Small-signal synchronization stability of grid-forming converter influenced by multi time-scale control interaction

The grid-forming (GFM) converters that simulate the dynamics of synchronous generators (SGs) and actively participate in grid voltage and frequency regulation are increasingly employed as grid inter-faces for renewable energy generation. Its synchronization stability with AC grid is also increasingly concerned in recent years. In this paper, the small-signal synchronization stability of GFM converters with virtual synchronous generator (VSG) control is investigated, with the influence of multi time -scale control interaction considered especially. First, based on multi time-scale dynamics analysis, an analogized Heffron-Phillips model is developed to physically depict the small-signal synchronization dynamics of VSG. The multi time-scale control interaction introduces an additional input torque to the equivalent motion of VSG's synchronization behavior. Based on damping torque analysis, the synchronization stability is depended by the inherent damping component of VSG's virtual rotor motion and the additional damping component introduced by multi time-scale control interaction. Qualitative and quantitative analysis reveal that the additional damping is negative and deteriorates the synchronization stability. When the negative additional damping is greater than the positive inherent damping, small-signal synchronization instability occurs due to insufficient damping. Finally, the influence factors including control parameters and grid strength are discussed.(c) 2022 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).