Multiharmonic Interaction and Stability Analysis of Two-Stage Double-Input Buck Inverter

Due to stronger nonlinear interaction and coupling effect, multi-input inverters can exhibit a variety of complex oscillations with multiple harmonics. This article develops a multiharmonic modal analysis method to uncover the occurrence reasons of various harmonics in the two-stage double-input Buck inverter. First, a frequency-selective approach is proposed to eliminate the time variance of the nonlinear averaged equations from both line frequency and second harmonic. Second, the nonlinear modal representation of the model obtained here is derived to capture various harmonic interactions and coupling effect from the viewpoint of both fundamental and second-order harmonic characteristics. Third, fundamental harmonic modal analysis is performed with the help of the trajectories of the fundamental modes, and significantly, the occurrence cause of two new harmonic components is explained in detail. And then, second-order harmonic modal analysis is used to discover a series of new nonlinear interacted harmonics, and the influence of these harmonics on different variables is evaluated by the second-order interaction indices. Furthermore, the coupling harmonic analysis is carried out to explore some coupling harmonics. In addition, the stability boundaries for different key parameters and load models are given to improve system stability. Finally, some experimental results are provided to validate the above analysis ones.