DC-DC Converters with
a Wide Load Range and
a Wide Input-Voltage Range
DC-DC Converters with
a Wide Load Range and
a Wide Input-Voltage Range
Proefschrift
ter verkrijging van de graad van doctor aan de Technische Universiteit Delft,
op gezag van de Rector Magnificus prof. ir. K. C. A. M. Luyben; voorzitter van het College voor Promoties,
in het openbaar te verdedigen op 29 april 2015 om 15:00 uur
door
Yeh TING
Diplom-Ingenieur, RWTH Aachen University, Duitsland geboren te Singapore, Singapore
DC-DC Converters with
a Wide Load Range and
a Wide Input-Voltage Range
Proefschrift
ter verkrijging van de graad van doctor aan de Technische Universiteit Delft,
op gezag van de Rector Magnificus prof. ir. K. C. A. M. Luyben; voorzitter van het College voor Promoties,
in het openbaar te verdedigen op 29 april 2015 om 15:00 uur
door
Yeh TING
Diplom-Ingenieur, RWTH Aachen University, Duitsland geboren te Singapore, Singapore
Promotor: Prof. Dr. J. A. Ferreira Co-promotor: Ir. S. W. H. de Haan Composition of the doctoral committee: Rector Magnificus
Prof. Dr. J. A. Ferreira, Delft University of Technology, promotor Ir. S. W. H. de Haan, Delft University of Technology, co-promotor
Independent members:
Prof. Dr. P. Palensky, Delft University of Technology
Associate Prof. Dr. H. Polinder, Delft University of Technology Prof. Dr. V. Katic, University of Novi Sad, Serbia
Prof. Dr. M. Liserre, Kiel University, Germany
Prof. Ir. M. A. M. M. van der Meijden, Delft University of Technology, reserve member
Cover designed by Yeh Ting
Printed by Ridderprint BV, Pottenbakkerstraat 15, 2984 AX, Ridderkirk, Netherlands
Copyright © 2015 by Yeh Ting ISBN: 978-94-6299-074-6
An electronic version of this dissertation is available at http://repository.tudelft.nl/.
Table of Contents
Acknowledgements ... i
List of figures ... ii
List of tables... x
List of acronyms and symbols ... xiii
Chapter 1 Introduction ... 1
1.1 DC-to-DC power conversion ... 1
1.1.1 Overview ... 1
1.1.2 High-power system architectures ... 3
1.2 Problem descriptions ... 8
1.2.1 Wide load range ... 8
1.2.2 Wide input-voltage range ... 9
1.3 Thesis objectives ... 11
1.4 Approach taken ... 12
1.5 Thesis layout ... 12
Chapter 2 Unidirectional DC-DC converters with a wide load range and wide input-voltage range... 15
2.1 Introduction ... 15
2.2 Overview of isolated DC-DC converter topologies ... 15
2.2.1 Types of topologies ... 15
2.2.2 Taxonomy of the topologies ... 17
2.2.3 Non-resonant topologies ... 18 Hard-switching ... 18 2.2.3.1 Soft-switching ... 20 2.2.3.2 2.2.4 Resonant topologies ... 22 Load resonant ... 22 2.2.4.1 Resonant switch ... 26 2.2.4.2 2.2.5 Hybrid topologies ... 26 Partial resonant... 26 2.2.5.1 Resonant transition... 29 2.2.5.2
Promotor: Prof. Dr. J. A. Ferreira Co-promotor: Ir. S. W. H. de Haan Composition of the doctoral committee: Rector Magnificus
Prof. Dr. J. A. Ferreira, Delft University of Technology, promotor Ir. S. W. H. de Haan, Delft University of Technology, co-promotor
Independent members:
Prof. Dr. P. Palensky, Delft University of Technology
Associate Prof. Dr. H. Polinder, Delft University of Technology Prof. Dr. V. Katic, University of Novi Sad, Serbia
Prof. Dr. M. Liserre, Kiel University, Germany
Prof. Ir. M. A. M. M. van der Meijden, Delft University of Technology, reserve member
Cover designed by Yeh Ting
Printed by Ridderprint BV, Pottenbakkerstraat 15, 2984 AX, Ridderkirk, Netherlands
Copyright © 2015 by Yeh Ting ISBN: 978-94-6299-074-6
An electronic version of this dissertation is available at http://repository.tudelft.nl/.
Table of Contents
Acknowledgements ... i
List of figures ... ii
List of tables... x
List of acronyms and symbols ... xiii
Chapter 1 Introduction ... 1
1.1 DC-to-DC power conversion ... 1
1.1.1 Overview ... 1
1.1.2 High-power system architectures ... 3
1.2 Problem descriptions ... 8
1.2.1 Wide load range ... 8
1.2.2 Wide input-voltage range ... 9
1.3 Thesis objectives ... 11
1.4 Approach taken ... 12
1.5 Thesis layout ... 12
Chapter 2 Unidirectional DC-DC converters with a wide load range and wide input-voltage range... 15
2.1 Introduction ... 15
2.2 Overview of isolated DC-DC converter topologies ... 15
2.2.1 Types of topologies ... 15
2.2.2 Taxonomy of the topologies ... 17
2.2.3 Non-resonant topologies ... 18 Hard-switching ... 18 2.2.3.1 Soft-switching ... 20 2.2.3.2 2.2.4 Resonant topologies ... 22 Load resonant ... 22 2.2.4.1 Resonant switch ... 26 2.2.4.2 2.2.5 Hybrid topologies ... 26 Partial resonant... 26 2.2.5.1 Resonant transition... 29 2.2.5.2
2.3 Analysis of the selected topologies ... 33
2.3.1 Methodology ... 33
2.3.2 Single Active Bridge (SAB) ... 34
2.3.3 Dual Active Bridge (DAB) ... 35
2.3.4 Full-bridge hybrid series resonant converter (FB-HSRC) ... 39
2.3.5 Sizing of the components ... 41
2.3.6 Component stress and utilisation factor ... 41
2.3.7 Losses and efficiencies ... 46
2.4 Summary and conclusions ... 49
Chapter 3 Reduction of losses in the Single Active Bridge... 51
3.1 Introduction ... 51
3.2 The Partial Resonant-Single Active Bridge ... 51
3.2.1 Topology ... 52
3.2.2 Operating waveforms ... 52
3.2.3 Effects of partial resonance ... 53
3.2.4 Operating principles ... 55
3.3 Conditions and limits for soft-switching ... 58
3.3.1 ZVS turn-on... 59
3.3.2 Quasi-ZCS turn-off ... 61
3.3.3 Quasi-ZVS turn-off ... 63
3.3.4 Summary ... 63
3.4 Power output of the PR-SAB ... 64
3.5 Comparison of the PR-SAB and the SAB ... 66
3.5.1 The PR-SAB with a wide load range and a wide input-voltage range ... 67
3.5.2 Component stresses and utilisation factors ... 68
3.5.3 Efficiencies ... 70
3.6 The experimental converter ... 71
3.6.1 Effects of variations in the snubber capacitance ... 72
Components conducting durations ... 72
3.6.1.1 RMS and average currents ... 73
3.6.1.2 Conduction losses ... 75 3.6.1.3 Switching losses ... 76 3.6.1.4 Efficiencies ... 78 3.6.1.6 3.6.2 Optimal PR-SAB snubber capacitance ... 79
3.6.3 Comparison of the losses... 80
3.6.4 Power output control ... 82
3.7 Experimental verification ... 82
3.7.1 Operating waveforms ... 83
3.7.2 Efficiency ... 84
3.8 Summary and conclusions ... 85
Chapter 4 Reduction of DCM turn-on losses in the Single Active Bridge ... 87
4.1 Introduction ... 87
4.2 Limits of ZVS turn-on for a wide load range and a wide input-voltage range operation ... 88
4.3 Existing methods for ZVS turn-on in DCM ... 90
4.3.1 Circulating current... 90
4.3.2 Saturable parallel inductor ... 92
4.3.3 Decoupled transformer ... 94
4.4 New methods for the reduction of switching losses in DCM ... 94
4.4.1 Quasi-ZCS turn-off in the SAB ... 95
SAB operating waveforms in DCM ... 95
4.4.1.1 Operating intervals in DCM... 96
4.4.1.2 4.4.2 Switchable snubber capacitor ... 97
4.4.3 Dual Current Pulse (DCP) control ... 99
4.4.4 Combination of switchable snubber capacitor and Dual Current Pulse control .... 102
4.5 Comparison and analysis of the turn-on losses reduction methods ... 103
4.5.1 Comparisons ... 103
4.5.2 Losses analysis ... 105
4.5.3 Efficiency analysis ... 107
4.6 Experimental results ... 109
4.6.1 The experimental converter ... 109
4.6.2 Operating waveforms ... 109
4.6.3 Efficiencies ... 111
2.3 Analysis of the selected topologies ... 33
2.3.1 Methodology ... 33
2.3.2 Single Active Bridge (SAB) ... 34
2.3.3 Dual Active Bridge (DAB) ... 35
2.3.4 Full-bridge hybrid series resonant converter (FB-HSRC) ... 39
2.3.5 Sizing of the components ... 41
2.3.6 Component stress and utilisation factor ... 41
2.3.7 Losses and efficiencies ... 46
2.4 Summary and conclusions ... 49
