Interaction Energy-Based Stability Analysis Method and Application in Grid-Tied Type-4 Wind Turbine Generator

Complex dynamic interaction between type-4 wind turbine generator (WTG) and ac grid causes subsynchronous oscillation (SSO). In view of this problem, this article proposes a stability analysis method based on interaction energy that can explicitly reveal how (positively or negatively) and to which degree the various interaction links between subsystems in modular state-space model change system stability level. Firstly, an energy model representation for modular state-space model of grid-tied type-4 WTG system, containing stored energy terms, dissipation energy terms, and interaction energy terms, is constructed and is proved to satisfy the condition of energy conservation. And then, according to Lyapunov's 2nd stability principle, it reveals that the increase of interaction energy term with time is what causes the system to go unstable. Besides, it points out that the interaction energy term has one to one relationship with interaction link. Thus, the effects of different interaction links on system stability level can be identified by analyzing the variation trend of different interaction energy terms. Finally, hardware-in-loop tests with RTLAB verify that the dynamic interaction effects among different subsystems are quantified according to the value of interaction energy. Thus, the interaction links that have large impact on system stability are selected, which can provide theoretical support for future adding compensation branches between subsystems to suppress oscillation (i.e., supplementary compensation branch-based damping control).