Advanced Control Algorithm for Three-Phase Shunt Active Power Filter Using Sliding DFT

This paper describes n digital control algorithm for a three-phase shunt active power filter (APF) using switching-sliding discrete Fourier transform (SSDFT). Traditionally, APF control algorithms use first harmonic detector circuits, which can be implemented using the SDFT algorithm. The classical SDFT algorithm is characterized by long-term stability issues, resulting from numerical errors. Many complex modifications to improve the stability of the SDFT algorithm have been proposed in the scientific literature. This article proposes a solution to the SDFT stability problem using the basic structure of the algorithm. The authors propose the use of the switching SDFT algorithm, where two original SDFT algorithms are implemented in parallel. Both algorithms are turned on alternately after a set period of time and reset to zero in order to reset numerical errors causing their unstable operation. Compared to the classical three-phase SDFT algorithm, the three-phase SSDFT requires only about 25% more arithmetic operations. The proposed approach has been validated using experimental tests and dramatically reduces the numerical errors. The control algorithm has been implemented using the TMS320F28379D microcontroller. The sampling method using only the internal A/D converter of a microcontroller is also presented. The article includes the experimental test results of the complete APF.