A Novel DC Loop Current Control Strategy for Paralleled UPS Inverter System Based on Decoupled Control Scheme

This paper proposes a novel Control strategy based on decoupled control scheme to eliminate DC loop current of paralleled uninterrupted power supply (UPS) inverter system. On the basis of the original paralleled system for load-sharing by active and reactive power control, a separate control circuit is added in each parallel inverter module to eliminate the DC component of output voltage. The voltage between the middle point of half bridge of inverter and the middle point of the DC bus capacitors is measured to accurately detect DC voltage offset of the inverter. Therefore, the DC component of each inverter output voltage can be regulated to zero. The method is based on the idea that DC voltage offset of each inverter is decoupled. Because each module only regulates its own DC voltage component, the DC Loop current control is decoupled. The experiment results in paralleled three-phase UPS inverter system verified the feasibility and reliability of the control strategy.