Design considerations for high-speed sensorless permanent magnet brushless DC motors

There is increasing interest in high-speed, viz. >100 krpm, permanent magnet, brushless DC motors for a wide range of applications. There is also significant interest in sensorless operation by detection of the zero-crossings of the back-EMF waveforms, for which a number of IC´s are available commercially. This paper describes some electromagnetic and mechanical design considerations specifically in relation to the sensorless operation and rotor resonances of 120 krpm high-speed brushless DC motors.