HIGH PERFORMANCE THREE PHASE AC/DC CONVERTERS FOR DATA CENTERS 1cm

246 Pages·2017·15.24 MB·English

HIGH PERFORMANCE THREE PHASE
AC/DC CONVERTERS FOR DATA
CENTERS
KAWSAR ALI
(B. Tech, NIT Durgapur, India)
A THESIS SUBMITTED
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
NATIONAL UNIVERSITY OF SINGAPORE
2017
Supervisor:
Dr Jimmy Chih-Hsien Peng
Examiners:
Associate Professor Ashwin M Khambadkone
Dr Sahoo Sanjib Kumar
Associate Professor Wilson Eberle, University of British Columbia
DECLARATION
I hereby declare that this thesis is my original work and it has
been written by me in its entirety. I have duly
acknowledged all the sources of information
which have been used in the thesis.
This thesis has also not been submitted for any degree
in any university previously.
________________________________
Kawsar Ali
12 December 2017
Acknowledgements
IowemysinceregratitudetomysupervisorDr. JimmyChih-HsienPengforhisadvice,
encouragement, and continuous support in my research. Not only did he take me in
his team when I was going through a turmoil in my Ph.D., he patiently guided me all
the way to produce a presentable thesis out of my work through numerous sessions of
feedback and discussions. I am extremely grateful to my previous- and co-supervisor
Dr. Pritam Das for introducing me to this research area and supervising my work for
the first three years, during which I finished the major part of my Ph.D. work. I also
express my sincere thanks to my previous co-supervisor Dr. Sanjib Kumar Panda for
histechnicalinputs,andespeciallyforhiskindunderstandingandsupportduringtough
times.
I am extremely grateful to Dr. Ashwin M. Khambadkone and Dr. Sanjib Kumar
Sahoo for their constructive guidance and critical inputs as Ph.D. thesis committee
members. Also, my sincere thanks to the anonymous reviewers of IEEE transactions
who helped me a lot to improve the quality of my research papers leading to their
eventual acceptance in the journals.
My special thanks to Mr. Y. C. Woo, Lab-in-Charge of Electrical Machines and
Drives Lab, for his persistent support throughout my Ph.D. I am also grateful for the
timely assistance from Mr. M. Chandra, Ms. Nurshaheeda and Mr. H.C. Seow.
The four years experience of my Ph.D. in NUS is something I will cherish for my
entire life. My profound thanks to my fellow research scholars, research engineers and
research fellows in Electrical Machines and Drives Lab for all the help to make my
stay more enjoyable and meaningful. My sincere thanks to Naga, Sindhu, Sandeep,
Subash,Cikai,Dongdong,Jeevan,Rajesh,Jayantika,Saurabh,Binita,Shiva,Ravikiran,
Elango, Ramprakash, Kanakesh, Amit, Kalpani, Carlos, Srinivash, Dr. Priyesh and Dr.
Aravinth. There are several other individuals who have helped me during my Ph.D.
and made me into who I am today. My warmest thanks to all of them. Finally, I am
grateful to Department of Electrical and Computer Engineering, National University of
3
Acknowledgements
Singapore (NUS) for providing me an opportunity to pursue Ph.D. in Singapore.
I owe so much appreciation to many warm-hearted, and wonderful friends inside
and outside of the NUS campus. Thanks to Neha, Naushad, Rusha, Saptak, Tanmay,
Soumya, Shalabh, Rahul, Raj for all the memories we created together in numerous
occasions. My four years flatmate Sai Kishore Ravi deserves a special mention here.
Also, Iwillcherishtheendlessphoneconversationsandonlinehangoutswithmyschool
friends Taushif, Jahanur, Selim, Hyder and Washim.
Ihavebeendeeplytouchedbytheendlessloveandboundlesssupportofmyparents
and my extended family – my brothers, sisters, uncles, aunts and my grandma. My
sincere thanks to all of them for always being on my side and keeping a sweet home
for me no matter what happens. I wish to dedicate to them what I have accomplished
today.
