| Wind power generation is experiencing a period of rapid and stable development in China,the application and development of voltage sourced converters high voltage direct current(VSC-HVDC)technology provide a good implementation scheme for long distance transportation of large-scale wind power.However,the oscillation phenomena from several hertz to several hundred Hertz appeared,during the commissioning and operation of flexible direct transmission projects of wind power at home and abroad.Because of the interaction between p ower electronic converter and its control system,the operation characteristics are more complex,it is urgent to study the oscillation mechanism of the system and the corr esponding suppression measures.In this paper,the oscillation problem of wind power integration via flexible HVDC is studied in depth,focusing on stability analysis method,oscillation mechanism,analysis and evaluation of oscillation characteristics,and suppression measures.Firstly,the simulation model of wind farm island integrat ion through flexible HVDC system is established,based on the RT-LAB real-time simulation platform and referring to the actual parameters of the zhangbei flexible dc demonstration project.After that,the equivalent circuit damping stability criterion f or oscillation analysis is proposed and verified by impedance measurement,based on the system stability analysis theory of impedance.On this basis,the impact on wide frequency-domain oscillation characteristics from control system of wind turbines and f lexible dc and external influencing factors is analyzed.By analyzing the impedance frequency characteristics of the system,the relationship between different influencing factors and the oscillation mode is obtained,and the oscillation mechanism in the w ide frequency-domain is analyzed.The design requirements of control parameters considering the stability of oscillation are put forward,considering the change of wind speed and the wind turbines number under different control parameters.Then,the oscillation risk assessment method based on the aggregated RLC circuit model is adopted to quantitatively analyze the oscillation characteristics of the system by fitting circuit parameters.The relationship between control system of wind turbines and MMC,wind speed and wind turbines number and the oscillation risk of the system is evaluated by using the virtual resonance damping and resonance frequencyFinally,an additional damping control method is proposed to suppress the oscillation.By introducing additional damping control loop into the MMC control loop at the delivery end to remodel the impedance,interconnection subsystem exhibits positive resistance characteristics at the resonance point,thus suppressing the Wide Frequency-Domain oscillation. |
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