Optimal gain-scheduled control of fixed-speed active stall wind turbines (original) (raw)
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This paper addresses state estimation and linear quadratic (LQ) control of variable speed variable pitch wind turbines. On the basis of a nonlinear model of a wind turbine, a set of operating conditions is identified and a LQ controller is designed for each operating point. The controller gains are then interpolated linearly to get a control law for the entire operating envelope. The states and the gain-scheduling variable are not online available and an observer is designed. This is done in a modular approach in which a linear estimator is used to estimate the nonmeasured state variables and the unknown input, aerodynamic torque. From the estimated aerodynamic torque and rotor speed and measured pitch angle the scheduling variable effective wind speed) is calculated by inverting the aerodynamic model. Simulation results are given that display good performance of the observers and comparisons with a controller designed by classical methods display the potential of the method.
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Rate bounded linear parameter varying control of a wind turbine in full load operation
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This paper considers the control of wind turbines using an LPV design technique. The controller design is done by a combination of a method that uses elimination of controller variables and a method using a congruent transformation followed by a change of variables. An investigation is performed to understand the gap between zero rate of variation and arbitrary fast rate of variation for the selected scheduling variable. In particular it is analysed for which rate of variation, the local performance level starts to deteriorate from the performance level that can be obtained locally by LTI controllers. A rate of variation is selected which is expected only to be exceeded outside the normal wind turbine operating conditions. For this rate of variation a controller has been designed and simulations show a performance level over the operating region which is very similar to what can be obtained by LTI designs for the specific operating condition. The LPV controller, however, works for the whole operating range with reasonably fast changes within this.
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A multi-body aeroelastic design code based on the implementation of the combined aeroelastic beam element is extended to cover closed loop operation conditions of wind turbines. The equations of a controller for variable generator speed and pitch-controlled operation in high wind speeds are combined with the aeroelastic equations of motion for the complete wind turbine, in order to provide a compound aeroservoelastic system of equations. The control equations comprise linear differential equations for the pitch and generator torque actuators, the control feedback elements (proportional-integral control) and the various filters acting on the feedback signals. In its non-linear form, the dynamic equations are integrated in time to provide the reference state, while upon linearization of the system and transformation in the non-rotating frame, the linear stability equations are derived. Stability results for a multi-MW wind turbine show that the coupling of the controller dynamics with the aeroelastic dynamics of the machine is important and must be taken into account in view of defining the controller parameters.
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Electric power systems are allowing higher penetration levels of renewable energy resources, mainly due to their environmental benefits. The majority of electrical energy generated by renewable energy resources is contributed by wind farms. However, the stochastic nature of these resources does not allow the installed generation capacities to be entirely utilized. In this context, this paper attempts to improve the performance of fixed-speed wind turbines. Turbines of this type have been already installed in some classical wind farms and it is not feasible to replace them with variable-speed ones before their lifetime ends. A fixed-speed turbine is typically connected to the electric grid with a Static VAR Compensator (SVC) across its terminal. For a better dynamic voltage response, the controller gains of a Proportional-Integral (PI) voltage regulator within the SVC will be tuned using a variety of optimization techniques to minimize the integrated square of error for the wind farm...
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Design of linear parameter varying control (LPV) for wind turbines is considered in this paper. Multivariable, robust control law, which can guarantee stability and desired performance in the whole operating region of the wind turbine, is obtained. LPV controller is compared with a classical controller.