A four-quadrant thrust controller for marine propellers with loss estimation and anti-spin : theory and experiments

In this paper a nonlinear thrust controller for fixed pitch marine propellers with torque loss estimation and an antispin strategy is presented. The controller, designed to operate in the four-quadrant plane composed by the shaft speed and the vessel speed, is a combination of a thrust controller developed for calm/moderate sea states and an anti-spin strategy to reduce power peaks and wear-and-tear in extreme sea conditions. The thrust controller aims at producing the demanded thrust independently from the propeller losses. The anti-spin algorithm lowers the shaft speed once large torque losses are detected and increases the shaft speed to normal when the loss situation is considered over. The torque losses are estimated with a nonlinear observer. The performance of the proposed controller is validated by experiments carried out in a towing tank.