Comparison of Induction Machine Performance with Distributed and Fractional-Slot Concentrated Windings

Fractional-slot concentrated windings have been gaining a lot of interest in permanent magnet synchronous machines. This is due to the several advantages provided by this type of windings which include: shorter non-overlapping end turns, higher efficiency, higher power density, higher slot fill factor, lower manufacturing cost, better flux-weakening capability resulting in wider constant power speed range, and fault-tolerance. However, the tradeoffs involved in using this type of windings in induction machines have not been addressed in literature. This paper examines induction machine performance with fractional-slot concentrated windings using the standard distributed lap windings as reference. Four designs are compared and various performance tradeoffs highlighted. The first machine has integral-slot distributed 2 slots/pole/phase lap winding and it serves as the reference winding. The second machine has a double-layer 1/2 slot/pole/phase winding, a workhorse for brushless DC machines. The third machine has double-layer 2/5 slot/pole/phase winding. Lastly, the fourth machine has single-layer 2/5 slot/pole/phase windings. The comparison includes torque-speed curves (including the effects of major space harmonic components), rotor bar losses, and ripple torque levels.