Power Support Strategy for Hybrid Commutated Converter based HVDC System during Receiving-End AC Faults

The conventional high voltage direct current (HVDC) system based on line commutated converter (LCC) is faced with the commutation failure (CF) problem. Exploiting the self-turn-off ability of integrated gate commutated thyristors (IGCTs), a hybrid commutated converter (HCC) has been proposed to resist CF. In LCC-HVDC systems, the CF prediction strategy (CFPRED) is applied to the receiving-end LCC, causing firing angle decrease, active power reduction, and reactive power consumption increase under AC faults. However, when HCC is used at the receiving end, it is unnecessary to employ CFPRED. Considering the forced commutation capability of HCC, a novel power support strategy (PSS) during receiving-end AC faults is presented in this paper. According to the AC voltage drop, an offset angle will be calculated based on the zero-sequence voltage detection or Clarke transformation. With the final firing angle delayed, HCC can maintain the DC voltage at a higher level, and also provide more active and reactive power support to the AC grid. Finally, the AC fault ride-through performance of the traditional LCC-HVDC system and the LCC-HCC-HVDC system is compared, and the effectiveness of the proposed PSS for HCC is verified by PSCAD/EMTDC simulation.