## 4 Results and Discussion
### Discussion  
The FTC is introduced to control the balanced short-circuit of the DFIG-based wind energy system. The MPPT and PAC are also applied during low, rated, and high wind speeds. In order to regulate the low and rated wind speeds, the MPPT controller is activated at the rotor side converter. The PAC controller is operated during the low, rated, and high wind speeds, as explained in Tables 2 and 3 and Figure 3. During the low wind speed, PAC remains disabled and MPPT is activated. The FTC scheme is operated during low, rated, and high wind speeds and regulates the short-circuit DC voltage overshoots values following its rated rate. The DC voltage is depicted in Figure 3 and Table 1, which is observed to be harmful for the healthy operation of the system and synchronization with the grid. For the sake of comparison, Figure 3 shows the line current and DC voltage values at different wind speed ranges. The simulation results are depicted with and without applying the proposed schemes. When the balanced short-circuit is impressive and the DC overshoots voltage is reduced by FTC and suppressed to close to its rated value, which is maintained at less than 1.15 kV, the power coefficient value (\(\text{C}_{\text{p}}\)) is close to the maximum value (i.e., 0.45 p.u) for wind speeds under the rated value. The \(\text{C}_{\text{p}}\) decreases for high wind speeds to prevent damage. The TSR value is kept constant, while the \(\text{C}_{\text{p}}\) decreased during high wind speeds and MPPT is activated during low wind speeds. According to Equation (6), we must keep TSR constant at its optimal value by changing the rotor speed. We observe the \(\text{C}_{\text{p}}\) and TSR responses in Table 2. Table 2 demonstrates that \(\text{C}_{\text{p}}\) decreases with wind speed, and the pitch angle (\(\beta\)) increases with the rate of wind speed. Meanwhile, the reactive (Q) power is approximately constant owing to the robust reactive controller and is measured to be close to zero, whereas the value of Q is observed to be higher under high wind speeds and faults, which is depicted in Table 1.  
In order to prevent the damage, cut-off, or shut-down of the power grid and DFIG system, the pitch angle is increased to obtain high wind speeds. Meanwhile, the DC voltage is close to its rated value (i.e., 1.150 kV) for all wind speed operations to keep the bus voltage of the wind farm close to the grid voltage for synchronization, as shown in Figure 3 and Table 2. Reactive power varies based on system operations, with the healthy and faulty results depicted in Table 2 and the simulation model parameters of DFIG presented in Appendix A (Table A1).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{
\begin{tabular}{c} **Wind Speed** \\ **Category** \\ \end{tabular} } & \multirow{2}{*}{**Operation Mode**} & \multicolumn{2}{c}{**Control States for PWM of Rotor Side Converter (RSC)**} \\ \cline{3-5}  & & **MPPT** & **PAC** & **HFTC** \\ \hline \multirow{2}{*}{Low} & Healthy & 1 & 0 & 0 \\  & Faulty & 0 & 1 & 1 \\ \multirow{2}{*}{Normal} & Healthy & 1 & 1 & 0 \\  & Faulty & 0 & 1 & 1 \\ \multirow{2}{*}{High} & Healthy & 0 & 1 & 0 \\  & Faulty & 0 & 1 & 1 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Hierarchical operation table of the implemented fault tolerant control (FTC) scheme. PAC, pitch angle control; MPPT, maximum power point tracking.