Frequency-coupled admittance modelling of grid-connected voltage source converters for the stability evaluation of subsynchronous interaction

Recently, subsynchronous interaction (SSI), a type of stability issue caused by interactions between power electronic converters and weak grids, has attracted great concerns. Many efforts have been made to use impedance/admittance-based methods for its modelling and analysis. However, most impedance/admittance models (IM/AMs) are aimed at higher-frequency dynamics and do not reflect the coupling effects between sub- and super-synchronous frequencies or the outer control loops, which, as indicated in this work, have significant impacts on the characteristics of SSI. To fill the gap, this study derives the explicit frequency-coupled AM for a typical grid-tied voltage-sourced converter by taking the coupling effects and outer-loop controls into full account and further investigates their impacts on the subsynchronous stability. The model itself and its effectiveness in predicting the stability of SSI have been validated with detailed electromagnetic transient simulations.