Landshut University of Applied Sciences Ingolstadt University of Applied Sciences Master's Thesis

104 Pages·2011·3.75 MB·English

Landshut University of Applied Sciences

Ingolstadt University of Applied Sciences

Applied Computational Mechanics

European School of CAE Technology

Master's Thesis

System Level Modeling and Simulation
for
Hybrid Electric Vehicle Propulsion

Author: Sreekanth Nallabolu

Issued on: 30-06-2010

Submitted on: 30-12-2010

First examiner: Prof. Dr. -Ing. Pörnbacher, Fritz

Second examiner: Prof. Dr. -Ing. Wolf, Thomas

i
ABSTRACT

In the recent years there has been observed an increasing concern about global
warming and greenhouse gas emissions. In addition to the environmental issues the predicted
scarcity of oil supplies and the dramatic increase in oil price puts new demands on vehicle
design. As a result energy efficiency and reduced emission have become one of the main
selling point for automobiles. Hybrid electric vehicles (HEV) have therefore become an
interesting technology for the governments and automotive industries.
HEV are more complicated compared to conventional vehicles due to the fact that
these vehicles contain more electrical components such as electric machines, power
electronics, electronic continuously variable transmissions (CVT), and embedded powertrain
controllers. Advanced energy storage devices and energy converters, such as Li-ion batteries,
ultracapacitors, and fuel cells are also considered. A detailed vehicle model used for an
energy flow analysis and vehicle performance simulation is necessary. Computer simulation
is indispensible to facilitate the examination of the vast hybrid electric vehicle design space.
There are various types of mathematical models and simulators available to perform
system simulation of vehicle propulsion. One of the standard methods to model the complete
vehicle powertrain is "Backward Quasistatic modeling" which is acquired in the present work
. In this method vehicle subsystems are defined based on empirical models in the form of
look-up tables and efficiency maps. The interaction between adjacent subsystems of the
vehicle is defined through the amount of power flow. This method is acquired in the present
work for a Series Hybrid Electric Vehicle with the aim to predict the vehicle performance
over driving profiles, estimate fuel consumption and pollution emissions.
i
Battery is a very important component in Hybrid Electric Vehicles. Usual approach to
model the battery at this level is based on equivalent circuit which needs empirical data. In
the present work a semi-physical battery model is introduced which on one side can be
simulated fast and on the other side include all important physical phenomena in the battery.
IEEE standard hardware description language VHDL-AMS is used to model this advanced
battery model. This detailed model of the battery is then coupled with the rest of the vehicle
which is modeled with empirical data. Finally a series hybrid electric vehicle with this
advanced battery model is simulated. A comparison of the simplified battery model with this
advanced battery model is done. Important phenomenon like "rate capacity effect" and "idle
period recovery" during charge and discharge cycles of the battery are shown to be accurately
simulated in the advanced battery model which are otherwise not modeled in the simplified
circuit based model. The physical explanation for these effects is also given. The work
depicts an in-depth modeling methodology for battery with physical reasoning and its
integration into hybrid electric vehicle design.
Two case studies are performed to evaluate the vehicle performance. In the first case
study the affect of the increase in the battery weight and capacity on vehicle performance is
evaluated. An optimum number of modules in the battery are determined for minimum fuel
consumption and maximum power. In the second case study a comparative study of the fuel
consumption and fuel economy of the vehicle for various drive cycles (Ex: City and Highway
etc) is performed. The energy losses in each subsystem in the vehicle are also determined and
the results are discussed qualitatively.

ii
ACKNOWLEDGEMENTS

I am deeply grateful to my supervisors, Rudnyi Evgeny Ph.D, and Prof. Dr. -Ing.
Pörnbacher Fritz for the guidance and support during the thesis. I feel extremely fortunate for
the opportunity to work with them. I also thank my colleague Eng. Lucas Kostetzer and
Madhukar Chatiri (M.Sc.) for their technical discussions and knowledge sharing. I wish to
thank my chief Dr. Günter Müller for providing me an opportunity to work in the field of
electro mobility. His idea of making simulation models for battery and electro mobility and
his regular encouragement gave me an opportunity to explore this field in depth. I also thank
all my professors during my master's course ESoCAET who have shared their knowledge of
numerical techniques and simulations.

iii
PUBLICATIONS

Conference Publications
Sreekanth Nallabolu, Lucas Kostetzer, Evgenii Rudnyi. Electro-thermal Simulation of a
Battery Pack . Proceedings of Grazer Symposium - Virtuelles Fahrzeug, pages 140-150, May
2010.

Sreekanth Nallabolu, Lucas Kostetzer, Evgenii Rudnyi. Electro-thermal Simulation of a
Battery Pack for HEV/EV. ANSYS Conference & 28th CADFEM Users' Meeting , November
2010.

Lucas Kostetzer, Sreekanth Nallabolu, Evgenii Rudnyi. Electro-thermal simulation and
experimental validation of Lithium Ion battery for EV/HEV applications. Berechnung und
Simulation im Fahrzeugbau 2010, pages 431-441 , November 2010.

Lucas Kostetzer, Sreekanth Nallabolu, Evgenii Rudnyi. Advanced battery modeling for
energy and thermal management of a vehicle. Internationales Stuttgarter Symposium -
Automobil- und Motorentechnik, Submitted, February 2011.

