Evaluation and Optimization of DFIG-Based WTs for Constant Inertia as Synchronous Generators

The power boost and response speed are two critical indexes to evaluate the inertia control performances. However, it is hard to obtain the two indexes directly in the time domain for different inertia control methods. How to justify the inertia control performances becomes a critical issue to address. Besides, the issue of whether the inertia control methods of wind turbines can present similar inertia characteristics as synchronous generators also attracts great attention. Targeting the above two questions, this article focuses on the representation, evaluation, and optimization of the inertia characteristics for the doubly fed induction generator (DFIG) based wind turbine. First, the phase motion model and inertia transfer function for the DFIG are established. On this basis, the relations between the inertia control performance in the time domain and the inertia transfer function in the frequency domain are clarified, which is explained through the conventional emulated inertia control. Furthermore, optimization methods for DFIGs to achieve constant inertia, combined with the parameter design guidelines, are demonstrated. Finally, the analysis and the optimized methods are validated by experiments.