igbt-low inductive design.pdf
TRANSCRIPT
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04.12.2007 1
Dealing with IGBT ModulesDealing with IGBT ModulesDealing with IGBT Modules
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04.12.2007 2
Table of Contents
Dealing with IGBT ModulesMotivationLow inductive DC-link designChoice of right SnubberGate Clamping Thermal managementParalleling Application of driver circuitParalleling Low inductive AC-Terminal connectionUsage of single switch GA type modulesConclusion
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04.12.2007 3
vCE(t)iC(t) VCC
IO
0t
0
t1
0t
pv(t)iC vCE
t2
Dependence of VCE, IC, Pv, Eswitch
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04.12.2007 4
vCE(t)iC(t) VCC
IO
0t
t1
0t
pv(t)
t2
Eswitch
vCE(t)iC(t) VCC
IO
0t
t1
0t
pv(t)
t2
Eswitch
di/dt
Influence of switching speeds
Increased switching speed, decreases the switching losses EswitchBut, leads to increased di/dt and therewith to higher over voltages
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04.12.2007 5
Porsche 911 - 2004
Porsche Diesel - 1960Would you use these different vehicles with
the same driver and in the same environment?
Motivation
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04.12.2007 6
Table of Contents
Dealing with IGBT ModulesMotivationLow inductive DC-link designChoice of right SnubberGate Clamping Thermal managementParalleling Application of driver circuitParalleling Low inductive AC-Terminal connectionUsage of single switch GA type modulesConclusion
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04.12.2007 7
Motivation
Why low inductive DC-link design?
Due to stray inductances in the DC link, voltage overshoots occur during switch off of the IGBT:
These voltage overshoots may destroy the IGBT module because they are added to the DC-link voltage and may lead to VCE > VCEmax
With low inductive DC-Link design (small Lstray) these voltage overshoots can be reduced significantly.
dtdiLv strayovershoot =
linkDCovershootCE vvv +=
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04.12.2007 8
Lstray = 100 nH
Low Inductance DC-link Design
The comparison of stray inductances showInside the module SEMIKRON reduced the inductances significantly
Outside the module the reduction of stray inductances is necessary, too
Lstray = 20 nH
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04.12.2007 9
Low Inductance DC-link Design
The mechanical design has a significant influence on the stray inductance of the DC-link
The conductors must be paralleled
Lstray = 100 %
Lstray < 20 %
loop
1 cm 10 nH
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04.12.2007 10
Low Inductance DC-link Design
The mechanical design has a significant influence on the stray inductance of the DC-link
The connections must be in line with the main current flow
Lstray = 100 %
Lstray = 30 %
remaining loop
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04.12.2007 11
Low Inductance DC-link Design
The mechanical design has a significant influence on the stray inductance of the DC-link
Also the orientation must be taken into regard
Lstray = 100 %
Lstray = 80 %
+-
+-
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04.12.2007 12
+ bus bar - bus bar
Low Inductance DC-link Design
Simulation of current distribution for the case of Lstray = 80 %
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04.12.2007 13
Lstray = 100 %
Lstray = 50 %
Low Inductance DC-link Design
The mechanical design has a significant influence on the stray inductance of the DC-link
A paralleling of the capacitors reduces the inductance further
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04.12.2007 14
Low Inductance DC-link Design
For paralleling standard modules a minimum requirement is DC-link design with two paralleled bars
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04.12.2007 15
Low Inductance DC-link Design
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04.12.2007 16
++
--~
Low Inductance DC-link Design
Paralleled half bridge IGBT modules
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04.12.2007 17
DC-link
SnubberCapacitor
3 x 2 x IGBT parallel
Heat Sink
Fan
Driver
Apple
SEMIKRON 3 Phase and Low Inductance Inverter
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04.12.2007 18
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2 IGBT Modules
Capacitor
Low inductive solution
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2 IGBT Modules
Capacitor
+
+-
-
+ ++
Typical solution
loop
Low Inductance DC-link Design
Comparison of different designsTwo capacitors in seriesTwo serial capacitors in parallel
parallel current paths
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04.12.2007 19
Low Inductance DC-link Capacitors
Also the capacitors have to be decidedCapacitors with different internal stray inductance are availableChoose a capacitor with very low stray inductance!Further: low ESR Equivalent Series ResistanceHigh IR Ripple Current Capability
Lstray = ?
Ask your supplier!
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04.12.2007 20
Table of Contents
Dealing with IGBT ModulesMotivationLow inductive DC-link designChoice of right SnubberGate Clamping Thermal managementParalleling Application of driver circuitParalleling Low inductive AC-Terminal connectionUsage of single switch GA type modulesConclusion
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04.12.2007 21
Motivation
Why use a snubber?
