Introduction to hybrid vehicle system modeling and control wei liu

5.4.3 SOL Determination under Storage Condition, 1685.4.4 SOL Determination under Cycling Condition, 172 5.4.4.1 Offline Lifetime Determination under Cycling Condition, 1735.4.4.2 Online

HYBRID VEHICLE SYSTEM MODELING AND CONTROL

INTRODUCTION TO HYBRID VEHICLE SYSTEM MODELING AND CONTROL

WEI LIU

A JOHN WILEY & SONS, INC., PUBLICATION

Cover design: Michael Rutkowski

Copyright © 2013 by John Wiley & Sons, Inc All rights reserved

Published by John Wiley & Sons, Inc., Hoboken, New Jersey

Published simultaneously in Canada

No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers,

MA 01923, (978) 750-8400, fax (978) 750-4470, or on the web at www.copyright.com Requests

to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008, or online at http://www.wiley.com/go/permission.

Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose No warranty may be created or extended by sales representatives or written sales materials The advice and strategies contained herein may not be suitable for your situation You should consult with a professional where appropriate Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages.

For general information on our other products and services or for technical support, please contact our Customer Care Department within the United States at (800) 762-2974, outside the United States at (317) 572-3993 or fax (317) 572-4002.

Wiley also publishes its books in a variety of electronic formats Some content that appears in print may not be available in electronic formats For more information about Wiley products, visit our web site at www.wiley.com.

Library of Congress Cataloging-in-Publication Data:

Liu, Wei, 1960 Aug

30-Introduction to hybrid vehicle system modeling & control / Wei Liu.

10 9 8 7 6 5 4 3 2 1

1.2 Hybrid Vehicle System Components, 5

1.3 Hybrid Vehicle System Analysis, 6

1.3.1 Power Flow of Hybrid Vehicles, 6

1.3.2 Typical Drive Cycles, 7

1.3.3 Vehicle Drivability, 8

1.3.4 Vehicle Fuel Economy and Emissions, 8

1.4 Controls of Hybrid Vehicle, 8

Application, 192.4 Transmission System in Hybrid Vehicle, 24

References, 24

3.1 Modeling of Internal Combustion Engine, 25

3.2 Modeling of Electric Motor, 32

3.3 Modeling of Battery System, 37

3.4 Modeling of Transmission System, 42

3.4.1 Modeling of Clutch and Power Split Device, 42

3.4.2 Modeling of Torque Converter, 50

3.4.3 Modeling of Gear Box, 52

3.4.4 Modeling of Transmission Controller, 53

3.5 Modeling of Final Drive and Wheel, 56

3.6 Modeling of Vehicle Body, 58

3.7 PID-Based Driver Model, 59

References, 61

4 Power Electronics and Electric Motor Drives of Hybrid Vehicle 63

4.1 Basic Power Electronic Devices, 63

4.1.1 Diodes, 64

4.1.2 Thyristors, 65

4.1.3 Bipolar Junction Transistors, 67

4.1.4 Metal–Oxide–Semiconductor Field Effect Transistors, 694.1.5 Insulated Gate Bipolar Transistors, 71

4.2 DC/DC Converter, 72

4.2.1 Basic Principle of DC–DC Converter, 72

4.2.2 Step-Down (Buck) Converter, 74

4.2.2.1 Steady-State Operation, 764.2.2.2 Output Voltage Ripple, 804.2.3 Step-Up (Boost) Converter, 83

4.2.4 Step-Down/Up (Buck–Boost) Converter, 86

4.2.5 DC–DC Converters Applied in Hybrid Vehicle

Systems, 904.2.5.1 Isolated Buck DC–DC Converter, 904.2.5.2 Four-Quadrant DC–DC Converter, 94

4.3 DC–AC Inverter, 94

4.3.1 Basic Concepts of DC–AC Inverters, 95

4.3.2 Single-Phase DC–AC Inverter, 99

4.3.3 Three-Phase DC–AC Inverter, 102

4.4 Electric Motor Drives, 106

4.4.1 BLDC Motor and Control, 106

4.4.1.1 Operation of BLDC Motor, 1064.4.1.2 Torque and Rotating Field Production, 1074.4.1.3 BLDC Motor Control, 108

4.4.1.4 BLDC Motor Torque–Speed Characteristics

and Typical Technical Parameters, 1134.4.1.5 Sensorless BLDC Motor Control, 1134.4.2 AC Induction Motor and Control, 115

4.4.2.1 Basic Principle of AC Induction Motor

Operation, 1154.4.2.2 Controls of AC Induction Motor, 1184.5 Plug-In Battery Charger Design, 124

4.5.1 Basic Configuration of PHEV/BEV Battery Charger, 1244.5.2 Power Factor and Correcting Techniques, 125

4.5.3 Controls of Plug-In Charger, 127

References, 129

5 Energy Storage System Modeling and Control 131

5.1 Introduction, 131

5.2 Methods of Determining State of Charge, 133

5.2.1 Current-Based SOC Determination, 133

5.2.2 Voltage-Based SOC Determination, 136

5.2.3 Extended Kalman Filter–Based SOC Determination, 1455.2.4 SOC Determination Based on Transient Response

Characteristics, 1475.2.5 Fuzzy Logic–Based SOC Determination, 149

5.2.6 Combination of Estimated SOCs by Different

Approaches, 1515.2.7 Further Discussion of SOC Calculations in Hybrid

Vehicle Applications, 1525.3 Estimation of Battery Power Availability, 154

5.3.1 PNGV HPPC Power Availability Estimation, 156

5.3.2 Revised PNGV HPPC Power Availability Estimation, 1585.3.3 Power Availability Estimation Based on Electrical CircuitEquivalent Model, 159

