Load Handling Performance Comparison Between a Digital and a Conventional Hydraulic Winch Drive

Offshore winches commonly use conventional hydraulic drives, which are characterized by low energy efficiency. Digital displacement motors have shown promise for improving the energy efficiency of winch drive applications as they utilize digital valves for their operation. This paper compares the performance of a novel digital hydraulic winch drive and a conventional hydraulic winch drive with respect to their ability to control the load position of a commercial offshore knuckle-boom crane accurately. The considered digital winch drive consists of a digital displacement motor that operates in parallel with an electric motor. The power rating of the electric motor is small compared to that of the hydraulic motor, and its role is to smooth out the torque output of the digital displacement motor. The analysis shows that a smoother torque output reduces valve switchings and, therefore, increases the digital displacement motor’s volumetric efficiency. The drives’ performance is evaluated via simulations in four scenarios with varying conditions. The digital drive exhibits enhanced accuracy, achieving up to a 24 mm reduction in maximum load position error in three test scenarios, and performs comparably to the conventional drive in the fourth. Notably, the digital system controls the load with greater smoothness and fewer oscillations. These findings suggest that a digital displacement motor operating together with an electric motor presents a promising alternative for offshore winch drive applications.