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A Design Study of a Future 10 kW Converter

Examensarbete utfört i elektroniksystem av

Sebastian Fant

LiTH-ISY-EX--08/4093--SE

Linköping 2008

A Design Study of a Future 10 kW Converter

Examensarbete utfört i elektroniksystem

vid Linköpings tekniska högskola

Sebastian Fant

LiTH-ISY-EX--08/4093--SE

Examinator: Kent Palmkvist

Handledare: Jonny Lindgren

Presentationsdatum

2008-03-18

Publiceringsdatum (elektronisk version)

Institution och avdelning

Institutionen för systemteknik

Department of Electrical Engineering

URL för elektronisk version

http://www.ep.liu.se

Publikationens title

A Design Study of a Future 10 kW Converter

Författare

Sebastian Fant

Sammanfattning

This master thesis aim to design and evaluate a high power 3-phase DC/AC and AC/AC converter. The

purpose is to use it for an electric motor in an aircraft possibly driving electric actuators or a propeller

in an UAV or a small vehicle. Factors such as power loss and weight are of importance and will be

estimated using known models supplied by various manufacturers of components. Different topologies

of semiconductors suitable for this purpose are examined and presented. Extensive resources have been

put to properly select the most suitable switching device according to their power loss and weight.

The need for filters and protective circuits will be estimated according to regulations of common

military avionic standards and will be included in the resulting estimation along with simulations to

evaluate their need and importance.

Snubber circuits will be presented and their specific ability to reduce voltage transients and

switching losses will be examined along with some simulations to illustrate their performance.

In the final part an estimation of efficiency and weight of higher and lower power models of the

same inverter has been made using the same procedure as presented in this paper. Engineering rules

have been formed from these estimations to simply be able to calculate the proportions of a future

inverter of arbitrary rated power.

Antal sidor: 93

Nyckelord

Inverter design, Power electronics, Snubber circuits, filter, IGBT

Språk

Svenska

x Annat (ange nedan)

Engelska

Antal sidor

Typ av publikation

Licentiatavhandling

x Examensarbete

C-uppsats

D-uppsats

Rapport

Annat (ange nedan)

ISBN (licentiatavhandling)

ISRN LiTH-ISY-EX--08/4093--SE

Serietitel (licentiatavhandling)

Serienummer/ISSN (licentiatavhandling)

Abstract

This master thesis aim to design and evaluate a high power 3-phase DC/AC and AC/AC

converter. The purpose is to use it for an electric motor in an aircraft possibly driving

electric actuators, a propeller in an UAV or a small vehicle. Factors such as power loss

and weight are of importance and will be estimated using known models supplied by

various manufacturers of components. Different topologies of semiconductors suitable

for this purpose are examined and presented. Extensive resources have been put to

properly select the most suitable switching device according to their power loss and

weight.

The need for filters and protective circuits will be estimated according to regulations of

common military avionic standards and will be included in the resulting estimation along

with simulations to evaluate their need and importance. Snubber circuits will be

presented and their specific ability to reduce voltage transients and switching losses will

be examined along with some simulations to illustrate their performance. In the final part

an estimation of efficiency and weight of higher and lower power models of the same

inverter has been made using the same procedure as presented in this paper. Engineering

rules have been formed from these estimations to simply be able to calculate the

proportions of a future converter of arbitrary rated power.

Keywords: Inverter design, Power electronics, Snubber circuits, filter, IGBT

Sammanfattning

Det här examensarbetet syftar till att designa och utvärdera en högeffektskonverter

kapabel att konvertera lik eller trefas växelspänning till en trefas växelspänning med

högre frekvens. Syftet är att driva en elektrisk motor för möjligtvis en domkraft eller en

propeller för en obemannad eller småskalig flygfarkost. Faktorer såsom förlusteffekt och

vikt är viktigt och kommer att uppskattas med hjälp av välkända modeller framtagna av

flertalet tillverkare av komponenter. Olika topologier av halvledarkomponenter passande

ändamålet är undersökta och presenterade. Mycket tid läggs på att hitta de perfekta

halvledarkomponenterna för ändamålet med tyngdpunkt på dess förlusteffekt och vikt.

Behovet av filter och skyddskretsars omfattning är uppskattade enligt standardiserade

bestämmelser för flygfarkoster och kommer i slutskedet att bidra med både vikt och

effektförluster. Simuleringar utförs i Matlab och Simulink för att visa dess behov och

prestanda. Olika typer av snubberkretsar presenteras med dess unika egenskaper som

syftar till att undertrycka spänningstransienter over de känsliga halvledarkomponenterna.

