| The 14 T MRI(magnetic resonance imaging)superconducting magnet power supply is one of the key research projects of The strategic Priority Research Program(Type-B)of Chinese Academy of Science(CAS).According to the large inductive load characteristics of the superconducting magnet(inductance:321 H,connection resistor:2 mΩ)and the high stability requirement of the magnet current stability(10 ppm/h)when the magnet is running under steady flow,the superconducting magnet power supply is designed in two aspects of the topology and the control system.Firstly,this paper introduces the design of the main topology of the power supply.By comparing and analyzing various high-stability power supply topologies in the market,the three-phase uncontrolled rectifier bridge in series with double-buck topology is proposed.After that,the paper elaborates the design idea of the main topology of the power supply from the aspects of the AC-DC topology design and the DC-DC topology design.Then,the average state-space method is used to mathematically model the main topology,which lays a foundation for the calculation of the parameters,the selection of the devices as well as the analysis of the function of the main topology.According to the design of the main topology of the power supply,the paper separately analyzes the input stage circuit,the primary Buck circuit and the secondary Buck circuit of the power supply.Based on the specifications of the power supply,the paper completes the calculation of parameters as well as the selection of the devices for each module of the main topology,which combines the mathematical model of the main topology,the equivalent load model and Fourier analysis.At the same time,the paper analyzes the functions of each module of the main topology,which verifies the rationality of the design of the main topology.Then,the paper elaborates the design of the high stability control system of the power supply.From the perspective of how to achieve high stability control system,the paper analyzes the influence on system stability when the parameters of the hardware of the control system change and the closed-loop control requirements of control system,which determines the overall design of high stability control system of the power supply.Furthermore,the paper introduces the selection scheme of the hardware(measurement circuit,ADC circuit,control chip,drive circuit)of the control system and the control scheme of the closed loop(bus voltage loop and triple closed loop control).Finally,the paper completes the design of high stability control system from the hardware implementation(selection)and the software implementation(the control strategy of the closed loop and fault protection).The experimental results are given. |
