FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
POWER CONVERSION APPARATUS;
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED
AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3,
MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 100-8310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

2
DESCRIPTION
5 Field
[0001] The present invention relates to a power
conversion apparatus including a converter main circuit and
an inverter main circuit.
10 Background
[0002] Patent Literature 1 below discloses a
configuration in which rectangular two-element modules, or
two-in-one modules, of respective phases included in an
inverter main circuit are arranged in a direction
15 orthogonal to a direction of the flow of cooling air from a
cooler, and the two-element modules are each disposed with
its long side extending in the direction orthogonal to the
direction of the flow of the cooling air. Patent
Literature 1 describes that, with this configuration, the
20 length in the direction of the flow of the cooling air can
be reduced and thus the cooling efficiency can be improved.
In addition, Patent Literature 1 describes that a similar
arrangement is applied also to the modules included in a
converter main circuit so that the cooling efficiency can
25 be improved.
Citation List
Patent Literature
[0003] Patent Literature 1: Japanese Patent No. 6429720
30
Summary
Technical Problem
[0004] However, Patent Literature 1 described above

3
merely discloses an arrangement configuration in which
consideration is given only to the modules of the inverter
main circuit or to the modules of the converter main
circuit. That is, there are no descriptions or suggestions
5 as to how the modules of both the inverter main circuit and
the converter main circuit are arranged when they are
cooled by a common cooler. Assume a configuration in which
the modules of both the inverter main circuit and the
converter main circuit are cooled by a common cooler. In
10 this case, it is necessary to consider various points of
view such as heat generated by adjacent modules and
characteristics of the cooling air flowing in the cooler,
in addition to the direction of the flow of the cooling air.
Therefore, in the case of a configuration in which the
15 modules of both the inverter main circuit and the converter
main circuit are cooled by the common cooler, even if the
technique of Patent Literature 1 is applied as it is, the
cooling efficiency cannot necessarily be improved.
[0005] The present invention has been made in view of
20 the above, and an object of the present invention is to
obtain a power conversion apparatus capable of improving
the cooling efficiency in a configuration in which the
modules of both the inverter main circuit and the converter
main circuit are cooled by a common cooler.
25
Solution to Problem
[0006] In order to solve the above-described problem and
achieve the object, a power conversion apparatus according
to the present invention includes: a converter main circuit
30 to convert AC power into DC power; an inverter main circuit
to convert, into AC power, the DC power obtained by
conversion by the converter main circuit; and a cooler to
cool first switching elements included in the inverter main

4
circuit and second switching elements included in the
converter main circuit, the cooler being used as a common
cooler. The first switching elements are modularized in
units of one or more elements to form first modules. The
5 second switching elements are modularized in units of one
or more elements to form second modules. The first and
second modules are mounted on a first surface that is a
module mounting surface of a base of the cooler. The first
modules are arranged in a first direction on the first
10 surface. The second modules are arranged such that two or
more second modules are continuously arranged in a second
direction orthogonal to the first direction on the first
surface.
15 Advantageous Effects of Invention
[0007] The power conversion apparatus according to the
present invention achieves the effect of enabling the
cooling efficiency to be improved in a configuration in
which the modules of both the inverter main circuit and the
20 converter main circuit are cooled by a common cooler.
Brief Description of Drawings
[0008] FIG. 1 is a diagram illustrating a circuit
configuration of a power conversion apparatus according to
25 a first embodiment.
FIG. 2 is a diagram illustrating a circuit
configuration of an inverter main circuit in the first
embodiment, different from that illustrated in FIG. 1.
FIG. 3 is a diagram illustrating a circuit
30 configuration of a converter main circuit in the first
embodiment, different from that illustrated in FIG. 1.
FIG. 4 is a diagram illustrating a circuit
configuration of a converter main circuit in the first

5
embodiment, different from those illustrated in FIGS. 1 and
3.
FIG. 5 is a diagram illustrating a first exemplary
arrangement in which main circuit elements of the power
5 conversion apparatus according to the first embodiment are
mounted on a cooler.
FIG. 6 is a diagram illustrating a second exemplary
arrangement in which the main circuit elements of the power
conversion apparatus according to the first embodiment are
10 mounted on the cooler.
FIG. 7 is a diagram illustrating a first simulation
result for describing a reason for arranging the main
circuit elements as illustrated in FIG. 5.
FIG. 8 is a diagram illustrating a second simulation
15 result for describing the reason for arranging the main
circuit elements as illustrated in FIG. 5.
FIG. 9 is a diagram illustrating a third simulation
result for describing the reason for arranging the main
circuit elements as illustrated in FIG. 5.
20 FIG. 10 is a diagram illustrating a fourth simulation
result for describing the reason for arranging the main
circuit elements as illustrated in FIG. 5.
FIG. 11 is a first diagram for describing a
configuration of a main part in a second embodiment.
25 FIG. 12 is a second diagram for describing the
configuration of the main part in the second embodiment.
Description of Embodiments
[0009] Hereinafter, a power conversion apparatus
30 according to embodiments of the present invention will be
described in detail with reference to the accompanying
drawings. Note that the present invention is not limited
to the following embodiments. In addition, although a

