This paper investigates the stability mechanisms and suppression strategies for sub-synchronous oscillations (SSOs) in hybrid wind farms (HWFs) consisting of doubly-fed induction generator (DFIG) and permanent magnet synchronous generator (PMSG)-based wind turbines. To address the challenges in mitigating SSOs due to the complex interactions between the generators in hybrid wind farms, as well as external and parameters disturbances, a state-space model of the HWF is developed to capture the impact of external disturbances and parameter uncertainties on system dynamics. Through eigenvalue and participation factor analyses, this paper examines the effects of uncertainties in voltage control parameters, grid line series compensation, and the fluctuating power outputs of DFIGs and PMSGs on SSO behavior. A robust SSO suppression controller based on H_∞ theory is proposed, demonstrating a substantial reduction in harmonic distortion and improved settling time compared to conventional control strategies under varying disturbances. The simulation results show that the proposed controller significantly enhances the system’s resilience to disturbances and uncertainties, effectively mitigating SSO and improving overall system stability.

This paper provides an H_∞ robust control strategy for a permanent magnet synchronous generator (PMSG)-based wind farm to realize subsynchronous resonance suppression (SSR) subject to uncertain system distortions and parameter perturbation. Firstly, an eighth-order state space mathematical model of a PMSG-based wind farm is established, including the grid-side converter (GSC), GSC controller, and phase-locked loop (PLL) model. Secondly, the SSR characteristics of a PMSG-based wind farm are analyzed through eigenvalue analysis. Thirdly, a robust subsynchronous damping controller is designed based on eigenvalue analysis of SSR. Finally, the designed robust subsynchronous damping controller is validated with case studies of wind farms. The results show that the controller can increase the stability of PMSG-based wind farm systems and restrain SSR.