Optimization Design of a Segmented Halbach Permanent-Magnet Motor Using an Analytical Model

We present an optimization design of a slotless permanent-magnet brushless dc motor (400 W, 6000 rpm), with two-segment Halbach arrays. The optimization is based on a motor analytical model which is obtained by solving the magnetic scalar potential using the Fourier series. We show that the iron-cored Halbach configuration is better than the classical one and that the air-cored Halbach configuration is even better. This means that the rotor iron can be completely omitted. We verify the results by using the finite-element method.

I. Introduction

Permanent-Magnet (PM) motors with Halbach arrays have become more and more attractive for many applications [1]. Compared to the magnetic field in the classical configurations (with the parallel or radial magnetization), that created by an Halbach array is more self-shielding, which means that it is not only the back iron which provides the return path of the magnetic flux. By adjusting the number of Halbach array segments, the air gap field can be shaped. However, too many segments significantly complicate the motor construction [2]. A special type of the Halbach excitation is the ideal one: it creates an ideal sinusoidal field and is completely self-shielding, but on the other hand it is extremely difficult to industrialize, as it requires a special magnetizer.