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Table 1, the optimization results for different weighting factors
α
,
β
,and
γ
are stated. The values
V
,
N
,and
C
stand for the overall fuel consump-
tion and emissions, these are calculated within the simulation. To obtain the
same dimensions all values are standardized to the reference values of the
non-hybrid strategy. Depending on the chosen weights, the strategy can be
Tabl e 1 . Optimization results.
αβ γ
x
J
V/V
nom
N/N
nom
C/C
nom
1
0
0
25.2%
0.7018
0.8378
0.9608
1.0291
0
1
0
21.6%
0.9162
0.8451
0.9572
1.0224
001
<
1.0000
1.0181
1.0000
1.0000
0
.
01
%
1
1
1
21.5%
2.6691
0.8424
0.9573
1.0213
switched to minimal fuel consumption/emissions. For example, minimal fuel
consumption is reached with an intensity of boost of
x
=25
.
2%
, the minimal
NOx
emissions are reached with
x
=21
.
6%
, and the minimal
PM
emis-
sions are reached with
x<
, which means a purely diesel vehicle. The
simulation results show a possible reduction of the fuel consumption by 16%
(
V
0
.
01%
) compared to a pure diesel vehicle. The emissions could not be
reduced drastically, only a marginal reduction of the
NOx
emissions could be
reached. The
PM
emissions increase by 2% compared to a pure diesel vehicle.
The reasons are the long phase of recharging compared to the driving time
and the operating strategy. The boost mode is activated in each acceleration
phase independent of the velocity. This causes a large increase in the specific
PM
emissions at high velocities, see Fig. 5(c). These rises can be avoided if
velocity constraints are introduced for Mode 3.
= 84%
5
Conclusions and Outlook on Future Research
In this paper, a mathematical modeling for a basic parallel hybrid structure,
with calculation performed in backward direction, has been presented. The
simulations were performed for a parallel hybrid structure with a specified
duty cycle. By minimization of an appropriate performance index, an opti-
mized operating strategy was found. The simulation and optimization results
show a reduction of fuel consumption of about 17% for a fixed duty cycle.
In future research, the optimization shall be extended to a larger number
of optimization parameters. Besides the optimization of the operating strat-
egy, the duty cycle will be optimized as well. Furthermore, alternative hybrid
structures are to be investigated.
