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In this letter, a robust quantized sampled–data controller is provided for a class of nonlinear systems affected by time–varying uncertainties, actuation disturbances and measurement noises. Sufficient conditions based on linear matrix inequalities and ensuring the existence of the proposed robust quantized sampled–data controller are given. Quantization of both state measurements and input signals is simultaneously considered. Input–to–state stability redesign technique is used in order to attenuate the effects of bounded actuation disturbances and of bounded observation errors. It is proved that, under suitably fast sampling and accurate quantization of the input/output channels, the proposed controller achieves the semi–global practical stability, with arbitrarily small final target ball, of the related quantized sampled–data closed–loop system provided that the observation errors do not affect (or affect marginally) the robustification term added in the controller and, that the bounds of the actuation disturbances as well as of the observation errors are a priori known. The theory here developed includes also the cases of time–varying sampling intervals and of non–uniform quantization of the input/output channels as well as the stability analysis of the inter–sampling system behavior. The provided results are validated through an example of one–link manipulator.

In this letter, the notion of GALES (Global Asymptotic Local Exponential Stability) is extended to nonlinear systems described by Retarded Functional Differential Equations. Necessary and sufficient Lyapunov-Krasovskii conditions ensuring the GALES of nonlinear time-delay systems are provided. The conditions related to the lower bound and to the dissipation rate of the Lyapunov-Krasovskii functional involve only the current value of the solution, making the provided tool easy to use. An example validating the results is presented.

In this paper, a controller for induction motors is proposed. A continuous feedback is first applied to obtain a discrete-time model in closed form. Then, on the basis of these exact sampled dynamics, a discrete-time controller ensuring speed and flux modulus reference tracking is determined, making use of the sliding mode technique. The resulting controller is hence hybrid, in the sense that it contains both continuous and discrete-time terms. It is shown how to implement such a hybrid controller using the so-called exponential holder, which is the only device to be implemented analogically, together with an analog integrator. Moreover, a discrete-time reduced-order observer is designed for rotor fluxes and load torque estimation. The performance of the proposed controller is finally studied by simulation and experimental tests.

Addressed here is the problem of designing a dynamic controller capable of performing rest-to-rest maneuvers for flexible spacecraft, by using attitude measures. This controller does not need the knowledge of modal variables and spacecraft angular velocity. The absence of measurements of these variables is compensated by appropriate dynamics of the controller, which supplies their estimates. The Lyapunov technique is applied in the design of this dynamic controller. Possible source of instability of the controlled system in real cases are the influence of the flexibility on the rigid motion, the presence of disturbances acting on the structure, and parameter variations. In order to attenuate their effects and to damp out undesirable vibrations affecting the spacecraft attitude, distributed piezoelectric actuators are used. In fact, in presence of disturbances and/or parameter variation the proposed controller ensures an approximate solution of the control problem.

The paper deals with linear and nonlinear regulation under sampling. It is shown that digital solutions exist under assumptions which are closely related to the existence of robust solutions to the continuous problem. Approximated solutions are computed starting from the continuous ones.