6
power conversion apparatus for driving an electric vehicle
will be described as an example in embodiments below, this
is not intended to exclude application to other uses.
Furthermore, in the accompanying drawings, for ease of
5 understanding, the scales of respective members may be
shown differently from what they are in reality. This may
also hold true for the relationships between the drawings.
[0010] First Embodiment.
FIG. 1 is a diagram illustrating a circuit
10 configuration of a power conversion apparatus according to
a first embodiment. FIG. 1 illustrates a basic circuit
configuration of a power conversion unit of a power
conversion apparatus 100 to be applied to an electric
vehicle to which alternating current is input. The power
15 conversion apparatus 100 includes a converter main circuit
20, an inverter main circuit 40, and a filter capacitor 30.
The converter main circuit 20 converts AC power into DC
power. The inverter main circuit 40 converts, into AC
power, the DC power obtained by the conversion by the
20 converter main circuit 20. That is, the power conversion
apparatus 100 according to the first embodiment is an
apparatus that performs power conversion twice, that is,
changing AC power to DC power and then converting the DC
power into AC power again.
25 [0011] A contactor 8 is disposed at an input end of the
power conversion apparatus 100. A transformer 6 is
connected to the contactor 8. Four motors 80 are connected
to an output end of the power conversion apparatus 100.
The four motors 80 drive the electric vehicle. An
30 induction motor is suitable for the motors 80.
[0012] One end of a primary winding of the transformer 6
is connected to an overhead line 1 via a current collector
2. An opposite end of the primary winding of the

7
transformer 6 is connected to a rail 4 via a wheel 3. The
rail 4 provides a ground potential. The power supplied
from the overhead line 1 is input to the primary winding of
the transformer 6 via the current collector 2. The power
5 generated in a secondary winding of the transformer 6 is
supplied to the converter main circuit 20 via the contactor
8.
[0013] The contactor 8 is disposed between the secondary
winding of the transformer 6 and the converter main circuit
10 20, and switches between supplying and not supplying power.
Note that a configuration in which both of two AC input
lines are turned on or off is illustrated as an example in
FIG. 1, but the contactor may be disposed on one of the AC
input lines.
15 [0014] The converter main circuit 20 includes a positive
arm and a negative arm. The positive arm includes
switching elements UPC and VPC. The negative arm includes
switching elements UNC and VNC. The switching element UPC
and the switching element UNC are connected in series to
20 form a U-phase leg. The switching element VPC and the
switching element VNC are connected in series to form a Vphase leg. The U-phase leg and the V-phase leg are
connected in parallel to each other to form a single-phase
bridge circuit. Note that, in the following description,
25 the U phase may be referred to as a “first phase”, and the
V phase may be referred to as a “second phase”.
[0015] The converter main circuit 20 converts the input
AC voltage into a desired DC voltage by performing pulse
width modulation (PWM) control on the switching elements
30 UPC, VPC, UNC, and VNC, and outputs the DC voltage.
[0016] The filter capacitor 30 and the inverter main
circuit 40 are connected in parallel to an output end of
the converter main circuit 20. The filter capacitor 30

8
serves as a DC power source. The filter capacitor 30
smooths the DC voltage output from the converter main
circuit 20. The inverter main circuit 40 receives the
voltage of the filter capacitor 30 as input, converts the
5 voltage into an AC voltage of a desired voltage and a
desired frequency, and applies the AC voltage to the motors
80.
[0017] The inverter main circuit 40 includes a positive
arm including switching elements UPI, VPI, and WPI and a
10 negative arm including switching elements UNI, VNI, and WNI.
The switching element UPI and the switching element UNI are
connected in series to form a U-phase leg. The switching
element VPI and the switching element VNI are connected in
series to form a V-phase leg. The switching element WPI
15 and the switching element WNI are connected in series to
form a W-phase leg. The U-phase, V-phase, and W-phase legs
are connected in parallel to each other to form a threephase bridge circuit. Note that, in the following
description, the U phase may be referred to as the “first
20 phase”, the V phase may be referred to as the “second
phase”, and the W phase may be referred to as a “third
phase”.
[0018] The inverter main circuit 40 performs PWM control
on the switching elements UPI, VPI, WPI, UNI, VNI, and WNI
25 to convert the DC voltage smoothed by the filter capacitor
30 into an AC voltage of a desired voltage and a desired
frequency, and applies the AC voltage to the motors 80.
[0019] Note that, in the following description, when the
switching elements of the converter main circuit 20 and the
30 inverter main circuit 40 are distinguished from each other
without reference numerals, the switching elements of the
inverter main circuit 40 may be referred to as “first
switching elements”, and the switching elements of the

9
converter main circuit 20 may be referred to as “second
switching elements”. In addition, the first and second
switching elements may be collectively referred to as “main
circuit elements”.
5 [0020] An insulated gate bipolar transistor (IGBT) with
an antiparallel diode incorporated therein illustrated in
FIG. 1 is an example of the switching elements UPC, VPC,
UNC, VNC, UPI, VPI, WPI, UNI, VNI, and WNI. However, other
switching elements may also be used. A metal-oxide10 semiconductor field-effect transistor (MOSFET) is another
example of the switching elements UPC, VPC, UNC, VNC, UPI,
VPI, WPI, UNI, VNI, and WNI. Moreover, as a material for
the switching elements, in addition to silicon (Si),
silicon carbide (SiC), gallium nitride (GaN), gallium oxide
15 (Ga2O3), diamond, and the like, which are wide bandgap
semiconductors, may also be used. When the switching
elements are formed of a wide bandgap semiconductor-based
material, it is possible to achieve low loss and high-speed
switching.
20 [0021] FIG. 2 is a diagram illustrating a circuit
configuration of an inverter main circuit in the first
embodiment, different from that illustrated in FIG. 1. The
circuit configuration of an inverter main circuit 40a
illustrated in FIG. 2 is different from the circuit
25 configuration of the inverter main circuit 40 illustrated
in FIG. 1 in that two switching elements are connected in
parallel in each arm.
[0022] In FIG. 2, switching elements UPI1 and UPI2 are
connected in parallel in a U-phase positive arm, switching
30 elements UNI1 and UNI2 are connected in parallel in a Uphase negative arm, switching elements VPI1 and VPI2 are
connected in parallel in a V-phase positive arm, switching
elements VNI1 and VNI2 are connected in parallel in a V-

