Switched sliding mode control strategy for networked systems

In this paper, a networked switched control strategy based on Sliding Mode Control is presented. The idea pursued in this work is to reduce to a minimum the packet rate over the network, in order to limit the problems induced by the transmission of the state measurement between the sensor and the controller, while providing performance comparable with that of a non networked Sliding Mode Control scheme. The proposed scheme includes a model based controller which contains the nominal model of the plant, and relies on a suitably defined triggering condition. The latter considers the amplitude of a sliding variable determined relying on nominal model, and enables the actual state transmission only when the sliding variable is within a predefined boundary layer. When the plant state is not transmitted, the model state is used to determine the control action. In this way, it is possible to guarantee the same robustness with respect to matched uncertainties as in conventional sliding mode control schemes, as well as the exponential stability of the origin of the controlled system state space, even if the actual system state is not always used to close the feedback. Moreover, in steady-state, when the boundary layer is reached, in order to avoid a continuous transmission of the actual state measurement, a mechanism based on a moving average of the current sliding variable is adopted, which allows to suitably deactivate the state transmission even within the boundary layer, yet maintaining some robustness. Simulation results demonstrates the effectiveness of the proposed strategy.