5.4 Battery Life Prediction, 165

5.4.1 Aging Behavior and Mechanisms, 165

5.4.2 Definition of State of Life, 167

5.4.3 SOL Determination under Storage Condition, 168

5.4.4 SOL Determination under Cycling Condition, 172

5.4.4.1 Offline Lifetime Determination under Cycling

Condition, 1735.4.4.2 Online SOL Determination under Cycling

Condition, 1735.5 Cell Balancing, 180

5.5.1 SOC Balancing, 181

5.5.2 Hardware Implementation of Balancing, 181

5.5.3 Cell Balancing Control Algorithms and Evaluation, 1845.6 Estimation of Cell Core Temperature, 192

5.6.1 Introduction, 192

5.6.2 Core Temperature Estimation of Air-Cooled

Cylinder-Type HEV Battery, 1935.7 Battery System Efficiency, 196

References, 197

6 Energy Management Strategies of Hybrid Vehicle 199

6.1 Introduction, 199

6.2 Rule-Based Energy Management Strategy, 200

6.3 Fuzzy Logic–Based Energy Management Strategy, 201

6.3.1 Fuzzy Logic Control, 202

6.3.2 Fuzzy Logic–Based HEV Energy Management

Strategy, 2096.4 Determination of Optimal ICE Operating Points of Hybrid

Vehicle, 218

6.4.1 Mathematical Description of Problem, 219

6.4.2 Procedures Determining Optimal Operating Points, 2206.4.3 Golden Section Search Method, 221

6.4.4 Determining Optimal Operating Points, 221

6.4.5 Example of Optimal Determination, 222

6.4.6 Performance Evaluation, 226

6.5 Cost Function–Based Optimal Energy Management Strategy, 2336.5.1 Mathematical Description of Cost Function–Based OptimalEnergy Management, 234

6.5.2 Example of Optimization Implementation, 237

6.6 Optimal Energy Management Strategy Incorporated with CyclePattern Recognition, 239

6.6.1 Driving Cycle/Style Pattern Recognition Algorithm, 2396.6.2 Determination of Optimal Energy Distribution, 240

References, 242

7 Other Hybrid Vehicle Control Problems 245

7.1 Basics of Internal Combustion Engine Control, 245

7.2 Engine Torque Fluctuation Dumping Control Through Electric

Motor, 247

7.2.1 Sliding-Mode Control, 248

7.2.2 Engine Torque Fluctuation Dumping Control Based on

Sliding-Mode Control Method, 2517.3 High-Voltage Bus Spike Control, 253

7.4 Thermal Control of HEV Battery System, 258

7.4.1 Combined PID Feedback with Feedforward Battery

Thermal System Control Strategy, 2607.4.2 Optimal Battery Thermal Control Strategy, 262

7.5 HEV/EV Traction Motor Control, 265

7.5.1 Traction Torque Control, 265

7.5.2 Anti-Rollback Control, 266

7.6 Active Suspension Control of HEV/EV Systems, 267

7.6.1 Suspension System Model of a Quarter Car, 269

7.6.2 Active Suspension System Control, 270

References, 277

8 Plug-In Charging Characteristics, Algorithm, and Impact

8.1 Introduction, 279

8.2 Plug-in Hybrid Vehicle Battery System and Charging

Characteristics, 280

8.2.1 AC-120 Plug-In Charging Characteristics, 280

8.2.2 AC-240 Plug-In Charging Characteristics, 281

8.2.3 Characteristics of Rapid Public Charging, 284

8.3 Impacts of Plug-in Charging on Electricity Network, 284

8.3.1 Impact on Distribution System, 286

8.3.2 Impact on Electric Grid, 288

8.4 Optimal Plug-In Charging Strategy, 289

8.4.1 Optimal Plug-In Charge-Back Point Determination, 2908.4.2 Cost-Based Optimal Plug-In Charging Strategy, 291

References, 298

9 Hybrid Vehicle Design and Performance Analysis 299

9.1 Hybrid Vehicle Simulation System, 299

9.2 Typical Test Driving Cycles, 300

9.3 Sizing Components and Drivability Analysis, 306

9.3.1 Drivability Calculation, 307

9.3.2 Preliminary Sizing of Main Components of Hybrid

Vehicle, 3109.3.2.1 Sizing Prime Mover, 3109.3.2.2 Sizing Transmission/Gear Ratio, 3129.3.2.3 Sizing Energy Storage System, 3129.3.2.4 Design Examples, 315

9.4 Fuel Economy and Emissions Simulation Calculations, 320

References, 323

Appendix A System Identification: State and Parameter

A.1 Dynamic Systems and Mathematical Models, 325

A.1.1 Types of Mathematical Models, 325

A.1.2 Linear Time-Continuous Systems, 326

A.1.2.1 Input–Output Model of Linear Time-Invariant

and Time-Continuous System, 326A.1.2.2 State Space Model of Linear Time-Invariant

and Time-Continuous System, 328A.1.3 Linear Discrete System and Modeling, 334

A.1.4 Linear Time-Invariant Discrete Stochastic Systems, 335A.2 Parameter Estimation of Dynamic Systems, 341

