Robust Technique Using the Optimized Grid Voltage Feedforward to Conquer the Impact Induced by Dual Factors for Grid-Connected Inverter in Weak Grid

For grid-connected inverter, phase-locked loop (PLL) is generally adopted to obtain the voltage phase information in order to make the grid current synchronized with the grid voltage. In the meantime, the grid voltage feedforward (GVF) is usually employed to improve the grid current quality. While, both of them may deteriorate the system stability in weak grid. This article focuses on the single-phase
LCL
-type grid-connected inverter, and aims to put forward the optimizing scheme of dealing with the instability caused by these dual factors. In view of this, the weighted GVF is adopted to make a tradeoff between the system stability and harmonics rejection ability. Because the GVF in weak grid will introduce a grid current branch, the bandwidth of the current loop will be improved, which is conducive to reducing the coupling effect of PLL and the current loop. Therefore, the weighted coefficient will also affect the PLL issue. Considering the limited effect of the weighted coefficient on enhancing the system stability, a voltage feedforward path is further added to improve the output admittance phase. The results show that the inverter with the improved feedforward path can maintain good robustness against the wide grid impedance variation.