Chapter 3 Reduction of losses in the Single Active Bridge... 51
3.1 Introduction ... 51
3.2 The Partial Resonant-Single Active Bridge ... 51
3.2.1 Topology ... 52
3.2.2 Operating waveforms ... 52
3.2.3 Effects of partial resonance ... 53
3.2.4 Operating principles ... 55
3.3 Conditions and limits for soft-switching ... 58
3.3.1 ZVS turn-on... 59
3.3.2 Quasi-ZCS turn-off ... 61
3.3.3 Quasi-ZVS turn-off ... 63
3.3.4 Summary ... 63
3.4 Power output of the PR-SAB ... 64
3.5 Comparison of the PR-SAB and the SAB ... 66
3.5.1 The PR-SAB with a wide load range and a wide input-voltage range ... 67
3.5.2 Component stresses and utilisation factors ... 68
3.5.3 Efficiencies ... 70
3.6 The experimental converter ... 71
3.6.1 Effects of variations in the snubber capacitance ... 72
Components conducting durations ... 72
3.6.1.1 RMS and average currents ... 73
3.6.1.2 Conduction losses ... 75 3.6.1.3 Switching losses ... 76 3.6.1.4 Efficiencies ... 78 3.6.1.6 3.6.2 Optimal PR-SAB snubber capacitance ... 79
3.6.3 Comparison of the losses... 80
3.6.4 Power output control ... 82
3.7 Experimental verification ... 82
3.7.1 Operating waveforms ... 83
3.7.2 Efficiency ... 84
3.8 Summary and conclusions ... 85
Chapter 4 Reduction of DCM turn-on losses in the Single Active Bridge ... 87
4.1 Introduction ... 87
4.2 Limits of ZVS turn-on for a wide load range and a wide input-voltage range operation ... 88
4.3 Existing methods for ZVS turn-on in DCM ... 90
4.3.1 Circulating current... 90
4.3.2 Saturable parallel inductor ... 92
4.3.3 Decoupled transformer ... 94
4.4 New methods for the reduction of switching losses in DCM ... 94
4.4.1 Quasi-ZCS turn-off in the SAB ... 95
SAB operating waveforms in DCM ... 95
4.4.1.1 Operating intervals in DCM... 96
4.4.1.2 4.4.2 Switchable snubber capacitor ... 97
4.4.3 Dual Current Pulse (DCP) control ... 99
4.4.4 Combination of switchable snubber capacitor and Dual Current Pulse control .... 102
4.5 Comparison and analysis of the turn-on losses reduction methods ... 103
4.5.1 Comparisons ... 103
4.5.2 Losses analysis ... 105
4.5.3 Efficiency analysis ... 107
4.6 Experimental results ... 109
4.6.1 The experimental converter ... 109
4.6.2 Operating waveforms ... 109
4.6.3 Efficiencies ... 111
5.1 Introduction ... 115
5.2 Modular DC-DC converters ... 116
5.2.1 Background ... 116
5.2.2 Architectures of modular DC-DC converters... 116
5.2.3 Main benefits ... 118
Wider load range and wider input-voltage range ... 118
5.2.3.1 Higher efficiency ... 119
5.2.3.2 5.2.4 Additional benefits ... 120
Current ripple reduction ... 120
5.2.4.1 Fault tolerance ... 120
5.2.4.2 5.2.5 Summary ... 120
5.3 IPOP modular DC-DC converter ... 121
5.3.1 IPOP modular DC-DC converter with SAB modules ... 121
5.3.2 Efficiency analysis ... 123
5.4 Efficiency improvements for the SAB IPOP DC-DC converter ... 125
5.4.1 Applying switchable snubber capacitors and DCP control ... 125
5.4.2 IPOP converter with PR-SAB modules ... 126
5.4.3 Optimisation of the PR-SAB module snubber capacitance ... 129
5.5 Non-uniform module power distribution ... 134
5.5.1 Introduction ... 134
5.5.2 Optimum power distribution ... 134
5.5.3 Efficiency ... 135
5.6 Experimental results ... 136
5.7 Summary and conclusions ... 139
Chapter 6 Wide input-voltage range with modular DC-DC converters ... 141
6.1 Introduction ... 141
6.2 ISOP connected modular DC-DC converter ... 142
6.2.1 ISOP modular DC-DC converter with SAB modules ... 142
6.2.2 Series module shutdown... 143
6.2.3 Efficiency analysis ... 144
6.3 Module shutdown and reactivation in the ISOP converter ... 146
6.3.1 Requirements ... 146
Voltage collapse switch current ... 147
6.3.1.2 6.3.2 Voltage and current waveforms ... 148
6.4 Module shutdown methods in the SAB ISOP converter ... 149
6.4.1 External IGBTs with a resistor ... 149
6.4.2 Internal IGBT with current control ... 150
Active region current control in the IGBT for module shutdown ... 151
6.4.2.1 IGBT collector current in safe operating area... 152
6.4.2.2 IGBT gate control signal ... 153
6.4.2.3 Control of the series IGBTs in the phase-arm ... 155
6.4.2.4 Analogue current control ... 155
6.4.2.5 6.5 Digital current control in the IGBT for module shutdown... 158
6.5.1 Introduction ... 158
6.5.2 Digital current control ... 158
6.5.3 The digital module shutdown controller ... 160
6.5.4 Experimental results ... 162
6.6 Comparison of the methods used for module voltage collapse ... 163
6.6.1 Peak currents and voltage collapse duration ... 164
6.6.2 Maximum junction temperature ... 166
6.6.3 Summary ... 168
6.7 Experimental results ... 169
6.7.1 Module shutdown and reactivation ... 169
6.7.2 Input range and efficiency ... 172
6.8 Summary and conclusions ... 173
Chapter 7 Conclusions and recommendations ... 175
7.1 Conclusions ... 175
7.2 Thesis contributions ... 178
7.3 Recommendations for future research... 179
Sizing of the passive components for the 100 kW SAB, DAB and FB-HSRC 181 Appendix A Device selection for the selected topologies... 192
Appendix B Losses calculation in the selected topologies ... 194
Appendix C Mathematical derivations for the PR-SAB... 198
Appendix D Implementation details of the PR-SAB ... 219 Appendix E
5.1 Introduction ... 115
5.2 Modular DC-DC converters ... 116
5.2.1 Background ... 116
5.2.2 Architectures of modular DC-DC converters... 116
5.2.3 Main benefits ... 118
Wider load range and wider input-voltage range ... 118
5.2.3.1 Higher efficiency ... 119
5.2.3.2 5.2.4 Additional benefits ... 120
Current ripple reduction ... 120
5.2.4.1 Fault tolerance ... 120
5.2.4.2 5.2.5 Summary ... 120
5.3 IPOP modular DC-DC converter ... 121
5.3.1 IPOP modular DC-DC converter with SAB modules ... 121
5.3.2 Efficiency analysis ... 123
5.4 Efficiency improvements for the SAB IPOP DC-DC converter ... 125
5.4.1 Applying switchable snubber capacitors and DCP control ... 125
5.4.2 IPOP converter with PR-SAB modules ... 126
5.4.3 Optimisation of the PR-SAB module snubber capacitance ... 129
5.5 Non-uniform module power distribution ... 134
5.5.1 Introduction ... 134
5.5.2 Optimum power distribution ... 134
5.5.3 Efficiency ... 135
5.6 Experimental results ... 136
5.7 Summary and conclusions ... 139
Chapter 6 Wide input-voltage range with modular DC-DC converters ... 141
6.1 Introduction ... 141
6.2 ISOP connected modular DC-DC converter ... 142
6.2.1 ISOP modular DC-DC converter with SAB modules ... 142
6.2.2 Series module shutdown... 143
6.2.3 Efficiency analysis ... 144
6.3 Module shutdown and reactivation in the ISOP converter ... 146
6.3.1 Requirements ... 146
Voltage collapse switch current ... 147
6.3.1.2 6.3.2 Voltage and current waveforms ... 148
6.4 Module shutdown methods in the SAB ISOP converter ... 149
6.4.1 External IGBTs with a resistor ... 149
6.4.2 Internal IGBT with current control ... 150
Active region current control in the IGBT for module shutdown ... 151
6.4.2.1 IGBT collector current in safe operating area... 152
6.4.2.2 IGBT gate control signal ... 153
6.4.2.3 Control of the series IGBTs in the phase-arm ... 155
6.4.2.4 Analogue current control ... 155
6.4.2.5 6.5 Digital current control in the IGBT for module shutdown... 158
6.5.1 Introduction ... 158
6.5.2 Digital current control ... 158
6.5.3 The digital module shutdown controller ... 160
6.5.4 Experimental results ... 162
6.6 Comparison of the methods used for module voltage collapse ... 163
6.6.1 Peak currents and voltage collapse duration ... 164
6.6.2 Maximum junction temperature ... 166
6.6.3 Summary ... 168
6.7 Experimental results ... 169
