الفهرس 
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Abstract
Vector controlled induction motor drives are increasingly used in high-dynamic performance drive systems. The major disadvantage of the indirect vector control scheme is machine parameters dependency. These parameters are rotor resistance that varies with temperature and frequency and magnetizing inductance that varies with flux level in the machine. This thesis is aimed at developing proposed vector controlled induction motor drives taking magnetic circuit saturation into account.
In this thesis, a mathematical dynamic model of an induction motor as influenced by magnetic circuit saturation is developed. In this model the actual value of magnetizing inductance is determined by taking into account the magnetic circuit saturation as measured in the laboratory. Moreover, a modified structure of indirect vector controller scheme is proposed which involves the saturated value of the magnetizing inductance. The transient performances of the proposed drive system are presented and compared with those calculated in the absence of magnetic circuit saturation. The present results demonstrate that consideration of magnetic saturation improves the theoretical perfections and serve to make the motor control more accurate.
To avoid the problems associated with the speed sensor, a model reference adaptive system (MRAS) is used to estimate the motor speed. The estimated speed has been strongly affected by the thermal variations of stator resistance especially at low speed region. To improve the drive performances at low speed, simultaneous estimation of stator resistance and motor speed based on a modified MRAS has been proposed for obtaining accurate estimation of motor speeds. An on-line magnetizing inductance estimator has been used within the modified MRAS speed estimator to take the effects of magnetic circuit saturation into account. Digital simulations are carried out in order to investigate how the transient performances of the proposed speed sensorless are influenced by magnetic circuit saturation. The results demonstrate that the proposed sensorless drive scheme with the modified MRAS gives very accurate estimation for motor speeds in a wide range of drive operation. This is in addition to, high dynamic performances have been achieved and the estimated stator resistance tracks well its actual values.
The slip speed calculator in the indirect vector control is strongly affected by the rotor resistance variation. An effective online method for rotor resistance estimation is introduced in the speed sensorless indirect vector controller scheme to eliminate the effects due to rotor resistance variations. This method is based on a MRAS taking magnetic saturation into account for achieving high-precise control of the drive scheme. In this sensorless scheme, the motor speed is estimated from the difference between the estimated synchronous speed and slip speed. Simulations results are presented to evaluate the effectiveness and robustness of the proposed sensorless drive system against rotor parameter variations. The present results show that the proposed sensorless gives accurate estimation of motor speed and rotor resistance. Also, desired and stable dynamic performances are obtained in a wide range of motor speed. Therefore, the proposed sensorless is robust and insensitive to rotor parameters variations.