Due to stray inductances in the DC link, voltage overshoots occur during switch off of the IGBT:
These voltage overshoots may destroy the IGBT module because they are added to the DC-link voltage and may lead to VCE > VCEmax
The snubber works as a low pass filter and takes over the voltage overshoot (caused by the energy which is stored in the stray inductances)
dtdiLv strayovershoot =
linkDCovershootCE vvv +=
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04.12.2007 22
Snubber Networks
Different snubber networks are in use
a) b) c) d)
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04.12.2007 23
Snubber Networks
SEMIKRON recommends for IGBT applications:Fast and high voltage film capacitor (MKP / MFP) as snubberparallel to the DC terminals
Not to increase Lstray, the snubber must be located directly at terminals of the IGBT module
DC-link Snubber
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04.12.2007 24
Not Sufficient Snubber Capacitors
But still: the snubber networks need to be optimisedThe wrong snubber does not reduce the voltage overshootsTogether with the stray inductance of the DC-link oscillations can occur
IGBT switch off (raise of VCE )before optimisation
Voltage overshoot
Oscillation
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04.12.2007 25
00
IGBT-switch-o ff.xls
VCE
t
V1VDC
V2
iC = operating currentdiC/dt = turn off
Determination of a snubber capacitor
Influence of DC-link stray inductance and snubber capacitor stray inductance
=
=
=
=
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04.12.2007 26
Not Sufficient Snubber Capacitors
These capacitors did not work satisfactory as snubber:
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04.12.2007 27
Available Snubber Capacitors
From different suppliers different snubber capacitors are available.In a trial and error process the optimum can be find, based onmeasurements.The different snubber capacitors have different stray inductance values. Again it is necessary to find one with lowest inductance.
good better
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04.12.2007 28
Optimal Snubber Capacitor
After introduction of optimised snubber capacitor:Significantly reduced voltage overshootsNo oscillations
IGBT switch off (raise of VCE )after optimisation
Voltage overshoot
No oscillation
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04.12.2007 29
Table of Contents
Dealing with IGBT ModulesMotivationLow inductive DC-link designChoice of right SnubberGate Clamping Thermal managementParalleling Application of driver circuitParalleling Low inductive AC-Terminal connectionUsage of single switch GA type modulesConclusion
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04.12.2007 30
Gate Clamping
Over voltages at the gate VGE > +/- 20 V can occur due toInduction at stray inductancesBurst impulses by EMC
The introduction of an additional gate clamping is necessaryClose to the gate terminals, what means 5 cmUse twisted pair wiring
-20 V VGE +20 V
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04.12.2007 31
Gate Clamping
Gate clamping with RGE from gate to emitter potential Keeps gate potential always on defined level also when supply voltage of the driver dropsPrevents charging of the gate, for highly resistive driver outputsOnly RGE is not sufficient for gate clamping. (See the following charts.)
VGE
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04.12.2007 32
Gate Clamping
Gate clamping with Schottky Diode from gate to supply voltage of driver
On driver board (distance to module 5 cm, twisted pair wires)Additional RGE is recommended
VGEV+ supply
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04.12.2007 33
Gate Clamping
Gate clamping with Zener Diode or Avalanche Diode from gate to emitter potential
On driver board (distance to module 5 cm, twisted pair wires)Or on auxiliary PCBParallel RGE is recommended
VGE
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04.12.2007 34
Gate Clamping
Auxiliary PCB directly at the IGBT moduleThe additional RGE ensures off-state of IGBT in case of failed wiring
RGoffRGon
RGEZ-diode
RGoffRGon
RGEZ-diode
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04.12.2007 35
Table of Contents
Dealing with IGBT ModulesMotivationLow inductive DC-link designChoice of right SnubberGate Clamping Thermal managementParalleling Application of driver circuitParalleling Low inductive AC-Terminal connectionUsage of single switch GA type modulesConclusion
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04.12.2007 36
Thermal Management
Taking thermal management into regardNo space between the paralleled modules lead to low stray inductances and minimum spaceBut the thermal stacking makes a current derating necessary
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04.12.2007 37
Thermal Management
20 30 mm space between the modules increase the inductances but reduces the thermal resistance to the heat sink significantly
Optimised thermal management leads to maximum possible current ratings
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04.12.2007 38
Table of Contents
Dealing with IGBT ModulesMotivationLow inductive DC-link designChoice of right SnubberGate Clamping Thermal managementParalleling Application of driver circuitParalleling Low inductive AC-Terminal connectionUsage of single switch GA type modulesConclusion
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04.12.2007 39
Worst Case: All Contacts Shorted
Different IGBT modules with differentSwitching speeds ton and toffGate thershold voltages VGE(th)Gate charge characteristic VGE = f(QG) and Miller Capacity CresTransfer characteristic IC = f(VGE)
