| CRAFT（Comprehensive Research Facility for Fusion Technology,fusion reactor host key system comprehensive research facility）is a nuclear fusion scientific device deployed and constructed in "Thirteenth Five-Year Plan" plan of China.The main construction content of the device is superconducting magnet research system and divertor.Research system,in which the superconducting magnet research system needs to be equipped with a set of highpower magnet power supply to ensure its stable testing.In this paper,from the perspective of optimizing the overvoltage suppression scheme of the CRAFT Toroidal Field（TF）magnet power converter,a corresponding optimal suppression scheme is designed for the types of overvoltage that may occur in the CRAFT TF magnet power converter system.Firstly,the thyristor commutation overvoltage suppression scheme is analyzed.The reverse recovery model of thyristor is introduced,and the distribution parameters of the bridge arm are introduced.The Q3 D module in the computer software ANSYS is used to extract the distribution parameter matrix of the bridge arm and the transient circuit model of the thyristor is constructed.The software MATLAB is used to calculate the peak value of the thyristor overvoltage and write The program draws a three-dimensional graph of the function relationship between the overvoltage peak value and the RC parameter,which is used as the basis for selecting device parameters.The SIMULINK simulation software is used to build the converter model,and the thyristor voltage and current waveforms are compared under the optimized and non-optimized conditions.The comparison results show that The optimized protection scheme has more advantages in suppressing overvoltage and improving the current sharing coefficient.Finally,the experimental verification is carried out under the working condition of the CRAFT TF magnet power converter prototype 50@250V@25k A.Secondly,the causes of the operating overvoltage are expounded,and the suppression measures of the operating overvoltage are analyzed,including the overvoltage on the grid side of the rectifier transformer and the overvoltage when the transformer is open at no-load.Based on the traditional overvoltage protection scheme,the optimal design is carried out.The software MATLAB is used to program the calculation of the overvoltage peak value of the transformer opening,and the function of the overvoltage peak value and the RC parameter is programmed to draw a three-dimensional diagram.The PSCAD simulation software is used to build the transformer complex transient model simulation.actual operating conditions.In this paper,a transient model is established according to the actual working conditions,combined with the protection device parameters selected by the commutation overvoltage protection device,it is feasible to share a set of RC protection devices with the thyristor operating overvoltage,which reduces unnecessary waste.A capacitor is installed on the valve side of the rectifier transformer to suppress the closing overvoltage of the transformer.Finally,the lightning protection problem of CRAFT TF magnet power converter overvoltage lightning strike is discussed,and the transformer grid-side lightning arrester and transformer valve-side metal oxide nonlinear resistor are selected to share the lightning strike over-voltage to achieve protection.The computer simulation software SIMULINK is used to build the lightning current model,the arrester model,and the converter model.Secondly,the influence of the lightning current amplitude,the installation position of the arrester and the grounding resistance on the lightning peak voltage on the thyristor valve is analyzed,and the grid side of the rectifier transformer is determined.Lightning arrester and load grounding resistance suppression scheme.The calculation and simulation results show that the adopted suppression measures can meet the requirements of the thyristor lightning strike protection level.Through analysis and research,the suppression strategy in this paper provides a solution for suppressing overvoltage in the CRAFT TF magnet power converter system,and the selection of protection devices is more accurate.Compared with the traditional scheme,the overvoltage suppression effect is better,and the problem of excessive current unbalance coefficient at the turn-on moment is avoided,and the reliability is higher.This scheme can provide certain engineering practice guidance and reference for future high-power power supply design.Figure [54] Table [20] Reference [86]... |
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