Effect of Magnetic Wedge Characteristics on Torque Ripple and Loss in Interior Permanent Magnet Synchronous Motor

An interior permanent magnet synchronous motor (IPMSM) is characterized by high efficiency in a wide range of applications. However, when operating at high speeds, torque ripple and rotor loss occur because of the spatial harmonics generated by fluctuations in the airgap permeance. This study demonstrates the suppression of torque ripple and harmonic loss by magnetic wedges using finite element analysis (FEA). First, the authors examined the torque and loss characteristics by varying the slot opening width and relative permeability of the magnetic wedge. Results indicate that the torque ripple can be suppressed even if the opening width is widened to half the slot pitch. However, this improvement effect saturates when the relative permeability of the magnetic wedge becomes larger than µr = 10. Furthermore, the authors confirmed the effect of the magnetic wedge by visualizing the harmonic components of the eddy current loss. The findings reveal that the eddy current loss represents a trade-off between the stator and rotor when using the magnetic wedge.