Virtual negatively resistive output impedance for power sharing among paralleled inverters in microgrid

In this paper, a new control method for paralleled inverters in microgrid is presented. The strategy of power sharing among inverters in microgrid can be divided into control with and without communication. When there is no communication among inverters, droop control is used to share power. But droop control is effective only when the transmission line is approximately pure inductive. Microgrid is in the distribution network in power system, so the resistive component in transmission line is very high. Under this condition, there is severe coupling in droop control and power sharing mechanism is invalid. In this paper, by making use of virtual impedance, the equivalent output impedance of inverter becomes negatively resistive, while its amplitude equals to the value of resistive component in transmission line, so the resistive component in transmission line will be neutralized. So the circuit can be viewed as inverter supplying power through pure inductive transmission line. Therefore, the coupling in droop control can be removed and power sharing mechanism is effective. The analysis of the proposed method and design procedure are provided. Simulation results validate the proposed control strategy.