Note: Descriptions are shown in the official language in which they were submitted.
113856Z
BACKGROUND OF THE INVENTION
The present invention relates to a new and improved
construction of cooling apparatus for electrical components,
especially semiconductor elements, of the power electronics
art.
Generally speaking, the cooling apparatus of the
invention is of the type comprising at least one assembly or
group of structural components containing at least one semi-
conductor element and at least one cooling element. These
elements are operatively connected with one another in mutual,
heat conducting and electrical pressure contact, the assembly
having a heat absorbing cooling fluid circulating thereabout.
During the operation of semiconductor components or
elements, such as for instance high-current diodes and thyristors,
electrical power losses arise which lead to temperature increases
at the semiconductor body. With increasing power for each semi-
conductor element and with increasing frequency there is an in-
crease of the electrical power losses which have been converted
into heat. It amounts to approximately one percent of the trans-
mitted electrical power. With infrequent overloads manufacturers
of semiconductor components permit, for instance, barrier layer-
temperatures up to 250 C for silicon rectifiers. Prior to des-
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truction such lose their blocking capability in the forward
direction at approximately 160C. For safety reasons the tem-
perature should not exceed about 125 C. The build-up of heat
in the semiconductor is dependent upon the power loss as a
function of time and the thermal conductlvity or dissipation
and heat storage capabilities of the s~miconductor elements.
Cooling agents are employed when working with
current intensities exceeding 100 amperes. Both air and also
liquid coolants are conventionally utilized. Liquid cooling
systems, owing to the danger of corrosion, are designed to work
in a closed circulation system with recooling by untreated water
or air. The semiconductor bodies are in heat conducting relation-
ship with cooling bodies having cooling ribs and formed of al-
uminum, aluminum alloys, copper or copper alloys or another
suitable metal, having a low thermal resistance.
Cooling devices for semiconductor elements are es-
pecially used in high-power or high-performance current rec-
tifiers in the field of energy generation, energy distribution, in
industrial applications and at vehicles. In this respect there
are employed thyristors having a continuous limiting current of
~ 700 amperes and a peak blocking voltage of ~ 3200 volts.
Further developments in current rectifier installations has
u~
resulted in the production of current rectifier arrays or
groups operating at increasingly greater power and at the
same time of more space-saving configuration, there being
attained power outputs exceeding 50 MW. Such requires good
heat dissipation or conduction within very narrow space require-
ments.
Air cooling is the simplest type of cooling in terms
of preparing and monitoring the cooling agent and the access-
ibility to the semiconductor components or elements. Such
frequentlyrequires air filters which, during periodic service
or maintenance times, must be dismantled, cleaned, dried and
again installed. In the case or current rectifiers having
power outputs exceeding 2 MW and for the operation of semi-
conductor elements, for instance in current rectifier banks or
arrays at railroad vehicles, requiring special protection
against contamination by metallic braking dust and so forth
and also against moisture attack from fog, rain and snow, liquid
cooling systems can be more suitable than air cooling systems.
Since liquids have much smaller heat transfer co-
efficients than air, it is possible to get by with much smaller
heat transmitting services when using liquid coolers. Water
possesses more favorable heat transfer coefficients than, for
instance, oil. Due to the danger of frost and the electrical con-
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ductivity of the water there is preferably employed an
electrically insulating coolant, such as transformer oil.
Now in ~erman Patent Publication ~ ~ it
is known to employ internally cooled heat transfer elements,
so-called cooling cells or cans, having an oil circulation
cooling for heat conduction or dissipation. In the flow path
of the cooling liquid there are arranged, essentially erpen-
dicular to the cell floors, plugs connected by their or a sim-
ilar material with such cell floors. These plugs possess a
square cross-section and have a diagonal thereof extending
transversely with respect to the flow direction. Due to this
arrangement of the plug-diagonals transversely with respect
to the flow direction turbulence phenomena arises, leading to
an improved transfer of the heat which is to be withdrawn from
the cell floors to the liquid. Such type cooling cells do how-
ever require a relatively high pressure for the liquid circu-
lation, since the openings for the influx and efflux of the
cooling liquid have a small cross-section. Sealing problems
particularly arise by virtue of the hose connections needed
for the liquid infeed and outfeed lines.
