A bang-bang controller is proposed which is able to ensure reference signal tracking with prespecified time-varying error bounds (the funnel) for nonlinear systems with relative degree one or two. For the design of the controller only the knowledge of the relative degree is needed. The controller is guaranteed to work when certain feasibility assumptions are fulfilled, which are explicitly give...

We study the recently introduced notion of output-input stability, which is a robust variant of the minimum-phase property for general smooth nonlinear control systems. The subject of this paper is developing the theory of output-input stability in the multi-input, multi-output setting. We show that output-input stability can be viewed as a combination of two system properties, one related to d...

In this paper, a state and unknown input observer is proposed for discrete-time linear systems with bounded unknown inputs and measurement disturbances. The design procedure is formulated using a set of linear matrix inequalities, and leverages delayed (or fixed-lag) estimates. The observer error states and/or user-defined performance outputs are guaranteed to operate at pre-specified performan...

This paper analyzes the stabilizability properties of nonlinear cascades in which a nonminimum phase linear system is interconnected through its output to a stable nonlinear system. It is shown that the instability of the zeros of the linear system can be traded with the stability of the nonlinear system up to a limit fixed by the growth properties of the cascade interconnection term. Below thi...

This paper analyzes the feasibility of quantifying design tradeoffs on the transient step response of a class of nonlinear systems. This feasibility analysis builds on available tools for the characterization of performance limitations in the optimal quadratic response of the class of strict feedback nonlinear systems. We present results that show that, as in linear systems, for certain classes...

Tracking of a reference signal (assumed bounded with essentially bounded derivative) is considered in the context of a class Σρ of multi-input, multi-output dynamical systems, modelled by functional differential equations, affine in the control and satisfying the following structural assumptions: (i) arbitrary – but known – relative degree ρ ≥ 1, (ii) the “high-frequency gain” is sign definite ...