Methods, systems, and apparatus for reducing cogging torque in an electric machine

A stator for use in an electric machine, said stator comprising:

• an outer ring concentric about an axial center line of the electric machine;
• and
• a plurality of stator teeth extending radially inward from said outer ring toward the axial center line, each of said plurality of stator teeth comprising a stator tooth tip having a first surface, said stator tooth tip comprising a first end, a second end, and a center section therebetween, said first end and said second end taper away from the axial center line such that a distance between said first surface and the axial center line is greater at said first end and said second end than at said center section, said first surface configured such that an amplitude of a native cogging torque fundamental is reduced, a higher harmonic back EMF is reduced, and a fundamental cogging torque at a pole pass frequency and a slot order frequency is not substantially increased.

A method for reducing cogging torque in an electric machine that includes a rotor and a stator, said method comprising:

• configuring the rotor to rotate relative to the stator, the stator including a plurality of stator teeth each including a stator tooth tip;
• and
• determining an angle of a first end of the stator tooth tip relative to a center section of the stator tooth tip that results in a graded air gap when assembled with the rotor, the graded air gap facilitates reducing an amplitude of the cogging torque at a fundamental frequency while maintaining or reducing the amplitude of the cogging torque at at least one other frequency.