**2. Wind turbine model**

The equation of wind turbine power is

© 2012 Jafari; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Jafari; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

$$P = \frac{1}{2} \,\rho A C\_p \nu\_w^{\;\;\;\;\;\phi} \tag{1}$$

where*ρ* is air density, *A*is area of turbine, *Cp*is power coefficient and *υw*is wind speed. The *C <sup>p</sup>* curve and equation are shown in Fig. 1 and given by equation (2) and (3)

$$C\_{\rho} = c\_{1} \left( c\_{2} \frac{1}{\left( \frac{1}{\lambda + c\_{8} \theta\_{\mu \text{ach}}} - \frac{c\_{9}}{1 + \theta^{3}} \right)} - c\_{3} \theta\_{\mu \text{ach}} - c\_{4} \theta^{s}\_{\ \mu \text{ach}} - c\_{6} \left( e^{-c\_{7} \left( \frac{1}{\lambda + c\_{8} \theta\_{\mu \text{ach}}} - \frac{c\_{9}}{1 + \theta^{3}} \right)} \right) \tag{2}$$

$$C\_p = 0.44 \left( 125(\frac{1}{\lambda} + 0.002) - 6.94 \right) \cdot e^{-16.8\left(\frac{1}{\lambda} + 0.002\right)} \tag{3}$$

where*θpitch* is blade pitch angle, *λ*is the tip speed ratio described by equation (4). The pa‐ rameters are given in Table 1.

$$
\mathcal{A} = \frac{\alpha\_M R}{\nu\_w} \tag{4}
$$

where *R* is blade radius.

**Figure 1.** Curve of *Cp* for different tip speed ratios λ .

The curve of Fig.1 has positive slope before *Cp* max and it has negative slope after *Cp* max.