C
AEG
EVGE VGE VGE
Due to hard connected gates, all IGBTs must have the same VGEThis means: all IGBTs do not switch independently from each other
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04.12.2007 40
Hard Connected Gate with Common Resistor
Hard connected GatesAll IGBTs have different gate threshold voltages VGE(th)IGBT1, with the lowest VGE(th) turns on first.The gate voltage is clamped to the Miller-Plateau. Therefore IGBTswith higher VGE(th) can not turn on. They turn on only after t1.The IGBT1 with low VGE(th) takes all the current and switching losses during turn on.On going process by negative thermal coefficient of VGE(th)
VGE
t
t1
VGE(th)
VGE
t
t1
VGE(th)
VGE
t
t1 1
VGE(th)
t1 n
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04.12.2007 41
Introduction of Gate Resistors
Separated by gate resistorsThe gate voltage of each IGBT can rise independent from the other one.Note: The gate resistors must be tolerated < 1 %
With individual gate resistors all IGBTs are independent from each other
C
AE
G
EVGE 1 VGE 2 VGE n
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04.12.2007 42
Introduction of Gate Resistors
Separated by gate resistorsAll IGBTs still have different gate threshold voltages VGE(th)But: The gate voltage of each IGBT can rise independently from the other ones.The higher Miller-Plateau will be reached after a short time t1. Only small differences in current sharing and switching losses between paralleled IGBTs.
VGE
t
t2t1
VGE(th)
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Worst Case: All Contacts Shorted
Taking stray inductances into regardDue to hard connected gates and varying transfer characteristics, all IGBTshave different switching times and speeds; dix/dt varies in each legThe circuit also has different stray inductances; LxTherewith vx = Lx x dix/dt varies in each leg (e.g.: 1000 A/s x 10 nH = 10 V)Nearly unlimited equalising currents i flow also via the thin connecting wiresOscillations between parasitic capacitances (semiconductors) and-inductances are not damped.
V1 V2 Vni =
C
AEG
E
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04.12.2007 44
Introduction of Auxiliary Emitter Resistors
The introduction of REx ( 10 % of RGx but min. 0,5 ) leads toLimitation of equalising currents i 10 ADamping of oscillations
C
AE
E
G
V1 V2 Vni 10 A
RE1RE2 REn
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04.12.2007 45
Introduction of Auxiliary Emitter Resistors
The introduction of REx leads also to a negative feedback:The equalising current i leads to a voltage drop VREx at the Emitter resistors REx
C
AE
E
G
i
VRE1 VRE2
fast IGBT slow IGBT
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04.12.2007 46
Introduction of Auxiliary Emitter Resistors
The introduction of REx leads also to a negative feedback:The voltage drop VRE1 reduces the gate voltage of the fast IGBT and decreases therewith its switching speed.The voltage drop VRE2 increases the gate voltage of the slow IGBT and makes it faster.During switch off: vice versa.
C
AE
E
G
i
fast IGBT slow IGBT
VRE1 VRE2
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04.12.2007 47
Additional Proposals
The introduction of Shottky-Diodes parallel to RExhelps to balance the emitter voltage during short circuit case.Dimensioning 100V, 1A.
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Additional Proposals
The introduction of clamping diodes prevents over voltages at the gate contacts.Therefore these clamping diodes must be placed very close to themodule connectors
C
AE
E
G
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04.12.2007 49
Conclusion Driving Paralleled IGBTs
Balanced switching behaviourIndependent switching due to introduction of RGxBalanced switching speeds due to negative feedback by introduction of REx
Limitation of equalising currentsDamping of oscillationsPrevention of gate over voltagesRefer also to SEMIKRON Application Manual - Power Modules
GermanEnglishChineseKoreanJapaneseRussian (on internet only)
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04.12.2007 50
Additional Parallel Board
PCB for paralleling IGBT close to the module connectorsSame track length on the boardShort, twisted pair wires from the board to the modules ( 5 cm)
RGonRGoff
RERGonRGoff
RE RGoffRGon
RE RGoffRGon
RE
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04.12.2007 51
Additional Parallel Board
Top Bot
IGBT Driver
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04.12.2007 52
Auxiliary Printed Circuit Board
Auxiliary PCB directly at the IGBT moduleThe additional RGE ensures off-state of IGBT in case of failed wiring Same track length on the boardShort, twisted pair wires from the main driver to the auxiliary PCB at the IGBT module
RGoffRGon
RGEZ-diode
RERGoffRGon
RGEZ-diode
RE
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04.12.2007 53
Table of Contents
Dealing with IGBT ModulesMotivationLow inductive DC-link designChoice of right SnubberGate Clamping Thermal managementParalleling Application of driver circuitParalleling Low inductive AC-Terminal connectionUsage of single switch GA type modulesConclusion
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04.12.2007 54
Motivation
Why symmetrical AC terminal connection for paralleled IGBTs?When the connection between the AC terminals have high inductance and different inductances, the current sharing of IC(output current) will be inhomogeneous and oscillations may occur.This would make a current derating necessary.
