A new technique to compensate for disturbance in sliding mode control systems

Sliding mode control systems provide an effective and robust means of controlling nonlinear plants. The main advantage of the systems is their insensitivity to disturbance and parameter uncertainties. However, the favourable performance is usually achieved at the price of chattering, i.e. the high-speed switching of the control signal. In this paper a new technique to attenuate the undesirable chattering is proposed. The technique is based on the observation, that in the sliding mode, information about the disturbance can be extracted from the discontinuous control signal. Therefore, the technique employs a simple first order low-pass filter, to estimate the unknown, possibly changing disturbance and to partly compensate for it. As a result of this compensation, the magnitude of the discontinuous control term is essentially reduced. The term does not depend on the admissible disturbance or its change rate, but only on the uncertainty of the disturbance at the initial time t=t₀. The technique proposed in this paper attenuates the undesirable chattering without any deterioration of the system performance