Permanent-magnet brushless direct-current motors are easy to maintain, compared with direct-current motors. Therefore, they are attracting attention. In this paper, the authors discuss a non-salient pole brushless direct-current motors. Usually, the quadrature armature current which contributes to torque generation is supplied in this motor. But, in this case that the source voltage cannot be increased by supplying the direct armature current, that is, equivalently field weakening, a quadrature armature current can be increased. Consequently, the motor torque increases. In the case that the load characteristics are settled, the motor torque can have a maximum Tm by adjusting a direct armature current. At this time the rotational speed and output are maximum also. Tm changes with the change of the motor parameters. Consequently, the motor parameters which maximize Tm are optimal. In this paper, the authors have clarified an optimal parameter determination method considering by the load torque-speed characteristics and, armature resistance by the power factor, and efficiency where the motor has optimal parameters and generates the maximum output. Furthermore, the theory obtained has been confirmed experimentally by the authors.
Variation of Saturated Reactances of a Salient-Pole Synchronous Motor in the Field-Weakening Region