A Sliding Mode Control for Induction Motors Using Adaptive Switching Control Law OSCAR BARAMBONES, AITOR GARRIDO, PATXI ALKORTA AND IZASKUN GARRIDO University of The Basque Country Department of Systems Engineering and Automatic Control E.U.I.T.I de Bilbao. Plaza de la Casilla, 48012 Bilbao SPAIN oscar.barambones@ehu.es Abstract: An adaptive sliding-mode control system, which is insensitive to uncertainties, is proposed to control the position of an induction motor drive. The designed sliding mode control presents an adaptive switching gain to relax the requirement for the bound of uncertainties. The switching gain is adapted using a simple algorithm which do not implies a high computational load. Stability analysis based on Lyapunov theory is also performed in order to guarantee the closed loop stability. Finally simulation results show, on the one hand that the proposed controller provides high-performance dynamic characteristics, and on the other hand that this scheme is robust with respect to plant parameter variations and external load disturbances. Key–Words: Sliding Mode Control, Induction Motor, Adaptive Control, Field Oriented Control. 1 Introduction In recent years the induction motors have been in- creasingly taking place of the DC motors in high per- formance electrical motor drives [5]. The main advan- tage of the DC motors is that their speed control can be carried out in a simple way, since the torque and flux are decoupled. However, the technique of vec- torial control [3] based on the rotor field orientation applied to the induction motors provides the decou- pling between the torque and flux in a similar way to the DC machine. Therefore, with the progress of the power electronics and the appearance of low cost and very fast microprocessors, the induction motor drives have reached a competitive position compared to DC machines. However, the control performance of the resulting linear system is still influenced by uncertain- ties, which usually are composed of unpredictable pa- rameter variations, external load disturbances and un- modelled and nonlinear dynamics [4]. In the past decade, the variable structure control strategy using the sliding-mode has been focussed on many studies and research for the control of the AC servo drive system [2], [1]. The sliding-mode con- trol offers many good properties, such as good per- formance against unmodelled dynamics, insensitivity to parameter variations, external disturbance rejection and fast dynamic response [6]. These advantages of the sliding-mode control may be employed in the po- sition and speed control of an AC servo system. How- ever, the traditional sliding control schemes require the prior knowledge of an upper bound for the system uncertainties using this bound for the switching gain calculation. This upper bound should be determined as precisely as possible, because the higher is the up- per bound, the higher value should be considered for the sliding gain, and therefore the control effort will also be high which is undesirable in practice. Then, to relax the requirement for the bound of uncertainties, an sliding mode control scheme with adaptive switch- ing gain is proposed to control the induction motor drive. The switching gain is adapted using a simple algorithm which do not implies a high computational load. 2 Induction motor model A dynamic model of an induction motor in a syn- chronously rotating d-q reference frame expressed in terms of state variables is given by the following equa- tions [3]: di sd dt = −  R s σL s + 1 − σ στ r  i sd + w e i sq + L m σL s L r τ r ψ rd + L m w r σL s L r ψ rq + 1 σL s V sd di sq dt = −w e i sd −  R s σL s + 1 − σ στ r  i sq − L m w r σL s L r ψ rd + L m σL s L r τ r ψ rq + 1 σL s V sq Proceedings of the 11th WSEAS International Conference on SYSTEMS, Agios Nikolaos, Crete Island, Greece, July 23-25, 2007 294