Simuleringar utförs i Pspice för att illustrera varje snubberkrets respektive för och

nackdelar samt prestanda. I slutskedet av rapport har det genomförts en uppskattning av

verkningsgraden och vikten gällande för konverters av högre och lägre märkeffekt. Det

har gjorts analogt med det tillvägagångssätt som använts i denna rapport. Ingenjörsregler

har blivit approximerade för att enkelt kunna uppskatta vikt och förlusteffekt för

godtycklig märkeffekt.

Nyckelord: Inverter design, kraft elektronik, snubberkretsar, högeffektsfilter, IGBT

III

Acknowledgements

This report is a result of my master-thesis project carried out at SAAB Aerosystems in

Linköping under supervision of the department of Electrical Engineering at the

University of Linköping. As a student at the programme for applied physics and electro

engineering I chose the alignment which felt the most natural and rewarding to me,

electronics. This master-thesis was chosen among several available projects due to my

interest in analog and high power electronics although the amount of the courses taken in

the field was few. As I expect the need for this competence will grow significantly in the

near I made the tactical choice by accepting the proposal offered to me.

Looking back over the time spent at SAAB Aerosystems it has been very interesting,

rewarded and has completely fulfilled my expectations. I have been given opportunities

to reflect the daily life of an avionic electrical engineer and the problems they face.

Great insight into the avionic industry has been given by my brilliant supervisor Lars

Austrin and I would like to thank him dearly for that. I would also like to thank Eduardo

Figueroa for giving me many discussions about the future life as an engineer and where it

might lead. I would like to thank Andreas Johansson for his revising and the many

practical hints he gave me. I would like to thank my co-worker Daniel Eidborn for a job

well done and I wish you all the luck in the future.

Thank you SAAB and especially the TDG department for providing the finances and

office necessary for completing this master-thesis.

Last but not the least I would like to thank my family and my friends for supporting me

and my studies throughout the years.

Linköping March 2008

Sebastian Fant

Table of contents

LIST OF FIGURES....................................................................................................................................VI

LIST OF TABLES......................................................................................................................................VI

1. INTRODUCTION............................................................................................................................... 1

1.1. OBJECTIVES ................................................................................................................................. 1

1.2. BACKGROUND .............................................................................................................................. 1

1.3. CHALLENGES ............................................................................................................................... 1

1.4. RESEARCH METHOD ..................................................................................................................... 2

1.5. DELIMITATIONS ........................................................................................................................... 2

1.6. STRUCTURE OF REPORT ................................................................................................................ 2

2. THEORY............................................................................................................................................. 5

2.1. CONVERTER PRINCIPLES............................................................................................................... 5

2.2. PRINCIPLES FOR CONTROL ........................................................................................................... 7

2.2.1. Switching frequency................................................................................................................ 7

2.3. POWER COMPONENTS................................................................................................................... 8

2.3.1. Switching transistors .............................................................................................................. 8

2.3.1.1. IGBT............................................................................................................................................ 8

2.3.1.2. MOSFET.................................................................................................................................... 12

2.3.1.3. BJT............................................................................................................................................. 13

2.3.2. Free-wheeling-diodes............................................................................................................13

2.3.2.1. Silicon Schottky......................................................................................................................... 14

2.3.2.2. Silicon Carbide Schottky............................................................................................................ 14

2.3.3. Rectifier .................................................................................................................................14

2.4. FILTERS.......................................................................................................................................16

2.4.1. Input filters ............................................................................................................................16

2.4.2. DC-bus filter..........................................................................................................................19

2.4.2.1. Capacitor bank ........................................................................................................................... 19

2.4.2.2. Choke inductor........................................................................................................................... 25

2.4.2.3. Output filters.....................................................................................................................26

2.5. SNUBBER CIRCUITS .....................................................................................................................30

2.5.1. Increased SOA.......................................................................................................................30

2.5.2. Reducing losses......................................................................................................................35

2.6. PRINCIPLES OF COOLING..............................................................................................................36

2.6.1. Thermal resistance ................................................................................................................36

2.6.2. Heat transfer..........................................................................................................................36

2.7. CHASSIS DESIGN..........................................................................................................................37

2.7.1. Cooling scenarios..................................................................................................................39

2.7.1.1. Exterior heatsink ........................................................................................................................ 39

2.7.1.2. Interior heat sink ........................................................................................................................ 42

2.7.1.3. Internal fluid cooling.................................................................................................................. 43

2.8. TRANSISTOR DRIVES ...................................................................................................................43