4
Contents
Acknowledgements 3
Summary 9
1 Introduction 30
1.1 Data Centers in Modern Energy Market . . . . . . . . . . . . . . . . . . 30
1.2 Existing Power System Topologies in Data Centers for Powering IT loads 32
1.2.1 AC Powered Data Centers . . . . . . . . . . . . . . . . . . . . . . 32
1.2.2 DC Powered Data Centers . . . . . . . . . . . . . . . . . . . . . . 34
1.2.2.1 48 V DC System . . . . . . . . . . . . . . . . . . . . . . 34
1.2.2.2 380 V DC System . . . . . . . . . . . . . . . . . . . . . 37
1.3 Literature Review of Three-Phase AC-DC Power Conversion for Data
Center Power Supplies . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
1.3.1 Two Stage Three-Phase AC-DC Power Conversion . . . . . . . . 40
1.3.1.1 Stage 1: Front-end PFC . . . . . . . . . . . . . . . . . . 40
1.3.1.2 Stage 2: Back-end DC-DC converter . . . . . . . . . . . 45
1.3.2 Single Stage Three-Phase AC-DC Power Conversion . . . . . . . 46
1.3.3 Output Voltage Ripple of Three-Phase AC-DC Converters . . . . 50
1.4 Literature Review on DC-DC Power Supplies for the ICT equipment . . 50
1.5 Summary of Literature Review . . . . . . . . . . . . . . . . . . . . . . . 51
1.6 Research Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
1.7 Proposed Single-Stage Three-Phase AC-DC Converter . . . . . . . . . . 54
1.8 Organization of the Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . 57
1.9 Contributions of the Thesis . . . . . . . . . . . . . . . . . . . . . . . . . 59
1.10 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
2 The Nine-Switch Converter – Review and Benchmark of Application 62
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
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Contents
2.2 Topology, Modulation and Control of the Nine-switch Converter . . . . 65
2.2.1 Switching constraint . . . . . . . . . . . . . . . . . . . . . . . . . 66
2.2.2 Modes of operation . . . . . . . . . . . . . . . . . . . . . . . . . . 67
2.2.2.1 AC-AC Common Frequency (AC-AC CF) mode . . . . 69
2.2.2.2 AC-AC Different Frequency (AC-AC DF) mode . . . . 70
2.2.2.3 AC-DC Different Frequency (AC-DC DF) mode . . . . 70
2.2.3 Space Vector PWM . . . . . . . . . . . . . . . . . . . . . . . . . 71
2.2.4 Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
2.3 LLA of Nine-Switch Converter for Different Modes of Operation . . . . 73
2.4 LLA of Nine-Switch Converter for Load-Source Combination in AC-DC
DF Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
2.4.1 Qualitative Reasoning for Existence of LLAs . . . . . . . . . . . 78
2.4.2 Mathematical Derivation of LLAs . . . . . . . . . . . . . . . . . 80
2.4.3 Efficient Load Sharing . . . . . . . . . . . . . . . . . . . . . . . . 86
2.5 Simulation Results and Discussions . . . . . . . . . . . . . . . . . . . . . 86
2.6 Theoretical Conduction Loss Comparison . . . . . . . . . . . . . . . . . 90
2.7 Experimental Results and Discussions . . . . . . . . . . . . . . . . . . . 91
2.7.1 For I /I <2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
D U
2.7.2 For I /I >2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
D U
2.8 Benchmark of Application Criteria of Nine-Switch Converter with Lower
Conduction Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
2.9 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
3 An APWM HB Series Resonant Converter with Magnetizing Current
Assisted ZVS 99
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
3.2 Steady State Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
3.2.1 Topology and Equivalent Circuit Model . . . . . . . . . . . . . . 102
3.2.2 Modes of Operation . . . . . . . . . . . . . . . . . . . . . . . . . 105
3.2.3 Calculation of Input Power . . . . . . . . . . . . . . . . . . . . . 108
3.3 Design Guidelines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
3.4 Design Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
3.4.1 Calculation of Transformer Turns Ratio . . . . . . . . . . . . . . 110
3.4.2 Design of Magnetizing Inductance . . . . . . . . . . . . . . . . . 110
3.4.3 Design of the Resonant Tank . . . . . . . . . . . . . . . . . . . . 113
3.4.4 Correction Factor and Quality Factor . . . . . . . . . . . . . . . 113
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Contents
3.4.5 Parameter Variations . . . . . . . . . . . . . . . . . . . . . . . . 114
