Design of continuous micro-control system for flat-top pulsed magnetic field
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摘要: 针对现有电容器放电开环控制产生的平顶脉冲磁场稳定度难以满足核磁共振要求这一问题,提出一种平顶磁场闭环连续微调控方案。在脉冲磁体中放置一个补偿线圈,其由蓄电池供电,采用前馈控制加反馈控制的策略,利用IGBT有源区对补偿线圈的磁场进行线性调控,补偿背景磁场的波动,形成高稳定度平顶磁场。为此,设计了IGBT工作于有源区的驱动电路,搭建了原型机进行实验,结果表明,该方法能够将磁场稳定度提升至50×10−6,验证了方案的可行性。Abstract: Aiming at the problem that the stability of the flat-top pulsed magnetic field generated by open-loop control of capacitor discharge is difficult to meet the requirements of nuclear magnetic resonance, this paper proposes a closed-loop continuous micro-control scheme for the flat-top magnetic field. A compensation coil is placed in the pulse magnet, which is powered by batteries, adopts the strategy of feedforward control and feedback control, uses the IGBT active region to linearly regulate the magnetic field of the compensation coil, compensates for the fluctuation of the background magnetic field, and forms a highly stable flat-top magnetic field. To this end, this paper designs a driving circuit for IGBTs working in the active region, and builds a prototype for experiments. The results show that the method proposed can increase the magnetic field stability to 50×10−6, which verifies the feasibility of the scheme.
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表 1 电路参数
Table 1. Circuit parameters
capacitor/
mFmagnet
inductance/mHmagnet
resistance/mΩcrowbar
resistance/mΩbattery
voltage/Vcompensate coil
inductance/μHcompensate coil
resistance (298 K)/Ωmagnet coil
constant/(kA·T−1)compensate coil
constant/(A·T−1)4.8 33.126 819.3 500 96 215.15 2.76 2 196 -
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