A.2.1 Least Squares, 341

A.2.2 Statistical Property of Least-Squares Estimator, 342

A.2.3 Recursive Least-Squares Estimator, 344

A.2.4 Least-Squares Estimator for Slow Time-Varying

Parameters, 347A.2.5 Generalized Least-Squares Estimator, 348

A.3 State Estimation of Dynamic Systems, 349

A.4 Joint State and Parameter Estimation of Dynamic Systems, 351A.4.1 Extended Kalman Filter, 351

A.4.2 Singular Pencil Model, 353

A.5 Enhancement of Numerical Stability of Parameter and State

Estimation, 356

A.5.1 Square-Root Algorithm, 357

A.5.2 UDUT Covariance Factorization Algorithm, 358

A.6 Modeling and Parameter Identification, 361

References, 363

Appendix B Advanced Dynamic System Control Techniques 365

B.1 Pole Placement of Control System, 366

B.2 Optimal Control, 371

B.2.1 Optimal Control Problem Formulation, 371

B.2.2 Pontryagin’s Maximum Method, 372

B.2.3 Dynamic Programming, 374

B.2.4 Linear Quadratic Control, 378

B.3 Stochastic and Adaptive Control, 381

B.3.1 Minimum-Variance Prediction and Control, 382

B.3.1.1 Minimum-Variance Prediction, 382B.3.1.2 Minimum-Variance Control, 385B.3.2 Self-Tuning Control, 387

B.3.3 Model Reference Adaptive Control, 389

B.3.4 Model Predictive Control, 391

B.4 Fault-Tolerant Control, 392

B.4.1 Hardware Redundant Control, 394

B.4.2 Software Redundant Control, 394

References, 395

During the last decade, hybrid electric vehicles have come on the market and newtechniques have been dramatically advanced and widely used In the evolution ofthe design of hybrid vehicle systems, there exist several paramount challenges.These are driven by the stricter requirements for fuel economy and emissionsand by progress in the technical development of power electronics, batteries, andother major components

Hybrid electric vehicles, combining an internal combustion engine with one

or more motors for propulsion, operate in the changing environments of ent fuels, load levels, and weather conditions Hybrid electric vehicle systemengineers are now being challenged to expand their horizons and extend theirconcepts and methods not only so they can be applicable to incompletely mod-eled systems but also to the systems whose models are initially poorly definedbut can be improved online during operation

differ-Modeling and control have played key roles in technological development,from overall system performance analysis to the calculation of manufacturingand servicing cost of new design To articulate these challenges and encouraged

by current hybrid vehicle system advancement, the author thought it necessary

to publish a book on the hybrid electric vehicle system modeling and control.The material assembled in this book is an outgrowth of my over ten years

of work on hybrid vehicle research, development, and production at NationalResearch Council Canada, Azure Dynamics and General Motors This book isintended to contribute to a better understanding of hybrid vehicle systems and

to present all the major aspects of hybrid vehicle modeling, control, simulation,performance analysis, and preliminary design

xv

There are many good articles about hybrid vehicle system modeling, lation, and control algorithms available However, up until now, there has notbeen a book that more systemically and deeply explores the connections betweenperformance analysis, modeling, and control design The motivation behind thisbook has been to provide adequate coverage to meet the ever-increasing demandfor engineers to look for rigorous methods for hybrid vehicle design and analysis.

simu-It is hoped that the sought-after conciseness and the selected examples illustratingthe methods of the modeling, simulation, and control will achieve this

The book consists of nine chapters and two appendices Chapter 1 provides

an introduction to hybrid vehicle system architecture, energy flow, and control

of a hybrid vehicle system Chapter 2 reviews the main components of a hybridsystem and their characteristics, including the internal combustion engine, electricmotor/generator, energy storage system, and fuel cell system

Chapter 3 presents the detailed mathematical models of hybrid system nents for system design and simulation analysis, including the internal combustionengine, transmission system, motor, generator, battery system, and vehicle bodysystem and driver The models presented in this chapter can be used for eitherindividual component analysis or building a whole vehicle simulation system.Chapter 4 introduces the power electronics and electric motor drives applied inhybrid vehicle systems The characteristics of commonly used power electronicswitches are presented first, and then the operation principles of the DC–DCconverter and DC/AC inverter are introduced The brushless DC motor and ACinduction motor and their control principles are also introduced for hybrid vehicleapplications Plug-in charger design is presented in the last part of the chapter.Chapter 5 addresses the energy storage system modeling and controls Therelated algorithms play a very important role in hybrid vehicle systems becausethey directly affect the overall fuel economy and drivability and safety of avehicle; however, due to the measurement availability, hybrid vehicle systemengineers are facing technical challenges in the vehicle required algorithms.State-of-charge determination algorithms and the technical challenges faced indevelopment are introduced Then, the power capability algorithms and state-of-life algorithms are discussed The hybrid vehicle cell balancing algorithm,battery cell core temperature estimation method, and battery system efficiencycalculation are also presented

compo-Chapter 6 is concerned with the solution of energy management problems

in the presence of different drive cycles Both direct and indirect methods ofoptimization are discussed The methods presented in this chapter can be treated

as the most general and practical techniques for the solution of hybrid vehicleenergy management problems

Chapter 7 elaborates other control problems in hybrid vehicle systems,including active engine fluctuation torque dumping control, voltage ripple control

in high-voltage buses, thermal control of the energy storage system, motortraction and anti-rollback control, and electric active suspension system control.Chapter 8 discusses the characteristics of AC-120, AC-240, and rapid pub-lic plug-in charging for the emerging plug-in hybrid and pure battery-powered

vehicles The impact of plug-in charging on electric grid and power tion systems is presented In addition, the various plug-in charging strategies,including the optimal charging strategy, are introduced.

