Improving Small-Signal Stability of Grid-Connected Inverters Based Phase-Locked Loop Compensation Under Weak Grid

In weak grid scenarios, the dynamic behavior of the phase-locked loop (PLL) can adversely affect system stability due to the influence of weak grid impedance. Establishing a small-signal output impedance model of grid-connected inverters is common practice for studying oscillation instability issues between the inverter and the weak grid. This paper proposes a stabilizing control strategy based on symmetric compensation of feed-forward perturbations to address the impact of PLL small perturbation coupling on current loop control. The strategy takes into full consideration the characteristics of small perturbation coupling in the control coordinate system and formulates a system of equations to derive the expression of the small perturbation feedforward compensation controller. By inversely compensating the small perturbation components that lead to current loop destabilization, the stability of the system under weak grid conditions is improved. Simulation results demonstrate that this strategy does not require adjusting controller parameters and directly compensates for disturbance components.