Patent Publication Number: US-2023156980-A1

Title: Power conversion device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This disclosure relates to a power conversion device. 
     2. Description of the Related Art 
     In a related-art power conversion device, a water passage defining member has a flow passage for cooling water. A power module is arranged on a first surface of the water passage defining member. Further, a capacitor module is arranged on a second surface of the water passage defining member. The second surface is a surface on a side opposite to the first surface across the flow passage (see, for example, Japanese Patent Application Laid-open No. 2013-176297). 
     In the above-mentioned related-art power conversion device, the power module is arranged on the first surface, and the capacitor module is arranged on the second surface. Thus, at the time of assembly of the power conversion device, the water passage defining member is required to be inverted. Thus, ease of assembly is poor. 
     SUMMARY OF THE INVENTION 
     This disclosure has been made to solve the above-mentioned problem, and has an object to provide a power conversion device which is improved in ease of assembly while preventing reduction in cooling performance. 
     According to at least one embodiment of this disclosure, there is provided a power conversion device, including: a semiconductor module; a smoothing capacitor configured to smooth an input voltage to the semiconductor module; a bus bar assembly configured to electrically connect at least two of the semiconductor module, the smoothing capacitor, and a power supply; and a cooler, wherein the semiconductor module, the bus bar assembly, and the smoothing capacitor are superposed on the cooler in the stated order from the cooler side, and wherein at least one of a cooling column-equipped member, which is at least one of the smoothing capacitor and the bus bar assembly, and the cooler is provided with a cooling column configured to transfer heat of the cooling column-equipped member to the cooler. 
     According to the power conversion device of this disclosure, ease of assembly can be improved while preventing reduction in cooling performance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view for illustrating a power conversion device according to a first embodiment. 
         FIG.  2    is an exploded perspective view for illustrating the power conversion device of  FIG.  1   . 
         FIG.  3    is a perspective view for illustrating a cooler main body of  FIG.  2   . 
         FIG.  4    is a perspective view for illustrating a state in which a plurality of semiconductor modules of  FIG.  2    are mounted on the cooler. 
         FIG.  5    is a sectional view of an assembly including the cooler and the plurality of semiconductor modules of  FIG.  4   . 
         FIG.  6    is a perspective view for illustrating a state in which a bus bar assembly of  FIG.  2    is mounted on the plurality of semiconductor modules of  FIG.  4   . 
         FIG.  7    is a sectional view of an assembly including the cooler, the plurality of semiconductor modules, and the bus bar assembly of  FIG.  6   . 
         FIG.  8    is a perspective view for illustrating a smoothing capacitor of  FIG.  2   . 
         FIG.  9    is a sectional view of the power conversion device of  FIG.  1   . 
         FIG.  10    is a sectional view for illustrating a modification example of the power conversion device according to the first embodiment. 
         FIG.  11    is a perspective view for illustrating a power conversion device according to a second embodiment. 
         FIG.  12    is a sectional view of the power conversion device of  FIG.  11   . 
         FIG.  13    is a sectional view of a power conversion device according to a third embodiment. 
         FIG.  14    is a sectional view of a power conversion device according to a fourth embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Now, embodiments of this disclosure are described with reference to the drawings. 
     First Embodiment 
       FIG.  1    is a perspective view for illustrating a power conversion device according to a first embodiment.  FIG.  2    is an exploded perspective view for illustrating the power conversion device of  FIG.  1   . A power conversion device  100  according to the first embodiment supplies AC power to a driving motor for a hybrid automobile or an electric automobile. However, uses of the power conversion device  100  are not particularly limited. 
     Further, the power conversion device  100  according to the first embodiment functions as an inverter that converts DC power from a battery into AC power so as to drive a rotating electric machine including the driving motor. Further, the power conversion device  100  according to the first embodiment functions as a converter that converts AC power output from a generator into DC power so as to charge the battery. 
     As illustrated in  FIG.  1    and  FIG.  2   , the power conversion device  100  includes a cooler  10 , a plurality of semiconductor modules  20 , a bus bar assembly  30 , a control board  40 , and a smoothing capacitor  50 . 
     The plurality of semiconductor modules  20 , the bus bar assembly  30 , the control board  40 , and the smoothing capacitor  50  are arranged on the cooler  10 . Further, the plurality of semiconductor modules  20 , the bus bar assembly  30 , the control board  40 , and the smoothing capacitor  50  are superposed in the stated order from the cooler  10  side. 
