Patent Publication Number: US-2022215997-A1

Title: Power Conversion Device

Description:
TECHNICAL FIELD 
     The present disclosure relates to a power conversion device and a method for manufacturing the power conversion device. 
     BACKGROUND ART 
     In general, the power conversion device includes electronic components such as a switching element, a rectifier element, and a magnetic component. The electronic components generate heat with operation of the power conversion device. The heat generated in the electronic components is transferred to a cooling body through a heat dissipation path, and is dissipated from the cooling body. In this way, temperatures of the electronic components are suppressed so as to be less than or equal to an allowable temperature of each electronic component. 
     In recent years, a calorific value of the electronic components mounted on the power conversion devices increases with increasing demand for downsizing and higher output of the power conversion device. For this reason, it is strongly required that heat dissipation of the power conversion device is enhanced. 
     As an example of the power conversion device, Japanese Patent No. 4231626 (PTL 1) describes an automobile motor drive device. In the automobile motor drive device described in PTL 1, among the electronic components accommodated in a housing, a power conversion element that is a high-heat generating component is disposed on a bottom surface of the housing. The bottom surface of the housing on which the power conversion element is disposed is integrated with the cooling body. A printed board on which a control element is mounted is fixed to a plate-shaped substrate installation portion formed inside the housing. The heat generated by the control element is transferred to the housing through the plate-shaped substrate installation portion. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Patent No. 4231626 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the automobile motor drive device described in PTL 1, the power conversion element that is the high-heat generating component is disposed on the bottom surface of the housing. Consequently, when a number of high-heat generating components increases due to an increase in the output of the power conversion device, it is necessary to increase an area of the bottom surface of the housing in order to dispose the high-heat generating components. As a result, a size of the power conversion device increases. Furthermore, in the automobile motor drive device described in PTL 1, the heat generated by the control element is transferred to the housing through the plate-shaped substrate installation portion. Consequently, a heat dissipation path becomes long. As a result, the heat dissipation is degraded. 
     The present disclosure has been made in view of the above problems, and an object of the present disclosure is to provide a power conversion device capable of suppressing an increase in a bottom area of the power conversion device and improving the heat dissipation, and a method for manufacturing the power conversion device. 
     Solution to Problem 
     A power conversion device according to an aspect of the present disclosure includes an electronic component, a first substrate, a first cooling body, a second substrate, a second cooling body, a third substrate, and a third cooling body. The electronic component includes a first component, a second component, and a third component. The first substrate includes a first principal surface on which the first component of the electronic component is mounted and a second principal surface opposite to the first principal surface. The first cooling body is thermally connected to the second principal surface of the first substrate. The second substrate includes a third principal surface on which the second component of the electronic component is mounted and a fourth principal surface opposite to the third principal surface. The second cooling body is thermally connected to the fourth principal surface of the second substrate. The third substrate includes a fifth principal surface on which the third component of the electronic component is mounted and a sixth principal surface opposite to the fifth principal surface. The third cooling body is thermally connected to the sixth principal surface of the third substrate. The second cooling body extends in a direction from the second principal surface toward the first principal surface of the first substrate. The third cooling body extends in the direction from the second principal surface toward the first principal surface of the first substrate. 
     Advantageous Effects of Invention 
     According to the power conversion device of the present disclosure, the electronic component is mounted not only on the first substrate but also on the second substrate and the third substrate. For this reason, even when the number of electronic components that are the high-heat generating components increases, the electronic components are mounted on the second substrate and the third substrate, whereby the first cooling body can be prevented from expanding. Consequently, it is possible to suppress the increase in the bottom area of the power conversion device. Furthermore, by mounting the electronic components on the second substrate and the third substrate, the heat dissipation path through which the heat generated by the electronic components mounted on the second substrate is transferred to the second cooling body can be shortened, and the heat dissipation path through which the heat generated by the electronic components mounted on the third substrate is transferred to the third cooling body can be shortened. Therefore, the heat dissipation can be improved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a circuit diagram of a power conversion device according to a first embodiment. 
         FIG. 2  is a perspective view schematically illustrating a configuration of the power conversion device of the first embodiment. 
         FIG. 3  is a perspective view schematically illustrating a configuration of a first printed board module of the power conversion device according to the first embodiment. 
         FIG. 4  is a perspective view schematically illustrating a configuration of a second printed board module of the power conversion device according to the first embodiment. 
         FIG. 5  is a perspective view schematically illustrating a configuration of a third printed board module of the power conversion device according to the first embodiment. 
         FIG. 6  is a sectional view taken along a line VI-VI in  FIG. 4 . 
         FIG. 7  is a sectional view corresponding to  FIG. 6  of a first modification of the power conversion device according to the first embodiment. 
         FIG. 8  is a sectional view taken along a line VIII-VIII in  FIG. 5 . 
         FIG. 9  is a sectional view corresponding to  FIG. 8  of a second modification of the power conversion device according to the first embodiment. 
         FIG. 10  is a flowchart illustrating a method for manufacturing the power conversion device of the first embodiment. 
         FIG. 11  is a perspective view illustrating electric connection between printed board modules of the power conversion device of the first embodiment. 
         FIG. 12  is a perspective view schematically illustrating a configuration of a third modification of the power conversion device according to the first embodiment. 
         FIG. 13  is a perspective view schematically illustrating a configuration of a fourth modification of the power conversion device according to the first embodiment. 
         FIG. 14  is a perspective view schematically illustrating a configuration of a power conversion device according to a second embodiment. 
         FIG. 15  is a perspective view schematically illustrating a configuration of a modification of the power conversion device according to the second embodiment. 
         FIG. 16  is a perspective view schematically illustrating a configuration of a power conversion device according to a third embodiment. 
         FIG. 17  is a perspective view schematically illustrating a configuration of a first printed board module of the power conversion device according to the third embodiment. 
         FIG. 18  is a perspective view schematically illustrating a configuration of a second printed board module of the power conversion device according to the third embodiment. 
         FIG. 19  is a perspective view schematically illustrating a configuration of a third printed board module of the power conversion device according to the third embodiment. 
         FIG. 20  is a perspective view schematically illustrating a configuration of a fourth printed board module of the power conversion device according to the third embodiment. 
         FIG. 21  is a perspective view schematically illustrating a configuration of a fifth printed board module of the power conversion device according to the third embodiment. 
         FIG. 22  is a perspective view schematically illustrating a configuration of a first modification of the power conversion device according to the third embodiment. 
         FIG. 23  is a perspective view schematically illustrating a configuration of a first printed board module in the first modification of the power conversion device of the third embodiment. 
         FIG. 24  is a perspective view schematically illustrating a configuration of a second printed board module in the first modification of the power conversion device of the third embodiment. 
         FIG. 25  is a perspective view schematically illustrating a configuration of a third printed board module in the first modification of the power conversion device of the third embodiment. 
         FIG. 26  is a perspective view schematically illustrating a configuration of a fourth printed board module in the first modification of the power conversion device of the third embodiment. 
         FIG. 27  is a perspective view schematically illustrating a configuration of a fifth printed board module in the first modification of the power conversion device of the third embodiment. 
         FIG. 28  is a perspective view schematically illustrating a configuration of a power conversion device according to a fourth embodiment. 
         FIG. 29  is a perspective view schematically illustrating a configuration of a power conversion device according to a fifth embodiment. 
         FIG. 30  is a perspective view schematically illustrating a configuration of a fifth modification of the power conversion device according to the first embodiment. 
         FIG. 31  is a perspective view schematically illustrating a configuration of a second modification of the power conversion device according to the third embodiment. 
         FIG. 32  is a circuit diagram illustrating a sixth modification of the power conversion device of the first embodiment. 
         FIG. 33  is a perspective view schematically illustrating a configuration of a power conversion device according to a sixth embodiment. 
         FIG. 34  is a circuit diagram illustrating the power conversion device of the sixth embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an exemplary embodiment will be described with reference to the drawings. In the following description, the same or corresponding parts are denoted by the same reference numerals, and overlapping description will not be repeated. 
     First Embodiment 
       FIG. 1  is a circuit diagram illustrating an example of a power conversion device according to a first embodiment. For example, the power conversion device illustrated in the circuit diagram of  FIG. 1  is a DC-DC converter that is mounted on an electric vehicle, converts an input voltage of a lithium ion battery of DC 100 V to 300 V into voltage of DC 12 V to 15 V, and outputs the voltage to charge a lead storage battery. The power conversion device illustrated in the circuit diagram of  FIG. 1  includes an input capacitor  1 , an inverter circuit unit  11  including four switching elements  2   a,    2   b,    2   c,    2   d,  a transforming unit  12  including transformers  3 ,  4 , a rectifier circuit unit  13  including eight rectifier elements  5   a,    5   b,    5   c,    5   d,    5   e,    5   f,    5   g,    5   h,  a smoothing circuit unit  14  including reactors  6 ,  7  and a smoothing capacitor  8 , an input terminal  9 , an output terminal  10 , and a control circuit unit  15 . Each electronic component indicated by a circuit symbol in  FIG. 1  may have an arbitrary number of a series configuration or a parallel configuration. 
     Each of switching elements  2   a,    2   b,    2   c,    2   d  is a transistor, a metal oxide semiconductor field effect transistor (MOSFET), an insulated gate bipolar transistor (IGBT), or the like. Rectifier element  5  is a power semiconductor element such as a diode, the MOSFET, or a thyristor. 
     In the power conversion device illustrated in the circuit diagram of  FIG. 1 , control circuit unit  15  executes switching control of inverter circuit unit  11  to convert a DC voltage input from input terminal  9  into an AC voltage. Transforming unit  12  converts the AC voltage converted by inverter circuit unit  11  into an arbitrary voltage by a winding ratio of transformers  3 ,  4 . Transformers  3 ,  4  electrically insulate input terminal  9  and output terminal  10  from each other. Rectifier circuit unit  13  converts the AC voltage supplied from transformers  3 ,  4  into the DC voltage again. Smoothing circuit unit  14  smooths the DC voltage converted by rectifier circuit unit  13  and stabilizes an output voltage. 
     In the power conversion device illustrated in the circuit diagram of  FIG. 1 , four switching elements  2   a,    2   b,    2   c,    2   d,  transformers  3 ,  4 , eight rectifier elements  5   a,    5   b,    5   c,    5   d,    5   e,    5   f,    5   g,    5   h,  and reactors  6 ,  7  are high-heat generating components. It is necessary to dissipate heat generated by these high-heat generating components and to make temperatures of the high-heat generating components less than or equal to an allowable temperature of each component. For example, the allowable temperature of each component is greater than or equal to 100° C. and less than or equal to 120° C. 
