Novel Thyristor-Based Module-Cascaded Converter to Eliminate Commutation Failure for LCC-HVDC Application

To eliminate commutation failure (CF) of line-commutated converter based high voltage direct current (LCC-HVDC) transmission system, this paper proposes a thyristor-based module-cascaded converter (TMCC), where each arm consists of multiple thyristor-based commutated modules (TCMs). The TCM is configurated as full-bridge scheme by thyristors, capacitor, inductor and arrester, to provide commutation voltage support and consume power under fault conditions. The working modes of TCM are presented, and the coordinated control strategy of TMCC is proposed for pre-charging state, normal operation state and forced commutated state. Moreover, the parameter design procedures for each element in TCM are also provided. Then, a dual-infeed HVDC system is modeled in PSCAD/EMTDC to analyze its transient response under AC fault conditions. This system incorporates a TMCC-HVDC link, where an LCC serves as the rectifier and a TMCC operates as the inverter. The results indicates that, with the proposed control strategy and the designed parameters, the voltage and current stresses of each element in TCMs can be regulated within an acceptable range. The proposed TMCC not only can eliminate its CFs, but also significantly strengthen the commutation failure immunity of remote LCC-HVDC link.