| With the development of flexible HVDC power transmission,the power of flexible DC converter valve is continuously increasing,and the sub-modules are developing towards miniaturization and compaction.The electromagnetic compatibility problem of converter valve is becoming more and more serious.As a key component,the drive control unit including the drive board,the central control board and the energy taking board will be disturbed by the magnetic field.Its reliable work in the harsh electromagnetic environment directly determines the safe and stable operation of the entire converter valve.The structure and control mode of flexible DC converter valve are complex,and the direct modeling and calculation are difficult.The spatial magnetic disturbance mechanism and distribution characteristics of the driving control unit are unclear,and the assessment requirements of magnetic field immunity of the existing secondary equipment are difficult to meet the practical engineering.Therefore,this thesis focuses on the spatial magnetic disturbance characteristics of the drive control unit of flexible DC converter valve.Firstly,according to the working principle and sub-module structure of flexible DC converter valve,a magnetic field modeling method based on line current equivalent is proposed,which can simplify the calculation of magnetic field and satisfy the error requirements.Two kinds of magnetic disturbance sources,power frequency and pulse of converter valve,are analyzed,and a magnetic field calculation method for the two kinds of disturbance forms is proposed,which can consider the random switching process of submodules,and the calculation process is simple and effective.Then,the double-pulse test and three-drag test based on the sub-module of flexible DC converter valve of Zhangbei Engineering were carried out,and the current of the sub-module’s flow branch and the transient magnetic field at the driving control unit were measured.Through the comparison between the measured waveform and the simulation results,the validity of the calculation method for the power frequency and pulse magnetic field of the converter valve proposed in this thesis is verified.Finally,the magnetic field contribution between the submodules is analyzed,and the spatial magnetic disturbance characteristics of the driving control unit of the flexible DC converter valve are studied.The level and distribution of power frequency and pulse magnetic field intensity are revealed from the perspectives of time and space.Combined with the magnetic field calculation results and the evaluation standard of magnetic field immunity of the existing secondary equipment,the magnetic field immunity of the drive control unit is analyzed.The research results in this thesis can provide data support for the electromagnetic environment assessment and electromagnetic compatibility research of flexible converter valves,and also provide reference for the research of magnetic immunity of secondary equipment in flexible DC converter valves. |