     Because a large current flows through wiring electrically connecting these high-heat generating components, Joule heat is generated in the wiring by electric resistance of the wiring itself. Consequently, the wiring itself that electrically connects the high-heat generating component also generates a high calorific value. Consequently, when the high-heat generating component is electrically connected by a circuit pattern formed on or in a printed board, it is necessary to dissipate the heat generated by the circuit pattern to make the printed board less than or equal to the allowable temperature. The allowable temperature of the printed board is 100° C. or more and 120° C. or less. 
       FIG. 2  is a perspective view illustrating a power conversion device  100  of the first embodiment.  FIG. 3  is a perspective view illustrating a first printed board module  71  included in power conversion device  100 .  FIG. 4  is a perspective view illustrating a second printed board module  72  included in power conversion device  100 .  FIG. 5  is a perspective view illustrating a third printed board module  73  included in power conversion device  100 . 
     As illustrated in  FIG. 2 , power conversion device  100  of the first embodiment includes an external cooling body  21 , first printed board module  71 , second printed board module  72 , and third printed board module  73 . First printed board module  71 , second printed board module  72 , and third printed board module  73  are electrically connected to one another by a harness  86  or the like as described later with reference to  FIG. 11 . 
     As illustrated in  FIGS. 2 to 5 , power conversion device  100  includes external cooling body  21 , a first printed board  31 , a first insulating member  41 , a first cooling body  51 , a first fixing member  61 , a second printed board  32 , a second insulating member  42 , a second cooling body  52 , a second fixing member  62 , a third printed board  33 , a third insulating member  43 , a third cooling body  53 , a third fixing member  63 , and an electronic component. External cooling body  21  includes a principal surface  21   a.    
     First printed board (first substrate)  31  includes a front surface (first principal surface) S 1  on which the electronic component (first component) is mounted and a back surface (second principal surface) S 2  facing first cooling body  51 . Second principal surface S 2  is opposite to first principal surface S 1 . First insulating member  41  is disposed between second principal surface S 2  of first printed board  31  and first cooling body  51 . First cooling body  51  is thermally connected to second principal surface S 2  of first printed board  31  through first insulating member  41 . First cooling body  51  is thermally coupled to external cooling body  21 . External cooling body  21  is thermally connected to first cooling body  51 . First cooling body  51  is thermally connected to second principal surface S 2  of first printed board  31 . First fixing member  61  is configured to fix first printed board  31  to first cooling body  51 . 
     Second printed board (second substrate)  32  includes a front surface (third principal surface) S 3  on which the electronic component (second component) is mounted and a back surface (fourth principal surface) S 4  facing second cooling body  52 . Fourth principal surface S 4  is opposite to third principal surface S 3 . Second insulating member  42  is disposed between fourth principal surface S 4  of second printed board  32  and second cooling body  52 . Second cooling body  52  is thermally connected to fourth principal surface S 4  of second printed board  32 . Second cooling body  52  is thermally connected to fourth principal surface S 4  of second printed board  32  through second insulating member  42 . Second cooling body  52  is configured to extend vertically with a surface connected to a surface  51   a  of first cooling body  51  facing first printed board  31  as a bottom surface. Second cooling body  52  extends from second principal surface S 2  of first printed board  31  toward first principal surface S 1 . Second cooling body  52  is thermally connected to first cooling body  51 . Second fixing member  62  is configured to fix second printed board  32  to second cooling body  52 . 
     Third printed board (third substrate)  33  includes a front surface (fifth principal surface) S 5  on which an electronic component (third component) is mounted and a back surface (sixth principal surface) S 6  facing third cooling body  53 . Sixth principal surface S 6  is opposite to fifth principal surface S 5 . Third insulating member  43  is disposed between sixth principal surface S 6  of third printed board  33  and third cooling body  53 . Third cooling body  53  is thermally connected to sixth principal surface S 6  of third printed board  33  through third insulating member  43 . Third cooling body  53  is thermally connected to sixth principal surface S 6  of third printed board  33 . Third cooling body  53  is configure to extend vertically with the surface connected to surface  51   a  of first cooling body  51  as the bottom surface. Third cooling body  53  extends from second principal surface S 2  of first printed board  31  toward first principal surface S 1 . Third cooling body  53  is thermally connected to first cooling body  51 . Third fixing member  63  is configured to fix third printed board  33  to third cooling body  53 . 
     The vertical direction is a direction substantially perpendicular to principal surface  21   a  of external cooling body  21 . First cooling body  51  constitutes the bottom surface of the support body of power conversion device  100 . Second cooling body  52  and third cooling body  53  constitute side surfaces of the support body of power conversion device  100 . 
     External cooling body  21  has thermal conductivity of 1.0 W/(m·K) or more, preferably 10.0 W/(m·K), and more preferably 100.0 W/(m·K) or more. External cooling body  21  is formed of a metal material such as copper, iron, aluminum, an iron alloy, and an aluminum alloy, resin having high thermal conductivity, or the like. External cooling body  21  may include a pipe passing cooling water therethrough. External cooling body  21  may include a dissipation fin or the like in order to promote heat dissipation to the surrounding atmosphere. 
     Each of first printed board  31 , second printed board  32 , and third printed board  33  may have a circuit pattern (not illustrated) formed on a surface or inside thereof. The circuit pattern has a thickness greater than or equal to 1 μm and less than or equal to 2000 μm. The circuit pattern is formed of a conductive material. For example, the circuit pattern is formed of copper, nickel, gold, aluminum, silver, tin, or an alloy thereof. For example, each of first printed board  31 , second printed board  32 , and third printed board  33  is made of a glass fiber-reinforced epoxy resin, a phenol resin, polyphenylene sulfide (PPS), or polyether ether ketone (PEEK). In other words, each of first printed board  31 , second printed board  32 , and third printed board  33  may be made of a material generally having low thermal conductivity. That is, each of first printed board  31 , second printed board  32 , and third printed board  33  may be a general-purpose printed board. First printed board  31 , second printed board  32 , and third printed board  33  may be made of a ceramic such as aluminum oxide, aluminum nitride, and silicon carbide. 
     Each of first insulating member  41 , second insulating member  42 , and third insulating member  43  has electric insulation. Each of first insulating member  41 , second insulating member  42 , and third insulating member  43  may have elasticity. Each of first insulating member  41 , second insulating member  42 , and third insulating member  43  may have a Young&#39;s modulus greater than or equal to 1 MPa and less than or equal to 100 MPa. Each of first insulating member  41 , second insulating member  42 , and third insulating member  43  has thermal conductivity greater than or equal to 0.1 W/(m·K), preferably greater than or equal to 1.0 W/(m·K). For example, each of first insulating member  41 , second insulating member  42 , and third insulating member  43  may be made of a rubber material such as silicon or urethane, a resin material such as acrylonitrile butadiene styrene (ABS), polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), or phenol, a polymer material such as polyimide, a ceramic material such as alumina or aluminum nitride, or a phase change material mainly made of silicon. Each of first insulating member  41 , second insulating member  42 , and third insulating member  43  may be made of a material in which particles such as aluminum oxide, aluminum nitride, and boron nitride are mixed in a silicon resin. 
     Each of first cooling body  51 , second cooling body  52 , and third cooling body  53  has the thermal conductivity greater than or equal to 1.0 W/(m·K), preferably greater than or equal to 10.0 W/(m·K), more preferably greater than or equal to 100.0 W/(m·K). Each of first cooling body  51 , second cooling body  52 , and third cooling body  53  is made of a metal material such as copper, iron, aluminum, an iron alloy, or an aluminum alloy, or resin having the high thermal conductivity. Alternatively, first cooling body  51 , second cooling body  52 , and third cooling body  53  may be electrically connected to other members such that their respective potentials become the same potential as the ground. Each of second cooling body  52  and third cooling body  53  is connected to and fixed to first cooling body  51  directly or through another member. Each of second cooling body  52  and third cooling body  53  is thermally connected to first cooling body  51 . 
     A heat conductive member (first heat conductive member) HC 1  such as heat conductive grease, a heat conductive sheet, or a heat conductive adhesive may be disposed on a contact surface between first cooling body  51  and second cooling body  52  and a contact surface between first cooling body  51  and third cooling body  53 . Heat conductive member (first heat conductive member) HC 1  includes at least one of the heat conductive grease, the heat conductive sheet, and the heat conductive adhesive. First cooling body  51  is thermally connected to each of second cooling body  52  and third cooling body  53  through heat conductive member (first heat conductive member) HC 1 . 
     First cooling body  51  may be in surface contact with external cooling body  21 . When first cooling body  51  and external cooling body  21  are brought into surface contact with each other, the heat conductive member such as the thermal conductive grease, the thermal conductive sheet, or the thermal conductive adhesive may be disposed on a contact surface between first cooling body  51  and external cooling body  21 . 
     Because first cooling body  51  and external cooling body  21  are thermally coupled to each other, the heat dissipation to the heat generated in first printed board module  71  is higher than the heat dissipation to the heat generated in second printed board module  72  and third printed board module  73 . Consequently, the electronic components disposed in first printed board module  71 , second printed board module  72 , and third printed board module  73  may be replaced, but preferably the electronic components (high-heat generating components) that generate a particularly high calorific value is disposed in first printed board module  71 . In the first embodiment, assuming that each of switching elements  2   a,    2   b,    2   c,    2   d  is particularly the high-heat generating component, each of switching elements  2   a,    2   b,    2   c,    2   d  is disposed in first printed board module  71 . 
     With reference to  FIGS. 3 to 10 , an example of first printed board module  71 , second printed board module  72 , and third printed board module  73  will be described below. 
     As illustrated in  FIG. 3 , first printed board module  71  includes first printed board  31 , first insulating member  41 , first cooling body  51 , first fixing member  61 , and the electronic component (first component). The electronic component (first component) is mounted on first printed board  31 . The electronic component (first component) is each of switching elements  2   a,    2   b,    2   c,    2   d  that are particularly high-heat generating components. First insulating member  41  is provided between first printed board  31  and first cooling body  51 . First insulating member  41  is preferably in surface contact with first printed board  31  and first cooling body  51 . First fixing member  61  fixes first printed board  31  to first cooling body  51 . 
     Input capacitor  1  and switching elements  2   a,    2   b,    2   c,    2   d  are mounted on a surface  31   a  of first printed board  31  opposite to the surface facing first cooling body  51 . Input terminal  9  (not illustrated) is mounted on surface  31   a.  Other electronic components may be mounted on surface  31   a.  Other electronic components may be mounted on the surface of first printed board  31  facing first cooling body  51 . The surface of first printed board  31  facing first cooling body  51  corresponds to second principal surface S 2 . Surface  31   a  of first printed board  31  opposite to the surface facing first cooling body  51  corresponds to first principal surface S 1 . 
