Downsizing the Electric Motors of Energy-Efficient Self-Contained Electro-Hydraulic Systems by Using Hybrid Technologies

The ongoing tendency toward the electrification of hydraulic systems, mainly in the form of self-contained solutions, poses design challenges in high-power applications. An electric motor drives positive-displacement machines used to control the motion of the hydraulic actuator (nonhybrid systems encompassing one or two pumps exist in the technical literature). All the power managed by the actuator passes through the electric motor, which leads to often oversized arrangements. These detrimental characteristics are especially pronounced when the power level increases approximately above 35–40 kW. Therefore, this research paper presents and studies a self-contained, electro-hydraulic, hybrid architecture intended to downsize the electric motor while maintaining the high-power output of the nonhybrid counterpart. After introducing the sizing process for the energy storage device and developing a suitable control strategy for the hybrid subsystem, the proposed concept is validated via high-fidelity dynamic models. The rated power of the electric prime mover can be cut by 70% in the considered application (a mid-size, knuckle-boom crane with an installed power of about 46 kW) without altering the performance in terms of motion control. The additional mass (about 310 kg) of the hybrid system is not expected to affect the load-carrying capacity significantly. As a result, the hybridization of self-sufficient systems is technically feasible for high-power applications. Drawbacks related to the system cost-effectiveness might, however, be experienced. An application-driven cost analysis should be conducted before implementing such a solution.