Modeling and control of a small wind turbine

This paper starts with a detailed survey of control methods commonly employed by commercially available small wind turbines. This detailed survey indicates that the most commonly used control method of small wind turbines is horizontal furling method. Such furling mechanism and resulting dynamics are described in the paper. Furling is used to control the aerodynamic power extraction from the wind. A dynamic model of a small wind turbine with furling dynamics is presented in this paper. Such small wind turbines are based on permanent magnet generators and their speed can be regulated using the load control. The extraction of maximum power output from such wind turbines is investigated using tip speed ratio control and hill-climbing control methods. The system is simulated in Matlab/Simulink to determine a suitable control strategy. Two dynamic controllers are designed and simulated. In the first method, a controller uses the wind speed and rotor speed information and controls the load in order to operate the wind turbine at the optimum tip speed ratio. The generator output is observed in varying wind condition as the furl angle increases and decreases. In the second method, a controller compares the output power of the turbine with the previous power and based on the comparison it controls the load. Using a hill-climbing algorithm the controller tries to extract the maximum power from the wind, while the generator output is observed as the furl angle increase or decreases. Finally, the output of these two controllers is compared and investigated to determine which controller leads to the best results.