Electromagnetic Characteristics And Structural Optimization Of HTS Induction Motor With HTS Armature

The high temperature superconducting(HTS)motors have the advantages of high reliability,high power density and high efficiency.However,most of the traditional superconducting motors use superconducting coils or superconducting bulks to play the role of permanent magnets on the rotor structure.The HTS coils or bulks on the rotor during high-speed operation will withstand large centrifugal forces,leading to a drop in the critical current of the superconducting material and affecting the performance of the superconducting motor.In addition,the rotor cooling system needs to adopt the dynamic seal structure,which leads to the further complexity of the motor structure and restricts the high-speed operation of the rotor.In order to solve these problems,a novel HTS induction motor with HTS armature is proposed for high speed operation,which meets the requirements of high power density,high efficiency,simple cooling and low cost.The electromagnetic mechanism,parameter analysis,AC loss of superconducting windings,design principle,system structure design and structural optimization design of HTS induction motor were studied.The main contents of the dissertation are as follows:The electromagnetic mechanism of HTS induction motor is studied by using LR circuit differential equation method.According to the electromagnetic constitutive relation.of HTS materials,the resistivity variation rule of high temperature superconductors was studied,and the regular characteristics of magnetic field penetration and current distribution of high temperature superconductors were analyzed;In combination with the E-J rule of superconducting materials,the LR form of ordinary differential equations of stator current and rotor current is derived,and the differential equations are discretized by Euler method.The discrete form of stator current and rotor current is obtained.Using this model,the electromagnetic characteristics and operation performance of HTS induction motor with HTS rotor,the HTS induction motor of HTS armature,and the fully-superconducting HTS induction motor are studied respectively.The result shows that the ratio of the rotor peak current to the critical current of HTS induction motor with HTS rotor and fully-superconducting HTS induction motor is greater than 1,which can lead to a risk of superconductor quench.In view of the background magnetic field dependence and anisotropy of HTS materials,combined with the double-layer winding structure of HTS induction motor in this dissertation,an analytical model of vertical and horizontal direction of leakage magnetic field in an open rectangular slot is established by using double image method.The magnetic field distribution characteristics of superconducting coils under different current transmission are analyzed by using this model;The influence laws of the electromagnetic parameters of the open rectangular slot on the surface magnetic field of the superconducting coils in the slot are studied.The results show that the maximum magnetic field on the surface of the superconducting coil can be reduced by increasing the slot width properly,and the maximum magnetic field on the surface of the superconducting coil can be increased linearly by both the transmission current and the number of turns of the coils.Aiming at the difficulty of calculating the AC loss of superconducting coils with high ratio of width to thickness,a T-A equations model is proposed to study the AC loss law of the 3D model of runway superconducting coils;Based on the basic theory of AC loss of superconducting materials,the analytical calculation model of AC loss of superconducting materials is established,and the AC losses of different influencing factors are calculated by analytic method;Combining the structure of superconducting coil and the technical parameters of superconducting material,the critical current of superconducting coil is estimated;Using T-A equations,the transmission AC losses of superconducting coils with different n values,different transmission currents,different frequencies and different coil sizes are studied.The results show that the T-A mathematical model is reliable.The mathematical model principle of HTS induction motor with HTS armature is put forward.The electromagnetic parameters of motor components are preliminarily designed by using frequency conversion motor program.Through the study of different parameters such as voltage and current,air gap size,winding density and maximum torque,the optimum performance parameters of the motor are obtained;In order to solve the reliability problem of the designed parameters,the finite element method is used to analyze the performance of the motor.The results show that the motor parameters can meet the performance requirements,but there is still room for optimization.The machining and fabrication technology of HTS induction motor with HTS armature such as stator,rotor,superconducting coil,low temperature holding system and so on are introduced;The critical current measurement system and AC loss test system for HTS tape and coils are built.The critical current and AC loss of HTS tapes and coils are measured.The test results prove the feasibility and the correctness of theoretical analysis of the HTS induction motor with HTS armature scheme.In order to solve the problem that the permutation of superconducting windings leads to the larger leakage magnetic field in the slot,the rectangular tooth structure is used to solve the problem,which effectively avoids the intersection of the coil end and optimizes the distribution of the magnetic force line.More stator slots can be added at the same size;In order to solve the problem that the stator iron core leads to the excessive weight of the motor,a kind of iron-free structure is proposed,and its electromagnetic performance is studied and optimized.The research results show that the structure is reasonable and effective.