Lyapunov Energy Function Construction and Application for Stability Analysis on Open-Loop Grid-Forming Energy Storage Systems

Centralized grid-forming (GFM) energy storages are important components for high proportion renewable energy power systems. The open-loop voltage magnitude control-based energy storage exhibits stronger transient voltage and frequency support abilities than the closed-loop voltage/current vector control. Tailored to the open-loop GFM energy storage system, this article takes the dynamic processes of the phase angle and converter internal voltage into account simultaneously, and constructs the Lyapunov energy function to evaluate the transient stability. The proposed approach is utilized to tune the virtual impedance parameters under the fault scenarios of grid voltage sag and phase jump, in order to deal with the overcurrent problems and ensure system transient stability. Theoretical analysis and experimental results from a GFM energy storage platform confirm that, the constructed Lyapunov function could provide a more accurate impedance boundary than the conventional phase portrait method.