Winding and Electromagnetic Analysis for 39-Slot/12-Pole Frameless Permanent Magnet Synchronous Motor

In applications like robot joint and medical instruments with limitations for space and mass, frameless motor is an ideal choice as it doesn't contain shell, bearing, etc. In view of frameless PMSM with 39 slots and 12 poles, a method adopting 6 sets of three-phase winding for phase division and arranging coils in wave winding is proposed in this paper. Specifically, three-phase winding in every set is differently divided by approximate 60° phase belt, so that composite electromotive forces (EMFs) attached to same phase in different sets are not coincide but adjacent. Then embed double-layer short-pitch distributed wave winding of each set of three-phase winding according to this phase division and successively connect coils belonging to same phase in series. In this way, not only deviations in amplitude and phase among three-phase fundamental EMF caused by single set of winding can be reduced, but also higher winding factor can be obtained. Additionally, it can also save the copper wire and make the winding end shorter to achieve lighter weight and higher efficiency. Theoretical analysis about EMF and magnetomotive force (MMF) in this paper showed the validity of this design, while simulation results proved that the frameless PMSM has excellent electromagnetic performance. Prototype machine also shows that the arrangement of copper wires is very uniform and there is no more additional winding end.