Improved Transient Performance by Lyapunov-based Integrator Reset of PI Thruster Control in Extreme Seas

PI controllers are often tuned such that the overall performance is a trade-off between performance in steady state and transient regimes. By introducing reset of the integrator value in these controllers, the performance in transient regimes may be increased without influencing the performance in steady state. An advantage of this strategy is that it can be integrated into an already existing controller as a separate module. This will only affect the performance in the transient regimes, by speeding up the controller response only when large control errors are measured. We will in this paper show how integrator reset can be used for anti-spin in local thruster speed control on ships with electric propulsion. Transient regimes arise when the ship is in extreme seas, where ventilation and in-and-out of water effects may give rise to loss in propeller thrust. In this paper, a Lyapunov function is used to decide when a reset of the integrator value is appropriate. The method is illustrated with experimental results