Virtual impedance based parallel operation of multi-converters in low voltage microgrids

Droop Control Method is effective to the parallel operation of multi-converters without communication system. However, in low voltage microgrids the line impedance is highly resistive, which results in the unbalances of load current sharing among the parallel-connected converters. In this paper, a virtual impedance control method is proposed to adjust the total equivalent impedance between converters and AC bus, which aims to improve the load current sharing accuracy. Moreover, a multi-structure virtual impedance control loop is presented to distribute the fundamental current and harmonic currents precisely, which can accommodate nonlinear loads current sharing. Simulation results verify that the proposed strategy is correct and effective.