Improved scheme of grid-connected inverters based on virtual PCC and impedance remodeling with enhanced steady-state and dynamic performance

Abstract

The issue of low-frequency oscillation (LFO) becomes more prominent when considering the phase-locked loop (PLL) impact of grid-connected inverter (GCI) under weak grid. Impedance analysis shows that the frequency interaction point outside the capacitive negative damping region can effectively avoid the oscillation. Therefore, a modified PLL scheme is designed to shape the characteristics of the GCI output impedances, which effectively tracks the grid phase through the virtual point of common coupling and adjusts the phase- frequency characteristic of the GCI equivalent output impedance towards an increasing phase angle. On this basis, the impedance remodeling strategy is used to improve the system, which further broadens the feasible range of stable operation and ensures the phase margin of the GCI. The comparison results indicate that proposed scheme demonstrates enhanced capability in suppressing LFO and exhibits a wider range of adaptability to grid impedance. Experimental validation has verified the accuracy of the theoretical analysis, leading to the conclusion that the GCI with proposed scheme possesses superior dynamic performance.