The advent of lithium ion batteries has brought a significant shift in the area of large format battery systems. Previously limited to heavy and bulky lead-acid storage batteries, large format batteries were used only where absolutely necessary as a means of energy storage. The improved energy density, cycle life, power capability, and durability of lithium ion cells has given us electric and hybrid vehicles with meaningful driving range and performance, grid-tied energy storage systems for integration of renewable energy and load leveling, backup power systems and other applications. This book discusses battery management system (BMS) technology for large format lithium-ion battery packs from a systems perspective. This resource covers the future of BMS, giving us new ways to generate, use, and store energy, and free us from the perils of non-renewable energy sources. This book provides a full update on BMS technology, covering software, hardware, integration, testing, and safety.

1 Introduction 17

1.1 Battery Management Systems and Applications 17

1.2 Scace of the Art 18

1.3 Challenges 22

2 Lithium-Ion Battery Fundamentals 25

2.1 Battery Operacion 25

2.2 Bactery Consrruccion 26

2.3 Battery Chemiscry 29

2.4 Safety 35

2.5 Longevity 38

2.6 Performance 39

2.7 Integration 40

3 Large-Format Systems 43

3.1 Definition 43

3.2 Balance of Plane 45

3.3 Load Interface 46

3.4 Variation and Divergence 47

3.5 Application Parameters 48

4 System Description 51

4.1 Typical Inputs 52

4.2 Typical Outputs 54

4.3 Typical Functions 56

4.4 Summary 57

5 Architectu res 59

5.1 Monolithic 59

5.2 Distributed 61

5.3 Semi-Distributed 61

5.4 Connection Methods 63

5.5 Additional Scalability 65

5.6 Battery Pack Architectures 66

5.7 Power Supply 67

5.8 Control Power 68

5.9 Computing Architecture 69

6 Measurerr1ent 71

6.1 Cell Voltage Measurement 71

6.2 Current Measurement 77

      6.2.1 Current Sensors 78

      6.2.2 Current Sense Measurement 84

6.3 Synchronization of Current and Volrage 86

6.4 Temperature Measurement 87

6.5 Measurement Uncertainty and Battery Management System Performance 92

6.6 Interlock Status 92

7 Control 95

7.1 Contactor Control 95

7.2 Soft Start or Precharge Circuits 97

7.3 Control Topologies 99

7.4 Concaccor Opening Transient s 101

7.5 Chatter Detection 102

7.6 Economizers 104

7.7 Concactor Topologies 105

7.8 Concactor Fault Detection 106

8 Battery Management System Functionality 111

8.1 Charging Strategies 111

      8.1.1 CC/CV Charging Method 111

      8.1.2 Target Voltage Method 112

      8.1.3 Constant Current Method 113

8.2 Thermal Management 114

8.3 Operational Modes 115

9 High -Voltage Electronics Fundamentals 119

9.1 High-Voltage DC Hazards 119

9.2 Safety of High-Voltage Electroni cs 120

9.3 Conductive Anodic Filaments 123

9.4 Floating Measurements 124

      9.4.1 Y-Capacicance 125

9.5 HV Isolation 125

9.6 ESD Suppression on Isolated Devices 128

9.7 Isolation Detection 130

10 Communications 133

10.1 Overview 133

10.2 Network Technologies 133

      10.2.1 PC/SPI 134

      10.2.2 RS-232 and RS-485 134

      10.2.3 Local Interconnect Network 136

      10.2.4 CAN 136

      10.2.5 Ethernet and TCP/IP 137

      10.2.6 Modbus 138

      10.2.7 FlexRay 138

10.3 Network Design 138

11 Battery Models 145

11.1 Overview 145

11.2 Thevenin Equivalent Circuit 146

11.3 Hysteresis 151

11.4 Coulombic Efficiency 153

11.5 Nonlinear Elements 154

11.6 Self-Discharge Modeling 157

11.7 Physia Based Battery Models 158

      11.7.1 Doyle-Fuller-Newman Model 158

      11.7.2 Single Particle Model 158

