Maximum power limits of small single-phase permanent magnet drives

The authors deal with the theoretical limitations on the field-weakening performance of small single-phase nonsalient permanent-magnet motors when driven from an inverter with limited volt-ampere rating. A specific normalisation is introduced to obtain advantageous normalised parameters. It is shown that a theoretical infinite constant power speed range can be achieved, even with the ohmic voltage drop, by properly choosing the armature flux linkage. The effect of normalised parameters on the output characteristics is analysed and presented in the normalised parameter plane. The number of turns of the winding is computed and applied to an existing singlephase hybrid motor. A wide range of normalised parameter values exists for ths structure.