     The cooler  10  is made of, for example, aluminum or an aluminum alloy. Further, the cooler  10  includes a cooler main body  11  and a cooler upper plate  12 . The cooler upper plate  12  is a rectangular flat plate. 
     The control board  40  includes a drive circuit (not shown) and a control circuit (not shown). The drive circuit drives the plurality of semiconductor modules  20 . The control circuit controls the drive circuit. 
     One control board  40  is illustrated in  FIG.  2   . However, the control board  40  may be divided into a plurality of boards in view of, for example, functionality, ease of layout, and productivity. Further, the control board  40  may be arranged at a position different from that illustrated in  FIG.  2   . For example, the control board  40  may be arranged on a side opposite to the bus bar assembly  30  with respect to the smoothing capacitor  50 . 
       FIG.  3    is a perspective view for illustrating the cooler main body  11  of  FIG.  2   . The cooler main body  11  includes a bottom portion  11   a , a side wall portion lib, a flow passage defining portion  11   c , a heat transfer fin  11   e , a plurality of first receiving portions  11   f , and a plurality of second receiving portions  11   g . Each of the first receiving portions  11   f  and the second receiving portions  11   g  has a block-like shape. 
     The bottom portion  11   a  has a rectangular flat plate-like shape. The side wall portion lib has a rectangular frame-like shape. Further, the side wall portion lib protrudes from a peripheral edge of the bottom portion  11   a  at a right angle with respect to the bottom portion  11   a.    
     The flow passage defining portion  11   c  is located on an inner side of the side wall portion lib, and protrudes from the bottom portion  11   a  in the same direction as the direction in which the side wall portion lib protrudes. The flow passage defining portion  11   c  has refrigerant flow passages lid each having a groove-like shape. 
     The refrigerant flow passages lid allow a refrigerant (not shown) to flow therethrough. In the first embodiment, water is used as the refrigerant. Specifically, the cooler  10  according to the first embodiment is a water-cooling cooler. The heat transfer fin lie faces the refrigerant flow passages  11   d.    
     The plurality of first receiving portions  11   f  and the plurality of second receiving portions  11   g  protrude from the bottom portion  11   a  in the same direction as the direction in which the flow passage defining portion  11   c  protrudes. Further, the plurality of first receiving portions  11   f  and the plurality of second receiving portions  11   g  are arranged between the side wall portion lib and the flow passage defining portion  11   c.    
     The first receiving portions  11   f  are adjacent to the flow passage defining portion  11   c . The plurality of second receiving portion  11   g  are arranged farther from the flow passage defining portion  11   c  than the plurality of first receiving portions  11   f  are. Further, a protrusion amount of each of the second receiving portions  11   g  from the bottom portion  11   a  is larger than a protrusion amount of each of the first receiving portions  11   f  from the bottom portion  11   a.    
       FIG.  4    is a perspective view for illustrating a state in which the plurality of semiconductor modules  20  of  FIG.  2    are mounted on the cooler  10 . The cooler upper plate  12  is joined to the flow passage defining portion  11   c  through intermediation of a sealing component (not shown). For example, a gasket is used as the sealing component. The cooler upper plate  12  may also be joined to the flow passage defining portion  11   c  by friction stir welding (FSW) or electron beam welding. 
     When the cooler upper plate  12  is mounted onto the flow passage defining portion  11   c , the refrigerant flow passages  11   d  are defined inside the cooler  10 . 
     The plurality of semiconductor modules  20  are mounted on the cooler upper plate  12 . Each of the semiconductor modules  20  includes a power semiconductor element (not shown). The power semiconductor element is, for example, an insulated gate bipolar transistor (IGBT). 
     Each of the semiconductor modules  20  generates heat as a result of its high-speed switching operation. The heat generated in each of the semiconductor modules  20  is transferred to the refrigerant flowing through the refrigerant flow passages  11   d  via the cooler upper plate  12 . 
       FIG.  5    is a sectional view of an assembly including the cooler  10  and the plurality of semiconductor modules  20  of  FIG.  4   , and is an illustration of a cross section taken parallel to an XZ plane of  FIG.  4   . A first heat transfer member  61  serving as a module heat transfer member is provided between each of the semiconductor modules  20  and the cooler upper plate  12 . As a material of the first heat transfer members  61 , a material having high heat conductivity, for example, grease, solder, adhesive, gap filler, or a compound is used. 
