Modeling and Stability Analysis of the Sub-synchronous Interactions in Weak AC Grids with Wind Power Integration

Abstract

Recently, sub-synchronous interactions (SSIs) between wind turbine generators and weak AC networks have generated great concerns. Traditional SSIs happened between doubly-fed induction generators (DFIGs) and AC grids with series-compensation. A new type of SSI incident has occurred recently in the AC network connected to a permanent magnet synchronous generator (PMSG) based wind farm, without series compensation. This incident has reignited the research interest in SSIs, especially those associated with PMSG and weak AC grids. Therefore, in order to analyze the characteristics of this new type of SSI, a simplified system model with multiple PMSGs connected with a weak AC grid is established in this paper. In addition, an eigenvalue analysis of the established small-signal model is conducted to investigate the SSI modes of the system. The small-signal stability study is validated by time-domain simulations. The results indicated that the stability of the PMSG based wind farms connected to a weak AC grid is mainly affected by the short-circuit ratio (SCR) and control parameters of the grid-side converter (GSC). A low SCR and inappropriate control parameters of GSC will cause the unstable oscillations in the power system.