Hybrid active filter for parallel harmonic compensation

The interest in the application of the active filters to power system harmonic compensation increases with the rise of the pollution of the utility networks by distorting electronic loads. The high cost of these filters limited, up to now, their diffusion in industrial applications. Acceptable results can be obtained by hybrid units, including passive filter networks associated with active units which integrate and control the passive filtering. The active section can be sized only at a fraction of the total compensating power rating. In the paper, the design criteria and the implementation of an industrial filter unit, intended for the compensation of medium-power distorting loads is described. The design criteria to obtain flexible and robust operation, good transient capability and insensitivity to the resonance conditions with the supply are outlined. The proportioning of the passive section is discussed, the filter control system, with some peculiar features, is detailed, and the experimental performance, in comparison with simulated behaviour, is reported