C~ qf'~ c,~
In~German Patent Publication No. 2,160,997~ there is
furthermore known to the art to arrange externally cooled,
large surface heat transfer elements between neighboring semi-
conductor elements in heat conducting relationship and to
accommodate such in a liquid container or vessel filled with
oil.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to
provide a new and improved construction of cooling apparatus
for electrical components which is not afflicted with the draw-
backs and shortcoming of the prior art cooling systems.
Another and more specific object of the present in-
vention aims at providing a new and improved construction of
cooling apparatus for semiconductor elements of the power
electronics art, possessing a relatively simple construction
which is favorable as concerns the fabrication economies and
rendering possible an improved heat dissipation or removal
in relation to heretofore known cooling devices.
Now in order to implement these and still further
objects of the invention, which will become more readily appar-
ent as the description proceeds, the cooling apparatus of the
present invention is manifested by the features that the semi-
conductor element and the cooling element are arranged within
a heat absorbing cooling fluid in a flow channel and surrounded
in an areal manner by walls or longitudinal partitions of the
flow channel.
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The cooling fluid or coolant can be gaseous or
vaporous, especially can be SF6-gas or a hydrogen-air mixture.
A particularly noteworthy advantage of the inventive
cooling apparatus resides in the fact that the arrangement of
the group of structuxal components containing the cooling and
semiconductor elements within the flow channels affords high
cooling efficiency both for liquid and also gaseous coolants.
With this cooling apparatus it is possible to attain, with
li~uid cooling, comparatively small thermal resistances of
less than 0.03 K/W using aluminum cooling elements and less
than 0.02 K/W with copper cooling elements, and with air cool-
ing there can be obtained thermal resistances of less than
0.05 K/W with aluminum cooling elements and less than 0.04 K/W
with copper cooling elements. A further advantage of the in-
vention is in terms of the fact that within a flow channel
there is afforded an improved heat dissipation or conductance
from the cooling elements to the cooling fluid.
An advantage of the employed elements, which in their
construction are similar to the heretofore known cooling cells
or cans, resides in the ~act that they do not require any
special cooling element encapsulation. Therefore, they are
easier and simpler to fabricate than such cooling cells. The
inlet and outlet openings for the cooling fluid in the cooling
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element can be designed to be larger than with the cooling
cells, so that the pressure gradient for each cooling element
is smaller. Consequently, the fluid pressure and the power
output which must be expended by the circulating pump or
ventilator, as the case may be, are smaller. Sealing prob-
lems at the cooling elements do not arise, since such are
immersed in the fluid or the fluid circulates thereabout. Due
to short line paths for the heat which is to be dissipated
within the cooling elements there is obtained, within very small
space, a high cooling efficiency. A particular advantage of
the cooling elements resides in the fact that they can be
stacked upon one another. The cooling apparatus does not re-
quire special maintenance and, with small space requirements
of the group of structural components, insures for their easy
exchangeability and hlgh longevity or service life.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood and objects
other than those set forth above, will become apparent when
consideration is given to the following detailed description
thereof. Such description makes reference to the annexed
drawings wherein:
Figure 1 illustrates in vertical sectional view
a cooling apparatus containing a number of groups of structural
components containing semiconductor elements and cooling ele-
ments within a cooling fluid container;
Figure 2 is a horizontal sectional view, according
to the sectional line II-II of Figure 1, illustrating the prin-
ciple of a clamping system having two groups of structural
components;
Figure 3 is a horizontal sectional view, taken sub-
stantially along the line III-III of Figure 2~ showing a par-
titioned cooling element having square heat conduction or
dissipation elements;
Figure 4 shows a cooling element in sectional view,
taken substantially along the line IV-IV of Figure 3;
Figure 5 is a bottom plan view of a cooling element
shown in the arrangements of Figures 3 and 4;
Figure 6 is a schematic horizontal sectional view of
