Mentor Graphics Mechanical Power Electronics Webinar Cooling design of the frequency converter for a...

Mentor Graphics MechanicalPower Electronics Webinar

Cooling design of the frequency converter for a wind power station

Dipl.-Ing Karim Segondwww.e-cooling.de

Mentor Graphics MechanicalPower Electronics Webinar

Agenda

Frequency converter and generator

IGBT power module

Thermal management• Heat transfer• Materials• Design• Low frequency load of the IGBT• Temperature cycles of the IGBT• 1D thermal equivalent circuit: Cauer and Foster models

3D thermal and flow calculation of the IGBT module with FloEFD

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Frequency converter & generator Field of application of frequency converter

• Photovoltaic• Wind power stations• Electric cars• Locomotives• Gas power plants• Feedwater pump drive trains …

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Frequency converter & generatorComponents & function

Components• Rectifier, intermediate circuit, inverter• Integrated rectifier and IGBT power modules

Function

Modulation of amplitudes and frequencies of AC-Voltage:

• Continuous speed control of drive train• Synchronisation for supply to the network

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Frequency converter & generatorWind power application

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Generator type• Double-fed asynchronous generator with slip-ring rotor• 2/ 3 of the installed on-shore plants

Design of the frequency converter • Only for slip power• For about ½ of the total power

Challenges• Minimal load change due to wind variations • Low frequency load of the power modules

Frequency converterWind turbine generator

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IGBT power module

Manufacturer• Semikron

Power• P=372 kW

Size• 106x61x30 mm

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IGBT power moduleInsulated Gate Bipolar Transistor

Electronics switch ON/OFF

Characteristics• IGBT Chip is made of Silicon• High block voltage rigidity due to i- Layer• Production from losses due to the switching • Limited dynamic characteristics

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IGBT power moduleOperating mode

• Feed of a gate voltage (GE) • Flood of the loading equipment• Formation of a conductive channel

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Thermal managementHeat transfer

Conduction

• Thermal conductivity λ [W/mK]• Thermal resistance Rth [K/W]

Convection• Free and forced convection • Heat transfer coefficient α [W/m²K]

Heat radiation• Emissivity coefficient of the surface ɛ [ - ]

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Thermal managementHeat radiation

radiation heat at max. Chip temperature

P(ɛ) ≈ 140 mW/cm² ≈ 1/1000 * Pv

negligible

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Thermal managementMaterials

Layer Materials λ [W/mK]

Chip Si, SiC 124

Solder SnAgCU 57

Baseplate Cu 390

Insulator Ceramic 24

Heatsink Al 235

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Thermal management Materials: TIM

The thermal interface material is placed between the base plate and the heat sink.

Without TIM λ=0.026 [W/mK] (air) With TIM λ=1 -10 [W/mK]

Best practise: thermal resistance measurement!, see DynTIM Webinars

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Thermal managementDesign

High current density and small sizes require an incessant improvement of the cooling

Cooling mediums• Air, watter or heat pipes• Theses cooling methods can be calculated with FloEFD!

Cooling methods• Avoiding or reducing losses• Good conductivity of the materials• Thermal paths as short as possible • Spreading of the heat• Air cooling with heat sinks• Use of fans

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Thermal managementLow frequency load of the IGBT

Thermal challenge• Change of load at low frequencies• Large temperature difference • Strong thermo-mechanical load of the materials• Reduction of the life expectancy• Service required more often

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Thermal managementTemperature cycles of the IGBT

• The life expectancy depends on the temperature cycles

• Excessive temperature variations lead to material deterioration

• Weakest part is the solder

• A temperature difference of 25K corresponds to a one milion cycles, which is only one year operation!

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Thermal managementTemperature cycles of the IGBT

• The reliability of power electronic components can be characterised by testing them at the limits of their operation

• Power Tester 1500A from MicReD is commercially avalaible

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Thermal management1D thermal equivalent circuit Cauer and Foster models

Advantages• Acceptable approximation of the temperatures• Can be used in mathematical tools or electric circuit simulator• Fast

Disadvantages• Only one dimensional • For large thermal model, it gets complicated and the precision

decreases

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Thermal managementCauer model

• Analogy to the electrical circuit• Each section is represented by a

temparature node• Simple model of the thermal-flow

path • Coupling of the thermal

characteristics

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3D thermal and flow simulation of the IGBT power module of a wind power generator with FloEFD

Karim Segondwww.e-cooling.de

Mentor Graphics MechanicalPower Electronics Webinar

Agenda

CAD geometry

Boundary conditions• materials• volume flow

50 Hz operation• Input of the losses• Results of the flow calculation • Results of the thermal calculation • Comparison results vs. tests

Low frequency operation

Summary

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CAD-Geometry Frequency converter

CAD Geometry with the courtesy from Semikron

Heatsink

IGBT power modul

Diode modul

Fans

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CAD-Geometry IGBT power module with heatsink

CAD Geometry free of mistakes required, rarely available …

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CAD-GeometryComponents of the IGBT module

TIM

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Boundary conditionsMaterials

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50 Hz operation / Set-Up

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Boundary conditionsMaterials

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Boundary conditionsPressure drop vs. volum flow

Curves with the courtesy from Semikron

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50 Hz operation• Stationary calculations• Same fan and volume flow for all four cases• Change of the IGBT and diode losses • Losses are homogeneously spread in the chips of the IGBT and diodes• In the following plots the losses correspond to a an IGBT loss of 57.5 W per chip.

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50 Hz operation The mesh

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50 Hz operation Free convection in the casing

Very low velocities ; v = 0.01…0.02 m/s

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50 Hz operation Streamlines

• Flow velocities on the heat sink are the highest• Very low pressure losses high flow efficiency

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50 Hz operation Chip Temperature

• T = 60…100°C• Temperature differences due to the pre-heating

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50 Hz operation Heat sink

• Temperature distribution ; T = 50…90°C

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50 Hz operation Heat sink

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50 Hz operation Streamlines colored with the temperatures

• Heating of the air• Part of the air is not used for cooling

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50 Hz operation Comparison calculation vs. tests

Pv_IGBT[W]

Pv_Diode[W]

T_Mess[°C]

T_Sim[°C]

23 17 46.5 49.6957.5 40 75 83.7543.5 34 65.4 72.2840.5 35.5 67 73.03

Reasons for differences• Thermal characteristics of the TIM material• Not precise temperature measurement• Inlet volume flow fixed (instead of fan curve dependant)

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Low frequency operation

• FloEFD transient option switched on • Input of the losses:

For f = 10 Hz and f = 0.1Hz

0);²(sin*2*5.57)( wtWtPv

Input of the losses for 10 Hz

-0.06 0.04 0.140

102030405060708090

Losses vs time

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Low frequency operation Surface temperatures (10 Hz and 0.1 Hz) Video frequency is real frequency

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Low frequency operation Air Temperature in casing for 10 Hz Video frequency is real frequency

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Low frequency operationIGBT temperatures for 0.1Hz

Calculation is convergedIGBT2.SLDASM [IGBT Temp 57.5_Transient_0.1Hz]

20

25

30

35

40

45

50

55

60

0 50 100 150 200 250 300 350 400 450 500

Physical time (s)

Tem

per

atu

re (

So

lid)

[°C

]

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Summary

Time and cost reduction thanks to FloEFD FloEFD suited for stastionary as well as transient calculations Optimisation of the design Good thermal input about TIM required Short period of training for new users CAD- Geometry is required for the simulation