Disturbance Observer Based Backstepping MIMO Control Design for a Marine Vessel in the Presence of Input Saturation and External Disturbance

In this article, a MIMO autopilot control for a marine vessel has been designed such that it can perform well in the presence of input saturation and external disturbances. In order to tackle input saturation, a method based upon fuzzy logic is presented. Fuzzy logic ensures that the control input doesn't enter saturation mode. A disturbance observer (DO) has been used to estimate the external disturbance and remove its effects from the system. All these methods are amalgamated with a backstepping control scheme. The stability of the disturbance observer based backstepping control with anti-saturation via fuzzy logic has been proved via Lyapunov stability criteria. For validation of the proposed controller, numerical simulation is performed on a model ship named Cybership II. In addition, the simulation results of the proposed controller are compared with the traditional backstepping and PID controllers. The effectiveness of the proposed control methodology can be inferred from these results.