Sub-Synchronous Oscillations Suppression in Weak Grids Using Adaptive Control and High-Pass Filter

This paper proposes a control strategy to mitigate sub-synchronous oscillations (SSO) in inverter-based power systems by integrating adaptive control and a high-pass filter (HPF) into the phase-locked loop (PLL) structure. Based on the enhanced PLL model, the positive-sequence impedance (Zpp) of a grid-connected inverter with an LCL filter is analytically derived, capturing the dynamic influence of control loops. While conventional PLL configurations are vulnerable to SSO, the proposed method, combining adaptive control tuning with HPF, effectively suppresses these oscillations. Theoretical analyses and frequency-domain simulations demonstrate improvements in system stability and dynamic performance, especially in scenarios with low short-circuit ratios (SCR).