An Energy Efficient Hydraulic Winch Drive Concept Based on a Speed-variable Switched Differential Pump

The application of valve driven hydraulic winch drives is related to substantial power losses, primarily due to throttle generated valve flows. More energy efficient solutions are also commonly applied in terms of conventional hydrostatic closed circuit drives as well as so-called secondary controls. Such solutions are typically constituted by many and rather expensive components, and are furthermore often suffering from low frequency dynamics. In this paper an alternative solution is proposed for winch drive operation, which is based on the so-called speed-variable switched differential pump, originally designed for direct drive of hydraulic differential cylinders. This concept utilizes three pumps, driven by a single electric servo drive. The concept is redesigned for usage in winch drives, driven by flow symmetric hydraulic motors and single directional loads as commonly seen in e.g. active heave compensation applications. A general drive configuration approach is presented, along with a proper control strategy and design. The resulting concept is evaluated when applied for active heave compensation. Results demonstrate control performance on level with conventional valve solutions in terms of motion tracking, however with improved efficiency, especially in the event that the electrical servo drive can realize four quadrant operation.