High-Frequency Isolated DC/AC and Bidirectional DC/DC Converters

236 Pages·2009·1.88 MB·English

High-Frequency Isolated DC/AC and Bidirectional DC/DC Converters
for PMSG-based Wind Turbine Generation System
by
Xiaodong Li
B.Eng., Shanghai Jiao Tong University, 1994
M.A.Sc., University of Victoria, 2004
A Dissertation Submitted in Partial Fulfillment of the
Requirements for the Degree of
DOCTOR OF PHILOSOPHY
in the Department of Electrical and Computer Engineering
(cid:176)c Xiaodong Li, 2009
University of Victoria
All rights reserved. This dissertation may not be reproduced in whole or in part, by
photocopying or other means, without the permission of the author.
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High-Frequency Isolated DC/AC and Bidirectional DC/DC Converters
for PMSG-based Wind Turbine Generation System
by
Xiaodong Li
B.Eng., Shanghai Jiao Tong University, 1994
M.A.Sc., University of Victoria, 2004
Supervisory Committee
Dr. Ashoka K. S. Bhat, Supervisor
(Department of Electrical and Computer Engineering)
Dr. Subhasis Nandi, Departmental Member
(Department of Electrical and Computer Engineering)
Dr. Harry H. L. Kwok, Departmental Member
(Department of Electrical and Computer Engineering)
Dr. Sadik Dost, Outside Member
(Department of Mechanical Engineering)
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Supervisory Committee
Dr. Ashoka K. S. Bhat, Supervisor
(Department of Electrical and Computer Engineering)
Dr. Subhasis Nandi, Departmental Member
(Department of Electrical and Computer Engineering)
Dr. Harry H. L. Kwok, Departmental Member
(Department of Electrical and Computer Engineering)
Dr. Sadik Dost, Outside Member
(Department of Mechanical Engineering)
ABSTRACT
In this dissertation, a high-frequency (HF) transformer isolated grid-connected
power converter system with battery backup function is proposed for a small-scale
wind generation system (less than 100 kW) using permanent magnet synchronous
generator (PMSG). The system includes a main HF isolated DC/AC grid-connected
converter and a bidirectional HF isolated DC/DC converter.
Through literature survey and some comparative studies, a HF isolated DC/DC
converter followed by a line connected inverter (LCI) is chosen as the grid-connected
scheme. After reviewing several topologies which were used in such a DC/AC con-
verter with an unfolding stage, a DC/AC grid-connected converter based on dual-
bridge LCL-type resonant topology is proposed. Through the control of the phase-
shift angle between the two bridges, a rectified sinusoidal dc link current can be
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modulated, which in turn can be unfolded by the LCI. This converter is analyzed
with Fourier series analysis approach. It is shown that all switches in both bridges
can work in zero-voltage switching (ZVS) at any phase-shift and load conditions. The
redundancy of the dual-bridge structure make it easy to accommodate higher power
flow. A design example of a 500 W converter is given and simulated. A prototype
is built and tested in the lab to validate its performance. The simulation and exper-
imental results show a reasonable match to the theoretical analysis. The expansion
to three-phase grid-connection is discussed with phase-shifted parallel operation of
three identical units. Input and output current harmonics of different arrangements
are analyzed to search for the best choice.
As the feature of a hybrid wind generation application, the battery backup func-
tion is fulfilled with a bidirectional HF transformer isolated DC/DC converter. This
dual-bridge series resonant converter (DBSRC) is analyzed with two ac equivalent
circuit approaches for resistive load and battery load respectively, which give same
results. Soft-switchingisachievedforallswitchesonbothsidesoftheHFtransformer.
Test plots obtained from simulation and experiment are included for validation.
