Wangwang Bai, Dezhou Yang, Zhongdan Zhang, Wanwei Li, and Ping Cai
Virtual synchronous generator (VSG), unbalanced grid voltage, power fluctuation, inverter
A DC side power fluctuation exists in the converter with virtual synchronous generator (VSG) control under the unbalanced grid voltage. It will affect the service life of battery equipment. This paper proposes a direct-feedforward-voltage control method to suppress the DC side power fluctuation in the inverter under the unbalanced grid voltage. Firstly, based on the equivalent circuit of the inverter in the rotating coordinate frame, the reason causing the DC side power fluctuation is obtained. The variables affecting the fluctuation are achieved. Secondly, a direct-feedforward-voltage control method to eliminate the fluctuation is proposed, in which the modulation wave is modified to generate an additional voltage in the inverter output voltage. Through interacting with the positive sequence current and the unbalanced grid voltage, a feedforward voltage is generated to eliminate the fluctuation of the DC side power. The feedforward voltage is formed by the negative sequence voltage of the power grid, the positive sequence output current, and the positive sequence output voltage. Finally, the control characteristics of the proposed control method are presented. Based on analysis of the power closed-loop transfer function, the proposed control method has a small influence on the power closed-loop and can achieve the power control precision of the VSG. Simulation and experimental results are proposed to verify the analysis and the effectiveness of the proposed control method of suppressing the DC side power fluctuation.
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