2. Background
Different from other kinds of HEV, PHEV has its own advantage: larger
inside battery that can support long time electrical driving (charge
depleting range). After the usable electrical energy runs out, PHEV will
open its engine to drive the transmission (charge sustaining range). So,
changing the batter size will result in different fuel consumption, and
the cost of car, etc. The goal of our project is to model PHEV, then to
find the fuel economy and the money cost for different batter sizes.
3. Steps
• Original Data Analysis
• Modeling PHEV
• Optimization
• Conclusion
• Disadvantages & Improvement
6. Battery
y = 0.8808x + 0.7249
R² = 0.9018
0
5
10
15
20
25
30
35
40
45
0 5 10 15 20 25 30 35 40 45 50
Battery Proposion
For some time during the test cycle (braking, decreasing),
the battery power is negative number, that is battery regen
time. Energy flows from transmission to the battery. Other
time if using battery, battery power should be positive
(proportion).
8. y = -0.047x + 210
R² = 0.0124
0
50
100
150
200
250
-150 -100 -50 0 50 100 150 200 250
Battery[V]
Battery [A]
Battery
Above plots produce the information about the idle power and
efficiency of battery as the form y=kx+b. it is also easy to find
the resistance of the battery by plotting the battery voltage VS
battery current (the result is 0.047Ω):
9. Engine
y = 0.3967x - 1.3199
R² = 0.795
-10
0
10
20
30
40
50
0 20 40 60 80 100 120 140
Engine Output Power [kW]
The other important part of a vehicle is engine. From the CD
part of the original data, engine on time is very short, that can
be negligible. But based on the fuel power during engine on for
the whole cycle, we can get the following plot and find the
engine efficiency and idle power:
12. Test Weight [lb] 3500
ETW [kg] 1635.19916
Target A [lb] 22.883
Target B [lb/mph] -0.15919
Target C [lb/mph^2] 0.020143
Fuel density [g/ml] 0.742
Fuel Net HV [BTU/lbm] 18493
e_Trans 0.8
Number of Ring gear teeth 78
Number of Pinion gear teeth 23
Number of Sun gear teeth 30
Final drive ratio 4.113
Wheel (P185/65R15) diameter 0.621
Wheel perimeter 1.950929038
Drive Motor Power [kW] 60
Engine Power [kW] 73
Battery [kWh] 4.4
Battery [V] 207
Battery [Ah] 21.25603865
Resistance [Ω] 0.047
Ele Prop Efficency (Batt to FD) 0.8808
Ele Regen Efficency (FD to Batt) 0.8687
Usable Ah 12.11594203
Rcda 15.92035097
UF 0.333645967
Vehicle Information
From the original data, we cannot find the transmission
efficiency, so in the above chart, e_Trans = 0.8 is based on our
assumption.
14. • If changing the battery size, the weight of the car will be different, so
the inertia force will be different, that means the power of the car will
be different at any time of the test cycle. Also, the engine on and
engine off time will be different. That means the original data will be
useless because we don’t know the engine behavior and how much
fuel consumption any every 0.1 second. That is the reason to build a
new PHEV model based on information we got before.
• We assume when engine on, no batter power, and when engine off,
no engine power. And for the CD range, engine on power is infinity.
For CS range, engine on power is 7.48kw (power of pre-transmission).
15. CD Act SOC% VS Model SOC%
0
0.2
0.4
0.6
0.8
1
1.2
0 200 400 600 800 1000 1200 1400 1600
sim soc% vs act soc%
soc% Act soc%
16. • Above plots is model SOC% vs original data SOC% of CD and CS range.
We can see the error is acceptable, that means in our model, how
battery use during the cycle is very simaliar to the oringinal one.
18. • And we need to check the fuel consumption, the way to calculate fuel
comsumption is using UF( utility factor). {1/(total fuel ecomomy)=
UF/(CD fuel economy )+(1-UF)/ (CS fuel economy)}
• So our model mpg is 100.723, and actual mpg is 96.22. The error is
around 4, which to some extent, is acceptable as well. That means
our model is good to simulate.
19. Actual mpg VS model mpg
Ah consumption 7.096826452
Rcda [mi] 12.71889185
UF 0.277858868
cd mpg
cs mpg 72.73640362
mpg 100.7232526
acc cd mpg 253.9081633
acc cs mpg 73.40117994
acc Rcda 15.92
acc UF 0.33364
acc FC 0.010392347
acc mpg 96.22465842
20. Optimization
• Enlarge Battery Capacity
• Reduce Engine Displacement
• Original Vehicle Weight
• After modeling PHEV, we need to change the battery size to find some
results. To avoid different A B C, we control the total vehicle weight to
be the same. So, if we enlarge the battery size, our way is to reduce
the engine displacement, then engine weight will be less. In our
optimization, we didn’t care about the electrical cost.
31. • For our model, the disadvantage is it fix UDDS better (mpg error is
around 4%). For highway cycle, the error is a littler larger than the
UDDS. Although it can also be acceptable, it still have room to reduce
that error. So, our model is nice, but not perfect.
• The reason to reduce the engine weight is to avoid the effect of
different A B C. So, if we can get some coast down data for that car
(find good data source on the internet or test it by ourselves). We can
try to not change the engine weight, and we can find how just 1
factor (battery size) influence the result, and then to decide if to
change the engine size. That way should be more precise.
