Taking Sensors Out of Motors

This article discusses that advanced signal processors are replacing the feedback sensors that had been required for motor control in applications ranging from disk drives to appliance motors. The traditional method of closed-loop motor control has been to use one or more sensors to provide feedback. A growing number of applications, however, are now eliminating the sensor through one of several methods, such as back electromotive force (EMF) or inductance measurement. Sensorless motors are best suited for applications where speed control is needed, but precise position control is not critical. Sensorless motors are proving to be most appropriate for applications where the position of the rotor does not have to be pinpointed with great accuracy and all that is needed is speed and torque control. Prime candidates for sensorless motors are applications where open-loop scalar control had been used but better speed regulation and more torque at low speed are needed.