الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
AC motors, especially the induction motors are now the most commonly used motors in industry due to their reliability, ruggedness and low cost. On the other hand, induction motors are nonlinear systems that are difficult to control. Many schemes have been proposed for the control of induction motor drives, and of course the most effective scheme is the field-oriented control (FOC). The FOC for induction motors partially linearize the system by controlling it in a frame that rotates along with the rotor flux vector. It involves the transformation of the stator current and rotor flux vectors in the fixed (a-b) stator reference frame into vectors in the rotating rotor flux frame. Angle information of rotor flux vector is needed to achieve FOC, and since the rotor flux is usually not measurable, the FOC is very sensitive to small errors in the rotor flux position estimation, which results in a coupling between torque and rotor flux dynamics. To improve the FOC, feedback linearization and input - output decoupling techniques based on differential geometry theory were applied to induction motors control. The resultant nonlinear state feedback controller has the deficiency that variations in load torque and rotor resistance cause loss of input-output decoupling, steady state tracking errors and deteriorated transient responses. To overcome this problem, an. adaptive input - output linearization using adaptation of rotor resistance and load torque variations was applied. But these nonlinear control methods result in relatively complex control algorithms.
Previous work of the sliding mode control applied to induction motor drives is reviewed in chapter 4.
In chapter 5 a new variable structure sliding mode control is introduced and applied to design a nonlinear variable structure sliding mode torque and flux controller for AC motor drives. Two case studies are given as examples of nonlinear AC motor drive systems: the induction motor drive and permanent magnet stepper motor drive. The variable structure sliding mode control is well known for its robustness against system parameter variations and external disturbances.
In the first case study we apply the variable structure sliding mode control theory to design a fast and robust torque and rotor flux control for induction motors. The proposed controller is given in the stationary (a-b) fixed stator reference frame, and hence no need for rotor flux angle inforn1ation as in the classical field oriented control. The regulating switching surfaces .