Hybrid Systems, Iterative Learning Control, and Non-minimum Phase

TL;DR

This paper develops a comprehensive theory of iterative learning control for hybrid systems, addressing existing gaps by creating new inversion methods and stability frameworks for piecewise affine models, enhancing control of complex nonlinear systems.

Contribution

It introduces a broadly applicable ILC synthesis framework for hybrid systems, including stable inversion techniques for PWA systems, filling critical gaps in hybrid control theory.

Findings

Developed a closed-form representation for hybrid systems.

Created a new ILC framework incorporating stable inversion.

Derived inversion theories for PWA systems.

Abstract

Hybrid systems have steadily grown in popularity over the last few decades because they ease the task of modeling complicated nonlinear systems. Legged locomotion, robotic manipulation, and additive manufacturing are representative examples of systems benefiting from hybrid modeling. They are also prime examples of repetitive processes; gait cycles in walking, product assembly tasks in robotic manipulation, and material deposition in additive manufacturing. Thus, they would also benefit substantially from Iterative Learning Control (ILC), a class of feedforward controllers for repetitive systems that achieve high performance in output reference tracking by learning from the errors of past process cycles. However, the literature is bereft of ILC syntheses from hybrid models. The main thrust of this dissertation is to provide a boradly applicable theory of ILC for deterministic, discrete-time hybrid systems, i.e. piecewise defined (PWD) systems. In summary, the three main gaps addressed by this dissertation are (1) the lack of compatibility between existing hybrid modeling frameworks and ILC synthesis techniques, (2) the failure of ILC based on Newton's method (NILC) for systems with unstable inverses, and (3) the lack of inversion and stable inversion theory for piecewise affine (PWA) systems (a subset of PWD systems). These issues are addressed by (1) developing a closed-form representation for PWD systems, (2) developing a new ILC framework informed by NILC but with the new ability to incorporate stabilizing model inversion techniques, and (3) deriving conventional and stable model inversion theories for PWA systems.