Vehicle-to-grid (V2G) technology enhances the utilization of renewable energy by enabling electric vehicles to inject stored renewable power into the grid. However, in singlephase residential grids, the grid background harmonics and grid frequency variations directly affect the feed-in grid current quality of the V2G inverter system. To address this issue, this paper proposes a novel feedforward dual-mode repetitive control (FDMRC) scheme, which adjusts adaptively the repetitive control (RC) gains according to the harmonics distribution of feed-in grid current. By introducing the feedforward channels into the dual-mode repetitive control, the FDMRC enlarges the open-loop gains at the frequencies of interest, while enhancing the dynamic performance of the system. In addition, the adaptive RC gains improve the harmonics suppression performance of the FDMRC system under varied grid background harmonics. Furthermore, stability analysis and detailed parameters optimization design for the FDMRC system are presented. The experimental platform of a single-phase V2G inverter is established to verify the effectiveness of the proposed FDMRC scheme, and the experimental results demonstrates that the proposed FDMRC scheme possesses enhanced harmonics suppression performance, strong frequency robustness, and fast dynamic performance under the scenarios of varied grid background harmonics and grid frequency variations.

The harmonic suppression performance of the odd-harmonic repetitive controller (ORC) will decrease when the microgrid frequency fluctuates due to power imbalance. This article presents a novel fractional order feedforward odd-harmonic repetitive controller (FO-FORC) for grid-tied inverters in microgrids. The feedforward ORC (FORC) with a feedforward channel has a much higher open-loop gain and a wider bandwidth at odd-harmonic frequencies than conventional ORC (CORC) without a feedforward channel. Therefore, the FORC can more efficiently suppress the odd harmonic of grid current while using fewer storage units. Nevertheless, the ratio of the sampling frequency of the FORC to the microgrid frequency can only be an integer, which degrades the harmonics suppression performance of the FORC with a fixed sampling frequency when the fundamental grid frequency changes in a relatively wide range. In order to settle the problem, based on a Thiran infinite impulse response (IIR) filter, this article proposes the FO-FORC with frequency adaptability to ensure that the resonance peaks of FO-FORC maintain at the real disturbance signal frequencies by online adjusting only a few coefficients of low-order IIR filter. The stability analysis, parameters design, and performance estimation are given. Comparative experiments verify the feasibility and superiority of the presented FO-FORC.

A novel fractional-order repetitive control based on phase angle information interpolation is proposed for single-phase LCL-type inverters in this paper. Conventional fractional-order repetitive control typically relies on inaccurate grid frequency information detected by a phase-locked loop or the frequency-locked loop, which may result in a potential degradation in harmonics suppression capability. To address this issue, phase information is investigated to implement the fractional order of the repetitive controller through the linear interpolation method. A major advantage of the proposed scheme lies in that it avoids explicit frequency calculation and reduces sensitivity to frequency estimation fluctuations compared with conventional fractional-order repetitive control, enhancing its frequency adaptability. The stability analysis and the design process for the proposed scheme based on a plug-in-type repetitive control are given. Experimental results support the efficacy and advantages of the proposed control strategy.