Development Of High Frequency And High Voltage DC Power Supply For 90kV Electron Microscope

The electron microscope can simultaneously obtain the atomic and electronic information of the material at the atomic scale,and the observation of the single atomic image in the sample has always been the long-term pursuit of the scientific community.With the gradual deepening of the understanding of the microworld and the higher requirements for the performance of the electronic microscope,the HVDC power supply as its core has also been widely concerned.Now,the applications of new power devices,high performance control chips and new control strategies provides a good developmental space for HVDC power supply of high frequency,modular and intelligent.Because the electron microscope requires high resolution and all-weather work,so the high voltage DC power supply should have the characteristics of low ripple,high stability and long-time work.However,the power supply developed in China is difficult to meet its performance requirements.Therefore,the development of HVDC power supply which has high performance has important research significance.In this paper,a HVDC power supply with low ripple and high stability is developed based on DSP to meet the performance index of high voltage dc power supply of electron microscope.Firstly,the article analyses the basic principle of the electronic microscope and the technical parameters of the HVDC power supply system,and completes the design of the high voltage acceleration power supply,the cathode filament heating power and the partial grid power supply.Secondly,according to the requirement of low ripple of high voltage power supply,the paper verifies the ripple size of multiple voltage doubling circuit by simulation and comparison,and selectes the dual full wave voltage doubling circuit suitable for this system,and designs the two stage boost circuit composed of high frequency boost transformer and voltage doubling circuit,which reduces the ratio of the original side to turn number of the boost transformer and solves the problem of transformer insulation.Finally,the thesis has a detailed theoretical analysis of the control system,and designs a double closed loop controller based on the pole placement to improve the stability of the HVDC power supply system and the controller meets the technical requirements of the high voltage power supply for the electronic microscope.Finally,the correctness and feasibility of the design is verified by the simulation experiment platform.A 90kV high voltage DC power supply prototype is built,and the ripple and stability of the output voltage are measured accurately.The experimental results show that the power supply has reached the requirements of the ripple and stability of the high voltage direct current power supply of the electron microscope.