Improved droop control of isolated microgrid with virtual impedance

Droop control is one of the widely used control methods in power systems to deal with the power allocation among all rotary generators. In a microgrid, due to the resistive lines, the characteristic of P-f and Q-V may not be fully decoupled. As a result, the droop control cannot be implemented completely. By modifying the parameters of an inverter controller, the inductive equivalent output impedance can be obtained. However, it cannot meet the requirement of Q-V based control. In this paper, a concept entitled `virtual impedance' is introduced to implement the droop control for microgrids. By this method, the equivalent impedance of the inverter, as well as the total equivalent impedance of the system, is with the inductive characteristic, which meets the requirements for implementation of P-f and Q-V control strategies. The proposed method is compared with the traditional strategy with PSCAD/EMTDC. The simulation results show that the proposed method can allocate both real and reactive powers effectively.