An Analytical Model for Stray Magnetic Field of External Rotor Permanent Magnet Motor Considering Unsaturated Magnetic Permeability

Stray magnetic field (SMF) is widely used in motor fault diagnosis due to its noninvasive advantage. To address the issue that unsaturated magnetic permeability (UMP) cannot be considered in existing analytical models (AMs), this article proposes an improved AM for SMF of external rotor permanent magnet motor (ERPMM). It consists of three vital parts: first, an improved subdomain (SD) model is proposed to calculate the magnetic permeability at different radii of the iron core; second, a multiple radial permeability iteration algorithm is developed and combined with the SD model to automatically predict permeability considering the influence of motor operating conditions and core radius; finally, the predicted magnetic permeability and the improved complex boundary conditions (BCs) are applied to enhance the computational accuracy of micro-Tesla magnetic fields. The harmonic law of SMF of ERPMM is investigated, as well as the functional mechanism of magnetic permeability on SMF through the improved AM. The accuracy is verified through experiments. The AM can achieve accuracy comparable to that of the finite element model (FEM), while being more efficient. This article provides a new idea to calculate the SMF efficiently and accurately.