EE463-Static Power Conversion-I

class: center, middle

# EE-463 STATIC POWER CONVERSION-I

# Thermal Design in Power Electronics

## Ozan Keysan

[ozan.keysan.me](http://ozan.keysan.me)

Office: C-113 <span class="meta">•</span> Tel: 210 7586

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# Thermal Design in Power Electronics

## Why is it important?

## Power Density (kW/l)

<img src="https://charbycharge.com/store/wp-content/uploads/elementor/thumbs/Size-comparison-new-Square-scaled-ppuhfc46u2z668adnegovyzyfzihsijlugdmjmc80w.jpg" alt="Drawing" style="width: 500px;"/>
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# Thermal Design in Power Electronics

## Survivability

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# Thermal Design in Power Electronics

## Expected Life

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# On the Machine (Load) Side

### Losses are dependent on temperature and temperature on losses
--

## Copper Losses \$\propto\$ Resistance

## $$R(T) = R(T_0)(1 + \alpha\Delta T)$$

### For copper (at 20 C)

### $$\alpha = 0.003862\;K^{-1}$$

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# Methods for Thermal Analysis
--

### From difficult to easy
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- ## Experimental
--

- ## CFD (Computational Fluid Dynamics)
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- ## FEA (Finite Element Analysis)
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- ## Lumped Parameter Model
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# Thermal CFD
## Requires intense computation

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# Thermal FEA

## No air-flow

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# Thermal Lumped Parameter Network

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# Basics of Heat Transfer
--

<img src="./images/heat-transmittance-means.jpg" alt="Drawing" style="width: 800px;"/>
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# Lumped Thermal Network

### Thermal systems can be represented as electric circuits
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## Temperature = Voltage
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## Heat Input = Current Source
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## Thermal Conductivity = Electrical Conductivity
--

## Heat Capacity = Capacitance

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# Thermal Conductivity
--
<img src="http://ecx.images-amazon.com/images/I/61oA4gophKL._SL1001_.jpg" alt="Drawing" style="width: 500px;"/>

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# Thermal Conductivity

<img src="http://www.kisinambalaj.com/image/cache/catalog/kap-grubu/bar1-800x600.JPG" alt="Drawing" style="width: 600px;"/>
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# Thermal Resistance

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# Thermal Resistance

### Similar to electrical resistance

#\$R= \dfrac{l}{kA}\$
--

- ## \$k\$: thermal conductivity

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# Thermal Conductivity of Some Materials
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- ## Water: 
--
0.58 W/(mK)
--

- ## Ice: 
--
2.2 W/(mK)
--

- ## Concrete:
--
 1-1.5 W/(mK)
--

- ## Wood:
--
0.12 W/(mK)

- ## Asbestos:
--
0.08 W/(mK)

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# Thermal Conductivity of Metals
--

- ## Aluminum: 
--
205 W/(mK)

--
- ## Iron: 
--
80 W/(mK)
--

- ## Copper: 
--
400 W/(mK)

- ## Gold: 
--
310 W/(mK)
--

- ## Epoxy: 0.35 W/(mK)
--

### [Ref](http://en.wikipedia.org/wiki/List_of_thermal_conductivities)
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# Conduction Heat Loss

# \$P = \dfrac{\Delta T}{R}\$

# \$P = \dfrac{T\_2 - T\_1}{R}\$

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# Convection

# Heat transfer on the surface between solids and liquids (or gaseous)
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# Convection

## Difficult to analyze accurately
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## Two types of Convection:
--

- ## Natural Convection
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- ## Forced Convection

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# Types of Flow
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- ## Laminar FLow
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- ## Turbulent Flow

### Enhanced heat transfer

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# Turbulance

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# Heisenberg:
--

<img src="https://i0.wp.com/ares.shiftdelete.net/580x330/original/16-12/13/heisenberg-breaking-bad-walter-white-gq.jpg" alt="Drawing" style="width: 600px;"/>
## Not Walter White

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# Heisenberg

### Werner Heisenberg: Key creator of quantum mechanics, uncertainity principle

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# Heisenberg: "I would ask God two questions;
--

#Why quantum mechanics, and why turbulence ?"
--

#I think he will have answer for the first one.

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## Convection Thermal Resistance
--

# \$R_c = \dfrac{1}{A h}\$
--

## A: Area
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## h: Convection heat transfer coefficient (W/m2/C)
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# h: Convection Heat Transfer Coefficient
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## Depends on the surface properties
--

## Flow Rate, density
--

## Reynolds Number
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## And others (Nusselt number, prandtl number)
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# Rule of Thumbs

### Not very accurate but useful for initial calculations
--

##  Heat Transfer Coefficient
--

- ## Air-Natural Convection: 5-10 W/(m2.C)
--

- ## Air-Forced Convection: 10-300 W/(m2.C)
--

- ## Liquid-Forced Convection: 50-20.000 W/(m2.C)

