| The scientific experiment environment of flat-top long-pulsed strong magnetic field with high stability combines the advantages of small ripples of stationary magnetic field and high strength of pulsed magnetic field, which is of great research value. Wuhan National High Magnetic Field Center(WHMFC) constructs a set of pulse power supply system of lead-acid storage battery. It possesses the features of large energy storage and stable voltage output, which is applicable to be taken as power supply of long-pulsed magnetic field. However, since its energy output is not controllable and characteristics of the variation of magnet resistance during discharge, the flat-top waveform with high stability can't be achieved. To solve the above issues, this thesis proposes a control scheme of pulsed magnetic field waveform at flat-top stage to improve stability of pulsed magnetic field at flat-top stage. Its main contents are as follows:First of all, an active compensation scheme based on parallel multiple branches is proposed, and the circuit topology and control strategy of the compensation device(the active compensation device based on IGBT-PWM control) are presented.. When the pulse current pulse of the magnet reaches its peak value, the compensation device will be actived and injects energy into the pulsed magnet in order to compensate the pulse current which decreases because the rise of magnet resistance. Compensator is made up with multi-stage active compensation units. At the flat-top stage, Activing the compensation units in squence can reduce the frequency of the IGBT switch during experimental process, and the IGBT's stress can be lignter, which is conducive to energy continuous injection and can extend duration of flat-top waveform. By analyzing the discharge characteristics of power system and changes of magnetic resistance at flat-top stage, compensator control system adopts Segmented PI control strategy. In order to ensure the highly precise and high-speed, the sampling process of pulse current shall be carried out in a short period of time. This thesis proposes a highly-precise data acquisition scheme based on the combination of 24-bit converters and 16 AD converters to reduce the relative error and improve the stability of the magnetic field.Secondly, the software and hardware design of the control system as well as the development of the prototype are described in details. Taking control system's the ability of computational redundancy and modular parallel processing capabilities into account, the structure of FPGA+DSP is adopted(FPGA model: EP3C40Q240, DSP model TMS320LF28335). FPGA realizes the function of data acquisition, communication with DSP and HMI data exchange. DSP realizes the function of digital filter and PI control algorithm. In this thesis, the software development of control system adopts top-down design mode, subdivides each function module of control system and develop modular one by one. The underlying software development based on Systemverilog can acquire the data of pulse current measurement signal, trigger the auxiliary branch IGBT, protect the device form over current, and interact with DSP real-time data.Finally, flat-top long-pulse magnetic field whose duration time is more than 150 ms, magnetic field intensity is more than 15 T and stability is within 300 ppm at flat-top stage is obtained by setting up the test circuit. Through the analysis of the experimental results, an upgrade scheme is put forward, and design idea which is aimed at realizing better performance of flat-top long-pulsed strong magnetic field in the future is also provided. |
PDF Full Text Request