A 3-phase 4-wire Shunt Active Filter with Selectable Harmonic Compensation and an Auto-Calibration Harmonic Algorithm

This paper presents the development of two prototypes units of a three-phase four-wire shunt active filter, one for an input voltage of 220 V and the other for 380 V. Both use the same hardware; the differences are in monitoring and control embedded in the microcontroller and can correct up to the 31st harmonic. Besides, the user can choose the harmonic(s) to be compensated. To correct unforeseen errors observed in the current sampling to be synthesized at the filter's input, a harmonic auto-calibration algorithm was created to correct the amplitude and angle of each harmonic of the sampled current. A current saturation algorithm was also implemented for each leg through the analysis of the phase sequences of each harmonic, preventing the current from exceeding the established and safe value. The two prototypes have been installed and in use at the BREE industrial plant, and they have been fixing harmonics for almost a year (BREE is a company that manufactures equipment and provides engineering services for reactive compensation, power quality, and energy efficiency and is a partner in this project).