Improved Dtc Of Induction Motor With Fuzzy Resistance Estimator

Direct torque control (DTC) minimizes the use of machine parameters [1, 2]. Among all methods of torque control in induction motor, direct torque control (DTC) seems to be particularly interesting being independent of machine rotor parameters and requiring no speed or position sensors [3, 4, 5]. In spite of its simplicity, DTC is capable of generating fast torque responses. In DTC the torque and stator flux are regulated to their command values by selecting the inverter switching state, which gives the proper changes in the torque flux [6]. As for any induction motor drive without Shaft encoder, employing stator voltages and currents carries out the flux estimator. As the speed decreases to lower values, the flux estimation deteriorates owing to the influence of inaccurate values of the stator resistance. A stator resistance error causes the estimated stator flux to deviate from its theoretical trajectory [3],[7]. The magnitude of stator current vector can be used, to correct the stator resistance of the controller to match the machine resistance, during any change in stator current of machine. The magnitude of stator current vector in direct torque control is a function of torque and flux [8].