| Under the background of double carbon target and low carbon transformation of energy,the demand for the development and utilization of new energy is increasing day by day.Offshore wind power energy has always attracted much attention in the new energy industry,in recent years,offshore wind power has extended from offshore to deep-sea,and the development direction is concentrated in large capacity and far sea area.Flexible low frequency transmission,as a new transmission mode,combines the comprehensive advantages of high voltage AC and high voltage DC transmission and has important value in the field of offshore wind power transmission.With the first flexible low frequency transmission demonstration project put into operation in Taizhou City,Zhejiang Province,flexible low frequency technology will also be widely used in offshore wind power transmission.There are a large number of power electronic equipment in the system.When the system fails,the system will appear switching overvoltage,which will bring impact to the equipment on both sides of the converter station.Switching overvoltage is an important factor affecting the safe operation of the whole transmission system,and it is also an important basis for insulation coordination of transmission system.Based on this,the switching overvoltage level of flexible low frequency transmission system is studied in this paper.For of all,this paper introduces the architecture of offshore wind power flexible low frequency transmission system,the most important equipment in the system is modular multilevel matrix converter(M3C),this paper describes the selected M3C modeling method and the control strategy of the system.A 330kV/300MW flexible low frequency transmission system of offshore wind power based on PSCAD/EMTDC platform is built,and the steady and dynamic characteristics of the model are investigated.Then,according to the flexible low frequency transmission system,the fault types of the system are analyzed,the representative voltage monitoring points are selected,the simulation calculation of the switching overvoltage under different fault is carried out,and the fault work with the highest switching overvoltage level is obtained,and the characteristics of the switching overvoltage are analyzed.Finally,based on the simulation result of switching overvoltage,the arrester is configured for the system,the parameters of arrester are selected and the layout scheme is designed,and the level of switching overvoltage of the system after adding arrester is compared.In this paper,the influence of the parameters of modular multilevel matrix converter on the switching overvoltage is also studied,including the capacitance of M3C sub-module,the inductance value of bridge arm and so on. |
