THE PARALLEL CONNECTION OF SINGLE PHASE DC TO AC POWER CONVERTERS Mr ...

173 Pages·1999·6.52 MB·English

THE PARALLEL CONNECTION OF SINGLE PHASE
DC TO AC POWER CONVERTERS
Mr. Joseph Woods
A Thesis
in
The Department
of
Electrical and Cornputer Engineering
Presented in Partial Fulfillment of the Requirements
for the Degree of
Master of Applied Science
Concordia University
Montreal, Quebec, Canada
March, 1999
Copyright O Joseph Woods, 1999
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ABSTRACT
TEiE PARAILLEL CONNECTION OF SINGLE PHASE
DC TO AC POWER CONVERTERS
Joseph Woods
Electrical power converter subsystems are placed between an ac-mains bus and a load
in order to condition the power being transferred, to protect the load and the ac source, and
to provide uninterruptible power supply (UPS) features. One method of providing the
required interface in, low to medium power applications ( 1. O to 150 kVA), is to connect
multiple converter modules in parallel. This approach has the advantages of increased
reliability, due to the redundancy of the system. and flexibiiity, since modules cm be added
or removed as needed.
The successful performance of a parallel-connected system depends on i) the modularity
of the individual converter units, ii) their response charactenstics, and iii) the quality of the
power they produce. A single-phase converter module and a parallel comection circuit is
proposed that meets these three objectives by using a fast control circuit for each converter,
insulated-gate bipolar transistors (IGBTs), a hi& switching fiequency (10 IcHz to 20 IcHz),
and a fiequency modulated (FM) communication scheme. Thus, the moddarity is enhanced
by using an FM signal in order to eliminate the wiring normally required to share the
converter output current control parameters.
DEDICATION
This Thesis is dedicated to the memory of the Iate Dr. P. D. Ziogas, with whom the author
began the studies that culminated in the production of the following work. The author dso
wishes to acknowledge the support and aid given by his supervisors, Dr. G. Joos and Dr. P.
Jain and his colleagues including, Mr. Jose Espinoza, Mr. Humberto Puihiero, and Mr.
Donato Vincenti at the P. D. Ziogas Mernorial Power Electmnics Laboratory. Finally,
appreciation is due to the authors family, wife Dorsey and son Denis for their support and
patience.
Table of Contents
1. TNTRODUCTION ..................................................... 1
1.1. The Origin of The Parallel Converter Topoiogy ...................... 1
1.1.1. Power Converters and Power Conditioning ................... 1
1.1.2. The Parallel Power Converter Circuit ...................... -33
1.2 Existing Parallel Converter Designs ............................... - 4
1.2.1. Converter Circuits in Paralle1 Topologies ................... - 6
12 .2. AC to AC Converters Connected in Parallel .................. 7
1.2.3- Problems Associated with Parallel-Connected Converter Systems
................................................ 12
1 The Scope and Contents of the Thesis ............................. 13
1.3.1. General Description of the Proposed System ................ 14
1- 3. 2 . Specifications of the Proposed System ..................... 17
1.4. Contributions of the Thesis ..................................... -20
1.4.1. The Development Strategy of the Thesis .................. -21
1A .2. The Contents of the Thesis ............................. -22
2 . DESIGN AND OPERATION OF THE DC TO AC INVERTER ................ 24
2.1. The Initial Design Stages ......................................- 24
2.2. Design of the Basic Converter Module ........................... -24
2.2. I . Fundamental Circuit Ratings ............................ 25
2.2.2. Component SeIection .................................- 25
2.2.3. Auxiiiary Subcircuits ................................... 25
2.3. The Rectifier and DC Bus Filter .................................. 26
2.3.1. The Input Fiiter ......................................- 27
2.3.2. The Rectifier and DC Filter .............................. 28
2.3 .3 . Rectifier and DC Bus Component Values ..................- 31
2.3 .4 . Simulated dc source performance ........................ -33
2.3.5. Construction of the DC Source ........................... 33
2.4. The Inverter and the Switching Control ............................ 3133
2.4.1. The Model of the Inverter and Switching Circuit .............- 34
2.4.2. The PWM Switching Scheme ........................... -35
2.4.3. Inverter Component Values ............................. -37
2.4.4. Sirnulated Inverter Performance .......................... 39
2.4.5. Construction of the hverter and the Switching Control ....... -40
2.5. The Output Filter and Transformer ................................ 40
2.5.1. The mode1 ofthe output filter ........................... -41
2.5.2. Output filter component values ........................... 42
2.5.3. Simulated output filter performance ......................- 43
2.5 .4 . Construction of the output filter .......................... -43
