An Accurate Subdomain Model for Magnetic Field Computation in Slotted Surface-Mounted Permanent-Magnet Machines

TLDR

The paper introduces an accurate analytical subdomain model for computing the open‑circuit magnetic field in surface‑mounted permanent‑magnet machines with arbitrary pole and slot configurations, including fractional slots, while accounting for stator slotting effects. The model is derived by solving field equations in each regular subdomain (magnet, air‑gap, stator slots) and applying interface boundary conditions, accurately capturing slot interaction, radial/parallel magnetization, rotor topology, magnet permeability, and periodic boundary conditions, and it yields back‑EMF, torque, cogging torque, and unbalanced magnetic force. The model outperforms the conventional one‑slot‑per‑pole subdomain model in accuracy, as confirmed by finite‑element and experimental validation.

Abstract

The paper presents an accurate analytical subdomain model for computation of the open-circuit magnetic field in surface-mounted permanent-magnet machines with any pole and slot combinations, including fractional slot machines, accounting for stator slotting effect. It is derived by solving the field governing equations in each simple and regular subdomain, i.e., magnet, air-gap and stator slots, and applying the boundary conditions to the interfaces between these subdomains. The model accurately accounts for the influence of interaction between slots, radial/parallel magnetization, internal/external rotor topologies, relative recoil permeability of magnets, and odd/even periodic boundary conditions. The back-electromotive force, electromagnetic torque, cogging torque, and unbalanced magnetic force are obtained based on the field model. The relationship between this accurate subdomain model and the conventional subdomain model, which is based on the simplified one slot per pole machine model, is also discussed. The investigation shows that the proposed accurate subdomain model has better accuracy than the subdomain model based on one slot/pole machine model. The finite element and experimental results validate the analytical prediction.