Abstract

In this paper, an accurate analytical subdomain model to calculate electromagnetic performances of bearingless flux-switching permanent magnet (BFSPM) machines is developed. The entire region of the machine is divided into six subdomains, including slots, air gap, magnets, and so on. According to the Neumann boundary conditions between the subdomains and the iron and the continuity conditions at the interface between the adjacent subdomains, the magnetic field distributions of subdomains are obtained by solving the Maxwell equations. In addition, a method to compensate the saturation effect is proposed, and the magnetic saturation of the stator and rotor is considered by the actual B-H characteristics. Based on the proposed analytical method, the air-gap flux density distributions of the machine with different iron material under linear and nonlinear conditions are predicted. Further, the electromagnetic performances including the cogging torque, electromagnetic torque, flux linkage, back-EMF, inductance, and suspension force are calculated. These analytical results are compared with those obtained by the Finite Element Analysis (FEA) to verify the accuracy of the proposed analytical method.

Highlights

  • In recent decades, flux-switching permanent-magnet (FSPM) machines have attracted many scholars’ attention for its high power density, high torque density, and robust rotor [1]–[3]

  • FSPM machines are generally supported by traditional mechanical bearings, and a severe friction will inevitably occur between the rotor and the bearing at the high speed, which may increase the maintenance cost, or cause damage to the machine

  • In order to solve this problem, scholars applied the bearingless technology to FSPM machines, which are the bearingless flux-switching permanent-magnet (BFSPM) machines

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Summary

INTRODUCTION

Flux-switching permanent-magnet (FSPM) machines have attracted many scholars’ attention for its high power density, high torque density, and robust rotor [1]–[3]. Zhou: Analytical Calculation of Electromagnetic Performances of Bearingless Flux-Switching Permanent-Magnet Machine equivalent circuit (MEC) method [17], relative permeance method [18], Schwarz-Christoffel transform method [19], and subdomain model method [20], [21]. The subdomain model method considers the interaction between slots, so it has higher accuracy and is suitable for the prediction of the electromagnetic performances of BFSPM machines. When a large suspension force is required or the load is heavy, a large current flows into the armature winding, and due to the unique structure of the BFSPM machine, the machine can generate strong flux focusing effect to result in the iron saturation.

GENERAL SOLUTION IN ROTOR SLOT The Laplace equation for rotor slots is:
SOLUTION OF COEFFICIENTS TO BE DETERMINED
INTERFACE BETWEEN PM-SLOT AIR GAP AND PM
SATURATION EFFECT COMPENSATION METHOD
SATURATION FACTOR OF THE STATOR
ANALYTICAL RESULTS AND FEA VALIDATION
AIR-GAP FLUX DENSITY UNDER LINEAR CONDITION
CONCLUSION
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