3.5 Design Implementation in Data Center PoL Converters . . . . . . . . . 116
3.5.1 Reference Design . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
3.5.2 Proposed Design . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
3.5.3 Physical Design of Magnetic Components . . . . . . . . . . . . . 118
3.6 Experimental Results and Discussions . . . . . . . . . . . . . . . . . . . 119
3.7 Comparison of Different APWM HB Resonant Topologies . . . . . . . . 126
3.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
4 A Nine-Switch Interleaved Three-Phase AC-DC Single Stage Isolated
Converter 128
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
4.2 Steady State Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
4.2.1 Topology and Equivalent Circuit Model . . . . . . . . . . . . . . 130
4.2.2 Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
4.2.3 Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
4.3 Design Aspects and Simulation of the Proposed Converter . . . . . . . . 136
4.3.1 Choice of DC-link Voltage . . . . . . . . . . . . . . . . . . . . . . 136
4.3.2 Choice of Switching Frequency . . . . . . . . . . . . . . . . . . . 137
4.3.3 Design of Boost Inductor and DC-link Capacitor . . . . . . . . . 138
4.3.4 Design of Resonant Tank and the High-Frequency Transformers. 138
4.3.5 Controller Design . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
4.3.5.1 Controller Design for Boost PFC Part . . . . . . . . . . 139
4.3.5.2 Controller Design for DC-DC Resonant Part . . . . . . 140
4.4 Prototype Implementation and Theoretical Loss Analysis . . . . . . . . 143
4.4.1 Switch RMS Currents . . . . . . . . . . . . . . . . . . . . . . . . 143
4.4.2 Occurrence of Soft Switching . . . . . . . . . . . . . . . . . . . . 145
4.4.3 Selection of Switching Devices . . . . . . . . . . . . . . . . . . . 147
4.4.4 Loss Distributions . . . . . . . . . . . . . . . . . . . . . . . . . . 147
4.4.4.1 Switch turn-on loss . . . . . . . . . . . . . . . . . . . . 149
4.4.4.2 Switch turn-off loss . . . . . . . . . . . . . . . . . . . . 149
4.4.4.3 Inductor core loss . . . . . . . . . . . . . . . . . . . . . 150
4.4.5 Validation of Choice of Sawtooth Carrier over Triangular Carrier 150
4.5 Results and Discussions . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
4.6 Cost Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
4.7 Results with 380V DC Output Voltage . . . . . . . . . . . . . . . . . . . 161
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Contents
4.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
5 Effect of Three-Carrier Modulation in Input Current Harmonics 166
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
5.2 For Double-edge Naturally Sampled PWM . . . . . . . . . . . . . . . . . 168
5.3 For Regular Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
5.3.1 Single-edge Regular Sampled PWM . . . . . . . . . . . . . . . . 171
5.3.2 Symmetrical Regular Sampled PWM . . . . . . . . . . . . . . . . 173
5.4 ValidationoftheThree-CarrierModulationintheProposedNine-Switch
Converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
5.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
6 Conclusions and Future Works 179
6.1 Summary of Work Done . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
6.2 Prospective Research Work . . . . . . . . . . . . . . . . . . . . . . . . . 182
6.2.1 Benchmarking of Nine-Switch Converter against BTB Converter 182
6.2.2 Bi-directional Battery Charger . . . . . . . . . . . . . . . . . . . 183
6.2.3 Study on Phase-Shedding . . . . . . . . . . . . . . . . . . . . . . 183
6.2.4 Reliability Study of the Converters . . . . . . . . . . . . . . . . . 184
6.2.5 Improvement of DC Bus Utilization . . . . . . . . . . . . . . . . 184
6.2.6 Hold Up Time (HUT) Analysis . . . . . . . . . . . . . . . . . . . 184
AppendixA HighStep-upAPWMConverterforIntegrationofPVMod-
ule to Data Center 186
A.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
A.2 Converter Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
A.3 Results and Discussions . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
A.3.1 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
A.3.2 Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
A.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
