MOSFET Modeling Aimed at Minimizing EMI in Switched DC/DC Converters Using Active Gate ...

165 Pages·2009·3.56 MB·English

THESISFOR THEDEGREE OFLICENTIATE OFENGINEERING
MOSFET Modeling Aimed at Minimizing EMI in
Switched DC/DC Converters Using Active Gate Control
ANDREAS KARVONEN
DepartmentofEnergy and Environment
DivisionofElectricPowerEngineering
CHALMERS UNIVERSITY OFTECHNOLOGY
Go¨teborg,Sweden 2009
MOSFETModelingAimedat MinimizingEMIinSwitched DC/DCConverters Using
ActiveGateControl
ANDREASKARVONEN
c ANDREASKARVONEN, 2009.
(cid:13)
LicentianteThesisat theGraduateSchool inEnergy and Environment
DepartmentofEnergy andEnvironment
DivisionofElectricPowerEngineering
ChalmersUniversityofTechnology
SE–41296 Go¨teborg
Sweden
Telephone[phone]
ChalmersBibliotek,Reproservice
Go¨teborg,Sweden 2009
To all of those who believed...
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MOSFET ModelingAimedat MinimizingEMIinSwitched DC/DC ConvertersUsing
ActiveGateControl
ANDREASKARVONEN
DepartmentofEnergy and Environment
Chalmers UniversityofTechnology
Abstract
This thesis deals with electromagneticinterference that can arise from switched DC/DC-
converters intended for low-power applications, e.g. within the telecom or automotive
industry. It analyzes measures and methods that can applied when a reduction of EMI
directly at the source without using any additional means such as shielding and filtering
is desired. By investigating the physical properties of the two most important ingoing
components, the diode and the MOSFET, an improved MOSFET model and a new gate
voltagecontrolmethodisproposed.Thismethodisreferred toasactivegatecontrolwith
a operating principle where a controller circuit shapes the desired output to a sinusoidal
trajectory during the entire switching event. By doing this, it is shown that the harmonic
content in the output signal can be reduced. The proposed MOSFET model is used as a
baseforextractingsuitablecontrollerparameterswiththehelpofalinearizedstate-space
system.Twodifferentoutputswereselectedandinvestigated,eitherthedrain-sourcevolt-
age or the drain current. The general conclusion from simulationsand measurements are
that active gate control where the drain current is selected as the controlled quantity has
good potential for reducing the harmonics and the emitted electromagnetic disturbance
in a switched DC/DC converter even though it sets high demands on the controller cir-
cuit. The analysis shows that a controller with static parameters derived on basis of the
proposed MOSFET model is not sufficient due to the complexity of the system which
includesmany nonlinearitiesand varyingparameters. In orderto obtain bettertransitions
that are valid over a wider range of operating points, adaptive control needs to be imple-
mented.Simulationsshowsthatby carefully selectingthecontrollerparameters based on
theproposed MOSFET model and adapting theparameters to thecurrent operatingpoint
an improvementinperformance and robustnesscan beachieved.
Index Terms: Electromagneticcompatibility,Electromagneticinterference, DC-DC
powerconversion,Semiconductordevicemeasurements,Semiconductordevice
modeling,MOSFET switches,Powersemiconductordiodes,Adaptivecontrol, State
spacemethods.
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Acknowledgements
ThefinancialsupportgivenbyVolvocarsAB,SAABMicrowaveSystems,Ericsson,SKF
and Vinnova is gratefully acknowledged. I would also like to thank all members in the
project group, Bjo¨rn Bergqvist who has been theproject leader, Johan Fa¨lt, Anders Frick
and Go¨ran Lindsten. A special thank is directed to Trygve Tuveson who initiated the
project and kept coming with new ideas throughout the project. Also, thanks to Pierre
Gildert who supported me when starting this thesis and Henrik Holst whose experiments
havetaken mefar.
At the department I would like to thank my supervisor Torbjo¨rn Thiringer who always
find some extra time for discussions, no matter the time and reason. My supportive col-
leaguesaregratefullyacknowledged;StefanLundbergforconstructivediscussions,Mas-
simo Bongiorno for techincal support and Julia Paixa˜o for the article. A special thank to
JohanA˚stro¨mwhoalwayslistentomyreflectionsandcontributewithnewcreativeideas.
ThankstoKristoferAnderssonattheMicrowaveElectronicsLaboratoryonChalmersfor
helping me with the equipment. The enlightenment from Professor Claes Breitholtz is
highly appreciated; the words shall act as a commandment for all coming work. Thanks
toallMasterThesisworkersthathavecontributed,especiallyNiklasFranssonandGustav
Johannesonfortheirgoodspiritand valuableresults.
