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

Abstract

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.

Electro-Hydraulic Variable-Speed Drive Networks—Idea, Perspectives, and Energy Saving Potentials

“…The flow decoupling scheme for the VDN-PP can be derived for the individual axes as they are hydraulically separated. The load and sum pressure dynamics may be found from Equations ( 10)- (13) as Equations ( 35)- (38), when neglecting cross port leakage and drain flows:…”

“…However, information on the bulk modulii is uncertain, and the piston velocities are not measured. Hence, estimates of the bulk modulii and the piston velocity references ẋ * 1 , ẋ * 2 , together with Equations ( 35)- (38), are used to estimate the pressure dynamics, with these estimates given by Equations ( 41)- (44). Here, ẋ = [ ẋ1 ẋ2 ] T , ω PP = [ω 1,0 ω 1,2 ω 3,0 ω 3,4 ] T and • * denotes a reference for a given state/input.…”

“…Combining Equations ( 35)- (38) and Equations ( 41)-( 44), and substituting ω 1,0 = ω * 1,0 , ω 1,2 = ω * 1,2 , ω 3,0 = ω * 3,0 and ω 3,4 = ω * 3,4 , the closed loop pressure dynamics appear as Equations ( 49) and (50).…”

“…For such drives, the cost of electric components may be considered a challenge for their broad application, and this has been addressed e.g., via component downsizing approaches. These include the use of hydraulic energy storages [38] and the use of valves enabling flow regenerative functionalities [39][40][41][42]. Comprehensive reviews on developments of such types of drives are available in [43,44].…”

Downsizing the electric machines of energy-efficient electro-hydraulic drives for mobile hydraulics

“…This approach becomes critical, or even infeasible, if the power level rises to several kilowatts; a bulky and expensive arrangement for the electric subsystem is needed (motors, drives, generator, and energy storage device) and an enormous quantity of electricity must be generated onboard. Therefore, hybrid actuators with self-contained energy storage can downsize the rated power of the electric machines [18], but additional components are needed. Downsizing the installed electric power can also be done by connecting the inlet port of speed-controlled pumps to a pressure rail supplied by a centralized pump [19][20] resulting in power being transferred to/from the actuators both hydraulically and electrically.…”