An Improved VDCOL Control Strategy for Mitigating Continuous Commutation Failure in HVDC Transmission

Abstract

To suppress the continuous commutation failure (CCF) and improve fault resilience of high voltage direct current (HVDC) due to alternative current (AC) fault occurred in inverter side, an improved voltage dependent current order limiter (VDCOL) control strategy considering real-time calculation of VDCOL starting voltage and virtual resistance comprehensively is proposed. By theoretical analysis, the traditional VDCOL starting voltage calculated by DC voltage fluctuates violently with long duration, which is a critical reason for CCF of HVDC after the first commutation failure (FCF). To reduce rapid shifts of conventional VDCOL starting voltage, an equation of VDCOL starting voltage characterized by AC voltage and DC current is established. In addition, considering transient characteristics of DC current under AC fault, virtual resistance is also introduced in mathematical equation of starting voltage. By integrating AC voltage, DC current and virtual resistance, VDCOL starting voltage which captures transient performance of AC / DC hybrid grid during fault occurrence and recovery stage can be calculated in real time. Based on CIGRE HVDC benchmark model, the proposed VDCOL control strategy is compared with the other two strategies in PSCAD/EMTDC. Comparison results verify that the improved VDCOL control method has the ability to mitigate CCF with a faster recovery time under various fault scenarios.