Virtual impedance attenuation based control of parallel inverters

Current sharing is a main problem in AC power supply system with multiple inverters parallel connected. Some methods are developed to eliminate the loop-current among inverters including droop control and virtual impedance. However, big voltage drop is inevitable for a good current sharing. This paper proposes a novel control algorithm with virtual impedance attenuation, which uses larger virtual impedance when communication is normal to achieve sound performance both of current sharing effect and voltage drop. Moreover, a compromise between current sharing and voltage drop elimination can also be obtained when communication fails. The theoretical analysis of the proposed method is verified through experiments on two three-phase 100kVA inverter prototypes.