Optimal Control of the Energy-Saving Hybrid Hydraulic-Electric Architecture (HHEA) for Off-Highway Mobile Machines

Most off-highway constructions and agriculture equipment use hydraulics, which has unmatched power density, for power transmission and throttling as a means for control. A novel hybrid hydraulic-electric architecture (HHEA) has recently been proposed to improve efficiency for high-power machines tha...

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Bibliographic Details
Published in:IEEE transactions on control systems technology 2022-09, Vol.30 (5), p.2018-2029
Main Authors: Siefert, Jacob, Li, Perry Y.
Format: Article
Language:English
Subjects:
Actuators
Computational efficiency
Computer architecture
Constrained optimization
Cost function
discrete options
Electric motors
Energy conservation
Energy consumption
Fluid flow
Highway construction
hybrid hydraulic-electric
Hydraulic systems
Hydraulics
Iterative methods
Lagrange multiplier
off-road vehicles
Optimal control
power-train
Rails
Throttling
Torque
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Summary:Most off-highway constructions and agriculture equipment use hydraulics, which has unmatched power density, for power transmission and throttling as a means for control. A novel hybrid hydraulic-electric architecture (HHEA) has recently been proposed to improve efficiency for high-power machines that would have been cost-prohibitive to electrify directly. HHEA uses a set of common pressure rails (CPRs) to transmit the majority of power hydraulically and small electric motor drives to modulate that power and to achieve precise control. This article proposes a computationally efficient Lagrange multiplier method (LMM) for computing the optimal sequence of pressure rail selections to minimize energy use. This is needed to evaluate HHEA's energy-saving potential and for iterative architecture design and sizing. An interesting complication is that the cost function is not fully defined until the candidate control sequence is fully specified. This issue is dealt with by decomposing the original problem into a set of sub-problems with additional constraints that can be solved efficiently. Computational effort can be further reduced if actuators are optimized individually instead of together. However, additional steps are required to prevent the constraint functions from becoming discontinuous with respect to the Lagrange multipliers, which is necessary for meeting the constraints. A case study of a construction machine demonstrates the efficacy of the method and shows that the HHEA reduces energy consumption by 68%-73% compared to the baseline load-sensing architecture.
ISSN:1063-6536
1558-0865
DOI:10.1109/TCST.2021.3131435