       FIG.  6    is a perspective view for illustrating a state in which the bus bar assembly  30  of  FIG.  2    is mounted on the plurality of semiconductor modules  20  of  FIG.  4   .  FIG.  7    is a sectional view of an assembly including the cooler  10 , the plurality of semiconductor modules  20 , and the bus bar assembly  30  of  FIG.  6   , and is an illustration of a cross section taken parallel to an XZ plane of  FIG.  6   . 
     The bus bar assembly  30  includes a plurality of sheet metal members  31  and a holding member  32 . The holding member  32  is made of a resin. The plurality of sheet metal members  31  and the holding member  32  are formed integrally by insert molding. With this configuration, the plurality of sheet metal members  31  are held in the holding member  32 . 
     The plurality of sheet metal members  31  electrically connect a DC power supply (not shown), the plurality of semiconductor modules  20 , the smoothing capacitor  50 , and an external device (not shown). The external device includes a rotating electric machine and an air conditioner. 
     The holding member  32  includes a holding member main body  32   a  having a flat plate-like shape and a plurality of first bus bar cooling columns  32   b  each having a bar-like shape. The holding member main body  32   a  is opposed to surfaces of the plurality of semiconductor modules  20 , which are on a side opposite to the cooler upper plate  12 . 
     The plurality of first bus bar cooling columns  32   b  protrude from the holding member main body  32   a  toward the bottom portion  11   a . Further, the plurality of first bus bar cooling columns  32   b  transfer heat of the bus bar assembly  30  to the cooler  10 . Specifically, the bus bar assembly  30  is a cooling column-equipped member including the plurality of first bus bar cooling columns  32   b  serving as heat transfer paths to the cooler  10 . 
     Each of the first bus bar cooling columns  32   b  is fastened to a corresponding one of the first receiving portions  11   f  with a first fastener  33 . A screw is used as each of the first fasteners  33 . 
     The bus bar cooling columns  32   b  are in contact with side surfaces of the flow path defining portion  11   c . The plurality of first bus bar cooling columns  32   b  may be made of a material different from a material of the holding member main body  32   a , for example, a metal. 
     A second heat transfer member  62  serving as a cooling column heat transfer member is provided between each of the first bus bar cooling columns  32   b  and a corresponding one of the first receiving portions  11   f . As a material of the second heat transfer members  62 , a material having high heat conductivity, for example, grease, solder, adhesive, gap filler, or a compound is used. 
     The heat received by the bus bar assembly  30  from the plurality of semiconductor modules  20  is transferred through the plurality of first bus bar cooling columns  32   b  to the plurality of first receiving portions  11   f  and the flow passage defining portion  11   c , and is released through the cooler  10 . 
       FIG.  8    is a perspective view for illustrating the smoothing capacitor  50  of  FIG.  2   .  FIG.  9    is a sectional view of the power conversion device  100  of  FIG.  1   , and is an illustration of a cross section taken parallel to an XZ plane of  FIG.  1   . 
     The smoothing capacitor  50  smooths an input voltage to the plurality of semiconductor modules  20 . Further, the smoothing capacitor  50  includes a case  51 , a capacitor element (not shown), and a plurality of capacitor bus bars  52 . The case  51  is made of a synthetic resin. 
     The capacitor element is provided in the case  51 . A rolled film capacitor is used as the capacitor element. The rolled film capacitor has a flat shape with an elliptical cross section. An epoxy resin is supplied to the case  51  to thereby seal the capacitor element within the case  51 . 
     The plurality of capacitor bus bars  52  are connected to the capacitor element. Further, each of the capacitor bus bars  52  protrudes to an outside of the case  51 , and is connected to a corresponding one of the sheet metal members  31 . 
     The case  51  includes a case main body  51   a  and a plurality of first capacitor cooling columns  51   b . The case main body  51   a  has a flat plate-like shape. Each of the plurality of first capacitor cooling columns  51   b  has a bar-like shape. The case main body  51   a  is opposed to a surface of the control board  40  on a side opposite to the bus bar assembly  30 . 
