Direct-Current Predictive Control Strategy for Inhibiting Commutation Failure in HVDC Converter

Commutation failures, which may lead to outage of HVDC systems, usually occur in line-commutated HVDC systems, especially in the inverter stations. As a method to reduce the risk of commutation failures, additional angle deducted from the firing order at the inverter station has its inherent limitations. In this paper, by analyzing the inverter transient process of normal commutation and commutation failure especially, it is shown that direct-current control can be used to inhibit the commutation failures and present an improvement strategy of control system on the inverter side. Based on the analysis of commutation failure prevention (CFPREV), an approach of direct current value setting is proposed, the selections of parameters in calculating process are CFPREV-based in order to implement it conveniently, and the dc current predictive control strategy is applied by modifying the conventional control system at the inverter. The validity is proved by simulation of the CIGRE HVDC model and multi-infeed HVDC model based on CIGRE HVDC, where various ac system faults in PSCAD/EMTDC are set manually. The results show that the proposed algorithm is very effective in inhibiting commutation failures or repetitive ones, and even would enhance fault-ride-through capability of HVDC system with commutation failures.