Predictive Direct Virtual Torque and Power Control of Doubly Fed Induction Generators for Fast and Smooth Grid Synchronization and Flexible Power Regulation

Predictive direct torque control of the electric motors has been well developed. It is simple and has excellent steady state and transient performance. However, further developments are still under investigation for applications in the field of power generation. This paper presents a predictive direct virtual torque and power control strategy for a doubly fed induction generator, which allows fast and smooth grid synchronization, and flexible active and reactive power regulation. In the no-load mode, predictive direct virtual torque control is employed to meet the grid synchronization conditions. In the grid-connected mode, predictive direct power control is utilized to achieve flexible active and reactive power regulation. To simplify the control system structure and improve the reliability, a sensorless rotor position scheme is proposed. Furthermore, a model-based predictive scheme is introduced to compensate for a one-step delay in the digital implementation. The proposed control strategy is very simple and robust. There is constant switching frequency, while the requirement of smooth and fast grid synchronization is fulfilled. The transition from no load to flexible power regulation is achieved without changing the switching table. The proposed control strategy was tested by simulation using MATLAB/Simulink and experimentally validated on a 20-kW laboratory prototype.