Transient Stability Analysis of Grid-Connected Converters Based on Reverse-Time Trajectory

Abstract: As the proportion of converter-interfaced renewable energy resources in the power system is increasing, the strength of the power grid at the connection point of wind turbine generators (WTGs) is gradually weakening. Existing research has shown that when connected with the weak grid, the dynamic characteristics of the traditional grid-following controlled converters will deteriorate, and unstable phenomena such as oscillation are prone to arise. Due to the limitations of linear analysis that can not sufficiently capture the stability phenomena, transient stability must also be investigated. So far, standalone time-domain simulations or analytical Lyapunov stability criteria have been used to investigate transient stability. However, time-domain simulations have proven to be computationally too heavy, while analytical methods are more complex to formulate, require many assumptions, and are conservative. This paper demonstrates an innovative approach to estimating the system boundaries via hybrid - linearised Lyapunov function-based approach and the time-reversal technique. The proposed methodology enables compensation for both time-consuming simulations and the conservative nature of Lyapunov functions. This work brings out the clear distinction between the system boundaries with different post-fault active current ramp rate controls. At the same time providing a new perspective on critical clearing times for wind turbine systems. Finally, the stability boundary is verified using time domain simulation studies.