The object of this thesis is to investigate the performance in detail and to improve the efficiency of an exterior-rotor burshless DC motor provided by a motor manufacturing company. The finite element software package FLUX3D will be adopted to conduct all the analyzing works. At first, the three-dimensional static magnetic model of the machine will be formulated by FLUX3D. After confirming the preliminary analyzing results with practical measurements, static magnetic circuit of the machine system will be established to seek the possible flux leakage paths. By adjusting the thickness of permanent magnets and the shapes of stator poles, the effectiveness of machine operational efficiency improvements as well as induced torque changes will be obtained. Finally, from these investigations, adequate suggestions for design and construct the associate machine will be provided.

A drive system of the electrical lighter vehicle with the brushless DC machine is developed in the thesis. The system consists of a control unit based on a digital signal processor (DSP) and a drive module which combines a drive circuit, a brushless DC machine, and associated wheels. The motive power is delivered directly to the wheels without a power transmission system. The driving comments and the monitored signals between the modules and the control unit are communicated by the Controller Area Network (CAN) Bus. Each module can be controlled independently. By modifying the software of the system, the proposed drive system can be implemented in various electrical vehicles without changing circuit design. The developed system can be operated at forward, backward, and rotating motions. By limiting the armature current, the vehicle can be operated under the power saving mode. During the regenerative braking, the battery set is charged by the regenerative current. The experimental results show that the highest efficiency of the machine is 80 % with the motoring operation.