Enabling high droop gain for improvement of reactive power sharing accuracy in an electronically-interfaced autonomous microgrid

In an autonomous microgrid, distributed generation (DG) units share the load while maintaining the voltage and frequency of the grid. This paper investigates the problem of proper load sharing. A control strategy is proposed to improve the accuracy of reactive power sharing in an electronically-interfaced autonomous microgrid. Increased droop gain improves the accuracy of power sharing, however, with a negative impact on the overall system stability. To enable high droop gains while maintaining the system stability, a reactive power injection loop around the conventional droop loop is proposed whereby the oscillatory behavior of the reactive power output of each DG is captured and fed back. The added loop comprises a high-pass filter and a proportional controller. The design of the controller gain is formulated as a pole-placement problem using a reduced-order small-signal model of the microgrid. The gain of the controller is selected to guarantee an adequate stability margin for a high droop gain. The proposed control scheme uses local power measurements and, hence, requires no communication among DG units. Mathematical explanation of how the method improves stability is provided. Simulations carried out in MATLAB/Simulink are used to illustrate the claims.