     As illustrated in  FIG. 4 , second printed board module  72  includes second printed board  32 , second insulating member  42 , second cooling body  52 , second fixing member  62 , and the electronic component (second component). The electronic component (second component) is mounted on second printed board  32 . The electronic components (second components) are, in particular, transformers  3 ,  4  and rectifier elements  5   a,    5   b,    5   c,    5   d,    5   e,    5   f,    5   g,    5   h,  which are the high-heat generating components. Second insulating member  42  is provided between fourth principal surface S 4  of second printed board  32  and second cooling body  52 . Second insulating member  42  is preferably in surface contact with second printed board  32  and second cooling body  52 . Second fixing member  62  fixes second printed board  32  to second cooling body  52 . 
     Rectifier elements  5   a,    5   b,    5   c,    5   d,    5   e,    5   f,    5   g,    5   h,  and transformers  3 ,  4  are mounted on surface  32   a  of second printed board  32  opposite to the surface facing second cooling body  52 . Other electronic components may be mounted on surface  32   a.  Other electronic components may be mounted on the surface of second printed board  32  facing second cooling body  52 . The surface of second printed board  32  facing second cooling body  52  corresponds to fourth principal surface S 4 . Surface  32   a  of second printed board  32  opposite to the surface facing second cooling body  52  corresponds to third principal surface S 3 . 
       FIG. 6  is a sectional view taken along a line VI-VI in  FIG. 4 . As illustrated in  FIG. 6 , an upper core  81  and a lower core  82  are in contact with each other and magnetically coupled to each other in a hole made in second printed board  32 . Coils  3   a,    3   b,    3   c  and coils  4   a,    4   b,    4   c  in  FIG. 1  are formed on second printed board  32  by a wiring pattern (not illustrated). Transformer  3  is formed by upper core  81 , lower core  82 , and coils  3   a,    3   b,    3   c  in  FIG. 1 . Transformer  4  is formed by upper core  81 , lower core  82 , and coils  4   a,    4   b,    4   c  in  FIG. 1 . 
     For example upper core  81  and lower core  82  are ferrite cores such as manganese-zinc (Mn—Zn)-based ferrite cores or nickel-zinc (Ni—Zn)-based ferrite cores. Upper core  81  and lower core  82  may be amorphous cores or eye-dust cores. 
     Lower core  82  is provided in a groove  52   a  formed in second cooling body  52 . A lower surface of lower core  82  is preferably in contact with second cooling body  52 . A heat conductive member such as heat conductive grease, a heat conductive sheet, or a heat conductive adhesive may be disposed between the lower surface of lower core  82  and second cooling body  52 . Lower core  82  may be fixed to second cooling body  52 . Upper core  81  may be fixed to lower core  82  using an adhesive. An insulating member (not illustrated) may be disposed between lower core  82  and second cooling body  52 . 
     As illustrated in  FIG. 6 , preferably upper core  81  and lower core  82  are pressed against second cooling body  52  by a pushing spring  83 . Pushing spring  83  is fixed onto second printed board  32  using a screw (not illustrated) or the like. In this case, upper core  81  and lower core  82  are fixed to second cooling body  52 , so that positional displacement can be prevented, and damage to upper core  81  and lower core  82  due to vibration can be prevented. An insulating member (not illustrated) may be disposed between upper core  81  and pushing spring  83 . 
     As illustrated in  FIG. 7 , upper core  81  and lower core  82  may be pressed against second cooling body  52  by a strut  84  and a pressing plate  85 . Pressing plate  85  is fixed to strut  84  so as to press upper core  81  against lower core  82 . Strut  84  is fixed to second printed board  32 . Strut  84  may pass through a hole (not illustrated) made in second printed board  32  to be fixed to second cooling body  52 . In this case, upper core  81  and lower core  82  are fixed to second cooling body  52 , so that positional displacement can be prevented, and damage to upper core  81  and lower core  82  due to vibration can be prevented. An insulating member (not illustrated) may be disposed between upper core  81  and pressing plate  85 . 
     As illustrated in  FIG. 5 , third printed board module  73  includes third printed board  33 , third insulating member  43 , third cooling body  53 , third fixing member  63 , and the electronic component (third component). The electronic component (third component) is mounted on third printed board  33 . The electronic components (third components) are particularly reactors  6 ,  7  that are high-heat generating components. Third insulating member  43  is provided between third printed board  33  and third cooling body  53 . Third insulating member  43  is preferably in surface contact with third printed board  33  and third cooling body  53 . Third fixing member  63  fixes third printed board  33  to third cooling body  53 . 
     Smoothing capacitor  8  and reactors  6 ,  7  are mounted on surface  33   a  of third printed board  33  opposite to a surface facing third cooling body  53 . Output terminal  10  (not illustrated) is mounted on surface  33   a.  Other electronic components may be mounted on surface  33   a.  Other electronic components may be mounted on the surface of third printed board  33  facing third cooling body  53 . The surface of third printed board  33  facing third cooling body  53  corresponds to sixth principal surface S 6 . Surface  33   a  of third printed board  33  opposite to the surface facing third cooling body  53  corresponds to fifth principal surface S 5 . 
       FIG. 8  is a sectional view taken along a line VIII-VIII in  FIG. 5 . As illustrated in  FIG. 8 , upper core  81  and lower core  82  are in contact with each other and magnetically coupled to each other in a hole made in third printed board  33 . Reactors  6 ,  7  are formed by a wiring pattern (not illustrated) formed on third printed board  33 , upper core  81 , and lower core  82 . 
     Lower core  82  is provided in a groove  53   a  formed in third cooling body  53 . The lower surface of lower core  82  is preferably in contact with third cooling body  53 . A heat conductive member such as heat conductive grease, a heat conductive sheet, or a heat conductive adhesive may be disposed between the lower surface of lower core  82  and third cooling body  53 . Lower core  82  may be fixed to third cooling body  53 . An insulating member (not illustrated) may be disposed between lower core  82  and third cooling body  53 . 
     As illustrated in  FIG. 8 , preferably upper core  81  and lower core  82  are pressed against third cooling body  53  by pushing spring  83 . Pushing spring  83  is fixed onto third printed board  33  using a screw (not illustrated) or the like. In this case, upper core  81  and lower core  82  are fixed to third cooling body  53 , so that the positional displacement can be prevented, and the damage to upper core  81  and lower core  82  due to the vibration can be prevented. An insulating member (not illustrated) may be disposed between upper core  81  and pushing spring  83 . 
     As illustrated in  FIG. 9 , upper core  81  and lower core  82  may be pressed against third cooling body  53  by strut  84  and pressing plate  85 . Pressing plate  85  is fixed to strut  84  so as to press upper core  81  against lower core  82 . Strut  84  is fixed to third printed board  33 . Strut  84  may pass through a hole (not illustrated) made in third printed board  33  to be fixed to third cooling body  53 . In this case, upper core  81  and lower core  82  are fixed to third cooling body  53 , so that the positional displacement can be prevented, and the damage to upper core  81 , lower core  82 , and the like due to the vibration can be prevented. An insulating member (not illustrated) may be disposed between upper core  81  and pressing plate  85 . 
     Control circuit unit  15  in  FIG. 1  may be mounted on one of first printed board  31 , second printed board  32 , and third printed board  33 . Control circuit unit  15  may be divided and mounted on at least two of first printed board  31 , second printed board  32 , and third printed board  33 . 
     With reference to  FIGS. 10 and 11 , a method for manufacturing power conversion device  100  of the first embodiment will be described below. 
     As illustrated in  FIGS. 10 and 11 , power conversion device  100  is manufactured through a preparation step S 100 , an assembly step S 200 , and a connection step S 300 . 
     The electronic components including the first component, the second component, and the third component, first printed board  31 , second printed board  32 , third printed board  33 , first cooling body  51 , second cooling body  52 , and third cooling body  53  are prepared in preparation step S 100 . 
     First printed board module  71 , second printed board module  72 , and third printed board module  73  are assembled in assembly step S 200 . First printed board module  71 , second printed board module  72 , and third printed board module  73  are electrically connected by harness  86 . That is, first printed board  31 , second printed board  32 , and third printed board  33  are electrically connected to one another. 
     Each of second printed board module  72  and third printed board module  73  is connected and fixed to first printed board module  71  in connection step S 300 . 
     In assembly step S 200 , each of first printed board module  71 , second printed board module  72 , and third printed board module  73  is manufactured through an electronic component mounting step, a printed board combination step, and a printed board fixing step. 
     The assembly step of first printed board module  71  will be described. In the electronic component mounting step, the electronic component (first component) is mounted on first principal surface S 1  of first printed board  31  by flow soldering, reflow soldering, or the like. First cooling body  51 , first insulating member  41 , and first printed board  31  on which the electronic component is mounted on surface  31   a  are combined in the printed board combination step. At this point, first cooling body  51  is thermally connected to second principal surface S 2  opposite to first principal surface S 1  of first printed board  31 . In the printed board fixing step, first printed board  31  is fixed to first cooling body  51  through first insulating member  41  by first fixing member  61 . 
     The assembly step of second printed board module  72  will be described. In the electronic component mounting step, the electronic component (second component) is mounted on third principal surface S 3  of second printed board  32  by flow soldering, reflow soldering, or the like. Second cooling body  52 , second insulating member  42 , second printed board  32  on which the electronic component is mounted on surface  32   a,  upper core  81 , and lower core  82  are combined in the printed board combination step. At this point, second cooling body  52  is thermally connected to fourth principal surface S 4  opposite to third principal surface S 3  of second printed board  32 . In the printed board fixing step, second printed board  32  is fixed to second cooling body  52  through second insulating member  42  by second fixing member  62 . 
     The assembly step of third printed board module  73  will be described. In the electronic component mounting step, the electronic component (third component) is mounted on fifth principal surface S 5  of third printed board  33  by flow soldering, reflow soldering, or the like. Third cooling body  53 , third insulating member  43 , third printed board  33  on which the electronic component is mounted on surface  33   a,  upper core  81 , and lower core  82  are combined in the printed board combination step. At this point, third cooling body  53  is thermally connected to sixth principal surface S 6  opposite to fifth principal surface S 5  of third printed board  33 . In the printed board fixing step, third printed board  33  is fixed to third cooling body  53  through third insulating member  43  by third fixing member  63 . 
     In assembly step S 200 , the electronic component (second component) and the electronic component (third component) are fixed to the grooves provided in second printed board  32  and third printed board  33 , respectively. 
     As illustrated in  FIG. 11 , second printed board module  72  and third printed board module  73  are electrically connected to first printed board module  71  by harness  86 . For example, harness  86  includes round hole terminals at both ends. A terminal block  87  is mounted on each of first printed board  31 , second printed board  32 , and third printed board  33 . First printed board  31 , second printed board  32 , and third printed board  33  are fixed to terminal block  87  while a screw (not illustrated) or the like is inserted into the round hole terminal of harness  86 , whereby each of second printed board module  72  and third printed board module  73  may be electrically connected to first printed board module  71 . 
