Patent Publication Number: US-10765044-B2

Title: Electric power conversion device

Description:
TECHNICAL FIELD 
     The present invention relates to an electric power conversion device. 
     BACKGROUND ART 
     In a known electric power conversion device including reactors, power modules and capacitors, a cooling water passage is formed in a specific area of a bottom plate of a case, and the reactors and the power modules are positioned on the part of the bottom plate corresponding to the cooling water passage while the capacitors are placed on other part of the bottom plate. See JP2017-135901A. The part of the bottom plate where the cooling water passage is absent has a relatively low upper surface so that the vertical dimension of the space defined above such a part can be maximized. 
     However, according to the electric power conversion device disclosed in JP2017-135901A, the capacitors are too remotely positioned from the cooling water passage to be adequately cooled. Also, because the reactors, the power modules and the capacitors are positioned on a single plane without any overlap, the area of the necessary floor space (footprint) is undesirably great. 
     SUMMARY OF THE INVENTION 
     In view of such a problem of the prior art, a primary object of the present invention is to provide an electric power conversion device which is configured to be favorably cooled, and compact in size. 
     The present invention achieves such an object by providing an electric power conversion device, comprising a reactor ( 31 ), a switching device ( 33 ) connected to the reactor, a capacitor ( 35 ), and a case ( 60 ) receiving the reactor, the switching device and the capacitor therein, wherein the case comprises: a first member ( 61 ) having a first region ( 73 ) defining therein a first passage ( 78 ,  79 ) in which a cooling medium flows, and a second region ( 74 ) disposed on a side of the first region; and a second member ( 88 ) disposed so as to at least partly overlap with the second region as seen from a direction orthogonal to the second region in a spaced apart relationship to the second region, and internally defining a second passage ( 91 ) connected to the first passage, and wherein the reactor is positioned in the first region, and one of the switching device and the capacitor is positioned on a surface of the second member facing away from the first member, the other of the switching device and the capacitor being positioned between the second member and the second region of the first member. 
     Since the power module and the capacitor overlap with each other with the support member interposed therebetween, the floor space (footprint) which the first member of the case is required to provide can be minimized. Further, since the reactor can be enlarged in the direction orthogonal to the first member, the space efficiency of the electric power converter can be enhanced while ensuring an adequate cross sectional area for the magnetic flux to the reactor. In addition, since the reactor is provided in the first region having the first passage, and the power module and the capacitor are provided in the second member having the second passage, all of the reactor, the power module and the capacitor can be efficiently cooled. 
     Preferably, the switching device is positioned on the surface of the second member facing away from the first member, and the capacitor is positioned between the second member and the second region of the first member. 
     Thereby, the switching device and the capacitor can be favorably cooled by the cooling medium flowing through the second passage, and owing to the mutually overlapping positioning of the switching device and the capacitor, the space efficiency of the case can be optimized. 
     Preferably, an inner surface of the second region is outwardly offset relative to an inner surface of the first region. 
     Since the second region does not have a passage through which the cooling medium flows, the second region may have a smaller thickness than the first region. Therefore, the available space inward of the second region can be widened as compared to the available space inward of the first region without requiring the second region of the first member to project further outward than the first region of the first member. 
     Preferably, a first connection hole ( 85 ) and a second connection hole ( 86 ) extending from the first passage open out at the inner surface of the first region, and a third connection hole ( 92 ) and a fourth connection hole ( 93 ) extending from the second passage open out at a surface of the second member on a side of the first member, the first connection hole being communicating with the third connection hole, and the second connection hole being communicating with the fourth connection hole. 
     According to this arrangement, the second passage formed in the second member can be connected to the first passage formed in the first region of the first member in an advantageous manner. 
     Preferably, the first passage includes an upstream first passage ( 78 ) and a downstream first passage ( 79 ), the upstream first passage communicating with a cooling medium inlet ( 81 ) provided at an outer surface of the case and the first connection hole, the downstream first passage communicating with a cooling medium outlet ( 82 ) provided at the outer surface of the case and the second connection hole. 
     Thereby, a continuous passage extending along the path provided by the cooling medium inlet, the upstream first passage, the second passage, the downstream first passage and the cooling medium outlet is formed so that the cooling medium can be circulated in a smooth manner. 
