Research On High Speed Permanent Magnet Outer Rotor Claw Pole Machine

Due to small volume, high efficiency, great power density and high integration,the high speed machine, as key component of high speed drive sysytem, is one of the great concerns in field of high-level equipment manufacturing. The high speed pernanent magnet(PM) motor is widely used in many fields such as flywheel energy storage, petrochemical products processing, high-speed spindle and so on. But most high speed PM motors with inner rotor structure, for which the carbon-fiber bandage must be used to against centrifugal force and to fasten the magnets on the rotor surface. So the equivalent air-gap length is increased and efficiency of heat dissipation is decreased. Inversely, with outer rotor structure these problems can be solved. The research work of this thesis is from the project“Study on outer PM rotor claw pole high speed motor and its control system with square wave supply”,which is supported by the National Natural Science Foundation of China. The study of the thesis is concentrated to electromagnetic performance analysis theory, rotor strength and its dynamic characteristic analysis method, magnetic field analytical model and comprehensive design method. The main contents are listed as follows:(1) Based on the research of structure characteristics and operation principal of high speed PM outer rotor claw pole motor, the equivalent magnetic-electrical model representing internal energy flow is built, and the complicted flux leakage and saturation influence are considered. By three dimentions magnetic field finite elements method(FEM), the induction electromotive force(EMF) and cogging torque have been analized, relationship between main size and performance index has been researched, which provides theoretical basis of electromagnetic design and performance analysis method.(2) The stress distribution nonlinear calculation model of outer toror is built based on the FEM,and the stress distribution of outer rotor yoke and PMs considering centrifugal force and temperature effect has been calculated, some influence factors on rotor stress distribution have been analyzed such as pole-arc coefficient, filling material and PM eagments. In addition, the outer rotor mode calculation model considering influences of detrusion and rotational inertia is built, then the influence of rotor axial length, bearings stiffness and gyroscopic effect to critical speeds and mode characteristics have been analyzed.(3) In view of the problems of time consuming for three dimension magnetic field calculation, by segmentation in shaft directions a new analytical calculation model of no load air gap magnetic field based on the method of the Fourier series and separation of variables is proposed, and then the expression of cogging torque and no load back EMF is derived, so the air gap magnetic field distribution, EMF and cogging torque are analized. Finally, In order to verify the accuracy of the analytical model, the finite element analysis and experiments are finished. The analytical results well agree with those obtained by the FEM and experiments, confirmed the feasibility of this method.(4) Based on the flux density variation track of claw pole, the iron loss model is built in consideration of three-dimension quadrature alternating magnetization and harmonic; then the influence factors of air friction loss are researched, which are rotor speed, rotor surface smoothness and axial wind speed; the copper loss calculation model considering proximity effect and skin effect is built; eddy current loss of PM and bearings friction loss are researched. The results of the finite element analysis results validate accuracy of above loss model, which provides theoretical basis of temperature field analysis and heat dissipation technology.(5) In view of many infulence factors such as rotor stress and dynamics characteristics, electromagnetic performance, loss calculation and so on, the comprehensive design theory and method for high speed PM outer rotor claw pole motor based on multiple physic fields analysis is proposed. An prototype of 1.5 kW has been designed and manufacted, its parameters and performance characteristics are measured by experiments, the accuracy of design theory and method is verified, which provides theoretical basis of its application.