Improved variable speed sensorless servo system by disturbance observer

An improved variable-speed sensorless servo system consisting of an inverter-fed permanent magnet field synchronous motor without any shaft-mounted sensors and with a disturbance torque observer is discussed. The sensorless servo system shows a tendency to become unstable by disturbance torques to the motor. A disturbance torque observer based on a digital signal processor was developed, and the motor current was compensated by the observed torque. Experimental results obtained by the prototype drive system with the disturbance torque observer are compared with those obtained by a sensorless servo system without the observer. These results predict the sufficient performance of the variable speed drive