EVS28 KINTEX, Korea, May 3-6, 2015

Parameter design of regenerative

braking strategy and battery range of

use of electric vehicle using the

Optimization Technique

Kiyoung Kim1, Seungwan Son1 , Sukwon Cha1 1School of Mechanical & Aerospace Engineering, Seoul National

University, Gwanak-ro 1, Gwanak-gu Seoul 151-744, Republic of Korea,

kims1988@snu.ac.kr

Introduction

I. Target electric vehicle

2

Mortor Inverter

Battery

forward direction

Mechanical connection Electrical connection

Component Value

Vehicle weight 1260kg

Radius of tire 0.35m

Reduction ratio 3.6

Motor 50kW

Battery capacity 16.4kWh

Rear drive Compact car

Target vehicle

Optimization Technique

I. Optimal parameter using Taguchi method

1. Statistical method developed by Genichi Taguchi

3

• Optimization using steepest gradient method

known J= J(x1, …., xn)

• Optimization using Taguchi method

unknown SN= SN(x1, …., xn)

SN: signal-to-noise ratio

Objective and function parameter

I. Objective

1. Maximization of efficiency of electric vehicle regardless of various

using condition

II. Function parameter

1. efficiency of electric vehicle (km/kWh)

4

max y =𝑦1

𝑦1,𝑟𝑒𝑓

𝑦1

𝑦1,𝑟𝑒𝑓

: efficiency

: efficiency reference

Forward simulator

I. Analysis of efficiency by simulation program based on

MATLAB/Simulink

5

Forward simulation program considering power train dynamics Simulation using component data map Determine traction power comparing vehicle speed with target speed

Design parameter

I. Initial SOC

II. SOC range of use

III. Ratio of front/rear hydraulic pressure based on vehicle

deceleration

Parameter combination in correlation

• Initial SOC & SOC range of use

6

Design parameter

I. Initial SOC

1. Different OCV and internal resistance for SOC

→ Different battery efficiency for SOC

→ To find optimal initial SOC

7

※SOC : State of Charge

=current charge amount

Maximum charge amount

Design parameter

II. SOC range of use

1. Different OCV and internal resistance for SOC

→ Different battery efficiency for SOC

→ To find optimal range of use

8

※SOC : State of Charge

=current charge amount

Maximum charge amount

Design parameter

I. Ratio of front/rear hydraulic pressure based on vehicle

deceleration

1. Total brake force = regenerative brake(motor) + mechanical brake(hybraulic)

2. Ideal brake distribution rate based on vehicle deceleration(blue line)

3. Real brake distribution rate only by mechanical brake (red line)

4. Regenerative braking makes up for deficient rear braking force

5. Meeting point ideal/real line as design parameter (green point)

9

Rear b

rake fo

rce(N

)

Front brake force(N)

0.2g

0.4g

0.6g 0.8g

Ideal brake force distribution

Real brake force distribution

Rear b

rake fo

rce(N

)

Front brake force(N)

0.2g

0.4g

0.6g 0.8g

Ideal brake force distribution

Real brake force distribution

Product using condition

I. Driving propensity of driver

1. Indexing based on Aggressiveness factor

2. Aggressiveness factor?

1) Based on required traction power

2) Effect on efficiency according to driving pattern

can be quantified

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𝐴𝑔𝑔 = 𝑎 · 𝑣 +𝑑𝑡

𝑣𝑑𝑡

<Fuel economy of conventional car for aggresiveness> <various driving cycle>

Level of design parameter and using condition

I. Level of design parameter on primary

II. Level of using condition on primary

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Design parameter Description on design parameter Level 1 Level 2 Level 3

A Initial SOC(0~1) 0.75 0.95 -

B SOC range of use(0~1) 0.55 0.60 0.65

C Meeting point ideal/real line 0.4g 0.6g 0.8g

Using condition Level 1 [𝑁1] mildest

Level2 [𝑁𝟐] harshest

aggressiveness 0.0697

(HWFET cycle) 0.1646

(UDDS cycle)

