Speed Sensorless Vector Control of Induction Motors Based on Robust Adaptive Variable Structure Control Law

Abstract

A novel sensorless adaptive robust control law is proposed to improve the trajectory tracking performance of induction motors. The proposed design employs the so called vector (or field oriented) control theory for the induction motor drives and the designed control law is based on an integral slidingmode algorithm that overcomes the system uncertainties. The proposed sliding-mode control law incorporates an adaptive switching gain to avoid calculating an upper limit of the system uncertainties. The proposed design also includes a new method in order to estimate the rotor speed. In this method, the rotor speed estimation error is presented as a first order simple function based on the difference between the real stator currents and the estimated stator currents.The stability analysis of the proposed controller under parameter uncertainties and load disturbances is provided using the Lyapunov stability theory. Finally simulated results show, on the one hand that the proposed controller with the proposed rotor speed estimator 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.

Smoothing out the adaptive variable structure control law for induction motors

“…Using the field-orientation control principle which implies that the current component i e ds is aligned in the direction of the rotor flux vectorψ r , and the current component i e qs is aligned in the direction perpendicular to it, the mechanical equation of an induction motor can be written as ( [4], [2]):…”

“…These advantages of the sliding-mode control may be employed in the position and speed control of an AC servo system. However, a frequently encountered problem in sliding control is that the control signal is not smooth since the sliding control law is discontinuous across the sliding surfaces; that is, the control signal changes its sign when the sliding variable does it, which causes the chattering phenomenon [2]. Chattering is undesirable in practice, since it involves high control activity and further may excite high-frequency dynamics.…”

“…In these situations many different strategies can be applied, from complex methods to confer self-excitation capability to the system without the presence of external exciting signals, to simpler approaches based on the use of dead zones. The latter solution will be adopted in this paper to avoid the possible drift phenomenon that may be appear in the sliding gain adaptation law proposed in [2].…”

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This paper presents a new variable structure control law that improves the performance of the control law presented in our previous work [2]. The new smoothed control law reduces the chattering phenomenon of the previous one, and therefore implies less activity control and diminish the mechanical fatigue of the system.

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“…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 ( [3], [1], [2]). The sliding-mode control offers many good properties, such as good performance against unmodelled dynamics, insensitivity to parameter variations, external disturbance rejection and fast dynamic response [6].…”