A Frequency Adaptive Ramp-Rate Based PR Controller for Seamless Transition of Three-Phase AC Microgrid Between SA to GI Modes

Voltage phase angle jumps (PAJ) during pre-synchronization interval pose a risk of failure of loads and tripping of inverters connected at point of common coupling (PCC), leading to system stability concerns. This paper presents a ramp rate control (RRC) based pre-synchronization strategy for frequency and phase compensation of PCC voltages during pre-synchronization interval. Moreover, a frequency adaptive proportional resonant (PR) based PCC voltage controller ensures exact tracking of reference signals under varying frequencies. RRC abides by regulations imposed by the IEEE 519 and 1547 standards for integrating distributed energy resources with utility grid. Seamless transition from standalone (SA) to grid interfaced (GI) mode during distorted grid voltage conditions and system performance during sudden changes in solar insolation level are also demonstrated, showing efficient functioning of control loop during adverse operating scenarios. Simulations and validations in a real-time test bench setup assess feasibility of proposed control for microgrid (MG).