This paper presents a study of maximizing motor system efficiency for a solar powered vehicle by providing guidelines for the setup and operation of the motor system. It describes the vehicle, the motor system, and the dynamometer used for testing. Solar racecars use the axial flux motor described in the work because of its high efficiency, direct drive feature, and lead screw driven variable air gap. We present efficiency test results at a range of operating points. Motor operation in drive and regeneration modes is covered. During regeneration mode testing, the axial flux motor system converts mechanical energy provided by the dynamometer to electrical energy. In drive mode, the dynamometer absorbs the mechanical energy produced by the axial flux motor. The parameters varied in studying motor efficiency are battery voltage, speed, torque, and air gap size. Regeneration efficiency as influenced by back EMF is discussed. Guidelines for motor operation are developed. For example, guidelines for setting the motor air gap as a function of speed are given. The users of solar powered vehicles can employ these guidelines to setup and operate the motor more efficiently through improved regenerative energy capture and decreased drive losses. Application of the guidelines may be extended to other electric and hybrid vehicles, thus improving automotive energy efficiency.
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