Modeling and Stability Analysis of the Three-phase Grid-connected Inverter Under DSOGI-PLL Considering Frequency-Adaptive Feedback

To deal with frequency deviation, the frequency-adaptive feedback (FAF) of phase-locked loop based on dual second-order generalized integrator (DSOGI-PLL) is necessary. However, in previous works, the FAF is usually ignored in small-signal impedance model of grid-connected inverter (GCI), which leads to inaccurate modeling and stability analysis. Therefore, considering the FAF, the models of DSOGI-PLL and GCI impedance are derived and verified in this article. It is found that the FAF introduces the positive feedback effect in PLL control loop and a decrease of low-frequency GCI impedance. It easily leads to instability in weak grids according to the impact of DSOGI-PLL parameters on stability. Then, a FAF approach based on low-pass filter (LPF) is presented to enhance stability. A parameter design guideline is also provided here. Finally, the experimental results demonstrate the effectiveness of the built model and stability analysis. In addition, based on the built model, the low-frequency passivity enhancement strategies for GCI under DSOGI-PLL with FAF can be further explored.