Multi-frequency coupled mechanism and propagation characteristics of subsynchronous oscillations induced by IBRs in power systems

Subsynchronous oscillations induced by inverter-based resources pose a significant threat to power system stability due to their wide propagation. This paper reveals a new propagation phenomenon of subsynchronous oscillations induced by inverter-based resources, characterized by multi-frequency coupling and a non-monotonic relationship between amplitude and oscillation frequency, revealing critical risks at non-resonant frequencies. To investigate this issue, the coupling mechanism and propagation characteristics of the multi-frequency coupled oscillations are analyzed. The study reveals that the multi-frequency coupling originates from the interaction between oscillation components and the synchronization control of inverter-based resources. This interaction introduces frequency coupling and generates the multiple frequency components in the instantaneous power. Furthermore, the non-monotonic characteristics is attributed to the frequency-dependent coupling impedances resulting from asymmetric interharmonic components generated by the frequency coupling. Building on this mechanism, a propagation coefficient based on instantaneous power amplitude is proposed to quantify propagation risk. Simulation results validate the proposed method, demonstrating its improved accuracy compared to existing analyses. • A novel multi-frequency coupled SSO propagation induced by IBRs is revealed. • The coupling mechanism of multi-frequency oscillation components is elucidated. • The effect of coupling impedances on non-monotonic characteristics is analyzed.