Analysis and Design of a High-Stability Flat-Top Pulsed Magnetic Field Based on the Coupled Double Capacitor Bank Circuits and the Linear Compensation
Zhang Shaozhe1,2, Wei Wenqi1,2, Fan Junxian1,2, Xie Jianfeng1,2, Han Xiaotao1,2
1. Wuhan National High Magnetic Field Center Huazhong University of Science and Technology Wuhan 430074 China; 2. State Key Laboratory of Advanced Electromagnetic and Technology School of Electrical and Electronic Engineering Huazhong University of Science and Technology Wuhan 430074 China
Abstract：Due to its high strength and stability, the flat-top pulsed magnetic field (FTPMF) is one of the most significant tools for studying the magnetization effect, magneto resistance effect, and electrical transport. The Wuhan National High Magnetic Field Center (WHMFC) in China has built experimental stations of nuclear magnetic resonance (NMR) and current voltage (I-V) based on FTPMF. It requires FTPMF strength exceeding 40 T, flat-top stability within 0.01%, and a flat-top duration exceeding 5 ms. Until now, only the institute of solid-state physics (ISSP) in Japan has achieved an FTPMF of this level based on a DC pulsed generator. However, constructing a large DC pulsed generator is costly and time-consuming. This paper proposes a high-stability FTPMF scheme to meet the requirements of NMR and I-V measurements, combined with coupled double capacitor bank circuits and linear magnetic field compensation. The coupled double capacitor bank circuits generate FTPMF with stability of about 1%, and the linear compensation circuit precisely adjusts the magnetic field to achieve high stability. Firstly, the circuit topology is expounded, including two capacitor circuits coupled by an air-core transformer, a main magnet, a compensating magnet embedded into the main magnet, and a linear regulating circuit of the compensating magnet. Then, the discharge process of the double capacitors is discussed based on circuit state equations. An optimized method for charging voltage and discharge sequence is proposed to generate the background magnetic field. A field-compensation magnet of 1 T is designed with three windings and two decoupling windings to reduce mutual inductance between the main magnet and the compensation magnet from 100 μH to 10 μH. A linear power supply is proposed based on the current control characteristics of the IGBT in the active region. The IGBT is connected in series with the compensation magnet. An IGBT driver with current and voltage feedback is designed to control the loop current through the gate voltage of the IGBT in the active region. A corresponding controller with feedback and feed forward is designed for high-precision compensation of the background magnetic field, with a detailed discussion of controller parameters and system stability analysis. The system's phase degree and amplitude margin are 38° and 50 dB, respectively. Finally, a system of FTPMF is constructed. The optimized method of the charging voltage and discharge sequence of the two capacitors is verified. The average relative error between the experimental and simulation waveforms is about 3%. The dual-capacitor coupled discharge system can realize a background magnetic field with a strength of 40 T, flat-top duration of 10 ms, and stability of 1%, laying a foundation for high-precision linear regulation. A FTPMF with a strength of 45.2 T/8 ms/0.02% is achieved by linear compensation, meeting the requirements of solid-state NMR experiments. The method of prolonging the flat-top duration is also pointed out.
张绍哲, 魏文琦, 樊俊显, 谢剑峰, 韩小涛. 基于双电容器耦合和线性补偿的高稳定度平顶脉冲强磁场调控系统分析与设计[J]. 电工技术学报, 2024, 39(2): 303-312.
Zhang Shaozhe, Wei Wenqi, Fan Junxian, Xie Jianfeng, Han Xiaotao. Analysis and Design of a High-Stability Flat-Top Pulsed Magnetic Field Based on the Coupled Double Capacitor Bank Circuits and the Linear Compensation. Transactions of China Electrotechnical Society, 2024, 39(2): 303-312.
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