Research on fast transient and 6n ± 1 harmonics suppressing repetitive control scheme for three-phase grid-connected inverters

The repetitive control technique is widely adopted in ac systems, because of its excellent steady-state tracking performance and low total harmonic distortion. The repetitive control method with one-sixth of the system fundamental period T₀ as the delay time has been proposed to achieve fast transient response. In this study, an improved control scheme based on the T₀/6 repetitive control is proposed for three-phase grid-connected inverters. The proposed scheme adopts T₀/6 as the delay time in the positive-rotating and negative-rotating synchronous reference frames to suppress the 6n ± 1 harmonics. Meanwhile, the proportional-integral regulator and the plug-in repetitive controller are combined to reinforce the system performance. A new auxiliary function based on the linear interpolation is proposed to maintain the ideal repetitive control performance when one-sixth of the ratio of the sampling frequency to the grid fundamental frequency is non-integer. The effectiveness of the proposed scheme on improving the T₀/6 repetitive control is confirmed by simulation and experimental results finally.