Resonant frequency offset suppression strategy of LCL grid-connected inverter using capacitor voltage feedforward in weak grid

The reason why the stability of LCL grid-connected inverter declines is that the resonance frequency of the system loop is shifted, which is caused by the wide range change of the grid impedance under the weak current grid. To solve this problem, this paper proposes a single sensor LCL grid-connected inverter loop resonant frequency offset suppression strategy based on capacitor voltage feedforward. The strategy uses the capacitor voltage proportional differential feedforward control to greatly suppress the system loop resonant frequency offset, and applies the capacitor voltage phase-locked for power factor correction to save a group of sensors, and realize the grid-connected inverter unity power factor. In addition, considering the influence of digital control delay on the system, the parameters of the proposed strategy were optimized when the damping ring delay is zero. These theoretical analysis show that the introduction of digital control delay will not affect the applicability of the proposed strategy. Finally, the effectiveness of the proposed control strategy was verified by experiments, and it has strong robustness to grid impedance. © 2022, Harbin University of Science and Technology Publication. All right reserved.