Thermal Characterization and Comparison of Intelligent Power Modules for Permanent-Magnet Synchronous-Motor Drives

A permanent magnet synchronous motor (PMSM) is a motor that uses permanent magnets to produce the air gap magnetic field rather than using windings. The replacement of rotor windings by permanent magnets results in simpler construction, reduction of losses, and greater efficiency. These motors show significant advantages, engaging the interest of engineers and industries for their utilization in many applications.

The properties of permanent magnet materials affect the performance of the motor, thus their knowledge is necessary to understand the increasing shift from DC and induction motors to PM motors. The earliest manufactured magnet materials were hardened steel. Magnets made from steel were easily magnetized. However, they could hold very low energy and it was easy to demagnetize. In recent years other magnet materials such as aluminum nickel and cobalt alloys (Alnico), strontium ferrite or barium ferrite (Ferrite), samarium cobalt (SmCo) and neodymium iron-boron (NdFeB) have been developed and used for making permanent magnets. The rare earth magnets are categorized into two classes: Samarium Cobalt (SmCo) magnets and Neodymium Iron Boride (NdFeB) magnets. SmCo magnets have higher flux density levels but they are very expensive. NdFeB magnets are the most common rare earth magnets used in motors these days.