Novel control strategy for parallel operation of UPS system

A parallel operation system of multiple UPS is used to increase power capacity of the system or to secure higher reliability at critical loads. In the parallel operation of UPS inverters, the load-sharing control to maintain the current balance between them is a matter of consequence. Because a UPS has low output impedance and quick response characteristics, in case of an unbalanced load inverter output current changes very rapidly and thereby could instantaneously reach an overload condition. In this paper, a highly precise load-sharing controller is proposed and implemented for the parallel operation system of two UPSs. After that, a good performance of the proposed method is verified by simulation in the parallel operation system with two UPS inverters.