Control architecture for paralleled current-source-inverter (CSI) based uninterruptible power systems (UPS)

This paper describes a theoretical and simulation study on a control strategy for the parallel operation of three-phase current source inverters (CSI), to be applied to uninterruptible power systems (UPS). A circulating current suppression strategy for parallel CSIs is proposed in this paper based on an auxiliary current control loop used to modify the reference currents by compensating the error currents between parallel inverters. The proposed method is coordinated together with droop and virtual impedance control. In this paper, droop control is used to generate the reference voltage of each inverter, and the virtual impedance is used to fix the output impedance of the inverters. In addition, a secondary control is used in order to recover the voltage deviation caused by the virtual impedance. and the auxiliary current control loop is added to acquire a better average current sharing performance among parallel CSIs, which can effectively suppress the circulating current. Simulation results are presented in order to verify the effectiveness of the proposed control methodology.