Grid-Forming Control with Self-Sustained Inertia and Transient Stability Enhancement for Type-IV Wind Turbines

Grid-Forming (GFM) wind turbines represent a promising solution for integrating wind power into power systems due to their inherent grid-supporting capabilities. However, existing studies on the transient stability of GFM wind turbines remain incomplete. In particular, the impact of machine-side and DC-link voltage dynamics on grid-side transient stability is often overlooked. Furthermore, the enhancement of transient stability in GFM wind turbines considering their multi-time-scale characteristics, has received limited attention. In this article, a Lyapunov-based energy function is derived that fully accounts for the dynamics of machine-side and DC-link voltage. Then, based on the extended invariance principle, the influence of system dynamic parameters on the transient stability of GFM wind turbines is revealed. An enhancement control strategy is proposed that leverages the fast response of the DC-link capacitor and the rotor's kinetic energy to actively absorb the power imbalances between the grid-side and machine-side during transients, effectively expanding the transient stability boundary and increasing the equivalent inertia. Both the theoretical analysis and the proposed strategy are verified through experiments.