Introduction

Analytical techniques, such as finite element analysis, provide accurate solutions for two- or three-dimensional field distributions in complex geometries, which in turn may be used to predict device performance with similar precision. However, these techniques require a detailed definition of the geometry and boundary conditions to be solved, which assumes that an initial design already exists. While providing an accurate field solution for a defined geometry, they will not optimize it - suggestions for changes to dimensions, materials, excitations, etc. must come from the designer, to be analyzed via a field solution. Consequently, while computer-based field analysis is an effective tool for simulating a known device, it is too cumbersome for design optimization.

Preliminary designs are usually performed using a magnetic circuit model of the device in which each component or magnetic flux path is represented by a discrete element. Equations representing the magnetic circuit components are derived in this Chapter, and the elements they define are used in an equivalent circuit (similar in many respects to an electrical analog circuit). This is a simple model, which can be easily optimized for any performance requirements. Thereafter, field analysis may be employed to verify the operation of the device, and to fine-tune the design.