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mode in each part according to Sec. 2. Recharging at the final destination is
considered by Mode 4. In acceleration phases, the diesel engine is supported
by the electrical motor, characterized by the intensity of boost
x
. This vari-
able, which quantifies the percentage of the electrical contribution to the total
traction power, represents the single optimization variable. In parts with a
constant velocity, load level increase according to Mode 4 is used to recharge
the energy storage. The coasting phases in Mode 5 are applied to save fuel
and to minimize the emissions. Unfortunately, coasting can be only utilized if
the timetable allows for extended travel times. During the whole duty cycle
auxiliaries are considered, which leads to a positive minimum power request
to the diesel engine.
1
b
fuel
in g/kWh
0.8
0.6
0.4
0.2
29
0
0
0.4
0.6
0.8
1
ω
/
ω
max
→
(a) Fuel consumption map.
(3)
(4)
(3)
(5)
(6)
(1)
(3)
(5)
(6)
(4)
1
0.8
0.6
0.4
0.2
0
250
300
350
400
450
0
50
100
150
200
time in s
→
(b) duty cycle with operating modes.
Fig. 4. Fuel consumption map for a diesel engine and fixed duty cycle.
4.2
Optimized Operating Strategy
An improved strategy can be found by minimizing the performance index (6).
For that purpose the fminsearch-optimizer of the optimization toolbox in
Matlab is used, which is based on the Nelder-Mead method. As single op-
timization variable, the intensity of the boost
x
is used. In every iteration
one complete simulation is performed including both the given duty cycle
as well as the recharging of the energy storage at the final destination. To
determine the global minimum, multiple starting points are employed. In