#### More info: [Estimating Parallel Plate-Fin Heat Sink Thermal Resistance](https://www.electronics-cooling.com/2003/02/estimating-parallel-plate-fin-heat-sink-thermal-resistance/), [Iterative calculation of the heat transfer coefficient](https://lisafea.com/pdf/Convection_heat_transfer_coefficient.pdf)

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# Radiation
--

## Radiant Heaters

<img src="http://willowbrookhangars.com/wp-content/uploads/2014/01/AmbiRad-radiant-tube-heater.jpg" alt="Drawing" style="width: 750px;"/>
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## Radiant Heaters

<img src="http://www.gardenista.com/wp-content/uploads/2015/04/img/sub/uimg/05-2012/700_endless-summer-and-dcs-patio-heaters-700x516.jpg" alt="Drawing" style="width: 700px;"/>
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# Reflective Blankets

<img src="https://images.tokopedia.net/img/cache/900/VqbcmM/2021/3/9/50961c99-b028-4775-8212-085ee86dcf7d.jpg" alt="Drawing" style="width: 500px;"/>
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# Radiation Heat Loss (Black body radiation)

### \$q_R\$: radiation heat flow (W/m2)

## \$q\_R = \rho \epsilon F (T\_1^4-T\_2^4)\$
--

### \$\rho\$: Stefan-Boltzmann constant (\$5.67\:10^{-8}  W/m^2/K^4\$ )
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### \$\epsilon\$: emissivity of radiating surface (ε ≤ 1)
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### \$F\$: view factor (≤ 1) – calculated from geometry
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### \$T\_1, T\_2\$ absolute temperature of radiant and ambient (K)
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# Radiation Heat Transfer

### \$h_R\$: heat transfer coefficient for radiation (for lumped parameter network)

## \$h\_R = \dfrac{\rho \epsilon F (T\_1^4-T\_2^4)}{T\_1 - T\_2}\$
--

### \$\rho\$: Stefan-Boltzmann constant=\$5.67\:10^{-8}  W/m^2/K^4\$
--

### \$\epsilon\$: emissivity of radiating surface (ε ≤ 1)
--

### \$F\$: view factor (≤ 1) – calculated from geometry

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# Emissivity of Materials
--

### Have you ever wondered why most heat sinks are black?
--

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# Emissivity of Materials

## Aluminum:
- ### Black anodized: 0.86
- ### Polished: 0.04-0.1

### Radiation is more dominant with naturally cooled heat sinks, than the ones with forced cooling

### More info:

- #### [Anodized Aluminum Heat sinks: What You Need to Know](https://www.gabrian.com/anodized-aluminum-heatsinks-what-you-need-to-know/)
- #### [How Heat Sink Anodization Improves Thermal Performance](http://www.qats.com/cms/2010/11/09/how-heat-sink-anondization-improves-thermal-performance-part-1-of-2/)

<!--
# Fluid Temperature Rise

### For a liquid cooled system

# \$\Delta T = \dfrac{P}{Q . d. C\_p}\$

### \$Q\$: Volume flow rate (m3/s)
### \$d\$: Density
### \$C\_p\$: Specific heat capacity (J/kgC)

-->

---
# Size vs Thermal Performance
--

---

### [Who’ll Freeze First? A Puzzle About Size and Staying Warm](http://noticing.co/on-size-and-warmth/)
---

### [Who’ll Freeze First? A Puzzle About Size and Staying Warm](http://noticing.co/on-size-and-warmth/)

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### [Who’ll Freeze First? A Puzzle About Size and Staying Warm](http://noticing.co/on-size-and-warmth/)

---

### [Who’ll Freeze First? A Puzzle About Size and Staying Warm](http://noticing.co/on-size-and-warmth/)

###[Size and Metobolism](http://noticing.co/on-size-and-metabolism/)
---

## (Heat \$\propto\$ Volume, but Heat Dissipation \$\propto\$ Area)
<img src="https://upload.wikimedia.org/wikipedia/commons/4/43/Angry_elephant_ears.jpg" alt="Drawing" style="width: 500px;"/>

### [Square-Cube Law by Prof. Walter Lewin](http://www.youtube.com/watch?v=qoM17ikreio)

### [Square-cube law, small is mighty](https://www.youtube.com/watch?v=qzq710aOHjE)

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## Thermal Design in Power Electronics
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- ### Determine your components
--

- ### Calculate the losses
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- ### Get the thermal resistances from data sheet
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- ### Determine the max. Heat sink thermal resistance
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- ### Find a heat sink, decide on cooling type (natural, forced)
--

- ### Iterate until you get a reasonable operating temp.

