Multifrequency Small-Signal Model for Single-Phase Grid-Tied Inverters Considering the Effect of PWM

Recent studies have shown that harmonic instability may occur at frequencies above the Nyquist frequency. To study this issue, the sidebands originating from modulation must be considered in the modeling. Some traditional models ignore the effect of pulsewidth modulation (PWM), so they cannot predict high-frequency instability (HFI). In this study, a multifrequency small-signal model for single-phase grid-tied inverters is built, which considers the behavior of PWM. Based on the established model, the dominant sideband components of the single-phase inverter system are extracted, and the admittance matrix is simplified from a high-order matrix to a 5 x 5 matrix to reduce the computation burden without losing too much accuracy. Some HFI cases are conducted to compare the accuracy between the traditional model and the proposed model. The results show that the proposed model is more precise than the traditional model in predicting the HFI information of the studied system. Finally, simulation and experimental results verify the correctness of the theoretical analyses presented above.