Low Torque Ripple and High Torque Trapezoidal Permanent Magnet Bi-Directional Magnetic Field Modulation Motor by Magnetomotive-Force-Oriented Design

In this paper, in order to suppress torque ripple and enhance output torque for bi-directional magnetic field modulation (BD-MFM) motors, a novel trapezoidal permanent magnet (PM) bi-directional magnetic field modulation (TBD-MFM) motor is proposed and designed from the perspective of magnetomotive-force-oriented design. First, the relationship between MMF, airgap magnetic flux density, and torque is explained based on the magnetic field modulation principle of BD-MFM motors. Then, the contribution of PM airgap flux density harmonics to cogging torque is calculated using Maxwell’s tensor method, and a harmonic torque contribution coefficient is defined to compare the torque contribution of the PM airgap flux density harmonics. Based on the above, the important PM airgap flux density harmonics are selected. In addition, by the design of PM directional arrangement, trapezoidal PM, and trapezoidal magnetic barrier from the perspective of MMF, an MMF-oriented design of the airgap flux density harmonics can be achieved. Finally, the electromagnetic performance of the proposed TBD-MFM motor is compared in detail. It is demonstrated that the proposed TBD-MFM motor achieves higher output torque and lower torque ripple, thereby verifying the effectiveness of the MMF-based design method.