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Description
High temperature superconducting materials are commonly used in permanent magnet motors for stator armature windings, which can increase the power density of the motor. The use of ferromagnetic materials in the stator reduces the magnetic field in the superconducting coil, which increases the current carrying capacity of the superconducting coil. The rotor uses permanent magnets for excitation. The advantage of this design is that it ensures that the superconducting coil does not incur high AC losses due to excessive current. However, high-temperature superconductivity is environmentally demanding, so additional cooling ducts are installed in the stator tank to keep the superconducting coil below a critical temperature.
The author notes that the magnetic properties of ferromagnetic materials deteriorate at very low temperatures, which leads to poorer permeability and higher iron losses. This will reduce the efficiency of the superconducting motor. In this manuscript, the magnetic properties of three types of motor core materials, namely, conventional non-oriented silicon steel, amorphous magnetic material and nanocrystalline magnetic material, are firstly tested under extremely low temperature environment. The three ferromagnetic materials were fabricated into identical circular samples to simulate the stator of the motor. Through the analysis of the test results, the changing law of low temperature magnetic properties of the three materials is found. Then amorphous magnetic material, which has lower iron loss and smaller change of magnetic properties, is used as the stator of the motor to design and study a high-temperature superconducting permanent magnet motor with a power of 200kW and a speed of 500rpm. Amorphous has a large magnetostriction, and the core laminations made from it cannot be over-compressed, which leads to serious noise and resonance problems in the motor compared with conventional non-oriented silicon steel. The effect of this situation is more pronounced for motors with low-speed operating conditions, which further affects the reliability of superconducting cooling ducts. Therefore, the author optimized the cogging torque and efficiency separately. In order to reduce the cogging torque while improving the efficiency, a multi-objective optimization method based on genetic algorithm is used. The stator structure is optimized by oblique slots, unequal width slots, introduction of auxiliary slots, etc. The number of stator slots and the number of rotor poles are reasonably selected, and the shapes of the stator and superconducting coil cooling pipes are optimized.
Finally, the effectiveness of the optimized design is proved by observing the cogging torque waveform and efficiency MAP diagrams, etc. through the finite element method. The related research in this paper can provide certain material selection basis and design ideas for superconducting motor research.