10
phase negative arm, switching elements WPI1 and WPI2 are
connected in parallel in a W-phase positive arm, and
switching elements WNI1 and WNI2 are connected in parallel
in a W-phase negative arm. It is possible to lower the
5 rated value of the current capacity of each switching
element by connecting the switching elements of each phase
arm in parallel.
[0023] FIG. 3 is a diagram illustrating a circuit
configuration of a converter main circuit in the first
10 embodiment, different from that illustrated in FIG. 1. The
circuit configuration of a converter main circuit 20a
illustrated in FIG. 3 is different from the circuit
configuration of the converter main circuit 20 illustrated
in FIG. 1 in that four switching elements are connected in
15 parallel in each arm.
[0024] In FIG. 3, switching elements UPC1, UPC2, UPC3,
and UPC4 are connected in parallel in a U-phase positive
arm, switching elements UNC1, UNC2, UNC3, and UNC4 are
connected in parallel in a U-phase negative arm, switching
20 elements VPC1, VPC2, VPC3, and VPC4 are connected in
parallel in a V-phase positive arm, and switching elements
VNC1, VNC2, VNC3, and VNC4 are connected in parallel in a
V-phase negative arm. It is possible to lower the rated
value of the current capacity of each switching element by
25 connecting the switching elements of each phase arm in
parallel.
[0025] FIG. 4 is a diagram illustrating a circuit
configuration of a converter main circuit in the first
embodiment, different from those illustrated in FIGS. 1 and
30 3. The converter main circuit 20 illustrated in FIG. 1 has
a two-level circuit configuration. Meanwhile, a converter
main circuit 20b illustrated in FIG. 4 has a three-level
circuit configuration. The converter main circuit 20b is

11
different from the converter main circuit 20 in this
respect.
[0026] In FIG. 4, switching elements UPC1A and UPC1B
connected in parallel and switching elements UPC2A and
5 UPC2B connected in parallel are connected in series in a Uphase positive arm. The cathode sides of diodes UD1A and
UD1B connected in parallel are connected to this connection
point. Each anode side of the diodes UD1A and UD1B is
connected to a midpoint which is a connection point of
10 filter capacitors 30P and 30N. Similarly, switching
elements UNC3A and UNC3B connected in parallel and
switching elements UNC4A and UNC4B connected in parallel
are connected in series in a U-phase negative arm. Each
anode side of diodes UD2A and UD2B connected in parallel is
15 connected to this connection point. The cathode sides of
the diodes UD2A and UD2B are connected to the midpoint
which is the connection point of the filter capacitors 30P
and 30N.
[0027] A V-phase positive arm and a V-phase negative arm
20 are configured in a similar manner to the U-phase positive
arm and the U-phase negative arm, respectively.
Specifically, switching elements VPC1A and VPC1B connected
in parallel and switching elements VPC2A and VPC2B
connected in parallel are connected in series in the V25 phase positive arm. The cathode sides of diodes VD1A and
VD1B connected in parallel are connected to this connection
point. Each anode side of the diodes VD1A and VD1B is
connected to the midpoint which is the connection point of
the filter capacitors 30P and 30N. Similarly, switching
30 elements VNC3A and VNC3B connected in parallel and
switching elements VNC4A and VNC4B connected in parallel
are connected in series in the V-phase negative arm. Each
anode side of diodes VD2A and VD2B connected in parallel is

12
connected to this connection point. The cathode sides of
the diodes VD2A and VD2B are connected to the midpoint
which is the connection point of the filter capacitors 30P
and 30N.
5 [0028] Whether to use a two-level converter main circuit
or a three-level converter main circuit is appropriately
determined according to needs of a user or an operating
environment. With regard to an electric vehicle, strict
regulations have been placed on inductive interference in a
10 specific frequency band so as to prevent malfunction of
ground devices. Therefore, in the case of reducing
harmonic current with high accuracy, a three-level circuit
is often chosen. Note that a switching element to be used
for a three-level circuit has an advantage over a switching
15 element to be used for a two-level circuit in that the
voltage resistance of each switching element can be reduced
by about half.
[0029] FIG. 5 is a two-dimensional diagram illustrating
a first exemplary arrangement in which the main circuit
20 elements of the power conversion apparatus according to the
first embodiment are mounted on a cooler. FIG. 5
illustrates a plurality of modules mounted on a base 12 of
a cooler 11. Specifically, FIG. 5 illustrates an example
in which the inverter main circuit 40a illustrated in FIG.
25 2 and the converter main circuit 20a illustrated in FIG. 3
are mounted on the base 12 of the cooler 11 that is a
common cooler.
[0030] In FIG. 5, each module is a two-element module
configured such that two switching elements are housed in
30 one module. Each module is mounted on a first surface 14
of the base 12. The first surface 14 is a module mounting
surface of the base 12. Note that an element substrate on
which each module is mounted is not illustrated in FIG. 5.

