Fractional Slot Windings with a Coil Span of Two Slots and Less Content of Low Order Harmonics

Fractional slot windings with a winding step of two slots can bridge the gap between classical distributed windings and fractional slot concentrated windings. Even though the harmonic content of such windings is lower than that one of fractional slot concentrated windings, harmonics with a small ordinal number compared to the pole pair number can still be annoying. This paper presents a method for the design of windings with reduced low order harmonic content. First it gives a short review on three-phase windings with a coil span of two slots. Thereafter it shows how an appropriate choice of another winding number for some coils or some swaps in the assignment of coils to phases can lower disturbing harmonics of low order. The design procedure uses the star of slots. It is applicable also to multiphase machines: a five-phase machine serves as example.