Impedance-Based Criterion Design for Grid-Following/Grid-Forming Switching Control of Wind Generation System

As wind farms connect with power grids via long-distance transmission lines and multiple transformers, the resulting networks exhibit inherently weak and fluctuating grid strength—subject to dynamic variations from external disturbances like generation tripping; thus, ensuring stable operation presents a critical challenge. To address this issue, grid-following/grid-forming mode switching has emerged as a strategic approach, where wind turbine generators strategically switch between grid-following control in strong grids and grid-forming control in weak grids. This paper proposes an impedance-based switching criteria design methodology, ensuring system stability under dynamic grid strength variations. Leveraging sequence impedance analysis in frequency domain, we establish a stability boundary for mode transitions. Simulation results demonstrate that the proposed criteria maintain stable operation, enhancing robustness against grid strength fluctuations.