Enhancement Methods for Transient Stability of Grid-Forming Converters with Low Damping

As the proportion of renewable energy sources in power systems increases, grid-forming (GFM) converters, which mimic the mechanism of synchronous generators, are gaining attention. As power electronic converters play a crucial role in power systems, GFM technology becomes increasingly essential. Although GFM converters provide advantages such as synchronization through power and offering inertia like synchronous generators, they suffer from drawbacks such as classical stability issues including synchronization stability. Moreover, unlike synchronous generators, they are highly vulnerable to overcurrent due to being composed of semiconductor components. Current limiters are essential for protecting semiconductor components from overcurrent, but they adversely affect transient stability. In this paper, the analysis of GFM converters with the introduction of virtual synchronous generator (VSG) control and circular current limiter is conducted. It is known that controlling to reduce active power references prevents wind-up in the outer power control loop when the current limiter operates. It is analyzed that this control not only prevents wind-up but also improves transient stability. Lastly, methods to enhance synchronization stability after grid fault without reducing inertia to zero in low-damping GFM converters are discussed.