A novel hybrid current control strategy applied in Three-Phase Four-Leg APF

A novel hybrid current control strategy applied in three-phase four-leg active power filter (APF) is proposed. For the three-phase four-leg APF, once the three-phase source currents after compensation are sinusoidal and balanced, the neutral current generated by unbalanced loads will be compensated by the neutral leg of APF automatically, thus the output currents control of three main power legs is independent from the neutral leg. The novel control strategy applies SVM to the output current control of three power legs, and employs hysteresis current control for the neutral leg. To achieve the expected compensation, an improved p-q method is applied in the detection of harmonic and reactive components of load currents. Furthermore, the exchange and redistribution of energy between the power system and APF which make the ideal compensation possible is also analyzed. The results of simulation demonstrate the validity of the proposed strategy.