A Fractional Phase Compensation Scheme of PRMRC for LCL Inverter Connected to Weak Grid

This paper proposes a fractional phase compensation(FPC) scheme for proportional resonance in parallel with multirate repetitive control (PRMRC) to suppress the grid-injected current harmonics and improve the stability of LCL inverter under weak grid condition. In the PRMRC, the proportional resonance control is introduced to overcome the disadvantages caused by inherent delay of repetitive control. Moreover, in order to expand the system stability range and improve the adaptability of the PRMRC in the weak grid, a Newton fractional filter is proposed to approximate the fractional part of the phase compensation term. The coefficients of the Newton fractional filter do not need to be adjusted online even when the grid impedance fluctuates, which greatly reduces the computational burden. The stability principle of the fractional phase compensation PRMRC scheme and the detailed parameter setting are discussed in the paper. Both simulation and experiment are carried out and the results verify the feasibility and effectiveness of the fractional phase compensation scheme of PRMRC (FPC-PRMRC) for LCL inverter connected to weak grid.