I. Introduction
Rare-Earth permanent-magnet (PM) brushless motors possess the advantages of high efficiency, high torque/power density, and low maintenance. These machines are usually assembled with the magnets premagnetized. However, as the motor size and the output power increase, the handling of the premagnetized components can be difficult. These increase the manufacturing cost [1], [2]. To highlight the differences in manufacturing techniques, Fig. 1(a) presents the conventional manufacture process for rare-earth PM motors, whereas Fig. 1(b) illustrates the process with postassembly magnetization. Problems occur in the steps of magnet insertion and rotor assembly, as shown in Fig. 1(a). Therefore, with this process, it is difficult to produce large PM motors with high power (into the kilowatt range). Postassembly magnetization represents a more satisfactory solution to these manufacturing problems. Here, the motor is fully assembled before the magnets are magnetized by applying a current pulse to the motor windings. This is commonly used when manufacturing cheaper and smaller ferrite magnet machines. Fig. 1(b) shows that magnetization is performed in the last step, and the assembly of the machine is more straightforward.
Manufacturing processes for brushless PM machines. (a) Conventional manufacture. (b) Postassembly magnetization.