     Preferably, the capacitor is in contact with the inner surface of the second region. 
     Thereby, the heat can be transferred from the capacitor to the second region of the first member in addition to the second member so that the capacitor can be cooled in an efficiently manner. 
     Preferably, a side of the switching device facing away from the second member is provided with a gate driver ( 52 ) for driving the switching device. 
     Thereby, the capacitor, the support member, the power module, and the gate driver can be stacked one upon the other so that the space efficiency of the case can be optimized. 
     Preferably, a side of the gate driver facing away from the switching device is provided with a control unit ( 51 ) for controlling the gate driver via insulating material. 
     Thereby, the capacitor, the support member, the power module, and the gate driver can be stacked one upon the other so that the space efficiency of the case can be optimized. 
     Preferably, an outer surface of the first region is provided with a recess ( 75 ,  76 ) which is recessed inward, and a cover ( 77 ) closing an open end of the recess to define the first passage in cooperation with the recess. 
     Thereby, the first passage can be easily formed. 
     Preferably, the reactor has a greater thickness as measured in a direction orthogonal to the second region than either the switching device or the capacitor. 
     Thereby, the space efficiency of the electric power conversion device can be enhanced while ensuring an adequate cross sectional area for the magnetic flux to the reactor. 
     Preferably, the first region of the first member includes a first bottom plate extending along a major plane, and the second region of the first member includes a second bottom plate extending substantially in parallel with the first bottom plate and offset from the first bottom plate in an outward direction. 
     Thereby, it becomes possible to arrange some of the components so as to overlap one another, and to interpose the second member which is provided with the second passage between selected two of the components. 
     Preferably, the case further comprises an outer plate member ( 77 ) opposing an outer surface of the first bottom plate in a spaced apart relationship so as to define the first passage jointly with the first bottom plate, an outer surface of the outer plate member being substantially flush with an outer surface of the second bottom plate. 
     Thereby, the first passage can be formed in such a manner that the bottom surface of the case is made entirely planar. The outer surface of the outer plate member may be provided with ribs so as to enhance the cooling of the cooling medium in the first passage. 
     Preferably, the second member comprises an inner plate member ( 88 ) extending substantially in parallel with the second bottom plate in a spaced apart relationship to define a chamber jointly with the second bottom plate. 
     Thereby, one of the components such as the capacitor can be received in this chamber so that the second passage can be effectively utilized to cool two components positioned on either side of the inner plate member. 
     Preferably, the first member further comprises a side wall extending upright from a periphery of the first member, and the case further comprises a cover member abutting a free end of the side wall to define a chamber jointly with the first member. 
     Thereby, the case can be fully enclosed by virtue of the cover member, the first member, the outer plate member that can jointly define a simple outer profile such as a rectangular outer profile. 
     The invention thus provides an electric power conversion device which is configured to be favorably cooled, and compact in size. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING(S) 
         FIG. 1  is a block diagram of an electric vehicle according to an embodiment of the present invention; 
         FIG. 2  is an electric circuit diagram of the electric vehicle; 
         FIG. 3  is a plan view of an FC-side converter with an upper case, a converter ECU and a support member omitted from illustration; 
         FIG. 4  is a vertical sectional view of the FC-side converter; 
         FIG. 5  is an enlarged vertical sectional view of an essential part of the FC-side converter; 
         FIG. 6  is a diagram showing a medium passage of the FC-side converter; 
         FIG. 7  is a plan view of the FC-side converter with the upper case and the converter ECU omitted from illustration; 
         FIG. 8  is a side view of the FC-side converter as viewed from the +Y side; 
         FIG. 9  is a diagram showing a layout of various elements of the FC-side converter; 
         FIG. 10  is a plan view of the support member and a wire harness; 
         FIG. 11  is a perspective view of the support member; and 
         FIG. 12  is a perspective view of the support member and the converter ECU. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     An electric vehicle according to an embodiment of the present invention is described in the following. 
