Design of a hybrid active filter for harmonics suppression in industrial facilities

Harmonic voltage amplification, due to unintentional series or parallel resonance of power factor correction capacitors, is a significant issue in the industrial power system. Conventional active filters intended to compensate the harmonic current producing by nonlinear loads would not be an effective solution in this scenario, and the harmonic voltage may still be significant. This paper proposes a hybrid active filter to suppress the harmonic resonance in industrial facilities. The hybrid active filter, which is composed of a capacitor and an active filter in series connection, operates as variable harmonic conductance with dynamically tuning characteristic according to the voltage total harmonic distortion, so the damping performance of the active filter can be adjusted in response to load change and power system variation. Therefore, the harmonic resonance would be avoided as well as harmonic voltage distortion can be maintained at an allowable level. Compared with the pure shunt active filter, the dc bus voltage of the proposed hybrid filter is dramatically reduced since the grid voltage is supported by the series capacitor. This feature provides a vital advantage of the active filter, in terms of both the kVA rating and the switching ripples. Operation principles are explained in detail, and computer simulations validate the effectiveness of the proposed approach.