An Analytical Model of Concentric Layer Structure for Canned Machines, Part II: Magnetic Field

Abstract

The can loss is the main constraint to high efficient and high power density operation of canned machines and most analyses are FE based or with resort to empirical equations. Detailed study of the can effect is necessary, which leads to detailed electromagnetic analysis. Electromagnetic field analysis plays the central role in predicting output characteristics. Besides the numerical methods [1, 2], analyses fall into semi-analytical [3, 4] or analytical methods. As to the analytical, a couple of alternatives are predominantly developed. One is the Maxwell’s theorem [5–11]. Specifically in [5, 6], the machine is divided into sub-domains (iron cores, airgap, slots and magnets). Our previous work has been applied on an induction, permanent magnet or switched reluctance machine [8, 12, 13]. Magnetic vector potential of each domain is calculated based on magneto-motive force (MMF) distribution as prerequisite. For simplicity a smooth airgap of constant radial length is assumed. By applying Carter’s factor [14] or airgap permeance function [8], the airgap is radially enlarged to account for slotting effect. Another alternative focuses on airgap flux density by studying respectively airgap permeance function and MMF distribution [9]. However when cans are concerned, both of these methods may cause numerical deviation.