Design Aspects for Fractional-Slot PMBLDC Motor

In this paper the design aspects for fractional slot permanent magnet brushless DC motors (PMBLDCM) are presented. Fractional slot machines are characterised by a noninteger number of slots per pole per phase. They have an inherently low cogging torque and possess a fault-tolerant capability. The concentrated phase coils, preferably placed on every other tooth with double the numbers of turns for an increased phase inductance, limit short circuit currents and can allow sustained operation under fault conditions. A further design consideration is the use of an irregular distribution of slots, which can enhance a low-to-free cogging torque operation and increased phase inductance. The paper concludes with some practical results from a 3 phase 12 slot 4 pole prototype machine.