2.5 .5 . The Interconnection and Supply of Converter Modules ........4 4
2.6.S ummary .................................................... 45
3. DESIGN AND PERFORMANCE OF THE CONVERTER CONTROL SYSTEM -47
3.1. Control Strategy for the Proposed System of Converter Modules ........ 47
3.1.1. The Mode1 of the CM System ...........................- 48
3.1.2. The Basic CM Controi Circuit ............................ 52
3.1.3. Control System Design Cntena ..........................- 53
3.2. The Current Control Circuit ....................................- 54
3.2.1. The h e rC urrent Control Loop .......................... 54
3 .2.2. The Performance of the Inner Cunent Controller .............5 7
3 .2 .3. The Transformer Magnetiung and Filter Capacitor Currents .... 58
3.2.4. Control of Load Sharing ............................... -58
3.3. The Voltage ControI Circuit .................................... -59
3.3.1. The Outer Voltage Control Loup ......................... -60
3 -3. 2 . The Performance of the Voltage Control Circuit .............. 66
3.3 .3 . The Simulation of the Voltage Controller ................... 66
3.4.S urnmary .................................................... 67
4 . THE FM CTJRRENT-SHARING COMMlMICATION SCHEME ............. 69
4.1. Control of Multiple Converter Modules ............................ 69
4.2. The Mode1 of the Paralleled System of Converters ................... 69
4.3. The Stability of the Proposed Control Scheme ..................... -73
4.4. The Curent Sharing Control Circuit ............................ -79
vii
4.4.1. The Description of the Current Sharing Controller ............8 0
4.4.2. The Frequency Modulated Communication Scheme ........... 83
4.4.3. The Simulation of the Frequency Modulation Controller ....... 85
4.5.S ummary ....................................................8 9
5 . PERFORMANCE OF THE CONVERTER MODULES ..................... -92
5.1. Testing The Converters ................................. .. .... -92
5.2. Design Criteria and Performance Objectives ....................... -92
5.2.1. The Selection of Power System Components ................ 95
5.2.2. The FM Communications Scheme ....................... -96
5.3. The Simulated Techniques for the Converter Modules ................ 96
5.3.1. The Simulation Software and Circuit Models ................ 97
5.3.2. The Simulation software schernatic ...................... -99
5.3 .3 . The model of the inverter .............................. 101
5.3 .4 . The transformer. filter elements and the loads .............. 101
5 -3. 5 . The control circuit .................................... 105
5.4. The Simulated Steady-State Response of the CM ................... 107
5.4.1. The steady-state response of the control and curent-sharing subcircuits
................................................ 108
5.4.2. The steady state response of the power subcircuit ............ 111
5.5. The transient response of the CM control and curent-sharing subcircuits
...................................................... 112
5.5.1. The transient response of the single-CM power subcircuit ..... 113
5.5.2. The Simuiated Response to an Abnormal Operating Conditions
.................................................. 113
5.6.Summai-v ................................................... 113
6 . IMPLEMENTATION AND SYS TEM PERFORMANCE .................... 117
6.1. The Performance of the System of Converters Connected in Paralle1 .... 117
6.2. The Software Models of the Circuit .............................. 117
6.2.1. The Simulated Transient Response of the Parailel Connected System
.................................................. 119
6.2.2. The simulated transient response of a two-CM system ....... 121
6.2.3. The transient response of a three converter system ........... 123
6.3. Consb-uction and Perforrîiance of the Expenmental Test Circuits ....... 126
6.3.1. Construction of the Prototype Circuits ..................... 126
6.3.2. The Transient Operation of the Prototype Sy stem ............ 127
6.3.3. The Steady State Response of the Experimentd System ....... 127
6.4. Performance and Design Considerations .......................... 129
6.4.1. The Effect of the RMS Circuits .......................... 131
6.4.2. The Effect of Error in the Voltage Reference ............... 131
6.4.3. The Assignment of the Signal Bandwidth on the Output Bus ... 132
6.5.S ummq ................................................... 132
7. CONCLUSIONS .................................................... 134
7.1. Summary .................................................. 134
7.2. Feature and Advantages of the Proposed Topology .................. 136
7.2.1. Performance of the Proposed System .................... 137
7.2.2. Design of the Proposed System ......................... 138
7.3. FutureWork ................................................ 139
REFERENCES ....................................................... 141
APPENDIX .......................................................... 145