Torque Ripple Minimization of Wound Field Synchronous Machines using Asymmetric Rotor Pole Spacing

Motors with low torque ripple are necessary for many applications such as automotive traction, robotics, and medical instrumentation. This paper presents a novel method to mitigate torque ripple in wound field synchronous machines (WFSM) using unequally pitched rotor poles. This method retains the same basic structure of salient pole WFSM rotors and does not require additional manufacturing steps. Details on the analytical formulation for the optimal pitch for alternate rotor poles to minimize the dominant order of torque ripple harmonic, along with FEA-based analysis are presented; the results for the unequally spaced rotor are compared with that of a baseline rotor and a 3-step skewed rotor through torque ripple maps, fourier analysis of torque waveforms, analysis of airgap radial pressure, and structural FEA analysis.