     The plurality of first capacitor cooling columns  51   b  protrude from the case main body  51   a  toward the bottom portion  11   a . Further, the plurality of first capacitor cooling columns  51   b  transfer heat of the smoothing capacitor  50  to the cooler  10 . Specifically, the smoothing capacitor  50  is a cooling column-equipped member including the plurality of first capacitor cooling columns  51   b  serving as heat transfer paths to the cooler  10 . 
     As described above, in the first embodiment, both of the bus bar assembly  30  and the smoothing capacitor  50  are the cooling column-equipped members. 
     Each of the first capacitor cooling columns  51   b  is fastened to a corresponding one of the second receiving portions  11   g  with a second fastener  53 . A screw is used as each of the second fasteners  53 . 
     The plurality of first capacitor cooling columns  51   b  may be made of a material different from that of the case main body  51   a , for example, a metal. 
     A third heat transfer member  63  serving as a cooling column heat transfer member is provided between each of the first capacitor cooling columns  51   b  and a corresponding one of the second receiving portions  11   g . As a material of the third heat transfer members  63 , a material having high heat conductivity, for example, grease, solder, adhesive, gap filler, or a compound is used. 
     Heat generated in the smoothing capacitor  50  is transferred from the plurality of first capacitor cooling columns  51   b  to the plurality of second receiving portions  11   g , and is released through the cooler  10 . 
     In the power conversion device  100  as described above, the plurality of semiconductor modules  20 , the bus bar assembly  30 , and the smoothing capacitor  50  are superposed on the cooler  10  in the stated order. More specifically, the plurality of semiconductor modules  20 , the smoothing capacitor  50 , and the bus bar assembly  30  are stacked on the same side with respect to the cooler  10 . 
     Thus, the plurality of semiconductor modules  20 , the bus bar assembly  30 , and the smoothing capacitor  50  can be mounted on the cooler  10  without inverting the cooler  10 . 
     Further, the smoothing capacitor  50  includes the plurality of first capacitor cooling columns  51   b . Thus, the first capacitor cooling columns  51   b  allow the heat generated in the smoothing capacitor  50  to be smoothly transferred to the cooler  10  so that the heat is released through the cooler  10 . 
     Further, the bus bar assembly  30  includes the plurality of first bus bar cooling columns  32   b . Thus, the first bus bar cooling columns  32   b  allow the heat received by the bus bar assembly  30  to be smoothly transferred to the cooler  10  so that the heat is released through the cooler  10 . 
     Thus, the power conversion device  100  according to the first embodiment is improved in ease of assembly while preventing reduction in cooling performance. 
     Further, the first heat transfer member  61  is provided at a thermal interface being a plane at which each of the semiconductor modules  20  and the cooler  10  are joined together. As a result, an air layer, which is otherwise formed at the thermal interface, is replaced by the first heat transfer member  61 . Thus, the heat generated in each of the semiconductor modules  20  can be more smoothly transferred to the cooler  10 . As a result, the cooling performance is improved. 
     Further, the second heat transfer member  62  is provided at a thermal interface being a plane at which each of the first bus bar cooling columns  32   b  and the cooler  10  are joined together. As a result, an air layer, which is otherwise formed at the thermal interface, is replaced by the second heat transfer member  62 . Thus, the heat received by the bus bar assembly  30  can be more smoothly transferred to the cooler  10 . As a result, the cooling performance is improved. 
     Further, the third heat transfer member  63  is provided at a thermal interface being a plane at which each of the first capacitor cooling columns  51   b  and the cooler  10  are joined together. As a result, an air layer, which is otherwise formed at the thermal interface, is replaced by the third heat transfer member  63 . Thus, the heat generated in the smoothing capacitor  50  can be more smoothly transferred to the cooler  10 . As a result, the cooling performance is improved. 
     Further, the plurality of second receiving portions  11   g  are arranged farther from the flow passage defining portion  11   c  than the plurality of first receiving portions  11   f  are. Each of the first bus bar cooling columns  32   b  is connected to a corresponding one of the first receiving portions  11   f , and each of the first capacitor cooling columns  51   b  is connected to a corresponding one of the second receiving portions  11   g . Thus, the power conversion device  100  is improved in ease of assembly. 
     Further, the plurality of first receiving portions  11   f  and the plurality of second receiving portions  11   g  protrude from the bottom portion  11   a . Thus, this configuration facilitates the connection of the first bus bar cooling columns  32   b  and the first capacitor cooling columns  51   b  to the cooler  10 . 