2.9. POWER SUPPLY............................................................................................................................45

2.10. CONTROLLER ..............................................................................................................................46

3. LOSSES..............................................................................................................................................47

3.1. SWITCHING LOSSES .....................................................................................................................47

3.1.1. Transistor ..............................................................................................................................47

3.1.2. Diode .....................................................................................................................................48

3.2. CONDUCTION LOSSES ..................................................................................................................49

3.2.1. Transistor ..............................................................................................................................49

3.2.2. Diode .....................................................................................................................................49

3.3. LOWEST LOSS ESTIMATION OF IGBT AND FWD .........................................................................50

3.4. RECTIFIER ...................................................................................................................................51

3.5. FILTERS.......................................................................................................................................52

3.5.1. Input filter..............................................................................................................................52

3.5.2. DC-bus filter..........................................................................................................................52

3.5.3. Output filter...........................................................................................................................53

3.6. CONTROLLER ..............................................................................................................................53

3.7. TRANSISTOR DRIVES ...................................................................................................................53

3.8. INTERNAL POWER SUPPLY ...........................................................................................................54

4. RESULTS...........................................................................................................................................55

4.1. POWER DENSITY ..........................................................................................................................55

4.2. SCALABILITY ..............................................................................................................................56

4.3. EFFICIENCY .................................................................................................................................56

4.4. RELIABILITY ...............................................................................................................................57

4.5. SIMULATIONS ..............................................................................................................................58

5. CONCLUSIONS................................................................................................................................59

6. FUTURE WORK...............................................................................................................................60

BIBLIOGRAPHY .......................................................................................................................................61

APPENDIX A1 – OUTPUT CHARACTERISTICS USING SURGE CURRENT LIMITER.........................................63

APPENDIX A2 – OUTPUT CHARACTERISTICS USING NO SURGE CURRENT LIMITER ..................................64

APPENDIX A3 – RECTIFIER/IGBT CURRENTS USING SURGE CURRENT LIMITER .......................................65

APPENDIX A4 – RECTIFIER/IGBT CURRENTS USING NO SURGE CURRENT LIMITER .................................66

APPENDIX B – SYSTEM SIMULATION MODEL ............................................................................................67

APPENDIX C1 – MAIN GRID VOLTAGE HARMONICS WITHOUT FILTER ......................................................68

APPENDIX C2 – MAIN GRID CURRENT HARMONICS WITHOUT FILTER ......................................................69

APPENDIX C3 – MAIN GRID VOLTAGE HARMONICS WITH FILTER.............................................................70

APPENDIX C4 – MAIN GRID VOLTAGE HARMONICS WITH 12-PULSE RECTIFIER .......................................71

APPENDIX C5 – MAIN GRID CURRENT HARMONICS USING 12-PULSE RECTIFIER......................................72

APPENDIX D1 – IGBT CHART 1.................................................................................................................73

APPENDIX D2 – IGBT CHART 2.................................................................................................................74

APPENDIX D3 – MOSFET/DIODE CHART ....................................................................................................75

APPENDIX E1 – DECOUPLING CAPACITOR SNUBBER CIRCUIT SCHEMATICS..............................................76

APPENDIX E2 – RESTRICTED DECOUPLING CAPACITOR SNUBBER CIRCUIT SCHEMATICS .........................76

APPENDIX E3 – RCD CHARGE/DISCHARGE SNUBBER CIRCUIT SCHEMATICS ...........................................77

APPENDIX E4 – RCD CLAMP-SNUBBER CIRCUIT SCHEMATICS .................................................................77

APPENDIX F – LAYOUT OF COMPONENTS WITHIN ENCLOSURE...................................................................78

List of figures

FIGURE 1 : INVERTER OVERVIEW..................................................................................................................... 5

FIGURE 2 : RECTIFIER STAGE........................................................................................................................... 5

FIGURE 3 : SMOOTHING STAGE........................................................................................................................ 5

FIGURE 4 : SWITCHING STAGE ......................................................................................................................... 6

FIGURE 5 : FILTERING OF PULSE TRAIN IN OUTPUT STAGE ............................................................................... 7

FIGURE 6 : SIMPLIFIED MODEL ........................................................................................................................ 8

FIGURE 7 : SYMBOL LAYOUT........................................................................................................................... 9

FIGURE 8: TURN-OFF BEHAVIOR ...................................................................................................................... 9

FIGURE 9: INTERNAL STRAY CAPACITANCES IN AN IGBT...............................................................................10