a cooling element having rhomboid heat conduction or dissipation
elements;
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Figure 7 is a sectional view, taken substantially
along the line VII-VII of Figure 6 of the cooling element
thereof;
Figures 8 and 9 are respective schematic horizontal
sectional views of two further constructions of cooling elements
having plate-shaped heat conduction elements; and
Figure 10 illustrates in schematic horizontal sectional
view a cooling element having zig-zag shaped heat conduction
or dissipation elements.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Describing now the drawings, the exemplary embodi-
ment of inventive cooling apparatus shown in Figure 1 will be
seen to comprise a container 13 filled with a suitable cooling
: fluid or medium or fluid coolant 14, for instance transformer
oil, SF6-gas, air or a hydrogen-air mixture. Within such con-
tainer 13 there are arranged adjacent and above one another a
number of groups of structural components orelements 6 which are
to be cooled. These component groups 6 are located in flow
channels 23 or equivalent structure which are bounded by ver-
tical lengthwise partitions or walls 20 and connected with
horizontal transverse partitions 21. The group of structural
components 6, best seen by referring to Figure 2, are to be con-
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ceived as arranged, together with their clamping device of
Figure 1, perpendicular to the plane of the drawing towards
the rear. The cooling fluid 14 flows, in the direction of the
arrow A,from below towards the top through such flow channels
or ducts 23. Between superimposed arranged longitudinal par-
titions 20 there are provided seallng elements 26 formed of
any suitable elastic, for instance rubber-like or elastomeric
material, which enable a flow of the cooling fluid 14 essen-
tially in the flow direction A between superimposed arranged
rows of the component groups 6. The cooling fluid 14 can be
maintained in a forced flow, with a pump 17 when working with
a liquid coolant and a ventilator or the like when working
with a gaseous fluid, through an external heat exchanger 18,
a fluid inlet channel 15, a fluid filter 27, through the flow
channels 23 in the container or vessel 13 and a fluid outlet
channel 16. By means of not particularly shown, but conventional
electrical lines the group of structural c~mponents 6 are
connected with terminal contacts 19 at the top of the container
13.
Now as best seen by referring to Figure 2, the com-
ponent group 6 can contain a number of tandemly arranged semi-
conductorelements 4, flow guide plates 5, for instance, formed
of sheet metal, and cooling elements 1, which are pressed
against one another at their contactsurfaces in a statically
defined clamping device. Such clamping device comprises, by
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~_e
way of example, essentially two traverses or crossties 10
or equivalent structure, both of the tension bolts 12, the
two segmented pressure or contact spheres 8 or equivalent
structure, the spring 9 and the tightening or clamping screw
or threaded bolt 11 or the like. With such type clamping
device or clamping means it is possible to clamp, with a pre-
determined tension, a group of components 6 by means of the
traverses 10 and the clamping screw 11. The spring force of
the spring 9 or equivalent resilient element is dimensioned
such that the contact pressure exerted upon the elements of
the structural group 6 remains within permissible threshold
values, even with the greatest possible temperature fluctuations
which are contemplated to be encountered. Such are dependent
upon the diameter of the active portion of the semiconductor
elements 4.
The semiconductor elements 4 of essentially disk-
shaped configuration, are cooled at both faces by metallic
cooling elements 1 having good thermal conductance or heat
dissipation properties. When working with small semiconductor
elements a one sided cooling may be sufficient. The disk sur-
faces of such semiconductor elements 4 are in electrical and
heat conducting connection with corresponding contact surfaces
24 of the cooling element base or floor 2 of the cooling ele-
ment 1, as best seen by referring to Figure 5. In order to
improve the heat transfer action it is possible to arrange
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between the disk surfaces of the semiconductor elements 4 and
the cooling element bases or floors 2 not particularly shown,
good heat conducting, thin metal layers or foils, for instance
formed of lead, nickel, aluminum, gold, silver or alloys, while
utilizing one or a number of such metals. Such type metal
layers can also be applied, for instance by electrolytic sep-
aration or precipitation, vapor deposition and cathode atomiz-
ation upon the contact semiconductor disk.
