Comparison of Radial Electromagnetic Force in Rotor-PM and Stator-PM Machines by General Airgap Field Modulation Theory

Radial electromagnetic force analysis is an important step for further vibration and acoustic investigation in electric machines. This paper investigates and compares the radial electromagnetic force harmonics in rotor permanent magnet (PM) machines and stator-PM machines in no-load mode based on the general airgap field modulation theory (GAFMT), taking a surface-mounted permanent magnet (SPM) machine and flux-reversal permanent magnet (FRPM) machine respectively as examples. By GAFMT, the difference in force harmonics is explained by revealing the mechanism of force modulation in these two types of machines. The teeth modulation effect is investigated as well.