distribu-Chapter 9 presents the techniques of sizing components and simulating systemperformance at the concept or predesign stage of a hybrid vehicle system Typicaltest cycles related with hybrid vehicle systems are detailed, and the calculations

of fuel economy and emissions are given

Appendix A reviews system identification and the state and parameter tion methods The commonly used mathematical models are introduced for hybridvehicle system control algorithm development The recursive least-squares andgeneralized least-squares techniques are presented for parameter estimation TheKalman filter and extended Kalman filter are also introduced to state estimationand joint parameter and state estimation In addition, needed computation stabilityenhancement techniques of practical hybrid vehicle systems are presented.Appendix B briefly introduces some advanced control methods which areneeded to improve the performance of a hybrid electric vehicle system Theseinclude system pole placement control, the objective function-based optimal con-trol, dynamic programming-based optimal control, and minimum variance andadaptive control techniques for systems with stochastic behaviors To enhance thereliability and safety of a hybrid vehicle system, fault-tolerant control strategiesare also briefly introduced

estima-This book is written as an engineering reference book on hybrid vehicle systemanalysis and design It is suitable for a training course on hybrid vehicle systemdevelopment with supplemental materials It should enable design engineers tounderstand hybrid vehicle system control algorithm design and development Itcan also be used for both undergraduate- and graduate-level hybrid vehicle systemmodeling and control courses I hope that the efforts here succeed in helping youunderstand better this most interesting and encouraging technology

Wei Liu, Ph.D., PE, P Eng

A H /C Heating/cooling surface area between battery pack and

heating/cooling channel

C a Air density correction coefficient for altitude

CapBOL Battery Ah capacity at beginning of life

CapEOL Designed battery Ah capacity at end of life

Cbat_life Battery life cost weight factor

Cdiff Diffusion capacitance of second-order electrical circuit battery

model

Cdl Double-layer capacitance of the first order and second-order

electrical circuit battery model

Cdyn Dynamic capacitance of battery electrical circuit model

Cele Electric power cost weight factor

Cenergy_balance Imbalanced energy cost weight factor

C gd Parasitic capacitance from gate to drain of MOSFET

C gs Parasitic capacitance from gate to source of MOSFET

D cf Distance between center of gravity and front wheel of vehicle

xix

D cr Distance between center of gravity and rear wheel of vehicle

F Faraday constant, number of Coulombs per mole of electrons

(9.6485309× 104 C· mol−1)

Factuator_max Maximum output force of actuator of active suspension system

Fwf Friction force acting on front wheel of vehicle

Fwr Friction force acting on rear wheel of vehicle

Gactuator(s) Transfer function of actuator of active suspension systemG(Cap) Decline of Ah capacity of battery system

