A novel autonomous control scheme for parallel, LCL-based UPS systems

摘要

This paper proposes a novel autonomous control scheme for equal load current distribution between n parallel-connected, LCL-based, three phase UPS units. The control is based on varying the capacitor reference voltage of each inverter as a function of its own output current, without exchanging information between the inverters. The load voltage is maintained fixed at the specified reference value. The control method is fast, precise and robust against load variations. Capacitor voltage and capacitor current are used in a dual-loop control at each inverter. The validity of the proposed method is verified by simulation and experiments on a system of two 5-kVA parallel inverters.