## 9 Discussion  
The proposed FFT-enabled POD-P controller effectively detects and mitigates inter-area oscillations in scenarios with 20%, 50%, and 80% renewable penetration. The POD-P controller parameters are optimally tuned using the NBA to enhance its damping performance. Simulation results confirm that FFT-based detection reliably identifies oscillatory modes regardless of the share of renewable generation in the system. This capability enables the POD-P controller to activate upon the detection of oscillations, effectively damping the oscillations through dynamic adjustments to the PPCs' active power setpoint. Once the oscillations are mitigated, the POD-P controller deactivates, minimizing unnecessary interventions and ensuring operational efficiency. In all scenarios, the POD-P controller successfully reduces the oscillation amplitudes and stabilizes the system, achieving damping ratios above the stability threshold of 5%. The system becomes less stable as renewable penetration increases, with reduced damping ratios observed in the electromechanical modes. This instability leads to prolonged oscillatory behavior, as seen in Scenarios 2 and 3. However, the initial frequency deviation following a disturbance is smaller in higher-renewable-penetration scenarios. Figure 14: Scenario 3 with anti-windup. POD-P activation signal _Enable_POD_ and PPC active power setpoint _Pout_ for each PV plant [p.u.]. Figure 13: Scenario 3 with anti-windup. 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.]. This behavior is attributed to 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. The results highlight that while higher renewable integration increases the risk of sustained oscillations, the proposed POD-P controller mitigates these challenges, ensuring system stability. Its ability to respond to successive disturbances further highlights the system's robustness. After resolving an initial disturbance, the FFT monitors system signals, reactivating the POD-P controller when subsequent events occur. This dynamic behavior ensures consistent stability, even under complex scenarios involving consecutive disturbances. A notable improvement in the POD controller is the integrating of an anti-windup filter, addressing the limitations observed under high-renewable-energy scenarios. Saturation of the active power output restricts the controller's response, leading to a decrease in system frequency. The anti-windup filter ensures the correct operation of the controller under such conditions and maintains grid stability while preventing excessive frequency deviations. The proposed methodology aligns with current regulatory frameworks, such as Commission Regulation (EU) 2016/631 and ACER Recommendation 03-2023 Annex 1, emphasizing the importance of renewable generators that include oscillation damping capabilities. Additionally, the Spanish draft Operation Procedure (PO) 12.2 explicitly requires Type D renewable plants to include POD controllers for inter-area oscillations from 0.1 Hz to 1.0 Hz. This demonstrates our methodology's practical applicability to meet regulatory standards. These results demonstrate that the proposed approach is a reliable and flexible solution for managing inter-area oscillations, particularly in power systems with high renewable penetration. Future research will address the limitations encountered in high-renewable scenarios, such as photovoltaic saturation and renewable generation constraints, by exploring alternative solutions. Additionally, the methodology will be applied to more extensive grid systems to evaluate its performance and robustness under varying operational and topological complexities.