Between neighboring semiconductor elements 4 of a
group of structural components or elements 6 there are arranged
two cooling elements 1, the bases or floors 2 of which, in each
case, are in pressure contact with the disk surfaces of the
semiconductor elements 4 and their heat conduction or dissi-
pation plugs or pins, that is to say, the heat conduction
elements 3 are in pressure contact with one another. Between
both of these cooling elements 1 and between the cooling ele-
ments 1 at both ends of the structural group 6 and the seg-
mented pressure or contact spheres 8 there can be arranged
the flow conducting plates 5, simultaneously usable as electrical
contacts. The current infeed brackets of such current con-
duction or conducting plates 5 protrude from the lateral
boundary of the cooling elements 1, as best seen by referring
to Figure 3. By incorporating such type flow conducting plates
5 it is possible to dispense with the use of other electrical
connection elements. With the structural group 6, illustrated
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i2
in Figure 2, the semiconductor elements 4 are arranged in a
Graetz bridge circuit confi~uration; they can however also be
connected, for instance, in series for other fields of applic-
ation.
As best seen by referring to the left-hand portion
of Figure 2, partitions or separation walls 22 are arranged
transversely with respect to the flow channels 23 and they
are connected with the transverse partitions or walls 20
arranged along the structural group 6 and at a slight spacing
with respect thereto between the traverses or crossties 10 of
the clamping device. The transverse partitions 22 insure that
a fluid circulation through the flow channel 23 is accomplished
essentially only through the recesses between the heat con-
ducting plugs or elements 3 in the cooling elements 1. They
prevent that there occurs in the flow channel 23 a flow essen-
tially about the semiconductor elements 4 and about the seg-
mented pressure spheres 8 of the clamping device. The partitions
20, 21, 22 consist of an electrical insulator, preferably
formed of a suitable plastics material resistant to, as needed,
SF6, oil and pressure.
As best seen by referring to Figures 3 to 10, the
cooling elements 1 possess a quadratic configuration and
essentially consist of a cooling element base or floor 2 and
arranged oriented perpendicular to the plane of the contact
1~8562
surface 24 of the cooling element base or floor 2, substan-
tially rod-shaped heat conducting plugs 3 or equivalent
structure having a square or rhomboid cross-section or heat
conducting or dissipation elements 3 formed as plate-shaped
or undulated elements. At the cooling element floors or bases
2 there can be arranged, externally of such contact surface 24,
turbulating pins 7 or equivalent structure which improve the
heat conductance from the cooling element 1 to the cooling
fluid 14. They are particularly suitable when using liquid
coolants. The heat conducting elements 3 are connected by the
material from which they are formed or an identical or like
material with the cooling element bases. Their cross-section
can reduce with increasing spacing from the cooling element
bases 2. It must at least be so large that there is insured
over such heat conducting elements 3 a faultless force trans-
mission by means of the clamping device. Plug-shaped or pin-
shaped heat conducting elements 3 advantageously have a diagonal
thereof disposed transversely with respect to the flow direction
A of the cooling fluid 14. When using rhomboid-shaped heat
conducting plugs or the like the shorter diagonal is aligned
transversely with respect to the flow direction A. The heat
conducting plugs are advantageously arranged at the same spacing
from one another. For each square centimeter of surface per-
pendicular to the lengthwise direction of such plugs there is
present, for instance, one heat conducting plug 3. The con-
nection or connecting portion for the heat conducting plug 3 with
the cooling element floor or base 2 is preferably shaped so
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~1`38562
as to be ogival or con~ergingly pointed. Due to this con-
figuration there is obtained a good heat transfer from the
cooling element base to the heat conducting plug 3 or the
like.
As best seen by referring to Figure 4, the cooling
element base 2 can have an irregular or non-uniform wall thick-
ness. Preferably the periphery or, as shown in broken lines,
the central and the peripheral region of the cooling element
base can have a lesser wall thickness than the region disposed
therebetween. Consequently, there is obtained a further improve-
ment in the heat conductance. The length 1 of the heat conduct-
ing elements amounts to two-fold to eight-fold, preferably
four-fold to six-fold, the maximum thickness _ of the cooling
element base or floor 2.
There can be mounted,as by mold ~ or casting, by way of
e~le, the longitudinal partitions 20 at tne cooling elements
1, as such has been illustrated in Figures 6 to 10. These
longitudinal or lengthwise partitions 20 augment the dissipation
of heat to the cooling fluid.
