SISO Impedance Modeling of Single Phase Inverter Considering Mirror Frequency Effect

Multi-Input and Multi-Output (MIMO) impedance model accounting for the mirror frequency effect has been developed for single phase inverters. However, the resulting impedance matrix is overly complex and has no actual physical meaning. To solve these problems, a new modeling method for single phase inverter considering the mirror frequency effect is presented in this paper by using a Single-Input and Single-Output (SISO) impedance. Since one major reason for the mirror frequency effect is Phase-Locked Loop (PLL), this paper first calculates the accurate response of T/4 delay PLL. Then the impedance of the inverter under the ideal grid is derived, and the mirror frequency effect is equal to an additional impedance in parallel with the previously derived impedance. The overall impedance can predict the oscillation frequencies precisely by applying the traditional Nyquist criteria. Simulations based on RT-LAB verify the correctness of theoretical analyses.