An analytical method for predicting the magnetic field of machines

What is it about?

A doubly-salient relative permeance method is presented herein to predict the magnetic field of bearingless flux-switching permanent-magnet machines (BFSPMMs). Firstly, the subdomain model method is used to compute the magnetic field of slotless BFSPMMs. Then, the slotting effect of the stator and rotor is obtained by the doubly-salient relative permeance method. By combining the two above, the air-gap magnetic field of slotted BFSPMMs can be obtained. The doubly-salient relative permeance method is based on the theory of the subdomain model method. The whole doubly-salient structure is divided into several subdomains, and the Laplace equations for subdomains are established. Then, according to the boundary conditions between subdomains and the core, and the continuity conditions between adjacent subdomains, the equations are solved to calculate the slotting effect. Based on the proposed analytical model, the flux density and electromagnetic performances including back-EMF, torque, and suspension force are predicted and compared with the finite element method (FEM) results. Furthermore, the back-EMF of the prototype motor is measured and the suspension experiments are carried out based on the analytical method. The comparison results and experiment results verify the validity of the analytical method.

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Why is it important?

Compared with the subdomain model method, the air-gap relative permeance method has higher universality and can be applied to the motors with different structures. However, the relative permeance function is generally obtained through the single-slot model with an infinite depth, so the magnetic interaction between slots is neglected, and the calculation accuracy is insufficient when it is applied to motors with the doubly-slotted structure. In addition, the traditional complex relative permeance function is not applicable for the doubly-slotted motors, which will lead to the failure to obtain the tangential flux density and greatly reduce the calculation accuracy of the electromagnetic performances. Therefore, it is of great significance to study a complex relative permeance function for doubly-slotted motors.

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