Direct current control strategy for seamless transfer of voltage source inverter in distributed generation systems

This paper presents a direct current control strategy that enables both islanding operation mode and grid-tied operation mode of three-phase inverter in distributed generation systems. With no need for switching between two corresponding modes or critical islanding detection, the proposed control strategy composes two current control loops, including an inductor current loop and a direct capacitor current loop are cascaded in the synchronous reference frame. In the grid-tied mode, the three-phase inverter is regulated as a current source just by the inductor current loop. The capacitor current limiter can be used to regulate the load voltage and guarantee the voltage quality upon the occurrence of islanding. Additionally, this paper presents the parameters design of the control strategy. Finally, the proposed control strategy is verified by the simulation result.