The impedance model of LCL single-phase grid-connected inverter is established
and the mechanism of phase reduction of inverter output impedance caused by PLL is analyzed. In order to improve the influence of phase-locked loop on system stability
a multi-objective constrained power grid voltage feedforward control strategy is proposed. Firstly
a positive impedance is obtained by designing the transfer function of the voltage feedforward channel at the common coupling point to offset the negative impedance introduced by the phase-locked loop. Secondly
in order to reduce the difficulty of engineering implementation of feedforward control strategy
the original feedforward transfer function is simplified by establishing multi-objective constraints from the aspects of amplitude-frequency deviation and phase-frequency deviation in basic frequency band and middle frequency band
and an approximate equivalent feedforward transfer function is designed. And the stability analysis is presented. Simulation and experiment verify that the proposed method effectively enhances the adaptability of grid-connected inverter in weak grid.
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