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Research Papers: Gas Turbines: Controls, Diagnostics, and Instrumentation

Optimal Transient Control Trajectories in Diesel–Electric Systems—Part II: Generator and Energy Storage Effects

[+] Author and Article Information
Martin Sivertsson

Division of Vehicular Systems,
Department of Electrical Engineering,
Linköping University,
Linköping SE-581 83, Sweden
e-mail: marsi@isy.liu.se

Lars Eriksson

Division of Vehicular Systems,
Department of Electrical Engineering,
Linköping University,
Linköping SE-581 83, Sweden
e-mail: larer@isy.liu.se

1Corresponding author.

Contributed by the Controls, Diagnostics, and Instrumentation Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received May 15, 2014; final manuscript received June 3, 2014; published online September 16, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(2), 021602 (Sep 16, 2014) (9 pages) Paper No: GTP-14-1239; doi: 10.1115/1.4028360 History: Received May 15, 2014; Revised June 03, 2014

The effects of generator model and energy storage on the optimal control of a diesel–electric powertrain in transient operation are studied. Two different types of problems are solved, minimum fuel and minimum time, with different generator models and limits as well as with an extra energy storage. For this aim, a four-state mean value engine model (MVEM) is used together with models for the generator and energy storage losses. In the optimization both the engines output power and speed are free variables. The considered transients are steps from idle to target power with different amounts of freedom, defined as requirements on produced energy, before the requested power has to be met. The main characteristics are seen to be independent of generator model and limits; they, however, shift the peak efficiency regions and therefore the stationary points. For minimum fuel transients, the energy storage remains virtually unused for all requested energies, for minimum time it is used to reduce the response time. The generator limits are found to have the biggest impact on the fuel economy, whereas an energy storage could significantly reduce the response time. The possibility to reduce the response time is seen to hold for a large range of values of energy storage parameters. The minimum fuel solutions remain unaffected when changing the energy storage parameters, implying it is not beneficial to use an energy storage if fuel consumption is to be minimized. Close to the minimum time solution, the fuel consumption with low required energy is quite sensitive to variations in duration, for larger energies it is not. Near the minimum fuel solution changes in duration have only minor effects on the fuel consumption.

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References

Nino-Baron, C. E., Tariq, A. R., Zhu, G., and Strangas, E. G., 2011, “Trajectory Optimization for the Engine-Generator Operation of a Series Hybrid Electric Vehicle,” IEEE Trans. Veh. Technol., 60(6), pp. 2438–2447. [CrossRef]
Nilsson, T., Fröberg, A., and Åslund, J., 2012, “Optimal Operation of a Turbocharged Diesel Engine During Transients,” SAE Int. J. Engines5(2), pp. 571–578. [CrossRef]
Sivertsson, M., and Eriksson, L., 2014, “Optimal Transient Control Trajectories in Diesel-Electric Systems—Part I: Modeling, Problem Formulation, and Engine Properties,” ASME J. Eng. Gas. Turbines Power, 137(2), p. 021601. [CrossRef]
Sivertsson, M., and Eriksson, L., 2013, “Generator Effects on the Optimal Control of a Power Assisted Diesel-Electric Powertrain,” IEEE 9th Vehicle Power and Propulsion Conference (VPPC 2013), Beijing, China, Oct. 15–18. [CrossRef]
Guzzella, L., and Sciarretta, A., 2013, Vehicle Propulsion Systems—Introduction to Modeling and Optimization, 3rd ed. Springer, Berlin.
Tomlab, 2012, ProptMatlab Optimal Control Software, Tomlab Optimization Inc., Seattle, WA, see http://www.tomdyn.com/

Figures

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Fig. 1

Structure of the MVEM. The modeled components as well as the connection between them.

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Fig. 2

Two trajectories that are both time optimal, but the fuel consumption differs by 10.6%. For higher Ereq the minimum time solution is not unique.

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Fig. 3

Torque versus engine speed for min mf and min T and different requirements on produced energy with the generator considered ideal. Red circles mark the end operating point.

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Fig. 4

Minimum fuel and minimum time solutions for Ereq = [170, 510, 850] kJ with and without a model for the generator losses

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Fig. 5

Effects of generator limits. Minimum fuel and minimum time solutions for Ereq = 510 kJ for the different generator limits.

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Fig. 6

Effects of energy storage. Minimum fuel and minimum time solutions for Ereq = [85, 510, 850] kJ. Standard-lim. As a reference the case without energy storage is also shown.

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Fig. 7

Torque and engine speed plot for the different limits, minT,Ereq=850 kJ, with and without energy storage

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Fig. 8

Torque and engine speed plot for the different limits, min mf,Pbatt = 0,Ereq = 850 kJ.

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Fig. 9

Change in energy storage usage and fuel and time consumption as a function of internal resistance. All consumption changes relative the case without energy storage, Pbatt = 0.

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Fig. 10

The losses in the energy storage as a function of internal resistance for Ereq = [85, 510, 850] kJ

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Fig. 11

Optimal energy storage size as a function of Ereq for different values of Ri

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Fig. 12

The effect on the fuel consumption of increasing the minimum time

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