VAr compensation and elimination of harmonics in three-phase four-wire system based on unified constant-frequency integration control

In this paper, an attempt has been made to design a shunt active power filter based on unified constant-frequency integration (UCI) control, for a three-phase four-wire system with unbalanced loads. The active power filter provides compensation currents in such a way that the utility supplies only the balanced fundamental frequency current at unity power factor, even if the load draws reactive and harmonic currents. The proposed scheme does not need to sense utility voltages, thereby reducing the complexity. In this paper, UCI control is applied to both four-leg and three-leg inverter topologies. The effectiveness of the proposed scheme is demonstrated by the simulation results.