A Control Algorithm for Active/Passive Hydraulic Winches Used in Active Heave Compensation

The most common active heave compensated offshore cranes have hydraulic winch systems. This paper investigates an active/passive hydraulic winch system with variable-displacement motors and variable-displacement pumps. The paper addresses the challenges when the active motors are set with a low displacement. The active motor displacement is shown to have significant impact on the dynamics of the closed loop hydraulic system. The classical control strategy for this type of system do not address these challenges and will in certain situations have significantly reduced performance. Therefor, a new control method is presented that utilize the variable displacement of the pumps and motors for speed control and to improve dynamics characteristics. The new winch controller is tested in a high-fidelity simulation model and is shown to improve low speed performance, reduce winch speed limitations by up to 30%, reduce system peak pressure by approximately 20%, and reduce control error by approximately 30%.