Virtual Variable Sampling Discrete Fourier Transform Based Selective Odd-Order Harmonic Repetitive Control of DC/AC Converters

Abstract

This paper proposes a frequency adaptive discrete Fourier transform (DFT) based repetitive control (RC) scheme for dc/ac converters. By generating infinite magnitude on the interested harmonics, the DFT-based RC offers a selective harmonic scheme to eliminate waveform distortion. The traditional DFT-based selective harmonic RC, however, is sensitive to frequency fluctuation since even very small frequency fluctuation leads to a severe magnitude decrease. To address the problem, the virtual variable sampling (VVS) method, which creates an adjustable virtual delay unit to closely approximate a variable sampling delay, is proposed to enable the DFT-based selective harmonic RC to be frequency adaptive. Moreover, a selective odd-order harmonic DFT filter is developed to deal with the dominant odd order harmonic. Because it halves the number of sampling delays in the DFT filter, the system transient response gets nearly a 50% improvement. A comprehensive series of experiments of the proposed VVS DFT-based selective odd-order harmonic RC controlled programmable ac power source under frequency variations are presented to verify the effectiveness of the proposed method.