Implementation issues of real time position estimation for induction motors using rotor slot harmonics

In this paper, an approach to identify rotor slot harmonics, from motor currents or from induced voltage in an internal or external search coil voltage is described. The importance of this method is that instantaneous value of the rotor slot harmonics can be determined in real time. In this manner, it is possible to determine motor speed or rotor position of a motor in a short enough time, for use in vector control. This method is independent of motor parameters. Using this method an additional feedback becomes available in implementation of so called “sensorless” vector controlled drives and therefore much better performance can be obtained. The paper describes how the data obtained from search coil or current can be handled and the method can be implemented on a microprocessor.