Research On Electromagnetic Basis Of Bearingless Switched Reluctance Motors

Bearingless switched reluctance motor (BSRM) is a novel magnetic suspension motor, which integrates the magnetic suspension winding into the same stator so that the rotor may suspend and rotate at one time because of similarity between the construction of a magnetic bearing and that of a switched reluctance motor (SRM) stator. BSRM not only extends theory and applicatioin of the bearingless motor, but also inherits and enhances high-speed performance and adaptability to atrocious surroundings of the SRM. Moreover, it also provides a new approach to solve the problem of noises and vibration for the SRM because it actively controls the radial displacement of a rotor.The dissertation focuses on electromagnetic characteristics and electric machine design of BSRM and full-period bearingless switched reluctance generator (BSRG). The principle and derivation of mathematic model of BSRM are introduced. 2D and 3D finite models of a BSRM with 12/8 structuture are set up, and then its electromagnetic characteristics are studied, which include its magnetic field distribution, inductance, torque and radial force characteristics. Inductance characteristics of BSRM are mainly studied. Formulas of calculating its widing inductances with an enhanced incremental energy method (EIEM) are deduced, and a novel method of fitting winding inductances for BSRM is presented. Moreover, the effects of rotor eccentricity, two winding magnetomotive forces and end magnetic-field effect on electromagnetic characteristics of BSRM are researched, respectively. The computational precision of DSMP, MVP and EFE are studied for solution of nonlinear magnetic field such as that of BSRM.On basis of the design of SRM, the dissertation researchs the key technology of BSRM design. The relationship between torque and pole arc angle, and that between radial and pole arc angle are analyzed. The general mathematical model of BSRM is proposed in order to solving limations of the presented model on pole arc angles. Optimal single-phase winding arrangements of BSRM are obtained based on its maximal output and convenient control, and then its three-phase winding arrangements are presented on the basis of the weast winding coupling. Two winding currents being equivent to two square-wave forms, the dissertation deduces computational formulas of main dimension and radial force of BSRM, based on the method of its equivalent magnetic circuit. Influences of different magnetomotive force combination of two windings on radial force and torque are analyzed, and then the method of calculating and optimizing winding turns of BSRM is proposed on the basis of the peak value of winding current. Moreover, design of the prototype validates the method presented in the dissertation. Main winding square-wave current strategy, least magntomotive force strategy and average radial force strategy are introduced, and the method of computing winding current and advanced angle based on each control strategy is analyzed. Dynamic magnetic field distributions of BSRM are gained by the transient analysis, and the results show that both control strategy and load influence its magnetic field characterisitics. Then eddy current losses and hysteresis losses of BSRM are sperated from its iron losses using a double frequency method. The effects of three control strategies on iron losses of BSRM are studies. At the low and medium operation speed, iron losses with three strategies are almost equal with each other. At the higher speed, iron losses of BSRM with the least magnetomotive force strategy are markedly less than that of other two strategies.Finally, the electromagnetic basis of full-period BSRG is studied. The levitation principle and generation mechanism of full-period BSRG are expatiated. On basis of derivation of mathematical model of BSRM, the dissertation deduces the mathematical model of full-period BSRG. Its model has higher precision because it can consider the coupling among suspened windings of single-pahse winding. Based on the design of BSRM, the optimal winding arrangements of full-period BSRG are obtained, and the computational formulas of its body dimension and radial force are proposed. Finally, a full-period BSRG is designed for testification of the method presented in the dissertation.