Modeling and Investigation of Asymmetric Rotor Eccentricities in Double-Rotor Single-Stator Axial-Flux Permanent Magnet Machines

The dual-rotor single-stator axial flux permanent magnet machine (DRSS AFPMM) demonstrates superior power density and torque output capabilities through dual air-gap topology and compact magnetic circuit design. However, the additional rotor introduces increased probability and complexity of eccentricity faults, manifesting as spatiotemporal asynchrony in dual air-gap magnetic flux density (MFD) distributions. Conventional single-rotor eccentricity models prove inadequate for characterizing asymmetric faults in this specialized architecture. A novel analytical modeling framework is developed for asymmetric eccentricity in DRSS AFPMMs, employing a coordinated representation system of phase displacement and normalized amplitude. This methodology maps dual-rotor eccentricity states to compound air-gap field modulation processes: rotor axis eccentricities (RAXE) are described through dynamic pole-pitch correction modeling, while rotor angular eccentricities (RAGE) are translated into air-gap permeance amplitude modulation principles. Subsequent analysis of the electromagnetic performance under asymmetric eccentricity conditions was conducted by double air-gap offset field superposition. A loss coefficient is established to evaluate flux linkage reduction under RAXE. Furthermore, a dual air-gap MFD deviation model is formulated to analyze back-EMF attenuation caused by magnetic excitation misalignment fault. The proposed methodology is validated through finite-element analysis and experimental testing, confirming its effectiveness in predicting fault-induced electromagnetic variations.