Stability Assessment and Damping Control for Grid-Forming Wind-Storage Systems with DC-Side Coupling Dynamics

This work develops a grid-forming control framework integrated with supplementary energy storage, so that permanent-magnet direct-drive wind turbines can deliver primary frequency regulation and inertial support services. Current stability research commonly concentrates on turbine-grid interactions, yet overlooks coupling dynamics at the DC-link, which motivates this study to establish a quantitative stability evaluation approach for grid-forming wind-storage systems with DC-side coupling taken into consideration. Small-signal impedance representations are firstly constructed for the machine-side converter (MSC), grid-side converter (GSC), and energy-storage converter with respect to the DC-link. On this basis, quantitative investigation is carried out to clarify how grid stiffness, inertia coefficient, droop gain, as well as charging/discharging operating modes of energy storage shape the DC-side stability margin of the hybrid system. To boost DC-link electrical damping, a supplementary stabilizing control scheme is embedded within the control loops of the energy-storage converter. Simulation outcomes reveal that the inertial support loop may inject negative damping and impair DC-link stability. Besides, discharging operation yields better stability performance for the wind-storage configuration relative to the charging condition. The devised stabilizing controller is capable of strengthening DC-side stability, enabling simultaneous inertial response and primary frequency support. Validations based on the PSCAD/EMTDC environment confirm the accuracy of theoretical deductions and the practical performance of the presented control solution.