Virtual Impedance Design for Power Quality and Harmonic Sharing Improvement in Microgrids

One of the main challenges of decentrally operated islanded microgrids has been proper harmonic sharing for parallel connected inverters. This is largely affected by differences in the feeder impedances of the inverters. Virtual impedances are able to improve the harmonic current sharing, at the cost of deteriorating the power quality at the outputs of the inverters. This paper proposes a method for minimally setting the virtual impedances based on an optimization algorithm and estimation of the feeder impedances. The scheme ensures proper sharing between the units, while the power quality at the inverter terminals are minimally affected. The scheme is verified by numerically simulating a test microgrid.