This paper presents a method for estimation of the stator flux components and rotor speed based on the theory of an adaptive control and a direct torque control (DTC). A linear observer for estimation of the stator flux is synthesized, by using a Lyapunov theory in order to guarantee stability for state estimation. The adaptive observer is associated to a direct torque control of an induction motor. To illustrate the performances and the robustness of this observer, a simulation results is presented.

In this paper, we introduced a robust approach to induction motor control combining fuzzy logic and variable structure with a sliding mode control. Fuzzy tuning schemes are employed to improve control performance as well as to reduce chattering in the sliding mode. This combination ensures system high performance and fast dynamic response with no overshoot. Becoming a very robust, insensitive to process parameters variation and external disturbances. 86Copyright ⓒ 2015 SERSC surface in the state space. It is a common opinion that the major drawback of sliding mode control is the so-called chattering phenomenon. Such a phenomenon consists of the oscillation of the control signal, tied to the discontinuous nature of the control strategy, at a frequency and with an amplitude capable of disrupting, damaging or, at least, wearing the controlled physical system (e.g., in mechanical systems with backlash).Several methods of chattering reduction have been reported. One approach [3-4] places a boundary layer around the switching surface such that the relay control is replaced by a saturation function. Another method [3,5] replaces a max-min-type control by a unit vector function. These approaches, however, provide no guarantee of convergence to the sliding mode and involve a tradeoff between chattering and robustness.Chattering Reduction be achieved without harming system robustness by combining the attractive features of fuzzy control with SMC [11][12][13] and [18]. Fuzzy logic, first proposed by Zadeh [14], has proven to be a potent tool for controlling ill-defined or parameter-variant plants. By incorporating heuristics engineering rules, a fuzzy logic controller can cope well with severe uncertainties, although a heavy computational burden may arise with some implementations. Fuzzy schemes with explicit expressions for tuning can avoid this problem [16].This paper presents a robust control system using sliding mode control that incorporates a fuzzy tuning technique. The proposed controller is applied to induction motor to control the speed and flux. The control law superposes equivalent control and fuzzy control. An equivalent control law is first designed then we introduce a fuzzy logic control (FLC) in this later the sign function is replaced in order to limit the chattering phenomenon originated by finite-frequency switching control and to preserve the main advantages of the original slidingmode approach (robustness, simplicity, and finite-time convergence).