A Superconducting Induction Motor with a High Temperature Superconducting Armature: Electromagnetic Theory, Design and Analysis

Abstract

Large electric superconducting machines are being sought to solve emissions challenges in aircraft and provide a solution to >12 MW wind turbine electricity generation. Superconducting motors with only high temperature superconducting (HTS) armatures can offer advantages of high reliability, high power density, and high efficiency compared with conventional superconducting motors. In this paper, a novel HTS squirrel-cage induction motor is proposed for high speed operation, which adopts the structure of HTS windings with a certain inclination angle in the stator slots. Due to the limitation of curvature radius of superconducting tapes, the pitch of HTS windings can be only set to 1 and adopt the short pitch arrangement structure, which such design details of the HTS motor would ensure the superconducting coils can undertake larger current and reduce AC losses. In order to keep the HTS windings in superconducting state and larger current density, a special fixed cryogenic cooling system below 70 K with the method of gas extraction and decompression, which is made of aramid fiber, has been fabricated and the whole structure of the stator is placed in liquid nitrogen. According to the motor control principles and electromagnetic field theory, the electrical performances of the novel designed stator-HTS motor, which driven by the variable-voltage variable-frequency (VVVF) inverter, are analyzed including the flux density distributions, the torque, the induced electromotive force, losses and efficiency by using the finite element method. Finally, the components of HTS squirrel-cage induction motor have been manufactured according to the designed parameters. Next step, the motor will be assembled and tested.Energies 2018, 11, 792 2 of 15 all-electric aircraft propulsion, electric vehicles and wind generators, etc., will change the development direction of the electrical machinery industry [8][9][10][11][12][13][14].However, most superconducting machines adopt superconducting material as the rotor poles for the field to supply high air-gap magnetic flux density, consequently the HTS motor has high power density and has been studied by many researchers and institutions, but this structure brings some problems such as cooling, maintenance, mechanical speed and manufacture cost, etc., and this technology is also complex [15][16][17][18]. In addition, because the superconducting magnets face an air gap with a high flux density at all times, the magnetic flux density in the superconducting coils is also high. This will affect the critical current of the superconducting tapes, so the operation temperature of superconducting magnets must decrease to 20-30 K to eliminate this influence. Therefore, the costs of cooling increase.We have focused on the HTS induction motor [19][20][21][22], in which the superconducting material is only applied to the stator part. The HTS induction motors avoid the key problems of the rotor dynamic seal and the rotor mechanical strength compared with the conventional superconducting motor under the ...

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