6.7.1 Module shutdown and reactivation ... 169
6.7.2 Input range and efficiency ... 172
6.8 Summary and conclusions ... 173
Chapter 7 Conclusions and recommendations ... 175
7.1 Conclusions ... 175
7.2 Thesis contributions ... 178
7.3 Recommendations for future research... 179
Sizing of the passive components for the 100 kW SAB, DAB and FB-HSRC 181 Appendix A Device selection for the selected topologies... 192
Appendix B Losses calculation in the selected topologies ... 194
Appendix C Mathematical derivations for the PR-SAB... 198
Appendix D Implementation details of the PR-SAB ... 219 Appendix E
Derivations for the IPOP modular converter ... 228 Appendix G Summary ... 231 Samenvatting ... 234 Publications list ... 237 Curriculum Vitae ... 239 References ... 240
Acknowledgements
First of all, I would like to thank Prof. Bram Ferreira and Sjoerd de Haan for giving me the opportunity to work on my PhD under their dual supervisions. I learned a great deal from them in the field of power electronics and also on how to approach difficult technical problems. I would also like to thank Frans Pansier for the numerous in-depth technical discussions we had and the practical advice he gave. During my time at the Delft University of Technology, I made many friends from the department. There are those like Emile, Ilija, Jianing, Kewei, Todor and Wenbo, with whom I interacted frequently, and often involving some kind of technical discussion. There are also those like Anil, Ivan, Milos, Prasanth, Martin, Marcelo, Johan, Rodrigo, Silvio and Tsegay whom I also talked to, often sharing life experiences. I thank them all for their time and also for sharing their knowledge. I would also like to thank Liu Dong, Jianing, Junyin, Wenbo, Xuezhou and Wang Yi who have, through the many lunches and conversations, greatly helped me improve my spoken Chinese during the years here. Also, special thanks to Kewei for helping me in the experiments that I had to conduct towards the end of my PhD studies. Also, I must thank Martin for his meticulous help in translating the summary of this thesis and my propositions into Dutch. I would also like to thank both past and present laboratory staff, Bart, Chris, Kasper and Rob, who helped me in getting familiar with the laboratory and its equipment. Not forgetting the secretaries in the department, past and present, I thank all of them for helping me with administrative matters as much as they could.
Also, I would like to acknowledge DSO National Laboratories, who awarded me a scholarship to pursue a PhD in the Netherlands. In addition, I would also like to pay tribute to the founding prime minister of Singapore, the late Mr Lee Kuan Yew, who sadly passed away on the 23rd March 2015. Through his character, vision and intellect, he created exceptional educational and economic policies in Singapore, from which I have benefited immersely. An example of his policy is the scholarship programme in Singapore, which made my undergraduate to PhD studies possible.
I would like to dedicate this thesis to my parents and my younger brother and especially to my wife and son. Special thanks to my younger brother, Yun, for helping me to compile the list of acronyms and symbols in this thesis. As he finished his PhD almost three years ago, I knew he had the experience in writing a thesis and thus sought out his help. I thank my parents for making frequent trips to the Netherlands to take care of household matters while I was busy. I also thank my son, Ryan, for accompanying and putting up with me in the study room while at home throughout these five years. Most importantly, I must thank my wife, Eliza, who was the key trigger for me to do my PhD. I thank her for her care throughout these five years in the Netherlands, and bearing with me during those stressful moments. However, while I was busy writing this thesis in the last months, she made me felt comfortable at home especially with her new found love for cooking, which resulted in many new delicious dishes.
Derivations for the SAB with circulating current ... 225
Appendix F Derivations for the IPOP modular converter ... 228
Appendix G Summary ... 231 Samenvatting ... 234 Publications list ... 237 Curriculum Vitae ... 239 References ... 240
Acknowledgements
First of all, I would like to thank Prof. Bram Ferreira and Sjoerd de Haan for giving me the opportunity to work on my PhD under their dual supervisions. I learned a great deal from them in the field of power electronics and also on how to approach difficult technical problems. I would also like to thank Frans Pansier for the numerous in-depth technical discussions we had and the practical advice he gave. During my time at the Delft University of Technology, I made many friends from the department. There are those like Emile, Ilija, Jianing, Kewei, Todor and Wenbo, with whom I interacted frequently, and often involving some kind of technical discussion. There are also those like Anil, Ivan, Milos, Prasanth, Martin, Marcelo, Johan, Rodrigo, Silvio and Tsegay whom I also talked to, often sharing life experiences. I thank them all for their time and also for sharing their knowledge. I would also like to thank Liu Dong, Jianing, Junyin, Wenbo, Xuezhou and Wang Yi who have, through the many lunches and conversations, greatly helped me improve my spoken Chinese during the years here. Also, special thanks to Kewei for helping me in the experiments that I had to conduct towards the end of my PhD studies. Also, I must thank Martin for his meticulous help in translating the summary of this thesis and my propositions into Dutch. I would also like to thank both past and present laboratory staff, Bart, Chris, Kasper and Rob, who helped me in getting familiar with the laboratory and its equipment. Not forgetting the secretaries in the department, past and present, I thank all of them for helping me with administrative matters as much as they could.
Also, I would like to acknowledge DSO National Laboratories, who awarded me a scholarship to pursue a PhD in the Netherlands. In addition, I would also like to pay tribute to the founding prime minister of Singapore, the late Mr Lee Kuan Yew, who sadly passed away on the 23rd March 2015. Through his character, vision and intellect, he created exceptional educational and economic policies in Singapore, from which I have benefited immersely. An example of his policy is the scholarship programme in Singapore, which made my undergraduate to PhD studies possible.
I would like to dedicate this thesis to my parents and my younger brother and especially to my wife and son. Special thanks to my younger brother, Yun, for helping me to compile the list of acronyms and symbols in this thesis. As he finished his PhD almost three years ago, I knew he had the experience in writing a thesis and thus sought out his help. I thank my parents for making frequent trips to the Netherlands to take care of household matters while I was busy. I also thank my son, Ryan, for accompanying and putting up with me in the study room while at home throughout these five years. Most importantly, I must thank my wife, Eliza, who was the key trigger for me to do my PhD. I thank her for her care throughout these five years in the Netherlands, and bearing with me during those stressful moments. However, while I was busy writing this thesis in the last months, she made me felt comfortable at home especially with her new found love for cooking, which resulted in many new delicious dishes.
