A Nonlinear Stability Analysis Method of Grid-Connected Inverter

Small signal analysis methods in frequency domain and time domain have been frequently proposed to identify stability issue of grid-connected inverter. However, it fails to deal with nonlinear characteristics caused by variation of different operating points. This paper presents a nonlinear stability analysis method to investigate the effects of nonlinear components on stability of grid-connected inverter, where the nonlinearity of inductor is addressed as an example to investigate the nonlinear stability mechanism. The model of nonlinear inductor is first established by describing function method. Then, the transfer function with nonlinear plant and linear plant is established by loop transformation method. Moreover, the nonlinear stability criterion is developed by identifying the relationship of describing function of nonlinear plant and Nyquist diagram of linear plant. Simulation and experimental results validate the effectiveness of the proposed nonlinear stability analysis method, which can provide the guideline to optimize inverter parameters at design stage so as to avoid the potential instability issues caused by nonlinear components.