SUMMARY (Induction Motor)

10.6
Sensorless drives operate without speed or position sensors, which increases their robustness and reduces the equipment cost. Quality of operation of sensorless drives falls between that of scalar control drives and vector control drives with speed/position sensors.
Estimators and observers of flux, torque, and speed constitute crucial components of control systems for sensorless ASDs. Estimators, based on dynamic equations of the induction motor, operate in the feedforward
manner, while observers, which use certain feedback arrangements, are capable of correction of their estimates. Correct information about motor parameters is also necessary for proper operation of sensorless drives. Therefore, parameter adaptation and self-commissioning are important parts of the control process in these drives.
Commercial ASDs can be divided into three major classes, namely, Constant Volts per Hertz, Sensorless Vector, and Field-Oriented drives. In addition to the flux, torque, speed, and position control systems, commercial drives possess numerous features enhancing their operation, and they are equipped with various protection systems. The drives cover a wide range of rated power, from a fraction of one kilowatt to tens of megawatts.