List of figures
Figure 1-1. The key applications of DC-DC converters, together with the corresponding power output and voltage ranges. ... 1 Figure 1-2. Power system architecture of telecom servers and data storage centres. ... 4 Figure 1-3. The power system architecture of an electric vehicle (EV)/plug-in hybrid vehicle
(PHEV), together with the EV charging station [11][12]. ... 5 Figure 1-4. Power system of a train consisting of the traction and auxiliary power supplies. .. 6 Figure 1-5. Power system of a more-electric aircraft, comprising a starter and generator from
the auxiliary power unit (APU) and the main engine. ... 7 Figure 1-6. Power system architecture of a renewable energy system incorporating a wind
generator, a photovoltaic generator and energy storage with HVDC
transmission. ... 8 Figure 1-7. Comparison of an ideal wide load range converter with (a) a single converter and
(b) a modular converter showing the increase in load range and the widening of load range at maximum efficiency with the use of parallel-connected (number of modules N = 3) modular DC-DC converters, showing the effect of the modules shutdown in reducing n operating modules from 3 to 1. ... 9 Figure 1-8. Comparison of an ideal wide input-voltage range converter with (a) a single
converter and (b) a modular converter showing the increase in the input-voltage range and the widening of the input-voltage range at maximum efficiency with the use of series-connected (number of modules N = 3) modular DC-DC
converters and with the reduction of n operating modules from 3 to 1. ... 10 Figure 1-9. Map of the thesis layout. ... 14 Figure 2-1. General block diagram of a non-resonant DC-DC converter with galvanic
isolation. ... 16 Figure 2-2. General block diagram of a resonant DC to DC converter with galvanic isolation
and a resonant network. ... 16 Figure 2-3. The taxonomy of high-power unidirectional DC-DC converters with galvanic
isolation. ... 18 Figure 2-4. Topology of the DC-DC HB converter with a diode full-bridge at the output and
output inductor Lo. The key current and voltage waveforms are also illustrated. . 19
Figure 2-5. Topology of the DC-DC FB converter with a diode full-bridge at the output and output inductor Lo. The key current and voltage waveforms are also illustrated. . 19
Figure 2-6. Topology of the DC-DC single active bridge (SAB) converter and its steady-state operating waveforms. ... 21 Figure 2-7. Topology of the DC-DC dual active bridge (DAB) converter and its steady-state
operating waveforms for the case where Uin = Uʹout. ... 22
Figure 2-8. Topology of the DC-DC series resonant converter (SRC) and its steady-state operating waveforms in the continuous conduction mode (CCM). ... 23 Figure 2-9. Topology of the DC-DC parallel resonant converter (PRC) with an input active
full-bridge and output diode full-bridge. ... 24
Figure 2-10. Topology of the DC-DC LLC resonant converter with an input active full-bridge and output diode full-bridge. ... 25 Figure 2-11. Topology of the DC-DC partial series resonant converter (PSRC). ... 26 Figure 2-12. Topology of the DC-DC output filter resonant converter (OFRC). ... 27 Figure 2-13. Topology of the DC-DC full-bridge hybrid series resonant (FB-HSRC)
converter... 27 Figure 2-14. The additional degree of control freedom in the FB-HSRC, compared to the
PSRC with two extra switches: S1 and S3. ... 29 Figure 2-15. Topology of a DC-DC ZVS-phase-shifted full-bridge converter (ZVS-PSFB)
with added snubber capacitors for resonant transition soft-switching. ... 30 Figure 2-16. Topology of an DC-DC ARCP-FB converter with additional auxiliary circuits,
compared with the ZVS-PSFB. ... 30 Figure 2-17. Operating intervals of the Single Active Bridge (SAB) depicting the equivalent
circuit in each operating interval shown in Figure 2-18(a). ... 34 Figure 2-18. Operating waveforms of the Single Active Bridge depicting voltages uc(t) and
ub(t) and current is(t); (a) in CCM and (b) in DCM. ... 35
Figure 2-19. Operating intervals of the Dual Active Bridge depicting the equivalent circuit in each operating interval. ... 36 Figure 2-20. Operating waveforms depicting the voltages uc(t) − ub(t) and current is(t) of the
Dual Active Bridge for (a) the buck mode where Uin > Uʹout and (b) the boost
mode where Uin < Uʹout under heavy loads. ... 37
Figure 2-21. Operating waveforms depicting the voltage uc(t) − ub(t) and the current is(t) of
the Dual Active Bridge for (a) the buck mode where Uin > Uʹout and (b) the boost
mode where Uin < Uʹout under light loads. ... 38
Figure 2-22. Operating intervals of the FB-HSRC depicting the equivalent circuit in each operating interval. ... 39 Figure 2-23. Operating waveforms depicting the voltages uc(t) and ub(t) and current is(t) with
the operating intervals of the FB-HSRC under both heavy and light loads. ... 40 Figure 2-24. Contour plots of the calculated efficiencies in (a) the SAB, (b) the DAB and
(c) the FB-HSRC over the entire operating range of Pout = 0 to 100 kW and
Uin = 500 to 1000 V. ... 48
Figure 3-1. Topology of the Partial Resonant-Single Active Bridge (PR-SAB) DC-DC converter, which is similar to the SAB except for the larger C1 and C2 values. ... 52 Figure 3-2. The operating intervals and the waveforms of voltages uc(t) and ub(t) and current
is(t) of the SAB and the PR-SAB with large capacitors C1 and C2, where the differences in their capacitor conducting durations are indicated. ... 53 Figure 3-3. A superimposed waveform of is(t) in the SAB and PR-SAB with the same Ls,
showing their differences at an equal power output and under the same operating conditions. ... 54 Figure 3-4. The ideal lossless equivalent circuits for the operating intervals 1 to 5 of the
PR-SAB derived from the operating waveforms in Figure 3-2. ... 55 Figure 3-5. An example of the PR-SAB operating locus in the Δt1 and Δt3 plane showing the
List of figures
Figure 1-1. The key applications of DC-DC converters, together with the corresponding power output and voltage ranges. ... 1 Figure 1-2. Power system architecture of telecom servers and data storage centres. ... 4 Figure 1-3. The power system architecture of an electric vehicle (EV)/plug-in hybrid vehicle
(PHEV), together with the EV charging station [11][12]. ... 5 Figure 1-4. Power system of a train consisting of the traction and auxiliary power supplies. .. 6 Figure 1-5. Power system of a more-electric aircraft, comprising a starter and generator from
the auxiliary power unit (APU) and the main engine. ... 7 Figure 1-6. Power system architecture of a renewable energy system incorporating a wind
generator, a photovoltaic generator and energy storage with HVDC
transmission. ... 8 Figure 1-7. Comparison of an ideal wide load range converter with (a) a single converter and
(b) a modular converter showing the increase in load range and the widening of load range at maximum efficiency with the use of parallel-connected (number of modules N = 3) modular DC-DC converters, showing the effect of the modules shutdown in reducing n operating modules from 3 to 1. ... 9 Figure 1-8. Comparison of an ideal wide input-voltage range converter with (a) a single
converter and (b) a modular converter showing the increase in the input-voltage range and the widening of the input-voltage range at maximum efficiency with the use of series-connected (number of modules N = 3) modular DC-DC
converters and with the reduction of n operating modules from 3 to 1. ... 10 Figure 1-9. Map of the thesis layout. ... 14 Figure 2-1. General block diagram of a non-resonant DC-DC converter with galvanic
isolation. ... 16 Figure 2-2. General block diagram of a resonant DC to DC converter with galvanic isolation
and a resonant network. ... 16 Figure 2-3. The taxonomy of high-power unidirectional DC-DC converters with galvanic
isolation. ... 18 Figure 2-4. Topology of the DC-DC HB converter with a diode full-bridge at the output and
output inductor Lo. The key current and voltage waveforms are also illustrated. . 19
Figure 2-5. Topology of the DC-DC FB converter with a diode full-bridge at the output and output inductor Lo. The key current and voltage waveforms are also illustrated. . 19
Figure 2-6. Topology of the DC-DC single active bridge (SAB) converter and its steady-state operating waveforms. ... 21 Figure 2-7. Topology of the DC-DC dual active bridge (DAB) converter and its steady-state
