Transient Synchronization Stability Analysis and Enhancement of an Islanded Microgrid Considering Interactions Between Andronov-Hopf Oscillator Based Inverter and Grid-Following Inverter

The grid-forming (GFM) inverter based on the Andronov-Hopf Oscillator (AHO) can actively support voltage and frequency. However, disturbances can lead to transient synchronization stability issues in the islanded microgrid composed of AHO inverter and grid-following (GFL) inverter. This paper establishes a dynamic power angle model, defining the equivalent mechanical and electromagnetic power as well as the equivalent damping term. Considering the time varying of the equivalent damping term, an iterative equal-area method is employed to analyze the impacts of system parameters, GFL parameters, and AHO parameters on the stability region under current unconstrained operation. Given that severe faults can cause the AHO inverter to enter the current limitation state, the corresponding stability conditions are derived. Based on this, a two-stage transient synchronization stability enhancement control strategy is proposed for both AHO and GFL inverters, and the stabilization mechanism is further analyzed. Simulation results and hardware-in-the-loop tests demonstrate that the proposed control strategy can transition the system to a new stable equilibrium point when current disturbances occur in the GFL inverter and ground faults happen.