单相并网逆变器多频阻抗模型及其在谐振环流分析中的应用

逆变器并联并网系统中存在带宽频率以外的谐振环流，不利于逆变器的安全运行。为分析并联系统中谐振环流特性，首先充分计及数字控制及脉宽调制非线性环节的影响，基于一维频谱分析法研究了调制波存在扰动时的逆变器输出电压谐波成分，提出了适用于单相逆变器并联并网系统的多频阻抗模型。基于该模型，采用广义奈奎斯特稳定判据明晰了控制载波相位对并联系统稳定性的影响，鉴别了逆变器间谐振环流所处的频率范围，指出逆变器输出阻抗模值的提升有助于谐振环流的抑制。实验结果表明，所提出的多频阻抗模型的正确性及其在并联并网逆变器谐振环流分析时的有效性。

Multi-frequency Impedance Model of Single-phase Grid-connected Inverter and Its Application in Analysis of Resonant Circulating Current

In the grid-connected system with paralleled inverters, the safe operation of inverters is challenged by the resonant circulating current which is usually located beyond the control bandwidth. In order to analyze the characteristics of resonant circulating current, the digital control and the nonlinear link of pulse width modulation are taken into consideration. Based on the one-dimensional spectrum analysis method, this paper studies the harmonic component of the inverter output voltage when the modulated wave is disturbed. Then the multi-frequency impedance model for the single-phase paralleled grid-connected inverters is developed. Based on the generalized Nyquist stability criterion, the influence of the control carrier phase on the parallel system stability is analyzed, and the frequency of the resonant circulating current can be readily predicted. Finally, it is pointed out that the enlargement of the modulus of the output impedance contributes to suppressing the resonant circulating current. The experimental results verified the correctness and effectiveness of the proposed multi-frequency impedance model.