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Optimal Transient Control Trajectories in Diesel-Electric Systems-Part 2: Generator and Energy Storage Effects

The effects of generator model and energy storage on the optimal control of a diesel-electric powertrain in transient operation is 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 4-state mean value engine model 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.

Martin Sivertsson and Lars Eriksson

Journal of Engineering for Gas Turbines and Power, 2015

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