Abstract

Electric vehicles are a key technology in the reduction of our carbon footprint and this has motivated significant research interest. The electrical traction motor is one of the main areas of research in attempts to further improve electric vehicle performance. The permanent magnet motor is the predominant device in this application because of its high specific torque. However, it has suffered from market speculation in the raw magnet materials which has generated efforts to develop electrical machines which have a high specific torque and do not contain rare earth materials.In the past the induction motor used to be the preferred motor for electric vehicles due to its low costs, low maintenance requirements, mature technology and robustness. The induction motor requires a higher specific torque to make it an alternative to permanent magnet machines. For this reason, this research had the primary aim of improving the specific torque of induction machines by undertaking a detailed review of the motor design because this process has conventionally focussed on the requirements for industrial applications. The first stage of the work presented in this thesis consisted of identifying the designs already in use for this purpose and the potential technologies applicable to the induction motor that could be transferred from other electric traction machines. A full review of the design process was also conducted in order to identify the key areas of the process with special reference to the electromagnetic design which used finite element techniques as the main modelling tool. New induction motor designs were developed which showed potential for improving the specific torque; two of these were selected for further refinement, prototyping and testing. Although these designs were modified to facilitate construction, some major difficulties were still encountered during the prototype rotor manufacture. The test results were used to validate the design process and to identify further improvements in the designs. The issues encountered with the rotor manufacture prototype however lead to some overheating during the experimental testing. Comments about the design experience gained during this research are summarized including suggestions for further research.