Virtual Impedance Control for Enhancing the Inertia Provision of Grid-forming Doubly-fed Induction Generator

Grid-forming converters (GFMs) are regarded as a solution to enhancing the frequency support ability of the power grid. Applying the virtual synchronous generator (VSG) technology, GFM mimics the swing function of synchronous generators (SGs). It is found in this paper, however, that the inertia provision of VSG-based grid-forming doubly-fed induction generator (VSG-DFIG) is limited. The root cause is analyzed, indicating that the resistive-inductive internal impedance is not beneficial to providing power support under unbalanced active power disturbances. To address this issue, the terminal voltage controller (TVC) is modified by adding a virtual impedance control, rather than applying supplementary controllers on the active power control sections. The virtual impedance control optimizes the characteristic of the equivalent inertia of the DFIG and strengthens the inertial response. Finally, preliminary simulation results are presented to verify the feasibility of the proposed control strategy.