17-03-2010, 11:01 AM
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Abstract:
The field oriented control emerged as an important approach for the control of AC machines, and continues to be explored and developed in the literature. The estimation of the rotor flux from the measurable variables was the only method used to implement the vector control of the induction machine. To replace the estimator based on the mathematical model of the system, which can lead to unintended errors due to uncertainties on the model and on the measures we use an appropriate observer.
Presented By:
Cherif Mokhtar, Azzedine Bendiabdellah, Abdelkader Mezouar and Ameur Fethi Aimer
Department of Electrical Engineering, University of Science and Technology Oran, Algeria.
INTRODUCTION
field orientation technique namely the Rotor flux orientation introduced by BLASCHKE in 1972, has made it possible to act independently on the rotor flux and the electromagnetic torque which gives us an induction machine as good in the areas of variable speed drive as a DC machine, but the aimed decoupling can not be insured in steady states when the rotor flux amplitude is kept constant, which presents a serious constraint especially for rotating machines at high speeds ( higher than the nominal speed) [1]. A Nonlinear control is often necessary for best performance. The sliding mode control is a technique that works as well with the linear systems as with nonlinear systems. This technique has two stages: Forcing the variable control of the system to reach an hyper-surface as quickly as possible, then slides until it reaches a certain point, during its second phase, the system is in a sliding state and its dynamic behaviour is independent of system parameters, as well as disturbances, and therefore insensitive to parameter variations. Whatever the technique used (classical or sliding mode control) knowledge of the values of state variables is required. The use of sensors causes the congestion of the installation and creates fragility and disability of precision. Faced with these problems, we use a sliding mode observer.
