# Robust Control Examples Applied to a Wind Turbine Simulated Model
## 2 Wind Turbine Simulated Model  
Today's wind turbines contribute to a larger and larger part of the world's power production. At the same time the size of the standard turbine has been increasing, as well. Turbines in the megawatt size, as most often installed at present, are expensive, and hence the reliability of their control techniques represents an important issue. They should be able to produce as much time as possible. A way to contribute to ensure this consists in introducing advanced control systems on the wind turbines. The state-of-the-art of advanced control schemes for industrial wind turbines shows that they are quite simple and often conservative [15]. For example, turbines deployments are turn off even at earlier malfunctions, to wait for service. Consequently, the use of advanced control schemes could improve the on-time of the turbine, even though that might result in production with limited power for some anomalous working conditions [15]. Some works on advanced control solutions for wind turbines were proposed. For example, an observer based scheme applied to the pitch system was presented in [16]. On the other hand, priority relation based scheme for change detection was presented in [17], whilst an unknown input observer applied to the wind turbine drive train in [18]. Furthermore, the wind turbine electrical conversion system was investigated in [19; 20; 21]. Therefore, in general, it would be beneficial to compare different control schemes for wind turbine application in order to find the best solutions, as considered in this paper. However, since a wind turbine is a large and complex system such a comparison can only be performed on a limited set of situations. Therefore, in order to test different advanced control techniques for wind turbine applications, this paper considered the benchmark model of a wind turbine process on system level, containing sensors, actuators and systems typical of an energy conversion plant. This benchmark model describes a realistic generic three-bladed horizontal variable speed wind turbine with a full converter coupling, formerly proposed in [22]. This generic turbine has a rated power of 4.8 MW. Since this model works on a system level, the fast control loops of the converters are not considered. Moreover, since it is a model on system level, its converter and pitch system models are simplified, because they are controlled by internal governors working at higher frequencies than the system model. This section outlines the wind turbine model, whose sampled inputs and outputs will be used for the proposed control designs, as shown in Section 3. More details concerning the accurate derivation of the simulator model can be found in preliminary works [23; 24] and definitely presented in [22]. In fact, this simulator was proposed for an international competition regarding fault diagnosis and fault tolerant control techniques started in 2009, whose results were summarized in [3; 25]. The wind turbine system exploited in this work uses a nonlinear dynamic model representing the wind acting on the wind turbine blades, thus producing the movement of the low-speed rotor shaft. The higher speed required by the electric converter is produced by means of a gear box. The simulator is described in more detail, e.g., in [22; 25]. A scheme of the wind turbine simulator considered in this paper is represented in Figure 1 with its main blocks. Both the generator speed \(\omega_{g}\) and the generator power \(P_{g}\) are controller by means of the two control inputs representing the generator torque \(\tau_{g}(t)\) and the blade pitch angle \(\beta(t)\). Several signals can be acquired from the wind turbine simulator.