G(R) Increment of internal resistance of battery system

Hcg Height from center of gravity to road of vehicle

Hgend Battery heat generation

Ibalancing_max Maximum balancing current of battery system

IGM Maximum peak positive gate current of thyristor

Imax _chg Maximum allowable charge current of battery system

Imax _dischg Maximum allowable discharge current of battery system

Jaxle Lumped inertia on axle transferred from powertrain

Kactuator Gain of actuator from input voltage to output force of active

suspension system

LiFePO4 Lithium iron phosphate

M c Total coolant mass of energy storage system

N C Teeth number of carrier of planetary gear set

N R Teeth number of ring gear of planetary gear set

N S Teeth number of sun gear of planetary gear set

Pa_pct Acceleration pedal position in percentage

Pbrake_pct Brake pedal position in percentage

Pmax _chg_bat Maximum allowable battery charging power

Pmax_dischg_bat Maximum allowable battery discharging power

Pmax_prop_mot Maximum allowable motor propulsive power

Pmax_regen_mot Maximum allowable motor regenerative power

Ppump Operation power of heating/cooling system pump

˙

Q H /C Energy transfer rate of heater/chiller

RBOL Battery internal resistance at beginning of life

REOL Battery internal resistance at end of life

Rct Charge transfer resistance of second-order electrical circuit

battery model

Rdiff Diffusion resistance of second-order electrical circuit battery

model

Rdyn Dynamic resistance of battery electrical circuit model

Ress Internal resistance of battery system

R g Universal gas constant: R = 8.314472 J · K−1· mol−1

Rint Battery cell internal resistance

Rohm Ohmic resistance of battery electrical circuit model

Rwf Reaction force acting on front wheel vehicle

Rwr Reaction force acting on rear wheel vehicle

SOCinit Initial state of charge of battery

SOCtarget Target state of charge of battery

Tactuator Time constant of actuator from input voltage to output force

Tc_init Initial coolant temperature

Tc_sp Coolant temperature setpoint

T d Derivative time constant of PID controller

Tess Energy storage system temperature

Tess_init Initial battery system temperature

Tess_sp Temperature setpoint of energy storage system

T i Integral time constant of PID controller

T J Maximum junction temperature of power electronics

T S Period of the PWM signal or sampling time period

V BE Base–emitter voltage of bipolar transistor

V CE Collector–emitter voltage of bipolar transistor

VDRM Peak repetitive forward blocking voltage of thyristor

Vdynamic Voltage on dynamic component of battery electrical circuit

model

VGM Maximum peak positive gate voltage of thyristor

Vmax Maximum allowable battery system terminal voltage

Vmin Minimum allowable battery system terminal voltage

V o Potential of battery electrical circuit model

VRRM Peak repetitive reverse blocking voltage of thyristor

VRSM Nonrepetitive peak reverse voltage of thyristor

VRWM Maximum working peak reverse voltage of power diode

Vterminal Battery system terminal voltage

femi_CO Carbon monoxide emissions

femi_HC Hydrocarbon emissions

femi_NOx Nitrogen oxide emissions

femi_PM Particulate matter emissions

gCO_hot Hot carbon monoxide emission rate

gfuel_hot Hot fuel economy rate

gHC_hot Hot hydrocarbon emission rate

gNox_hot Hot nitrogen oxide emission rate

gPM_hot Hot particulate matter emission rate

hbat Battery heat transfer coefficient

i ds d axis or air-gap flux current of AC induction motor

i qs q axis or torque current of AC induction motor

i Qs Stator quadrature-axis current of AC induction motor

i Ds Stator direct-axis current of AC induction motor

i Qr Rotor quadrature-axis current of AC induction motor

i Dr Rotor direct-axis current of AC induction motor

kaero Aerodrag factor

k d Distortion factor of plug-in charger

krrc Rolling resistance coefficient

ksplit Split coefficient to engine and electric motor

n e Number of electrons transferred in cell reaction

r C Carrier radius of planetary gear set

r R Ring gear radius of planetary gear set

r S Sun gear radius of planetary gear set

v Qs Stator quadrature-axis voltage of AC induction motor

v Ds Stator direct-axis voltage of AC induction motor

v Qr Rotor quadrature-axis voltage of AC induction motor

v Dr Rotor direct-axis voltage of AC induction motor

 Qs Motor stator quadrature-axis flux linkage

 Ds Motor stator direct-axis flux linkage

 Qr Motor rotor quadrature-axis flux linkage

 Dr Motor rotor direct-axis flux linkage

λ Forgetting factor of recursive least-squares estimator

λfuel Fuel economy temperature factor

λNOx Nitrogen oxide emission temperature factor

λPM Particulate matter emission temperature factor

ηpt_eng Engine power drivetrain efficiency

ηpt_mot Electric motor power drivetrain efficiency

τaccess Lumped torque of mechanical accessories

τcct Closed-throttle torque of engine

τdemand Vehicle demand torque

τregen Regenerative torque

τtrac Traction torque from powertrain

ω c Angular velocity of carrier of planetary gear set

ωmax _eng Maximum allowable angular velocity of engine

ωmax _mot Maximum allowable angular velocity of motor

ω R Angular velocity of ring gear of planetary gear set

ω s Angular velocity of sun gear of planetary gear set

ARMAX Autoregressive moving average exogenous model

DOE Department of Energy; also design of experiment

xxv

ECU Electronic/engine control unit

e-CVT Electronic continuously variable transmission

EDLC Electrochemical double-layer capacitor

EREV Electric range extended hybrid vehicle

HPPC Hybrid pulse power characterization test

IGBT Insulated gate bipolar transistor

MOSFET Metal–oxide–semiconductor field effect transistor

PHEV Plug-in hybrid electric vehicle

PID Proportional integral derivative controller

PNGV Partnership for a new generation of vehicles

RPM Revolution per minute

SISO Single-input– single-output system

VITM Voltage, current, and temperature measurement unit

INTRODUCTION

In recent decades, hybrid electric vehicle technology has advanced significantly inthe automotive industry It has now been recognized that the hybrid is the idealtransition from the all-petroleum vehicle to the all-electric vehicle In popularconcepts, the hybrid electric vehicle (HEV) is thought of as a combination of aninternal combustion engine (ICE) and an electric motor

The paramount importance of hybrid vehicle system technology is that thefuel economy can be noticeably increased while meeting the increased stringentemission standards and drivability requirements Thus, hybrid vehicles can play acrucial role in resolving the world’s environmental problems and growing energyinsecurity In addition, hybrid technology has been promoting the technology ofthe electric motor, power electronics, and batteries to maturity (Chan, 2002;Powers and Nicastri, 2000)

The HEV is a complex system of electrical and mechanical components Itspowertrain control problems are complicated and often have conflicting require-ments Moreover, they are generally nonlinear, exhibit fast parameter variation,and operate under uncertain and changing conditions; for example, the vehiclehas to run well on a cold January day in Northern Ontario as well as a swelteringday in Death Valley Many of the control design objectives are very difficult toformalize and many of the variables of greatest concern are not measurable TheHEV system control is a fundamentally multivariable problem with many actua-tors, performance variables, and sensors It is often important to take advantage

of these interactions with multivariable designs; however, multivariable designs

Introduction to Hybrid Vehicle System Modeling and Control, First Edition Wei Liu.

© 2013 John Wiley & Sons, Inc Published 2013 by John Wiley & Sons, Inc.

