Suppression of Even-Order Harmonics and Torque Ripple in Outer Rotor Consequent-Pole PM Machine by Multilayer Winding

The fractional slot concentrated winding consequent pole (CP) permanent magnet (PM) synchronous machines can improve the PM utilization ratio. However, the even-order harmonics exist in phase back electromotive forces (EMFs) for specific slot and pole number combinations, resulting in high torque ripple. Therefore, the multilayer winding is employed in this paper to reduce the torque ripple by suppressing the even-order harmonic back EMFs. The principles of both even-order harmonic back EMFs and torque ripple suppression by the four-layer windings are illustrated. The electromagnetic characteristics of the CP PM machine with four-layer windings are compared with that of PM machines with the traditional and CP rotors by finite-element analysis. It is demonstrated that the four-layer winding can suppress the even-order harmonic back EMFs and torque ripple in the machine with CP rotor. The prototypes of both the traditional rotor and CP rotors with four-layer wingdings are manufactured and tested to verify the theoretical analysis.