Note: Descriptions are shown in the official language in which they were submitted.
HIGH-DENSITY LOW-INDUCTANCE POWER INVERTER
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] None
TECHNICAL FIELD
[0002] The present disclosure relates to electronic circuits, and in
particular, to
power inverters for electric automotive vehicles.
BACKGROUND
[0003] A power inverter for an electric automotive vehicle is typically
a power
conversion device that converts a DC voltage, such as from the vehicle's
battery, to a
suitable AC voltage to drive an electric motor, for example.
[0004] Generally, these power inverters include an inverter power
circuit using
semiconductor switches, such as insulated-gate bipolar transistors (IGBTs)
that are
finely controlled by a controller, to yield a suitable output voltage.
[0005] Specifically, the inverter input receives direct electrical
current and
supplies an alternating current as the output. Components of the inverter
typically
include power modules, DC capacitor, DC bus bars, and heatsink. The DC portion
of
the power conversion device generally comprises two electrical nodes: a
positive and a
negative. The AC portion of the power conversion device comprises N electrical
nodes
where N is the number of output phases.
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[0006] The DC capacitor and DC bus bars are connected between the
positive
electrical nodes and negative electrical nodes, whereas the power modules are
interconnected between the DC and AC electrical nodes. The power modules may
be
configured in a half-bridge configuration, wherein an upper switch which is
connected
between the positive electrical node and the phase N node, and the lower
switch which
is connected between the phase N node and the negative node. Other
configurations,
such as full-bridge configuration may also be possible.
[0007] Typically, the main power components such capacitor and power
modules, are arranged side-by-side with electrical connections between them
formed by
bus bars on top. FIG. 1 illustrates a power inverter 10 with the commonly
known side-
by-side arrangement of the components. As shown, the power inverter 10
includes two
DC input busbars 12 that may receive DC energy source from a battery (not
shown) for
example. Power modules 16 are positioned next to the DC link capacitor 14 in a
coplanar fashion. The capacitor 14 is electrically coupled to the DC input of
the power
modules 16 via busbar 18 on top. The AC output of power modules 18 are
electrically
coupled to the output phase busbars 20. As may be appreciated by those skilled
in the
art, by being placed in a coplanar fashion as shown in FIG. 1, the main power
components of the inverter 10 may require relatively long electrical
connections that
may introduce considerable parasitic inductance into the switching circuits.
The large
parasitic inductances may in turn cause more stress on the semiconductor
switches and
thereby reduce the electrical current capacity of the inverter system.
[0008] Furthermore, as shown in FIG. 1, known inverters 10 typically
employ one
large DC link capacitor, such as capacitor 14, to be shared amongst all of the
power
modules 16, which may further contribute to the parasitic inductance of the
inverter 10.
Additionally, the single large capacitor may require additional cooling
elements to
dissipate the heat generated therein, which may result in a bigger inverter
package that
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is more costly to manufacture.
[0009] Further still, for certain high performance applications, it may
be desirable
to use the latest fast-switching power semiconductor technology, such as
silicon
carbide. However, the use of such fast switching semiconductor devices in a
power
conversion system generally requires the entire power electronic assembly to
be
optimized for low stray (parasitic) inductance.
[0010] Accordingly, there is a need for an improved power inverter that
is more
compact with minimized parasitic inductance.
SUMMARY OF THE INVENTION
[0011] In accordance with an example embodiment of the present
disclosure,
there is provided a power inverter, comprising: a busbar assembly configured
to receive
a DC energy source, the busbar assembly having a first connection surface and
an
opposing second connection surface; a power module configured to be
electrically
coupled to the busbar assembly from the first connection surface; and a
capacitor
configured to be electrically coupled to the busbar assembly from the second
connection surface; wherein the power module is aligned with the capacitor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Reference will now be made, by way of example, to the
accompanying
drawings which show example embodiments of the present application, and in
which:
[0013] FIG. 1 shows an isometric view of a prior art power inverter in
which the
main power components are arranged in a side-by-side fashion that is commonly
known
in the art;
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[0014] FIG. 2 shows an exploded isometric view of an inverter in
accordance with
one exemplary embodiment of the present disclosure;
[0015] FIG. 3 shows a partial isometric view taken along line A-A of the
inverter in
FIG. 2;
[0016] FIG. 4 shows an isometric view of an inverter in accordance with
another
exemplary embodiment of the present disclosure;
[0017] Similar reference numerals may have been used in different
figures to
denote similar components.
