An invaluable academic reference for the area of high-power converters, covering all the latest developments in the field

High-power multilevel converters are well known in industry and academia as one of the preferred choices for efficient power conversion. Over the past decade, several power converters have been developed and commercialized in the form of standard and customized products that power a wide range of industrial applications. Currently, the modular multilevel converter is a fast-growing technology and has received wide acceptance from both industry and academia. Providing adequate technical background for graduate- and undergraduate-level teaching, this book includes a comprehensive analysis of the conventional and advanced modular multilevel converters employed in motor drives, HVDC systems, and power quality improvement.

Modular Multilevel Converters: Analysis, Control, and Applications provides an overview of high-power converters, reference frame theory, classical control methods, pulse width modulation schemes, advanced model predictive control methods, modeling of ac drives, advanced drive control schemes, modeling and control of HVDC systems, active and reactive power control, power quality problems, reactive power, harmonics and unbalance compensation, modeling and control of static synchronous compensators (STATCOM) and unified power quality compensators. Furthermore, this book:

Sixing Du, PhD, is a Postdoctoral Fellow in the Department of Electrical and Computer Engineering at Ryerson University in Toronto, Canada.

Apparao Dekka, PhD, is a Postdoctoral Fellow in the Department of Electrical and Computer Engineering at Ryerson University in Toronto, Canada. He has made significant contributions to the control and application of the MMCs.

Bin Wu, PhD, is a Professor in the Department of Electrical and Computer Engineering at Ryerson University in Toronto, Canada. He is a co-author of several Wiley-IEEE Press books.

Navid Zargari, PhD, is a Manager& Product Architect in MV Drives R&D at Rockwell Automation, Toronto, Canada. He is a co-author of the Wiley publicationPower Conversion and Control of Wind Energy Systems.