13
Furthermore, although not illustrated in FIG. 5, a heat
pipe or a radiating fin for cooling the switching elements
housed in each module is provided on a second surface which
is opposite the first surface 14. An arrow indicates the
5 direction of the flow of cooling air that flows into and
out of the cooler 11.
[0031] FIG. 5 illustrates four sections on the first
surface 14. The four sections are a first section 41, a
second section 42, a third section 43, and a fourth section
10 44. The first section 41 extends in a second direction
orthogonal to a first direction in which cooling air flows.
The second section 42, the third section 43, and the fourth
section 44 are adjacent to the first section 41 along the
first direction, and the second section 42, the third
15 section 43, and the fourth section 44 are arranged in this
order along the second direction.
[0032] In the first section 41, a module 41a corresponds
to the switching elements UPI1 and UNI1 in FIG. 2, and a
module 41b corresponds to the switching elements UPI2 and
20 UNI2 in FIG. 2. Similarly, a module 41c corresponds to the
switching elements VPI1 and VNI1 in FIG. 2, and a module
41d corresponds to the switching elements VPI2 and VNI2 in
FIG. 2. A module 41e corresponds to the switching elements
WPI1 and WNI1 in FIG. 2, and a module 41f corresponds to
25 the switching elements WPI2 and WNI2 in FIG. 2. In this
manner, the modules 41a to 41f including all the first
switching elements included in the inverter main circuit
40a are arranged in the first section 41. That is, the
modules 41a to 41f are modules housing switching elements
30 that operate as U-phase, V-phase, and W-phase switching
elements of the two-level inverter main circuit. Note that
the modules 41a to 41f may be referred to as “first modules”
in the following description.

14
[0033] Next, in the second section 42, a module 42a
corresponds to the switching elements UPC1 and UNC1 in FIG.
3. Similarly, a module 42b corresponds to the switching
elements UPC2 and UNC2 in FIG. 3, a module 42c corresponds
5 to the switching elements UPC3 and UNC3 in FIG. 3, and a
module 42d corresponds to the switching elements UPC4 and
UNC4 in FIG. 3. In this manner, the modules 42a to 42d
including second switching elements that operate as U-phase
switching elements among the second switching elements
10 included in the two-level converter main circuit 20a are
arranged in the second section 42.
[0034] The third section 43 is a non-mounting section in
which no module is arranged as illustrated. The reason why
the third section 43 is a non-mounting section will be
15 described later.
[0035] Furthermore, in the fourth section 44, a module
44a corresponds to the switching elements VPC1 and VNC1 in
FIG. 3. Similarly, a module 44b corresponds to the
switching elements VPC2 and VNC2 in FIG. 3, a module 44c
20 corresponds to the switching elements VPC3 and VNC3 in FIG.
3, and a module 44d corresponds to the switching elements
VPC4 and VNC4 in FIG. 3. In this manner, the modules 44a
to 44d including first switching elements that operate as
V-phase switching elements among the second switching
25 elements included in the two-level converter main circuit
20a are arranged in the fourth section 44.
[0036] Note that the modules 42a to 42d and 44a to 44d
may be referred to as “second modules” in the following
description.
30 [0037] FIG. 6 is a two-dimensional diagram illustrating
a second exemplary arrangement in which the main circuit
elements of the power conversion apparatus according to the
first embodiment are mounted on the cooler. Specifically,

15
FIG. 6 illustrates an example in which the inverter main
circuit 40a illustrated in FIG. 2 and the converter main
circuit 20b illustrated in FIG. 4 are mounted on the base
12 of the cooler 11 that is a common cooler.
5 [0038] As with FIG. 5, FIG. 6 illustrates the first
section 41, the second section 42, the third section 43 and
the fourth section 44 on the first surface 14. The
definitions of these sections are the same as those in FIG.
5.
10 [0039] Modules to be arranged in the first section 41 of
FIG. 6 are the same as those illustrated in FIG. 5, and
description thereof is omitted here.
[0040] Next, in the second section 42, a module 42e
corresponds to the switching element UPC1A and the diode
15 UD1A in FIG. 4. Note that a combination of the switching
element UPC1A and the diode UD1A may be referred to as an
“upper potential-side outer element” in the following
description. In addition, the part corresponding to the
transistor of the lower-side switching element of the
20 module 42e is shown in a light color in FIG. 6 in line with
the circuit configuration of FIG. 4. This indicates that
the function of the transistor is not used and only the
function of the diode is used in the lower-side switching
element of the module 42e. The same applies to modules 42f,
25 42g, and 42h to be described below.
[0041] The module 42f corresponds to the switching
element UPC1B and the diode UD1B in FIG. 4, the module 42g
corresponds to the switching element VPC1A and the diode
VD1A in FIG. 4, and the module 42h corresponds to the
30 switching element VPC1B and the diode VD1B in FIG. 4.
[0042] As described above, the modules 42e to 42h
housing second switching elements that operate as U-phase
upper potential-side outer elements among the second

