Dealing with IGBT Modules

Dealing with IGBT Modules1

Dealing with IGBT Modules Motivation Low inductive DC-link design Choice of right Snubber Gate Clamping Thermal management Paralleling – Application of driver circuit Paralleling – Low inductive AC-Terminal connection Usage of single switch “GA” type modules ConclusionTable of Contents2

Dealing with IGBT Modules Motivation Low inductive DC-link design Choice of right Snubber Gate Clamping Thermal management Paralleling – Application of driver circuit Paralleling – Low inductive AC-Terminal connection Usage of single switch “GA” type modules ConclusionTable of Contents3

v CE (t)i C (t)0V CCi Cv CE( )p v (t)I O00t1t2ttpv=EswitchiC⋅vCEt2 p t= ∫v⋅t1dtDependence of V CE , I C , P v , E switch4

Increased switching speed, decreases the switching lossesE switch But, leads to increased di/dt and therewith to higher overvoltagesv= −v CE (t)i C (t) V CCv CE (t)i C (t) V CCLstray×dditI O0I O0di/dtp v (t)tp v (t)tE switch0t1E switcht2t0t1t2tInfluence of switching speeds5

Would you usethese different vehicles withthe same driver and inthe same environment?Porsche Diesel - 1960Porsche 911 - 2004Motivation6

Dealing with IGBT Modules Motivation Low inductive DC-link design Choice of right Snubber Gate Clamping Thermal management Paralleling – Application of driver circuit Paralleling – Low inductive AC-Terminal connection Usage of single switch “GA” type modules ConclusionTable of Contents7

Why low inductive DC-link design? Due to stray inductances in the DC link, voltage overshoots occurduring switch off of the IGBT:vovershoot = Lstray× These voltage overshoots may destroy the IGBT module because theyare added to the DC-link voltage and may lead to V CE > V CEmaxdidtvCE= vovershoot+vDC−link With low inductive DC-Link design (small L stray ) thesevoltage overshoots can be reduced significantly.Motivation8

The comparison of stray inductances show Inside the module SEMIKRON reduced the inductances significantlyL stray = 20 nH Outside the module the reduction of stray inductances is necessary, tooL stray = 100 nHLow Inductance DC-link Design9

The mechanical design has a significant influence on thestray inductance of the DC-link The conductors must be paralleledL stray = 100 %loop1 cm² ≈ 10 nHL stray < 20 %Low Inductance DC-link Design10

The mechanical design has a significant influence on thestray inductance of the DC-link The connections must be in line with the main current flowL stray = 100 %remaining loopL stray = 30 %Low Inductance DC-link Design11

The mechanical design has a significant influence on thestray inductance of the DC-link Also the orientation must be taken into regardL stray = 100 %+ -+ -L stray = 80 %Low Inductance DC-link Design12

Simulation of current distributionfor the case of L stray = 80 %+ bus bar - bus barLow Inductance DC-link Design13

The mechanical design has a significant influence on thestray inductance of the DC-link A paralleling of the capacitors reduces the inductance furtherL stray = 100 %L stray = 50 %Low Inductance DC-link Design14

For paralleling standard modules a minimum requirement isDC-link design with two paralleled barsLow Inductance DC-link Design15

Low Inductance DC-link Design16

Paralleled half bridge IGBT modules~-+-+Low Inductance DC-link Design17

FanDC-linkDriverSnubberCapacitor3 x2 x IGBT parallelAppleHeat SinkSEMIKRON 3 Phase and Low Inductance Inverter18

Comparison of different designs Two capacitors in series Two serial capacitors in parallelTypical solutionLow inductive solution2 IGBT Moduls2 IGBT Modulsloop++-+- --++-+---+++---+-++-parallelcurrent pathsCapacitorCapacitorLow Inductance DC-link Design19

Also the capacitors have to be decided Capacitors with different internal stray inductance are available Choose a capacitor with very low stray inductance! Further: low “ESR” Equivalent Series Resistance High “I R ” Ripple Current CapabilityL stray = ?Ask your supplier!Low Inductance DC-link Capacitors20

Dealing with IGBT Modules Motivation Low inductive DC-link design Choice of right Snubber Gate Clamping Thermal management Paralleling – Application of driver circuit Paralleling – Low inductive AC-Terminal connection Usage of single switch “GA” type modules ConclusionTable of Contents21

