Compound Line-commutated Converter with Commutation Voltage Compensation and Power Consumption Capability for Commutation Failure Suppression

To mitigate commutation failures (CFs) of a line-commutated converter based-high voltage direct current transmission system (LCC-HVDC), an evolved thyristor based full bridge sub-module (ET-FBSM) and a compound LCC (CLCC) topology are proposed with the capability of commutation voltage compensation and DC power consumption. Under AC fault conditions, additional commutation voltage for LCC can be compensated, and rise of DC current can be suppressed, by switching the control modes of ET-FBSM, to reduce risks of CFs and improve the dynamic characteristics of LCC-HVDC systems. In this paper, working modes of the ET-FBSM and a coordinated control strategy between ET-FBSM and converter valve are presented, and the parameter selection approach for the ET-FBSM is provided. Then, a CLCC-HVDC system with ET-FBSMs embedded in the inverter station is developed in PSCAD/EMTDC to verify effectiveness of the proposed topology. Simulation results show the proposed topology can significantly reduce risks of CFs and improve dynamic performances of the overall system.