Study On A New Type Of Power Supply Similar To Flat-Top Pulsed Magnetic Field Based On Capacitor Energy Storage

High magnetic field can change the properties of matter,it is an important extreme condition for scientific research.Steady magnetic field and pulsed magnetic field have both advantages and limitations.Stable magnetic field has high stability and long duration,the maximum magnetic field is about 45T,and the costs are high.The pulsed strong magnetic field has high intensity,but the pulse duration is short.Flat-Top Pulsed Magnetic Field(FTPMF),which combines the advantages of high intensity of pulsed magnetic field and high stability of steady-state magnetic field,can meet the requirements of scientific experiments such as specific heat test and NMR,and is an important development direction in the field of pulsed strong magnetic field.As one of the core equipment of the high magnetic field device,the power supply is directly related to the quality of the magnetic field waveform.At present,the most widely used pulsed high magnetic field power supply is the capacitor energy storage type,its structure is relatively simple and reliable,and it is easy to modularize.This dissertation mainly discusses a new type of pulse power supply based on capacitor energy storage,which can produce a similar flat-top magnetic field,which is a kind of pulse width lengthened,and can approximate the pulse peak as flat-top for a period of time.In view of the three important stages of the FTPMF,the magnetic field rising stage,the maintenance of the flat-top and the magnetic field descending stage,the corresponding solutions and optimization schemes are given in this dissertation.The article introduces the basic structure of the pulse magnet and the nonlinear change of its DC resistance caused by factors such as joule heat in the pulse current environment are introduced,and an ideal mathematical model is established to illustrate the effect.Then the basic principle of the capacitor type pulse power supply is analyzed emphatically.The working process of the power supply is divided into two stages:discharge and continuous current.Through analysis and reasoning,some factors can affect the waveform of magnetic field current by power supply parameters,including current peak value,oscillation period and current change rate,etc.,which provide guidance for the design and research of the power supply.In order to obtain an ideal flat-top wave,a new design scheme of pulse power supply similar to flat-top wave is given.First,special high and low voltage capacitor combined discharge is used to improve the current change rate,realize the rapid rise of the magnetic field,and leave more heating margin for the pre-cooled magnet.Second,maintain low voltage large capacitor discharge to extend the discharge cycle,while reducing the current change rate,so as to maintain the duration near the peak magnetic field,and form a pulse magnetic field similar to the flat-top wave.Finally,in the phase of magnetic field decline,the surplus magnet current is transferred and discharged through the input of the AZCS to achieve the purpose of rapid decline,reduce the joule heat accumulation of the magnet.In this dissertation,the working process of the three stages of flat-top wave power supply is analyzed in detail,and the advantages of this design are given by comparing the classic short pulse waveform with the simulation.At last,the energy storage of low-voltage capacitors is compensated,the influence of nonlinear changes in magnet resistance on the magnetic field is compensated,resulting in a more similar flat top wave under real working conditions.The discharge module of the high-voltage capacitor has been redesigned,drawing on the circuit structure based on Marx generator to achieve capacitor voltage doubling while reducing the voltage level of a single group of capacitors.This is beneficial for capacitor selection and charging power supply design,improving capacitor life while reducing design costs.Analyzing the charging method of the power supply,it is concluded that using a bridge series resonant converter high-frequency switching power supply is very suitable as a charging power supply for capacitors,which can achieve constant current fast charging in an open loop state and is less affected by load changes.Theoretical reasoning and parameter design of a constant current charging power supply are combined,and simulation verification is basically consistent with the design results.In order to verify the capacitor energy storage type flat top wave pulse power supply scheme designed in this article,a prototype power supply was developed,including the realization of software and hardware control and protection.Finally,the experimental results of the prototype power supply are given.The measured waveform data is in good agreement with the simulation results,indicating that the power supply has good flat-top effect and the scheme is highly feasible.The last chapter is the summary and deficiency of the research content,including the follow-up research work.