## 8 Simulation Results
### Scenario 2  
In Scenario 2, PV plants supply 50% of the total generation of the grid, with synchronous generators contributing 50%. This corresponds to 3070.40 MW from the PV plants and approximately 3057.5 MW from synchronous generation (see Table 1).  
The system is first simulated with the FFT detection function disabled to observe the impact of increased renewable penetration. The integration of PV plants reduces the damping ratio of the electromechanical mode to 1.76%, reflecting the reduced stability of the system as renewable penetration increases. Figure 7a shows the frequency response of the grid terminals. Compared to Figure 4a, the initial peak is narrower, but the oscillations persist for a longer duration. This behavior is attributed to the diminished system inertia, which limits the system's ability to resist immediate changes in frequency following a disturbance, resulting in a smaller initial frequency deviation. However, the lower damping ratio exacerbates the system's susceptibility to sustained oscillations, leading to their prolonged decay. Figure 7b focuses on the frequency at the PV plant terminals and the synchronous generator speeds, highlighting the longer-lasting oscillatory behavior.  
Once the FFT detection function is enabled, the POD-P controller actively damps the oscillation by adjusting the active power setpoint in the PPC. With the POD-P controller activated, the damping ratio increases to 10.61%, demonstrating the effectiveness of the control mechanism in stabilizing the system despite the reduced inertia. Figure 8a illustrates the significant reduction in frequency oscillations across all grid terminals, showcasing the damping mechanism's effectiveness. Figure 8b zooms in on the frequency at the PV plant terminals and synchronous generator speeds, highlighting the stabilized response.  
Figure 9 illustrates the FFT-triggered activation signal Enable_POD of the POD-P controllers, along with the corresponding dynamic adjustments of the PPC active power setpoint Pout at each PV plant. The FFT function continuously monitors the system, ensuring that the controller operates only when necessary and is deactivated once the oscillations are sufficiently mitigated. This optimized response prevents unnecessary interventions and highlights the adaptability of the control mechanism. The same sequence is applied during the second event, confirming the consistency of the POD-P controller's performance across different scenarios and grid conditions.  
Figure 6: Scenario 1. POD-P activation signal _Enable_POD_ and PPC active power setpoint _Pout_ for each PV plant [p.u.].  
Figure 8: Scenario 2. System response with the POD-P controller activated following the terminal short-circuit event (t = 5 s) and the line short-circuit event (t = 80 s): (a) frequency at all grid terminals [p.u.]; (b) frequency at PV terminals [p.u.] and speed of synchronous generators [p.u.].  
Figure 7: Scenario 2. System response without the POD-P controller activated following the terminal short-circuit event (t = 5 s) and the line short-circuit event (t = 80 s): (a) frequency at all grid terminals [p.u.]; (b) frequency at PV terminals [p.u.] and speed of synchronous generators [p.u.].  
Figure 9: Scenario 2. POD-P activation signal _Enable_POD_ and PPC active power setpoint _Pout_ for each PV plant [p.u.].