Grid-connected Inverter Control Strategy for Eliminating the Influence of Phase-locked Loop in Weak Grid

The introduction of phase-locked loop (PLL) in a weak grid is not conducive to the stability of grid-inverter system. The small signal model of PLL is established in the form of complex variable, and the influence of PLL on the stability of inverter is analyzed. Starting with the disturbance components of voltage, current and duty cycle brought by PLL, the opposite amount is injected into the controller to reduce the negative influence of PLL, so as to suppress the frequency coupling and improve the stability of inverter. The experimental results demonstrate the effectiveness of the proposed strategy. Comparing the proposed control strategy with the method of reducing the bandwidth of the PLL and adding the virtual impedance method in the PLL structure, the experimental results show that the dynamic performance of the inverter is better after adopting the proposed strategy.