DESCRIPTION OF EXAMPLE EMBODIMENTS
[0018] With reference to FIGS. 2 and 3, there is provided an inverter 22
in
accordance with one exemplary embodiment of the present disclosure in what is
referred to as a "flat configuration". In the illustrated embodiment, inverter
22 includes a
printed circuit board (PCB) control board 24, capacitors 26, a laminated
busbar
assembly 28, power modules 30, and a heat sink 32.
[0019] The PCB control board 24 is well known in the art. Typically,
gate drivers
located on the PCB control board 24 control the IGBTs in the power modules 30
by
regulating their supply voltage. Additional circuitry may be located on the
PCB control
board 24 to issue command inputs and signals from various sensors to control
the gate
driver stage.
[0020] The inverter 22 may be electrically coupled to an external
battery (not
shown) through what is typically referred to as a DC link. DC link capacitors
26 may be
used to stabilize the DC link and protect the battery and the power modules
30, by
temporarily absorbing electrical energy, for example, to minimize ripple from
the
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switching operation.
[0021] In the illustrated embodiment, the inverter 22 includes six
capacitors 26
= arranged in two coplanar rows of three capacitors 26. However, it is to
be appreciated
that any number of capacitors 26 may be arranged in any suitable manner as
discussed
in further detail below.
[0022] Each capacitor 26 includes a first metal contact 34 running along
a first
longitudinal side of the capacitor thereby defining a positive capacitor node,
and a
second metal contact 36 running along a second opposing longitudinal side of
the
capacitor thereby defining a negative capacitor node. Each electrical contact
34 and 36
includes three flanges 38 configured to be electrically coupled onto the
laminated
busbar assembly 28. It is to be appreciated that the number or size of flanges
38 may
vary.
[0023] As best shown in FIG. 3, each flange 38 is configured with a
mounting
opening 39 configured to receive a fastener 40. In some embodiments, fasteners
40
may be of metallic construction and are electrically conductive. In some
embodiments,
fastener 40 maintains firm electrical contact between flanges 38 and layers of
the
laminated busbar 28 by exerting a downward pressure onto flange 38 up against
portions of the laminated busbar assembly 28. Busbar spacers 42 may serve as a
backstop. It is be appreciated that other means of establishing electrical
connection
between the flanges 38 and laminated busbar assembly 28 may be used. In some
embodiments, the capacitor 26 may be customized with a desired form-factor as
will be
discussed in more detail below.
[0024] In some embodiments, such as the one shown in FIGS. 2 and 3,
inverter
22 includes the same number of power modules 30 as the number of capacitors
26. As
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shown, the six power modules 30 are similarly arranged in two rows of three.
In some
embodiments, the power modules 30 may be IGBT power modules that typically
contain
semiconductor devices (not shown) arranged in, for example, "half-bridge"
configurations with two IGBT's being connected in series extending from a
positive DC
input node 44 to a negative DC input node 46. It is to be appreciated that
other types of
semiconductor-based power modules, such as full bridge configurations based
modules, may be used.
[0025] As shown, each power module 30 includes a positive DC input node
44
and a negative DC input node 46, as well as a phase output node 48. Each node
44
and 46 include a corresponding number of fastener receiving openings 50
configured to
secure, and form electrical contact with, fasteners 40. In the illustrated
embodiment, the
phase output node 48 is electrically coupled to an extension busbar 52, which
may
extend outside of the inverter package (not shown) for forming electrical
connections
with other components such as the motor (not shown).
[0026] In some embodiments, busbars spacers 42a and 42b, collectively
referred
to as busbar spacers 42, may be used to elevate the laminated busbar assembly
28
above the phase output busbars 52 to, at least in part, electrically insulate
the DC
laminated busbar assembly 28 from the busbar 52 which carries AC phase output
signals. In some embodiments, the busbar spacers 42 are electrically
conductive and
may serve to form electrical contacts between the DC input nodes 44, 46 of the
power
module 30 and the laminated busbar assembly 28. As shown in the illustrated
embodiment, both of the positive DC input node 44 and the negative DC input
node 46
are in electrical contact with busbar spacers 42a and 42b respectively. The
busbar
spacers 42 extend up to, and forms electrical contact with, respectively
layers within the
laminated busbar assembly 28 as will be discussed in more detail below.
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[0027] In the illustrated embodiment, the power modules 30 are in
thermal
contact with heat sink 32. Heat sink 32, as is commonly known in the art, may
be liquid
or air cooled. In some embodiments, all electrical contacts between the
capacitors 26,
the busbar assembly 28, and the power module 30 may also be thermally
conductive
such that heat generated within the power modules 30, as well as within the DC
link
capacitors 26, and the busbar assembly 28 may be, at least partially,
extracted through
the heat sink 32.
