Control strategies for active power filter in three-phase four-wire systems

In this paper, new control strategies for an active power filter (APF) under balanced and unbalanced load conditions in three-phase four-wire power systems are presented. A reference current generator is designed and space vector modulation (SVPWM) is employed to eliminate harmonic currents in each phase and in the neutral line along with compensation to the reactive power. A per-phase harmonic reference generator (PPHRG) is shown to increase the performance. DC bus voltage control is achieved by compensating the per-phase error on a-b-c axis frame. In the proposed approach, zero state vectors are suitably modified during unbalanced load conditions to achieve better performance. Simulation results show that the active power filter is capable of compensating the load harmonics and the reactive power in three-phase four-wire system