Asymmetrical Advancing Angle Difference and its Application in Predicting Continuous Commutation Failure for LCC-HVDC Systems Under Asymmetrical Faults

Commutation failure (CF) is a frequent dynamic event at the inverter of LCC-HVDC systems caused by AC side faults, most of which are asymmetrical faults. Among different types of CF, the continuous CF (CCF) is the most severe one, which can lead to inverter blocking, interruption of active power transfer, and even system blackout. However, existing research does not consider the magnitude changes and phase shifts of all three phase commutation voltages when predicting CCFs. Therefore, this paper first proposes an indicator, Asymmetrical Advancing Angle Difference (AAAD), that considers the impact of both magnitude changes and phase angle shifts of commutation voltages on commutations under asymmetrical faults. Then by analyzing the impact of the control systems, the AAAD is used to predict CCFs under asymmetrical faults. The proposed CCF prediction approach reduces the prediction error by up to 67% compared with previous methods. A case study using the modified 4-machine-2-area LCC-HVDC system is carried out to demonstrates the accuracy of the proposed CCF prediction method.