## 1 Introduction  
Today, technological developments in wind energy are aimed at controlling ever larger turbines, as the longer the blades are, the more torque is produced to install higher-capacity generators. The size of the most sold turbines currently has a sweeping area of 12,272 m\({}^{2}\) (125 m in diameter) and generates up to 7.5 MW [1]. Nonetheless, as of 2016, more and more wind turbines with a sweeping area diameter of 174 m and a production of 9.5 MW are being used [2]. The most recent launch on the market is the V164-10 wind turbine with a sweeping area diameter of 164 m and 10 MW of production, available for sale now and ready to be installed until 2021 [3]. According to the specifications of these large wind turbines, the rotor shaft height is 110 m and requires a nominal wind speed between 10 and 25 m/s [2,3] with an unobstructed air flow. However, in places where there are less wind resources, it is necessary to install \"small wind turbines.\" The IEC 61400-1: 2014 standard requires that small wind turbines have a rotor swept area of less than 200 m\({}^{2}\) (16 m in diameter), a voltage of less than 1000 V AC or 1500 V DC, and a nominal wind speed of between 6 and 10 m/s [4]. According to the global wind atlas, there is a significant wind potential as at least 50% of the globe has an average wind speed greater than 6.04 m/s at 10 m high [5]. The limitation is that these areas include urban areas with tall buildings, roofs, wooded areas, cliffs, or mountains that suggest atypical wind behavior with turbulence and gusts [4]. Therefore, it is necessary that wind turbines operate with different wind speeds and take full advantage of this natural resource. For each size and aerodynamic model of turbine, there is a tip speed ratio (TSR) that relates the wind speed to the rotation speed of the rotor [6]. To maintain the TSR at optimal values with wind speeds greater than nominal, the pitch angle of the blades must be controlled to reduce the effects of wind force on the rotor and decrease the rotor speed [7; 8]. The control model used in standard wind conditions is a derivative-integral-proportional (PID) or any of its variants, but for atypical wind conditions, it is no longer valid, because the sensitivity of the rotor rotation speed to the pitch angle varies in different ways [9; 10]. This variation is nonlinear and implies a control response according to the magnitude of the change in wind speed [11]. A fuzzy logic controller (FLC) interprets the knowledge acquired in a set of mathematical rules, and obtains solutions through fuzzy inference, so it is possible to compensate for the nonlinearity of perturbations caused by wind speed randomness [12]. Fuzzy inference rules are adjusted according to human experience, intuition, wind range classification, and deductive reasoning [13; 14; 15]. Typically, an FLC consists of two input signals, the error in the controlled variable (\(\mathrm{e}\mathrm{r}\)) and the variation in the error of the controlled variable (\(\mathrm{\Delta}\mathrm{e}\mathrm{r}\)), and an output variable. In wind energy applications, the output is the set point of the pitch angle. In [16; 17; 18; 19; 20], the authors used active power as the input variable, and in [21; 22; 23], the generator shaft speed was used as the controlled variable. In [24] researches use as inputs the error of the active power and generator shaft speed. In [25] is added a third variable, used the error power, variation of the power error and generator shaft speed error. In [26] is proposed changing the input variables to wind speed and the error of generator shaft speed. Finally, in [27] is used as input the voltage and the error in voltage. All these FLC applications got better performance than a PID controller, however, they do not report their performance when drastic changes in wind speed occur [28]. Unlike existing solutions, this article proposes a control strategy based on diffuse logic, where the membership functions of the controller are hierarchically determinate by three levels of control.