Simulation of 4 paralleled IGBT modules with
inhomogeneous current sharing
leads to oscillations
IC
t
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04.12.2007 55
Symmetrical AC Connection
Why symmetrical AC terminal connection for paralleled IGBTs?The sketch shows that Lstray,DC and Lstray,AC are connected in seriesThis makes clear why both have to be reduced and both have to besymmetric in each legto ensure even current distribution to avoid oscillations
C
G
E
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04.12.2007 56
Symmetrical AC Connection
AC link designShort connections with identical current path length for each moduleWide and thick barsFlexible interconnections for large systems might be necessary to compensate differences in thermal expansionLong hole drillings' can compensate mechanical tolerances
Isolated supporting poles take over vibrations and forces from heavy AC cables
Look for a symmetric AC-connection so that the current sharing will be even over all modules
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04.12.2007 57
Table of Contents
Dealing with IGBT ModulesMotivationLow inductive DC-link designChoice of right SnubberGate Clamping Thermal managementParalleling Application of driver circuitParalleling Low inductive AC-Terminal connectionUsage of single switch GA type modulesConclusion
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04.12.2007 58-
~
+1
2
3
1
2
3
-
+
~
1
1
2
2
?
Motivation
Optimisation problemIn order to optimise the thermal management it seems to be useful splitting the current of one half bridge topology into two modules.
The question is: what is better use two paralleled half bridges, or two single switches in series connection?
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04.12.2007 59
-
~
+1
2
3
1
2
3 -
+
~1 1
2 2
3 3
Paralleling GB Modules
How to parallel half bridge IGBT modules
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04.12.2007 60
-+
~
1
2
2
1
-
+
~
1
1
2
2
Paralleling of GA Modules
How to use single switch IGBT modules as half bridge
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04.12.2007 61
Increased switching speed, decreases the switching losses EswitchBut, leads to increased di/dt and therewith to higher over voltages
vCE(t)iC(t) VCC
IO
0t
t1
0t
pv(t)
t2
Eswitch
vCE(t)iC(t) VCC
IO
0t
t1
0t
pv(t)
t2
Eswitch
di/dt
Influence of Switching Speeds
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04.12.2007 62
-+
~
1
2
2
1
-
~
+1
2
3
1
2
3
GA or GB?
Comparison For GB modules the diodes for commutation are placed in the samemodule. Therewith the stray inductance is as low as possible.Paralleled GB modules allow higher switching speeds
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04.12.2007 63
GA or GB?
Comparison In half bridge modules the snubber capacitors can be placed closed to the terminals with short - and therewith low inductive connections. So that the snubbers work very efficient.Paralleled GB modules allow higher switching speeds
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04.12.2007 64
Conclusion
Advantages of paralleled half bridges
The current per module is only 50 % of the maximum currentThe di/dt is much reduced, therewith the voltage overshoot is small (v = - L x di/dt)The half bridge module has much lower stray inductances, what reduces the voltage overshoot againSnubber capacitors can be placed very close to the terminals, so that they work very efficientThe switching speed can be increased and therewith the switchinglosses are reduced
SEMIKRON recommends the use of paralleled half bridge modules instead of single switch modules
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04.12.2007 65
SEMIKRONs Recommended Solution
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04.12.2007 66
Table of Contents
Dealing with IGBT ModulesMotivationLow inductive DC-link designChoice of right SnubberGate Clamping Thermal managementParalleling Application of driver circuitParalleling Low inductive AC-Terminal connectionUsage of single switch GA type modulesConclusion
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04.12.2007 67
Conclusion
When using latest generations of IGBT modules it is recommended and advantageous to
Do a low inductive (sandwich) DC-link designDecide for low inductive DC-link capacitorsOptimise the snubber capacitors Optimise thermal management which leads to maximum possible current ratings
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04.12.2007 68
Conclusion
For paralleled modulesThe driver must be powerful enough
Some additional components are necessary (e.g. REx) and must be located close to every single module
The DC- and AC connection must be symmetric and low inductive
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04.12.2007 69
Thank you very much for your attention
Refer also to SEMIKRON Application Manual - Power Modules
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04.12.2007 70
Document status: preliminary
Date of publication: 2006-06-08
Revision: 1.3
Prepared by: Christian DaucherWith assistance fromDr. Arendt WintrichNorbert Pluschke
Information furnished in this document is believed to be accurate and reliable. However, no representation or warranty is given and no liability is assumed with respect to the accuracy or use of such information. Furthermore, this technical information specifies semiconductor devices but promises no characteristics. No warranty or guarantee expressed or implied is made regarding delivery, performance or suitability. Specifications mentioned in this document are subject to change without notice. This document supersedes and replaces all information previously supplied and may be supersede by updates.
