Adaptive Scheme for Stability Margin Estimation of Grid-Connected DFIG Based Wind Turbines

With the increasing adoption of wind power into the grid, ensuring the reliable protection of wind farm generators against grid faults has emerged as a crucial concern. Instability, as a consequence of severe disturbances, poses a significant threat, capable of inflicting damage to network equipment. In the Doubly-Fed Induction Generator (DFIG), one of the most-used technologies in wind farms, activation of the crowbar circuit results in the blocking of the power converter and control system. This action temporarily shifts the DFIG operational mode to that of a squirrel-cage induction generator, causing reactive power absorption and voltage drop. This can potentially lead to rotor overspeed and an unstable state. Since the stability margin of the DFIG is affected by various factors like wind speed, network topology, and more, accurately identifying the unstable equilibrium point of the generator seems essential to effectively safeguard the generator and avoid unnecessary shutdowns. For doing so, this study introduces an adaptive approach for assessing the stability margin of a grid-connected DFIG, utilizing locally measured quantities. Notably, this technique operates in a setting-free manner, offering a desirable feature for protective relaying. The effectiveness of the presented approach is verified through various test scenarios using MATLAB®/Simulink, demonstrating its proper operation and straightforward implementation.