Continuously variable transmission (CVT) control, for a grid-connected wind turbine, is studied beyond the proof-of-concept by analytically and systematically designing and tuning controllers using various methods. Three different approaches are used for CVT controller design. These include typical torque (TT) control, classical proportional-integral-derivative controls, and modern control theory for disturbance tracking control and realizable drivetrain dampers. Entire control systems ranging from wind turbine start-up through rated conditions are designed, implemented, and simulated with nonlinear plant models using full-field turbulent wind inputs.Various controller designs, based on rigid and rotationally-flexible drivetrain models, are compared for turbulent flow simulations of the nonlinear model with rotor rotation, drivetrain twist, and system load twist degrees of freedom. For the rigid drivetrain, the TT controller has less control action and better energy capture than the proportional controller. For the flexible drivetrain model, the proportional controller proves to be infeasible for practical implementation due to excessive drivetrain torque fluctuations. The TT controller with a realizable drivetrain damper proves to have the best damping characteristics, lowest CVT workload, and best power regulation. For the flexible system load model, the TT controller with a realizable damper has the best results again, with the exception of generator shaft loading conditions. The thorough comparison of CVT controllers leads to identification of controller feasibility, actuator workload, and achievement of objectives.
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