A hybrid sensorless stator-flux oriented control method for induction motor drives

In the proposed paper, an improved sensorless vector control method for induction motor drive systems is presented. The proposed method is based on a combined heuristic flux observer, which is designed especially for low speed operation, for a wide variety of load conditions. A closed-loop flux observer is achieving precise flux estimation for the load condition, while another observer is capable for low or no-load operation in the low speed range, without having the drift problems of the conventional observers. Combining the two observers results to an optimized observer, which obtains precise flux estimation in the low-speed range. Based on this, a direct stator-flux-oriented vector control method is implemented. In addition, sensorless speed control of the induction motor is achieved using a speed observer based on the model reference adaptive schemes theory and an optimally tuned speed controller. In the current work, the principle of operation of the closed-loop observer, as well as operation problems occurring at low and zero-load are discussed. In the need of efficient operation at zero-load, another observer is introduced. The two observers are combined and the resulting observer is presented. The operation and efficiency of the proposed method is investigated using the simulation and then experimental proof is obtained, where characteristic results are shown.