Instantaneous current share method for modular UPS through virtual impedance

The current-sharing control strategies based on phasors are commonly used in parallel inverter systems. However, their low regulation speed, low accuracy and incapable of restraining the instantaneous circulating currents make them be more and more replaced by instantaneous control methods. In this paper, the transient model of circulating currents between parallel inverters is discussed, and an instantaneous current-sharing control method is proposed based on virtual impedance, which is realized through instantaneous circulating currents feedback. The virtual impedance will not influence output characteristic of whole parallel system. Simulations and experiments show this method achieves good performance and is suitable to high performance modular UPS system.