     Terminal block  87  is preferably disposed such that a length of harness  86  is shortened. In other words, as illustrated in  FIG. 11 , preferably terminal block  87  is disposed such that a distance between two terminal blocks  87  connected by harness  86  is shortened. In this case, the electrical resistance of harness  86  can be reduced because the length of harness  86  is shortened. For this reason, Joule heat generated in harness  86  can be reduced. 
     In the connection step, second cooling body  52  included in second printed board module  72  and third cooling body  53  included in third printed board module  73  are connected and fixed to first cooling body  51  included in first printed board module  71  directly or through another member. In this case, each of second cooling body  52  and third cooling body  53  is disposed so as to extend from second principal surface S 2  of first printed board  31  toward first principal surface S 1 . First cooling body  51  is thermally coupled to external cooling body  21  by a method such as surface contact with external cooling body  21 . 
     In connection step S 300 , second cooling body  52  and third cooling body  53  are thermally connected to first cooling body  51 . 
     Effects of power conversion device  100  of the first embodiment will be described below. 
     According to power conversion device  100  of the first embodiment, the electronic components are mounted not only on first printed board  31  but also on second printed board  32  and third printed board  33 . For this reason, even when the number of electronic components that are the high-heat generating components increases, the electronic components are mounted on second printed board  32  and third printed board  33 , whereby the expansion of first cooling body  51  can be suppressed. Consequently, it is possible to suppress an increase in the bottom area of power conversion device  100 . The electronic components are mounted on second printed board  32  and third printed board  33 , so that the heat dissipation path through which the heat generated by the electronic components mounted on second printed board  32  is transferred to second cooling body  52  can be shortened, and the heat dissipation path through which the heat generated by the electronic components mounted on third printed board  33  is transferred to third cooling body  53  can be shortened. Therefore, the heat dissipation can be improved. 
     Power conversion device  100  of the first embodiment includes external cooling body  21  thermally connected to first cooling body  51 . A first heat dissipation path dissipating the heat to external cooling body  21  can be formed through first printed board  31 , first insulating member  41 , and first cooling body  51  as a heat dissipation path dissipating the heat generated by the circuit pattern formed on the surface or inside of first printed board  31  and the heat generated by switching elements  2   a,    2   b,    2   c,    2   d  that are the high-heat generating components mounted on first printed board  31 . For this reason, the heat dissipation of power conversion device  100  can be improved with respect to the heat generated in the circuit pattern formed on the surface or inside of first printed board  31  and the heat generated in the high-heat generating component mounted on first printed board  31 . As a result, power conversion device  100  of the first embodiment can operate with high output. 
     When first insulating member  41  is brought into surface contact with first printed board  31  and first cooling body  51 , the area of the contact surface between first insulating member  41  and first printed board  31  and the area of the contact surface between first insulating member  41  and first cooling body  51  can be widened, so that contact thermal resistance of the contact surface between first insulating member  41  and first printed board  31  and contact thermal resistance of the contact surface between first insulating member  41  and first cooling body  51  can be reduced to improve the heat dissipation of the first heat dissipation path. As a result, power conversion device  100  of the first embodiment can operate with high output. 
     A second heat dissipation path dissipating the heat to external cooling body  21  can be formed through second printed board  32 , second insulating member  42 , second cooling body  52 , and first cooling body  51  as a heat dissipation path dissipating the heat generated by the circuit pattern formed on the surface or inside of second printed board  32 , the heat generated by rectifier elements  5   a,    5   b,    5   c,    5   d,    5   e,    5   f,    5   g,    5   h  that are the high-heat generating components mounted on second printed board  32 , and the heat generated in transformers  3 ,  4 . The length of the heat dissipation path can be shortened because the second heat dissipation path does not include the plate-shaped substrate installation portion as compared with the configuration described in PTL 1, so that the heat dissipation can be improved. For this reason, the heat dissipation of power conversion device  100  can be improved with respect to the heat generated in the circuit pattern formed on the surface or inside of second printed board  32  and the heat generated in the high-heat generating component mounted on second printed board  32 . As a result, power conversion device  100  of the first embodiment can operate with high output. 
     When second insulating member  42  is brought into surface contact with second printed board  32  and second cooling body  52 , the area of the contact surface between second insulating member  42  and second printed board  32  and the area of the contact surface between second insulating member  42  and second cooling body  52  can be widened, so that the contact thermal resistance of the contact surface between second insulating member  42  and second printed board  32  and the contact thermal resistance of the contact surface between second insulating member  42  and second cooling body  52  can be reduced to improve the heat dissipation of the second heat dissipation path. As a result, power conversion device  100  of the first embodiment can operate with high output. 
     As illustrated in  FIG. 7 , when upper core  81  and lower core  82  are fixed to second cooling body  52  by strut  84  fixed to second cooling body  52  and pressing plate  85 , the heat generated in transformers  3 ,  4  can be dissipated to external cooling body  21  through pressing plate  85 , strut  84 , second cooling body  52 , and first cooling body  51 , so that the heat dissipation of power conversion device  100  can be improved with respect to the heat generated in transformers  3 ,  4 . As a result, power conversion device  100  of the first embodiment can operate with high output. 
     When the lower surface of lower core  82  is in direct contact with second cooling body  52 , when the lower surface of lower core  82  is in contact with second cooling body  52  through a heat conductive member such as thermal conductive grease, a thermal conductive sheet, or a thermal conductive adhesive, or when the lower surface of lower core  82  is in contact with second cooling body  52  through an insulating member, the heat generated in transformers  3 ,  4  can be dissipated to external cooling body  21  through second cooling body  52  and first cooling body  51 , so that the heat dissipation of power conversion device  100  can be improved with respect to the heat generated in the transformers  3 ,  4 . As a result, power conversion device  100  of the first embodiment can operate with high output. 
     A third heat dissipation path for dissipating heat to external cooling body  21  can be formed through third printed board  33 , third insulating member  43 , third cooling body  53 , and first cooling body  51  as a heat dissipation path dissipating the heat generated by the circuit pattern formed on the surface or inside of third printed board  33  and the heat generated by reactors  6 ,  7  that are the high-heat generating components mounted on third printed board  33 . The length of the heat dissipation path can be shortened because the third heat dissipation path does not include the plate-shaped substrate installation portion as compared with the configuration described in PTL 1, so that the heat dissipation can be improved. For this reason, the heat dissipation of power conversion device  100  can be improved with respect to the heat generated by the circuit pattern formed on the surface or inside third printed board  33  and the heat generated by the high-heat generating component mounted on third printed board  33 . As a result, power conversion device  100  of the first embodiment can operate with high output. 
     When third insulating member  43  is brought into surface contact with third printed board  33  and third cooling body  53 , the area of the contact surface between third insulating member  43  and third printed board  33  and the area of the contact surface between third insulating member  43  and third cooling body  53  can be widened, so that the contact thermal resistance of the contact surface between third insulating member  43  and third printed board  33  and the contact thermal resistance of the contact surface between third insulating member  43  and third cooling body  53  can be reduced to improve the heat dissipation of the third heat dissipation path. As a result, power conversion device  100  of the first embodiment can operate with high output. 
     As illustrated in  FIG. 9 , when upper core  81  and lower core  82  are fixed to third cooling body  53  by strut  84  fixed to third cooling body  53  and pressing plate  85 , the heat generated in reactors  6 ,  7  can be dissipated to external cooling body  21  through pressing plate  85 , strut  84 , third cooling body  53 , and first cooling body  51 , so that the heat dissipation of power conversion device  100  can be improved with respect to the heat generated in reactors  6 ,  7 . As a result, power conversion device  100  of the first embodiment can operate with high output. 
     When the lower surface of lower core  82  is in direct contact with third cooling body  53 , when the lower surface of lower core  82  is in contact with third cooling body  53  through a heat conductive member such as thermal conductive grease, a thermal conductive sheet, or a thermal conductive adhesive, or when the lower surface of lower core  82  is in contact with third cooling body  53  through an insulating member, the heat generated in reactors  6 ,  7  can be dissipated to external cooling body  21  through third cooling body  53  and first cooling body  51 , so that the heat dissipation of power conversion device  100  can be improved with respect to the heat generated in reactors  6 ,  7 . As a result, power conversion device  100  of the first embodiment can operate with high output. 
     In addition, because first cooling body  51  and external cooling body  21  are thermally coupled, the heat dissipation of the first heat dissipation path is higher than the heat dissipation of the second heat dissipation path and the third heat dissipation path. Consequently, among the high-heat generating electronic components, the particularly high-heat generating electronic component is mounted on first printed board  31 , so that the heat dissipation of power conversion device  100  can be improved with respect to the heat generated by these components. As a result, power conversion device  100  of the first embodiment can operate with high output. 
     Preferably first cooling body  51  has a small thickness in a direction substantially perpendicular to surface  31   a  of first printed board  31 . As a result, the heat dissipation can be improved because the lengths of the first heat dissipation path, the second heat dissipation path, and the third heat dissipation path are shortened. 
     Preferably second cooling body  52  has a large thickness in a direction substantially perpendicular to surface  32   a  of second printed board  32 . Consequently, the heat dissipation can be improved because the thermal resistance of second cooling body  52  included in the second heat dissipation path can be reduced. 
     Preferably third cooling body  53  has a large thickness in a direction substantially perpendicular to surface  33   a  of third printed board  33 . Consequently, the heat dissipation can be improved because the thermal resistance of third cooling body  53  included in the third heat dissipation path can be reduced. 
     That is, referring to  FIG. 30 , the thickness of first cooling body  51  in the direction in which second principal surface S 2  is opposite to first principal surface S 1  is preferably smaller than the thickness of second cooling body  52  in the direction in which fourth principal surface S 4  is opposite to third principal surface S 3  and the thickness of third cooling body  53  in the direction in which sixth principal surface S 6  is opposite to fifth principal surface S 5 . 
     In power conversion device  100  of the first embodiment, first cooling body  51  can be thermally connected to first printed board  31  through first insulating member  41 . Second cooling body  52  can be thermally connected to second printed board  32  through second insulating member  42 . Third cooling body  53  can be thermally connected to third printed board  33  through third insulating member  43 . 
     In power conversion device  100  of the first embodiment, second cooling body  52  is thermally connected to first cooling body  51 , and third cooling body  53  is thermally connected to first cooling body  51 . For this reason, the heat generated by the electronic component mounted on second printed board  32  can be dissipated from first cooling body  51  through second cooling body  52 , and the heat generated by the electronic component mounted on third printed board  33  can be dissipated from first cooling body  51  through third cooling body  53 . 
     In power conversion device  100  of the first embodiment, first cooling body  51  is thermally connected to each of second cooling body  52  and third cooling body  53  through first heat conductive member HC 1 . For this reason, by first heat conductive member HC 1 , the heat transfer efficiency from second cooling body  52  to first cooling body  51  can be improved, and the heat transfer efficiency from third cooling body  53  to first cooling body  51  can be improved. 