Why use a snubber? Due to stray inductances in the DC link, voltage overshoots occurduring switch off of the IGBT:vovershoot = Lstray× These voltage overshoots may destroy the IGBT module because theyare added to the DC-link voltage and may lead to V CE > V CEmaxdidtvCE= vovershoot+vDC−link The snubber works as a low pass filter and “takes over” thevoltage overshoot (caused by the energy which is stored inthe stray inductances)Motivation22

Different snubber networks are in usea) b) c) d)Snubber Networks23

SEMIKRON recommends for IGBT applications: Fast and high voltage film capacitor (“MKP” / “MFP”) as snubberparallel to the DC terminalsDC-linkSnubber Not to increase L stray , the snubber must be located directly atterminals of the IGBT moduleSnubber Networks24

But still: the snubber networks need to be optimised The wrong snubber does not reduce the voltage overshoots Together with the stray inductance of the DC-link oscillations canoccurIGBT switch off(raise of V CE )before optimisationVoltage overshootOscillationNot Sufficient Snubber Capacitors25

Influence of DC-link stray inductance and snubber capacitorstray inductanceΔV L di∆VV 2DC∆V 1dtVCE1 stray snubber C= ×IGBT-switch-of f .xls−ΔVL1stray snubber di dt−=CLΔV ×2 stray DC bus2 −= C−snubberi2CΔV2L 2×bus=stray DC− −iC2Csnubber00t i C = operating current di C /dt = turn offDetermination of a snubber capacitor26

These capacitors did not work satisfactory as snubber:Not Sufficient Snubber Capacitors27

From different suppliers different snubber capacitors areavailable. In a “trial and error” process the optimum can be find, basedon measurements. The different snubber capacitors have different strayinductance values. Again it is necessary to find one withlowest inductance.goodbetterAvailable Snubber Capacitors28

After introduction of optimised snubber capacitor: Significantly reduced voltage overshoots No oscillationsIGBT switch off(raise of V CE )after optimisationVoltage overshootNo oscillationOptimal Snubber Capacitor29

Dealing with IGBT Modules Motivation Low inductive DC-link design Choice of right Snubber Gate Clamping Thermal management Paralleling – Application of driver circuit Paralleling – Low inductive AC-Terminal connection Usage of single switch “GA” type modules ConclusionTable of Contents30

Over voltages at the gate V GE > +/- 20 V can occur due to Induction at stray inductances Burst impulses by EMC-20 V ≤ V GE ≤ +20 V The introduction of an additional gate clamping isnecessary Close to the gate terminals, what means ≤ 5 cm Use twisted pair wiringGate Clamping31

Gate clamping with “R GE ” from gate to emitter potential Keeps gate potential always on defined level – also when supplyvoltage of the driver drops Prevents charging of the gate, for highly resistive driver outputs Only R GE is not sufficient for gate clamping. (See the following charts.)V GEGate Clamping32

Gate clamping with “Schottky Diode” from gate to supplyvoltage of driver On driver board (distance to module ≤ 5 cm, twisted pair wires) Additional “R GE “ is recommendedV + supplyV GEGate Clamping33

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 PCB Parallel “R GE “ is recommendedV GEGate Clamping34

Auxiliary PCB directly at the IGBT module The additional R GE ensures off-state of IGBT in case of failed wiringZ-diodeR GEZ-diodeR GER GoffR GonR GoffR GonGate Clamping35

Dealing with IGBT Modules Motivation Low inductive DC-link design Choice of right Snubber Gate Clamping Thermal management Paralleling – Application of driver circuit Paralleling – Low inductive AC-Terminal connection Usage of single switch “GA” type modules ConclusionTable of Contents36

Taking thermal management into regard No space between the paralleled modules lead to low strayinductances and minimum space But the thermal stacking makes a current derating necessaryThermal Management37

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 possiblecurrent ratingsThermal Management38

Dealing with IGBT Modules Motivation Low inductive DC-link design Choice of right Snubber Gate Clamping Thermal management Paralleling – Application of driver circuit Paralleling – Low inductive AC-Terminal connection Usage of single switch “GA” type modules ConclusionTable of Contents39

Different IGBT modules with different Switching speeds t on and t off Gate thershold voltages V GE(th) Gate charge characteristic V GE = f(Q G ) and „Miller Capacity“ C res Transfer characteristic I C = f(V GE )CGAEV GE V GE V GEEDue to hard connected gates, all IGBTs must have the same V GEThis means: all IGBTs do not switch independently from each otherWorst Case: All Contacts Shorted40