FIGURE 10 : TYPCIAL IGBT TURN-ON............................................................................................................11

FIGURE 11 : TYPICAL IGBT TURN-OFF ..........................................................................................................12

FIGURE 12: IGBT WITH FWD ........................................................................................................................13

FIGURE 13: OVERVEIW OF THE RECTIFIER ......................................................................................................15

FIGURE 14 : INPUT FILTER ..............................................................................................................................17

FIGURE 15 : TYPICAL IMPEDANCE FOR INPUT FILTER VS. HARMONICS OF GRID FREQUENCY...........................17

FIGURE 16 : PROTECTIVE CIRCUITS: SIMPLE, SERIES AND PARALLEL CONNECTION.........................................21

FIGURE 17 : CHARGE AND DISCHARGE TIME OF CAPACITOR BANK.................................................................22

FIGURE 18 : ELECTRICAL LAYOUT OF CAPACITOR BANK ................................................................................24

FIGURE 20 : OUTPUT FILTER ...........................................................................................................................26

FIGURE 21 : DECOUPLING AND RESTRICTED DECOUPLING CAPACITOR ...........................................................30

FIGURE 22 : SWITCING DEVICE VOLTAGE WITHOUT SNUBBER CIRCUIT...........................................................31

FIGURE 23 : DEVICE VOLTAGE WITH DECOUPLING CAPACITOR.......................................................................32

FIGURE 24 : DEVICE VOLTAGE WITH DISCHARGE RESTRICTED DECOUPLING CAPACITOR................................33

FIGURE 25 : RCD CHARGE-DISCHARGE SNUBBER AND RCD CLAMP-SNUBBER............................................34

FIGURE 26 : RCD CHARGE-DISCHARGE SNUBBER .........................................................................................34

FIGURE 27 : RCD CLAMP-SNUBBER...............................................................................................................35

FIGURE 28 : SCETCH OF CHASSIS ....................................................................................................................40

FIGURE 29 : THERMAL RESISTIVITY ESTIMATION ...........................................................................................40

FIGURE 30 : HEATSINK LAYOUT .....................................................................................................................41

FIGURE 31: THERMAL RESISTANCE FACTOR VS. AIRFLOW ..............................................................................42

FIGURE 32 : DESCRIPTIVE DRIVER INTERNAL CIRCUIT (IGBT WITHIN DASHED LINE) .....................................43

FIGURE 33 : APPROXIMATE OUTPUT CHARACTERISTICS .................................................................................49

List of tables

TABLE 1 : INPUT CURRENT HARMONICS..........................................................................................................16

TABLE 2 : VOLTAGE HARMONICS ON GRID .....................................................................................................18

TABLE 3 : INPUT FILTER COMPONENTS ...........................................................................................................19

TABLE 4 : DC-BUS FILTER COMPONENTS........................................................................................................26

TABLE 5 : OUTPUT FILTER COMPONENTS........................................................................................................29

TABLE 6 : SNUBBER CHARACTERISTICS..........................................................................................................36

TABLE 7 : SWITCHING CHARACTERISTICS VS. DRIVER DIMENSIONS ................................................................44

TABLE 8 : DRIVER COMPONENTS ....................................................................................................................45

TABLE 9 : POWER SUPPLY SPECIFICATIONS AND DIMENSIONS ........................................................................46

TABLE 10 : CONTROLLER COMPONENTS .........................................................................................................46

TABLE 11 : SUITABLE DISCRETE IGBTS .........................................................................................................50

TABLE 12: SUITABLE IGBT MODULES ...........................................................................................................51

TABLE 13 : SUITABLE RECTIFIERS ..................................................................................................................52

TABLE 14 : DC-BUS FILTER LOSSES WHEN USING 230/400 VAC INPUT ..........................................................52

TABLE 15 : DC-BUS FILTER LOSSES WHEN USING 115/200 VAC INPUT ..........................................................53

TABLE 16 : APPROXIMATE SEPARATED WEIGHT FOR 230/400VAC APPLICATIONS.........................................55

TABLE 17 : APPROXIMATE SEPARATED WEIGHT FOR 115/200VAC APPLICATIONS.........................................55

TABLE 18 : APPROXIMATE SEPARATED LOSSES @ 6 KHZ SWITCHING FREQUENCY.........................................57

VII

TABLE 19 : APPROXIMATE SEPARATED LOSSES @ 10 KHZ SWITCHING FREQUENCY.......................................57

TABLE 20 : APPROXIMATE SEPARATED LOSSES @14 KHZ SWITCHING FREQUENCY .......................................57