Stability Analysis and Control Design of Grid-Forming Converters With DC-Link Effect

Grid-forming converters are increasingly utilized as the interface between distributed energy resources and utilities, owing to their advantageous features. However, they may encounter transient stability issues during grid faults, particularly when considering the dc-link effect. This article establishes a transient energy function which enables stability analysis of the grid-forming converter with dc-link effect based on Lyapunov direct method, revealing that transient instability is mainly induced by power imbalance and negative damping effect. To address this issue, an enhanced dc-link voltage control is proposed to facilitate temporarily energy storage and inertia adjustment, thereby improving transient stability and avoiding possible overvoltage in grid-forming converters. Theoretical analysis and validations have been provided to verify the effectiveness.