Hard connected Gates All IGBTs have different gate threshold voltages ∆ V GE(th) IGBT1, with the lowest V GE(th) turns on first. The gate voltage is clamped to the Miller-Plateau. Therefore IGBT’swith higher V GE(th) can not turn on. They turn on only after ∆t 1 . The IGBT1 with low V GE(th) takes all the current and switching lossesduring turn on. On going process by negative thermal coefficient of V GE(th)V GE∆V GE(th)tt∆t 1 1∆t 1 nHard Connected Gate with Common Resistor41

Separated by gate resistors The gate voltage of each IGBT can rise independent from the otherone. Note: The gate resistors must be tolerated < 1 %CGAEV GE 1V GE 2V GE nEWith individual gate resistors all IGBTs are independent from each otherIntroduction of Gate Resistors42

Separated by gate resistors All IGBTs still have different gate threshold voltages ∆V GE(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 ∆t 1 . Only smalldifferences in current sharing and switching losses between paralleled IGBTs.V GE∆V GE(th)∆t 1t∆t 2Introduction of Gate Resistors43

Taking stray inductances into regard Due to hard connected gates and varying transfer characteristics, all IGBTshave different switching times and speeds; di x /dt varies in each leg The circuit also has different stray inductances; L x Therewith v x = L x x di x /dt varies in each leg (e.g.: 1000 A/µs x 10 nH = 10 V) Nearly unlimited equalising currents i flow also via the thin connecting wires Oscillations between parasitic capacitances (semiconductors) and -inductances are not damped.CGAEi = ∞V 1 V 2 V nEWorst Case: All Contacts Shorted44

The introduction of R Ex (≈ 10 % of R Gx but min. 0,5 Ω) leads to Limitation of equalising currents i ≤ 10 A Damping of oscillationsCGR E1R E2R EnAEi ≤ 10 AV 1 V 2 V nEIntroduction of Auxiliary Emitter Resistors45

The introduction of R Ex leads also to a negative feedback: The equalising current i leads to a voltage drop V REx at the Emitterresistors R ExCfast IGBTslow IGBTGAEV RE1V RE2iEIntroduction of Auxiliary Emitter Resistors46

The introduction of R Ex leads also to a negative feedback: The voltage drop V RE1 reduces the gate voltage of the fast IGBT anddecreases therewith its switching speed. The voltage drop V RE2 increases the gate voltage of the slow IGBT andmakes it faster. During switch off: vice versa.fast IGBTCslow IGBTGAEV RE1iV RE2EIntroduction of Auxiliary Emitter Resistors47

The introduction of Shottky-Diodes parallel to R Ex helps to balance the emitter voltage during short circuit case. Dimensioning ≈ 100V, 1A.Additional ProposalsThis circuit is patented by SEMIKRON,but SEMIKRON customers are allowed to use it together with SEMIKRON power semiconductor modules.48

The introduction of clamping diodes prevents over voltages at the gate contacts. Therefore these clamping diodes must be placed very close to the moduleconnectorsCGAEEAdditional Proposals49

Balanced switching behaviour Independent switching due to introduction of R Gx Balanced switching speeds due to negative feedback be introduction of R Ex Limitation of equalising currents Damping of oscillations Prevention of gate over voltages Refer also to “SEMIKRON Application Manual - Power Modules” German English Chinese Korean Japanese Russian (on internet only)Conclusion50

PCB for paralleling IGBT close to the module connectors Same track length on the board Short, twisted pair wires from the board to the modules (≤ 5 cm)R GonR GonR GoffR GoffR E R GoffR ER ER GonR ER GoffR GonAdditional Parallel Board51

Top BotIGBT DriverAdditional Parallel Board52

Auxiliary PCB directly at the IGBT module The additional R GE ensures off-state of IGBT in case of failed wiring Same track length on the board Short, twisted pair wires from the main driver to the auxiliary PCB at theIGBT moduleZ-diodeR GEZ-diodeR GER ER GoffR GonR ER GoffR GonAuxiliary Printed Circuit Board53

Dealing with IGBT Modules Motivation Low inductive DC-link design Choice of right Snubber Gate Clamping Thermal management Paralleling – Application of driver circuit Paralleling – Low inductive AC-Terminal connection Usage of single switch “GA” type modules ConclusionTable of Contents54

