Research on control strategies for distributed inverters in low voltage micro-grids

Taking into account the configuration of low voltage distributed grids. The micro-grid that is consisted of three-phase four-leg inverters is proposed in this paper. Then, a decomposing sequence control strategy and a droop control method are explored. Positive, negative and zero sequence components can be controlled by the decomposing sequence control method independently. The decomposing sequence control algorithm is implemented in dq0 reference frame, which can achieves voltage regulation with low THD and fast transient response, and inverters can output a set of symmetric ac voltages under various loads. Meanwhile, inverter´ output impedance is fixed through a virtual impedance scheme. The droop-control method is applied to regulate the frequency and amplitude of inverters output voltages, which only use local measurements of the inverter. These control strategies can improve the modularity, reliability and flexibility of the distributed power supplies. The total loads are shared among inverters by the propose control strategies. Simulation results are provided from two 6KVA parallel-connected inverters in an island micro-grid, which verifies the validity of method proposed.