BLDC motors with surface mounted PM rotor for wide constant power operation

This paper presents different methods to adapt the characteristics of surface mounted permanent magnet motors in order to perform a constant mechanical power operation on a wide speed range while minimizing the inverter current rating. Different armature configurations (conventional lap winding, concentrated winding and polyphase claw pole structures with centralized-concentrated windings) are compared by means of simplified analytical design models. A special drive configuration which maximizes torque to amp ratio is also presented. This configuration is using a multi-star winding motor with different number of turns. An experimental validation is presented in the case of a 3-phase brushless DC motor fed by 120° rectangular current waveforms.