[0028] The laminated busbar assembly 28 is a unified metallic structure
for power
distribution between power modules 30 and capacitors 26. The busbar assembly
28
may be electrically coupled to a DC energy source, such as a battery (not
shown) and
serves as a power distribution component within the inverter 22. Specifically,
the
illustrated laminated busbar assembly 28 includes a first electrical layer 54
and a
second electrical layer 56. As shown a positive DC contact tab 58a extends
perpendicularly from an edge of the first electrical layer 54. Similarly, a
negative DC
contact tab 58b extends perpendicularly from an edge of the second electrical
layer 56.
The DC input contacts 58 may be configured to be in electrical contact with a
DC
energy source, such as a battery (not shown). In some embodiments, DC input
contact
58a may be in electrical contact with the positive electrical node of the DC
energy
source, and input contact 58b may be in electrical contact with the negative
electrical
node of the DC energy source. Contact 58a may be integrally formed with the
first
electrical layer 54 to define a positive node, and similarly, contact 58b may
be integrally
formed with the second electrical layer 56 to define a negative node. As
shown, three
non-conductive insulation layers 58 may cover and separate the first and
second
electrical layers 54 and 56, thereby electrically insulating the positive node
from the
negative node. Those skilled in the art would appreciated that other means for
establishing DC link with the DC energy source may be possible.
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[0029] The first and second electrical layers 54, 56 may be of metallic
construction and are electrically conductive. In the example embodiment shown
in
FIGS. 2 and 3, the laminated busbar assembly 28 is substantially flat as
defined by the
overall shape and size of the two electrical layers 54 and 56. The dimensions
of the
busbar 28 may be varied depending on, among other factors, the number and size
of
the main power components of the inverter and/or the arrangement of such
components.
[0030] In the illustrated embodiment, the capacitors 26 are arranged in
coplanar
fashion on a first connection surface 60 of the laminated busbar 28. The
flanges 38
extending from the first metal contact 34 of the capacitor 26 are in
electrical contact with
the first electrical layer 54 of the laminated busbar 28. The flanges 38
extending from
the second metal contact 36 of the capacitor 26 are in electrical contact with
the second
electrical layer 56.
[0031] The power modules 30 are arranged in coplanar fashion just below
the
second connection surface 62. Busbar spacers 42a, extending from the positive
DC
input node 44 of the power module 30 are in electrical contact with the first
electrical
layer 54. Busbar spacers 42b, extending from negative DC input node 46 of the
power
module 30, are in electrical contact with the second electrical layer 56.
[0032] In the illustrated embodiment, the number of DC link capacitors 26
is
identical to that of power modules 30. Thus, each power module 30 may have a
corresponding DC link capacitor 26 connected thereto, which may reduce the
parasitic
inductance compared to the known art.
[0033] Further, in embodiments such as the one shown in FIGS. 2 and 3,
the
capacitors 26 may be customized with a form factor that is similar to that of
the power
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modules 30. This may permit each capacitor 26 to be in vertical alignment
directly over
one of the power modules 30s below as shown in the figures. Accordingly, each
opening 39 on the flanges 38 from the capacitor 26 may be in vertical
alignment with
one of the openings 50 on the DC input nodes of the power module 30, which may
advantageously minimize the electrical connection distance and hence minimize
the
parasitic inductance introduced therein. Advantageously, the low inductance
connection
between the power modules 30 and capacitors 26 may allow the capacitors 26 to
act as
snubbers that, for example, may limit the voltage overshoot across the upper
or lower
IGBT switches inside the power modules 30 when switching from "closed" to
"opened"
state (turn-off of the switches).
[0034] Furthermore, by arranging the capacitors 26 and the power modules
30 on
two separate and parallel planes directly over one another, the inverter 22 in
accordance with the present disclosure may allow higher density inverters with
a more
compact inverter package.
[0035] FIG. 4 illustrates an inverter 72 in accordance with another
exemplary
embodiment of the present disclosure in what is referred to as the "U-shaped
configuration". Generally stated, inverter 72 employs a U-shaped laminated
busbar that
may position capacitor and power module pairs around a centrally received heat
sink.
Thereby further reducing the footprint of the inverter 72.
[0036] Capacitors 26 and power modules 30 shown in FIG. 4 are similar to
those
disclosed above with respect to FIGS. 2 and 3.
