## 5 Contribution of Wind Power in Frequency Control  
In order to investigate the effectiveness of the proposed control strategies in frequency control of a system with high percentage of wind power penetration, a simulated test system containing two zones connected to each other via a tie line is considered. Each zone consists of a conventional thermal plant and a WF, supplying local load demand. Today, there exist power systems in which the percentage of wind power in supplying the total load demand is quite high. Also, with growing global demand for more green energy, and advances in wind technology, it is conceivable that wind penetration levels in power systems can grow even higher. Hence, an appropriate test system must be considered to give a close estimation of developing power systems with high percentage of wind power penetration. For this purpose, in the considered power system, 30% of the total load is supplied by WTGs and the other 70% is supplied by conventional units. Under these conditions, a proper simulation of the whole power system can be achieved. The capacity of each thermal unit is 20 MVA and each WTG capacity is 2 MW. In addition, load demand variations are considered to be supplied by WTGs. The model of the thermal plants is based on the proposed model in [9]. The values of the thermal units' parameters in the model are shown in Table 3. \begin{table}
\begin{tabular}{c c} \hline
**Roughness** & **Land Cover Types** \\
**Length Z** & \\ \hline
0.0002 m & Water surfaces: seas and Lakes \\
0.0024 m & Open terrain with smooth surface, e.g., concrete, airport runways, mown grass etc. \\
0.03 m & Open agricultural land without fences and hedges; maybe some far apart buildings and very gentle hills \\
0.055 m & Agricultural land with a few buildings and 8 m high hedges seperated by more than 1 km \\
0.1 m & Agricultural land with a few buildings and 8 m high hedges seperated by approx. 500 m \\
0.2 m & Agricultural land with many trees, bushes and plants, or 8 m high hedges seperated by approx. 250 m \\
0.4 m & Towns, villages, agricultural land with many or high hedges, forests and uneven terrain \\
0.6 m & Large towns with high buildings \\
1.6 m & Large cities with high buildings and skyscrapers \\ \hline \end{tabular}
\end{table} 
Table 2: Different roughness lengths and their land cover types. Data from [29]. In this paper, WTGs with the capacity of 2 MW have been employed in the simulations. The values of the WTGs' parameters in the model are shown in Table 4[30]. Figure 6 demonstrates the simulated scheme of the test system, which is composed of two zones. Each zone consists of a thermal unit with an interconnected WF supplying a local load demand. Two considered zones have been connected to each other via a tie line. It has been assumed that each zone consists of 4 WTGs as representatives of an individual WF. In order to perform a realistic modeling, different geographical zones have been considered for WTGs' locations in two WFs. In the simulations, WF1 roughness length varies between 0.03 and 0.055. WF2 roughness length varies between 0.1 and 0.2. In order to compare different frequency control scenarios and the proposed control strategy described in this paper, simulations have been conducted on the test system and the results are reported here. Three control strategies are studied as follows:  
1. Using a lookup table to allocate weighting factors to individual WTGs in two simulated WFs. 2. Using FLC to allocate weighting factors to individual WTGs in two simulated WFs. \begin{table}
\begin{tabular}{c c c c} \hline
**Parameter** & **Value** & **Parameter** & **Value** \\ \hline P\({}_{\text{rated}}\) & 2 MW & X\({}_{\text{m}}\) & 3.5 PL \\ L\({}_{\text{ss}}\) & 3.6 PU & r\({}_{\text{s}}\) & 0.0043 P.U \\ L\({}_{\text{rr}}\) & 3.78 PU & r\({}^{\prime}\)r & 0.012 P.U \\ C\({}_{\text{f}}\) & 0.7 PU & R & 50 m \\ \hline \end{tabular}
\end{table} 
Table 4: Value of parameters in wind turbine generators’ (WTGs’) model. Figure 6: The proposed test system.