Sensorless speed measurement in induction motor drives using a double algorithm approach : a thesis submitted to the Institute of Information Sciences and Technology, Massey University, in partial fulfillment of the requirements for the degree of Master of Technology in Information Sciences and Technology
Sensorless speed control in induction motor drives is a new emerging field offering many benefits over traditional methods. The thesis examines a method of improving the performance of sensorless speed control systems using a double algorithm approach. The rotor slot harmonics are used to determine the speed of an induction motor. This is possible as the rotor slots produce slot harmonics in the airgap field, which modulate the stator flux linkage at a frequency proportional to the rotor speed. This method, however, has limitations, at low revolutions the harmonics cannot be detected. An empirically derived formula is used to determine the speed of rotation in the speed range where the rotor slot harmonics cannot be used. The rotor slot harmonics are located and the empirical formula determined for a given 0.33HP induction motor. The final proposed system uses both mentioned methods and is simulated to determine the theoretical performance. The speed detection algorithm using the rotor slot harmonics is also implemented, with good results.