The stable operation of a bearingless permanent magnet slice motor (BPMSM) requires smooth and controllable radial suspension force. However

existing methods for slot/pole quantity selection cannot consider the coupling between magnetic field harmonics

leading to suspension force ripples when the fundamental wave of the suspension field harmonics differed from the permanent magnets by a pair of poles. To overcome this limitation

the generation mechanism of radial suspension force is analyzed based on the magnetic field modulation effect

and the conditions required for harmonic-induced ripples are determined. The causes of suspension force ripples are classified

and three constraints for selecting the slot/pole quantities to achieve high suspension performance are derived. Simulations are then conducted to identify feasible slot/pole matching selection that eliminates harmonic coupling. Finally

a 6-slot/2-pole BPMSM is manufactured and experimentally tested. Both simulation and experimental results verify that the proposed method can effectively reduce suspension force ripples and enhance the suspension performance of BPMSMs.