Modeling and evaluation of laminated windings

Abstract

Electrical machines in electrical vehicles are sometimes put under a lot of stress when for example climbing an uphill road. In order for the machine to cope with the heat generation that comes of running extended periods of time near or at peak power one needs a highly developed cooling system. At the division of Industrial Electrical Engineering and Automation (IEA), located at Lunds Tekniska Högskola (LTH), a new and innovative winding design is developed which make cooling the machine more efficient. The winding consists of a laminated sheet which is rolled in a spiral. There is a small space between each winding turn making it possible for an air stream to flow through cooling the conductive sheets. The cooling capabilities of such design are evaluated throughout this thesis. Measurements are performed on two prototype winding built at IEA. The measurement rig are built solely for this purpose mainly in order to maintain the right measurement, a great deal of time during the thesis is put on perfecting the rig. Beside measurements are numerical models of the winding built in Comsol Multiphysics, both in 2 and 3 dimensions. Besides numerical modeling is an analytical model built with help of Matlab. The analytical model is used, among else, to simulate transient conditions and drive cycle analysis of an electrical machine suited for a bus. Results from simulations and measurement show that the laminated winding is able to cope with high amounts current without harm due to the effective cooling. Simulations show an ability to use current densities in the winding stretching towards 30 A/mm2 and still are able to keep tolerable temperatures. Results also point out weaknesses in the winding construction in form of sensitivity to winding geometries of certain type as well as unevenly spaced winding turns. Ways to improve the cooling performance of the winding by altering the geometry and improving the construction process are discussed in this thesis. The electrical machines used today are often oversized in order to thermally handle the periods of excessive power need. The effectiveness of such a machine is best during these short stretches of high power output even if they nominally are driven at a much lower power where the effectiveness is worse. The laminated winding design enables the use of smaller machines with peak efficiency at nominal drive that still are able to cope the periods of extreme power need due to the effective cooling