Research on Switching Overvoltage of VSC Station in Hybrid HVDC System

The LCC- VSC hybrid DC transmission system combines the advantages of LCC and VSC. However, the impact of new system structure and control and protection strategy on switching overvoltage of VSC station is unclear. The research in this paper is based on
$\mathrm{a}\pm500\text{kV}$
hybrid DC transmission system with LCC-D-MMC topology. An electromagnetic transient simulation model has been built using PSCAD/EMTDC, and the characteristics of switching overvoltage of VSC station at the inverter side have been studied in this paper, which was generated by typical faults in converter station and on the pole line. The research results show that: due to the existence of series diodes on the neutral bus, diode terminals will withstand reverse voltage and block under various faults in the converter station and on the pole line, which has a great impact on the electromagnetic transient process of converter station after the fault; The VSC station in the hybrid DC system with LCC-D-MMC topology will not be blocked when a single pole grounding fault occurred on the DC line, and the amplitude of overvoltage on the neutral bus is high and the duration of it is long, which leads the energy absorbed by arresters on neutral bus to accumulate continuously; And the single pole grounding fault also cause the energy accumulation of the arrester connected in parallel between the diode terminals.