A HVDC Subsequent Commutation Failure Mitigation Strategy Based on Modified Firing Angle Order by Firing Angle Measurements

Commutation failures in line commutated converter based high voltage direct current systems (LCC-HVDC), especially continuous commutation failures, can easily cause lockup in DC systems, and drastic power changes and protection malfunctions in AC systems. In order to suppress the subsequent commutation failure in LCC-HVDC, the commutation process and the control structure of the HVDC system are analyzed. Then, the dynamic responses of the phase-locked loop and firing angle order are analyzed during the recovery process after the first commutation failure in LCC-HVDC; the deviation between firing angle order and firing angle measurements and its influence on the commutation process are analyzed. Therefore, a HVDC subsequent commutation failure mitigation strategy based on modified firing angle order by firing angle measurements is proposed. The firing angle order is compensated by the deviation between the firing angle order and firing angle measurements to improve the precision of the firing angle control and the fault recovery performance of LCC-HVDC. A CIGRE benchmark was built in PSCAD/EMTDC to verify the proposed strategy. The simulation results show that the proposed strategy can effectively suppress the subsequent commutation failure of LCC-HVDC under single-phase and three-phase to ground fault conditions.