      11.8 Seate-Space Representations of Battery Models 161

      References 163

12 Parameter Identification 165

12.1 Brute-Force Approach 165

12.2 Online Parameter Identification 166

12.3 SOC/OCY Characterization 167

12.4 Kalman Filtering 168

12.5 Recursive Least Squares 168

12.6 Electrochemical Impedance Spectroscopy 169

13 Limit Algorithms 171

13.1 Purpose 171

13.2 Goals 172

13.3 Limit Strategy 172

13.4 Determining Safe Operating Area 173

13.5 Temperature 174

13.6 SOC/DOD 177

13.7 Cell Voltage 179

13.8 Faults 180

13.9 First-Order Predictive Power Limit 180

13.10 Polariza tion-Dependent Limit 181

13.11 Limit Violation Detection 181

13.12 Limits with Multiple Parallel Strings 182

14 Charge Balancing 183

14.1 Balancing Strategies 184

14.2 Balancing Optimization 185

14.3 Charge Transfer Balancing 187

      14.3.1 Flying Capacitor 188

      14.3.2 Inductive Charge Tra nsfer Balancing 190

      14.3.3 Transformer Charge Balancing 193

14.4 Dissipacivc Balancing 193

14.5 Balancing Faults 197

15 State-of-Charge Estimation Algorithms 199

15.1 Overview 199

15.2 Challenges 199

15.3 Definitions 201

15.4 Coulomb Councing 203

15.5 SOC Corrections 204

15.6 OCV Measuremencs 205

15.7 Tcmperacure Compensacion 206

15.8 Kalman Filtering 206

15.9 Ocher Observer Methods 2 1 1

Reference 212

16 State-of Health Estimation Arithms 213

16.1 Scare of Health 213

16.2 Mechanisms of Failure 215

16.3 Predicrive SOH Models 2 16

16.4 Impedance Derecrion 219

      16.4.1 Passive Methods 219

      16.4.2 Acrive Merhods 22 1

16.5 Capaciry Esrimarion 223

16.6 Self-Discharge Derecrion 226

16.7 Paramerer Esrimarion 226

16.8 Dual-Loop System 226

16.9 Remaining Useful Life Estimation 227

16.10 Particle Filters 227

Reference 229

17 Fault Detection 231

17.1 Overview 231

17.2 Failure Detection 231

      17.2.1 Overcharge/Overvo ltage 231

      17.2.2 Over-Temperature 235

      17.2.3 Overcu rrent 235

      17.2.4 Battery Imbalance/Excessive Self-Discharge 236

      17.2.5 Internal Short Circuit Detection 237

      17.2.6 Detect.ion of Lichium Placing 237

      17.2.7 Venting Detection 237

      17.2.8 Excessive Capacity Loss 238

17.3 Reaction Strategies 238

References 239

18 Hardware Implementation 241

18.1 Packaging and Product Development 241

18.2 Battery Management System IC Selection 242

18.3 Component Selection 248

      18.3.1 Microprocessor 248

      18.3.2 Other Components 249

18.4 Circuit Design 250

18.5 Layout 252

18.6 EMC 252

18.7 Power Supply Architectures 253

18.8 Manufactu ring 254

19 Software lmementation 257

19.1 Safety-Critical Software 258

19.2 Design Goals 259

19.3 Analysis of Safety-Critical Software 259

19.4 Validation and Coverage 260

19.5 Model Implementation 262

19.6 Balancing 263

19.7 Temperature Impact on State of Charge Estimation 264

20 Satety 265

20.1 Functional Safety 265

20.2 Hazard Analysis 265

20.3 Safety Goals 269

20.4 Safety Concepts and Strategies 270

20.5 Reference Design for Safety 270

21 Data Collection 275

21.1 Lifetime Data Gathering 275

22 Robustness and Reliability 279

22.1 Failure Mode Analysis 280

22.2 Environmental Durability 283

22.3 Abuse Conditions 285

22.4 Reliability Engineering 286

23 Best Practice 287

23.1 Engineering System Development 287

23.2 Industry Standards 288

23.3 Quality 289

24 Future Develoments 291

24.1 Subcell Modeling 291

24.2 Adaptive Algorithms 291

24 .3 Advanced Safety 292

24.4 System Integration 292

Endnotes 293

About the Author 295

Index 297

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