     The first bus bar cooling columns  32   b  may be connected to the bottom portion  11   a  or the side wall portion lib. 
     The first capacitor cooling columns  51   b  may be connected to the bottom portion  11   a  or the side wall portion lib. 
     Now,  FIG.  10    is a sectional view for illustrating a modification example of the power conversion device  100  according to the first embodiment, and is an illustration of a cross section corresponding to  FIG.  5   . A cooler upper plate  12  of the modification example has a hole  12   a  having a rectangular shape in its center. 
     A heat sink  21  is fixed to each of semiconductor modules  20 . The heat sink  21  includes a heat sink base portion  21   a  and a heat transfer fin  21   b . The heat sink base portion  21   a  is fixed to each of the semiconductor modules  20 . Further, the heat sink base portion  21   a  is superposed on a portion of an upper surface of the cooler upper plate  12 , which corresponds to an edge of the hole  12   a , and is fixed to the cooler upper plate  12 . 
     A sealing component (not shown) is provided between the cooler upper plate  12  and each of the heat sink base portions  21   a . The heat transfer fins  21   b  pass through the hole  12   a  and protrude beyond a lower surface of the cooler upper plate  12  toward the bottom portion  11   a . The illustration of the heat transfer fin  11   e  and the first heat transfer members  61  is omitted. 
     The effects obtained by the power conversion device  100  according to the first embodiment can also be achieved with the above-mentioned configuration. 
     Second Embodiment 
     Next,  FIG.  11    is a perspective view for illustrating a power conversion device  100  according to a second embodiment.  FIG.  12    is a sectional view of the power conversion device  100  of  FIG.  11   , and is an illustration of a cross section taken parallel to an XZ plane of  FIG.  11   . 
     A holding member  32  of a bus bar assembly  30  according to the second embodiment further includes a plurality of second bus bar cooling columns  32   c  each having a bar-like shape. 
     The plurality of second bus bar cooling columns  32   c  protrude from a holding member main body  32   a  toward a bottom portion  11   a  in parallel to a plurality of first bus bar cooling columns  32   b . Further, the plurality of second bus bar cooling columns  32   c  transfer heat of the bus bar assembly  30  to a cooler  10 . 
     The second bus bar cooling columns  32   c  are in indirect contact with a bottom portion  11   a  through intermediation of second heat transfer members  62 . Further, the second bus bar cooling columns  32   c  are in contact with side surfaces of a flow passage defining portion  11   c . The plurality of second bus bar cooling columns  32   c  may be made of a material different from a material of a holding member main body  32   a , for example, a metal. 
     Heat received by the bus bar assembly  30  is transferred through the plurality of first bus bar cooling columns  32   b  and the plurality of second bus bar cooling columns  32   c  to the cooler  10 , and is released through the cooler  10 . 
     A case  51  of a smoothing capacitor  50  according to the second embodiment further includes a plurality of second capacitor cooling columns  51   c , each having a bar-like shape. 
     The plurality of second capacitor cooling columns  51   c  protrude from the case main body  51   a  toward the bottom portion  11   a  in parallel to a plurality of first capacitor cooling columns  51   b . Further, the plurality of second capacitor cooling columns  51   c  transfer heat of the smoothing capacitor  50  to the cooler  10 . 
     The second capacitor cooling columns  51   c  are in indirect contact with the bottom portion  11   a  through intermediation of third heat transfer members  63 . The plurality of second capacitor cooling columns  51   c  may be made of a material different from a material of the case main body  51   a , for example, a metal. 
     Heat generated in the smoothing capacitor  50  is transferred through the plurality of first capacitor cooling columns  51   b  and the plurality of second capacitor cooling columns  51   c  to the cooler  10 , and is released through the cooler  10 . 
     The other components in the second embodiment are similar or identical to those in the first embodiment. 
     In the power conversion device  100  as described above, the bus bar assembly  30  includes the plurality of second bus bar cooling columns  32   c . Thus, the plurality of second bus bar cooling columns  32   c  allow the heat received by the bus bar assembly  30  to be more smoothly transferred to the cooler  10  so that the heat is released through the cooler  10 . As a result, the cooling performance is improved. 
     Further, the smoothing capacitor  50  includes the plurality of second capacitor cooling columns  51   c . Thus, the plurality of second capacitor cooling columns  51   c  allow the heat generated in the smoothing capacitor  50  to be more smoothly transferred to the cooler  10  so that the heat is released through the cooler  10 . As a result, the cooling performance is improved. 
