SHC-PWM Closed-Loop Control Based on PI Controllers for Active Power Filters

The increase of non-linear loads connected to the grid has led to the use of active power filters (APF) to reduce the low-order current harmonics injected by this kind of loads. In case of high-power medium-voltage applications, low switching frequency optimized modulators are preferred over standard carrier based-PWM. Therefore, in this work the selective harmonic control - PWM (SHC-PWM) modulation technique is used. SHC-PWM allows to synthesize low-order harmonics in amplitude and phase with low switching frequency. A closed-loop control system for APFs is proposed in order to address the control dynamic challenges related to low switching frequency modulation techniques. The closed-loop control uses a Kalman filter to estimate the harmonic currents in the grid side, a proportional-integral controller and SHC-PWM modulator based on artificial neural network. Simulation results are provided for a 3-level NPC converter to verify the effectiveness of the proposed control.