Result of primary process

I. 𝐿18(21ⅹ32) Array

12

Combination

Design parameter Using condition

Function parameter

S/N ratio

I. Table and graph of S/N ratio for level of design parameter

Analysis on sensitivity

13

Level

Max. difference

S/N

ratio

S/N

ratio

S/N

ratio Level of B

Level of A

Level of C

Design parameter A does not influence on function parameter due to low sesitivity

Design parameter B and C influence on function parameter due to high sesitivity

Analysis on parameter correlation

I. Table and graph of Correlation A with B

14

slope of design parameter A&B for level is similar

→ Low correlation between A and B

Estimation of S/N ratio

I. Estimation of S/N ratio and comparison with result

1. Design parameter B&C influence on S/N ratio

2. Design parameter A and A-B do not influence on S/N ratio

15

Combination

Design parameter Using condition

Function parameter

S/N ratio

Level2 of A is selected because S/N ratio is lager than that of level 1 of A

Level of design parameter and using condition

I. Level of design parameter on second

II. Level of using condition on second

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Design parameter Description on design parameter Level 1 Level 2 Level 3

A Initial SOC(0~1) - 0.95 -

B SOC range of use(0~1) 0.65 0.70 0.75

C Meeting point ideal/real line 0.8g 0.85g 0.9g

Using condition Level 1 [𝑁1] mildest

Level2 [𝑁𝟐] harshest

aggressiveness 0.0697

(HWFET cycle) 0.1646

(UDDS cycle)

Result of second process

I. 𝐿9(32) Array

17

Combination

Design parameter Using condition

Function parameter

S/N ratio

I. Table and graph of S/N ratio for level of design parameter

Analysis on sensitivity

18

Level

Max. difference

S/N

ratio

S/N

ratio

Level of B Level of C

Design parameter B&C do not influence on function parameter

No need to third process

B C

Estimation of S/N ratio

I. Estimation of S/N ratio and comparison with result

1. Design parameter B&C do not influence on S/N ratio

2. Combination number 6 is optimal combination

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S/N ratio more bigger than primary process

Combination

Design parameter Using condition

Function parameter

S/N ratio

Conclusion

I. Determine Optimal parameter of EV using Taguchi method

II. Design parameter 1. Initial SOC

2. SOC range of use

3. Ratio of front/rear hydraulic pressure based on vehicle deceleration

III. Product using condition 1. Aggressiveness factor

IV. Optimal design parameter combination

1. Select parameter combination making S/N ratio maximized

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Design parameter Description on design parameter Optimum

A Initial SOC(0~1) 0.95

B SOC range of use(0~1) 0.7

C Meeting point ideal/real line 0.9g

Acknowledgement & Reference

This work was supported by the Hyundai Motor Company and the National Research

Foundation of Korea(NRF) grant funded by the Ministry of Science, ICT &

Future Planning (MSIP) (No. 2009-0083495).

• Daeheung Lee et. Al., “System Efficiency Analysis for Next Generation Eco-Friendly

Vehicles with Aggressiveness of Real-World Driving Schedules” , Transactions of KSAE,

2010.11, pp. 3178-3183

• Mehrdad Ehsani et. Al., “Modern Electric, Hybrid Electric, and Fuel Cell Vehicles”, 2nd

edition, CRC Press, 2010

• 김종원, “공학설계 : 창의적 신제품 개발방법론”, 서울 : 문운당, 2008

• Ho Gi Kim, “Suppression Control of the Drivetrain-Oscillations of an Electric Vehicle using

Taguchi method.”, Transaction of KSME, 2009. 5 Vol.33 No.5 pp.463-468

• Chunhua Zheng, “ A study on Battery SOC Estimation by Regenerative Braking in Electric

Vehicle” Transaction of KSAE, Vol. 20 No. 1, pp.119-123

• Yongsun Bak, “Development of regenerative braking co operative control algorithm for

electric vehicle equipped with booster brake” Transactions of KSAE, 2013.5, pp. 1800-1804

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