Mitigation Method of Resonance between Paralleled On-line UPS

On-line uninterrupted power supply (UPS) is used to guarantee stable power supply in case of grid faults. It is widely applied in industry, commerce, medical and transportation. In many application scenarios, several on-line UPSs are required to work in parallel due to high load demand. However, high-frequency resonance might occur in the output current of paralleled UPSs. This paper provides impedance model analysis of the resonance and proposes a mitigation method based on digital notch filter. Through this method, the resonance can be mitigated significantly, and voltage dynamic performance is not deteriorated. The effectiveness of the proposed method is verified through experimental tests.