Lyapunov-Based Integrator Resetting With Application to Marine Thruster Control

Abstract

This paper addresses the idea of improving transient behavior by internal state resetting of dynamic controllers, such as controllers with integral action or adaptation. The concept presented here assumes that for a given closed-loop system with a dynamic controller, improved transient performance is achieved when reset of controller states gives negative jumps in the Lyapunov function value. The Lyapunov function constitutes a part of the controller algorithm. By combining this with existing stability theory for switched systems, the stability analysis of the overall system follows directly. The framework assumes that a Lyapunov function is given, and that full state measurement is available for feedback. Moreover, an estimator is needed to give a coarse estimate of the system equilibrium point. An anti-spin feature in local thruster speed control on ships with electric propulsion is in this paper presented as an application for the given framework. Transients arise when the ship operates in extreme seas, where disturbances such as ventilation and in-and-out of water effects may give rise to loss in propeller thrust. A Lyapunov function is used to decide appropriate reset of the integrator state of a standard Pi-controller. The method is illustrated with experimental results.