Fuzzy Logic-Based Regulator for Seamless Transition Between Multiple Operating Modes in Inverter-Based Microgrids

This paper introduces a Fuzzy Logic–based Smooth Transition Regulator (FL-STR) to enable seamless transitions between different microgrid operation modes. The proposed method is compatible with various inverter control topologies, including conventional grid-forming inverters (GFMIs), vector current control grid-following inverters (VCC-GFLIs), and PLL-less grid-following inverters. Unlike existing methods in the literature, which are limited to nonlinear inverter topologies, the proposed FL-STR offers broader applicability while reducing the implementation complexity. Specifically, it eliminates the need for detailed system modeling, complex parameter tuning, and weighting matrix design. Moreover, it is less sensitive to tuning parameters and does not rely on accurate linear state-space models, which are often unavailable for commercial inverters. The performance of the proposed method is evaluated in MATLAB/Simulink for transitions between GFMIs and VCC-GFLIs, as well as between GFMIs and voltage-modulated direct power control (VMDPC) inverters. Further validation was carried out through a hardware-in-the-loop (HIL)-based real-time implementation utilizing an NI sbRIO GPIC evaluation kit with an emulated wind turbine system and a photovoltaic system.