where Tsmn( x3) is the nominal value of the signal Tsm which is continuous and bounded on a compact set Un; d(t) is the uncertain part of the signal due to changes in the wind speed and it is assumed to be bounded too. The nominal part of this signal is continuous and can be approximated by a radial basis function (RBF) neural network [31,32]. Thus, the scaled mechanical torque can be described as follows [34] .