Direct Flux-Vector Control of Stand-Alone DFIG-Based Wind Energy Conversion System

This article presents direct flux-vector control (DFC), a new control strategy based on direct torque control (DTC), for a doubly fed induction generator (DFIG) driven by wind, feeding AC loads without grid access. For this type of application, the amplitude and frequency of the stator voltage must be rightly controlled. In the proposed topology, two separated closed loops are employed, containing a proportional–integral (PI) controller and a hysteresis controller in which the amplitude and frequency of the stator voltage are controlled by adjusting the magnitude and angle of the rotor flux, respectively. This method boasts an uncomplicated implementation, does not require a rotor position/speed sensor or any reference-frame transformation, and only requires knowledge of the rotor resistance. The Dynamic performance of direct flux-vector control is tested in Matlab/Simulink under different sudden load and wind speed conditions. The results demonstrated the high performance of the method, the amplitude and frequency of the stator voltage were precisely adjusted, and the controller was not affected by parameter variations. Furthermore, the proposed control operates in both subsynchronous and supersynchronous speed modes and no shaft-mounted speed sensors or speed estimators were required. The new control DFC was shown to be robust and effective.