Design of Power Decoupling Strategy for Single-Phase Grid-Connected Inverter Under Nonideal Power Grid

Because a single-phase inverter has a power coupling between the dc bus and the ac side, the dc bus always requires large electrolytic capacitors for the power decoupling. Although the active power decoupling circuit can restrain the ripple voltage with twice the fundamental frequency on the dc bus and reduce the required capacitance, previous research works mainly focused on the power coupling of an ideal power grid, and just decoupled the ripple power with twice the fundamental frequency. This study analyzes the power coupling in a nonideal power grid, and designs a novel decoupling method for the power with multiharmonic frequency on the dc bus. By modifying the reference values of dc series split-capacitors, the system control structure can be simplified, and the multifrequency-coupled power decoupling can be realized. Moreover, a notch filter is introduced into the dc voltage feedback path for further reducing the influence of the power coupling on the inverter output current quality. The proposed method can achieve the objective of the multifrequency-coupled power decoupling, even under a weak power-grid environment. Finally, numerical simulations and experimental results are provided to verify the effectiveness of the proposed method in comparison with the traditional capacitor decoupling framework and the dual-voltage control decoupling scheme.