Direct torque control (DTC) of an induction motor fed by a voltage source inverter is a simple
scheme that does not need long computation time. The main advantage of DTC technique is that it
is not sensitive to the variation of motor parameters except the stator resistance in its flux observer
especially at low speed operation. The stator resistance can be changes during the motor operation
due to ambient temperature or frequency. This paper, introduces an additional on Line fuzzy
controller used to estimate the stator resistance for the DTC flux observer. The inputs for the
proposed fuzzy controller are speed and stator current errors between the traditional DTC flux
observer values, which using constant value of the stator resistance equals to the nominal value,
and their values using the proposed on line stator resistance estimator values. The induction motor
saturated pi model is used which is more practical than the approximate linear model especially in
the large motors. The saturation function and the motor parameters are identified experimentally.
The proposed technique response is checked at sinusoidal and trapezoidal reference speeds. The
results show good improvements of the DTC response using the proposed adaptive fuzzy
controller during on line variation in the stator resistance of the induction motor