Calculation And Analysis Of3D Electromagnetic And Temperature Fields In High Speed Permanent Magnet Generator With Back Rounded Stator Windings

With the extensive use of high speed permanent magnet generators (HSPMG)in distributed energy supply system, flywheel energy storage and aerospace field,the HSPMG becomes the very important research direction in electrical machinedomain. Compared with the conventional electrical machine, the sleeve used toprotect the magnets increases the effective air-gap length. While the generator isoperating at high speed, eddy current losses will be caused in rotor alloy sleeve,which may increase the working temperature in the generator. So this paper hasdone some researches about the electromagnetic and temperature fieldsconsidering the structural features and problems in HSPMG.First of all, based on the structure of back wounded armature windings and thealloy sleeve in a HSPMG prototype, the3-D calculation model ofelectromagnetic field is established. The flux density distributions in the statorcore section and the end region are studied, while the generator is operating atnon-load and rated load. The influences of effective air-gap length and thegenerator length on non-load magnetic flux leakage coefficient are also analyzed.Secondly, according to the structure features of stator closed oil coolingsystem, a3-D temperature and fluid coupling analysis model is established.Based on the studies about the distribution characteristics of losses in HSPMG,the temperature field is coupling analyzed and the3-D temperature distributionsin such HSPMG are determined. From the calculation results, the variation oftemperature along the axial direction in different components of the generator isstudied. Finally, the eddy current losses appearing in the sleeve increase the generatorworking temperature, which may reduce the generator performance and evencause thermal demagnetization of the magnets. Thus, a sleeve scheme designedwith low eddy current losses is necessary, and a rotor structure with copperplating is presented in this paper. The eddy current loss in the generator iscalculated using the finite element method. The results show the effectiveness ofthe copper plating in reducing the eddy current losses in the rotor, and theinfluences of the sleeve thickness and the copper layer thickness on rotor eddycurrent losses are analyzed. Using the fluid-thermal coupling method, thetemperature distributions of the generator with different copper layer thicknessesare comparatively analyzed based on the theories of fluid mechanics and heattransfer. The relationship between the temperature and the copper layer thicknessis obtained, and finally the temperature of the permanent magnets, which is thepart most seriously affected by the temperature, is given with different copperlayer thicknesses. The obtained conclusions may provide useful reference for thedesign and research of HSPMG.