The evaluation method of commutation failure based on the quasi-steady-state formula cannot accurately estimate the situation nearby the commutation failure boundary. And the method based on the electromagnetic transient simulation of the detailed engineering model is accurate, but the efficiency is low and the workload is large.
In order to improve the efficiency of commutation failure risk assessment and take into account the accuracy, based on the state equation of the equivalent network, this paper proposes a simplified calculation model of the commutation voltage in the DC system after AC fault, and applies the calculation results to the risk assessment of commutation failure. Through the simulation software PSCAD/EMTDC, the validity of the calculation model is verified from two aspects: the commutation area and the evaluation results of commutation failure. The simulation results show that the commutation area obtained by the model is very close to the commutation area obtained by the simulation software in the first commutation process after the AC fault. And applying this model can estimate the situation of commutation failure with accuracy and efficiency.