Sensor-less speed control of an induction motor

Vector control systems of induction motors without speed sensors have been earnestly developed to obtain a simple construction. To estimate the rotor speed, these systems require information of machine parameters such as secondary resistance. Therefore their performance is sensitive to variations of secondary winding temperature. The authors propose two useful calculation methods for a speed sensorless system. The first is a rotor speed calculation method by which the exact speed can be computed directly. The method does not require information of the secondary resistance, which makes it free from variations of secondary resistance. The second is a direct secondary resistance calculation method. It can be applied to compensation in speed sensorless vector control for exact speed estimation of secondary resistance. The effectiveness of the proposed methods are verified by digital simulation and experimental results. In this article, the influence of the machine and control circuit parameters are also examined