Unified constant-frequency integration control of four-arm three-phase four-wire active power filter with vector operation

This paper presents a unified constant-frequency integration (UCI) control for a three-phase four-wire active power filter (APF) with vector operation. Using this method only AC mains current and zero voltage crossing point are sensed. No sensors for the load current and the APF inductor current are required. Furthermore, there is no need to calculate the reference for APF inductor current so that complicated digital computation is eliminated. Three-phase unity-power-factor and low THD are achieved by integration with reset along with a few logic and linear components. And the amount of switching are operated at high frequency reduced, thus, the switching losses is optimized. In this paper analysis and simulation are carried out with the four-arm inverter, the simulation results verified that the APF with UCI control can effectually compensate the harmonics, reactive current and zero sequence current.