Dealing with IGBT ModulesTable of ContentsDependence of VCE, IC, Pv, EswitchInfluence of switching speedsMotivationTable of ContentsMotivationLow Inductance DC-link DesignLow Inductance DC-link DesignLow Inductance DC-link DesignLow Inductance DC-link DesignLow Inductance DC-link DesignLow Inductance DC-link DesignLow Inductance DC-link DesignLow Inductance DC-link DesignLow Inductance DC-link DesignSEMIKRON 3 Phase and Low Inductance InverterLow Inductance DC-link DesignLow Inductance DC-link CapacitorsTable of ContentsMotivationSnubber NetworksSnubber NetworksNot Sufficient Snubber CapacitorsDetermination of a snubber capacitorNot Sufficient Snubber CapacitorsAvailable Snubber CapacitorsOptimal Snubber CapacitorTable of ContentsGate ClampingGate ClampingGate ClampingGate ClampingGate ClampingTable of ContentsThermal ManagementThermal ManagementTable of ContentsWorst Case: All Contacts ShortedHard Connected Gate with Common ResistorIntroduction of Gate ResistorsIntroduction of Gate ResistorsWorst Case: All Contacts ShortedIntroduction of Auxiliary Emitter ResistorsIntroduction of Auxiliary Emitter ResistorsIntroduction of Auxiliary Emitter ResistorsAdditional ProposalsAdditional ProposalsConclusion Driving Paralleled IGBTsAdditional Parallel BoardAdditional Parallel BoardAuxiliary Printed Circuit BoardTable of ContentsMotivationSymmetrical AC ConnectionSymmetrical AC ConnectionTable of ContentsMotivationParalleling GB ModulesParalleling of GA ModulesInfluence of Switching SpeedsGA or GB?GA or GB?ConclusionSEMIKRONs Recommended SolutionTable of ContentsConclusionConclusionDealing with IGBT ModulesTable of ContentsDependence of VCE, IC, Pv, EswitchInfluence of switching speedsMotivationTable of ContentsMotivationLow Inductance DC-link DesignLow Inductance DC-link DesignLow Inductance DC-link DesignLow Inductance DC-link DesignLow Inductance DC-link DesignLow Inductance DC-link DesignLow Inductance DC-link DesignLow Inductance DC-link DesignLow Inductance DC-link DesignSEMIKRON 3 Phase and Low Inductance InverterLow Inductance DC-link DesignLow Inductance DC-link CapacitorsTable of ContentsMotivationSnubber NetworksSnubber NetworksNot Sufficient Snubber CapacitorsDetermination of a snubber capacitorNot Sufficient Snubber CapacitorsAvailable Snubber CapacitorsOptimal Snubber CapacitorTable of ContentsGate ClampingGate ClampingGate ClampingGate ClampingGate ClampingTable of ContentsThermal ManagementThermal ManagementTable of ContentsWorst Case: All Contacts ShortedHard Connected Gate with Common ResistorIntroduction of Gate ResistorsIntroduction of Gate ResistorsWorst Case: All Contacts ShortedIntroduction of Auxiliary Emitter ResistorsIntroduction of Auxiliary Emitter ResistorsIntroduction of Auxiliary Emitter ResistorsAdditional ProposalsAdditional ProposalsConclusion Driving Paralleled IGBTsAdditional Parallel BoardAdditional Parallel BoardAuxiliary Printed Circuit BoardTable of ContentsMotivationSymmetrical AC ConnectionSymmetrical AC ConnectionTable of ContentsMotivationParalleling GB ModulesParalleling of GA ModulesInfluence of Switching SpeedsGA or GB?GA or GB?ConclusionSEMIKRONs Recommended SolutionTable of ContentsConclusionConclusion