Current-limit control method to prevent subsequent commutation failure of LCC-HVDC based on adaptive trigger voltage

With the wide construction of the line-commuted converter-based high-voltage direct current (LCC-HVDC), a large-scale AC/DC hybrid grid pattern has gradually formed. LCC-HVDC is prone to subsequent commutation failure (SCF) during the recovery process of first commutation failure (FCF). This phenomenon poses a great threat to the safe and stable operation of the power grid. LCC-HVDC is equipped with several controllers to prevent SCF. However, these controllers adopt preset fixed parameters and ignore the fault severity and LCC-HVDC self-regulation. The controller effect may not match the dynamic demand of the FCF recovery and even become the driving force of SCF. Accordingly, a new method is proposed on the basis of the quantification of the FCF recovery consequence, and it can avoid SCF by dynamically adjusting the DC current command according to a variable slope of U-d - -Id-ord curve. First, the causes and influencing factors of SCF are presented by analyzing the recovery process of CF under the AC grid fault. Second, the correlation factors of the FCF recovery path are analyzed, and the idea of adaptive control against SCF based on the critical slope is proposed. Third, the critical slope of the U-d - Id-ord curve is derived with considering the influence of the initial state of the fault and constant extinction angle control. Then, a current-limit control method to prevent SCF based on the adaptive trigger voltage is proposed with considering the influence of the DC current variation on power angle stability. Finally, simulation results verify the effectiveness of the proposed method in preventing SCF.