| The number of worldwide cancer patients increases year by year,and China is also among the high epidemic countries of tumorous diseases.The radiotherapy with the Brag peak of proton beam current is one of the most promising technologies for the treatment of cancer.To improve the medical conditions for the masses,Shanghai Municipal Development and Reform Commission and Shanghai Science and Technology Commission arrange a project on the research and manufacture of the first proton treatment demonstration equipment.In the project,the maximum excitation current needed in the three inject/extract magnets should reach 3200A.In addition,the eight-hour stability should be better than 2.5×10-4,and the ripple current less than 1×10-4.At present,the large current of accelerator magnet power supply is usually realized with thyristor or IGBT functioning as the switching device.Since thyristor is limited by the power frequency,the power frequency ripple of output current could hardly be suppressed.IGBT also has obvious disadvantages for its high conductive voltage and the conduction loss of large current output.Despite of low conduction loss and high switching speed,the current capacity of a single MOSFET is limited.Considering the project requirements and the magnet load characteristics,MOSFET was selected as the switching device.For the first time,module parallel technology was employed in the magnet power of proton accelerator,to realize highly stable output of large current.The modular design is beneficial to flexible configuration of the power redundancy,and the reliability of the power could be improved.It also breaks up the integrated power supply into parts,greatly shortening the maintain time of the power supply.In addition,the concept of modularization makes the design and testing of the integrated power supply less difficult,which lays a solid foundation for the standardization of the power supply.During the development of the power,the modular power was designed and computed with the help of some simulating design software,such as MathCAD,OrCAD and MATLAB.In the dissertation,we deduced the relationship between current ripple amplitude and switching frequency under phase-shift parallel structure.According to the relationship,DC-DC modular power was designed,and the circuit parameters and switch driving mode were determined.To guarantee the inter-module current output balance,independent digital control was adopted to realize the deep negative feedback of modular power,providing solutions for the current sharing of parallel power.The modular power broke up the detection of large current into parts,and homemade Sinap-DCCT400A current transducer was adopted.These measures significantly reduce the cost.To enhance the performance of current transducer,the linear error mechanism of current transducer with zero flux was investigated,and a method was proposed to assess and improve the linear error.The dissertation provided multiple testing results of the power supply,all of which met the operation requirements and design indices.It has been validated that the modular implementation of large current with high stability is feasible advantageous.The three magnet power supplies were in service and they have kept no failure operation since April,2017. |
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