operating waveforms for the case where Uin = Uʹout. ... 22
Figure 2-8. Topology of the DC-DC series resonant converter (SRC) and its steady-state operating waveforms in the continuous conduction mode (CCM). ... 23 Figure 2-9. Topology of the DC-DC parallel resonant converter (PRC) with an input active
full-bridge and output diode full-bridge. ... 24
Figure 2-10. Topology of the DC-DC LLC resonant converter with an input active full-bridge and output diode full-bridge. ... 25 Figure 2-11. Topology of the DC-DC partial series resonant converter (PSRC). ... 26 Figure 2-12. Topology of the DC-DC output filter resonant converter (OFRC). ... 27 Figure 2-13. Topology of the DC-DC full-bridge hybrid series resonant (FB-HSRC)
converter... 27 Figure 2-14. The additional degree of control freedom in the FB-HSRC, compared to the
PSRC with two extra switches: S1 and S3. ... 29 Figure 2-15. Topology of a DC-DC ZVS-phase-shifted full-bridge converter (ZVS-PSFB)
with added snubber capacitors for resonant transition soft-switching. ... 30 Figure 2-16. Topology of an DC-DC ARCP-FB converter with additional auxiliary circuits,
compared with the ZVS-PSFB. ... 30 Figure 2-17. Operating intervals of the Single Active Bridge (SAB) depicting the equivalent
circuit in each operating interval shown in Figure 2-18(a). ... 34 Figure 2-18. Operating waveforms of the Single Active Bridge depicting voltages uc(t) and
ub(t) and current is(t); (a) in CCM and (b) in DCM. ... 35
Figure 2-19. Operating intervals of the Dual Active Bridge depicting the equivalent circuit in each operating interval. ... 36 Figure 2-20. Operating waveforms depicting the voltages uc(t) − ub(t) and current is(t) of the
Dual Active Bridge for (a) the buck mode where Uin > Uʹout and (b) the boost
mode where Uin < Uʹout under heavy loads. ... 37
Figure 2-21. Operating waveforms depicting the voltage uc(t) − ub(t) and the current is(t) of
the Dual Active Bridge for (a) the buck mode where Uin > Uʹout and (b) the boost
mode where Uin < Uʹout under light loads. ... 38
Figure 2-22. Operating intervals of the FB-HSRC depicting the equivalent circuit in each operating interval. ... 39 Figure 2-23. Operating waveforms depicting the voltages uc(t) and ub(t) and current is(t) with
the operating intervals of the FB-HSRC under both heavy and light loads. ... 40 Figure 2-24. Contour plots of the calculated efficiencies in (a) the SAB, (b) the DAB and
(c) the FB-HSRC over the entire operating range of Pout = 0 to 100 kW and
Uin = 500 to 1000 V. ... 48
Figure 3-1. Topology of the Partial Resonant-Single Active Bridge (PR-SAB) DC-DC converter, which is similar to the SAB except for the larger C1 and C2 values. ... 52 Figure 3-2. The operating intervals and the waveforms of voltages uc(t) and ub(t) and current
is(t) of the SAB and the PR-SAB with large capacitors C1 and C2, where the differences in their capacitor conducting durations are indicated. ... 53 Figure 3-3. A superimposed waveform of is(t) in the SAB and PR-SAB with the same Ls,
showing their differences at an equal power output and under the same operating conditions. ... 54 Figure 3-4. The ideal lossless equivalent circuits for the operating intervals 1 to 5 of the
PR-SAB derived from the operating waveforms in Figure 3-2. ... 55 Figure 3-5. An example of the PR-SAB operating locus in the Δt1 and Δt3 plane showing the
Figure 3-6. Diagram showing the PR-SAB operating regions in DCM and CCM over the entire operating range with the is(t) waveforms for the four corner cases labelled
as (a) to (d). ... 68 Figure 3-7. The contour plots of the calculated efficiencies in (a) the PR-SAB, and in (b) the
SAB over the entire operating range. ... 71 Figure 3-8. The conducting durations for (a) S1, D1 and C1 for C1 from 5 to 200 nF at
C2 = 20 nF, and (b) for S2, D2 and C2 for C2 from 5 to 50 nF at C1 = 75 nF at Uin = 600 V and Pout = 3.4 kW. ... 73
Figure 3-9. The is peak and is RMS as C1 increases from 5 to 200 nF with C2 = 20 nF at
Uin = 600 V... 74
Figure 3-10. The RMS currents of (a) S1, D1 and C1 for C1 from 5 to 200 nF at C2 = 20 nF,
and of (b) S2, D2 and C2 for C2 from 5 to 50 nF at C1 = 75 nF at Uin = 600 V. .... 74
Figure 3-11. Conduction losses of (a) S1, D1 and C1 for C1 from 5 to 200 nF with C2 = 20 nF,
and (b) for S2, D2 and C2 for C2 from 5 to 50 nF with C1 = 75 nF at Uin = 600 V... 76
Figure 3-12. Estimated switching losses during quasi-ZVS turn-off in (a) S1 for C1 from 5 to 200 nF with C2 = 20 nF and in (b) S2 for C2 from 5 to 50 nF with C1 = 75 nF at Uin = 600 V... 77
Figure 3-13. The load range for (a) C1 from 5 to 200 nF with C2 = 20 nF and (b) for C2 from 5 to 50 nF with C1 = 75 nF at Uin = 600 V. ... 78
Figure 3-14. The efficiency curves of the PR-SAB (a) for C1 from 5 to 200 nF with C2 = 20
nF and (b) for C2 from 5 to 50 nF with C1 = 75 nF at Uin = 500 V, 600 V and
700 V. ... 79 Figure 3-15. The (a) PBCM of the PR-SAB in kW and (b) η in % for C1 from 5 to 200 nF and
C2 from 5 to 50 nF at Uin = 700 V... 80
Figure 3-16. A comparison of the conduction losses and switching losses in the PR-SAB and SAB when Uin equals (a) 500 V, (b) 600 V and (c) 700 V. ... 81
Figure 3-17. Representations of the PR-SAB operating loci at Uin = 600 V. ... 82
Figure 3-18. The experimental converter used to obtain the PR-SAB and SAB experimental results. ... 83 Figure 3-19. Oscilloscope waveforms showing is(t), uc(t) and ub(t) at Pout = 3.4 kW and
Uin = 600 V for (a) the SAB and (b) the PR-SAB. ... 84
Figure 3-20: A comparison of the calculated and measured efficiencies in the PR-SAB and the SAB at: (a) Uin = 500 V, (b) Uin = 600 V and (c) Uin = 700 V. ... 85
Figure 4-1. Topology of the Single Active Bridge (SAB) DC-DC converter from Figure 2-6(a). ... 87 Figure 4-2. Magnified view of the current is(t) and voltage ub(t) waveforms in CCM during S2 or S4 turn-off at t = Ts/2, depicting ZVS turn-on where Ioff ≥ Imin. ... 89 Figure 4-3. Magnified view of the current is(t) and voltage ub(t) waveforms in DCM during S2 or S4 turn-off at t = Ts/2, depicting the turn-on losses where Ioff = 0. ... 89
Figure 4-4. Magnified view of the current is(t) and voltage ub(t) waveforms in CCM nearing
BCM during S2 or S4 turn-off at t = Ts/2, depicting the turn-on losses where
Ioff < Imin. ... 89
Figure 4-5. SAB with parallel inductance Lp to enable the circulating current for ZVS turn-on
in DCM. ... 91 Figure 4-6. Magnified view of the current is(t) and voltage ub(t) waveforms in DCM with
circulating current during S2 or S4 turn-off at t = Ts/2, depicting ZVS turn-on
where Ioff = Imin. ... 91 Figure 4-7. SAB with saturable parallel inductance Lp, which is controlled to maintain the
minimum circulating current Imin required for ZVS turn-on in DCM across its entire operating range. ... 92 Figure 4-8. Magnified view of the current is(t) and voltage ub(t) waveforms at (a) low Pout and
(b) high Pout during S2 or S4 turn-off at t = Ts/2, where Ioff = Imin with the use of a saturable inductor Lp. ... 93
Figure 4-9. Decoupled transformer implemented with a bidirectional switch Saux in the SAB. ... 94 Figure 4-10. Steady-state operating waveforms of current is(t) and voltages uc(t) and ub(t) in
the SAB during DCM with (a) ZCS turn-off and (b) quasi-ZCS turn-off. ... 96 Figure 4-11. The equivalent circuit of the dead-time interval 6 during DCM for (a) ZCS
turn-off and for (b) quasi-ZCS turn-turn-off. ... 97 Figure 4-12. The auxiliary circuit, which consists of the snubber capacitor Caux and a
bidirectional switch made up of two anti-parallel IGBTs Saux1 and Saux2 as shown
in the SAB. ... 98 Figure 4-13. The operating intervals and waveforms of the SAB in DCM with low loss
turn-on resulting from the auxiliary circuit in Figure 4-12. ... 99 Figure 4-14. The operating intervals and waveforms of the SAB showing DCP control in
DCM to reduce the hard-switched turn-on losses by 50%, in comparison with those from the quasi-ZCS turn-off in Figure 4-10(b). ... 100 Figure 4-15. SAB topology with the auxiliary circuit consisting of the snubber capacitor Caux,
the IGBT Saux and the diode Daux. ... 102
Figure 4-16. The operating intervals and waveforms of the SAB showing DCP control in DCM with a low-loss turn-on resulting from the auxiliary circuit in Figure 4-15. ... 103 Figure 4-17. The switching losses Psw of the selected losses reduction methods at (a)
