SiC-MOSFET shunt active power filter based on half-cycle SDFT and repetitive control

Abstract

The switching frequency of traditional active power filter (APF) is usually between 10 kHz and 20 kHz. To better suppress switching subharmonics, the output filters of APFs usually use LCL-filters. However, LCL-filters not only have complex parameter design but also introduce resonance points, which complicate the design of the circuit and control algorithm of APFs. In this paper, SiC-MOSFET is used as the power device of APF, the switching frequency of APF is increased to 50 kHz. In this case, using L-filter instead of LCL-filter can also suppress the switch subharmonics to a smaller level, which simplifies the circuit design and control algorithm design at the same time. In addition, when the sampling frequency and switching frequency are higher, the sampling points and switching times in a power frequency cycle increase exponentially, so the accuracy of harmonic extraction and output current control will be higher. Then, the common harmonic extraction algorithms of APFs, sliding window discrete Fourier transform (SDFT) and current control algorithm, repetitive control (RC), are analyzed in the frequency domain. A modified half-cycle SDFT and half-cycle RC are proposed, which reduces the inherent delay of the algorithms by half, and reduces the dynamic response time of APFs from two to one power frequency cycle, thus improving the dynamic response performance of APFs.