Soft-Switching PWM Full-Bridge Converters
Topologies, Control, and Design

Soft-switching PWM full-bridge converters have been widely used in medium-to-high power DC-DC conversions for topological simplicity, easy control and high effi ciency. Early works on soft-switching PWM full-bridge converter by many researchers included various topologies and modulation strategies. However, these works were scattered, and the relationship among these topologies and modulation strategies had not been revealed. This book intends to describe systematically the soft-switching techniques for pulse-width modulation (PWM) full-bridge converters, including the topologies, control and design, and it reveals the relationship among the various topologies and PWM strategies previously proposed by other researchers. The book not only presents theoretical analysis, but also gives many detailed design examples of the converters.

• Describes the soft-switching techniques for pulse-width modulation (PWM) full-bridge
  converters systematically
• Covers topologies, control and design, from the basics, through to applications and
  development
• Deliberates the soft-switching PMW control technique rather than the standard PWM
  control technique
• Presents detailed theoretical analysis with design examples for various possible
  variations to the full-bridge topology using the soft-switching technique

Soft-Switching PWM Full-Bridge Converters: Topologies, Control, and Design is an essential and valuable reference for graduate students and academics majoring in power electronics and power supply design engineers. Senior undergraduate students majoring in electrical engineering and automation engineering would also fi nd this book useful.

Preface xiii

Acknowledgment xvii

List of Abbreviations xix

1 Topologies and Operating Principles of Basic Full-Bridge Converters 1

1.1 Introduction 1

1.1.1 Development Trends in Power Electronics Technology 1

1.1.2 Classification and Requirements of Power Electronics Converters 2

1.1.3 Classification and Characterization of dc–dc Converters 3

1.2 Isolated Buck-Derived Converters 4

1.2.1 Forward Converter 4

1.2.2 Push–Pull Converter 7

1.2.3 Half-Bridge Converter 10

1.2.4 Full-Bridge Converter 11

1.2.5 Comparison of Isolated Buck-Derived Converters 12

1.3 Output Rectifier Circuits 14

1.3.1 Half-Wave Rectifier Circuit 14

1.3.2 Full-Wave Rectifier Circuit 15

1.3.3 Full-Bridge Rectifier Circuit 17

1.3.4 Current-Doubler Rectifier Circuit 18

1.4 Basic Operating Principle of Full-Bridge Converters 21

1.4.1 Topologies of Full-Bridge Converters 21

1.4.2 Pulse-Width Modulation Strategies for Full-Bridge Converters 21

1.4.3 Basic Operating Principle of a Full-Bridge Converter with a Full-Wave Rectifier Circuit and a Full-Bridge Rectifier Circuit 21

