SPEED SLIDING MODE CONTROL OF SENSORLESS INDUCTION MACHINE
In this paper, a direct field oriented induction motor drive with a sliding mode controller (SMC) is presented. The design includes rotor speed estimation from measured stator terminal voltages and currents. For that reason we have defined a simple speed estimator. The (SMC) technique finds its stronger justification in the utilization of a robust nonlinear control law to model uncertainties. The used control algorithm is a sliding mode associated with a particular function "sat" to limit chattering effects that presents a serious problem in applications to variable structure systems. Simulation tests under load disturbances and parameter uncertainties are provided to evaluate the consistency and performance of the proposed control technique. K e y w o r d s: induction machine, motor drives, sliding mode control, sensorless machine The control of the induction machine (IM) must take into account machine specifics: the high order of the model, nonlinear functioning as well as the coupling between the different variables of control. Furthermore, the machine parameters depend generally on the operating point and vary either on the temperature (resistance) or with the magnetic state of the induction machine, without taking into account the variation. These parametric variations modify the performances of the control system when we use a regulator or a control law with fixed parameters. The new industrial applications necessitate speed variators having high dynamic performances, good precision in permanent regime, high capacity of overload in the whole range of speed and robustness to different perturbations. Thus, the recourse to robust control algorithms is desirable in stabilization and in tracking trajectories. The variable structure control (VSC) possesses this robustness using the sliding mode control that can offer many good properties such as good performance against unmodelled dynamics, insensitivity to parameter variation, external disturbance rejection and fast dynamic [5 11] These advantages of sliding mode control can be employed in the position and speed control of an alternative current servo system. Using field oriented control (FOC) of the induction machine, the knowledge of rotor speed and flux is necessary. Tachogenerators or digital shaft position encoders are usually used to detect the rotor speed of motors. These speed sensors lower the system reliability and require special attention to noise. In addition, for some special applications such as very high speed motor drives, there exist difficulties in mounting these speed sensors. Recently many researches have been carried on the design of speed sensorless control schemes. In this work the speed is obtained based on the measurement of stator voltages and currents. However, the estimation is usually complex and heavily dependent on machine parameters. Therefore, although sensorless vector controlled drives are commercially available at this time, the parameter uncertainties impose a challenge in the control performances. In this paper, we begin with the IM oriented model