PHEV Vehicle Level Control StrategySSummary

November 2008November 2008

Aymeric RousseauyArgonne National Laboratory

Sponsored by Lee Slezak

This presentation does not contain any proprietary, confidential, or otherwise restricted information

Objective: Assess Fuel Displacement Potential of Various PHEVs Control StrategiesVarious PHEVs Control Strategies

Higher Electric Power

Higher Electric Energy Higher Control Freedom

Fuel Savings Potential

Depending on various driven distance, several possible modes:– Below AER (All‐Electric Range) : Electric‐only (EV)

– Above AER: EV? CS(Charge Sustaining)? Blended? 

Common Strategy= EV+CS Blended Strategykm/h

SOC

% %km/h

lowICE

highICE

offoff

Veh. speed

SOChighICE

off

highICE

off off

s

EV MODE

off

CS MODE

s

BLENDED BLENDED

2

Control Optimization/Design Investigates Strategies Potential

Innovative 3-way Approach to Control OptimizationGl b l O ti i ti

tSOCtP

tJtSOCtP '0,000 ,1',1 tU 0 Optimal Control

Teng Tmcωmc

Global Optimization

tSOCtP nm ,

tJtSOCtP MMMM ',' ,1,1

0

tU M

TX 0X.

.

.

.

.

.

Optimal Control, Minimal Fuel Cons.

Backward model (not PSAT) Bellman Principle

ωeng

Backward model (not PSAT) p

PSAT Various PSAT C t l St t iVarious

Control Design

Control StrategiesVarious Control Principles Rule-Based Control Design

Heuristic OptimizationOptimally tuned

ParametersPSAT

Heuristic Optimization

3

Existing Control Logic DIRECT Algorithm

Global Optimization Showed Minimal Fuel Consumption Achieved in Blended Mode

Global Optimization

Consumption Achieved in Blended Mode

0 9

1

UDDS 10 ( ti )Japan 10-15 x25 (optim)Japan 10-15 x25 (simu)

0 7

0.8

0.9NEDC x10(optim)UDDS x10 (optim)

3 cycles demonstrated

0.6

0.7

SO

C

Blended strategy is optimal

0.4

0.5

Example of EV+CS Mode for

0 10 20 30 40 50 60 70 80 90 1000.2

0.3Example of EV+CS Mode for comparison

4

% of total distance

Control Strategy Design Showed Significant ImprovementsImprovements

EV/C

S

0 0%

2.0%

Up to 9% less

ase

Ove

r

-2.0%

0.0%0 16 32 48 64 80 96 112

fuel consumed when driving distance is 20 migy

Incr

ea

-6.0%

-4.0%

Differential EnginePower distance is 20 mi

uel E

nerg

-8.0%

Full Engine Power

Optimal EnginePower

Trip distance (km)Fu -10.0%

Power Split 10 miles AER (Prius), run on several UDDS cycles

5

p ( ), y

Different Optimization Methods Showed Control Depends on DistanceDepends on Distance

Global Optimization Heuristic Optimization (UDDS)30O

N

UDDS 20ld

25

ch IC

E is

UDDSHWFETLA92 18

20

N th

resh

ol

15

20

abov

e w

hic

14

16

W) I

CE

ON

10

15

eels

(kW

) a

12

14

whe

els

(kW

0 10 20 30 40 505

Distance (miles)

Pwr w

he

10 20 30 40 50 6010

Distance (miles)

Pwr w

6

Small SUV, Parallel Pre-tx, 10 miles AER

“ Engine On” Is Linked to Wheel Power35

=.95

Cycle:

Global Optimization

25

30

h P(

ICE=

ON

)= Cycle:

HWFETUDDS

LA92

15

20

) abo

ve w

hich

10 miles20 miles

Driven Distance

0

5

10

wr w

heel

s (kW

) 20 miles40 miles

Power at wheels above which ICE is on 95% of the time, similar to wheel 

0 50 100 150 200 2500P

Plug-to-wheel Electric Consumption (Wh/km)

power threshold used in rule‐based controls

Higher Electric Energy Use → ICE starts “later”

Wheel Power Threshold follows linear trend

7

Wheel Power Threshold follows linear trend

Little influence of driving cycle

Engine Power Depends on Cycle and Electricity Use

Global Optimization

Electricity Use

30

35

W)

20

25

age

Pow

er (k

W

Cycle:

HWFETUDDS

LA92

10

15

Engi

ne A

vera

10 miles

Driven Distance

0 50 100 150 200 2500

5E

Plug-to-wheel Electric Consumption (Wh/km)

20 miles40 miles

UDDS: ICE power increases with Wh/km

LA92: ICE power constant, because cycle is aggressive enough for the ICE to operate 

g p ( )

8

efficiently

Charging from ICE Likely When ICE is Predominant and Wheel Power is Low

Global Optimization

Predominant and Wheel Power is Low

0.35

0.4

Cycle:UDDS

0 2

0.25

0.3 Engine Efficiency

HWFET

Driven

LA92

0.1

0.15

0.2

Share of Engine Output Energy Used to Charge the Battery

10 miles20 miles40 miles

Distance

0 50 100 150 200 2500

0.05

Pl t h l El t i C ti (Wh/k )

UDDS: when ICE is used often, it has to operate often above requested wheel power

