| In order to lay the foundation for the construction of negative-ion-based neutral beam injection(N-NBI)system in China Fusion Engineering Test Reactor(CFETR),Huazhong University of Science and Technology has undertaken part of the development of CFTER NNBI prototype.The CFETR N-NBI prototype needs a 200 kV/25 A inverter-type DC highvoltage power supply for its ion accelerator.This inverter-type power supply is composed of power conversion stage,isolated boost transformer and high voltage generation stage.The main task of high voltage generation stage is to generate and transmit DC high voltage,and suppress surge when the breakdown of acceleration grid occurs.Correspondingly,the key equipment is the high-voltage diode rectifier and the core snubber on the transmission line.In order to protect the power system and accelerator from being damaged by stray parameters in high-voltage environment,and to improve the utilization rate of devices and materials,in this paper,the key issues such as voltage-balancing technology under the influence of parasitic capacitance and the magnetic properties of core snubber under pulse excitation are studied,and the engineering design scheme for the high-voltage diode rectifier and the core snubber of the 200 k V/25 A AGPS is put forward.In view of the breakdown risk of diode in high-voltage rectifier,this paper systematically studies the series technology for a large number of diodes.The influence of parasitic capacitance at connection point on the voltage distribution is analyzed.The parameter relationships between RC absorbing circuits are derived,which can balance the reverse recovery voltage of the series-connected diode.The validity of dynamic voltage-balancing circuit is verified by double pulse test on a prototype.A design method for parallel circuit of diode considering reverse recovery overvoltage suppression,dynamic and static voltage balancing and loss control is proposed and applied to the design of high-voltage diode rectifier.Surge suppression characteristics of core snubber and attenuation process of arc current when breakdown occurs are studied in this paper.Based on the saturation-wave theory,a new equivalent magnetizing inductance expression is deduced,and the equivalent circuit model of the core snubber is improved.By comparing the simulated and measured results of a snubber prototype made of iron-based nanocrystalline,accuracy of the equivalent circuit model and its feasibility for design are verified.Through simulation analysis and prototype test,the influence of reverse bias diodes in high-voltage rectifier on the arc current is discussed,and the effectiveness of secondary winding to prevent saturation is verified.The high-voltage diode rectifier and core snubber of the accelerator power supply for CFETR N-NBI prototype are designed in this paper.The rectifier is oil-impregnated insulation.300 diodes are connected in series to form a bridge arm,and the rectifier has a cylindrical arm structure composed of series sector modules.The result of 3D electrostatic field simulation in Maxwell verifies that the rectifier has sufficient insulation strength.According to the parasitic capacitance matrix obtained by simulation,the non-isoparametric RC absorbing circuit is designed,which has good overvoltage suppression and voltage balancing effect verified by simulation.The snubber core made of 1j51 has been designed.It is verified by simulation that the snubber could limit the breakdown arc current to less than 1 k A for safe operation,and it is found the surge suppression effect of the distributed core snubber is better than that of the centralized one.In this paper,the key technology research and engineering design of high-voltage generation stage has provided a theoretical basis and engineering experience for the construction of accelerator power supply for CFETR N-NBI prototype,and is valuable to the treatment of stray parameters in other related high-voltage equipments. |
PDF Full Text Request