A Unified Power Control Method for Standalone and Grid-Connected DFIG-DC System

This letter proposes a unified power control method for the doubly fed induction generator dc (DFIG-DC) system, which can seamlessly transfer from the grid-connected mode to the standalone mode without changing a control strategy and vice versa. There is no need to detect the interconnection switch to identify whether it is grid connected or standalone. The dc voltage and stator active power are both positive correlations with the magnitude of a rotor current vector, which indicates that these two objectives can be combined as the unified power to generate the rotor current reference. The stator frequency can be controlled by the rotating speed of the rotor current vector without calculating the stator frequency, which can reduce the parameter dependence. Finally, the experiments based on a 1-kW DFIG-DC setup are carried out to verify the proposed unified power control method.