## 5 Result Analysis  
A detailed analysis of the time domain simulation results is presented here for the four case studies presented in the last section.  
1. Case 1 represents the implementation of three wind farms in the stable IEEE nine-bus three-generator system with high penetration (25%) that leads to significant system instability appearing in frequency oscillation around 60.2 Hz-59.8 Hz. This forces frequency relays to trip in some portions of the system. Also, there are great fluctuations in the output power of wind farms in the range of 0-0.6 pu which leads to oscillations in the transmitted power between 0 and 1.7 pu. Hence, the majority of loads in this case cannot be met with a continuous power supply within acceptable frequency limits, which decreases the reliability and power quality of the system with harming loads, especially those are sensitive for frequency fluctuations and voltage flicker, with a decrease in their life time.
2. Case 2 shows the application of the first hybrid GA-fuzzy based control approach to the governor system of the conventional generators. As a result, the proposed constant frequency of 60 Hz is achieved as shown in Figure 11. Besides, output power fluctuations of wind farms still exist in range of 0-0.6 pu which derive to the transmitted power deviations in lower amounts compared to those in case 1. Hence, the first controller succeeded in damping frequency oscillations but some fluctuations still appeared in power responses.
3. Case 3 involves the proposed scenario presenting implementation of the two hybrid GA-fuzzy based control approaches in the power system. The first approach is applied for the governor of conventional generators, while the second is used for the pitch angle control system of wind farms. Simulation results shown in Figure 12 confirm the ability of the first controller to keep frequency constant at 60 Hz. Also, the second controller can suppress the output power fluctuations of wind farms and ensure constant power at around 0.63 pu (63 MW) of each wind farm, even with variable wind speed, due to effective blade pitch angle control as shown in Figure 12. Beside this, control techniques succeeded to damp transmitted power oscillations ensuring continuous power supply to customers with high power quality.
4. To validate the robustness of the proposed control schemes in emergencies, a three-phase to ground fault at the most loaded transmission line is considered in case 4. The fault occurs at \(t=30\) s and is cleared at \(t=50\) s. Simulation results indicate the ability of the control techniques to damp frequency and wind power fluctuations, with reducing sudden overshoots at times of fault occurrence and clearance, respectively. As a result of transmission line outage, the transmitted power via the remaining transmission lines is redistributed to compensate the transmission line outage and ensure continuous power feeding for loads. After fault clearance, the power system comes back safely to its normal operating point thanks to the proposed control schemes with damping all power and frequency fluctuations and ensuring continuous power supply of the system with high power quality without any harmful effects to the sensitive loads even in severe operating conditions is ensured.