An internal model control approach to the design of yaw-rate-control ship-steering autopilot

This technical communication is concerned with the design of inland ship-steering autopilots characterized by turning rate regulation rather than heading regulation found on most ocean-going vessel autopilots. The autopilot design is based on the internal model control approach which allows clear connections between the controller structure and that of the ship model to be established. To fully utilize the limited rudder power without introducing the controller wind-up, which may lead to undesirable long transients, an inverse of the rudder saturation (SAT) and slew rate limitation (SRL) is implemented in the controller. Specifically, an inversion by feedback technique is employed by implementing the noninverted dynamics in a local feedback loop. This resolves the difficulty associated with inversion of the SAT and SRL mathematically. Consequently, high turning rate maneuver can be achieved in case of emergency encounters without causing the controller wind-up. This feature is particularly important for inland ships, since unexpected encounters with other ships are quite common and the capability of quick response is vital to ensure safe maneuvers.