16
switching elements included in the three-level converter
main circuit 20b are arranged in the second section 42.
[0043] In addition, unlike in FIG. 5, modules 43e to 43h
are arranged in the third section 43 as illustrated in FIG.
5 6. Specifically, the module 43e corresponds to the
switching elements UPC2A and UNC3A in FIG. 4. Note that a
pair of the switching elements UPC2A and UNC3A may be
referred to as an “inner element” in the following
description. The same applies to the modules 43f, 43g, and
10 43h to be described below.
[0044] The module 43f corresponds to the switching
elements UPC2B and UNC3B in FIG. 4, the module 42g
corresponds to the switching elements VPC2A and VNC3A in
FIG. 4, and the module 42h corresponds to the switching
15 elements VPC2B and VNC3B in FIG. 4.
[0045] Furthermore, in the fourth section 44, a module
44e corresponds to the switching element UNC4A and the
diode UD2A in FIG. 4. Note that a combination of the
switching element UNC4A and the diode UD2A may be referred
20 to as a “lower potential-side outer element” in the
following description. In addition, the part corresponding
to the transistor of the upper-side switching element of
the module 44e is shown in a light color in FIG. 6 in line
with the circuit configuration of FIG. 4. This indicates
25 that the function of the transistor is not used and only
the function of the diode is used in the upper-side
switching element of the module 44e. The same applies to
modules 44f, 44g, and 44h to be described below.
[0046] The module 44f corresponds to the switching
30 element UNC4B and the diode UD2B in FIG. 4, the module 44g
corresponds to the switching element VNC4A and the diode
VD2A in FIG. 4, and the module 44h corresponds to the
switching element VNC4B and the diode VD2B in FIG. 4.

17
[0047] As described above, the modules 44e to 44h
housing first switching elements that operate as U-phase
lower potential-side outer elements among the second
switching elements included in the three-level converter
5 main circuit 20b are arranged in the fourth section 44.
[0048] Note that the only difference between the
exemplary arrangements illustrated in FIGS. 5 and 6 is
whether modules are mounted in the third section 43. Even
when the modules 42e to 42h illustrated in FIG. 6 are used
10 as the upper potential-side outer elements and the modules
44e to 44h illustrated in FIG. 6 are used as the lower
potential-side outer elements in the three-level converter
main circuit illustrated in FIG. 6, it is sufficient if the
function of the transistors is set to be unused and it is
15 not necessary to arrange different elements. In addition,
all the modules can have the same structure. Therefore, a
substrate on which the modules are mounted according to the
arrangement illustrated in FIG. 5 or 6 can be used as a
standard substrate or a standard package. As a result,
20 even if the circuit configuration of the converter main
circuit is changed from, for example, a two-level circuit
configuration to a three-level circuit configuration
according to needs of the user or the operating environment,
individual design changes can be reduced to a required
25 minimum.
[0049] Note that two modules are arranged in parallel
for each phase in the converter main circuit and the
inverter main circuit illustrated in FIG. 6, but this is
not a limitation. A single module, that is, a single two30 element module, may be arranged for each phase in the
converter main circuit and the inverter main circuit.
Furthermore, four modules are arranged in parallel for each
phase in the converter main circuit illustrated in FIG. 5,

18
and two modules are arranged in parallel for each phase in
the inverter main circuit illustrated in FIG. 5. However,
this is not a limitation. Two modules may be arranged in
parallel for each phase in the converter main circuit, and
5 a single two-element module may be arranged for each phase
in the inverter main circuit. When the material for the
switching element is a non-wide bandgap semiconductor such
as silicon (Si), the number of defects in a chip is small
even if the switching element has a large capacity, so that
10 the module can be manufactured without deteriorating yields.
Accordingly, the standard substrate or the standard package
can be downsized.
[0050] Furthermore, each module has been described as a
two-element module in FIGS. 5 and 6, but the modules are
15 not limited thereto. Each module may be a four-element
module configured such that four switching elements are
housed in one module. Even when the four-element module is
used, the effects described above can be obtained.
[0051] Next, a description will be given of the reason
20 why the inner elements are arranged in the third section 43
when the converter main circuit is a three-level circuit.
[0052] In general, fluid flowing in a pipe having a
uniform pressure loss follows a phenomenon called “HagenPoiseuille flow”, so that the speed of flow is maximized in
25 the central portion of the pipe, and becomes zero near the
wall surface of the pipe. Although simulation results are
not illustrated, the same has been confirmed also in fluid
simulation for a heat pipe cooler using traveling wind.
That is, it has been confirmed that the speed of flow is
30 high in the central portion of the cooler. Utilizing this
phenomenon, an element having a large calorific value is
disposed in the central portion where the speed of flow is
relatively high, in the first embodiment. When the

19
converter main circuit has a three-level circuit
configuration, the inner element corresponds to the element
having a large calorific value. As already described, the
inner elements are arranged in the third section 43
5 corresponding to the central portion of the cooler, in FIG.
6. This arrangement can improve the cooling efficiency in
the cooler. In addition, since the cooling efficiency can
be improved, it is possible to further reduce the size and
weight of the cooler.
10 [0053] Next, the reason why no module is mounted in the
third section 43 when the converter main circuit is a twolevel circuit will be described with reference to FIGS. 7
to 10. FIG. 7 is a diagram illustrating a first simulation
result for describing a reason for arranging the main
15 circuit elements as illustrated in FIG. 5. FIG. 8 is a
diagram illustrating a second simulation result for
describing the reason for arranging the main circuit
elements as illustrated in FIG. 5. FIG. 9 is a diagram
illustrating a third simulation result for describing the
20 reason for arranging the main circuit elements as
illustrated in FIG. 5. FIG. 10 is a diagram illustrating a
fourth simulation result for describing the reason for
arranging the main circuit elements as illustrated in FIG.
5.
25 [0054] A simulation model is illustrated in the upper
part of each of FIGS. 7 to 10. As illustrated in each
drawing, the simulation model is based on the assumption
that a heat pipe method is used to perform cooling, and a
large number of heat pipes 16 are provided on a second
30 surface 15 which is opposite the first surface 14 of the
base 12. The first surface 14 as the module mounting
surface is divided into nine blocks, and the blocks are
numbered from (1) to (9). Blocks (1) to (3) correspond to

