Commutation Failure Prediction Method Considering Commutation Voltage Distortion and DC Current Variation

Commutation failure (CF) at the inverter side is one of the most common failures in the line-commutated converter-based high voltage direct current (LCC-HVDC) system. Effective prediction of CF helps to formulate and implement protection measures timely. Since abnormal commutation voltage and DC current are the main reasons causing CF, these two factors should be fully considered in CF prediction. In this paper, to consider the effect of commutation voltage distortion, the time-domain response of the commutation voltage Fourier coefficient is deduced based on the first-order circuit response. To consider the effect of DC current variation, the time-domain response of the DC current is derived by superimposing its steady-state component and transient component, respectively. Based on these two predictive value, the extinction angle (EA) during the commutation is calculated according to the commutation voltage-time area, and the criterion based on EA is proposed to predict the occurrence of CF. The simulation results of the test system built in the PSCAD/EMTDC demonstrate the effectiveness and validity of this method.