About the Authors xiii

Preface xvii

Acknowledgments xxi

Acronyms xxiii

Symbols xxvii

About the Companion Website xli

Part I General Aspects of Conventional mmc

1 Review of High-Power Converters 3

1.1 Introduction 3

1.2 Overview of High-Power Converters 4

1.3 Voltage Source Converters 6

1.3.1 Neutral-Point Clamped Converter 8

1.3.2 Active Neutral-Point Clamped Converter 10

1.3.3 Flying Capacitor Converter 11

1.3.4 Nested Neutral-Point Clamped Converter 12

1.3.5 Cascaded H-bridge Converter 13

1.3.6 Cascaded Neutral-Point Clamped Converter 15

1.4 Current Source Converters 16

1.4.1 Load-Commutated Current Source Converter 16

1.4.2 PWM Current Source Converter 18

1.5 Matrix Converters 19

1.5.1 Direct Matrix Converter 19

1.5.2 Indirect Matrix Converter 20

1.5.3 Multi-Modular Matrix Converter 21

1.6 Modular Multilevel Converters 23

1.6.1 Converter Technology 24

1.6.2 Applications 24

1.6.3 Technical Challenges 31

1.7 Summary 33

References 34

2 Fundamentals of Modular Multilevel Converter 37

2.1 Introduction 37

2.2 Modular Multilevel Converter 38

2.2.1 Converter Con guration 39

2.2.2 Con guration of Submodules 39

2.2.3 Comparison of Submodules 46

2.2.4 Principle of Operation 48

2.3 Pulse Width Modulation Schemes 49

2.3.1 Phase-Shifted Carrier Modulation 51

2.3.2 Level-Shifted Carrier Modulation 59

2.3.3 Sampled Average Modulation 60

2.3.4 Space Vector Modulation 65

2.3.5 Staircase Modulation 73

2.4 Summary 77

References 77

3 Classical Control of Modular Multilevel Converter 79

3.1 Introduction 79

3.2 Overview of Classical Control Method 80

3.3 Submodule Capacitor Voltage Control 82

3.3.1 Leg Voltage Control 82

3.3.2 Voltage Balance Strategy 83

3.4 Output Current Control 88

3.4.1 Reference Frame Theory 88

3.4.2 Control of MMC with Passive Load 92

3.5 Circulating Current Control 95

3.5.1 Mathematical Model 96

3.5.2 Control in Synchronous-dq Reference Frame 97

3.5.3 Control in Stationary-abc Reference Frame 100

3.6 Summary 101

References 101

4 Model Predictive Control of Modular Multilevel Converter 103

4.1 Introduction 103

4.2 Mathematical Model of mmc 105

4.2.1 Continuous-Time Model 105

4.2.2 Discretization Methods 108

4.2.3 Discrete-Time Model 110

4.3 Extrapolation Techniques 113

4.3.1 Vector Angle Extrapolation 113

4.3.2 Lagrange Extrapolation 113

4.4 Cost Function and Weight factors 114

4.4.1 Formulation of Cost Function 114

4.4.2 Selection of Weight Factors 116

4.5 Direct Model Predictive Control 117

4.5.1 Design Procedure 117

4.5.2 Control Algorithm 120

4.6 Indirect Model Predictive Control 124

4.6.1 Design Procedure 125

4.6.2 Control Algorithm 127

4.7 Summary 128

References 128

Part II Advanced Modular Multilevel Converters

5 Passive Cross-Connected Modular Multilevel Converters 133

5.1 Introduction 133

5.2 Passive Cross-Connected mmc 134

5.2.1 Con guration of Power Circuit 134

5.2.2 Switching States and Output Voltage 135

5.3 Principle of Operation 138

5.3.1 Modeling of PC-MMC 138

5.3.2 Phase-Shifted Carrier Modulation for PC-MMC 140

5.4 Low/Zero Frequency Operation of PC-MMC 144

5.4.1 Equivalent Circuit 145

5.4.2 Design of Cross-Connected Capacitor 146

5.4.3 Submodule Capacitor Voltage Ripple 148

5.4.4 Common-Mode Voltage 151

5.5 Classical Control of PC-MMC 153

5.5.1 Output Current Control 154

5.5.2 Submodule Capacitor Voltage Control 156

5.5.3 Synthesis of Modulation Signals 159

5.6 Summary 162

References 162

6 Active Cross-Connected Modular Multilevel Converters 165

6.1 Introduction 165

6.2 Active Cross-Connected mmc 166

6.2.1 Circuit Con guration of AC-MMC 166

6.2.2 Switching States and Output Voltage 166

6.3 Principles of Operation 169

6.3.1 Modeling of AC-MMC 170

6.3.2 Phase-Shifted Carrier Modulation for AC-MMC 171

6.4 Low-Frequency Operation of AC-MMC 176

6.4.1 Equivalent Circuit 176

6.4.2 Submodule Capacitor Voltage Ripple 178

6.4.3 Common-Mode Voltage 181

6.4.4 Current Stress on Semiconductor Devices 184

6.5 Classical Control of AC-MMC 185

6.5.1 Output Current Control 186

6.5.2 Submodule Capacitor Voltage Control 186

6.5.3 Synthesis of Modulation Signals 189

6.6 Summary 192

References 192

7 Star and Delta-Channel Modular Multilevel Converters 195

7.1 Introduction 195

7.2 Star-Channel Modular Multilevel Converter 196

7.2.1 Circuit Con guration of Star-Channel mmc 196

7.2.2 Switching States and Output Voltage 197

7.3 Principles of Operation 200

7.3.1 Modeling of Star-Channel mmc 200

7.3.2 Phase-Shifted Carrier Modulation for Star-Channel mmc 203

7.4 Low-Frequency Operation of Star-Channel mmc 207

7.4.1 Equivalent Circuit 208

7.4.2 Submodule Capacitor Voltage Ripple 209

7.4.3 Common-Mode Voltage 213

7.5 Classical Control of Star-Channel mmc 216

7.5.1 Output Current Control 217

7.5.2 Submodule Capacitor Voltage Control 217

7.5.3 Synthesis of Modulation Signals 221

7.6 Delta-Channel Modular Multilevel Converter 223

7.7 Comparison of Advanced Modular Multilevel Converters 225

7.8 Summary 226

References 227

Part III Applications of Modular Multilevel Converters

8 Modular Multilevel Converter Based Medium-Voltage Motor Drives 231

8.1 Introduction 231

8.2 Fundamentals of MMC-Based Motor Drive 232

8.2.1 System Con gurations 232

8.2.2 Control Schemes 233

8.3 Voltage-Oriented Control of Grid-Side mmc 234

8.3.1 Principle of voltage orientation 235

8.3.2 Implementation of PLL 236

8.3.3 Block diagram of VOC 237

8.4 Indirect Field-Oriented Control of Motor-side mmc 240

8.4.1 Principle of Field Orientation 241

8.4.2 Rotor Flux Vector Estimator 242

8.4.3 Block diagram of IFOC approach 244

8.5 Low-Speed Operation of MMC-based Motor Drive 248

8.5.1 Analysis of Submodule Capacitor Voltage Ripple 248

8.5.2 Analysis of MMC with High-Frequency Voltage and Current Injection 254

8.5.3 Estimation of High-Frequency Voltage and Current Magnitude 256

8.5.4 Minimization of Submodule Capacitor Voltage Ripple 257

8.6 Common-Mode Voltage Issues and Blocking Schemes 262

8.6.1 De nition of Common-Mode Voltage 262

8.6.2 Blocking of Common-Mode Voltage 264

8.7 Transformer-less MMC-based Motor Drive 265

8.8 Summary 269

References 269

9 Role of Modular Multilevel Converters In The Power System 271

9.1 Introduction 271

9.2 MMC-Based HVDC Transmission Systems 272

9.2.1 Two-Terminal System 273

9.2.2 Multi-Terminal System 274

9.2.3 DC-Side Short-Circuit Fault Protection 275

9.2.4 HVDC Circuit Breakers 277

9.3 Control of Two-Terminal MMC-Based HVDC System 278

9.3.1 Sending-End Converter Control 279

9.3.2 Receiving-End Converter Control 281

9.4 Control of Multi-Terminal MMC-Based HVDC System 286

9.4.1 Voltage Margin Control Scheme 288

9.4.2 Voltage Droop Control Scheme 293

9.5 MMC-based Static Synchronous Compensator 294

9.5.1 System Con guration 295

9.5.2 Reactive Power Compensation 295

9.5.3 Compensation of Unbalanced AC-Grid Currents 298

9.6 MMC-based Uni ed Power Quality Conditioner 306

9.7 Summary 307

References 307

Appendix A MATLAB Demo Projects 311

References 312

Index 313