High-order Sliding-mode Observer For Sensorless Induction Motors

The induction motor (IM) has been extensively used in many applications due to its simply construction, lower repair and maintenance costs, high reliability and relatively low manufacturing cost. The field orientation control (FOC) technique makes the IMs similar to the DC motors. But FOC needs the accurate information on both the magnitude and the position of the rotor flux and the rotor speed for the transformation. The information can be obtained from the direct measurements or indirect estimation methods. The former needs special sensors and is difficult for practical applications. Now the latter is generally used for obtaining the rotor flux and speed using the stator voltage and current. A lot of methods have been proposed, such as Luenberger observer. However, these methods are all dependent on accurate mathematical model of IM, and lack of robustness. Sliding-mode has attractive advantages of robustness to disturbances and low sensitivity to the system parameter variations. Sliding-mode observer can be used for the estimation using the equivalent control signal. The phenomena of the chattering exists in traditional sliding-mode control restricting the actual application of sliding-mode control.This paper proposes rotor flux and speed estimation methods based on high-order sliding-mode and terminal sliding-mode for implementing the FOC of IMs. The rotor flux and speed of the motor can be estimated using the smooth equivalent control signal of the observer. Simulation research using Matlab software shows that the high-order sliding-mode observer realizes the accurate observation of rotor flux and speed, has robustness, and effectively restrains the phenomena of chattering existing in traditional sliding mode control.Finally, this paper builds software and hardware experimental platform for the sensorless IM system based on high-order sliding-mode observer, using the PCI-1710U data acquisition card manufactured by Advantech Company, and acqui siting the stator voltage and current in the Lab VIEW. Then this paper uses the acqui sited data into the observer in MATLAB to observe the rotor flux and speed, and compare the results to the reference given by the vector control system to verify the correctness of the theory through the actual experiment.