A Frequency Adaptive Control Approach of Grid-Tied PV System for Simultaneous Mitigation of Current Harmonics and Power Oscillations Under Adverse Grid Voltages

This paper proposes a frequency-adaptive control approach for three-phase single-stage grid-tied photovoltaic (GTPV) systems, incorporating a frequency-adaptive proportional multiresonant (FAPMR) current controller to suppress grid current harmonics under voltage distortion induced by nonlinear loads. An improved second-order generalized integrator-based frequencylocked loop (ISOGI-FLL) is embedded within the FAPMR framework to improve grid synchronization accuracy and eliminate frequency oscillations. The proposed control approach mitigates active and reactive power oscillations during unbalanced grid faults while enhancing the GTPV system's resilience to grid frequency deviations. By operating in the stationary <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\alpha \beta)$</tex> reference frame, the approach eliminates the need for Park's transformation, reducing computational overhead. Experimental validation via real-time simulations on an OPAL-RT OP4510 platform under a software-in-the-loop (SIL) framework confirms the method's efficacy across diverse grid disturbances, including harmonic-polluted voltages, frequency fluctuations, and unbalanced fault conditions.