An Active Filter With Resonant Current Control to Suppress Harmonic Resonance in a Distribution Power System

A shunt active filter operated as a harmonic conductance is able to suppress a harmonic resonance in the distribution power system. However, due to the inherent phase-lagging in digital signal processing, the active filter really behaves as a harmonic admittance instead of conductance. This may induce unintentional harmonic amplification at other locations in the feeder when starting the active filter, which is similar to the so-called whack-a-mole phenomenon. This paper presents an active filter with resonant current control to suppress a harmonic resonance. The current control is realized by parallel-connected bandpass filters tuned at harmonic frequencies to ensure that the active filter functions as an approximately pure conductance. The conductance at dominant harmonic frequencies can be separately and dynamically adjusted to guarantee the damping performance. In addition, in order to address the harmonic resonance, the line distributed-parameter model of a radial feeder is developed considering harmonic damping by variable conductance and admittance, respectively. Simulation results show that the active filter with the resonant control provides a better damping performance compared with other control methods. A lab-scale prototype circuit rated at 220 V/20 kVA also validates the effectiveness of the proposed method.