Design of fractional slot windings with coil span of two slots for use in six-phase synchronous machines

Abstract

The use of a winding step of two slots attempts to strike a balance between traditional distributed windings and fractional slot concentrated windings. It promises less ohmic losses and space for the end windings than distributed windings and less harmonics than fractional slot concentrated windings. This paper gives an introduction into the design of windings with a winding step of two slots for six-phase machines. The design procedure relies on the star of slots. Whereas for a given combination of slots and poles, the winding of a three-phase machine is unique, there exist several winding designs for six-phase machines. They differ by the shape of the phase belts and by the phase shift between the two three-phase subsystems. The definition of two characteristic figures facilitates the comparison of these windings: one describes the content of sub-harmonics in the magnetomotive force, the other is a measure for rotor eddy losses. The comparison reveals that windings with 12 small phase belts are better as long as fault tolerance is not an issue. If this is the case, windings with wider phase belts and a proper choice of pole number and phase shift are superior.

Keywords

• rotors
• eddy currents
• machine windings
• synchronous machines
• permanent magnet machines
• fault tolerance
• finite element analysis
• common distributed windings
• end windings
• traditional distributed windings
• winding step
• six-phase synchronous machines
• fractional slot windings
• phase shift
• phase belts
• six-phase machines
• winding designs
• three-phase machine
• slots