Impact of DFIG‐based wind farm integration on sub‐synchronous torsional interaction between HVDC and thermal generators

In western China, large-scale wind power is generally bundled with thermal power, and transmitted to eastern China by high-voltage direct current (HVDC) systems. This constitutes the wind–thermal bundled system transmitted by HVDC (WTBH). In this study, a typical studied system of WTBH is presented, and its models for eigenvalue analysis are introduced. To improve the efficiency of eigenvalue analysis, an improved block modelling method is proposed for building the state-space model of WTBH. By eigenvalue analysis and electromagnetic transient (EMT) simulation, the impact of doubly-fed induction generator (DFIG)-based wind farm integration on sub-synchronous torsional interaction (SSTI) between thermal generators (TGs) and HVDC was investigated. The sensitivity of the operating parameters of DFIG-based wind farms was analysed, including wind speed, wind farm scale, and distance between the wind farm and HVDC rectifier station. The obtained results show that the integration of DFIG-based wind farms can mitigate the SSTI between the TG and HVDC. The system becomes more stable as the wind speed and wind farm scale increase or the distance between the wind farm and HVDC rectifier station decreases. The conclusions of this study are validated through EMT simulations in PSCAD/EMTDC, and provide theoretical reference for practical WTBH projects.