Impact of Winding Inductances and Other Parameters on The Design and Performance of Brushless DC Motors

The computer aided design process of two electronically operated brushless dc motors intended for use in electric vehicle propulsion is described. The components of this process are a time domain dynamic simulation model of the brushless dc motor system in which the machine paramenters, inductances and emfs, are obtained entirely from finite element field analysis of the magnetic circuit arrived at by the designer. This computer aided design process is used to determine the correct winding configurations for two machines, the permanent magnet rotor one of which is of samarium cobalt, and of ferrite for the other. Both machines are required to achieve 15 hp continuous and 35 hp peak ratings as motors, subject to the constraints of a maximum dc supply voltage of 120 V and a maximum current of 400 A due to limitations on the available power switching components. In addition, the effects of changes in the firing angle of the inverter transistors, with respect to the induced winding emf´s, are examined. The results of this work demonstrate that the performance of such systems is inductance limited especially in high speed (frequency) applications. The two machine designs selected as a result of this analysis were fabricated and subsequently tested in the laboratory. Both machines met the desired performance goals as predicted by the computer aided design process.