Journal: eTransportation

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Publisher

Elsevier

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ISSN

2590-1168

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2022 - 20232
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Publications 1 - 2 of 2
  • Battery health target tracking for HEVs: Closed-loop control approach, simulation framework, and reference trajectory optimization
    Item type: Journal Article
    Widmer, Fabio; Ritter, Andreas; Ritzmann, Johannes; et al. (2023)
    eTransportation
    In this paper, we address the trade-off between primary energy consumption and battery wear for hybrid electric vehicles in an optimal manner, for which we provide three contributions: First, we suggest a control structure to track a battery lifetime target in a closed control loop by incorporating periodic measurements of the state of health. This feedback enables the energy management system to reliably meet the target lifetime in the presence of disturbances and model mismatch. We validate the control scheme in a case study featuring a battery-assisted trolley bus. In this case study, we show that without the proposed measurement feedback and in the presence of disturbances and model mismatch, the sub-optimal use of the battery can either result in an increase in energy consumption of up to 9% over the vehicle's lifetime or in a prematurely required battery replacement. Second, to speed up the necessary calculations, we devise an algorithm that is able to perform simulations of a complete vehicle lifetime in less than a minute. A comparison to a standard simulation approach shows that our approach is able to accurately calculate both energy consumption and battery degradation with an error of less than 1% on average, while the execution time is reduced by a factor of about 70000. Third, we numerically optimize the battery health trajectory over the vehicle lifetime. We show that, while a quadratic health trajectory leads to improved energy efficiency, for the specific vehicle and cell technology considered in our case study, a linear trajectory results in only a small energy penalty of 0.05% over the vehicle lifetime.
  • Battery lifetime extension through optimal design and control of traction and heating systems in hybrid drivetrains
    Item type: Journal Article
    Widmer, Fabio; Ritter, Andreas; Duhr, Pol; et al. (2022)
    eTransportation
    In this paper, we investigate the optimal design and control of an integrated energy and thermal management system (IETMS) of a battery-assisted trolley bus that is subject to minimum battery lifetime requirements. Therefore, we jointly optimize both the control trajectories of the traction and the heating systems and the design of the thermal energy buffer. We further analyze the resulting Pareto fronts which characterize the trade-off between the battery lifetime and the energy consumption. This holistic approach fills a gap in the literature published, namely the formulation of an optimization problem that combines component sizing with a battery-health-aware IETMS. While the model derived allows the formulation of a convex optimal control problem for a given vehicle design, the combined design and control problem is non-convex. Therefore, we perform grid searches within a reasonable subset of the design space and show that the problem is smooth, has only one stationary point, and that the solver converges to the optimal solution even for the simultaneous, non-convex problem formulation. We further present a case study showing that, if an IETMS is used, a realistic bus service life without battery replacement can be achieved with a reduction of energy consumption of up to 7% on some driving missions, compared to a heuristic heating strategy. If the design of the thermal system is co-optimized, battery lifetime can be extended further by up to 15% without affecting the amount of energy consumed. In summary, our study reveals a potential to make electric transportation more efficient in terms of both energy and costs based on a holistic consideration of battery-health-aware IETMS with optimized component dimensioning.
Publications 1 - 2 of 2