1

may make control strategies less robust to parameter variation and uncertaintiesand thus may be more difficult to calibrate In this book, we will systematicallyintroduce the HEV control problems, from powertrain architecture and modeling

to design and performance analysis

There are basically two different hybrid architectures: (i) The series hybrid, inwhich the engine, coupled with a generator, powers the generator that rechargesthe batteries and/or supplies electric energy to the electric motor The motor, inturn, provides torque to the wheels (ii) The parallel hybrid vehicle is propelled byeither the engine or the electric motor or both The electric motor works as a gen-erator to recharge the batteries during regenerative braking or when the engine isproducing more power than needed to propel the vehicle Although possessing theadvantageous features of both series and parallel HEVs, the series–parallel HEV

is relatively more complicated and costly Nevertheless, this system architecturehas been used in some modern HEVs as advanced control and manufacturingtechnologies can be applied

1.1.1 Series Hybrid

A series HEV, as shown in Fig 1-1, has power sources in electromechanicalseries The electrical powertrain only provides propulsion power to the drivewheels, and an engine–generator pair unit (Genset) recharges the energy stor-age system (ESS) that provides energy to the electrical powertrain Therefore,generally speaking a series hybrid vehicle is an electric vehicle with a Genset

to supply electrical energy when the vehicle’s battery lacks sufficient energy topower the vehicle

Because of the simplicity of its control, this type of hybrid vehicle can be found

in practical uses, especially in heavy/medium-duty delivery trucks and shuttle

ELECTRIC HYDRAULIC PUMP

12V LOW VOLTAGE

DC-DC CONVERTER

POWERTRAIN

CONTROL MODULE

Fig 1-1. Rear-wheel-drive series hybrid electric vehicle layout.

buses In this type of system, the primary function of the Genset is to extendthe range of the electric vehicle beyond what is possible on a battery alone Thistype of HEV can globally optimize the energy sources, but the implementationcost is high.

1.1.2 Parallel Hybrid

In contrast to the series HEV, a parallel HEV blends ICE power output with tric motor/generator power output There are multiple potential points connectingthese two power sources to the drivetrain depending on the availabilities of thecomponents In a parallel HEV configuration, shown in Fig 1-2, an electricalpowertrain system is connected to the conventional powertrain system through aclutch that enables the vehicle to be driven by the electric motor or engine sepa-rately or together The maximum power rating of the electrical powertrain is nor-mally smaller than that of the engine-based conventional powertrain in a parallelhybrid vehicle The principle of sizing the electric powertrain is that the electricmotor and ESS can deliver the required power for a given drive cycle In addition,the conventional powertrain must be able to provide sufficient flexible torque thatcan be smoothly and efficiently combined with the torque from the electric motor

elec-to meet the elec-torque requirements of propelling the vehicle The engine may beturned on and off frequently in response to the system control strategy

1.1.3 Series – Parallel Hybrid

In a series–parallel configuration the electric motor, the electric generator, theinternal combustion engine, and the wheels of the vehicle can be linked togetherthrough one or multiple planetary gear sets or other devices Figure 1-3 showsthe series–parallel configuration in which the power provided by the engine getssplit and transmitted to the wheels through two paths: series and parallel The

ESS (BATTERIES)

HIGH VOLTAGE JUNCTION BOX

12V LOW VOLTAGE

ELECTRIC HYDRAULIC PUMP

DC-DC CONVERTER POWERTRAIN

HIGH VOLTAGE JUNCTION BOX

ELECTRIC HYDRAULIC PUMP

12V LOW VOLTAGE DC-DC

Fig 1-3. Rear-wheel-drive series–parallel hybrid layout.

series path leads through the electric generator connected to the ESS to the

elec-tric motor to the wheels In this path, the mechanical power of the engine getsconverted to electric power through the generator, and the electric power canpartly flow to the ESS or entirely to the wheels through the electrical driveline

In the parallel path, the engine is connected through the ring gear to the

con-ventional drivetrain In this path, the mechanical power of the engine is partly

or entirely transmitted mechanically to the wheels, and the part not transmitted

to the wheels will be converted to electric power through the electric motor tocharge the battery; if the entire mechanical power of the engine cannot meet thevehicle demand power, the electric motor drivetrain will supply additional torque

to the wheels The series–parallel hybrid electric configuration acts at all times as

a combination of the series and the parallel configurations It allows the electricmotor drivetrain to adjust the engine load to achieve the optimal fuel economy.The percentage of power flowing through the series and parallel paths deter-mines the performance of a series–parallel hybrid vehicle Although the powerflow can be set by controlling the speed of the planetary gear set, a sophisti-cated control system is needed to control the power flow to achieve the best fuelefficiency

The above comparison of the series and parallel configurations leads to theconclusion that, in city driving conditions, series hybrid behavior is preferablebut, during highway driving conditions, a parallel hybrid action is generallydesired Therefore, the series–parallel configuration combines the positiveaspects of the series configuration— independence of engine operation from thedriving conditions— with the advantage of the parallel configuration— efficientmechanical drivetrain The complexity of the control task for the series–parallelconfiguration is the main distinct point compared to the series or parallelsystem

1.2 HYBRID VEHICLE SYSTEM COMPONENTS

Compared with a traditional vehicle, the ESS, electric motors, transmission tem, and power electronics modules such as DC-DC converters and DC-ACinverters are key in hybrid vehicle systems In order to size these componentsand analyze hybrid system performance, it is necessary to establish their modelsbased on either physical principles or test data

sys-(a) The ESS One of the most important subsystems in hybrid vehicle, theESS directly affects the efficiency of the vehicle In hybrid vehicle appli-cations, the batteries need to have high energy density, low internal resis-tance, and long cycle and calendar life Depending on the design objective,higher power density batteries are generally used for traditional HEVsand higher energy density batteries are needed for plug-in HEVs Anotherenergy storage component attracting R&D attention for HEV applications

is the ultracapacitor, which lasts indefinitely and has extremely rapid chargeand discharge rates These advantages make ultracapacitors ideal for pro-viding the surges required for accelerating an electrically powered vehicleand for efficiently accumulating charge during regenerative braking Due tothe low energy density and high self-discharge rate, ultracapacitors are notconsidered an energy storage device for plug-in HEVs However, the com-bination of ultracapacitors and higher energy density batteries may haveconsiderable potential for all HEVs as it both provides power and energydensity advantages and decreases the size of the entire ESS On the otherhand, with significant reduction in manufacturing cost, lithium-ion (Li-ion)batteries have been widely regarded as the best choice for hybrid and pureelectric vehicles

