| Due to its excellent acceleration performance, great abilities for sharp curves and slopes, high reliability, low noise and maintains, etc., the linear motor rail-wheel transit system become the primary scheme for the urban transit system. Linear induction motor is the core device of the linear motor rail-wheel transit system, thus, the development and application of the linear motor rail-wheel transit system are limited for the low factor and efficiency of the linear induction motor. Replacing the copper windings by using high-temperature superconducting windings, the excitation loss of linear induction motors will sharply cut down. And the efficiency of the linear motor will be improved significantly. Since the high-temperature superconducting linear induction motor (HTS LIM) is a novel electric machine, many key technical works should be made to investigate the performances of the machine. Thus, the dissertation focuses on the numerical calculation method, core structure design, further reduce the loss of HTS LIM, and the magnetic shield of the flux density around HTS windings. The contents of the dissertation are arranged as follows:For the nonlinear electromagnetic properties of the HTS windings and the large time constant of HTS motor, the iteration convergence process of the transient electromagnetic calculation is very slow. Taking the HTS LIM as the study objective, the equivalent method of the HTS windings’nonlinear electromagnetic properties are proposed. Then the relations between the parameters of the machine and the transverse edge effects are studied by using analytical method and the equivalent method of the transverse edge effects during2-D electromagnetic calculation is also presented. Based on the researches above, multi-iteration2-D transient electromagnetic field calculation model of HTS LIM considering HTS windings’nonlinear electromagnetic properties and transverse edge effects are established. Then, the electromagnetic field distributions and the operation characteristics of HTS LIM are analyzed. The test bench of HTS LIM is developed and the operation characteristics of HTS LIM are measured. Compared with the measured results, the errors of the speed and the thrust obtained from the established calculation model are0.7%and7.7%, respectively. It can meet the requirements in engineering.The HTS windings utilized in the HTS LIM are excited by ac source, therefore it is more complicated than that excited by dc source. To investigate the influence of the iron core structure on HTS LIM, the electromagnetic field distributions, operation characteristics, and the critical field of HTS LIM with slotted iron core, noslot iron core, and air core are analyzed. The research contents show that if the three machines are excited with same current supply, the machine with slotted iron core can improve the air gap flux density and the eddy current eddy density. However, when the machines are fed on the same voltage supply, the first harmonic content of the air gap flux density and the operation characteristics of the machine with noslot iron core are larger than the others. However, due to its larger excitation current, the flux density around HTS windings are larger than the allowable value. The HTS windings may quench. The machine with slotted iron core can effectively reduce the excitation current and the flux density around HTS windings. When the specific speed of the machine is larger than0.1, the flux density around HTS windings is smaller than allowable value. In addition, the reasonable design of iron core can further improve the transport current of HTS windings.The dissertation also proposed the method that replacing the compound secondary by using copper-iron (Cu-Fe) alloy which is both conductivity in electricity and magnetism to further reduce the loss of HTS LIM. The electromagnetic field distributions, operation characteristics, and critical magnetic field of HTS LIMs with different secondary material electromagnetic properties are studied by using numerical method. Then the influence of the copper-iron alloy thickness on HTS LIM is also investigated. The researches show that the copper-iron alloy can effectively improve the air gap flux density, and improve the influence of end effects on air gap flux density and eddy current density distributions. Although the operation characteristics of HTS LIM with copper-iron alloy secondary is lower than the machine with aluminum-iron compound secondary, but the specific loss is reduced significantly. For example, the locked primary specific loss of the machine developed by using16%copper-iron alloy is reduced4.6%; however the operation specific loss (when the specific speed is0.75) is reduced by10.47%. Due to the skin effect, the optimum thickness of the copper-iron alloy is5mm. the locked primary specific loss of the machine with5mm copper-iron alloy can reduced by7.75%than that with3mm copper-iron alloy. In addition, the flux density around HTS windings increases as the copper-iron thickness, but the max parallel flux density and max perpendicular flux density are smaller than0.1T and0.2T, respectively. This can ensure HTS windings operate safely.The magnetic shield can reduce the flux density around HTS windings and improve the transport current of HTS windings. The dissertation proposed the slot leakage magnetic coefficient and HTS winding’s surface magnetic decrease coefficient to evaluate the influence of magnetic shield on slot leakage magnetic field and the flux density around HTS windings. Then the slot leakage magnetic coefficient and the HTS winding’s surface magnetic decrease coefficient of HTS LIM with different magnetic shields are calculated by using numerical method. And the influences of the magnetic shields on the operation characteristics of HTS LIM are also studied. In addition, the calculation method of slot leakage inductance is also presented. The results show that magnetic conductivity shields can reduce the flux density around HTS windings but increase the slot leakage flux density, however the magnetic repulsion shields can reduce the flux density around HTS windings while has little influence on slot leakage flux density. The magnetic decrease effect of HTS shield is great; the flux density around HTS windings can be reduced to8.6%times less than the original flux density. |
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