Comparison and simulation of rotor flux estimators in stationary and rotating reference frame in the vector control of induction motors for low-speed applications

The appropriate speed control of induction motors especially at low speeds for rail transportation systems, lifting platforms with high power, electric motors and deep floating shafts, etc. is of particular importance. The vector control method using the two-phase and three-phase transformations and Clarke Park transformations is able to separate the components of the control components of flux and torque control of the motor. This separation makes the basis of vector control which we can apply control approaches on flux and torque individually like DC motors. In free mode sensor, an estimator is used to the speed of motor in the control process. At low speeds because of the frequency dependent parameters and the motor temperature in estimator equations, the accuracy in the in the rotor flux estimators comes down. In the reference frame status was dependent on the stator equations and the stator parameters are effective and in the rotating reference frame, the rotor time constant is a factor in the estimator. In this paper the performances of rotor flux estimators both stationary and rotating reference frames are compared for use at low speeds. The results of this study has been demonstrated the simulation results. These results suggest that using the idea on the rotor flux estimators in rotating reference frames, it is suitable for low speed applications. The idea is to correct the rotor constant time. Therefore, using an estimator, it can be expected to have a significant improvement in the torque dynamic response and rotor speed at low speeds.