Clustering Analysis and Mitigation of Subsynchronous Oscillation of Offshore Wind Farm via the VSC-HVDC Grid-Connected System

There is a risk of subsynchronous oscillation (SSO) in offshore wind farm via the VSC-HVDC grid-connected system, and the nonlinearity and uncertainty of the system bring challenges to the study of SSO. This paper proposed a data-driven method to analyze the influence of the combination of wind speed and current fluctuation at point of common coupling of the wind farm on SSO, and proposed a nonlinear control strategy to mitigate SSO. FFT based on Nuttall window interpolation was applied to detect the SSO component in the power data corresponding to the results of small-signal analysis. Meanwhile, Gaussian mixture model clustering algorithm was adopted to cluster the factor combination, and the clustering quality was evaluated by three internal validity indicators. The influence of wind speed/current fluctuation clustering on SSO was analyzed from the perspective of the amplitude change of the SSO component. Finally, a SSO mitigation strategy based on feedback linearization sliding mode control was proposed, which was applied to the rotor-side converter of DFIG and the wind farm-side converter of VSC-HVDC. The simulation results show that when the combination of wind speed/current fluctuation factors belongs to partial clustering, the SSO of the system will be worsen. The proposed control strategy has good SSO mitigation effect and strong robustness for the influence of wind speed and current fluctuation.