Atleastbutnotlast,themostimportantsupport;myfriendsandmyfamily.Awarmthank
to all of you that have supported, hugged and encouraged when disbelief have struck.
Withoutyou thiswouldnothavebeen possible.
Andreas Karvonen
Go¨teborg,Sweden
Spring,2009
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Contents
Abstract v
Acknowledgements vii
Contents ix
1 Introduction 1
1.1 Problem Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Objectivesand Scope ofThesis . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 ContributionswithPresent Work . . . . . . . . . . . . . . . . . . . . . . 3
1.3.1 MOSFET Modeling . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3.2 ActiveGateControl . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3.3 DoubleMOSFET Switching . . . . . . . . . . . . . . . . . . . . 4
1.4 OutlineofThesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.5 Publications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Semiconductors andConverters 7
2.1 ComponentBackground . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 Thepn-Diode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2.1 Modelingofthepn-Diode . . . . . . . . . . . . . . . . . . . . . 9
2.3 TheSchottkyDiode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.4 ThePiN-Diode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.4.1 ConductivityModulationand On-StateLosses . . . . . . . . . . 15
2.4.2 Turn-onBehaviorofthePiN-Diode . . . . . . . . . . . . . . . . 16
2.4.3 Turn-offBehaviorofthePiN-Diode . . . . . . . . . . . . . . . . 16
2.4.4 PiN DiodeModeling . . . . . . . . . . . . . . . . . . . . . . . . 19
2.5 TheMOSFET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.5.1 Operating RegionsforthePowerMOSFET . . . . . . . . . . . . 21
2.5.2 Internal Capacitances oftheMOSFET . . . . . . . . . . . . . . . 23
2.5.3 TheMOSFET inconductingState . . . . . . . . . . . . . . . . . 24
2.5.4 Turn-OnBehavioroftheMOSFET . . . . . . . . . . . . . . . . 26
2.5.5 Turn-OffBehavioroftheMOSFET . . . . . . . . . . . . . . . . 28
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Contents
2.5.6 TheMOSFET modelinSPICE . . . . . . . . . . . . . . . . . . 30
2.5.7 PSPICE MOSFETModelsAdapted forSwitchingApplications . 31
2.6 EMIGenerated bySwitched DC/DC Converters . . . . . . . . . . . . . . 33
2.6.1 Hard SwitchingConverters . . . . . . . . . . . . . . . . . . . . . 33
2.6.2 SimulatingEMIfromaSwitched DC/DC Converter . . . . . . . 36
2.6.3 RandomSwitching . . . . . . . . . . . . . . . . . . . . . . . . . 37
2.6.4 GateVoltageControl . . . . . . . . . . . . . . . . . . . . . . . . 40
3 Semiconductor Modeling 43
3.1 Nodal AnalysisVs. StateVariableApproach . . . . . . . . . . . . . . . . 43
3.2 Improvingand verifyingthediodemodel . . . . . . . . . . . . . . . . . 45
3.2.1 Determiningthepn-JunctionCapacitance . . . . . . . . . . . . . 45
3.2.2 ValidationoftheReverseRecovery . . . . . . . . . . . . . . . . 47
3.2.3 ImplementationofaDiodeModelBased onCharge Locations . . 50
3.3 A NovelMOSFET ModelBased onCircuit Analysis . . . . . . . . . . . 51
3.3.1 ParameterExtractionforaPowerMOSFET . . . . . . . . . . . . 53
3.3.2 MOSFET ModelUnderStaticConditions . . . . . . . . . . . . . 55
3.3.3 MOSFET ModelUnderDynamicConditions . . . . . . . . . . . 61
3.3.4 SwitchingWithPurely ResistiveLoad . . . . . . . . . . . . . . . 70
3.3.5 ComparisonofSimulationsand Measurements . . . . . . . . . . 71
4 ActiveGateControl andController Design 75
4.1 ActiveGateControl-Theoretical Derivation. . . . . . . . . . . . . . . . 75
4.2 ControllerDesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
4.3 Selecting theoutputofthesystem . . . . . . . . . . . . . . . . . . . . . 83
4.4 ControllerDesign . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
5 Implementation ofActiveGateControl 91
5.1 Step ResponseoftheSystem . . . . . . . . . . . . . . . . . . . . . . . . 93
5.2 SinusoidalStep ResponseoftheSystem . . . . . . . . . . . . . . . . . . 98
5.3 ControllerDesignWithVaryingParameters . . . . . . . . . . . . . . . . 101
5.4 RobustnessoftheCircuit . . . . . . . . . . . . . . . . . . . . . . . . . . 108
5.5 SwitchingLosseswithActiveGateControl . . . . . . . . . . . . . . . . 109
6 Conclusions 113
7 Future Work 115
WrittenReferences 117
Internet References 124
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