Gird-Forming Distributed Generation Inverter Control for A Smooth Transition from Grid-Connected to Islanded Operation Mode in Microgrids

One of attractive features of microgrids (MGs) is their capability to meet the local load demands uninterruptedly even during islanding events. To realize a smooth transition from the grid-connected (GC) operation mode to islanded (IS) mode in MGs, two different grid-forming control strategies, featuring stability enhanced grid-support functionalities, were proposed in this paper for grid-tied inverters (GTIs) of distributed generations (DGs). With proposed controls, GTIs are able to ride through IS events with very slight fluctuations as well as regulate the MG frequency and voltage under IS mode. The corresponding MG operation mode transition behaviors were studied and compared under a high penetration from inverter-interfaced DGs, including a flexible combined heat and power (F-CHP) cogeneration plant and a photovoltaic (PV) generation plant. Simulation results based on a 13-bus test feeder in the MATLAB-Simulink platform are provided to verify the effectiveness of the proposed control paradigms. Also, a simplified hardware testbed with modular power converters was implemented, experimental results under different operating scenarios are presented for validation purposes.