Output Impedance Reshaping of Grid-connected Inverter Based on Voltage Feedforward under Extremely Weak Grid

Aiming at the stability problem of grid-connected inverter under extremely weak grid, firstly, the q-axis output impedance model is constructed, and the stability margin of grid-connected inverter under extremely weak grid is analyzed. Then, an accurate transfer function of output impedance reshaping strategy based on the voltage feedforward is constructed, which can improve the phase-frequency characteristics of the output impedance without changing the amplitude-frequency characteristics at the intersection frequency, and thus improve the stability. However, the discretization of the above transfer function is relatively complicated. Considering the output impedance characteristics under extremely weak grid, the voltage feedforward transfer function is simplified and optimized under the condition that the amplitude of output impedance phase boosting does not produce large deviation and the complexity of engineering implementation is much reduced. Finally, the hardware-in-loop simulation results verify the effectiveness of output impedance reshaping strategy.