This paper addresses the high-frequency resonance issue that arises during the parallel operation of online UPS systems by establishing and analyzing an impedance model and proposes a scheme to suppress it by cascading a digital notch filter within the voltage loop controller. The experiments have proven that this scheme effectively suppresses high-frequency resonance. In the full paper, the modeling process showing detailed root cause analysis will be demonstrated. The impact of the proposed method on voltage dynamic will also be evaluated and demonstrated in the full paper.
