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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
Mentor Graphics MechanicalPower Electronics Webinar
Frequency converter & generator Field of application of frequency converter
• Photovoltaic• Wind power stations• Electric cars• Locomotives• Gas power plants• Feedwater pump drive trains …
Mentor Graphics MechanicalPower Electronics Webinar
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
Mentor Graphics MechanicalPower Electronics Webinar
Frequency converter & generatorWind power application
Mentor Graphics MechanicalPower Electronics Webinar
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
Mentor Graphics MechanicalPower Electronics Webinar
IGBT power module
Manufacturer• Semikron
Power• P=372 kW
Size• 106x61x30 mm
Mentor Graphics MechanicalPower Electronics Webinar
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
Mentor Graphics MechanicalPower Electronics Webinar
IGBT power moduleOperating mode
• Feed of a gate voltage (GE) • Flood of the loading equipment• Formation of a conductive channel
Mentor Graphics MechanicalPower Electronics Webinar
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 [ - ]
Mentor Graphics MechanicalPower Electronics Webinar
Thermal managementHeat radiation
radiation heat at max. Chip temperature
P(ɛ) ≈ 140 mW/cm² ≈ 1/1000 * Pv
negligible
Mentor Graphics MechanicalPower Electronics Webinar
Thermal managementMaterials
Layer Materials λ [W/mK]
Chip Si, SiC 124
Solder SnAgCU 57
Baseplate Cu 390
Insulator Ceramic 24
Heatsink Al 235
Mentor Graphics MechanicalPower Electronics Webinar
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
Mentor Graphics MechanicalPower Electronics Webinar
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
Mentor Graphics MechanicalPower Electronics Webinar
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
Mentor Graphics MechanicalPower Electronics Webinar
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!
Mentor Graphics MechanicalPower Electronics Webinar
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
Mentor Graphics MechanicalPower Electronics Webinar
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
Mentor Graphics MechanicalPower Electronics Webinar
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
Mentor Graphics MechanicalPower Electronics Webinar
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
Mentor Graphics MechanicalPower Electronics Webinar
CAD-Geometry Frequency converter
CAD Geometry with the courtesy from Semikron
Heatsink
IGBT power modul
Diode modul
Fans
Mentor Graphics MechanicalPower Electronics Webinar
CAD-Geometry IGBT power module with heatsink
CAD Geometry free of mistakes required, rarely available …
Mentor Graphics MechanicalPower Electronics Webinar
CAD-GeometryComponents of the IGBT module
TIM
Mentor Graphics MechanicalPower Electronics Webinar
Boundary conditionsMaterials
Mentor Graphics MechanicalPower Electronics Webinar
50 Hz operation / Set-Up
Mentor Graphics MechanicalPower Electronics Webinar
Boundary conditionsMaterials
Mentor Graphics MechanicalPower Electronics Webinar
Boundary conditionsPressure drop vs. volum flow
Curves with the courtesy from Semikron
Mentor Graphics MechanicalPower Electronics Webinar
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.
Mentor Graphics MechanicalPower Electronics Webinar
50 Hz operation The mesh
Mentor Graphics MechanicalPower Electronics Webinar
50 Hz operation Free convection in the casing
Very low velocities ; v = 0.01…0.02 m/s
Mentor Graphics MechanicalPower Electronics Webinar
50 Hz operation Streamlines
• Flow velocities on the heat sink are the highest• Very low pressure losses high flow efficiency
Mentor Graphics MechanicalPower Electronics Webinar
50 Hz operation Chip Temperature
• T = 60…100°C• Temperature differences due to the pre-heating
Mentor Graphics MechanicalPower Electronics Webinar
50 Hz operation Heat sink
• Temperature distribution ; T = 50…90°C
Mentor Graphics MechanicalPower Electronics Webinar
50 Hz operation Heat sink
Mentor Graphics MechanicalPower Electronics Webinar
50 Hz operation Streamlines colored with the temperatures
• Heating of the air• Part of the air is not used for cooling
Mentor Graphics MechanicalPower Electronics Webinar
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)
Mentor Graphics MechanicalPower Electronics Webinar
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
Mentor Graphics MechanicalPower Electronics Webinar
Low frequency operation Surface temperatures (10 Hz and 0.1 Hz) Video frequency is real frequency
Mentor Graphics MechanicalPower Electronics Webinar
Low frequency operation Air Temperature in casing for 10 Hz Video frequency is real frequency
Mentor Graphics MechanicalPower Electronics Webinar
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
]
Mentor Graphics MechanicalPower Electronics Webinar
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