Quantitative calculation method and its overvoltage suppression strategy for sending-end transient voltage of LCC-HVDC under commutation failure

In the line-commutated-converter based high voltage direct current (LCC-HVDC) transmission system, commutation failure (CF) can cause the problem of sending-end transient overvoltage. A quantitative calculation and a suppression strategy of transient overvoltage are proposed in this paper, so as to realize the analysis and effective suppression of the transient overvoltage by considering the dynamic reactive power response characteristics of the rectifier station during the process of CF. Firstly, the influence of different direct current (DC) system control units and parameters on the transient overvoltage is analyzed, and the DC current is revealed to be the primary influencing factor. Then, the approximate analytical expression of the DC current is derived. Further, the quantitative calculation method of the sending-end transient voltage is proposed by substituting into the DC current expression. On this basis, the minimum allowable values of DC current and rectifier’s reactive power consumption are obtained according to the upper limit of sending-end transient overvoltage. Then, a cooperative control strategy for transient overvoltage suppression is designed, which combines rectifier’s current control and inverter’s voltage control. It can effectively suppress the overvoltage while avoiding subsequent CF. Finally, based on the CIGRE benchmark model in PSCAD/EMTDC, the correctness and effectiveness of the quantitative calculation method and suppression strategy are verified.