Systematic, Lyapunov-Based, Safe and Stabilizing Controller Synthesis for Constrained Nonlinear Systems

TL;DR

This paper introduces a systematic method for synthesizing safe and stabilizing controllers for constrained nonlinear systems using CPA Lyapunov functions, formulated via non-convex optimization and semi-definite programming.

Contribution

It presents a novel approach combining CPA Lyapunov functions with multi-stage design to enlarge the ROA and ensure safety and stability in constrained nonlinear control.

Findings

Effective enlargement of the region of attraction.

Successful application to control-affine nonlinear systems.

Numerical examples demonstrate improved stability and safety.

Abstract

A controller synthesis method for state- and input-constrained nonlinear systems is presented that seeks continuous piecewise affine (CPA) Lyapunov-like functions and controllers simultaneously. Non-convex optimization problems are formulated on triangulated subsets of the admissible states that can be refined to meet primary control objectives, such as stability and safety, alongside secondary performance objectives. A multi-stage design is also given that enlarges the region of attraction (ROA) sequentially while allowing exclusive performance for each stage. A clear boundary for an invariant subset of closed-loop system's ROA is obtained from the resulting Lipschitz Lyapunov function. For control-affine nonlinear systems, the non-convex problem is formulated as a series of conservative, but well-posed, semi-definite programs. These decrease the cost function iteratively until the design objectives are met. Since the resulting CPA Lyapunov-like functions are also Lipschitz control (or barrier) Lyapunov functions, they can be used in online quadratic programming to find minimum-norm control inputs. Numerical examples are provided to demonstrate the effectiveness of the method.