Optimal Power Coordinated Control Strategy for DFIG-Based Wind Farm to Increase Transmission Capacity of the LCC-HVDC System Considering Commutation Failure

The line commutated converter (LCC)-based high voltage direct current (HVDC) transmission system is an effective scheme for long-distance transmission of wind power. Commutation failure is a common failure of LCC-HVDC transmission system. During the commutation failure, the overvoltage of the sending alternating current (ac) grid will occur to disconnect the wind farm from the utility grid and limit the transmission capacity of the system. It is necessary to suppress the overvoltage of the sending ac grid under commutation failure to increase the transmission capacity of the LCC-HVDC system. In this article, a mathematical model of the transient overvoltage peak value of the sending ac grid under commutation failure is established. The mathematical model can quantitatively analyze the influence of the reactive power of the wind farm and the transmission capacity of the LCC-HVDC system on the overvoltage peak value of the sending ac grid. Based on the mathematical model, a power coordinated control strategy for wind farms is proposed to improve the reactive power support capability under grid overvoltage. The proposed control strategy can effectively suppress the overvoltage of the sending ac grid and increase the transmission capacity of the LCC-HVDC system. The accuracy of the mathematical model is verified by simulation, and the superiority of the power coordinated control strategy is verified by the control hardware-in-the-loop (CHIL) experiment.