     Further, the plurality of second bus bar cooling columns  32   c  and the plurality of second capacitor cooling columns  51   c  are in indirect contact with the bottom portion  11   a , but are not fixed to the cooler  10  with screws. Thus, the number of positions at which the bus bar assembly  30  and the smoothing capacitor  50  are fixed to the cooler  10  does not increase, and reduction in ease of assembly is prevented. 
     Third receiving portions may also be provided on the bottom portion  11   a . Each of the third receiving portions has a block-like shape, and protrudes in the same direction as a direction in which the flow passage defining portion  11   c  protrudes. The second bus bar cooling columns  32   c  may be in contact with the third receiving portions instead of being in indirect contact with the bottom portion  11   a.    
     Further, the second bus bar cooling columns  32   c  may be in contact with at least one of the first bus bar cooling columns  32   b  or the side wall portion  11   b.    
     Further, fourth receiving portions may also be provided on the bottom portion  11   a . Each of the fourth receiving portions has a block-like shape, and protrudes in the same direction as the direction in which the flow passage defining portion  11   c  protrudes. The second capacitor cooling columns  51   c  may be in contact with the fourth receiving portions instead of being in indirect contact with the bottom portion  11   a.    
     Still further, the second capacitor cooling columns  51   c  may be in contact with at least one of the first capacitor cooling columns  51   b  or the side wall portion  11   b.    
     Third Embodiment 
     Next,  FIG.  13    is a sectional view of a power conversion device  100  according to a third embodiment, and is an illustration of a cross section corresponding to a cross section taken parallel to the XZ plane of  FIG.  1   . 
     The power conversion device  100  according to the third embodiment further includes a cooling plate  54  made of a metal. As a material of the cooling plate  54 , for example, copper or aluminum is used. 
     The cooling plate  54  includes a flat plate portion  54   a  and a pair of leg portions  54   b . The flat plate portion  54   a  is in indirect contact with a surface of a case main body  51   a , which is opposed to a control board  40 . 
     The leg portions  54   b  protrude from the flat plate portion  54   a  toward a bottom portion  11   a , and are in indirect contact with the bottom portion  11   a . A fourth heat transfer member  64  serving as a first cooling plate heat transfer member is provided between each of the leg portions  54   b  and the bottom portion  11   a . As a material of the fourth heat transfer members  64 , a material having high heat conductivity, for example, grease, solder, adhesive, gap filler, or a compound is used. 
     A fifth heat transfer member  65  serving as a second cooling plate heat transfer member is provided between the flat plate portion  54   a  and a case main body  51   a . As a material of the fifth heat transfer member  65 , a material having high heat conductivity, for example, grease, solder, adhesive, gap filler, or a compound is used. 
     The cooling plate  54  is connected to a cooler  10  through intermediation of the fourth heat transfer members  64 . Further, the cooling plate  54  is connected to a smoothing capacitor  50  through intermediation of the fifth heat transfer member  65 . Specifically, a cooling plate connection member in the third embodiment is the smoothing capacitor  50 . 
     Heat generated in the smoothing capacitor  50  is transferred through a plurality of first capacitor cooling columns  51   b  and the cooling plate  54  to the cooler  10 , and is released through the cooler  10 . 
     The other components in the third embodiment are similar or identical to those in the first embodiment. 
     In the power conversion device  100  as described above, the cooling plate  54  is provided between the smoothing capacitor  50  and the cooler  10 . Thus, the cooling plate  54  allows heat generated in the smoothing capacitor  50  to be more smoothly transferred to the cooler  10  so that the heat is released through the cooler  10 . As a result, cooling performance is improved. 
     Further, the fourth heat transfer member  64  is provided at a thermal interface being a plane at which each of the leg portions  54   b  and the bottom portion  11   a  are joined together. As a result, an air layer, which is otherwise formed at the thermal interface, is replaced by the fourth heat transfer member  64 . Thus, the heat generated in the smoothing capacitor  50  can be more smoothly transferred to the cooler  10 . As a result, the cooling performance is improved. 