Uin = 400 V and at (b) Uin = 700 V, as obtained from the analyses. ... 106
Figure 4-18. The conduction losses Pcond of the selected losses reduction methods at (a)
Uin = 400 V and at (b) Uin = 700 V, as obtained from the analyses. ... 107
Figure 4-19. The efficiencies η of the selected losses reduction methods demonstrating the highest reduction of the DCP control with switchable snubber capacitors at (a) Uin = 400 V and at (b) Uin = 700 V. The light-load efficiency improvements are
indicated. ... 108 Figure 4-20. (a) The SAB experimental converter used to obtain the measurement results, and (b) the enlarged view of the auxiliary circuit attached to the converter. ... 109 Figure 4-21. The waveforms of is, ub and uc in (a) and uaux in (b) obtained with the
experimental converter for one switching cycle at Uin = 600 V and Pout = 500 W
in DCM, showing DCP and the effects of the switchable snubber capacitor during the dead-time. ... 110
Figure 3-6. Diagram showing the PR-SAB operating regions in DCM and CCM over the entire operating range with the is(t) waveforms for the four corner cases labelled
as (a) to (d). ... 68 Figure 3-7. The contour plots of the calculated efficiencies in (a) the PR-SAB, and in (b) the
SAB over the entire operating range. ... 71 Figure 3-8. The conducting durations for (a) S1, D1 and C1 for C1 from 5 to 200 nF at
C2 = 20 nF, and (b) for S2, D2 and C2 for C2 from 5 to 50 nF at C1 = 75 nF at Uin = 600 V and Pout = 3.4 kW. ... 73
Figure 3-9. The is peak and is RMS as C1 increases from 5 to 200 nF with C2 = 20 nF at
Uin = 600 V... 74
Figure 3-10. The RMS currents of (a) S1, D1 and C1 for C1 from 5 to 200 nF at C2 = 20 nF,
and of (b) S2, D2 and C2 for C2 from 5 to 50 nF at C1 = 75 nF at Uin = 600 V. .... 74
Figure 3-11. Conduction losses of (a) S1, D1 and C1 for C1 from 5 to 200 nF with C2 = 20 nF,
and (b) for S2, D2 and C2 for C2 from 5 to 50 nF with C1 = 75 nF at Uin = 600 V... 76
Figure 3-12. Estimated switching losses during quasi-ZVS turn-off in (a) S1 for C1 from 5 to 200 nF with C2 = 20 nF and in (b) S2 for C2 from 5 to 50 nF with C1 = 75 nF at Uin = 600 V... 77
Figure 3-13. The load range for (a) C1 from 5 to 200 nF with C2 = 20 nF and (b) for C2 from 5 to 50 nF with C1 = 75 nF at Uin = 600 V. ... 78
Figure 3-14. The efficiency curves of the PR-SAB (a) for C1 from 5 to 200 nF with C2 = 20
nF and (b) for C2 from 5 to 50 nF with C1 = 75 nF at Uin = 500 V, 600 V and
700 V. ... 79 Figure 3-15. The (a) PBCM of the PR-SAB in kW and (b) η in % for C1 from 5 to 200 nF and
C2 from 5 to 50 nF at Uin = 700 V... 80
Figure 3-16. A comparison of the conduction losses and switching losses in the PR-SAB and SAB when Uin equals (a) 500 V, (b) 600 V and (c) 700 V. ... 81
Figure 3-17. Representations of the PR-SAB operating loci at Uin = 600 V. ... 82
Figure 3-18. The experimental converter used to obtain the PR-SAB and SAB experimental results. ... 83 Figure 3-19. Oscilloscope waveforms showing is(t), uc(t) and ub(t) at Pout = 3.4 kW and
Uin = 600 V for (a) the SAB and (b) the PR-SAB. ... 84
Figure 3-20: A comparison of the calculated and measured efficiencies in the PR-SAB and the SAB at: (a) Uin = 500 V, (b) Uin = 600 V and (c) Uin = 700 V. ... 85
Figure 4-1. Topology of the Single Active Bridge (SAB) DC-DC converter from Figure 2-6(a). ... 87 Figure 4-2. Magnified view of the current is(t) and voltage ub(t) waveforms in CCM during S2 or S4 turn-off at t = Ts/2, depicting ZVS turn-on where Ioff ≥ Imin. ... 89 Figure 4-3. Magnified view of the current is(t) and voltage ub(t) waveforms in DCM during S2 or S4 turn-off at t = Ts/2, depicting the turn-on losses where Ioff = 0. ... 89
Figure 4-4. Magnified view of the current is(t) and voltage ub(t) waveforms in CCM nearing
BCM during S2 or S4 turn-off at t = Ts/2, depicting the turn-on losses where
Ioff < Imin. ... 89
Figure 4-5. SAB with parallel inductance Lp to enable the circulating current for ZVS turn-on
in DCM. ... 91 Figure 4-6. Magnified view of the current is(t) and voltage ub(t) waveforms in DCM with
circulating current during S2 or S4 turn-off at t = Ts/2, depicting ZVS turn-on
where Ioff = Imin. ... 91 Figure 4-7. SAB with saturable parallel inductance Lp, which is controlled to maintain the
minimum circulating current Imin required for ZVS turn-on in DCM across its entire operating range. ... 92 Figure 4-8. Magnified view of the current is(t) and voltage ub(t) waveforms at (a) low Pout and
(b) high Pout during S2 or S4 turn-off at t = Ts/2, where Ioff = Imin with the use of a saturable inductor Lp. ... 93
Figure 4-9. Decoupled transformer implemented with a bidirectional switch Saux in the SAB. ... 94 Figure 4-10. Steady-state operating waveforms of current is(t) and voltages uc(t) and ub(t) in
the SAB during DCM with (a) ZCS turn-off and (b) quasi-ZCS turn-off. ... 96 Figure 4-11. The equivalent circuit of the dead-time interval 6 during DCM for (a) ZCS
turn-off and for (b) quasi-ZCS turn-turn-off. ... 97 Figure 4-12. The auxiliary circuit, which consists of the snubber capacitor Caux and a
bidirectional switch made up of two anti-parallel IGBTs Saux1 and Saux2 as shown
in the SAB. ... 98 Figure 4-13. The operating intervals and waveforms of the SAB in DCM with low loss
turn-on resulting from the auxiliary circuit in Figure 4-12. ... 99 Figure 4-14. The operating intervals and waveforms of the SAB showing DCP control in
DCM to reduce the hard-switched turn-on losses by 50%, in comparison with those from the quasi-ZCS turn-off in Figure 4-10(b). ... 100 Figure 4-15. SAB topology with the auxiliary circuit consisting of the snubber capacitor Caux,
the IGBT Saux and the diode Daux. ... 102
Figure 4-16. The operating intervals and waveforms of the SAB showing DCP control in DCM with a low-loss turn-on resulting from the auxiliary circuit in Figure 4-15. ... 103 Figure 4-17. The switching losses Psw of the selected losses reduction methods at (a)
Uin = 400 V and at (b) Uin = 700 V, as obtained from the analyses. ... 106
Figure 4-18. The conduction losses Pcond of the selected losses reduction methods at (a)
Uin = 400 V and at (b) Uin = 700 V, as obtained from the analyses. ... 107
Figure 4-19. The efficiencies η of the selected losses reduction methods demonstrating the highest reduction of the DCP control with switchable snubber capacitors at (a) Uin = 400 V and at (b) Uin = 700 V. The light-load efficiency improvements are
indicated. ... 108 Figure 4-20. (a) The SAB experimental converter used to obtain the measurement results, and (b) the enlarged view of the auxiliary circuit attached to the converter. ... 109 Figure 4-21. The waveforms of is, ub and uc in (a) and uaux in (b) obtained with the
experimental converter for one switching cycle at Uin = 600 V and Pout = 500 W
in DCM, showing DCP and the effects of the switchable snubber capacitor during the dead-time. ... 110
Figure 4-22. The waveforms of is, ub and uc in (a) and uaux in (b) obtained with the
experimental converter for one switching cycle at Uin = 600 V and Pout = 3 kW in
CCM. ... 111 Figure 4-23. Comparison of the analysed and measured efficiencies obtained with the
experimental converter at (a) Uin = 400 V, (b) Uin = 500 V (c) Uin = 600 V and
(d) Uin = 700 V from 500 W to 3 kW. ... 112
Figure 5-1. The four possible architectures in a two-module galvanic isolated converter system for the connections of: (a) parallel and output-parallel, (b) series and output-parallel, (c) series and output-parallel and (d) input-parallel and output-series. ... 117 Figure 5-2. Currently available switching devices shown according to their maximum voltage and current ratings [1]. ... 118 Figure 5-3. Efficiency as a function of power output for an N = 3 parallel modular converter,
showing the efficiency improvements at light load with phase-shedding. ... 119 Figure 5-4. Topology of the Single Active Bridge used in the modules of the IPOP
converter... 121 Figure 5-5. An IPOP modular DC-DC converter with N = 4 SAB modules, where the specific module number m = 1 to 4. ... 122 Figure 5-6. The analysed efficiency ηIPOP,n of the SAB IPOP modular DC-DC converter as a
function of the power output Pout for n = 1 to 4. ... 124
