并网变换器的多频率耦合等幅振荡分析

The interaction between grid-connected voltage source converter and the AC grid may lead to electromagnetic oscillations. Due to the influence of the non-linearity of controller, the oscillation cannot diverge continuously and eventually a sustained oscillation appears. Many existing researches use the describing function to model the limiter of the converter to calculate the amplitude and frequency of the sustained oscillation. However, the influence of high-order oscillation components caused by the non-linearity on the oscillation is ignored. In this paper, the existing method is improved and a method considering high-order oscillation components is proposed. The describing function of asymmetric limit considering the high-order oscillation component is derived. The amplitude and frequency characteristics of sustained oscillation considering the high-order oscillation components are analyzed. This method is adopted in the analysis of oscillations considering both single-axis and dual-axis limitations. Finally, the proposed method is verified by simulations in the PSCAD/EMTDC. Theoretical analysis and simulation results show that the proposed analysis method improves the analysis accuracy of sustained oscillations of the grid connected converter, and quantitatively calculate the amplitude of high-order oscillation component.