Summary As both pitch controller and torque controller are intended to maintain generator speeds close to a set point near the rated wind speed, it is necessary to implement a decoupling strategy between these two controllers in variable‐speed pitch‐regulated wind turbines. A basic power‐decoupling control strategy typically utilizes a power comparator as the switch logic for torque and pitch controllers. Because of the high inertia of the rotor, the turbine could easily suffer serious overshoot of the generator speed and may even deteriorate under extreme mechanical load in the case of gusts. On the basis of the idea of compromising between mechanical load and wind‐energy capture, an optimal power‐decoupling control strategy is proposed based mainly on a pitch‐power proportion integration (PI) loop. Simulations and field testing show that the proposed strategy can effectively reduce mechanical load by allowing pitch action to take place in advance, before rated power is reached under gust conditions.

Summary For large‐scale commercialized wind turbines, using the speed‐torque lookup table is a traditional strategy to achieve optimum tip‐speed ratio tracking. Due to the constraint of the minimum grid‐connected generator speed and the rated generator speed, the strategy can only use the slashes to describe these 2 transition zones. This affects the smoothness of the output power, shrinks the optimum tip‐speed range, and loses the generating energy. Based on an analysis of the nonlinear aerodynamics of the wind turbine, this paper presents a strategy of realizing optimal power generation control that dynamically updates the output torque limit value of the controller. The strategy solves the problems of unmeasurable wind speed and inability to track wind speed and achieves the target of maximum wind energy capture below rated wind speed. Simulation and field test results proved the correctness of the algorithm.

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The R ayleigh-Ritz method of calculating the natural vibration frequency of a structure in the second or further order is very complicated. This paper describes a simplified method of calculating the first and second order natural vibrational frequencies of wind turbine towers.