1.4.4 Basic Operating Principle of a Full-Bridge Converter with a Current-Doubler Rectifier Circuit 24

1.5 Summary 32

References 32

2 Theoretical Basis of Soft Switching for PWM Full-Bridge Converters 33

2.1 PWM Strategies for Full-Bridge Converters 33

2.1.1 Basic PWM Strategy 33

2.1.2 Definition of On-Time of Power Switches 36

2.1.3 A Family of PWM Strategies 36

2.2 Two Types of PWM Strategy 38

2.2.1 The Two Diagonal Power Switches Turn Off Simultaneously 39

2.2.2 The Two Diagonal Power Switches Turn Off in a Staggered Manner 41

2.3 Classification of Soft-Switching PWM Full-Bridge Converters 43

2.4 Summary 44

Reference 44

3 Zero-Voltage-Switching PWM Full-Bridge Converters 45

3.1 Topologies and Modulation Strategies of ZVS PWM Full-Bridge Converters 45

3.1.1 Modulation of the Lagging Leg 45

3.1.2 Modulation of the Leading Leg 47

3.1.3 Modulation Strategies of the ZVS PWM Full-Bridge Converters 47

3.2 Operating Principle of ZVS PWM Full-Bridge Converter 49

3.3 ZVS Achievement of Leading and Lagging Legs 54

3.3.1 Condition for Achieving ZVS 54

3.3.2 Condition for Achieving ZVS for the Leading Leg 54

3.3.3 Condition for Achieving ZVS for the Lagging Leg 54

3.4 Secondary Duty Cycle Loss 55

3.5 Commutation of the Rectifier Diodes 55

3.5.1 Full-Bridge Rectifier 56

3.5.2 Full-Wave Rectifier 57

3.6 Simplified Design Procedure and Example 59

3.6.1 Turn Ratio of Transformer 59

3.6.2 Resonant Inductor 59

3.6.3 Output Filter Inductor and Capacitor 60

3.6.4 Power Devices 60

3.6.5 Load Range of ZVS 61

3.7 Experimental Verification 62

3.8 Summary 66

References 66

4 Zero-Voltage-Switching PWM Full-Bridge Converters with Auxiliary-Current-Source Networks 67

4.1 Current-Enhancement Principle 68

4.2 Auxiliary Current-Source Network 69

4.3 Operating Principle of a ZVS PWM Full-Bridge Converter with Auxiliary-Current-Source Network 72

4.4 Conditions for Achieving ZVS in the Lagging Leg 78

4.5 Parameter Design 78

4.5.1 Parameter Selection for the Auxiliary-Current-Source Network 79

4.5.2 Determination of Lr, Cr, and Ic 79

4.5.3 Design Example 80

4.6 Secondary Duty Cycle Loss and Selection of Dead Time for the Drive Signals of the Lagging Leg 81

4.6.1 Secondary Duty Cycle Loss 81

4.6.2 Selection of Dead Time between Drive Signals of the Lagging Leg 82

4.6.3 Comparison with Full-Bridge Converter with Saturable Inductor 82

4.7 Experimental Verification 85

4.8 Other Auxiliary Current-Source Networks for ZVS PWM Full-Bridge Converters 87

4.8.1 Auxiliary Current-Source Networks with Uncontrolled Auxiliary Current Magnitude 87

4.8.2 Auxiliary Current-Source Networks with Controlled Auxiliary Current Magnitude 89

4.8.3 Auxiliary Current-Source Network with Auxiliary Current Magnitude Proportional to Primary Duty Cycle 89

4.8.4 Auxiliary Current-Source Network with Auxiliary Current Magnitude Adaptive to Load Current 91

4.8.5 Auxiliary Current-Source Networks with Adaptive Resonant Inductor Current 97

4.9 Summary 98

References 98

5 Zero-Voltage-and-Zero-Current-Switching PWM Full-Bridge Converters 101

5.1 Modulation Strategies and Topologies of a ZVZCS PWM Full-Bridge Converter 101

5.1.1 Modulation of the Leading Leg 101

5.1.2 Modulation of the Lagging Leg 103

5.1.3 Modulation Strategies of ZVZCS PWM Full-Bridge Converters 103

5.1.4 Method for Resetting the Primary Current at Zero State 103

5.2 Operating Principle of a ZVZCS PWM Full-Bridge Converter 110

5.3 Theoretical Analysis 113

5.3.1 Peak Voltage of the Block Capacitor 113

5.3.2 Achieving ZVS for the Leading Leg 113

5.3.3 Maximum Effective Duty Cycle Deff max 114

5.3.4 Achieving ZCS for the Lagging Leg 114

5.3.5 Voltage Stress of the Lagging Leg 114

5.3.6 Blocking Capacitor 115

5.4 Simplified Design Procedure and Example 115

5.4.1 Transformer Winding-Turns Ratio 115

5.4.2 Calculation of Blocking Capacitance 115

5.4.3 Verification of the Transformer Turns Ratio and Blocking Capacitance 116

5.4.4 Dead Time between the Gate Drive Signals of the Leading Leg 117

5.5 Experimental Verification 117

5.6 Summary 119

References 120

6 Zero-Voltage-Switching PWM Full-Bridge Converters with Clamping Diodes 121

6.1 Introduction 121

6.2 Causes of Voltage Oscillation in the Output Rectifier Diode in ZVS PWM Full-Bridge Converters 122

6.3 Voltage Oscillation Suppression Approach 125

6.3.1 RC Snubber 125

6.3.2 RCD Snubber 125

6.3.3 Active Clamp Circuit 126

6.3.4 Auxiliary Winding of Transformer and Clamping Diode Circuit 126

6.3.5 Clamping Diode Circuit 127

6.4 Operating Principle of the Tr-Lead-Type ZVS PWM Full-Bridge Converter 128

6.5 Operating Principle of the Tr-Lag-Type ZVS PWM Full-Bridge Converter 133

6.6 Comparisons of Tr-Lead-Type and Tr-Lag-Type ZVS PWM Full-Bridge Converters 138

6.6.1 Clamping Diode Conduction Times 138

6.6.2 Achievement of ZVS 139

6.6.3 Conduction Loss in Zero State 140

6.6.4 Duty Cycle Loss 140

6.6.5 Effect of the Blocking Capacitor 140

6.7 Experimental Verification 143

6.8 Summary 146

References 147

7 Zero-Voltage-Switching PWM Full-Bridge Converters with Current Transformers to Reset the Clamping Diode Currents 149

7.1 Introduction 149

7.2 Operating Principle of the ZVS PWM Full-Bridge Converter with Clamping Diodes under Light Load Conditions 150

7.2.1 Case I: 0.5Vin¨MZr1 < ILf (t1)¨MK < Vin¨MZr1 (Referring to Figure 7.2a) 156

7.2.2 Case II: ILf (t1)¨MK < 0.5Vin¨MZr1 (Referring to Figure 7.2b) 156

7.3 Clamping Diode Current-Reset Scheme 158

7.3.1 Reset Voltage Source 158

7.3.2 Implementation of the Reset Voltage Source 160

7.4 Operating Principle of the ZVS PWM Full-Bridge Converter with Current Transformer 162

7.4.1 Operating Principle under Heavy Load Conditions 162

7.4.2 Operating Principle under Light Load Conditions 167

7.5 Choice of Current Transformer Winding Turns Ratio 173

7.5.1 Clamping Diode Current-Reset Time 173

7.5.2 Output Rectifier Diode Voltage Stress 174

7.5.3 Current Transformer Winding Turns Ratio 174

7.6 Experimental Verification 175

7.7 Summary 179

References 180

8 Zero-Voltage-Switching PWM Full-Bridge Converters with Current-Doubler Rectifiers 181

8.1 Operating Principle 182

8.2 Realization of ZVS for the Switches 187

8.3 Design Considerations 188

8.3.1 Transformer Winding Turns Ratio 189

8.3.2 Output Filter Inductance 189

8.3.3 Blocking Capacitor 192

8.4 Experimental Results 193

8.5 Summary 197

References 198

Appendix 199

Bibliography 203

Index 207