Analysis of the Constant Amplitude Oscillation Mechanism in the Grid-Connected Inverter System by Combining Impedance Analysis and the Describing Function Method

Thereare a large number of nonlinear elements in the grid-connected inverter system, which not only affect the system stability but also result in complex oscillatory behaviors after the system becomes unstable. Aiming at the problem of constant amplitude oscillation caused by the nonlinearity of current limiter in the grid-connected inverter system, this paper combines the impedance analysis method with the describing function method to establish the system impedance model that takes into account the influence of the limiter. The mechanism of the constant amplitude oscillation is explored from the perspective of the closed-loop feedback principle. Furthermore, the generation conditions and frequency characteristics of the constant amplitude oscillation are determined by drawing the Nyquist plot and Bode plot of the inverter impedance. Finally, the correctness of the theoretical analysis is verified by means of time-domain simulation.