A Method Based on Constant Reactive Power Control of Inverter to Suppress the Subsequent Commutation Failure in HVDC System

AC side fault is the main reason for commutation failure of HVDC system. In the process of AC fault occurrence or removal, or even system recovery, the reactive power impact caused by converter station to AC system is likely to cause subsequent commutation failure due to the influence of commutation bus voltage change and DC control. However, due to the long response time, reactive power compensation equipment is usually difficult to respond in time to suppress subsequent commutation failure, so it is often used as an auxiliary means. In recent years, many methods have been proposed to control the reactive power by optimizing the DC control mode, but most of them do not take into account the transmission delay between the rectifier side and the inverter side. In order to solve these problems, this paper proposes a two-terminal coordination control strategy based on dynamic reactive power control of the inverter station, taking the extinction Angle of the inverter station as the control quantity. Firstly, the variation trend of reactive power of inverter with DC current and extinction angle is analyzed. The operating range of extinction angle, DC current and reactive power in quasi-steady state is analyzed. Then, a method based on constant reactive power control of inverter to suppress the subsequent commutation failure is proposed. By setting the new VDCOL(voltage dependent current order limitation) parameters on the rectifier, and calculating the reference value of the extinction angle in real time according to the AC bus voltage and DC current on the inverter, the reactive power of the inverter is controlled during AC fault. On the one hand, the inverter side controls the reactive power of the inverter station by controlling the extinction Angle. When the AC bus voltage or DC current value detected by the inverter side changes, the reactive power switching capacity can be controlled in real time by directly changing the extinction Angle of the inverter side. The extinction Angle, DC voltage and inverter side AC voltage are coupled to each other and meet the constraints of quasi-steady state equation. On the other hand, the operation range of DC current can be calculated according to the quasi-steady-state equation on the rectifier side, and according to the new current instruction given, it can meet the reactive power quantitative demand of the inverter side at the rated extinction Angle. The DC voltage measured by the rectifier side gives the DC current instruction in real time, which is no longer transmitted by the inverter side, so as to avoid the deterioration of the system performance caused by the transmission delay. Finally, the CIGRE HVDC model and GuiGuang Ⅱ HVDC model in PSCAD/EMTDC are taken as examples. After the improvement, subsequent commutation failure occurs when AC fault is more serious, and the system recovers more smoothly. The results verify that the proposed method can effectively improve the system's support capability during AC fault and reduce the probability of subsequent commutation failure. This paper mainly studies the dynamic reactive power control strategy of inverter station under three-phase symmetric fault, and the dynamic reactive power control method for single-phase ground fault needs to be further developed. © 2023 Chinese Machine Press. All rights reserved.