Figure 5-7. Efficiency gain with phase-shedding of the SAB modular IPOP converter for n = 4 showing efficiency improvements of up to 17% at light loads... 124 Figure 5-8. The analysed efficiency η of the enhanced SAB IPOP modular DC-DC converter with switchable snubber capacitor and DCP control as a function of power output Pout for n = 1 to 4. ... 126
Figure 5-9. Efficiency η of the SAB module over a range of Pout from 0 kW to 3.5 kW and for
C1 from 5 nF to 250 nF with the point of maximum efficiency ηmax at the
optimum snubber capacitance C1opt. ... 126 Figure 5-10. Efficiencies of a PR-SAB IPOP modular converter for n = 1 to 4 indicating the
forbidden load zones (shaded) when phase-shedding is applied. ... 128 Figure 5-11. The minimum power Pmin,n and maximum power Pmax,n of the IPOP converter
for n = 1 and n = 2 as functions of C1. ... 130 Figure 5-12. Flowchart for optimisation of the C1 values in the IPOP modular converter with
the initial values of C1,m,init. ... 132 Figure 5-13. Efficiency comparisons of the SAB IPOP converter with the PR-SAB IPOP
converters for non-optimised and for optimised snubber capacitance across the full load range with phase-shedding. ... 133 Figure 5-14. The power ratio in the modules of an IPOP converter for m = 1 to 4 with
non-uniform power distribution optimised for the highest overall efficiency across the full load range. ... 135 Figure 5-15. Efficiencies of the IPOP converter for non-uniform and uniform module power
distribution with C1,m optimisation. ... 135 Figure 5-16. Experimental set-up with n = 4 modules connected as an IPOP modular
converter... 136
Figure 5-17. Inductor Ls current measurements, is,m, from m = 1 to 4 with uniform power
distribution for the PR-SAB IPOP modular converter at Pout = 10 kW and
Pm,out = 2.5 kW. ... 137
Figure 5-18. Inductor Ls current measurements, is,m, from m = 1 to 4 with non-uniform power
distribution for the PR-SAB IPOP modular converter at Pout = 4.6 kW when P1,out and P2,out = 0 kW; P3,out = 2.5 kW and P4,out = 2.1 kW. ... 137 Figure 5-19. Measurement results shown against the analysed results with phase-shedding
from n = 1 to 4 for (a) SAB modules and PR-SAB modules with optimised C1 and (b) optimised C1 with uniform and non-uniform module power
distribution. ... 138 Figure 6-1. A two-module input-series and output-parallel (ISOP) DC-DC converter. ... 141 Figure 6-2. An ISOP modular DC-DC converter with N = 3 SAB modules, where the specific module number m = 1 to 3. ... 143 Figure 6-3. Extension of the input-voltage range and the increase in efficiency with series
module shutdown in an ISOP DC-DC converter for n = 3 modules... 144 Figure 6-4. Analysed efficiency η of the SAB ISOP modular DC-DC converter as a function
of power output Uin for n = 3 at 2.6 kW... 145
Figure 6-5. Efficiency gain with module shutdown of the SAB modular IPOP converter from n = 3 to n = 1 with efficiency improvements of up to 2.2% at 0.8 kW. ... 146 Figure 6-6. N = 2 ISOP modular DC-DC converter, showing the current bypass switch
required for module shutdown and reactivation for module m = 2. ... 147 Figure 6-7. Typical waveforms of the module input current and voltage during module
shutdown and reactivation. ... 148 Figure 6-8. Implementation of the current bypass switch with two external IGBTs and a
resistor for module shutdown and reactivation. ... 150 Figure 6-9. Implementation of the current bypass switch with internal IGBTs in the input
bridge of the converter module for module shutdown and reactivation. ... 150 Figure 6-10. Plot of iC against uCE of an IGBT with increasing uGE in its active (shaded) and
saturation regions with the path of iC and uCE during module shutdown. ... 151
Figure 6-11. Safe Operation Area (SOA) of an IGBT with iCmax = f(uCE) which is used to
derive the maximum permissible collector current in the IGBT at a given uCE.. 152
Figure 6-12. The waveforms of iC and uCE during module shutdown with internal IGBTs
(see Section 6.4.2) within the SOA obtained from the iteration of time steps Δt = 1 μs. ... 153 Figure 6-13. The transfer functions of iC with uGE for a range of uCE that are used to determine
the function uGE = g(uCE,iCmax). ... 154
Figure 6-14. The function uGE = h(t) required to control the IGBT within its SOA limits
during module shutdown, as obtained from iteration with uGE = g(uCE,iCmax) for
the worst-case current pulse where uCE,0 = Uin,2. ... 154
Figure 6-15. The discharge of Cin,2 through two series-connected IGBTs in the phase-arm
during module shutdown. ... 155 Figure 6-16. The block diagram of the IGBT shutdown control, where the functions
Figure 4-22. The waveforms of is, ub and uc in (a) and uaux in (b) obtained with the
experimental converter for one switching cycle at Uin = 600 V and Pout = 3 kW in
CCM. ... 111 Figure 4-23. Comparison of the analysed and measured efficiencies obtained with the
experimental converter at (a) Uin = 400 V, (b) Uin = 500 V (c) Uin = 600 V and
(d) Uin = 700 V from 500 W to 3 kW. ... 112
Figure 5-1. The four possible architectures in a two-module galvanic isolated converter system for the connections of: (a) parallel and output-parallel, (b) series and output-parallel, (c) series and output-parallel and (d) input-parallel and output-series. ... 117 Figure 5-2. Currently available switching devices shown according to their maximum voltage and current ratings [1]. ... 118 Figure 5-3. Efficiency as a function of power output for an N = 3 parallel modular converter,
showing the efficiency improvements at light load with phase-shedding. ... 119 Figure 5-4. Topology of the Single Active Bridge used in the modules of the IPOP
converter... 121 Figure 5-5. An IPOP modular DC-DC converter with N = 4 SAB modules, where the specific module number m = 1 to 4. ... 122 Figure 5-6. The analysed efficiency ηIPOP,n of the SAB IPOP modular DC-DC converter as a
function of the power output Pout for n = 1 to 4. ... 124
Figure 5-7. Efficiency gain with phase-shedding of the SAB modular IPOP converter for n = 4 showing efficiency improvements of up to 17% at light loads... 124 Figure 5-8. The analysed efficiency η of the enhanced SAB IPOP modular DC-DC converter with switchable snubber capacitor and DCP control as a function of power output Pout for n = 1 to 4. ... 126
Figure 5-9. Efficiency η of the SAB module over a range of Pout from 0 kW to 3.5 kW and for
C1 from 5 nF to 250 nF with the point of maximum efficiency ηmax at the
optimum snubber capacitance C1opt. ... 126 Figure 5-10. Efficiencies of a PR-SAB IPOP modular converter for n = 1 to 4 indicating the
forbidden load zones (shaded) when phase-shedding is applied. ... 128 Figure 5-11. The minimum power Pmin,n and maximum power Pmax,n of the IPOP converter
for n = 1 and n = 2 as functions of C1. ... 130 Figure 5-12. Flowchart for optimisation of the C1 values in the IPOP modular converter with
the initial values of C1,m,init. ... 132 Figure 5-13. Efficiency comparisons of the SAB IPOP converter with the PR-SAB IPOP
converters for non-optimised and for optimised snubber capacitance across the full load range with phase-shedding. ... 133 Figure 5-14. The power ratio in the modules of an IPOP converter for m = 1 to 4 with
non-uniform power distribution optimised for the highest overall efficiency across the full load range. ... 135 Figure 5-15. Efficiencies of the IPOP converter for non-uniform and uniform module power
distribution with C1,m optimisation. ... 135 Figure 5-16. Experimental set-up with n = 4 modules connected as an IPOP modular
converter... 136
Figure 5-17. Inductor Ls current measurements, is,m, from m = 1 to 4 with uniform power
distribution for the PR-SAB IPOP modular converter at Pout = 10 kW and
Pm,out = 2.5 kW. ... 137
Figure 5-18. Inductor Ls current measurements, is,m, from m = 1 to 4 with non-uniform power
distribution for the PR-SAB IPOP modular converter at Pout = 4.6 kW when P1,out and P2,out = 0 kW; P3,out = 2.5 kW and P4,out = 2.1 kW. ... 137 Figure 5-19. Measurement results shown against the analysed results with phase-shedding
from n = 1 to 4 for (a) SAB modules and PR-SAB modules with optimised C1 and (b) optimised C1 with uniform and non-uniform module power
distribution. ... 138 Figure 6-1. A two-module input-series and output-parallel (ISOP) DC-DC converter. ... 141 Figure 6-2. An ISOP modular DC-DC converter with N = 3 SAB modules, where the specific module number m = 1 to 3. ... 143 Figure 6-3. Extension of the input-voltage range and the increase in efficiency with series
