A new AC fault ride-through strategy for HVDC link with serial connected LCC-VSC hybrid inverter

Abstract

HVDC link with line commutated converter (LCC) as a rectifier at the power sending end, and with a serial connected LCC and voltage source converter (VSC) hybrid inverter (SLVHI) at the power receiving end, is adopted for future Baihetan HVDC engineering project in China. To realize the AC fault ride-through (FRT) of SLVHI, a new strategy based on DC chopper (DCC) is proposed in this paper. Firstly, the mathematical model is built to investigate the VSC DC overvoltage mechanism after SLVHI commutation failure (CF) and related factors. Secondly, a modified DCC topology of SLVHI is designed to adjust unbalanced power dissipation based on voltage drop depth. Thirdly, an enhanced voltage-dependent current order limiter (VDCOL) is proposed to deal with the unbalanced power after DCC switching off. With the cooperation between modified DCC and enhanced VDCOL, the proposed FRT strategy can realize CF mitigation and VSC DC overvoltage suppression simultaneously. Finally, the inverter side AC FRT performances of the HVDC link with SLVHI are studied by PSCAD/EMTDC. The simulation results validate the proposed strategy's effectiveness and superiority, with better CF mitigation and VSC DC overvoltage suppression abilities than other existing FRT strategies under different fault scenarios.