     In power conversion device  100  of the first embodiment, first cooling body  51 , second cooling body  52 , and third cooling body  53  constitute the support body of the power conversion device  100 . For this reason, the amount of the support body can be reduced as compared with the case where the cooling body does not also serve as the support body, and resultantly power conversion device  100  of the first embodiment can be downsized. 
     As described above, in power conversion device  100  of the first embodiment, first cooling body  51 , second cooling body  52 , and third cooling body  53  constitute the support body of power conversion device  100 . However, a support body may be newly provided in addition to first cooling body  51  to third cooling body  53 . 
     First cooling body  51 , second cooling body  52 , and third cooling body  53  may be used as a current path. For example, in a circuit diagram of a sixth modification of the power conversion device according to the first embodiment in  FIG. 32 , first cooling body  51 , second cooling body  52 , and third cooling body  53  may be used as the current path between A and A′. At this time, first cooling body  51 , second cooling body  52 , and third cooling body  53  are electrically connected to one another. At this point, the circuit pattern formed on the printed board and the cooling body are electrically connected to each other at a necessary portion. That is, first cooling body  51  and the circuit pattern formed on first printed board  31 , second cooling body  52  and the circuit pattern formed on second printed board  32 , and third cooling body  53  and the circuit pattern formed on third printed board  33  may be electrically connected as necessary. For the electric connection, for example, using a conductive material such as a metal screw as fixing members  61 ,  62 ,  63 , first cooling body  51  and the circuit pattern formed on first printed board  31  may be electrically connected by first fixing member  61 , second cooling body  52  and the circuit pattern formed on second printed board  32  may be electrically connected by second fixing member  62 , and third cooling body  53  and the circuit pattern formed on third printed board  33  may be electrically connected by third fixing member  63 . 
     The number of harnesses  86  electrically connecting first printed board module  71 , second printed board module  72 , and third printed board module  73  can be reduced using first cooling body  51 , second cooling body  52 , and third cooling body  53  as a current path, and a space where harness  86  is disposed can be reduced. As a result, power conversion device  100  of the first embodiment can be downsized. 
     Further, in the configuration described in PTL 1, the electronic component is disposed in a space formed in the housing. In the configuration described in PTL 1, similarly to the first embodiment, when the printed board is fixed to the bottom surface and the side surface of the housing through the insulating member, it is necessary to perform the disposition of the insulating member, the disposition of the printed board, the fixing of the printed board, and the electric connection between the printed boards in a substantially surrounded space, and workability is poor. As a result, the thickness of the insulating member is easy to vary, and thermal design considering the variation is required. When the terminal blocks fixed to the printed board are electrically connected to each other by the harness having the round hole terminals at both ends, the round hole terminals at both ends of the harness need to be screwed to the terminal blocks in the substantially surrounded space. For this reason, when the substantially surrounded space is narrow, the fixing position of the terminal block needs to be designed in consideration of screwing work. 
     On the other hand, the method for manufacturing power conversion device  100  of the first embodiment includes preparation step S 100 , assembly step S 200 , and connection step S 300 . Consequently, the work of disposing first insulating member  41 , second insulating member  42 , and third insulating member  43  on first cooling body  51  constituting the bottom surface of the support body and second cooling body  52  and third cooling body  53  constituting the side surfaces of the support body to fix first printed board  31 , second printed board  32 , and third printed board  33  and the work of electrically connecting first printed board module  71 , second printed board module  72 , and third printed board module  73  are not needed in the substantially enclosed space. As a result, it is not necessary to perform the thermal design in consideration of thickness variation of first insulating member  41 , second insulating member  42 , and third insulating member  43  due to poor workability. When terminal block  87  is electrically connected by harness  86  provided with the round hole terminals at both ends, it is not necessary to design the mounting position of the terminal block in consideration of the screwing work due to the fact that the round hole terminals at both ends of harness  86  need to be screwed to terminal block  87  in the substantially enclosed space. 
     In the method for manufacturing power conversion device  100  of the first embodiment, second cooling body  52  and third cooling body  53  are thermally connected to first cooling body  51  in connection step S 300 . 
     In the method for manufacturing power conversion device  100  of the first embodiment, in assembly step S 200 , the electronic component (second component) and the electronic component (third component) are fixed to the grooves provided in second printed board  32  and third printed board  33 , respectively. For this reason, the electronic component can be certainly fixed. 
     As illustrated in  FIG. 12 , power conversion device  100  of the first embodiment may be configured such that first cooling body  51  is disposed so as to be sandwiched between second cooling body  52  and third cooling body  53 . 
     As illustrated in  FIG. 13 , in power conversion device  100  of the first embodiment, first cooling body  51  may be integrally formed with external cooling body  21 . In this case, first cooling body  51  also serves as external cooling body  21 . First cooling body  51  is thermally coupled to external cooling body  21  by a method such as integral formation with external cooling body  21 . 
     Second Embodiment 
     With reference to  FIG. 14 , a power conversion device  100  according to a second embodiment will be described. The second embodiment has the same configuration, operation, and effect as those of the first embodiment described above unless otherwise specified. Consequently, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof will not be repeated. 
     Power conversion device  100  of the second embodiment basically has the same configuration as power conversion device  100  of the first embodiment. Power conversion device  100  of the second embodiment is different from power conversion device  100  of the first embodiment in that power conversion device  100  of the second embodiment includes a fourth cooling body  54  and a fifth cooling body  55 . 
     Fourth cooling body  54  is configure to extend vertically with a surface connected to surface  51   a  of first cooling body  51  as a bottom surface. Fourth cooling body  54  extends from second principal surface S 2  of first printed board  31  toward first principal surface S 1 . Fifth cooling body  55  is configure to extend vertically with a surface connected to surface  51   a  of first cooling body  51  as a bottom surface. Fifth cooling body  55  extends from second principal surface S 2  of first printed board  31  toward first principal surface S 1 . 
     Each of fourth cooling body  54  and fifth cooling body  55  is connected to and fixed to at least one of first cooling body  51 , second cooling body  52 , and third cooling body  53  directly or through another member. Each of fourth cooling body  54  and fifth cooling body  55  is thermally connected to each of first cooling body  51 , second cooling body  52 , and third cooling body  53 . Fourth cooling body  54  is thermally connected to first cooling body  51 , second cooling body  52 , and third cooling body  53 . Fifth cooling body  55  is thermally connected to first cooling body  51 , second cooling body  52 , and third cooling body  53 . 
     A heat conductive member such as thermal conductive grease, a thermal conductive sheet, or thermal conductive adhesive (second heat conductive member) HC 2  may be disposed on a contact surface between each of fourth cooling body  54  and fifth cooling body  55  and each of first cooling body  51 , second cooling body  52 , and third cooling body  53 . Heat conductive member (second heat conductive member) HC 2  includes at least one of heat conductive grease, the heat conductive sheet, and the heat conductive adhesive. Fourth cooling body  54  is thermally connected to each of first cooling body  51 , second cooling body  52 , and third cooling body  53  through heat conductive member (second heat conductive member) HC 2 . Fifth cooling body  55  is thermally connected to each of first cooling body  51 , second cooling body  52 , and third cooling body  53  through heat conductive member (second heat conductive member) HC 2 . Each of fourth cooling body  54  and fifth cooling body  55  constitutes the side surfaces of the support body of power conversion device  100 . 
     Even in this case, power conversion device  100  of the second embodiment can obtain the effect equivalent to that of power conversion device  100  of the first embodiment. Furthermore, in addition to the second heat dissipation path dissipating the heat to external cooling body  21 , the following two heat dissipation paths are formed through second printed board  32 , second insulating member  42 , second cooling body  52 , and first cooling body  51  as a heat dissipation path dissipating the heat generated by the circuit pattern formed on the surface or inside of second printed board  32 , the heat generated by rectifier elements  5   a,    5   b,    5   c,    5   d,    5   e,    5   f,    5   g,    5   h  that are the high-heat generating components mounted on second printed board  32 , and the heat generated by transformers  3 ,  4 . A first is the heat dissipation path dissipates the heat to external cooling body  21  through second printed board  32 , second insulating member  42 , second cooling body  52 , fourth cooling body  54 , and first cooling body  51 . A second is the heat dissipation path dissipates the heat to external cooling body  21  through second printed board  32 , second insulating member  42 , second cooling body  52 , fifth cooling body  55 , and first cooling body  51 . For this reason, the heat dissipation of power conversion device  100  can be enhanced with respect to the heat generated by the circuit pattern formed on the surface or inside of second printed board  32  and the heat generated by the high-heat generating component mounted on second printed board  32 . In addition to the third heat dissipation path dissipating the heat to external cooling body  21 , the following two heat dissipation paths are formed through third printed board  33 , third insulating member  43 , third cooling body  53 , and first cooling body  51  as a heat dissipation path dissipating the heat generated by the circuit pattern formed on the surface or inside of third printed board  33  and the heat generated by reactors  6 ,  7  that are the high-heat generating components mounted on third printed board  33 . A first is the heat dissipation path dissipating the heat to external cooling body  21  through third printed board  33 , third insulating member  43 , third cooling body  53 , fourth cooling body  54 , and first cooling body  51 . A second is the heat dissipation path dissipating the heat to external cooling body  21  through third printed board  33 , third insulating member  43 , third cooling body  53 , fifth cooling body  55 , and first cooling body  51 . For this reason, the heat dissipation of power conversion device  100  can be enhanced with respect to the heat generated by the circuit pattern formed on the surface or inside third printed board  33  and the heat generated by the high-heat generating component mounted on third printed board  33 . As a result, power conversion device  100  of the second embodiment can operate with high output. 
     In power conversion device  100  of the second embodiment, fourth cooling body  54  is thermally connected to each of first cooling body  51 , second cooling body  52 , and third cooling body  53  through heat conductive member (second heat conductive member) HC 2 . Fifth cooling body  55  is thermally connected to each of first cooling body  51 , second cooling body  52 , and third cooling body  53  through heat conductive member (second heat conductive member) HC 2 . For this reason, the heat transfer efficiency from fourth cooling body  54  to first cooling body  51 , second cooling body  52 , and third cooling body  53  can be improved by second heat conductive member HC 2 , and the heat transfer efficiency from fifth cooling body  55  to first cooling body  51 , second cooling body  52 , and third cooling body  53  can be improved. 
     As illustrated in  FIG. 15 , power conversion device  100  of the second embodiment may be configured such that first cooling body  51  is disposed so as to be sandwiched between fourth cooling body  54  and fifth cooling body  55 . 
     In power conversion device  100  of the second embodiment, as illustrated in  FIG. 14 or 15 , second printed board  32  and third printed board  33  may be disposed such that surface (third principal surface) S 3  of second printed board  32  on which the electronic component is mounted faces surface (fifth principal surface) S 5  of third printed board  33  on which the electronic component is mounted. 
