Dynamic Performance Improvement of a Wind Turbine System based on Doubly Fed Induction Generator (DFIG) by utilizing a multiple Model Predictive Controller (MPC) strategy

Novel control strategies that improve the cost effectiveness of Wind Energy Conversion Systems (WECS) are proposed in this paper. The main focus is on grid-connected Variable- Speed Variable-Pitch (VSVP) wind turbines equipped with Doubly Fed Induction Generators (DFIGs).At the wind turbine control level, a multivariable control strategy based on model predictive control techniques is proposed. The proposed control strategy is described for the whole operating region of the wind turbine, i.e. both partial and full load regions. Pitch angle and generator torque are controlled simultaneously to maximize energy capture, diminish drive train loads and smooth the power generated while reducing the pitch actuator activity. This has the effect of improving the efficiency and the power quality of the electrical power generated, and increasing life expectancy of the installation. Furthermore, safe and acceptable operation of the system is guaranteed by incorporating all relevant constraints on the physical variables of the WECS in the controller design. In order to cope with nonlinearities in the WECS and continuous variations in the operating point, a multiple model predictive controller is suggested which provides desired performance throughout the whole operating region. A VSVP wind turbine has two operating regions, with different control objectives, partial and full load regions. The wind turbine control problem is described in both regions. The partial load regions controller should maximize the wind turbine energy capture. This is done by continuously adjusting the turbine speed and thus tip speed ratio should be at its optimal value. By also fixing the blades’ pitch angle at its optimal value the power conversion efficiency is maximized. In the full load regions, the main control objective is to regulate both the output power and the generator speed at their rated values. This should be achieved in the presence of a severely fluctuating disturbance. The regulation of the WECS variables can be achieved by manipulating the pitch angle set point and/or the generator torque set point. Harvested mechanical power of a wind turbine can be regulated by changing power coefficient that can be interpreted as a variable gain controlled by tip speed ratio and pitch angle. Consequently, manipulating the pitch angle results in deviations in the power extracted by the wind turbine and, indirectly, induces deviations in the turbine speed via the drive train dynamics. Similarly, the generator torquecan affect the turbine speed through the drive train dynamics and can be used to control the power generated by the wind turbine by controlling tip speed ratio. The esign of a multivariable controller, that can harmonize the use of both the pitch and torque control, can significantly enhance the transient response of the system and reduce the pitch actuator activity.

کلیدواژه ها:

Wind Energy ، DFIG ، Model predictive control ، Multivariable control