This paper presents the theory and design of a novel hybrid mechanical-electrical variable speed wind turbine transmission, and discusses a robust control solution for optimal power output of the wind turbine equipped with such a transmission. The novel, planetary differential transmission would be driven by the variable speed rotor and controlled by a control system to ensure a constant speed of the main generator at a wide range of wind speed variations. Analysis shows that this would lead to an increase in the wind turbine energy output, estimated to be in the range of 15% to 20%, compared to a wind turbine with the same rotor and a fixed transmission. Using robust control design techniques, a single controller is synthesized for efficient operation over the entire anticipated wind speed range. The control system automatically varies the rotor speed to optimize its power output for slow wind speed variation and attenuates high frequency wind gust effects to reduce the resulting fatigue damage. Overall, the new concept provides a cost effective solution for variable speed wind turbine operation. The improved system performance is demonstrated using the results of a numerically simulated dynamic model of the proposed system.
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