Investigation of Impacts of Wind Source Dynamics and Stability Options in DC Power Systems With Wind Energy Conversion Systems

Wind energy conversion systems (WECSs), based on permanent magnet synchronous generators (PMSGs), are becoming common sources in dc grids. However, in previous dc grids integration studies, turbine-generator mechanical dynamics are represented by a single-mass model. A practical direct-drive connection in a PMSG-WECS yields lightly-damped torsional speed oscillations because of the double-mass mechanical nature of the generator and the wind turbine. Active damping strategies are usually employed to suppress the mechanical oscillations in a full back-to-back converter interfacing PMSG-WECSs into ac grids; nevertheless, the active damper performance in dc grids is unknown, particularly under dc grid uncertainties and, more importantly, the presence of dynamic and constant power loads commonly used in dc grids. To fill out this gap, this paper presents a detailed modeling and comprehensive stability assessment of a dc grid with a high penetration level of wind power generation. Moreover, stability enhancement strategies are proposed to increase the damping of the entire system, considering different operating and installation scenarios that might face a system integrator/designer. Time-domain simulation studies, based on nonlinear models, are conducted to validate the analytical results. Furthermore, hardware-in-loop real-time simulation studies demonstrate the feasibility of hardware implementation.