20
the first section 41 in FIGS. 5 and 6. Blocks (4) and (7)
correspond to the second section 42 in FIGS. 5 and 6.
Blocks (5) and (8) correspond to the third section 43 in
FIGS. 5 and 6. Blocks (6) and (9) correspond to the fourth
5 section 44 in FIGS. 5 and 6. Note that blocks (1), (4),
and (7) are blocks on the upper side with respect to
gravity, and blocks (3), (6), and (9) are blocks on the
lower side with respect to gravity.
[0055] In addition, a rectangular parallelepiped box in
10 each block illustrated in the upper part of FIGS. 7 to 10
is a heating element that indicates a module. FIG. 7
assumes a three-level converter main circuit, where all
blocks are filled with module boxes. Meanwhile, FIGS. 8 to
10 each assume a two-level converter main circuit, and no
15 module is placed in some blocks. FIG. 7 corresponds to the
second exemplary arrangement illustrated in FIG. 6, and FIG.
8 corresponds to the first exemplary arrangement
illustrated in FIG. 5. In addition, a numerical value
shown in each block represents the magnitude of current
20 flowing through a module placed in a corresponding block.
As illustrated in the drawings, the present simulation is
based on the assumption that a current flowing through the
module of the inverter main circuit and a current flowing
through the module of the converter main circuit are equal.
25 Furthermore, in the three-level converter main circuit, it
is assumed that a current flowing through the outer element
is 1/2 of a current flowing through the inner element.
[0056] Furthermore, in the lower parts of FIGS. 7 to 10,
temperature rise values observed after a certain current
30 flows through the blocks having the same initial
temperature are represented as numerical values. Note that
in FIGS. 7 to 10, a current flowing through the converter
main circuit and a current flowing through the inverter

21
main circuit are equal.
[0057] The following can be seen from the simulation
results illustrated in FIGS. 7 to 10.
(i) Blocks (1), (4), and (7) have been compared with
5 blocks (3), (6), and (9) in each of FIGS. 7 and 8. Blocks
(4) and (7) in FIG. 9 have been compared with blocks (6)
and (9) in FIG. 10. In addition, blocks (6) and (9) in FIG.
9 have been compared with blocks (4) and (7) in FIG. 10.
As a result, it can be seen that the cooling efficiency is
10 higher on the upper side.
(ii) Comparison between FIG. 9 and FIG. 10 shows that
the cooling efficiency in FIG. 10 is higher on average.
This is partially due to the result set forth in (i) above.
(iii) In FIGS. 9 and 10, temperature is highest at a
15 heating element (block (9) in FIG. 9, and block (7) in FIG.
10) located downstream and farthest from the non-mounting
portion.
(iv) Among FIGS. 8 to 10, a difference ΔT in heating
element temperature is smallest in FIG. 8 (ΔT=Tmax20 Tmin=10.7K: difference between (9) and (2)).
(v) Among FIGS. 8 to 10, the maximum value Tmax of
increase in cooler temperature in the converter main
circuit is smallest in FIG. 8 (FIG. 8: Tmax=76.7K, FIG. 9:
Tmax=82.6K, and FIG. 10: Tmax=79.2K).
25 [0058] Based on the above results, the arrangement
configuration of FIG. 8 is adopted in the first embodiment.
When a two-level converter main circuit is used as the
converter main circuit, no module is mounted in the third
section 43, and the main circuit elements of the converter
30 are arranged in sections other than the third section 43,
that is, the second section 42 and the fourth section 44,
as described above.
[0059] As described above, the power conversion

22
apparatus according to the first embodiment includes the
first switching elements and the second switching elements.
The first switching elements are modularized in units of
one or more elements to form first modules. The second
5 switching elements are modularized in units of one or more
elements to form second modules. The first and second
modules are mounted on a first surface that is a module
mounting surface of a base of the cooler. The first
modules are arranged in the first direction on the first
10 surface. The second modules are arranged such that two or
more second modules are continuously arranged in the second
direction orthogonal to the first direction on the first
surface. As a result, the cooling efficiency can be
improved in the configuration in which the modules of both
15 the inverter main circuit and the converter main circuit
are cooled by the common cooler.
[0060] In addition, mainstream drive systems of electric
vehicles include “truck control” and “collective control”.
In the “truck control”, four motors for driving electric
20 vehicles are mounted on a truck and driven in twos. In the
“collective control”, four motors for driving electric
vehicles are collectively driven. In the related art, a
system configuration for the “truck control” is greatly
different from a system configuration for the “collective
25 control”, so that it has been necessary to individually
design the configuration of the main conversion device for
each drive system. In contrast, the power conversion
apparatus according to the first embodiment can reduce
individual design changes to a required minimum even if the
30 drive system is changed. In addition, since the present
embodiment has adopted a configuration in which the modules
of both the inverter main circuit and the converter main
circuit are cooled by the common cooler, it is not

