On Robust Quantized Sampled-Data Tracking Control of Nonlinear Systems

In this article, the robust quantized sampled-data tracking control problem of nonlinear systems affected by actuation disturbances and observation errors is studied. In particular, results concerning the robustification and the quantized sampled-data implementation of tracking controllers are provided for nonlinear systems in control-affine form. Inspired by the well-known notion of steepest descent feedbacks, the novel notion of steepest tracking feedback (STF) is introduced and the input-to-state stability (ISS) redesign method is used in order to design a new control term able to attenuates the effects of bounded actuation disturbances and of suitably bounded observation errors. Then, it is shown that the digital implementation of STFs (continuous or not), robustified via the ISS redesign methodology, ensures the semiglobal practical stability of the related quantized sampled-data closed-loop system, with arbitrarily small final target ball of the origin. Time-varying sampling intervals and the nonuniform quantization in the input/output channels are allowed. The proposed methodology is validated through a numerical example concerning a continuous stirred tank reactor.