     When second printed board  32  and third printed board  33  are disposed such that surface (third principal surface) S 3  of second printed board  32  on which the electronic component is mounted faces surface (fifth principal surface) S 5  of third printed board  33  on which the electronic component is mounted, and when first cooling body  51  to fifth cooling body  55  are made of metal, first cooling body  51  to fifth cooling body  55  play a role of an electromagnetic shield that prevents power conversion device  100  from malfunctioning due to an electromagnetic wave noise emitted from another electronic device or the like disposed around power conversion device  100 . In general, with the operation of the power conversion device, the electromagnetic wave is emitted from inverter circuit unit  11  including switching elements  2   a,    2   b,    2   c,    2   d,  transforming unit  12  including transformers  3 ,  4 , rectifier circuit unit  13  including eight rectifier elements  5   a,    5   b,    5   c,    5   d,    5   e,    5   f,    5   g,    5   h,  and smoothing circuit unit  14  including reactors  6 ,  7  and smoothing capacitor  8 . When second printed board  32  and third printed board  33  are disposed such that surface (third principal surface) S 3  of second printed board  32  on which the electronic components are mounted faces surface (fifth principal surface) S 5  of third printed board  33  on which the electronic components are mounted, and when first cooling body  51  to fifth cooling body  55  are made of metal, first cooling body  51  to fifth cooling body  55  play a role of an electromagnetic shield that prevents the electromagnetic wave noise emitted from inverter circuit unit  11  including switching elements  2   a,    2   b,    2   c,    2   d,  transforming unit  12  including transformers  3 ,  4 , rectifier circuit unit  13  including eight rectifier elements  5   a,    5   b,    5   c,    5   d,    5   e,    5   f,    5   g,    5   h,  and smoothing circuit unit  14  including reactors  6 ,  7  and smoothing capacitor  8  from being discharged to the outside of power conversion device  100 . For this reason, the amount of the electromagnetic shield can be reduced as compared with the case where the cooling body does not also serve as the electromagnetic shield, and resultantly power conversion device  100  of the second embodiment can be downsized. 
     As described above, in power conversion device  100  of the second embodiment, when second printed board  32  and third printed board  33  are disposed such that surface (third principal surface) S 3  of second printed board  32  on which the electronic component is mounted faces surface (fifth principal surface) S 5  of third printed board  33  on which the electronic component is mounted, and when first cooling body  51  to fifth cooling body  55  are made of metal, first cooling body  51  to fifth cooling body  55  also serve as the electromagnetic shield. However, an electromagnetic shield may be newly provided in addition to first cooling body  51  to fifth cooling body  55 . 
     Third Embodiment 
     With reference to  FIGS. 16 to 21 , a power conversion device  100  according to the third embodiment will be described below. The third embodiment has the same configuration, operation, and effect as those of the second embodiment described above unless otherwise specified. Consequently, the same components as those in the second embodiment are denoted by the same reference numerals, and the description thereof will not be repeated. 
     Power conversion device  100  of the third embodiment basically has the same configuration as power conversion device  100  of the second embodiment. Power conversion device  100  of the third embodiment is different from power conversion device  100  of the second embodiment in that power conversion device  100  of the third embodiment includes a fourth printed board module  74  and a fifth printed board module  75 . 
     Fourth printed board module  74  includes a fourth printed board  34 , a fourth insulating member  44 , a fourth cooling body  54 , a fourth fixing member  64 , and an electronic component. 
     Fourth printed board (fourth substrate)  34  includes a front surface (seventh principal surface) S 7  on which the electronic component (fourth component) is mounted and a back surface (eighth principal surface) S 8  facing fourth cooling body  54 . Seventh principal surface S 7  is opposite to eighth principal surface S 8 . Fourth insulating member  44  is disposed between eighth principal surface S 8  of fourth printed board  34  and fourth cooling body  54 . Fourth cooling body  54  is thermally connected to eighth principal surface S 8  of fourth printed board  34 . Fourth cooling body  54  is thermally connected to eighth principal surface S 8  of fourth printed board  34  through fourth insulating member  44 . Fourth cooling body  54  is configured to extend vertically with the surface connected to surface  51   a  of first cooling body  51  facing first printed board  31  as the bottom surface. Fourth cooling body  54  extends from second principal surface S 2  of first printed board  31  toward first principal surface S 1 . Fourth cooling body  54  is thermally connected to each of first cooling body  51 , second cooling body  52 , and third cooling body  53 . Fourth fixing member  64  is configured to fix fourth printed board  34  to fourth cooling body  54 . 
     Fifth printed board module  75  includes a fifth printed board  35 , a fifth insulating member  45 , a fifth cooling body  55 , a fifth fixing member  65 , and an electronic component. 
     Fifth printed board (fifth substrate)  35  has a front surface (ninth principal surface) S 9  on which an electronic component (fifth component) is mounted and a back surface (tenth principal surface) S 10  facing fifth cooling body  55 . Ninth principal surface S 9  is opposite to tenth principal surface S 10 . Fifth insulating member  45  is disposed between tenth principal surface S 10  of fifth printed board  35  and fifth cooling body  55 . Fifth cooling body  55  is thermally connected to tenth principal surface S 10  of fifth printed board  35 . Fifth cooling body  55  is thermally connected to tenth principal surface S 10  of fifth printed board  35  through fifth insulating member  45 . Fifth cooling body  55  is configured to extend vertically with the surface of first cooling body  51  connected to surface  51   a  facing first printed board  31  as the bottom surface. Fifth cooling body  55  extends from second principal surface S 2  of first printed board  31  toward first principal surface S 1 . Fifth cooling body  55  is thermally connected to each of first cooling body  51 , second cooling body  52 , and third cooling body  53 . Fifth fixing member  65  is configured to fix fifth printed board  35  to fifth cooling body  55 . 
     Power conversion device  100  of the third embodiment includes first printed board module  71 , second printed board module  72 , third printed board module  73 , fourth printed board module  74 , and fifth printed board module  75 . First printed board module  71 , second printed board module  72 , third printed board module  73 , fourth printed board module  74 , and fifth printed board module  75  are electrically connected to one another by a harness or the like. That is, first printed board  31 , second printed board  32 , third printed board  33 , fourth printed board  34 , and fifth printed board  35  are electrically connected to one another. 
     With reference to  FIGS. 17 to 21 , examples of first printed board module  71 , second printed board module  72 , third printed board module  73 , fourth printed board module  74 , and fifth printed board module  75  in power conversion device  100  of the third embodiment will be described below. 
     As illustrated in  FIG. 17 , first printed board module  71  includes first printed board  31 , first insulating member  41 , first cooling body  51 , first fixing member  61 , and an electronic component. The electronic component is mounted on first printed board  31 . First insulating member  41  is disposed between first printed board  31  and first cooling body  51 . First fixing member  61  fixes first printed board  31  to first cooling body  51 . 
     Input capacitor  1  and switching elements  2   a,    2   b,    2   c,    2   d  are mounted on a surface  31   a  of first printed board  31  opposite to the surface facing first cooling body  51 . Input terminal  9  (not illustrated) is mounted on surface  31   a.  Other electronic components may be mounted on surface  31   a.  Other electronic components may be mounted on the surface of first printed board  31  facing first cooling body  51 . 
     As illustrated in  FIG. 18 , second printed board module  72  includes second printed board  32 , second insulating member  42 , second cooling body  52 , second fixing member  62 , and an electronic component. The electronic component is mounted on second printed board  32 . Second insulating member  42  is disposed between second printed board  32  and second cooling body  52 . Second fixing member  62  fixes second printed board  32  to second cooling body  52 . 
     Rectifier elements  5   a,    5   b,    5   c,    5   d  and transformer  3  are mounted on surface  32   a  of second printed board  32  opposite to the surface facing second cooling body  52 . Other electronic components may be mounted on surface  32   a.  Other electronic components may be mounted on the surface of second printed board  32  facing second cooling body  52 . 
     As illustrated in  FIG. 19 , third printed board module  73  includes third printed board  33 , third insulating member  43 , third cooling body  53 , third fixing member  63 , and an electronic component. The electronic component is mounted on third printed board  33 . Third insulating member  43  is disposed between third printed board  33  and third cooling body  53 . Third fixing member  63  fixes third printed board  33  to third cooling body  53 . 
     Rectifier elements  5   e,    5   f,    5   g,    5   h  and transformer  4  are mounted on surface  33   a  of third printed board  33  opposite to the surface facing third cooling body  53 . Other electronic components may be mounted on surface  33   a.  Other electronic components may be mounted on the surface of third printed board  33  facing third cooling body  53 . 
     As illustrated in  FIG. 20 , fourth printed board module  74  includes fourth printed board  34 , fourth insulating member  44 , fourth cooling body  54 , fourth fixing member  64 , and an electronic component (fourth component). The electronic component (fourth component) is mounted on fourth printed board  34 . The electronic component (fourth component) is particularly reactor  6  that is the high-heat generating component. Fourth insulating member  44  is disposed between fourth printed board  34  and fourth cooling body  54 . Fourth fixing member  64  fixes fourth printed board  34  to fourth cooling body  54 . Fourth insulating member  44  is preferably in surface contact with fourth printed board  34  and fourth cooling body  54 . 
     Smoothing capacitor  8  and reactor  6  are mounted on surface  34   a  of fourth printed board  34  opposite to the surface facing fourth cooling body  54 . Output terminal  10  (not illustrated) is mounted on surface  34   a.  Other electronic components may be mounted on surface  34   a.  The surface of fourth printed board  34  facing fourth cooling body  54  corresponds to eighth principal surface S 8 . Surface  34   a  of fourth printed board  34  opposite to the surface facing fourth cooling body  54  corresponds to seventh principal surface S 7 . Other electronic components may be mounted on the surface of fourth printed board  34  facing fourth cooling body  54 . 
     As illustrated in  FIG. 21 , fifth printed board module  75  includes fifth printed board  35 , fifth insulating member  45 , fifth cooling body  55 , fifth fixing member  65 , and the electronic component (fifth component). The electronic component (fifth component) is mounted on fifth printed board  35 . The electronic component (fifth component) is particularly reactor  7  that is the high-heat generating component. Fifth insulating member  45  is disposed between fifth printed board  35  and fifth cooling body  55 . Fifth fixing member  65  fixes fifth printed board  35  to fifth cooling body  55 . Fifth insulating member  45  is preferably in surface contact with fifth printed board  35  and fifth cooling body  55 . 
     Smoothing capacitor  8  and reactor  7  are mounted on surface  35   a  of fifth printed board  35  opposite to the surface facing fifth cooling body  55 . Output terminal  10  (not illustrated) is mounted on surface  35   a.  Other electronic components may be mounted on surface  35   a.  The surface of fifth printed board  35  facing fifth cooling body  55  corresponds to tenth principal surface S 10 . Surface  35   a  of fifth printed board  35  opposite to the surface facing fifth cooling body  55  corresponds to ninth principal surface S 9 . Other electronic components may be mounted on the surface of fifth printed board  35  facing fifth cooling body  55 . 
