Safety Control Synthesis with Input Limits: a Hybrid Approach

TL;DR

This paper presents a hybrid safety controller that enforces state and input constraints using barrier functions and Lyapunov-based methods, acting only when necessary to maintain safety while preserving system transparency.

Contribution

It introduces a novel hybrid safety control approach with barrier pairs and a Min-Quadratic Barrier function, extending LQR-Trees for safe region augmentation.

Findings

Effective in simulation examples

Ensures strict safety constraints

Preserves system operation within safe regions

Abstract

We introduce a hybrid (discrete--continuous) safety controller which enforces strict state and input constraints on a system---but only acts when necessary, preserving transparent operation of the original system within some safe region of the state space. We define this space using a Min-Quadratic Barrier function, which we construct along the equilibrium manifold using the Lyapunov functions which result from linear matrix inequality controller synthesis for locally valid uncertain linearizations. We also introduce the concept of a barrier pair, which makes it easy to extend the approach to include trajectory-based augmentations to the safe region, in the style of LQR-Trees. We demonstrate our controller and barrier pair synthesis method in simulation-based examples.