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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