23
necessary to design the power conversion apparatus in such
a way as to increase the distance between a cooler on the
windward side (for example, a converter cooler) and a
cooler on the leeward side (for example, an inverter
5 cooler) as in the related art. As a result, the length of
the electric vehicle in a traveling direction can be
shortened, and the main conversion device can be downsized.
[0061] Second Embodiment.
In a second embodiment, a description will be given of
10 a connection form of main circuit wires for further
improving the cooling performance in addition to the
effects of the first embodiment. FIG. 11 is a first
diagram for describing a configuration of a main part in
the second embodiment. FIG. 11 illustrates a configuration
15 in which the modules 42a and 44a in the standard package
illustrated in FIG. 5 and the filter capacitor 30 are
electrically connected by a laminated bus bar 18 that is a
main circuit wire. Furthermore, FIG. 12 is a second
diagram for describing the configuration of the main part
20 in the second embodiment. FIG. 12 illustrates a
configuration in which the modules 42e, 43e, and 44e in the
standard package illustrated in FIG. 6 and the filter
capacitors 30P and 30N are electrically connected by a
laminated bus bar 19 that is a main circuit wire.
25 Furthermore, in FIGS. 11 and 12, the same or equivalent
components as those described in the first embodiment are
denoted by the same reference numerals, and redundant
description is appropriately omitted. Note that each main
circuit wire includes a wire portion through which a
30 direct-current component of switching current flows and a
wire portion through which an alternating-current component
of the switching current flows, but for the sake of
simplicity, only the wire portion through which the direct-

24
current component of the switching current flows is
illustrated in each of FIGS. 11 and 12.
[0062] The cooler 11 includes a plurality of the heat
pipes 16 and a plurality of fins 17. The heat pipes 16
5 project from the second surface 15 of the base 12 and are
inclined upward. The fins 17 have a rectangular flat
plate-like shape, and are fixed to the plurality of heat
pipes 16. That is, the heat pipes 16 are arranged in a
matrix on the second surface 15 of the base 12 such that
10 the heat pipes 16 project from the second surface 15 and
are inclined upward at a certain angle to a line
perpendicular to the second surface 15 of the base 12.
Each fin 17 has a plurality of through holes, and the heat
pipes 16 are inserted into the through holes. Note that
15 although FIGS. 11 and 12 each illustrate a case where the
number of the heat pipes 16 is six and the number of the
fins 17 is eight as an example, the configuration is not
limited to thereto.
[0063] In FIGS. 11 and 12, an x-axis represents a
20 direction in which cooling air flows, which is the first
direction described above. A y-axis represents the abovedescribed second direction orthogonal to the first
direction. A z-axis represents a third direction
orthogonal to both the first and second directions.
25 Terminals of each module extend in the third direction, and
terminals of each capacitor extend in the second direction.
Note that the arrangements of the capacitors illustrated in
FIGS. 11 and 12 are examples, and the arrangement of the
capacitors is not limited to these arrangements. The
30 terminals of each capacitor may extend in a direction other
than the second direction.
[0064] In FIG. 11, the filter capacitor 30 and the
modules 42a and 44a are electrically connected by the

25
laminated bus bar 18 having an L-shaped cross section.
Furthermore, in FIG. 12, the filter capacitors 30P and 30N
and the modules 42e, 43e, and 44e are electrically
connected by the laminated bus bar 19 having an L-shaped
5 cross section. The laminated bus bars 18 and 19 are parts
in which a thin metal plate and an insulator are integrally
covered with a laminate material. FIG. 11 illustrates a
first conductor 18a and a second conductor 18b each formed
as a thin metal plate. FIG. 12 illustrates a first
10 conductor 19a, a second conductor 19b, and a third
conductor 19c each formed as a thin metal plate. Note that
a laminated bus bar not covered with a laminate material
may be used instead of the laminated bus bars 18 and 19.
Furthermore, the cases where the laminated bus bars 18 and
15 19 each have an L-shaped cross section have been
illustrated in FIGS. 11 and 12 as an example, but this is
not a limitation. The cross sections of the laminated bus
bars 18 and 19 may be in a shape other than an L-shape.
[0065] In FIG. 11, when the switching elements of the
20 modules 42a and 44a perform switching operation, a
switching current flows through the first conductor 18a and
the second conductor 18b included in the laminated bus bar
18. Furthermore, in FIG. 12, when the switching elements
of the modules 42e and 43e perform switching operation, a
25 switching current flows through the first conductor 19a and
the second conductor 19b included in the laminated bus bar
19. Furthermore, when the switching elements of the
modules 43e and 44e perform switching operation, a
switching current flows through the second conductor 19b
30 and the third conductor 19c included in the laminated bus
bar 19. These switching currents serve as reciprocating
currents flowing in opposite directions at the same time as
illustrated in the drawings. Therefore, magnetic flux

26
generated around the laminated bus bars 18 and 19 will be
canceled by the reciprocating currents. Furthermore, since
the elements are arranged in such a way as to minimize an
inductance loop in each of FIGS. 11 and 12, main circuit
5 inductance can be reduced.
[0066] As described above, according to the power
conversion apparatus in the second embodiment, the above
characteristics enable a reduction in surge voltage to be
generated at the time of switching the main circuit
10 elements. Furthermore, the three-level configuration
illustrated in FIG. 12 is also advantageous in that a
snubber circuit is not necessary. In addition, in a case
where the main circuit elements are arranged in parallel,
it is also possible to obtain the effect of equalizing the
15 values of currents flowing through the elements arranged in
parallel. Moreover, a reduction in surge voltage enables
switching speed to be increased. An increase in switching
speed is equivalent to an increase in the speed of turning
off the switching operation, and can be achieved by a
20 reduction in resistance. A reduction in resistance enables
heat loss to be reduced. Therefore, the cooling
performance can be improved.
[0067] Note that the configuration illustrated in each
of the above embodiments shows an example of the subject
25 matter of the present invention, and it is possible to
combine the configuration with another technique that is
publicly known, and is also possible to omit or change part
of the configuration without departing from the gist of the
present invention.
30
Reference Signs List
[0068] 1 overhead line; 2 current collector; 3 wheel;
4 rail; 6 transformer; 8 contactor; 11 cooler; 12 base;

