Research On The Mechanism And The Source Network Cooperative Suppression Of Subsynchronous Oscillation In AC/DC System With Large-scale Wind Power

In later years,wind energy has been widely exploited as a clean,renewable energy source.It has been found in existing studies that there is a risk of subsynchronous oscillations when wind farms are connected to the grid via cascade lines,with High Voltage Direct Current(HVDC)or with weak AC systems,and that the problem of sub-synchronous oscillations in areas where new energy sources are gathered is becoming increasingly prominent,influencing the and stable and safe operation the grid.Most of the current research is based on the phenomenon of subsynchronous oscillations caused by the interaction between wind farms and the series compensation lines,or on the basis of this research on the role of additional power electronics,the mechanism of sub-synchronous oscillations in grid-connected wind power systems without cascade lines has not been explored;in the actual engineering of complex operating conditions,the randomness and uncertainty of wind power output characteristics of various sub-synchronous oscillation suppression measures The randomness and uncertainty of wind power output under complex operating conditions in practical projects have put forward higher requirements on the adaptability of various sub-synchronous Therefore,based on a summary of the current status of research at home and abroad,the main research content of this paper is as follows.Firstly,this paper establishes and specifies mathematical models for doubly-fed and directly-driven wind turbines respectively,laying the theoretical foundation for the subsequent analysis of sub-synchronous oscillations in wind farms.The harmonic response method and the complex torque coefficient method are used to investigate the mechanism of sub-synchronous oscillations in thermal turbines induced by wind farms.Subsequently,the factors influencing the sub-synchronous oscillation characteristics are analyzed,including the torsional characteristics of the turbine shaft system,wind speed,wind farm capacity,wind farm inverter control parameters and the electrical distance from the wind farm to the turbine,and the correctness of the theoretical analysis is verified using time-domain simulations in the first benchmark model and the nodal system.Secondly,this paper establishes a mathematical model for the occurrence of subsynchronous oscillations in wind farms connected to the AC/DC grid,It mainly includes the wind farm system model and the VSC-HVDC system model.Based on the idea of the complex torque coefficient method,the damping characteristics of wind farm grid-connected systems are derived using transfer functions,the mechanism of s subsynchronous oscillation in AC/DC system with large-scale wind power is analyzed,and the factors that affect the subsynchronous oscillation characteristics of wind farm rotor side converters and VSC-HVDC converter control parameters are studied,and the correctness of the theoretical analysis is verified using time-domain simulations.Finally,based on the study of the mechanism of sub-synchronous oscillations,this paper investigates sub-synchronous oscillation suppression measures applicable to wind farms connected to the grid.In this paper,an additional damping controller is applied to the converter on the rotor side of the wind turbine on the source side,and the typical FACTS devices,including STATCOM and SSSC,with designed additional damping controllers,are used on the grid side.Then,a sub-synchronous oscillation suppression strategy for source-network collaboration is proposed by co-optimizing the grid-side STATCOM device and the rotor-side control of the wind turbine,and time-domain simulations are carried out in an AC-DC system containing large-scale wind power to verify the effectiveness of the proposed suppression strategy.