Impedance Adaptive Dual-Mode Control of Grid-Connected Inverters With Large Fluctuation of SCR and Its Stability Analysis Based on D-Partition Method

The stable operation of grid-connected inverters (GCIs) with traditional current source mode (CSM) control is affected by the large fluctuations of short-circuit ratio (SCR) under weak grids. Improved CSM control enhances the stability of GCIs under weak grids but remains unstable for very weak grids, while the stability of GCIs with voltage source mode (VSM) is just the opposite. Therefore, previous research works have proposed the impedance adaptive dual-mode control strategy: when the SCR is large, the GCI is controlled by CSM, and when the SCR is small, it is controlled by VSM. However, the existing literature still lacks the analysis of the parameter stability region and mode switching boundary of GCI in different modes. Therefore, based on the D-partition method, this article derives the parameter stability region of GCI in different modes under the constraints of multiple performance indexes such as phase and gain margin, current-loop bandwidth and phase-locked loop bandwidth, and the switching boundaries of CSM and VSM are also proposed. Finally, based on the grid impedance identification algorithm, the impedance adaptive dual-mode control is realized, which effectively improves the stability of GCI when SCR fluctuates greatly, and the experimental results verify the correctness of the above analysis.