Research on fast transient and 6n±1 harmonics compensating repetitive control scheme for three-phase systems

The repetitive control technique is widely adopted in AC systems, because it can achieve excellent tracking performance and low total harmonic distortion (THD) when regulating periodic signals. This paper proposes an improved repetitive control scheme for three-phase systems. The proposed scheme adopts one-sixth of the fundamental period as the delay time in the positive-rotating and negative-rotating synchronous reference frames (SRF), and can achieve fast transient response and 6n±1 harmonics compensation. In this paper, the proportional-integral (PI) regulator and the plug-in repetitive control are combined in the control loop, to improve the even harmonics compensation under the unbalanced system. And the design methodology for the auxiliary function of the repetitive control is discussed to maintain its performance when one-sixth of the ratio of the sampling frequency to the fundamental frequency is not an integer. The effectiveness of the proposed scheme is confirmed by simulation and experimental results finally.