Sensorless control of PMSM drives

When compared to induction motors, permanent magnet synchronous motors (PMSMs) feature higher torque density, improved efficiency and increased constant power speed range. These distinct advantages have resulted in PMSMs being employed in a myriad of industrial applications. Traditionally, the open -loop V/f control scheme has been the preferred method for PMSM drives owing to its inherent simplicity. Nevertheless, as this method is derived from the steady-state model of the machine and does not rely on any motor feedback information, it offers very poor dynamic performance and is susceptible to external disturbances. Thus, its adoption is limited to applications whose transients are relatively unimportant or occur over long intervals. If high torque and speed dynamic performance is required, the vector control method becomes a necessity.