(b) Transmissions Hybrid vehicle systems bring some specific demands fortransmission design Generally speaking, the hybrid vehicle transmissionmust be able to manage ICE driving, electric-only driving, and combina-tions of the two Functionally, it has to support functions of stop–start,regenerative braking, and shifting ICE working range; therefore, the trans-mission must also be able to adjust its parameters to match the actual drivingscenarios That is, a hybrid vehicle system mainly relies on the transmission

to implement optimal performance for multiple types of drive cycles ratherthan a particular cycle Other challenges for hybrid transmission designinclude minimizing additional weight, cost, and packaging

(c) Electric Motors Efficient, light, powerful electric motors also play keyroles in hybrid technology Depending on the architecture of an HEV,the electric motor can be used as a peak-power regulation device, a load-sharing device, or a small transient source of torque The HEV electricmotors need to operate well in two modes—normal and extended In the

“normal” mode, the motor exerts constant torque throughout the rated speedrange Above the rated speed, the motor enters its “extended” mode inwhich torque decreases with speed In HEVs, the electric motor delivers the

necessary torque for adequate acceleration during its normal mode before itchanges to its extended mode for steady speeds Depending on the designobjectives, direct current (DC), brushless DC, and alternative current (AC)induction motors can be selected for HEVs.

The second function of electric motors is to capture the energy from erative braking The electric motors for HEV applications need to havethe capacity to operate equally well as a generator when driven by someexternal rotational force Applying the brake pedal in an HEV normallysignals the control system motor to generate negative torque, switch offthe ICE, or let the vehicle’s momentum drive the electric motor via thedrivetrain When the electric motor generates negative torque, the mechan-ical energy of the vehicle will be converted to AC electric energy by themotor, and then the inverter system on the motor assembly inverts the AC

regen-to DC regen-to recharge the battery system The control system tasks includeoptimizing the regenerative braking strength while activating the conven-tional hydraulic braking system in accordance with the pressure applied tothe brake pedal Gentle deceleration generally maximizes the use of theregenerative system, but emergency braking sometimes needs to utilize theconventional braking system As stop–start urban driving involves frequentacceleration and deceleration, the regenerative braking system and controlstrategy are crucial for improving the fuel efficiency of a hybrid vehicle

(d) Power Electronic Modules Similar to batteries, electric motors, and missions, DC–DC converters and DC–AC inverters are very importantdevices in hybrids The function of the DC–DC converter in HEVs/EVs

trans-is to convert the high voltage supplied by the ESS to a lower voltagewhich normally supplies 12 V electric power to various accessories such

as headlamps and wipers The function of the inverter in HEVs/EVs is toconvert the DC voltage of the ESS to high AC voltage to power propulsionmotor Under regenerative braking, this process is reversed: The output ACpower of the motor, operating as a generator, is converted to DC power tocharge the battery The efficiencies of these power electronic devices havesignificant impact on the overall efficiency of the vehicle

1.3.1 Power Flow of Hybrid Vehicles

Different types of HEV configuration have different power flow path In serieshybrid power flow, shown in Fig 1-4, the propulsion power comes from theelectric motor which converts electric energy to the required mechanical energy,while the motor can be powered by either the generator or the ESS Theengine–generator pair can either power the electric motor or charge the ESS.During regenerative braking, the motor works as a generator which convertsbraking mechanical energy to electric energy to charge the ESS When cranking

Engine Generator Motor

Propel power

Regenerative power

Crank power

Energy storage system

Fig 1-4. Power flow of series hybrid vehicle.

Engine GeneratorMotor

Energy storage system

Propel power

Regenerative power

Crank power

Fig 1-5. Power flow of parallel hybrid vehicle.

the engine, the battery will provide electric energy to the generator which works

as a motor In a parallel hybrid, the vehicle can be powered by either the engine

or electric motor or both depending on the system state and control objectives.During regenerative braking, the captured brake energy will be converted intoelectric energy by the electric motor and stored in the ESS The ESS will powerthe Generator/motor to crank the engine when key started The power flow path

of a parallel hybrid system is shown in Fig 1-5

1.3.2 Typical Drive Cycles

Since the vehicle’s fuel economy and emissions are strongly affected by mental factors such as road condition, traffic, driving style, and weather, it is not

environ-a good wenviron-ay to judge environ-a vehicle’s fuel economy or emissions benviron-ased on environ-actuenviron-al fuelconsumption and emissions measured on the road To get around this problem,the automobile industry and governments have developed a series of standardtests to measure the fuel consumption and emission of a vehicle under repeatableconditions where different vehicles are compared fairly to each other These testsare called drive cycle tests and are routinely conducted on all new car designs.Most test drive cycles will be described in Chapter 9

