关键词: Nyquist图, 矢量比例积分控制（VPI）, 闭环异常峰, 相位补偿, 参数整定

Abstract: This paper proposes a novel method to evaluate and optimize the performance of single-phase grid-connected inverter system with VPI controllers through Nyquist diagrams. This approach allows to remove the limitation presented by Bode diagrams and its stable criterion that the crossover frequency must be higher than resonant frequency. A systematic method is proposed to obtain the highest stability and avoidance of closed-loop anomalous peaks: it is achieved by the maximization of the Nyquist trajectory distance to the critical point. The parameter design process of the improved VPI control method is simplified. It is no longer difficult to achieve a tradeoff between stability and transient response speed. The effectiveness and feasibility of the proposed control strategy are verified by results from theoretical analysis and experiments.

Key words: Nyquist diagrams, Vector Proportional Integral（VPI）, closed-loop anomalous peaks, phase compensation, parameter design