A New Virtual Impedance Method for Parallel Inverters with Droop Control

This paper proposes a new virtual impedance method for parallel inverters. To achieve wireless control, the droop control method is adopted, and virtual output impedance is usually added to alleviate the unbalance of output impedance between each inverter and then, improve power sharing accuracy. However, resistive virtual impedance usually causes a certain voltage drop, while inductive virtual impedance leads to a certain phase delay for the output voltage. To solve this problem, a new virtual inductive impedance method combining with a negative resistance is proposed. Thus the output impedance would be corrected to be a pure inductance, which results in better load sharing accuracy for the droop controlled parallel inverters. Simulation and experimental results are presented for a parallel connected inverter to validate this method.