Virtual variable sampling discrete fourier transform based selective harmonic repetitive control of DC/AC converters

This paper proposes a frequency adaptive discrete Fourier transform (DFT) based repetitive control (RC) scheme for DC/AC converter. DFT-based RC is an improved RC scheme aiming to eliminate waveform distortion on selected harmonics without influencing the overall system stability. However, the traditional DFT-based RC is insufficient to accommodate frequency fluctuation as fractional delay period in one signal cycle will lead to the large magnitude pulse deviates away from the desired frequency. To address the problem, virtual variable sampling method is proposed to develop a flexible and precise way to achieve a fixed integer delay with virtual variable sampling. By applying this method, the DFT-based RC can easily accomplish frequency adaptation. Comparing the traditional DFT-based RC, it not only reduces computation load but also increases the system stability. A complete series of experiments of programmable AC power source under frequency tuning are presented to verify the effectiveness of the proposed method.