Region of Attraction Estimation for Linear Quadratic Regulator, Linear and Robust Model Predictive Control on a Two-Wheeled Inverted Pendulum

TL;DR

This paper develops a hybrid analytical and data-driven approach to estimate the region of attraction for a two-wheeled inverted pendulum under different control strategies, balancing formal guarantees with empirical insights.

Contribution

It introduces a combined Lyapunov-based and Monte Carlo method for RoA estimation, applicable to nonlinear, constrained, and underactuated systems.

Findings

Lyapunov-based invariant sets provide conservative RoA bounds.

Monte Carlo estimation captures more realistic RoA beyond analytical bounds.

Method effectively evaluates controller performance with formal and empirical insights.

Abstract

Nonlinear underactuated systems such as two-wheeled inverted pendulums (TWIPs) exhibit a limited region of attraction (RoA), which defines the set of initial conditions from which the closed-loop system converges to the equilibrium. The RoA of nonlinear and constrained systems is generally nonconvex and analytically intractable, requiring numerical or approximate estimation methods. This work investigates the estimation of the RoA for a TWIP stabilized under three model-based control strategies: saturated linear quadratic regulator (LQR), linear model predictive control (MPC), and constraint tightening MPC (CTMPC). We first derive a Lyapunov-based invariant set that provides a certified inner approximation of the RoA. Since this analytical bound is highly conservative, a Monte Carlo-based estimation procedure is then employed to obtain a more representative approximation of the RoA, capturing how the controllers behave beyond the analytically guaranteed region. The proposed methodology combines analytical guarantees with data-driven estimation, providing both a formally certified inner bound and an empirical characterization of the RoA, offering a practical way to evaluate controller performance without relying solely on conservative analytical bounds or purely empirical simulation.