[0037] The power modules 30 are mounted onto a first surface 74 and a
second
surface 76 of the heat sink 32. Although it is shown that the same number of
power
modules 30 are mounted onto each of the first and second surfaces 74 and 76,
it is to
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be appreciated that the distribution of the power modules 30 on the two
surfaces may
differ.
[0038] The U-shaped laminated busbar assembly 78 is configured to sleeve
over
the heat sink 32 and power modules 30 as shown. Specifically, the laminated
busbar
assembly 78 may be of similar construction as busbar assembly 28 but having a
base
portion 80 and two elongated portions 82a, 82b respectively extending
perpendicularly
from a first and a second longitudinal ends of the base portion 80.
[0039] As shown, the electrical contact tabs 58a and 58b may be
positioned over
the base portion 80 for forming electrical connections with an external DC
energy
source, such as a battery (not shown). The elongated portions 82a and 82b may
be
configured to extend over all of the power modules 30 mounted onto each of
surfaces
74 and 76 of the heat sink 32. The base portion 80 defines a gap between the
elongated portion 82a and 82b so as to be able to receive the heat sink 32
mounted
with power modules 30 therein.
[0040] Each of the elongated portions 82a and 82b defines an interior
surface 84
and an opposing exterior surface 86. The DC input nodes of power modules 30
are
electrically coupled to the first and second electric layers 54, 56 of the
busbar assembly
74 from the interior surface 84. In some embodiments, such as the one shown in
FIG. 4,
busbar spacers 42a and 42b are used in the same way as disclosed above. The
phase
output 87 of the power modules may extend sideways as shown in the figure.
[0041] The first and second metal contacts 34, 36 of capacitors 26 may be
electrically coupled to the corresponding electrical layers of the laminated
busbar
assembly 74 from the exterior surface 86.
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[0042] In the illustrated embodiment, each of the power modules 30 is
aligned
with a corresponding capacitor 26 so as to minimize the distance therebetween,
which
may in turn minimize the parasitic inductance introduced by the electrical
connection.
[0043] As shown, two PCB control boards 88a and 88b are respectively
positioned above the capacitors 26 that are on the exterior surface 86 of the
top
elongated portion 82a, and below the capacitors 26 mounted on the exterior
surface 86
of the bottom elongated portion 82b. In some embodiments, each of the control
boards
88a and 88b is configured to control the power modules 30 respectively mounted
on
elongated portions 82a and 82b.
[0044] Certain adaptations and modifications of the described
embodiments can
be made. Therefore, the above discussed embodiments are considered to be
illustrative and not restrictive. The present disclosure is not to be limited
in scope by the
specific embodiments described herein. Further example embodiments may also
include all of the steps, features, compositions and compounds referred to or
indicated
in this description, individually or collectively and any and all combinations
or any two or
more of the steps or features.
[0045] Throughout this document, the use of the word "a" or "an" when
used in
conjunction with the term "comprising" in the claims and/or the specification
may mean
"one", but it is also consistent with the meaning of "one or more", "at least
one", and
"one or more than one". Similarly, the word "another" may mean at least a
second or
more. The words "comprising" (and any form of comprising, such as "comprise"
and
"comprises"), "having" (and any form of having, such as "have" and "has"),
"including"
(and any form of including, such as "include" and "includes") or "containing"
(and any
form of containing, such as "contain" and "contains"), are inclusive or open-
ended and
do not exclude additional, unrecited elements or process steps.
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[0046] In the present specification and in the appended claims, various
terminology which is directional, geometrical and/or spatial in nature such as
"longitudinal", "horizontal", "front", "forward", "backward", "back", "rear",
"upwardly",
"downwardly", etc. is used. It is to be understood that such terminology is
used for ease
of description and in a relative sense only and is not to be taken in any way
as
specifying an absolute direction or orientation.
[0047] The embodiments described herein may include one or more range of
values (for example, size, displacement and field strength etc.). A range of
values will
be understood to include all values within the range, including the values
defining the
range, and values adjacent to the range that lead to the same or substantially
the same
outcome as the values immediately adjacent to that value which defines the
boundary to
the range. For example, a person skilled in the field will understand that a
10%
variation in upper or lower limits of a range can be totally appropriate and
is
encompassed by the disclosure. More particularly, the variation in upper or
lower limits
of a range will be 5% or as is commonly recognized in the art, whichever is
greater.
[0048] Throughout this specification relative language such as the words
'about'
and 'approximately' are used. This language seeks to incorporate at least 10%
variability to the specified number or range. That variability may be plus 10%
or
negative 10% of the particular number specified.
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