Adaptive Advancement Angle Compensation for Suppressing Commutation Failures During Rectifier- and Inverter-Fault Recovery

Line-Commutated Converter (LCC) based High-Voltage Direct Current (HVDC) systems are susceptible to commutation failure (CF) during fault recovery not only for faults at inverter, but also for faults at rectifier side. Although the mechanism of CF under each scenario (fault at inverter and fault at rectifier) have been widely discussed, no existing methods can mitigate CFs under both scenarios. This is because the lack of detailed comparative analysis for the root cause of CFs under both scenarios. In this study, it is shown that the essence of CF during fault recovery for faults at both ends are in fact the same – long duration of CC control at both end converters and inability of CEA control to maintain commutation margin after control mode switching during fault recovery. As a result, the inverter cannot maintain a stable operating point during fault recovery. Based on this, an adaptive advancement (beta) angle (ABA) control is proposed that can mitigate CFs during fault recovery for faults at both ends. The proposed control features a direct control of inverter advancement angle that ensures a sufficient commutation margin during recovery. At the same time, the negative impacts of the increase of reactive power consumption are minimized by avoiding the ‘over advancement’ of inverter firing angle. From the V-I trajectory point of view, the trajectory of the system is constrained at the stable operating point during recovery process. PSCAD simulation demonstrates the effectiveness of the proposed method.