Axial Force Negative Stiffness in Axial‐Flux Electric Machines

ABSTRACT This paper examines the axial force negative stiffness of the induction and permanent magnet (PM) axial‐flux machines. Simplified analytical models are used to identify the key normalised machine parameters which affect the variation of the axial force with the airgap length. The analytical results are validated against finite‐element simulation and experimental results from axial force tests comparing the negative stiffness of the induction and PM axial‐flux machines. Finally, the effect of load, the use of double‐sided machines and tilting torque are examined.