Combined feedback and feedforward control strategy of parallel hybrid filter

Active power filters (APF) may substitute the passive ones in some cases or serve as an additional tool, together with PF, for improving the harmonic spectra of the load current and supply voltage. In such a case we call that configuration a hybrid filter (HF). In the paper, a combined feedback and feedforward control strategy of the parallel hybrid filter (PHF) is presented, which features a small sensitivity against a disturbed supply voltage system and enables us to set grid phase currents in the phase with respective voltages. The expected properties of the PHF control system have been confirmed by experimental tests in the laboratory. The experimental data show that the modified control strategy yields better results than those obtained by using the control system reported previously, especially in case of an unsymmetrical and non-sinusoidal voltage system and the demand of zero reactive power withdrawn from the grid.