Current Order Based Recovery Strategy for Successive Commutation Failure Inhibition in Multi-infeed HVDC Systems

Commutation failure (CF) of one dc system may lead to the successive CF of the adjacent dc system due to the close electrical distance and reactive power interaction in multi-infeed HVDC systems, resulting in serious regional power loss. In order to effectively inhibit the successive CF and realize the orderly recovery, a coordinated recovery strategy based on additional current order is proposed in this paper. In this strategy, voltage at ac busbar of the inverter is used as a criterion of reactive power margin, and the corresponding additional current order is calculated according to the judgement of reactive power margin. Considering different strength of dc systems, the multi-infeed short circuit ratio (MISCR) is utilized to calculate the proportionality factor for current order correction. Finally, by the superposition of voltage dependent current order limiter (VDCOL) and the additional current order, the current setting value of rectifier side is obtained to realize the incremental recovery. The test system is built in PSCAD/EMTDC, and the simulation result verify the validation of the proposed strategy.