Cooperation Norway-USA in the field of wind energy

The wind turbine industry has undergone a growth of 30-40% per year, making wind energy a significant source of electrical energy in many countries. The turbines have grown from 50kW to 5 MW over some 25 years, and since for comparable designs the weight of the blades and drive train grows faster than the energy production, it becomes imperative to make comparatively lighter blades and drivetrains for the large wind units. One important mean to achieve this is the topic of my thesis, individual pitch cont rol, which means that the orientation of each blade relative to the plane of the rotor (?angle of attack?) is adjusted continuously to cope with variations in the wind velocity. The rotor on large turbines typically undergoes one revolution in about 4 sec onds, and since the necessary adjustment of the angle of attack is in the order of 1-2 degrees, such adjustments are not too hard to effectuate. One problem is the difficulty in giving precise definitions of the objectives of the regulation strategies. F or instance: decreasing the angle of attack will decrease the lift force acting on the blade, but will decrease the torque which is input to the drivetrain even more, since the torque depends only on the component of the force in the plane of the rotor. T he torque of course also depends on the pitching of the 2 other blades, but will in addition be influenced by the electrical controls implemented at the opposite end of the drivetrain, in connection with the generator. To fix ideas: The torque can be kept relatively constant even if the moment from the wind temporarily reduces, by reduction of rotational velocity. But this in turn will change the wind forces. Due to the complexity of the factors influencing the pitch regulation strategies, it is of outmo st importance that we can discuss these matters with other competent people with experience in this field, and fortunately some of the best can be found at NREL and at MIT.