Overvoltage Suppression Under Commutation Failure Based on Improved Voltage-Dependent Current Order Limiter Control Strategy

Commutation failure (CF) in the line-commutated converter based high-voltage direct-current system will result in a large amount of reactive power surplus on the rectifier ac system. It will cause the transient overvoltage and lead to the massive disconnection of the renewable sources. In this article, the mechanism of the transient overvoltage caused by CF is analyzed and the suppression strategy based on improved voltage-dependent current order limiter (VDCOL) control is proposed. First, during the process of CF, the dynamic behavior of reactive power consumption of the rectifier is analyzed. It is proposed that when the inverter returns to normal commutation, the sudden increase of the inverter dc voltage will cause the decreasing of the dc current, which will result in the large decreasing of reactive power consumption of the rectifier. Then, the dynamic change process of the rectifier ac voltage is deduced. Second, the peak value of transient overvoltage as affected by the occurrence and removal time of the short-circuit fault is deduced and analyzed. Then, by improving the operating characteristic of the VDCOL control, the control strategy of overvoltage suppression is proposed. Based on the PSCAD platform's CIGRE-HVDC benchmark model, the effectiveness of the proposed strategy is verified by the simulation results.

I. Introduction

The line-commutated-converter based high voltage direct current (HVDC) transmission technology has the advantages of large transmission capacity, low power loss, and flexible transmission power adjustment, and is widely used in new energy transmission [1], [2]. However, as one of the abnormal conditions of dc transmission systems, commutation failure (CF) will cause the great reduction of rectifier reactive power consumption and then the overvoltage to the rectifier ac system [3], [4]. It seriously threatens the stability of wind farms and even the whole power system [5], [6]. During the period of CF, the dc control system affects the dynamic change of rectifier dc voltage and dc current, and then the reactive power consumption of rectifier [7], [8]. Because the voltage-dependent current order limiter (VDCOL) control provides the dc current reference value to the dc control system, it will affect the reactive power characteristic of the rectifier. Therefore, the VDCOL control has played an important role in the development of rectifier ac overvoltage.