磁共振成像系统中匀场电源参数优化设计
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摘要
在匀场电源中,存在LC输出滤波器与负载电感谐振造成系统不稳定和阻尼电阻带来阻尼损耗大的问题。通过建立系统的数学模型推导了控制信号到输出电流的传递函数,由传递函数得到谐振频率和阻尼系数的表达式。在此基础上,提出了一种根据谐振频率和阻尼系数的约束范围来对滤波器和控制环路参数进行优化设计的方案。该方案降低了阻尼损耗,同时具有良好的动态性能和稳态性能。最后,搭建了一台48 V/5 A的实验样机。实验结果表明,系统在跟踪频率为100 Hz、幅值为5 A的梯形参考电流下,延时时间仅为60μs,阻尼损耗仅为4.4 W,验证了理论分析的正确性。
The instability of system caused by the resonance between the LC output filter and the load inductance,and the great damping loss brought by damping resistance are existed in shimming power.The transfer function of control signal to output current is derived by establishing the mathematical model of the system.The resonance frequency and damping coefficient are expressed in the transfer function.On the basis,a solution to optimize the parameters design of filter and control loop in the constraints of resonant frequency and damping coefficient is proposed.Damping loss is significantly reduced,and the system has good dynamic and steady-state performances.Finally,a 48 V/5 A prototype is built.Experimental results show that the delay time is only 60 μs and the damping loss is only 4.4 W when tracking 100 Hz gradient reference current with 5 A,thus the validity of the theoretical analysis is verified.
The instability of system caused by the resonance between the LC output filter and the load inductance,and the great damping loss brought by damping resistance are existed in shimming power.The transfer function of control signal to output current is derived by establishing the mathematical model of the system.The resonance frequency and damping coefficient are expressed in the transfer function.On the basis,a solution to optimize the parameters design of filter and control loop in the constraints of resonant frequency and damping coefficient is proposed.Damping loss is significantly reduced,and the system has good dynamic and steady-state performances.Finally,a 48 V/5 A prototype is built.Experimental results show that the delay time is only 60 μs and the damping loss is only 4.4 W when tracking 100 Hz gradient reference current with 5 A,thus the validity of the theoretical analysis is verified.
引文
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[2]李思奇,蒋晓华.基于数字控制的磁共振成像用梯度放大器[J].中国电机工程学报,2010,30(27):83-89.
[3]许德志,汪飞,阮毅.LCL-LLCL和LCCL滤波器无源阻尼分析[J].中国电机工程学报,2015,35(18):4725-4735.
[4]曹彬,李思奇,毕大强,等.梯度放大器高性能控制系统的开发[J].电力电子技术,2008,42(2):27-30.
[5]蒋丹丹,李思奇,蒋晓华.两级电平结构MBI梯度放大器研究[J].电力电子技术,2006,40(6):104-106.
[6] CHEN Daolian,WAN Guoling.Differential Buck DC/DC Chopper Mode Iinverters With High-frequency Link[J].IEEE Trans. on Power Electronics,2011,26(5):1444-1451.
[7]刘虔,彭力,唐诗颖,等.一种基于图解LCL滤波器设计与优化方法[J].中国电机工程学报,2012,32(36):36-43.
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