Multiphysics Design Of MJ-class High Temperature Superconducting Energy Storage Magnet

With the access of new energy sources and the development of smart grids,the factors affecting power quality are increasing.The superconducting energy storage system(SMES)can effectively balance the load fluctuation of the power system,maintain the stability of voltage and frequency,and reduce the low frequency oscillation of the power system.Therefore,the power quality is effectively improved.The SMES is the core component of the whole energy storage system.Its operational stability mainly determines the stability of the entire energy storage system.Therefore,in the design,the energy storage magnet is in various physical fields such as electromagnetic,temperature and mechanics.The performance has always been an indicator that designers pay close attention to.Therefore the multi-physics comprehensive analysis design of SMES is of great significance in practical engineering.In the thesis,the high-temperature superconducting energy storage magnet(HTS-SMES)is analyzed in three modes:natural charging,energy storage and discharge,and the relationship between magnet current and stored energy is obtained.The SPWM control is designed for large-capacity energy storage magnets.The strategy controls the chopper to complete the controlled charging and discharging of the magnet,and realizes the switching of three working modes based on the digital control mode.According to the equivalent circuit,the controlled charging and discharging simulation model is built on the Simulink platform in MATLAB.The results show that the smaller the controlled discharge voltage,the longer the discharge time and the smoother the current curve.In order to meet the high current density requirements of HTS-SMES,a composite conductor is selected to wind the energy storage coil.Firstly,the electromagnetic characteristics of three conventional composite conductors,TSTC,CORC and Roebel were analyzed.The results show that the magnetic flux density of the TSTC composite conductor is large,the magnetic flux density of the CORC composite is related to the distribution position of the strip winding on the skeleton,the The flux density distribution of Roebel is generally uniform.Then the critical currents of three conventional composite conductors are experimentally analyzed.Finally,considering the economic warp,winding and impregnation curing process,four strip-stacked TSTC composite conductors were selected as the energy storage coil winding wires of the design.In addition to the loss of the magnet,the losses generated by the external conduction-cooled components are also the main heat source in the system.According to the eddy current loss distribution,the structure of the conduction-cooled plate of the magnet is determined as a plate with inner groove structure.The thermocouple coupling model was used to analyze the temperature characteristics of different epoxy resin insulation materials.Then the influence on the temperature characteristics of the superconducting coil was analyzed.Through analysis,c-type resin-based material was selected as the impregnating materials for this design.Through multi-physics coupling analysis,the distribution parameters of electromagnetic,temperature and Lorentz force in the dynamic and stable operation of the magnet were analyzed.Combining the simulation results at different charging rates,the integrated energy storage unit is close to the center of the magnet as a weak area.Based on this characteristics,it is proposed to strengthen the design or design the skeleton of the energy storage unit in the design.This way can prevent the weak area of the magnet from working for a long time in a high magnetic field and high temperature environment.Finally,the pancake coil was wound and subjected to impregnation and solidification experiments to verify the effect of the new epoxy resin on the properties of the magnet and the low-temperature stability.The impregnation and solidification of the coils A and B were carried out by vacuum pressure impregnation and immersion impregnation.The critical current of the coil after the immersion was tested and found to be 2.08%and 3.16%less than before,which verified the feasibility of the new epoxy resin material in practical applications.