Sreekanth Nallabolu, Lucas Kostetzer, Evgenii Rudnyi. System Simulation of Hybrid Vehicle
Propulsion with an Advanced Battery Model. Antriebssysteme 2011, Submitted, September
2011.

iv
CONTENTS

Page
Abstract ................................................................................................................................ i
Acknowledgements ............................................................................................................ iii
Publications ........................................................................................................................ iv
List of Tables .................................................................................................................... viii
List of Figures .................................................................................................................... ix
Nomenclature ..................................................................................................................... xi
SYMBOLS ....................................................................................................................... xiii

Chapters:
1. Introduction .................................................................................................................... 1
1.1. Motivation .............................................................................................................. 1
1.2. The energy conversion process ............................................................................... 2
1.3. Hybrid electric vehicle technology .......................................................................... 5
1.3.1. Introduction to hybrid electric vehicles ...................................................... 5
v
1.3.2. Topology of hybrid electric vehicle............................................................ 7
1.3.3. Energy management in HEVs .................................................................... 9
1.4. Introduction to modeling HEV propulsion ............................................................ 10
1.4.1. Need for HEV simulation ........................................................................ 10
1.4.2. Modeling methods ................................................................................... 12
1.4.3. Capabilities of existing commercial tools ................................................. 14
1.5. Contribution and organization of thesis ................................................................. 15
2.Modeling Subsystems of Powertrain ............................................................................. 17
2.1. Vehicle energy flow .............................................................................................. 17
2.1.1. Vehicle longitudinal dynamics ................................................................. 17
2.1.2. Significance of standard drive cycles ....................................................... 21
2.1.3. Powertrain losses and performance limits ................................................ 25
2.2. Modeling tools and methods used ......................................................................... 26
2.2.1. Implemented modeling methodology ....................................................... 26
2.2.2. Modeling assumptions ............................................................................. 29
2.3. Component realization .......................................................................................... 29
2.4. Modeling Powertrain components ......................................................................... 31
2.4.1. Fuel converter .......................................................................................... 33
2.4.2. Electric components ................................................................................ 43
2.4.3. Transmission ........................................................................................... 53
2.4.4. Vehicle, Wheel & Axle ............................................................................ 57
3.Battery Simulation ......................................................................................................... 60
3.1. Battery .................................................................................................................. 60
vi
3.2. Equivalent Circuit based battery model ................................................................. 63
3.3. Semi-physical battery cell model .......................................................................... 70
3.4. Comparison of simplified circuit model and Semi-physical model ........................ 70
4.Case studies .................................................................................................................... 74
4.1. Impact of battery weight on vehicle performance .................................................. 74
4.2. Performance of Series Hybrid Electric Vehicle in Different Drive Cycles ............. 80
5.Summary and Discussion ............................................................................................... 83
References ......................................................................................................................... 86

vii
LIST OF TABLES

Table Page

Table 1.1. Energy density of various on-board energy carriers .............................................. 4
Table 2.1. Variables used in Quasistatic model for Engine .................................................. 39
Table 2.2. Variables used for Quasistatic modeling for Motor ............................................. 47
Table 4.1. Vehicle specifications of Series Hybrid Electric Vehicle..................................... 76

viii
LIST OF FIGURES

Figure Page

Fig. 1.1. The three stages of energy conversion ..................................................................... 3
Fig. 1.2. Hybrid Electric Vehicle ........................................................................................... 5
Fig. 1.3. Topology of different Hybrid Electric Vehicles ....................................................... 9
Fig. 1.4. Complex interdependency of HEV components .................................................... 11
Fig. 2.1. Schematic representation of the forces acting on a vehicle ..................................... 19
Fig. 2.2. Velocity profiles of the U.S. regulatory cycles....................................................... 24
Fig. 2.3. Comparison of Quasistatic Backward looking model and reality ........................... 27
Fig. 2.4. Schematic view of power flow in series Hybrid Electric Vehicle ........................... 32
Fig. 2.5. Working principle of a 4-stroke gasoline engine .................................................... 33
Fig. 2.6. Schematic of principle of operation of dynamometer ............................................. 35
Fig. 2.7. Examples of p-V diagram ...................................................................................... 36
Fig. 2.8. Typical engine fuel map ........................................................................................ 37
Fig. 2.9. Conceptual sketch for Internal Combustion Engine model..................................... 41
Fig. 2.10. Engine Torque, Fuel consumption and Emissions ................................................ 42
Fig. 2.11. Motor efficiency map and maximum torque ........................................................ 46
Fig. 2.12. Conceptual sketch for Electric Machine (Motor/Generator) model ...................... 48
Fig. 2.13. Torque and Power in motor model ...................................................................... 49
Fig. 2.14. Conceptual sketch for Generator model ............................................................... 50
Fig. 2.15. Conceptual sketch for power bus model .............................................................. 51
Fig. 2.16. Conceptual sketch for final drive model .............................................................. 52
Fig. 2.17. Torque and Speed in Gearbox ............................................................................. 55
Fig. 2.18. Conceptual sketch for Gearbox model ................................................................. 56
Fig. 2.19. Conceptual sketch for Wheel and Axle model ..................................................... 59
Fig. 2.20. Behavior of Vehicle and Wheel blocks with a sudden increase in speed request. . 59
Fig. 3.1. Thermodynamics, Chemical kinetics and Transport in Li-ion cell during charging 62
ix