Hybrid Impedance Reshaping Method of Grid-Connected Inverters in Weak Grid

Both the phase-locked loop (PLL) and the common coupling point (PCC) voltage feedforward may have impacts on the inverter system stability in weak grid. Therefore, a hybrid impedance reshaping control strategy is proposed in the paper. Firstly, the inverter impedance model is established. Next, the system stability is analyzed under weak grid, reflecting on the influence of PLL and the PCC voltage feedforward. Then, to improve the inverter system stability, the band-pass filter is added to the feedforward branch of PCC voltage, since it can attenuate the influence of unstable factors. Moreover, a new phase-locked loop structure containing a first-order decoupled complex filter is proposed, taking into account the fundamental positive voltage extraction characteristics of the first-order decoupled complex filter. The parameters of the hybrid impedance reshaping strategy are designed in detail. Finally, simulation is carried out to prove the theory analysis and hybrid impedance reshaping strategy in the paper.