Magnetism And Solid Coupling Vibration Mechanism Of Stator System In Asynchronous Machine

As the electromagnetic conversion device between mechanical energy and electrical energy, electrical machines are widely used in the civil and defense industry. The electromagnetic vibration of the stator system, which is one of the main noise sources, can directly affect the noise level of electrical machines. Therefore, with the development of the large and super-large electrical machines, it is very significant to study magnetism and solid coupling mechanism of the stator system.The engineering background of this thesis is based on large propulsion motor with the application requirement of vibration and noise reduction in the civil and defense industry. Through modeling of the stator structure and the study on magnetism and solid coupling vibration, this thesis attempts to obtain an accurate physical model, a calculating method of the electromagnetic force, and the mechanism of the magnetism and solid coupling vibration on stator system. Moreover, it will provide a theoretical basis for the design of the large electrical machines. The main contributions of the thesis are summarized as follows:1. Based on the principle prototype of the large propulsion motor, a double-shell model with different length between the inner and outer shells of the stator system is built. The new double-shell model can be used in a wider application range. Using this model, the vibration modes can be described by the analytical expression, and different boundary conditions between inner and outer shells can be respectively considered. Meanwhile, the natural characteristics of the double-shell stator system with different length rates can be calculated.2. By the analysis of the electromagnetic force compositions in the air-gap magnetic field, the expression of the electromagnetic force is obtained when the radial deformation of the stator system and air-gap magnetic field are coupled. It is found that the electromagnetic force, which is generated by air-gap eccentricity magnetic field and acts on the inner surface of the stator core, is composed of electromagnetic force wave terms, linear electromagnetic stiffness terms, nonlinear electromagnetic stiffness terms and parametric excitation terms, moreover, rotor rotating related terms.3. The methodology of nonlinear vibration on coupled mechanical and electric dynamic systems is applied to study the vibration of asynchronous machines. The parametric resonance, combined parametric and forced resonances, and double resonances on double-shell stator system in air-gap magnetic field are solved by the method of multiple scales. Through response equations, the stability of stationary solution and the singularity of bifurcation equation are analyzed. The numerical results show the influences of electromagnetic and mechanical parameters on nonlinear dynamics behavior when the magnetism and solid vibration on stator system of asynchronous machine is excited. And some new laws are obtained.4. The magnetism and solid coupling vibration equation with both the air-gap electromagnetic force and ponderomotive force is obtained for the electromagnetically excited vibration on stator system of electrical machines. For further study on the characteristics of ponderomotive force, based on Maxwell equations and the electromagnetic constitutive relation, the expressions of the electromagnetic field and electromagnetic force are derived by solving the eddy equations and the boundary conditions. Furthermore, the influences of geometric parameters on the electromagnetic field and the electromagnetic force, and the ponderomotive force on magnetism and solid coupling vibration are analyzed. The electromagnetic excitations of magnetism and solid coupling vibration on stator system are modified by the analysis of ponderomotive force in stator core. The conclusions presented in this paper provide a theoretical basis for the study on stator and rotor coupling vibration in the future.