MANY VARIABLE speed applications found in industry today make use of AC induction motor and drive technology. AC technology is both cost effective and highly commoditized. However, when machine designers are called upon to maximize performance in variable speed applications, they often select the permanent magnet synchronous motor (PMSM) over AC induction alternatives. In performance driven applications, the physical capabilities inherent to the PMSM motor can tip the scale in favor of this more expensive technology.
This article examines the typical selection criteria and justification for PMSM technology. Multiple application examples are discussed including; high-speed centrifuges, turbo compressors, instrument grade spindles, and handheld tools. Basic PMSM motor and drive operation is also examined. Three practical drive techniques are presented to improve motor efficiency, precision and bandwidth in high performance applications. The discussed techniques include; center aligned modulation, mapped encoder feedback correction, and adaptive torque feed forward.