LA92: ICE operates efficiently, even in CS mode because average ICE power is high

Plug-to-wheel Electric Consumption (Wh/km)

9

LA92: ICE operates efficiently, even in CS mode because average ICE power is high

5 Vehicles with Different Energy and AERGlobal Optimization

90 90

Power to meet EV-mode requirements on UDDS…

70

80

90

65.8046

y (A

h) …Different UDDS All-Electric Range

10 miles AER on UDDS

40

50

60

44.5589

y C

apac

ity

UDDS

10

20

30

11.9045

23.2123

Bat

tery

5 10 20 30 400

10

All-Electric Range (miles)

10

For a Given Electric Consumption, AER Has Little Influence on Control

Global Optimization

For a given electric consumption, ICE‐On behavior does not depend on the energy sizing…

b ibl l i i i li i d l i

40954095

…but possible electric energy consumption is limited : same electric consumption corresponds to different SOC 

25

30

35

40

ch P

(ICE=

ON

)=.9

Maximal battery depletion

25

30

35

40

ch P

(ICE=

ON

)=.9

AER5AER10AER20AER30AER40

10

15

20

AER10

AER20

AER30

AER40

(kW

) abo

ve w

hic

10

15

20

s (kW

) abo

ve w

hi AER40

0 0.2 0.4 0.60

5

AER5

SOC0 - SOC

end

Pwr w

heel

s CS mode

0 50 100 150 200 2500

5

Electric Energy Consumption (Wh/km)

Pwr w

heel

s

11

UDDS, 20 mi

Minimal Fuel Consumption Distance Traveled < AER

Global Optimization

Distance Traveled  AER

– Decrease in fuel consumption is proportional to increase in AER

– 1.5 L/100 km difference between UDDS and LA92

5

6

7

(L/1

00km

)

Driven Distance: 10 miles

250

300

350

(Wh/

k)

Driven Distance: 40 miles

Wh/km (UDDS)Wh/km (HWFET)Wh/km (LA92)

3

4

5

el C

onsu

mpt

ion

L/100km (UDDS)L/100km (HWFET)L/100k (LA92)

150

200

250

Cti

( )

0

1

2

Min

imal

Fue

5 10 20 30 40

L/100km (LA92)

5 10 20 30 405 10 20 30 400

50

100

Elt

iE

12

5 10 20 30 40AER (miles)

5 10 20 30 405 10 20 30 40AER (miles)

Fuel Consumption Follows a Linear Trend and Depends on Wh/km

Global Optimization

p

Small AER vehicles consume slightly less fuel due to lower weight, but difference in consumption is minimal

For a given electric consumption, fuel consumption is comparable

For 2 vehicles (e.g. AER 30 & AER 40) travelling less than their AER (e.g. 20 mi on UDDS), same EV mode electric consumption 

4

5

6

100k

m)

AER5AER10AER20AER30

UDDS, 20 miles

2

3

4

onsu

mpt

ion

(L/1 AER30

AER40

0 50 100 150 200 2500

1

2

Fuel

Co

13

0 50 100 150 200 250

Plug-to-wheel Electric Consumption (Wh/km)

5 Vehicles With Different PowerGlobal Optimization

120

Same Battery Energy… … Different Electric Power

100

89.4366

104.3427

W)

60

80

59.6244

74.5305

10 miles AER ony

Pow

er (k

W

20

4044.7183

AER on UDDS

Bat

tery

0.6 0.8 1 1.2 1.40

20

Power Scaling Ratio

14

Power Scaling Ratio

Maximum Power Impacts Wheel Power Threshold for Engine ON

Global Optimization

Threshold for Engine ON The engine starts “earlier” when the electric system has lower 

powerpower

30

35

E=O

N)=

.95

Ratio 0.6Ratio 0.8

20

25

e w

hich

P(IC

E

Ratio 1Ratio 1.2Ratio 1.4

5

10

15

ls (k

W) a

bove

20 miles UDDS

0 50 100 150 2000

5

Electric Energy Consumption (Wh/km)

Pwr w

heel

15

Less Electric Power Results in Higher Fuel Consumption

Global Optimization

Consumption

Especially true on aggressive cycle (LA92), and distance traveled close to AER

Hi h l t i d t i ifi tl d f l ti Higher electric power does not significantly reduce fuel consumption

UDDS seems to be a good choice for power requirements (In terms of energy use)

4

5

L/10

0km

)

200

250

n (W

h/km

)

2

3

Con

sum

ptio

n (L

100

150

gy C

onsu

mpt

ion

L/100km (UDDS)L/100km (HWFET)L/100km (LA92)

Wh/km (UDDS)Wh/km (HWFET)Wh/km (LA92)

0

1

Min

imal

Fue

l

0

50

Elec

tric

Ene

rg

16

0.6 0.8 1 1.2 1.4

Power Scaling Ratio

Control Strategy Assessment Provided Insights on PHEVs Optimal OperationsPHEVs Optimal Operations

When the trip distance is greater than the All Electric Range, i h i h h h i (bl d d l) iusing the engine throughout the trip (blended control) is 

preferable to depleting the battery as fast as possible

Optimum control depends on the distanceOptimum control depends on the distance

Engine On/Off is linked to wheel power demand and available electrical energy

When used, engine should be operated at high efficiency

17