1. Department of Electrical Engineering Harbin Institute of Technology Harbin 150001 China; 2. Shanghai Jiankun Information Technology Company Shanghai 200032 China
Abstract：The generation mechanism and suppression method of frequency coupling in three-phase grid-connected converters are studied in this paper. The admittance model of three-phase grid-connected converter was built in complex vector form in static coordinate system. and the controller model was established considering the influence of current loop, phase-locked loop (PLL) and DC-link voltage loop. Then, the effects of PLL and DC-link voltage loop on the frequency coupling characteristics were studied according to the model. With the help of the block diagram of the equivalent transfer function of the system, the influence of the frequency coupling components on the system stability was analyzed under weak grid conditions. PLL controls the q-axis voltage and the DC-link voltage loop controls the d-axis current, leading to the asymmetry of the dq-axis in the system. In order to suppress the frequency coupling characteristics, an improved control method for compensating the asymmetric effects of PLL and voltage loop is proposed. The theoretical analysis shows that the proposed method can effectively suppress the frequency coupling phenomenon and improve the system stability. Finally, the effectiveness of the proposed frequency coupling suppression method is verified by experiments.
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2019, Vol. 34 