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Contents
Supervisory Committee ii
Abstract iii
Table of Contents v
List of Abbreviations ix
List of Symbols x
List of Tables xi
List of Figures xiii
Acknowledgements xxxi
Dedication xxxii
Chapter 1 Introduction 1
1.1 History of Wind Energy Utilization . . . . . . . . . . . . . . . . . . . 1
1.2 Variable-Speed versus Constant-Speed . . . . . . . . . . . . . . . . . 3
1.3 WTGS Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3.1 Induction Generator . . . . . . . . . . . . . . . . . . . . . . . 7
1.3.2 Synchronous Generator . . . . . . . . . . . . . . . . . . . . . . 9
1.4 Motivation and Objective . . . . . . . . . . . . . . . . . . . . . . . . 11
vi
1.5 Outline of the Dissertation . . . . . . . . . . . . . . . . . . . . . . . . 16
1.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Chapter 2 ComparisonandSelectionofSuitableHFIsolatedDC/AC
Grid-Connected Converter 18
2.1 High frequency converter with soft switching . . . . . . . . . . . . . . 19
2.2 ComparisonandselectionofHFisolatedDC/ACgridconnectionschemes 22
2.2.1 Stage 1: DC to HF AC . . . . . . . . . . . . . . . . . . . . . . 22
2.2.2 Stage 2: HF AC to LF AC . . . . . . . . . . . . . . . . . . . . 24
2.3 Topologies of HF isolated DC-to-LFAC converter including an unfold-
ing LCI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.3.1 Topology 1: Variable frequency sinusoidally-modulated PWM
converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
2.3.2 Topology 2: Fixed frequency sinusoidally-modulated LCL-type
SRC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
2.3.3 Topology 3: Fixed frequency sinusoidally-modulated parallel
dual SRC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
2.3.4 Topology4: Fixedfrequencysinusoidally-modulatedseriesdual
SRC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
2.3.5 Pros and cons of the four topologies . . . . . . . . . . . . . . . 42
2.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Chapter 3 A Phase-Modulated High-Frequency Dual-Bridge LCL
DC/AC Resonant Converter 60
3.1 Principle of a HF Isolated Dual-Bridge LCL Resonant Converter . . . 61
3.2 Fourier Series Analysis of the Proposed Converter . . . . . . . . . . . 67
3.3 Design Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
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3.4 Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
3.5 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
3.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Chapter 4 Multi-cell Operation of HF Isolated Dual LCL Reso-
nant Converter 116
4.1 Multi-cell operation of high power single-phase grid connection . . . . 117
4.1.1 Multi-cell operation of high power three-phase grid connection 118
4.1.2 Input dc current harmonics . . . . . . . . . . . . . . . . . . . 118
4.1.3 Y connection of three cells to three-phase grid . . . . . . . . . 120
4.1.4 ∆ connection of three cells to three-phase grid . . . . . . . . 121
4.2 Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
4.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
Chapter 5 A Bidirectional HF Isolated Dual-bridge SRC for Bat-
tery Charging 129
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
5.2 Principle of the Proposed Bidirectional Battery Charger . . . . . . . 131
5.2.1 Charging (Controlled Rectifier) Mode . . . . . . . . . . . . . . 133
5.2.2 Discharging (Regeneration) Mode . . . . . . . . . . . . . . . . 137
5.3 AC Equivalent Circuit Analysis for DBSRC . . . . . . . . . . . . . . 137
5.3.1 Normalization and Definitions . . . . . . . . . . . . . . . . . . 139
5.3.2 Method I for Voltage Source Load . . . . . . . . . . . . . . . 140
5.3.3 Method II for Resistive Load . . . . . . . . . . . . . . . . . . . 142
5.4 Design Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
5.5 Simulation and experiment results . . . . . . . . . . . . . . . . . . . . 156
5.5.1 Simulation results . . . . . . . . . . . . . . . . . . . . . . . . . 156
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5.5.2 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . 157
5.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
Chapter 6 Conclusions 170
6.1 Summary of Work Done . . . . . . . . . . . . . . . . . . . . . . . . . 170
6.2 Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
6.3 Suggestions for Future Work . . . . . . . . . . . . . . . . . . . . . . . 173
Appendix A Circuit layout of simulations in Chapter 2 186
Appendix B Implementation of control circuit of Chapter 3 191
Appendix C Phasor domain analysis of the dual-bridge LCL converter194
Appendix D Simulation layout of Chapter 4 199
Appendix E Design of RC snubber 200
Appendix F More Simulation Results of DBSRC in Chapter 5 202
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List of Abbreviations
ac, AC alternative current
BJT bipolar junction transistor
DBSRC dual-bridge series resonant converter
dc, DC direct current
DFIG doubly-fed induction generator
EMI electro-magnetic interference
FFT fast fourier transformation
HF high frequency
IG induction generator
IGBT insulated-gate bipolar transistor
MOSFET metal-oxide-semiconductor field-effect transistor
MPPT maximum power point tracking
PFC power factor correction
PMSG permanent magnet synchronous generator
SCIG squirrel cage induction generator
SCR silicon controlled rectifier
SG synchronous generator
THD total harmonics distortion
WRIG wound rotor induction generator
WRSG wound rotor synchronous generator
WTGS wind turbine generation system
ZCS zero-current switching
ZVS zero-voltage switching
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List of Symbols
α, β, θ, φ angles
ω angular frequency
c, C capacitance
d, D diodes
f, F frequency
i, I current
J normalized current
l, L inductance
M voltage gain
n, n , n , n transformer ratio
p s t
P power
r, R resistance
s, S switches
t time
v, V voltage
X reactance
Z impeadance