1.3.3 Vehicle Drivability

Drivability can be understood as the capacity of a vehicle to deliver the torquerequested by the driver at the time expected It is often evaluated subjectivelybut can also be quantified objectively through accelerometers Problems such ashesitation, powertrain excitation during acceleration (acceleration pedal tip-in),and deceleration (acceleration pedal back-out) maneuvers are identified in thisattribute Compared with conventional vehicles, hybrid vehicles have more oper-ational modes The delivered torque is associated not only with the states of theICE, electric motor/converter, and ESS but also with the energy managementstrategy determining how to divide the vehicle required power between the ICEand the electric motor To achieve the maximum fuel economy and meet emis-sion standards under different driving situations, an HEV has to employ morecomplex control strategies to meet the drivability requirements The complexity

of the control and powertrain systems makes it a challenge to analyze an HEV’sdrivability

1.3.4 Vehicle Fuel Economy and Emissions

The actual fuel consumption and emissions of ICE-driven vehicles can be sured directly Since HEVs, especially plug-in HEVs, can make use of an externalelectric source (such as the public electric grid), the electric energy withdrawnfrom that source must be separately accounted for when performing fuel con-sumption and emissions calculations

Since the hybrid vehicle is a complex system of electrical and mechanical ponents which contain multidisciplinary technologies, modern control systemtechniques and methodologies are playing important roles in hybrid technol-ogy (Powers and Nicastri, 2000) An HEV’s performance is affected by manymultidisciplinary interrelated factors; therefore, advanced control strategies couldsignificantly improve performance and lower cost The overall control objectives

com-of a hybrid vehicle are to maximize fuel economy and minimize emission Inorder to achieve the objectives, some key system variables must be optimallygoverned, including mainly energy flow of the system, availability of energyand power, temperature of subsystems, and dynamics of the engine and electricmotor Some typical HEV control problems are as follows:

(a) Have the ICE work on the optimal operating points Each ICE has optimaloperating points on its torque–speed plane in terms of fuel economy andemissions If the ICE operates on these points, the maximum fuel econ-omy, the minimum emissions, or a compromise between fuel economy andemissions can be achieved It is a challenging control objective for an HEV

to have the ICE operate on these points at various operating conditions

(b) Minimize ICE dynamics As an ICE has inertia, additional energy isconsumed to generate the related kinetics whenever the operating speedchanges Therefore, the operating speed of the ICE should be kept constant

as much as possible, and any fast fluctuations should be avoided HEVsmake it possible to minimize the dynamics under changing load, road, andweather conditions

(c) Optimize ICE operation speed According to the working principle of anICE, its fuel efficiency is low if the ICE operates at low speed The ICEspeed can be independently controlled with the vehicle speed and even can

be shut down when its speed is below a certain value in order to achievemaximum benefits

(d) Minimize ICE turn on/off times The ICE in an HEV can be turned on andoff frequently as it has a secondary power source; furthermore, when ICEshould be turned on/off can be determined based on an optimal controlmethod to minimize fuel consumption and emissions

(e) Optimally manage battery state of charge ( SOC) The battery’s SOC needs

to be controlled optimally so as to provide sufficient energy to power thevehicle and accept regenerative energy during braking or downhill as well

as maximize its service life The simplest control strategy is to turn theICE off if the battery’s SOC is too high and turn the ICE on if the SOC istoo low A more advanced control strategy should be able to regulate theoutput power of the ICE based on the actual SOC level of the ESS

(f) Optimally control the voltage of the high-voltage bus Actual voltage ofthe high-voltage bus of an HEV has to be controlled during dischargingand charging to avoid being over or under the limits; otherwise, the ESS

or other components may be permanently damaged

(g) Optimize power distribution Since there are two power sources in anHEV, the most challenging and important control task is to split the vehi-cle demand power to the ICE and the electric motor based on the drivingscenario, road and weather conditions, and state of the ESS to achieve thebest fuel economy, minimum emissions, and maximum service life of theESS

(h) Follow zero-emission policy In certain areas such as tunnels or workshops,some HEVs may need to be operated in the pure electric mode

(i) Optimally control HEV transmission system The most recent HEV tems not only possess the features of the parallel hybrid, but also incorporateunique advantages of the series hybrid Key in this implementation is toemploy an advanced transmission system that provides at least two mechan-ical transmission channels through clutch control In city driving, the HEVsystem maximally uses the advantage of a series hybrid If full-throttleacceleration is needed, the required power is simultaneously delivered bythe ICE and electric motor, but the ICE is operated at the steady speed asmuch as possible During normal driving, the power is collaboratively fed

sys-by the ICE and electric motor to achieve maximum fuel economy

Chan, C C “The State of the Art of Electric and Hybrid Vehicles.” Proceedings of the

IEEE , 90(2), 248–275, February 2002.

Powers, W F., and Nicastri, P P “Automotive Vehicle Control Challenges in the 21st

Century.” Control Engineering Practice, 8, 605–618, 2000.

• Electric motor with DC/DC converter, DC/AC inverter, and controller

• Energy storage system

• Transmission system

The prime mover of a hybrid vehicle is its main energy source, which generally isone of gasoline, diesel, or fuel cells The selection of the prime mover is mainlybased on the requirements of drivability, fuel economy, and emission

2.1.1 Gasoline Engine

The gasoline engine is the most developed machine that converts naturalfossil energy to mechanical work to propel a vehicle The main advan-tages of this type of engine are its high specific power (power–weight ratio), wide range of rotational speed, and higher mechanicalefficiency To perform hybrid system design and performance analysis, theengineer needs to understand the ICE’s torque/power versus speed and fuel

Introduction to Hybrid Vehicle System Modeling and Control, First Edition Wei Liu.

© 2013 John Wiley & Sons, Inc Published 2013 by John Wiley & Sons, Inc.

11