The cooling elements l also can ha~e a rectangular or
plate-shaped configuration, and the longer side of the rectangle
can have a length amounting to three to twenty times the length
of the shorter side of the rectangle. Moreover, the shorter
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side of the rectangle or the narrow side of the plate, as the
case may be, can be oriented essentially transversely with
respect to the flow direction A of the cooling fluid, as illus-
trated in Figure 8, or can deviate from such direction by an
angle of preferably less than 45, as shown in Figure 9.
The heat conducting elements 3 are arranged in rows
parallel to one another. Heat conducting elements of neighbor-
ing rows are offset relative to one another, i.e., in the flow
direction A of the fluid coolant aligned with the gap of
neighboring heat conducting elements within the preceding or
subsequent row. Plug-shaped heat conducting elements of a
row can be arranged partially in the intermediate spaces of
the heat conducting elements of a neighboring row, as shown
in Figure 6.
According to another construction, it is possible for
the heat conducting elements to be oriented essentially in
the flow direction A of the fluid coolant, and structured
so as to be of surface-like or aereal configuration in an
undulated or zig-zag shape, as shown in Figure 10.
What is important for the different shapes of the
heat conducting elements is that there be present a slight
flow resistance for the cooling fluid or coolant with rel-
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atively pronounced turbulence. In order to obtain a high
cooling capacity or efficiency the heat exchange surfaces
are also relatively large, their cross~section small and the
transport paths of the heat or thermal energy to be removed
are maintained as short as possible within the cooling element.
As large as possible number of cooling surfaces are to be pro-
vided as close as possible to the heat source.
There will now be explained the mode of operation of
the inventive cooling apparatus based upon the showing of
Figures 1 and 2. By means of the circulation pump or the
ventilator 17, a fluid coolant 14 is conveyed through the
flow channels 23. The componentgroups 6, arranged in the flow
channels 23, have the circulated coolant flowing thereabout
and the electrical power losses, released in the form of heat
by the semiconductor elements 4,are absorbed by the fluid
coolant 14, removed and delivered to the surroundings by means
of an external heat exchanger 18. By virtue of the partitions
22 arranged transversely with respect to the direction of
flow in the flow channels 23, the fluid coolant flows essen-
tially through the cooling elements 1 or, as the case may be,
through compound cooling elements 25 formed of two identical
or similar cooling elements 1, and, if desired, having arranged
therebetween a flow guide plate 5. The cooling elements are
in heat conducting and electrical connection with one another
by means of their heat conducting elements 3. The heat which
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is to be removed is predominantly transmitted from the heat
conducting plugs or elements 3 to the turbulently flowing
fluid coolant, and the flow essentially is directed perpen-
dicular to the direction of orientation of the heat conducting
elements.
When using hydrogen or a hydrogen-air mixture as the
fluid coolant, there are to be employed specialty steels or
coverings for the housing and lines in order to avoid the
passage of hydrogen ions. When using air as the fluid coolant
there is unnecessary a closed fluid circulation system employ-
ing heat exchanger, particularly then when there does not
exist any danger as concerns moisture and frost. To counter~
act against possible contamination of the semiconductor elements
there is then required an air filter 27 for cleaning the infed
air. Air velocities of 4 m/s to 12 m/s are standard. The
pressure gradient within a heat conducting element is dependent
upon the throughflow rate of the fluid medium and upon the
mobility of the fluid molecules, i.e., upon the temperature.
Of course, the subject matter of the invention is
not limited to what has been shown in the drawings. Thus, for
instance, the container 13 for the cooling fluid or coolant
14 can be provided with cooling ribs, by means of which the
heat can be transferred to the surroundings or to the prevail-
ing air stream, and the fluid circulation system is arranged
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within such container or vessel. The heat conducting elements
3 of the cooling elements 1 also can be, for instance, circular,
oval, ~star-shaped or parallelpiped. Their axes can be at an
angle, differing from 90 , with respect to the plane of the
contact surface 24 of the cooling element base 2. The number
of heat conductingplugs per square centimeter (cm2) of cooling
element base surface can be greater or smaller than one. The
cooling element base can have a uniform wall thickness. The
partitions or walls 20, 21 of the flow channels 23 can be
arranged at an angle with respect to the container walls which
differs from 90. Also, it is possible to use as the coolant
different cooling agents than those herein mentioned.
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