Nonlinear Stability Investigation of Type-4 Wind Turbines With Non-Autonomous Behavior Based on Transient Damping Characteristics

As wind and solar power penetration increases, more and more conventional power plants are being replaced; as a result, the nature of transient stability of the system evolves where the converter’s behaviour play dominating role during network events. This has necessitated a re-assessment of the nonlinear stability of the system. So far, the energy function-based transient stability method applied to synchronous machines has been applied to the converter-based system. However, there is ambiguity in terms of the damping quantification capturing the non-autonomous behaviour of the wind turbine systems, such as post-fault active current ramp rate control. This work aims to clarify the similarity between the synchronous machine model and a reduced large signal model of a wind turbine, and the difference in terms of the damping characteristics and how this impacts the system’s stability from a nonlinear perspective. A non-autonomous energy function is discussed that analytically proves that a wind turbine system with post-fault active ramp rate control is more stable compared to no ramp rate control. Finally, the stability boundary (region of attraction) is constructed and validated using time-domain simulation studies in PSCAD.