     Even in this case, power conversion device  100  of the third embodiment can obtain the effect equivalent to that of power conversion device  100  of the second embodiment. Furthermore, in power conversion device  100  of the third embodiment, a fourth heat dissipation path dissipating the heat to external cooling body  21  can be formed through fourth printed board  34 , fourth insulating member  44 , fourth cooling body  54 , and first cooling body  51  as a heat dissipation path dissipating the heat generated by the circuit pattern formed on the surface or inside of fourth printed board  34  and the heat generated by smoothing capacitor  8  and reactor  6 , which are the high-heat generating components mounted on fourth printed board  34 . The length of the heat dissipation path can be shortened because the fourth heat dissipation path does not include the plate-shaped substrate installation portion as compared with the configuration described in PTL 1, so that heat dissipation can be improved. For this reason, the heat dissipation of power conversion device  100  can be improved with respect to the heat generated by the circuit pattern formed on the surface or inside of fourth printed board  34  and the heat generated by the high-heat generating component mounted on fourth printed board  34 . As a result, power conversion device  100  of the third embodiment can operate with high output. 
     The area of the contact surface between fourth insulating member  44  and fourth printed board  34  and the area of the contact surface between fourth insulating member  44  and fourth cooling body  54  can be increased when fourth insulating member  44  is brought into surface contact with fourth printed board  34  and fourth cooling body  54 . For this reason, the contact thermal resistance of the contact surface between fourth insulating member  44  and fourth printed board  34  and the contact thermal resistance of the contact surface between fourth insulating member  44  and fourth cooling body  54  can be reduced, so that the heat dissipation of the fourth heat dissipation path can be improved. As a result, power conversion device  100  of the third embodiment can operate with high output. 
     A fifth heat dissipation path dissipating the heat to external cooling body  21  can be formed through fifth printed board  35 , fifth insulating member  45 , fifth cooling body  55 , and first cooling body  51  as a heat dissipation path dissipating the heat generated by the circuit pattern formed on the surface or inside of fifth printed board  35  and the heat generated by smoothing capacitor  8  and reactor  7 , which are the high-heat generating components mounted on fifth printed board  35 . The length of the heat dissipation path can be shortened because the fifth heat dissipation path does not include the plate-shaped substrate installation portion as compared with the configuration described in PTL 1, so that heat dissipation can be improved. For this reason, the heat dissipation of power conversion device  100  can be improved with respect to the heat generated by the circuit pattern formed on the surface or inside of fifth printed board  35  and the heat generated by the high-heat generating component mounted on fifth printed board  35 . As a result, power conversion device  100  of the third embodiment can operate with high output. 
     When fifth insulating member  45  is brought into surface contact with fifth printed board  35  and fifth cooling body  55 , the area of the contact surface between fifth insulating member  45  and fifth printed board  35  and the area of the contact surface between fifth insulating member  45  and fifth cooling body  55  can be widened, so that the contact thermal resistance of the contact surface between fifth insulating member  45  and fifth printed board  35  and the contact thermal resistance of the contact surface between fifth insulating member  45  and fifth cooling body  55  can be reduced to improve the heat dissipation of the fifth heat dissipation path. As a result, power conversion device  100  of the third embodiment can operate with high output. 
     Preferably a thickness of fourth cooling body  54  is increased in a direction substantially perpendicular to surface  34   a  of fourth printed board  34 . Consequently, the heat dissipation can be improved because the thermal resistance of fourth cooling body  54  included in the fourth heat dissipation path can be reduced. 
     Preferably a thickness of fifth cooling body  55  is increased in a direction substantially perpendicular to surface  35   a  of fifth printed board  35 . Consequently, the heat dissipation can be improved because the thermal resistance of fifth cooling body  55  included in the fifth heat dissipation path can be reduced. 
     That is, referring to  FIG. 31 , preferably each of fourth cooling body  54  and fifth cooling body  55  in the direction orthogonal to the direction from second principal surface S 2  toward first principal surface S 1  of first printed board  31  is thicker than first cooling body  51  in the direction in which second principal surface S 2  is opposite to first principal surface S 1 . 
     A high-heat generating component can be mounted on each of fourth printed board  34  and fifth printed board  35  in addition to first printed board  31 , second printed board  32 , and third printed board  33 . Consequently, thermal interference of the heat generated in each high-heat generating component can be suppressed because the distance between the high-heat generating components mounted on the printed board can be increased, so that the heat dissipation of power conversion device  100  can be improved with respect to the heat generated in each high-heat generating component. As a result, power conversion device  100  of the third embodiment can operate with high output. 
     The electronic component can also be mounted on each of fourth printed board  34  and fifth printed board  35  in addition to first printed board  31 , second printed board  32 , and third printed board  33 . For this reason, because a component mounting area is increased, first printed board  31 , second printed board  32 , and third printed board  33  can be downsized as compared with the first and second embodiments. As a result, power conversion device  100  of the third embodiment can be downsized. 
     The electronic components mounted on first printed board  31 , second printed board  32 , third printed board  33 , fourth printed board  34 , and fifth printed board  35  included in power conversion device  100  of the third embodiment may be interchanged. For example, power conversion device  100  of the third embodiment may be configured as illustrated in  FIGS. 22 to 27 . Examples of first printed board module  71 , second printed board module  72 , third printed board module  73 , fourth printed board module  74 , and fifth printed board module  75  in  FIGS. 23 to 27  will be described below. 
     As illustrated in  FIG. 23 , switching elements  2   a,    2   b,    2   c,    2   d  are mounted on surface  31   a  of first printed board  31  opposite to the surface facing first cooling body  51 . Other electronic components may be mounted on surface  31   a.  Other electronic components may be mounted on the surface of first printed board  31  facing first cooling body  51 . 
     As illustrated in  FIG. 24 , input capacitor  1 , reactors  6 ,  7 , and smoothing capacitor  8  are mounted on surface  32   a  of second printed board  32  opposite to the surface facing second cooling body  52 . Input terminal  9  (not illustrated) is mounted on surface  32   a.  Other electronic components may be mounted on surface  32   a.  Other electronic components may be mounted on the surface of second printed board  32  facing second cooling body  52 . 
     As illustrated in  FIG. 25 , transformers  3 ,  4  are mounted on surface  33   a  of third printed board  33  opposite to the surface facing third cooling body  53 . Other electronic components may be mounted on surface  33   a.  Other electronic components may be mounted on the surface of third printed board  33  facing third cooling body  53 . 
     As illustrated in  FIG. 26 , rectifier elements  5   a,    5   b,    5   c,    5   d  are mounted on surface  34   a  of fourth printed board  34  opposite to the surface facing fourth cooling body  54 . Other electronic components may be mounted on surface  34   a.  Other electronic components may be mounted on the surface of fourth printed board  34  facing fourth cooling body  54 . 
     As illustrated in  FIG. 27 , rectifier elements  5   e,    5   f,    5   g,    5   h  are mounted on surface  35   a  of fifth printed board  35  opposite to the surface facing fifth cooling body  55 . Other electronic components may be mounted on surface  35   a.  Other electronic components may be mounted on the surface of fifth printed board  35  facing fifth cooling body  55 . 
     Power conversion device  100  of the third embodiment may not include fifth printed board  35 , fifth insulating member  45 , and fifth fixing member  65 . In other words, power conversion device  100  may include external cooling body  21 , first printed board module  71 , the second printed board module  72 , third printed board module  73 , fourth printed board module  74 , and fifth cooling body  55 . First printed board module  71 , second printed board module  72 , third printed board module  73 , and fourth printed board module  74  are electrically connected to one another by a harness or the like. 
     The electronic components disposed in first printed board module  71 , second printed board module  72 , third printed board module  73 , fourth printed board module  74 , and fifth printed board module  75  may be exchanged, but preferably the high-heat generating component is particularly disposed in first printed board module  71 . 
     Fourth Embodiment 
     With reference to  FIG. 28 , a power conversion device  100  according to a fourth embodiment will be described below. The fourth embodiment has the same configuration, operation, and effect as those of the second embodiment or the third embodiment described above unless otherwise specified. Consequently, the same components as those in the second or third embodiment are denoted by the same reference numerals, and the description thereof will not be repeated. 
     Power conversion device  100  of the fourth embodiment basically has the same configuration as power conversion device  100  of the second embodiment or the third embodiment. Power conversion device  100  of the fourth embodiment is different in that a space substantially surrounded by first cooling body  51 , second cooling body  52 , third cooling body  53 , fourth cooling body  54 , and fifth cooling body  55  is filled with a sealing member  91 . 
     Power conversion device  100  of the fourth embodiment includes sealing member  91 . The space surrounded by first cooling body  51 , second cooling body  52 , third cooling body  53 , fourth cooling body  54 , and fifth cooling body  55  is filled with sealing member  91 . Sealing member  91  seals the electronic components mounted on first printed board  31 , second printed board  32 , third printed board  33 , fourth printed board  34 , and fifth printed board  35 . 
     Sealing member  91  may be made of a material having the thermal conductivity greater than or equal to 0.1 W/(m·K), preferably 1.0 W/(m·K). Sealing member  91  is made of a material having volume resistivity greater than or equal to 1×10 10  Ω·m, preferably greater than or equal to 1×10 12  Ω·m, and more preferably greater than or equal to 1×10 14  Ω·m. In other words, sealing member  91  has the electric insulation property. Sealing member  91  may have the Young&#39;s modulus greater than or equal to 1 MPa. Sealing member  91  may be made of a resin material having elasticity. Sealing member  91  may be made of a resin material such as polyphenylene sulfide (PPS) and polyether ether ketone (PEEK), which are contain a thermally conductive filler. Sealing member  91  may be made of a rubber material such as silicon or urethane. 
     A method for manufacturing power conversion device  100  of the fifth embodiment will be described below. 
     The fourth component and the fifth component included in the electronic components, fourth printed board  34  and fifth printed board  35 , and fourth cooling body  54  and fifth cooling body  55  are prepared in preparation step S 100  of  FIG. 10 . 
     In assembly step S 200 , the electronic component (fourth components) is mounted on seventh principal surface S 7  of fourth printed board  34 , and fourth cooling body  54  is thermally connected to eighth principal surface S 8  opposite to seventh principal surface S 7  of fourth printed board  34 . The electronic component (fifth component) is mounted on ninth principal surface S 9  of fifth printed board  35 , and fifth cooling body  55  is thermally connected to tenth principal surface S 10  opposite to ninth principal surface S 9  of fifth printed board  35 . 
     In connection step S 300 , fourth cooling body  54  and fifth cooling body  55  are disposed so as to extend in the direction from second principal surface S 2  toward first principal surface S 1  of first printed board  31 . A space surrounded by first cooling body  51 , second cooling body  52 , third cooling body  53 , fourth cooling body  54 , and fifth cooling body  55  is filled with sealing member  91 . 