Why symmetrical AC terminal connection for paralleled IGBTs? When the connection between the AC terminals have high inductance anddifferent inductances, the current sharing of I C (output current) will beinhomogeneous and oscillations may occur. This would make a current derating necessary.Simulation of 4paralleled IGBTmodules withinhomogeneouscurrent sharingleads to oscillations200.0I C150.0100.050.00-50.00 10.00u 20.00u 30.00u 40.00u 50.00utMotivation55

Why symmetrical AC terminal connection for paralleled IGBTs? The sketch shows that L stray,DC and L stray,AC are connected in series This makes clear why both have to be reduced and both have to besymmetric in each leg to ensure even current distribution to avoid oscillationsCGESymmetrical AC Connection56

AC link design Short connections with identical current path length for each module Wide and thick bars Flexible interconnections for large systems might be necessary tocompensate differences in thermal expansion ‘Long hole drillings' can compensate mechanical tolerances Isolated supporting polestake over vibrations andforces from heavy AC cables Look for a symmetric AC-connection so that the currentsharing will be even over all modulesSymmetrical AC Connection57

Dealing with IGBT Modules Motivation Low inductive DC-link design Choice of right Snubber Gate Clamping Thermal management Paralleling – Application of driver circuit Paralleling – Low inductive AC-Terminal connection Usage of single switch “GA” type modules ConclusionTable of Contents58

Optimisation problem In order to optimise the thermal management it seems to be be usefulsplitting the current of one half bridge topology into two modules. The question is: what is better – use two paralleled half bridges, or twosingle switches in series connection?1+11+33~?21~22-2-Motivation59

How to parallel half bridge IGBT modules++111 133~-2 2223 3-~Paralleling of GB modules60

How to use single switch IGBT modules as half bridge+1+-21~12212-~Paralleling of GA modules61

Increased switching speed, decreases the switching lossesE switch But, leads to increased di/dt and therewith to higher overvoltagesv CE (t)i C (t) V CCv CE (t)i C (t) V CCv Ls = − tray ×dtdiI O0I O0di/dtp v (t)tp v (t)tE switch0t1E switcht2t0t1t2tInfluence of switching speeds62

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 speeds1+1+-1233~212-2~GA or GB?63

Comparison In half bridge modules the snubber capacitors can be placed closed tothe terminals with short - and therewith low inductive connections. Sothat the snubbers work very efficient. Paralleled GB modules allow higher switching speedsGA or GB?64

Advantages of paralleled half bridges The current per module is only 50 % of the maximum current The 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 thevoltage overshoot again Snubber capacitors can be placed very close to the terminals, so that theywork very efficient The switching speed can be increased and therewith the switching lossesare reduced SEMIKRON recommends the use of paralleled half bridgemodules instead of single switch modulesConclusion65

SEMIKRONs recommended solution66

Dealing with IGBT Modules Motivation Low inductive DC-link design Choice of right Snubber Gate Clamping Thermal management Paralleling – Application of driver circuit Paralleling – Low inductive AC-Terminal connection Usage of single switch “GA” type modules ConclusionTable of Contents67

Dealing with IGBT Modules When using latest generations ofIGBT modules it is recommended andadvantageous to Do a low inductive (“sandwich”) DC-linkdesign Decide for low inductive DC-link capacitors Optimise the snubber capacitors Optimise thermal management whichleads to maximum possible current ratingsConclusion68

Dealing with IGBT Modules For paralleled modules The driver must be powerful enough Some additional components arenecessary (e.g. R Ex ) and must belocated close to every single module The DC- and AC connection must besymmetric and low inductiveConclusion69

Thank you very much for your attention Refer also to “SEMIKRON Application Manual - Power Modules”70

Document status:preliminaryDate of publication: 2006-04-04Revision: 1.3Prepared by:Christian DaucherWith assistance fromDr. Arendt WintrichNorbert PluschkeInformation furnished in this document is believed to be accurate and reliable. However, no representation or warranty isgiven and no liability is assumed with respect to the accuracy or use of such information. Furthermore, this technicalinformation specifies semiconductor devices but promises no characteristics. No warranty or guarantee expressed orimplied is made regarding delivery, performance or suitability. Specifications mentioned in this document are subject tochange without notice. This document supersedes and replaces all information previously supplied and may besupersede by updates.71

IGBT modules are ESD sensitive devices. Thus they will delivered with a short circuit connection betweengate terminal and auxiliary emitter terminal Remove this connection and handle the modules only whenit is assured, that the environment is ESD proofAdditional72