Development Of Scanning Power Supply For Proton Therapy Device

The Shanghai Proton Therapy Facility is a cutting-edge medical device developed in China.The nozzle is the key technical equipment of proton therapy facility.The scanning power supply provides the excitation current for the scan magnet of the nozzle.The rate of change and stability of the current directly affect the scanning speed and accuracy of the nozzle,which affects the treatment time and treatment effect.The goal of this research is to develop a fast scanning power supply for the nozzle.The power supply requires current to be extremely fast and stable and bidirectional linear within a certain step size,as well as high current change rate,stability and ripple and other technical indicators.Firstly,this research determined the topology of power supply by the investigation of the domestic and international scanning power supply.The power supply adopts modular design,mainly includeing AC-DC rectifier,power frequency filtering,DC-DC power conversion,high frequency filtering,output compensation and close-loop control module.Among them,in order to reduce the bus voltage ripple and simplify the power control system,the AC-DC module adopts 12-pulse uncontrolled rectification;The DC-DC module adopts interleaved parallel connection and passive current sharing to increase the working frequency of the output current ripple and reduce the amplitude of the current ripple;the control system adopts current negative feedback + PI control.Secondly,according to the technical specifications of the power supply and the topology of the circuit,the detailed theoretical design of the power supply and the selection of key components are given,and the relevant technical indicators are designed and optimized.In addition,the problem of zero-crossing distortion of the output current of the scanning power supply is analyzed in detail.In order to eliminate this problem,a new technical method is presented: the working mode of the H-bridge converter is that the inductor current is continuous and crosses zero(CCM + RZC).Then,the rationality of the parameter design of the AC-DC module transformer and power frequency filter circuit was verified by Simulink software;the rationality of the parameter design of the DC-DC module inductance and capacitance and compensation was verified by Mathcad and Simplis software.At the same time,the detailed design process and parameter selection are given for the auxiliary circuit of the power supply and output filter inductor.Finally,the prototype of scanning power supply was built and experimentally verified.This experimental results show that the output current of the power supply changes linearly regardless of the zero-crossing transition at light load or full load,and there is no distortion at the zero point.The maximum output current of the power supply is 360 A in both directions;the output current ripple can reach 1ppm;the current resolution is 5 ppm;the maximum dynamic response speed of the current is 90 kA /s,the 5% full-scale transition time is 1.43 ms,and the short-term stability 35 ppm.The scheme skillfully solves the problem of zero-crossing distortion of the output current.The results of this study provide method for solving the problems of zero-crossing distortion of output current,bidirectional output system instability and others in the future.