Research on Fault Control Strategy for Two Terminal Weak Feed Systems Considering Step-Down V/f Control

After an asymmetric fault occurs in a two-terminal weak feed AC system, negative sequence components affect the safe and stable operation of the power system may occur. Therefore, it is necessary to suppress the negative sequence component to improve the stability and reliability of the power system. In this paper, the overcurrent and overvoltage problems caused by negative sequence current · suppression control strategy and negative sequence voltage suppression control strategy on modular multilevel converter (MMC) side are compared. Then, a new control strategy is proposed, which uses the step-down V/ $f$ control strategy and the negative sequence current suppression control strategy on the MMC side to quickly limit the fault current amplitude and effectively avoid the non-fault phase overvoltage. After theoretical analysis and PSCAD simulation, analyze the electrical quantity changes under different types of control strategies. The simulation results show that the proposed fault control strategy effectively limits the negative sequence current amplitude and non-fault phase overvoltage. Under different control strategies, the electrical characteristics of the system vary significantly. The above characteristics can provide a theoretical basis for the analysis of protection adaptability and the study of new protection principles.