A decoupled current droop control method for parallel inverters in microgrids

The well-known active power-frequency and reactive power-voltage amplitude droop control is widely used in the coordinated control of parallel inverters in microgrids. However, the dynamics of the conventional droop method is slow due to the low-pass filters used for power calculation purposes. Stability concerns also exist in the conventional droop method. This paper proposes a novel droop control scheme, which is based on droop relations between the output voltages and currents in a synchronous reference frame (SRF). The SRF voltage and current are decoupled by introducing a virtual current vector, which is aligned with the voltage vector. The proposed current droop relation forms automatically a virtual impedance loop, which can compensate the line impedance mismatch. In addition, a proportional regulator-based phase-locked loop is used to synchronize the parallel inverters in an equalized manner. The proposed method provides accurate current sharing, faster dynamics and higher system stability in diverse line impedance conditions. The effectiveness of the proposed method is verified by both simulations and experiments.