     Further, the fifth heat transfer member  65  is provided at a thermal interface being a plane at which the flat plate portion  54   a  and the case main body  51   a  are joined together. As a result, an air layer, which is otherwise formed at the thermal interface, is replaced by the fifth heat transfer member  65 . Thus, the heat generated in the smoothing capacitor  50  can be more smoothly transferred to the cooler  10 . As a result, the cooling performance is improved. 
     Further, the cooling plate  54  is made of a metal. Thus, the heat generated in the smoothing capacitor  50  can be more smoothly transferred to the cooler  10 . As a result, the cooling performance is improved. 
     Fifth receiving portions may also be provided on the bottom portion  11   a . Each of the fifth receiving portions protrudes in the same direction as a direction in which a flow passage defining portion  11   c  protrudes. The cooling plate  54  may be in contact with the fifth receiving portions instead of being in indirect contact with the bottom portion  11   a . Still further, the cooling plate  54  may be fastened to the fifth receiving portion with fasteners. 
     Further, the cooling plate  54  may be in contact with at least one of the first capacitor cooling columns  51   b  or the side wall portion  11   b.    
     Still further, the power conversion device  100  according to the third embodiment may include the second capacitor cooling columns  51   c  which have been described in the second embodiment. In this case, the cooling plate  54  may be in contact with the second capacitor cooling columns  51   c.    
     Still further, when a control board  40  is not arranged between the smoothing capacitor  50  and a bus bar assembly  30 , the flat plate portion  54   a  may be sandwiched between the smoothing capacitor  50  and the bus bar assembly  30 . Specifically, a cooling plate connection member may be both of the smoothing capacitor  50  and the bus bar assembly  30 . 
     Fourth Embodiment 
     Next,  FIG.  14    is a sectional view of a power conversion device  100  according to a fourth embodiment, and is an illustration of a cross section corresponding to a cross section taken parallel to the XZ plane of  FIG.  1   . 
     In the fourth embodiment, at least a part of a cooling plate  54  is embedded in a case  51 . In the example of  FIG.  14   , the entirety of the cooling plate  54  is embedded in the case  51 . Further, the cooling plate  54  is arranged inside the case  51  at a distance from a plurality of capacitor bus bars  52 . Further, an epoxy resin is supplied to the case  51  to thereby integrate the cooling plate  54  with the case  51 . 
     The other components in the fourth embodiment are similar or identical to those in the third embodiment. 
     In the power conversion device  100  as described above, the cooling plate  54  is embedded in the case  51 . Thus, heat generated in the smoothing capacitor  50  can be more smoothly transferred to the cooler  10 . As a result, cooling performance is improved. 
     In the fourth embodiment, only a part of the cooling plate  54  may be embedded in the case  51 . 
     In the third and fourth embodiments, a cooling plate made of a metal, which is independent of the cooling plate  54 , may be provided between a bus bar assembly  30  serving as a cooling plate connection member and the cooler  10 . 
     Further, in the first to fourth embodiments, the number of bus bar cooling columns and the number of capacitor cooling columns are not limited to particular numbers. 
     Still further, in the first to fourth embodiments, the cooler  10  may include the bus bar cooling columns as a part of the cooler  10 . In this case, the bus bar cooling columns protrude from the bottom portion  11   a  toward the bus bar assembly  30  to be in contact with the bus bar assembly  30  directly or through intermediation of heat transfer members. 
     Still further, both of the cooler  10  and the bus bar assembly  30  may be provided with the bus bar cooling columns. 
     Still further, in the first to fourth embodiments, the cooler  10  may include the capacitor cooling columns as a part of the cooler  10 . In this case, the capacitor cooling columns protrude from the bottom portion  11   a  toward the smoothing capacitor  50  to be in contact with the smoothing capacitor  50  directly or through intermediation of heat transfer members. 
     Still further, both of the cooler  10  and the smoothing capacitor  50  may be provided with the capacitor cooling columns. 
     Still further, the cooling column-equipped member may be the smoothing capacitor  50  alone. Specifically, the bus bar cooling columns may be omitted. 
     Still further, the cooling column-equipped member may be the bus bar assembly  30  alone. Specifically, the capacitor cooling columns may be omitted. 
     Still further, as a material of the cooling columns, for example, aluminum may be used. 
     Still further, the refrigerant is not limited to water, and may be a fluid other than water. 
     Still further, the bus bar assembly  30  is only required to electrically connect at least two of the semiconductor modules  20 , the smoothing capacitor  50 , and the power supply.