Mechanical Design and Cooling Techniques

Transcription

1 Lecture Power Electronics Mechanical Design and Cooling Techniques Prof. Dr. Ing. Ralph Kennel Technische Universität München Arcisstraße München

2 Power Module and Disc Design 2

3 Housings plastic aluminium silicon aluminium AlN substrate soldering copper molybdenium aluminium silicon Aluminium metal substr. copper Power Module simple mounting (screws) insulation to ground suitable for single chips undefined fault behaviour explosion posiible Disc Design double sided cooling fault shortcut suitable for series connection low flexibility mechanical provisions for pressing 3

4 Insulated Gate Bipolar Transistor (IGBT) Mechanical Design 4

5 Driver Circuits 5

6 Cooling Techniques Cooling of Power Devices thermâl equivalent circuit natural convection forced air cooling liquid cooling 6

7 Electrical Equivalent Circuit for Modelling of Thermal Behaviour Dualism : heat source current source thermal energy current temperature electrical potential temperature difference voltage thermal resistance electrical resistance heat capacitance electrical capacitance does not exist electrical inductance 7 therefore temperature can physically not oscillate

8 Elektrical Equivalent Circuit for Modelling of Thermal Behaviour in case of simple heat distributions of low complexity the components of the equivalent circuit can be calculated from the geometry of the design and the physical parameters of the material like in the case of electrical resistors for more complex heat distributions FEM simulation software is available in the market 8

9 Elektrical Equivalent Circuit for Modelling of Thermal Behaviour Alternative : by measurement as in the analysis of electrical circuits e. g. by measuring step response(s) 9

10 Elektrical Equivalent Circuit for Modelling of Thermal Behaviour advantage of electrical equivalent circuit : transient heat dissipation can be calculated simply by methods of network theory and signal analysis 10

11 natural convection heat transfer from heat sink to surrounding air depends on : temperature difference active surface speed of airflow therefore the heat sink must contain material of good thermal conductivity (aluminium, copper etc.) thick root and as many ribs as possible provide surface as wide as possible (mostly as aluminium profile) have a dark surface be mounted vertically (chimney effect) 11

12 more designs of heat sinks punched and molded sheet metal plug-on star-shaped or flag-like heat sink made of aluminium made of phosphorus bronze made of sheet steel base plate made of aluminium, with pressed in cooling sheets 12

13 Forced Air Cooling in comparison to natural cooling (convection) the thermal resistance of the heat sink can be reduced to 1/5... 1/15 by forced air cooling 13

14 Forced Air Cooling in comparison to natural cooling (convection) the thermal resistance of the heat sink can be reduced to 1/5... 1/15 by forced air cooling with respect to the major part of convection in the cooling a black/dark surface does not really have an effect in case of forced air cooling 14

15 Liquid Cooling lower temperature drop between heat sink surface and cooling liquid higher power transfer or lower temperature of the chip (long life time) with respect to ist high thermal capacitance (specific heat c p = 4,187 kj/kg *K) water is suitable for heat transfer more than other liquids (oil or glycol) 15

16 Liquid Cooling Liquid Cooling in the Cooling System of a Vehicle: by additional mixing of e. g. glycol the thermal capacitance of the liquid is reduced at the same time viscosity and specific weight of the cooling liquid increases with increasing percentage of glycol thermal resistance between heat sink and cooling liquid increases significantly 50 % glycol addition increase of R thhw by % 90 % glycol addition increase of R thhw by % 16

17 Liquid Cooling by Heat Pipes Heatpipes are for heat transport are used, to transmit the heat from a device to the heat sink (e. g. in case of cramped space condition)... improve the temperature distribution as well as the dynamic behaviour 17