Pole-change motors using phase-mixing techniques

The paper outlines the development of a new type of pole-change motor giving three or five speeds. The development is an extension of the principles of `phase-mixing¿, which were explained in an earlier paper which described a continuously-variable-speed brushless induction motor. In the earlier machine a fraction of the periphery could not be used owing to the continuously variable pole-pitch requirement, and the stator windings in the active arc were fed from phase-shifting regulators. The present paper shows how acceptance of a finite number of specific speeds may be exploited to enable the whole of the periphery of the machine to be used, and, at the same time, to replace the phase-shifting regulators by switches. The complexity of the switch arrangement depends on the number of speeds required. The paper concludes by describing 2-speed machines based on the phase-mixing principle in which the number of terminals on the machine is reduced to six. Theoretical investigation of the harmonic effects is considered, and this material is supported by experimental results obtained from several machines. High values of copper utilization and low harmonic content are shown to be possible with the phase-mixing technique.