely, the virtual impedance method. Such method can limit the fault current effectively and need no extra devices, which can avoid the block of the whole HVDC system on one side, and save the cost of the construction on the other side. The theoretical analysis shows that the proposed method can improve the high-frequency characteristic of the DC system and realise the fault current limitation effect. The simulations validate the analysis finally.