Sensorless speed torque control of induction machines has been widely used in many industrial applications. The simple method of direct vector control can provide tacholess control as well as more complex approaches. In this method, the motor flux can be obtained by measuring voltage and current and integrating motor back electromotive force. The only required motor parameter is stator resistance. However, implementation of an integrator is not an easy task because a pure integrator has dc-offset problem. In addition, variations of stator resistance due to changes in temperature highly deteriorates the accuracy of this method at low speeds. In this paper, to overcome the dc-offset problem, a modified integrator is used, and a method for estimating stator resistance is proposed. This method represents accurate torque control over a wide range of speed and load conditions, even at zero rotor speed and heavy load torque.

Keywords: Induction motor, Direct Vector Control, Stator Resistance Estimation, Modified Integrator

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