A Soft-Start Self-Adaptive PILC-PLL Control for Smooth Operation With Low Trips for an Abnormal Grid Tied SPVS With RoCoF Constraints

Abnormal grid conditions like voltage distortion, amplitude sag/ swell, phase angle jump (PAJ) may result in spurious transients leading to fictitious fluctuations in estimated frequency and phase angles by phase locked loops (PLLs). These PLLs are also not immune to provide accurate grid voltage information under severe harmonics and DC offsets in grid voltage. These extreme conditions lead to violation of the IEEE std. 1547-2018 leading to frequent disconnections of renewable energy dominated microgrid networks tied to grid. To make microgrid operation immune to such fictitious transients assuming rate of change of frequency (RoCoF) constraints of grid, within purview of IEEE std. 1547-2018 for interconnected systems, this work proposes a soft-start self-adaptive control for grid-tied solar photovoltaic system (SPVS). Control presents a cascaded second order generalized integrator (CSOGI) based prefilter with a self-adaptive in-loop comb phase locked loop (SA-PILC-PLL) control. Prefilter ensures effective filtering of grid voltages and currents with support from ILC-PLL for ripple free accurate frequency estimation. Incorporation of pre and in-loop comb based PLL (PILC-PLL) ensures elimination of dominant harmonics and DC offsets from grid currents for improved system power quality as per the IEEE std. 519-2022, even during extreme supply voltage scenario. Self-adaptive and soft-start enhancements in PILC-PLL provide enhancements utilizing known information of grid RoCoF constraint to improvise accuracy in supply frequency estimation with reduced fictious overshoots restraining false trips of microgrid. System operation with seamless operation and enhanced system power quality is validated with simulation and experimental results.