Adaptive implementation strategy of virtual impedance for paralleled inverters UPS

Abstract

In paralleled inverters UPS system, Virtual impedance is applied widely in inverter to decouple the active power and reactive power of inverter and improve the power average sharing accuracy. Proper virtual impedance also can estimate the circulating currents resulted from the asymmetric parameters of different inverter modules. In practical paralleled inverters system, when one inverter prepares to connect into system, the design of virtual impedance in this inverter will be difficult if the parameters of other operating inverters are unknown. In this paper, an adaptive virtual impedance implementation strategy is proposed, namely the virtual impedance of inverter can be adjusted adaptively to suppress the circulating current. Comparing with the traditional virtual impedance implementation method, where the virtual impedance is set directly, by using the proposed strategy, the virtual impedance of inverter can be set automatically. Moreover, the circulating current can be eliminated more effectively. Finally, both the simulation and experimental results demonstrate the effectiveness of the proposed method.