Experimental Validation of Power and Torque Thruster Control

Results from laboratory experiments with an electrically driven propeller controlled by three different control systems are presented, showing the advantages of torque and power thruster control over shaft speed control. For fixed pitch propellers, the industrial standard today is shaft speed control based on a static mapping from desired thrust force to desired shaft speed. When the operating conditions change due to vessel motion, waves and current the propeller loading changes. The results are fluctuating thrust production and load torque, which lead to mechanical wear and tear and unpredictable power consumption. This may lead to severe deterioration of the performance of a vessel; the power fluctuations force the operators to have more generators running than necessary, and the mechanical wear and tear lead to vessel down-time due to repairs. Alternatives to shaft speed control are torque and power control, based on static mappings from desired thrust to desired torque and power respectively. This paper demonstrates by experimental results that significant performance improvements can be achieved by changing to torque or power thruster control.