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The aim of the present research work has been to design an optimal MIMO LQG controller to reduce the drive-train, blades and tower mechanical stresses of a wind turbine (WT), and at the same time, to involve the WT in the grid primary frequency regulation when it is operating in full load (FL) zone. To verify the effectiveness of the proposed controller, the achieved results are compared to those obtained by a base-line controller based on a PI regulator. Simulation results show that thanks to these controllers, WT can effectively contribute to the grid frequency regulation, tracking tightly the generator power reference which depends on that frequency. Compared with the base-line controller, the LQG controller significantly reduces the mechanical stresses of the WT?s most costly components. [ABSTRACT FROM AUTHOR]

Abstract: The objectives of this work have been to design and analyze a discrete Linear Quadratic Gaussian (LQG) controller which contributes to the primary frequency control of the grid and to the reduction of the drive-train fatigue loads of a Wind Turbine (WT). The WT rotational speed and electrical power are controlled using the generator torque and the pitch angle as control variables. The rotational speed and electrical power references are generated in a higher control level depending on the wind speed and a frequency droop. The controller has been designed in Matlab® and has been simulated in Simulink®, in some linear simulation models corresponding to different operating points. These linear models have been obtained from a 5 MW WT model implemented in the commercial wind turbine simulation tool Bladed. The results validate the efficiency of the designed controller, in comparison with another discrete LQG controller which has not been designed to reduce drive-train fatigue loads. [Copyright &y& Elsevier]

Abstract: This paper presents the design of a robust –– controller of a variable speed pitch regulated wind turbine (VSPRWT) for above rated wind speeds (ARWS). An introduction of the subject and a state of the art review for controllers in ARWS are carried out. Afterwards, the studied VSPRWT and its validated model are presented. Then, the operating zone and control scheme are described. This system is non-linear and its linearising allows for the analysis of its behaviour, thereby obtaining the discrete-time control model as well as defining the controller''s concrete objectives. The digital controller, which is designed following the pole assignment with sensitivity function shaping method, provides satisfactory simulation trial results. [Copyright &y& Elsevier]

Abstract: Wind energy technology has experienced important improvements this last decade. The transition from fixed speed to variable speed wind turbines has been a significant element of these improvements. It has allowed adapting the turbine rotational speed to the wind speed variations with the aim of optimizing the aerodynamic efficiency. A classic controller that has slow dynamics relative to the mechanical dynamics of the drive train is implemented in commercial wind turbines. The objective of the work related in this paper has been to evaluate the implementation, on a test bench, of a controller whose dynamics can be adjusted to be faster and to compare in particular its aerodynamic efficiency with the conventional controller. In theory, the higher dynamics of the non-classic controller has to lead to a better efficiency. A 180kW wind turbine whose simulation model has been validated with field data is emulated on an 18kW test bench. The emulator has also been validated. Test bench trials are a very useful step between numerical simulation and trials on the real system because they allow analyzing some phenomena that may not appear in simulations without endangering the real system. The trials on the test bench show that the non-conventional controller leads to a higher aerodynamic efficiency and that this is offset by higher mechanical torque and electric power fluctuations. Nevertheless, the amplitudes of these fluctuations are relatively low compared to their rated values. [Copyright &y& Elsevier]

The design of a double-loop robust digital control algorithm for a wind turbine (WT) containing a doubly-fed induction machine is presented. The operating zone considered is that obtained when the rotational speed is limited to its rated value and the generated electricity has not reached its corresponding rated value. It is not particularly easy to find descriptions of controllers for this working zone in the existing literature. The rotational sampling effect may produce drive-train torque oscillations when a WT operates at constant speed. Consequently, its control system, which consists of two levels of control loops, has to be able to address these oscillations and be able to minimise flicker emission and dynamical loads in the drive train. These specifications, along with the robustness of the synthesised controller, lead to a reduced cost for the generated electricity and to a higher power quality, compared to those obtained using more classical WT control strategies that do not account for the peculiarities of the considered operation zone. The inner control loops govern the machine electromagnetic torque. The outer control-loop is synthesised using the discrete pole-placement with sensitivity function shaping method, to keep the rotational speed at its rated value and to reduce electromagnetic torque oscillations. The designed and synthesised control algorithms are tested on a simulation model validated using field data. Simulation results show that the proposed regulator reduces both flicker emission and dynamical drive-train loads, when compared to a classical PI regulator tuned to show an identical cut-off frequency and integral action. [ABSTRACT FROM AUTHOR]