| The standardized design and operational reliability enhancement of flexible DC converter valve are impending with the construction of high shares of renewables and power electronics power system.The valve control board at submodule level,as a key equipment directly arranged inside the submodule,is located in a complex and harsh electromagnetic environment.Strong magnetic field disturbance will cause confusion in the logical function of the valve control board itself,as well as fuzzy execution commands.This will increase the possibility of issues such as board crashes and false alarms,resulting in power outages and property losses,seriously threatening the operational reliability of flexible DC transmission projects.Therefore,this article focuses on the problem of magnetic field disturbance on the valve control board of the flexible DC converter valve.It conducts in-depth research from the analysis of magnetic field disturbance sources,magnetic field calculation methods,and magnetic field disturbance characteristics,and finally proposes improvement suggestions for magnetic field disturbance suppression.Firstly,based on the existing equivalent power experimental circuit of the MMC converter valve submodule,a simulation circuit that comprehensively considers the influence of stray inductance inside and outside the submodule was built in Saber software using the IGBT behavior model and the fast recovery diode model.By comparing the effectiveness of the simulation circuit with the measured results,the mechanism of internal magnetic field disturbance in the submodule during normal operation of the flexible DC converter valve was clarified,and the main power frequency magnetic field and pulse magnetic field disturbance sources suffered by the valve control board were obtained.Secondly,random functions were used to simulate the non-sequential switching process of submodules.In addition,starting from the physical entity structure of converter valve and half bridge submodule,this paper proposes specific line current equivalent schemes for magnetic field disturbance sources of different frequencies on the basis of considering the influence of skin effect on current distribution,and finally obtains a magnetic field disturbance calculation model of valve control board of the flexible DC converter valve to meet the engineering needs.The effectiveness of this calculation method was verified by comparing the measured magnetic field disturbance level with the equivalent operation experimental platform of the submodule.Finally,a valve control board magnetic field disturbance calculation model was established for a±500kV MMC valve tower used in a practical project.The magnetic field disturbance time domain and spatial distribution patterns of various valve control boards at different submodules in the valve tower during normal operation of the converter valve were calculated,and the improvement suggestions were proposed for the suppression of magnetic field disturbances of valve control board from two different perspectives:suppressing disturbance sources and blocking disturbance coupling paths.The research work in this paper can provide theoretical and data support for the evaluation of the electromagnetic environment inside the converter valve tower and the research on the magnetic field immunity of secondary equipment in flexible DC projects,help to remedy the shortcomings of the reliability research on the level of equipment of flexible DC converter valve in China at present.This is of great significance for solving the electromagnetic compatibility problem of flexible DC converter valve and promoting the large-scale engineering application of flexible DC transmission technology. |
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