module shutdown in an ISOP DC-DC converter for n = 3 modules... 144 Figure 6-4. Analysed efficiency η of the SAB ISOP modular DC-DC converter as a function
of power output Uin for n = 3 at 2.6 kW... 145
Figure 6-5. Efficiency gain with module shutdown of the SAB modular IPOP converter from n = 3 to n = 1 with efficiency improvements of up to 2.2% at 0.8 kW. ... 146 Figure 6-6. N = 2 ISOP modular DC-DC converter, showing the current bypass switch
required for module shutdown and reactivation for module m = 2. ... 147 Figure 6-7. Typical waveforms of the module input current and voltage during module
shutdown and reactivation. ... 148 Figure 6-8. Implementation of the current bypass switch with two external IGBTs and a
resistor for module shutdown and reactivation. ... 150 Figure 6-9. Implementation of the current bypass switch with internal IGBTs in the input
bridge of the converter module for module shutdown and reactivation. ... 150 Figure 6-10. Plot of iC against uCE of an IGBT with increasing uGE in its active (shaded) and
saturation regions with the path of iC and uCE during module shutdown. ... 151
Figure 6-11. Safe Operation Area (SOA) of an IGBT with iCmax = f(uCE) which is used to
derive the maximum permissible collector current in the IGBT at a given uCE.. 152
Figure 6-12. The waveforms of iC and uCE during module shutdown with internal IGBTs
(see Section 6.4.2) within the SOA obtained from the iteration of time steps Δt = 1 μs. ... 153 Figure 6-13. The transfer functions of iC with uGE for a range of uCE that are used to determine
the function uGE = g(uCE,iCmax). ... 154
Figure 6-14. The function uGE = h(t) required to control the IGBT within its SOA limits
during module shutdown, as obtained from iteration with uGE = g(uCE,iCmax) for
the worst-case current pulse where uCE,0 = Uin,2. ... 154
Figure 6-15. The discharge of Cin,2 through two series-connected IGBTs in the phase-arm
during module shutdown. ... 155 Figure 6-16. The block diagram of the IGBT shutdown control, where the functions
Figure 6-17. Use of a delay circuit to implement a simplified analogue current control to generate uGE = hʹ(t). ... 156
Figure 6-18. (a) Close-up top-view of the module shutdown controller for simplified
analogue implementation, and (b) the module shutdown controller integrated into the converter module. ... 157 Figure 6-19. Measured waveforms of uGE(t) and iC(t) during module shutdown with the
implemented analogue shutdown controller. ... 157 Figure 6-20. Block diagram of the IGBT shutdown control where the functions iC = f(uCE)
and iC = g(uCE) are implemented digitally with a CPLD as LUT 1 and LUT 2,
respectively ... 159 Figure 6-21. Block diagram of the IGBT shutdown control for accurate universal IGBT
control with iC input. ... 159
Figure 6-22. Functional block diagram of the module shutdown digital controller for controlling the IGBT collector current within the SOA during module
shutdown. ... 161 Figure 6-23. (a) Top-side of the IGBT module shutdown controller and (b) with the IGBT
driver attached to the module shutdown controller board... 162 Figure 6-24. (a) The generated uGE1 and uGE3 waveforms from the module shutdown controller
and (b) the resulting Uin, uCE3 and iC, where iC is limited to an initial value of 1 A
during shutdown. ... 163 Figure 6-25. Experimental results showing iC and Uin,2 during voltage collapse at Cin = 30 µF
and an initial Uin,2 = 400 V for voltage collapse with external IGBT and
resistor. ... 164 Figure 6-26. Experimental results showing iC and Uin,2 during voltage collapse at Cin = 30 µF
and an initial Uin,2 = 400 V for the maximum voltage collapse current at (a) iCmax,
(b) 3 A and (c) 0.6 A. ... 165 Figure 6-27. Relationship between the thermal impedance ZthJC and the single current
pulse-width Δtdis in the utilised IGBT model IKW25N120H3. ... 167
Figure 6-28. Input voltages and currents for (a) module m = 1 and (b) module m = 2 during and after module shutdown at Uin = 550 V and Pout = 1.5 kW. ... 170
Figure 6-29. Input voltages and currents for (a) module m = 1 and (b) module m = 2 during and after module reactivation at Uin = 550 V and Pout = 1.5 kW. ... 171
Figure 6-30. (a) Uout during and after module shutdown and (b) during and after module
reactivation at Uin = 550 V and Pout = 1.5 kW. ... 172
Figure 6-31. The measured (*) and calculated efficiencies across the entire input-voltage range of the ISOP modular converter for n = 2 modules with module
shutdown. ... 173
Appendix
Figure A-1. The required operating region of the DC-DC converter showing the operating point used to design the converter. ... 181 Figure C-1. Graph showing tan(δ) versus fs for a metallized polypropylene (MKP) dielectric
material... 195
Figure D-1. A triangle with angle α, adjacent a, opposite o and the hypotenuse h side
labelled. ... 201 Figure D-2. A triangle with angle α, adjacent a, opposite o and the hypotenuse h side
labelled. ... 212 Figure E-1. The operating loci of the possible cases shown in the Δt1 and Δt3 plane for the
PR-SAB, with indications of Pmin, PBCM and Pmax. ... 223
Figure F-1. Steady-state operating waveforms of the current is(t) and voltages uc(t) and ub(t)
Figure 6-17. Use of a delay circuit to implement a simplified analogue current control to generate uGE = hʹ(t). ... 156
Figure 6-18. (a) Close-up top-view of the module shutdown controller for simplified
analogue implementation, and (b) the module shutdown controller integrated into the converter module. ... 157 Figure 6-19. Measured waveforms of uGE(t) and iC(t) during module shutdown with the
implemented analogue shutdown controller. ... 157 Figure 6-20. Block diagram of the IGBT shutdown control where the functions iC = f(uCE)
and iC = g(uCE) are implemented digitally with a CPLD as LUT 1 and LUT 2,
respectively ... 159 Figure 6-21. Block diagram of the IGBT shutdown control for accurate universal IGBT
control with iC input. ... 159
Figure 6-22. Functional block diagram of the module shutdown digital controller for controlling the IGBT collector current within the SOA during module
shutdown. ... 161 Figure 6-23. (a) Top-side of the IGBT module shutdown controller and (b) with the IGBT
driver attached to the module shutdown controller board... 162 Figure 6-24. (a) The generated uGE1 and uGE3 waveforms from the module shutdown controller
and (b) the resulting Uin, uCE3 and iC, where iC is limited to an initial value of 1 A
during shutdown. ... 163 Figure 6-25. Experimental results showing iC and Uin,2 during voltage collapse at Cin = 30 µF
and an initial Uin,2 = 400 V for voltage collapse with external IGBT and
resistor. ... 164 Figure 6-26. Experimental results showing iC and Uin,2 during voltage collapse at Cin = 30 µF
and an initial Uin,2 = 400 V for the maximum voltage collapse current at (a) iCmax,
(b) 3 A and (c) 0.6 A. ... 165 Figure 6-27. Relationship between the thermal impedance ZthJC and the single current
pulse-width Δtdis in the utilised IGBT model IKW25N120H3. ... 167
Figure 6-28. Input voltages and currents for (a) module m = 1 and (b) module m = 2 during and after module shutdown at Uin = 550 V and Pout = 1.5 kW. ... 170
Figure 6-29. Input voltages and currents for (a) module m = 1 and (b) module m = 2 during and after module reactivation at Uin = 550 V and Pout = 1.5 kW. ... 171
Figure 6-30. (a) Uout during and after module shutdown and (b) during and after module
reactivation at Uin = 550 V and Pout = 1.5 kW. ... 172
Figure 6-31. The measured (*) and calculated efficiencies across the entire input-voltage range of the ISOP modular converter for n = 2 modules with module
shutdown. ... 173
Appendix
Figure A-1. The required operating region of the DC-DC converter showing the operating point used to design the converter. ... 181 Figure C-1. Graph showing tan(δ) versus fs for a metallized polypropylene (MKP) dielectric
material... 195
Figure D-1. A triangle with angle α, adjacent a, opposite o and the hypotenuse h side
labelled. ... 201 Figure D-2. A triangle with angle α, adjacent a, opposite o and the hypotenuse h side
labelled. ... 212 Figure E-1. The operating loci of the possible cases shown in the Δt1 and Δt3 plane for the
PR-SAB, with indications of Pmin, PBCM and Pmax. ... 223
Figure F-1. Steady-state operating waveforms of the current is(t) and voltages uc(t) and ub(t)
