Steady-State Sensitivities of Marine Propulsion Control Techniques

This paper presents a steady-state sensitivities analysis of four well-known propulsion control techniques: shaft speed, torque, power and integrative torque–power controllers applied to a ducted marine propeller driven by an electrical motor. Also, this work proposes a variation in the latter technique and analyzes its sensitivities as well. The control loop scheme follows the structure of propulsion control in a dynamic positioning system. The sensitivity concept is used to perform the analysis, which consists of a normalization of the equilibrium point with respect to its reference value. The effect of inaccuracies between the control model and plant parameters over the equilibrium points is considered and analyzed in three scenarios for each controller. Simulations with a ducted propeller model are performed to provide further information about sensitivities, and the results are compared by using performance measurements based on the mean absolute error. The results provide detailed information on each controller’s characteristics in steady state in the whole operation range regarding shaft speed, torque, power and thrust.