A full-dq based adaptive virtual impedance compensation in virtual power frame for droop-controlled parallel inverters under unbalanced conditions

Distributed generation (DG) is connected through three-phase inverter to the microgrid. The virtual power based droop control can guarantee the pure decoupling between active and reactive power irrespective of low-voltage or high-voltage microgrid application if the line-impedance information is known in advance. However, unbalances are commonly existent in practice so that this conventional control fails in application due to the significant coupling between active and reactive power. To overcome this problem and further extend virtual power based method into unbalanced conditions, this paper proposes an improved virtual power decoupling technique using full-dq transformation, which is utilized to identify arbitrary unbalanced components under unbalanced conditions. The identified unbalances are further compensated as an virtual impedance so as to ensure the pure decoupling of active and reactive power in the virtual power frame. Finally, simulation results are provided to verify the effectiveness of the proposed method under unbalanced conditions.