| When the high-temperature superconducting magnet works in the continuous current mode,due to the existence of joint resistance,magnetic flux creep and AC loss,the current of the closed superconducting loop will decay,and it cannot work in the closed-loop constant current mode.At present,there are two main ways of magnetizing high-temperature superconducting magnets: direct power drive and non-contact magnetic field induction.The traditional direct drive method of power supply requires access to the current lead.The current lead is connected between the room temperature environment and the low temperature environment of the magnet,which will form a leakage heat source.When the lead is energized and excited,the lead itself will generate Joule heat to form an additional heat source.For high-current superconducting magnets,the heat loss power of the leads is large,and the cooling burden is extremely high.Therefore,the traditional excitation method has large energy loss,large equipment volume and high cost requirements.High-temperature superconducting flux pump technology is a new type of non-contact magnetization technology that can inject direct current into superconducting closed-loop circuits without electrical contact.It uses the principle of electromagnetic induction to gradually accumulate external discrete magnetic fluxes to superconducting magnets.an induced current is generated in the strip,so that the magnetization of the high-temperature superconducting magnet can be realized,and the high-temperature superconducting magnet can operate efficiently and stably in the continuous current mode.Clarifying the excitation mechanism of high-temperature superconducting flux pump is of great significance for improving the trapping magnetic field,improving the efficiency and stability of the flux pump,and obtaining efficient and compact superconducting magnets.In this paper,the physical models of the macroscopic magnetic flux quantum coupling theory and the dynamic resistance theory are analyzed,and the operation mechanism of the two theories in the high-temperature superconducting flux pump is discussed.Based on the principle of generation,the optimal value of the relationship parameters in the formula group and the actual parameters in the model of this subject are selected to fit the characteristic curve of the linear magnetic flux pump,and the relationship coefficients and characteristic parameters were analyzed.The three-dimensional modeling design and optimization research of the excitation part of the high-temperature superconducting flux pump was carried out.Based on COMSOL Multiphysics,a three-dimensional model was built,and the multi-physics numerical finite element simulation calculation method was used to analyze the corresponding changes of the parameters such as the driving current and air gap in the linear magnetic flux pump device and the characteristic parameters of the traveling wave magnetic field.In order to reduce the number of special applications and the heat loss of the device,reduce the cooling burden,and improve the overall cooling efficiency of the system,the optimal solution of the operating parameters of the linear magnetic flux pump is proposed.Considering the actual platform construction,the device chooses an air gap of 1mm and a phase difference of the drive current of 120 °.The most suitable current amplitude is0.5～1A.Finally,the heat loss of the whole device is calculated according to the optimized parameters,including Joule heat and iron loss.When the driving current is1 A,the iron loss is about 0.53 W,and the thermal power of the coil is about 2.3W.Comparing the parameters with the refrigerator,it can meet the cooling load requirements of the conduction cooling type magnetic flux pump device.The simulation modeling and calculation of high-temperature superconducting induction strip and load coil were carried out.High-temperature superconducting coated conductors can be used as current-carrying conductors in many scenarios that require large-capacity and low-loss power transmission.It is of great significance to accurately calculate the influence of various parameters of the magnetic field on the AC loss of high-temperature superconductors.The AC loss of the superconducting part of the linear flux pump device based on the traveling wave magnetic field is studied by finite element simulation,including the parallel high temperature superconducting strip and the high temperature superconducting double-cake load coil placed in the induction area.Based on the numerical analysis method,a two-dimensional simulation model of three horizontally parallel high-temperature superconducting tapes were established.the relationship between the AC loss characteristics of the strip at different positions is analyzed.The results show that the AC loss of the two ends of the three parallel high-temperature superconducting tapes is always greater than that of the middle band because the magnetic field induced by the middle band is superimposed on the two end bands.And when the gap is reduced,the interaction of AC losses in the middle and end strips becomes more pronounced.In addition,the self-field loss and magnetization loss of the coil are further studied,and the AC loss characteristics of the high-temperature superconducting coil under the condition of AC transmission current and external AC magnetic field,which are affected by the magnetic field amplitude,frequency,phase and other parameters are analyzed.The results show that when the external AC magnetic field is small,the AC loss of the coil is mainly affected by the transmission current,and the influence of the magnetic field is almost negligible.When the amplitude of the external AC magnetic field is large enough,the AC loss curves under each transmission current condition are relatively close,and the external magnetic field has already played a leading role in the overall AC loss of the coil.Based on the previous simulation work,the experimental platform of the linear magnetic flux pump system under liquid nitrogen was built.The optimized parameters of each part in the system are comprehensively considered,and the optimal device parameters are selected based on the mutual influence of each characteristic parameter.The construction of the linear flux pump system is divided into the driving circuit part,the wireless excitation part,the high temperature superconducting load coil part and the measurement system part.This work provides a parameter optimization design scheme for the subsequent construction of a conduction-cooled magnetic flux pump,and lays a theoretical foundation and experimental verification for the further application of the linear magnetic flux pump in the closed-loop operation of the actual high-temperature superconducting magnet. |
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