  High penetration of wind power with conventional grid following controls for
inverter-based wind turbine generators (WTGs) weakens the power grid,
challenging the power system stability. Grid-forming (GFM) controls are
emerging technologies that can address such stability issues. Numerous
methodologies of GFM inverters have been developed in the literature; however,
their applications for WTGs have not been thoroughly explored. As WTGs need to
incorporate multiple control functions to operate reliably in different
operational regions, the GFM control should be appropriately developed for the
WTGs. This paper presents a review of GFM controls for WTGs, which covers the
latest developments in GFM controls and includes multi-loop and single-loop
GFM, virtual synchronous machine-based GFM, and virtual inertia control-based
GFM. A comparison study for these GFM-based WTGs regarding normal and abnormal
operating conditions together with black-start capability is then performed.
The control parameters of these GFM types are properly designed and optimized
to enable a fair comparison. In addition, the challenges of applying these GFM
controls to wind turbines are discussed, which include the impact of DC-link
voltage control strategy and the current saturation algorithm on the GFM
control performance, black-start capability, and autonomous operation
capability. Finally, recommendations and future developments of GFM-based wind
turbines to increase the power system reliability are presented.
