Transient over-voltage analysis of the transmission system that renewable energy generation delivered through multi-HVDC

With the rapid development of renewable energy generation (REG) and HVDC projects, a large amount of renewable energy power is sent through single HVDC, or even multiple HVDCs. In this application scenario, the transient over-voltage at the sending-end of HVDC, caused by commutation failure or a blocking fault of HVDC, is the primary constraint on the HVDC operating power level. This paper analyses the transient over-voltage risk of the transmission system, that REG delivered through multiple HVDCs, and its mechanism is proposed. It is pointed out that multiple HVDCs having both same sending-end and receiving-end, or adjacent HVDCs having same sending-end and meanwhile the sending-end grid is weak, will increases the risk of transient over-voltage. Based on the short-circuit ratio and the multi-HVDC short-circuit ratio, a simplified practical calculation method of the transient over-voltage of the transmission system with REG delivered through multiple HVDCs is proposed. Finally, through simulation, the correctness of the above conclusions is verified.