Appendix B Implementation of Control in TI DSP F28335 198
B.1 The Problem with Generation of XOR-ed Pulses . . . . . . . . . . . . . 198
B.2 Indirect XOR-ed Pulses from F28335 Microcontroller . . . . . . . . . . . 199
B.3 The Controller Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
B.3.1 Sinusoidal PWM . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
B.3.2 Space Vector PWM . . . . . . . . . . . . . . . . . . . . . . . . . 214
8
Summary
To improve the efficiency of the MW level power consumption in data centers and
to achieve a Power Usage Effectiveness (PUE) closer to 1.0~1.2, cooling has by far
become the most important aspect of modern day data center operations. Apart from
improvement of the cooling technology itself, focus is being given on reduction of heat
generation,especiallyfromthepowersystemsinsidethedatacenter. Migrationtowards
aDCbasedpowerarchitecturehasproventobepromisinginthisregardmainlybecause
of reduction of number of conversion stages and the absence of phase balancing or
harmonic issues. While 48 V DC has already been in place in most telecom central
offices, modern data centers are shifting towards the more efficient 380 V DC system.
The common practice for converting the utility three-phase AC to regulated and
isolatedDCisatwostageconversionscheme,whichalsoensuresunitypowerfactorand
lessthan5%TotalHarmonicDistortion(THD)oftheinputcurrents. Inordertoreduce
thecost,size,andcomplexityassociatedwithtwo-stageAC-DCpowerconversion,active
research is ongoing to come up with single-stage converters that integrate the functions
of Power Factor Correction (PFC) and isolated AC-DC conversion in a single power
converter. However,obtainingaregulatedandisolatedDCvoltagefromthree-phaseAC
supply in a single stage comes at the cost of the inefficient Discontinuous Conduction
Mode(DCM)oftheinputcurrents. Findingasolutionforasingle-stageconversionwith
Continuous Conduction Mode (CCM) of the input currents is the need of the hour.
This thesis proposes a novel Silicon Carbide (SiC) based nine-switch single-stage
isolatedthree-phaseAC-DCconverter,whichintegratesathree-phaseActiveFront-End
(AFE) boost PFC rectifier and three phase-interleaved half-bridge DC-DC resonant
converters in a single stage. In a conventional two-stage configuration this integration
requires twelve switches, which means the proposed converter yields a 25% saving in
activeswitchcount. Anovelmodulationschemeusingthreeseparate120◦ phaseshifted
high frequency carriers for the three legs of the converter is developed to drive the
switches. It is shown that such modulation scheme leads to interleaved operation of
9
Summary
thethreeDC-DCresonantconvertersintegratedwithintheproposedtopologyresulting
in 67% lower output DC voltage ripple than the conventional two-stage configuration.
Mostimportantly,despitebeingasingle-stagetopology,theproposedconverteroperates
in CCM, and thus eliminates all the issues related to DCM.
This thesis also proposes a novel Asymmetrical Pulse-Width Modulated half-bridge
(APWM HB) DC-DC resonant converter with naturally extended range of zero-voltage
switching (ZVS), applicable for the Point-of-Load (PoL) converters of data centers to
improve their efficiency. The novelty of this converter is in its design, which uses the
magnetizing current and eliminates the need of extra components (like LC network)
that are otherwise used in APWM HB resonant converter for ensuring ZVS over wide
range of line and load variation. Empirical formulae are derived to design the resonant
network systematically in a flow-chart based manner. A new optimal method of design
ofthemagnetizinginductanceofthehigh-frequencytransformerisalsopresented,which
is equally applicable to a standard LLC converter.
Finally, while reviewing and discussing about the nine-switch converter, this thesis
also benchmarks, both analytically and experimentally, the application criteria of the
nine-switch converter for having lower conduction loss than the twelve-switch back-to-
back (BTB) converter.
All the analytical works in this thesis have been validated with appropriate experi-
mental prototypes, and their measured efficiencies are compared with relevant existing
works.
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