The simplified control of three-phase four-leg shunt active power filter for harmonics mitigation, load balancing and reactive power compensation

In this paper, the simplified control of three-phase four-leg shunt active power filter for harmonics mitigation, load balancing and reactive power compensation is proposed. In order to calculate the harmonics, current imbalance and reactive power, the load currents are detected and transformed to dq0 variables. By using the low-pass filter, the fundamental active power current can be separated from the d-axis current. Therefore, the commanded active power filter currents are consist of d-axis harmonic currents, q-axis and 0-axis currents. These components are regulated by the PI controller with feedforward utility voltage via the four-leg space vector inverter. Moreover, the design guidelines of space vector phase-locked loop (PLL), current controllers and DC-bus voltage controller are also presented. Validity of the proposed control schemes is confirmed by the simulation.