Unbalanced Axial Forces in Axial-Flux Machines

This paper performs an analysis of the variation of unbalanced forces with airgap length in axial-flux machines. A simple analytical approach is used to provide insights into these key parameters and the results compared with finite-element results for both axial-flux permanent magnet (PM) and induction machines. For PM and current-driven induction machines, the two most important parameters are the ratio of the effective magnet/core magnetic path length to the nominal airgap, and the ratio of the saturation flux density to the nominal airgap flux density. For voltage-driven induction machines, the key parameter is the ratio of stator leakage inductance to the nominal magnetising inductance.