An accurate reactive power sharing control strategy for DG units in a microgrid

A popular power control and load demand sharing method for distributed generation (DG) units in microgrid is the frequency and voltage droop control. However, in a low voltage microgrid, due to the effects of nontrivial feeder impedance, the conventional droop control is subject to the real and reactive power coupling and steady-state reactive power errors. Furthermore, different microgrid configurations (looped network or radial system) and the different locations of loads make the DG reactive power sharing even more challenging. To improve the power control and sharing accuracy, this paper proposes a control strategy that estimates the reactive power sharing errors of DG units through injecting small real power disturbances. With the estimated reactive power errors, the conventional reactive power droop control can be improved with zero steady-state sharing error, just like the real power sharing through frequency droop control. The proposed method can work in both grid-connected mode and islanding mode and is effective for all types of microgrid configurations and load locations.