27
14 first surface; 15 second surface; 16 heat pipe; 17
fin; 18, 19 laminated bus bar; 18a, 19a first conductor;
18b, 19b second conductor; 19c third conductor; 20, 20a,
20b converter main circuit; 30, 30P, 30N filter
5 capacitor; 40, 40a inverter main circuit; 41 first
section; 41a, 41b, 41c, 41d, 41e, 41f, 42a, 42b, 42c, 42d,
42e, 42f, 42g, 42h, 43e, 43f, 43g, 43h, 44a, 44b, 44c, 44d,
44e, 44f, 44g, 44h module; 42 second section; 43 third
section; 44 fourth section; 80 motor; 100 power
10 conversion apparatus; UD1A, UD1B, UD2A, UD2B, VD1A, VD1B,
VD2A, VD2B diode; UPC, VPC, UNC, VNC, UPI, VPI, WPI, UNI,
VNI, WNI, UNC1, UNC2, UNC3, UNC4, UNC3A, UNC3B, UNC4A,
UNC4B, UNI1, UNI2, UPC1, UPC2, UPC3, UPC4, UPC1A, UPC1B,
UPC2A, UPC2B, UPI1, UPI2, VNC1, VNC2, VNC3, VNC4, VNC3A,
15 VNC3B, VNC4A, VNC4B, VPC1, VPC2, VPC3, VPC4, VPC1A, VPC1B,
VPC2A, VPC2B, VPI1, VNI1, VPI2, VNI2, WNI1, WNI2, WPI1,
WPI2 switching element.

28
We Claim :
1. A power conversion apparatus comprising:
a converter main circuit to convert AC power into DC
power;
5 an inverter main circuit to convert, into AC power,
the DC power obtained by conversion by the converter main
circuit; and
a cooler to cool first switching elements included in
the inverter main circuit and second switching elements
10 included in the converter main circuit, the cooler being
used as a common cooler, wherein
the first switching elements are modularized in units
of one or more elements to form first modules,
the second switching elements are modularized in units
15 of one or more elements to form second modules,
the first and second modules are mounted on a first
surface that is a module mounting surface of a base of the
cooler,
the first modules are arranged in a first direction on
20 the first surface, and
the second modules are arranged such that two or more
second modules are continuously arranged in a second
direction orthogonal to the first direction on the first
surface.
25
2. The power conversion apparatus according to claim 1,
wherein
the second direction is a direction of cooling air
that flows into and out of the cooler.
30
3. The power conversion apparatus according to claim 1 or
2, wherein
the first modules are each a two-element module

29
configured such that two of the first switching elements
are housed in one module, and
the second modules are each a two-element module
configured such that two of the second switching elements
5 are housed in one module.
4. The power conversion apparatus according to any one of
claims 1 to 3, wherein
the first modules are arranged in a first section of
10 the first surface,
the second modules are arranged in at least a second
section and a fourth section among the second section, a
third section, and the fourth section of the first surface,
and
15 the second, third, and fourth sections are adjacent to
the first section along the first direction, and are
arranged in order of the second, third, and fourth sections
along the second direction.
20 5. The power conversion apparatus according to claim 4,
wherein
the converter main circuit is a two-level converter
main circuit,
the inverter main circuit is a two-level inverter main
25 circuit, and
none of the second modules is mounted in the third
section.
6. The power conversion apparatus according to claim 5,
30 wherein
the first modules are arranged in the first section,
the first modules operating as first-phase, second-phase,
and third-phase switching elements of the inverter main

30
circuit,
the second modules are arranged in the second section,
the second modules operating as first-phase switching
elements of the converter main circuit, and
5 the second modules are arranged in the fourth section,
the second modules operating as second-phase switching
elements of the converter main circuit.
7. The power conversion apparatus according to claim 4,
10 wherein
the converter main circuit is a three-level converter
main circuit,
the inverter main circuit is a two-level inverter main
circuit, and
15 the second modules are mounted in the third section.
8. The power conversion apparatus according to claim 7,
wherein
the first modules are arranged in the first section,
20 the first modules operating as first-phase, second-phase,
and third-phase switching elements of the inverter main
circuit,
the second modules are arranged in the second section,
the second modules operating as upper potential-side outer
25 elements of the converter main circuit,
the second modules are arranged in the third section,
the second modules operating as inner elements of the
converter main circuit, and
the second modules are arranged in the fourth section,
30 the second modules operating as lower potential-side outer
elements of the converter main circuit.
9. The power conversion apparatus according to any one of

31
claims 5 to 8, comprising:
a filter capacitor to smooth DC voltage output from
the converter main circuit, wherein
terminals of the first and second modules extend in a
5 third direction orthogonal to each of the first and second
directions,
the terminals of the first and second modules and a
terminal of the filter capacitor are electrically connected
by a bus bar, and
10 a reciprocating current flows between a plurality of
conductors included in the bus bar.