Design optimization of an axial gap permanent magnet brushless DC motor for electric vehicle applications

This paper describes a method of design and multiobjective optimization of an axial field permanent magnet brushless DC machine (BDCM), primarily aimed for electric vehicle propulsion applications. The disc type permanent magnet brushless DC motor has two stator windings connected in parallel with its rotor sandwiched between them. The simplified design equations for an axial gap trapezoidal back EMF motor are obtained and programmed using the software package QPRO. Then using classical design approach, design parameters for a 100 hp, 3200 RPM, 216 V BDCM are obtained. This design configuration is then used as the starting design point for the multiobjective optimization process, where the objective is to maximize the efficiency and the specific power. The feasibility frontier is obtained as a set of optimal solutions, from which a most suitable design parameters can be selected depending on the user preferences. The advantage of this method is that much time is saved in developing the optimization program. Also, the motor design engineer does not have to be an expert in optimization theory in order to obtain a superior design with a very short time.