     Even in this case, the power conversion device  100  according to the fourth embodiment can obtain the same effects as those of power conversion devices  100  of the second and third embodiments. Furthermore, in power conversion device  100  of the fourth embodiment, a heat dissipation path dissipating the heat to external cooling body  21  can be formed through sealing member  91 , first cooling body  51 , second cooling body  52 , third cooling body  53 , fourth cooling body  54 , and fifth cooling body  55  as a heat dissipation path dissipating the heat generated by the circuit pattern formed on the surface or inside of the printed board and the heat generated by the high-heat generating component mounted on the printed board. For this reason, the heat dissipation of power conversion device  100  can be improved with respect to the heat generated in the circuit pattern formed on the surface or inside of the printed board and the heat generated in the high-heat generating component mounted on the printed board. As a result, power conversion device  100  can operate with high output. 
     In general, in order to prevent the creeping discharge between the electronic components, it is necessary to secure a creeping distance according to a voltage applied to each electronic component between the electronic components. In power conversion device  100  of the fourth embodiment, creeping discharge hardly occurs because sealing member  91  having the electric insulation property fills the space between the electronic components. Consequently, a creeping distance between the electronic components can be shortened. For this reason, power conversion device  100  of the fourth embodiment can downsize first printed board  31 , second printed board  32 , and third printed board  33  as compared with power conversion device  100  according to the first to third embodiments. As a result, power conversion device  100  of the fourth embodiment can be downsized. 
     When sealing member  91  fills the space between the printed board and the cooling body, the necessity of the insulating member disposed between the printed board and the cooling body can be eliminated. Therefore, the number of components constituting power conversion device  100  can be reduced. 
     Fifth Embodiment 
     With reference to  FIG. 29 , a power conversion device  100  according to a fifth embodiment will be described below. The fifth embodiment has the same configuration, operation, and effect as those of the first to fourth embodiments unless otherwise specified. Consequently, the same components as those of the first to fourth embodiments are denoted by the same reference numerals, and the description thereof will not be repeated. 
     Power conversion device  100  of the fifth embodiment basically has the same configuration as power conversion device  100  of the first to fourth embodiments. Power conversion device  100  of the fifth embodiment is different from power conversion device  100  of the first to fourth embodiments in that power conversion device  100  of the fifth embodiment includes a sixth printed board (sixth substrate)  36 , an electronic component (sixth component) mounted on sixth printed board  36 , and a sixth fixing member  66 . 
     Power conversion device  100  of the fifth embodiment includes the electronic component (sixth component) and the sixth printed board (sixth substrate) on which the electronic component (sixth component) is mounted. 
     Sixth fixing member  66  fixes sixth printed board  36  to at least one of second cooling body  52 , third cooling body  53 , fourth cooling body, and fifth cooling body  55 . Sixth printed board  36  is fixed to at least one of first cooling body  51 , second cooling body  52 , third cooling body  53 , fourth cooling body  54 , and fifth cooling body  55  by sixth fixing member  66 . For example, as illustrated in  FIG. 29 , sixth printed board  36  may be fixed to second cooling body  52  and third cooling body  53  by sixth fixing member  66 . In this case, sixth printed board  36  is fixed to second cooling body  52  and third cooling body  53  in connection step S 300  of  FIG. 10 . 
     The components that are not the high-heat generating components included in power conversion device  100 , such as input capacitor  1 , smoothing capacitor  8 , and control circuit unit  15  (not illustrated) are mounted on a surface  36   a  of sixth printed board  36  opposite to the surface facing first cooling body  51 . The calorific value of the electronic component (sixth component) mounted on sixth printed board  36  is smaller than the calorific value of each of the electronic component (first component) mounted on first printed board  31 , the electronic component (second component) mounted on second printed board  32 , and the electronic component (third component) mounted on third printed board  33 . These calorific values are calorific values during the operation of power conversion device  100 . Input terminal  9  and output terminal  10  (not illustrated) are mounted on surface  36   a.  A part or all of the electronic components mounted on surface  36   a  of sixth printed board  36  may be mounted on a surface  36   b  opposite to surface  36   a  of sixth printed board  36 . 
     Even in this case, power conversion device  100  of the fifth embodiment can obtain the same effects as those of power conversion device  100  of the first to fourth embodiments. In general, the components that are not the high-heat generating components, for example, input capacitor  1 , smoothing capacitor  8 , and control circuit unit  15  (not illustrated) have lower-heat resistance temperatures than the high-heat generating components. For this reason, when the high-heat generating component and the component that is not the high-heat generating component are mounted on the same printed board, it is necessary to perform the thermal design such that a temperature of the component that is not the high-heat generating component does not exceed an allowable temperature due to the heat generated by the high-heat generating component. In power conversion device  100  of the fifth embodiment, because the component that is not the high-heat generating component is mounted on the printed board different from the high-heat generating component, it is not necessary to perform the thermal design such that the temperature of the component that is not the high-heat generating component does not exceed the allowable temperature due to the heat generated in the high-heat generating component. 
     Sixth Embodiment 
     With reference to  FIGS. 33 and 34 , a power conversion device  100  according to a sixth embodiment will be described below. The sixth embodiment has the same configuration, operation, and effect as those of the first embodiment described above unless otherwise specified. Consequently, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof will not be repeated. 
     Power conversion device  100  of the sixth embodiment basically has the same configuration as power conversion device  100  of the first embodiment. Power conversion device  100  of the sixth embodiment is different from power conversion device  100  of the first embodiment in that power conversion device  100  of the sixth embodiment includes a low-resistance current path member (current path member)  88 . 
     Low-resistance current path member  88  is formed of any conductive material such as copper or nickel or gold or aluminum or silver or tin, or an alloy thereof. Low-resistance current path member  88  has volume resistivity less than or equal to 1.0×10 −6  Ω·m, preferably less than or equal to 1.0×10 −7  Ω·m. A part or all of first cooling body  51 , second cooling body  52 , and third cooling body  53  form a current path (first energization path) A-A′. 
     As illustrated in  FIG. 34 , low-resistance current path member  88  forms a current path (second energization path) B electrically connected in parallel to current path A-A′ including a part or all of first cooling body  51 , second cooling body  52 , and third cooling body  53 . 
     Specific examples of current path A-A′ and current path B will be described below. For example, as illustrated in  FIG. 33 , current path A-A′ includes third cooling body  53 , first cooling body  51 , and second cooling body  52 , and electrically connects third printed board  33  and second printed board  32 . At this point, for example, as illustrated in  FIG. 33 , current path B may be constructed with third cooling body  53 , low-resistance current path member  88 , and second cooling body  52  so as to electrically connect third printed board  33  and second printed board  32 . 
     The electric resistance of current path B formed from low-resistance current path member  88  is desirably lower than the electric resistance of current path A-A′. A material constituting current path B and a shape of current path B can be determined independently of a material and a shape of current path A-A′ including a part or all of first cooling body  51 , second cooling body  52 , and third cooling body  53 . Consequently, when current path A-A′ is made of aluminum, the electric resistance of current path B can be made smaller than the electric resistance of the current path A-A′ by forming current path B with a conductor, for example, copper having volume resistivity smaller than that of aluminum. The path length of current path B is made shorter than the path length of current path A-A′, or the sectional area of current path B is made larger than the sectional area of current path A-A′, whereby the electric resistance of current path B can be made smaller than the electric resistance of current path A-A′. 
     Even in this case, power conversion device  100  of the sixth embodiment can obtain the same effects as those of power conversion device  100  of the first embodiment. 
     In power conversion device  100  of the first embodiment, when first cooling body  51 , second cooling body  52 , and third cooling body  53  are used as, for example, current path A-A′ in  FIG. 32 , the current flows through first cooling body  51 , second cooling body  52 , and third cooling body  53 . At this point, the temperatures of first cooling body  51 , second cooling body  52 , and third cooling body  53  increase because Joule heating proportional to the square of the current value is generated in first cooling body  51 , second cooling body  52 , and third cooling body  53 . As a result, as the temperatures of first cooling body  51 , second cooling body  52 , and third cooling body  53  increase, the temperatures of the high-heat generating components mounted on first printed board  31 , second printed board  32 , and third printed board  33  also increase, so that the heat dissipation decreases to the high-heat generating components mounted on first printed board  31 , second printed board  32 , and third printed board  33  of power conversion device  100  of the first embodiment. 
     On the other hand, in power conversion device  100  of the sixth embodiment, low-resistance current path member  88  forms current path B electrically connected in parallel to current path A-A′. For this reason, a part of the current flowing through current path A-A′ is divided into current path B. As a result, the current flowing through current path A-A′ decreases, and Joule heating generated in first cooling body  51 , second cooling body  52 , and third cooling body  53  decreases. As a result, in power conversion device  100  of the first embodiment, as compared with the case that first cooling body  51 , second cooling body  52 , and third cooling body  53  are used as, for example, current path A-A′ in  FIG. 32 , the heat dissipation can be improved with respect to the high-heat generating component mounted on first printed board  31 , second printed board  32 , and third printed board  33 . 
     In addition, the larger the amount of current diverted to current path B is increased in the current flowing through current path A-A′ as the electric resistance of current path B formed by low-resistance current path member  88  is decreased than the electric resistance of current path A-A′. For example, when the electric resistance of current path B is a half of the electric resistance of current path A-A′, the amount of current flowing through current path A-A′ is reduced to one third as compared with the case where current path B does not exist. Consequently, because the Joule heating is proportional to the square of the current value, the heating of current path A-A′ is reduced to one ninth as compared with the case where the current path B is not provided. 
     Although only one low-resistance current path member  88  is illustrated in  FIG. 33 , a plurality of current paths B electrically connected in parallel to current path A-A′ may be formed by combining a plurality of low-resistance current path members  88 . 
     In addition, the above-described embodiments can be appropriately combined. 
     It should be considered that the disclosed embodiment is an example in all respects and not restrictive. The scope of the present disclosure is defined by not the description above, but the claims, and it is intended that all modifications within the meaning and scope of the claims and their equivalents are included in the present invention. 
     REFERENCE SIGNS LIST 
       21 : external cooling body,  31 : first printed board,  32 : second printed board,  33 : third printed board,  34 : fourth printed board,  35 : fifth printed board,  36 : sixth printed board,  41  to  45 : first insulating member to fifth insulating member,  51  to  55 : first cooling body to fifth cooling body,  61  to  66 : first fixing member to sixth fixing member,  71  to  75 : first printed board module to fifth printed board module,  81 : upper core,  82 : core,  83 : spring,  84 : strut,  85 : pressing plate,  86 : harness,  87 : terminal block,  88 : low-resistance current path member,  91 : sealing member,  100 : power conversion device, HC 1 : first heat conductive member, HC 2 : second heat conductive member, S 1  to S 10 : first principal surface to tenth principal surface, S 100 : preparation step, S 200 : assembly step, S 300 : connection step