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# Typical Thermal Circuit

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# Typical Thermal Circuit

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# Typical Thermal Circuit

### Capacitances can be neglected for steady state analysis.
### Be careful with low heat capacity (tiny) components

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# Design Exercise
--

- ### [IGBT: STGW40H120DF2](http://www.st.com/resource/en/datasheet/stgw40h120df2.pdf)
--

### Find relevant parameters:

### Package Type

### Junction to Case Thermal Resistance

### Junction to Ambient (if used without a heatsink)

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# Design Exercise
- ### [IGBT: STGW40H120DF2](www.st.com/resource/en/datasheet/stgw40h120df2.pdf)

### Don't forget the freewheeling diode

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# Choose a Heatsink

### [How to mount heatsinks?](https://usermanual.wiki/Pdf/AN416620Heat20Sink20Mounting20Guide.1650589937/pdf)

#### Useful links:[Online Heat Sink Calculator](https://www.heatsinkcalculator.com), [Heat Sink Calculator](https://www.allaboutcircuits.com/tools/heat-sink-calculator/),  [Characteristics of common packages](http://www.giangrandi.ch/electronics/thcalc/thcalc.shtml), [Heat Sink Calculator, Forced Cooling](https://heatscapecal.com/)

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# Choose a Heatsink
### Suitable for TO-247 Package
--

<img src="https://www.fischerelektronik.de/fileadmin/_migrated/pics/leiterplattenkuehlkoerper_20_2.jpg" alt="Drawing" style="width: 400px;"/>
--

- ### [R2A-CT4-38E -  Heat Sink](http://www.newark.com/ohmite/r2a-ct4-38e/to-247-heat-sink/dp/73T7839)
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# Choose a Heatsink
### Suitable for TO-247 Package

## Check:

- ### Heatsink to ambient thermal resistance
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- ### Thermal resistance vs. air flow

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# How to
--

- ## Calculate losses?
--

- ## Junction temperature
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- ## Maximum operating limit

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# Tips & Things to consider
--

## Beware of hot spot and other heat sources!

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# Tips & Things to consider

## Beware of hot spot and other heat sources!

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# Tips & Things to consider
--

## Transients operating conditions!
### Can be dominant for small (low heat capacity) components

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# Tips & Things to consider

## Consider air flow  (both for forced and natural cooling)

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# Tips & Things to consider

## Consider air flow  (both for forced and natural cooling)

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# Tips & Things to consider
--

## Ambient Temperature
### Not always at 25 C. Check the standards
--

- ## Commercial: 0 ° to 70 °C
- ## Industrial: -40 ° to 85 °C
- ## Military: -55 ° to 125 °C

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# Tips & Things to consider
--

## Non idealities in contact surface

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# Tips & Things to consider
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## Imperfections of the contact surface

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## That's why we use TIM ( Thermal Interface Material)

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# Tips & Things to consider

## Thermal Interface Materials

- ## Greases, Putties
- ## (Adhesive) Thermal Pads
- ## Epoxy, Potting compounds
- ## [and others](https://www.digikey.com/eewiki/display/Motley/Thermal+Interface+Materials)

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# Tips & Things to consider

## Too much paste does more harm than good

## Insufficient thermal paste

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# Tips & Things to consider

## Too much paste does more harm than good

## Ideal thickness

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# Tips & Things to consider

## Too much paste does more harm than good

## Excessive thermal paste

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# Tips & Things to consider

## Avoid excessive mounting torque

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# Tips & Things to consider
--

## Non-uniform cooling
### Especially on stacked components on single heatsink

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# Useful Readings:
### Application notes are your friends
--

- ### [Thermal Resistance Theory and Practice](https://www.infineon.com/dgdl/smdpack.pdf?fileId=db3a304330f6860601311905ea1d4599)
- ### [Thermal resistance of IGBT Modules, Semikron](https://www.semikron.com/dl/service-support/downloads/download/semikron-application-note-thermal-resistances-of-igbt-modules-en-2014-11-30-rev-01/)
- ### [Thermal effects and junction temperature evaluation of Power MOSFETs](http://www.st.com/content/ccc/resource/technical/document/application_note/7b/bb/a2/32/f5/9d/46/2f/DM00241971.pdf/files/DM00241971.pdf/jcr:content/translations/en.DM00241971.pdf)
- ### [Heat sink Characteristics, IR](https://www.infineon.com/dgdl/an-1057.pdf?fileId=5546d462533600a401535591d3170fbd)
- ### [Thermal Design of Power Electronic Circuits](https://arxiv.org/pdf/1607.01578.pdf)

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# Useful Readings (cont.):

- ### [How to mount heat sinks?](https://www.eg.bucknell.edu/~dkelley/eceg351/FairchildHeatsinkMountingGuide.pdf)
- ### [A thermal management example](https://www.digikey.com/eewiki/pages/viewpage.action?pageId=68976759)
- ### [A Thermal Management Example Part 2:](https://www.digikey.com/eewiki/pages/viewpage.action?pageId=71958564)
- ### [Thermal Interface Materials](https://www.digikey.com/eewiki/display/Motley/Thermal+Interface+Materials)
- ### [How to select a heat sink](https://www.cuidevices.com/blog/how-to-select-a-heat-sink)

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## You can download this presentation from: [keysan.me/ee463](http://keysan.me/ee463)