     As shown in  FIG. 1 , the electric vehicle  1  includes a fuel cell  2  (FC), an FC-side converter  3  (electric power conversion device), a battery  4 , a battery-side converter  5 , a PDU  6  (Power Drive Unit), and a motor generator  7 . The FC-side converter  3  and the battery-side converter  5  each consist of a DC/DC converter, and the PDU  6  consists of an inverter. The FC-side converter  3 , the battery-side converter  5 , and the PDU  6  are controlled by an ECU  8  ( FIG. 2 ). 
     The fuel cell  2  generates electric energy by chemical reaction using hydrogen and oxygen as raw materials. The electric power generated by the fuel cell  2  is supplied to the motor generator  7  via the FC-side converter  3  and the PDU  6 , and supplied to the battery  4  via the FC-side converter  3  and the battery-side converter  5 . The power of the battery  4  is supplied to the motor generator  7  via the battery-side converter  5  and the PDU  6 . 
     The motor generator  7  is a power source for propelling the electric vehicle  1 , and receives power supply from at least one of the power supply device and the battery  4  to drive the drive wheels of the electric vehicle  1 . When the electric vehicle  1  decelerates, the motor generator  7  operates as a generator so as to apply a braking force to the drive wheels, and generate regenerative electric power. The regenerative power is supplied to the battery  4  via the PDU  6  and the battery-side converter  5 . 
     The electric circuit of the FC-side converter  3  is described in the following with reference to  FIG. 2 . As shown in  FIG. 2 , the FC-side converter  3  is a multiphase converter including a plurality of voltage converters  15  that are connected in parallel to one another. More specifically, the FC-side converter  3  includes a primary side positive line  16 , a secondary side positive line  17 , a negative line  18 , and first to fourth voltage converters  15 A to  15 D connected between the primary side positive line  16  and the secondary side positive line  17 . Each element of the first voltage converter  15 A is indicated by a suffix A, each element of the second voltage converter  15 B is indicated by a suffix B, and each element of the third voltage converter  15 C is indicated by a suffix C, and each element of the fourth voltage converter  15 D is indicated by a suffix D. When various elements of the first to fourth voltage converters  15 A to  15 D are collectively referred to, the suffixes are omitted. 
     A terminal end of the primary side positive line  16  is provided with a primary side positive terminal  21 , and a terminal end of the negative line  18  is provided with a primary side negative terminal  22 . The primary side positive terminal  21  and the primary side negative terminal  22  jointly form a primary side connection portion  23 , and are connected to a positive pole and a negative pole of the fuel cell  2 , respectively. A terminal end of the secondary side positive line  17  is provided with a secondary side positive terminal  25 . The other terminal end of the negative line  18  is provided with a secondary side negative terminal  26 . The secondary side positive terminal  25  and the secondary side negative terminal  26  jointly form a secondary side connection portion  27  which is connected to the PDU  6  and the battery-side converter  5 . 
     The first to fourth voltage converters  15 A to  15 D are each provided with a reactor  31  and a diode  32  which are connected in series in the power line extending between the primary side positive line  16  and the secondary side positive line  17  in that order from the side of the primary side positive line  16 , and a switching device  33  connected between the node between the reactor  31  and the diode  32  and the negative line  18 . Thus a step-up chopper circuit is formed. A secondary side capacitor  35  (smoothing capacitor) is connected between the negative line  18  and the secondary side positive line  17 . 
     All the diodes  32  and the switching devices  33  included in the first to fourth voltage converters  15 A to  15 D are integrated as a single power module  37  (switching unit). The power module  37  includes a circuit board supporting the diodes  32  and the switching devices  33 , and a molding resin which covers the diodes  32  and the switching devices  33  to define the outer shape of the power module  37 . The power module  37  includes a first positive terminal  41  serving as a primary side positive terminal of the first voltage converter  15 A, a second positive terminal  42  serving as a primary side positive terminal corresponding to the second voltage converter  15 B, a third positive terminal  43  serving as a primary side positive terminal corresponding to the third voltage converter  15 C, a fourth positive terminal  44  serving as a primary side positive terminal corresponding to the fourth voltage converter  15 D, a fifth positive terminal  45  serving as a secondary side positive terminal, and a negative terminal  46  connected to the negative line  18 . The power module  37  also has a drive signal terminal  47  configured to receive a drive signal for each switching device  33 . The drive signal terminal  47  includes a plurality of terminal pieces corresponding to the respective switching devices  33 . 
     The negative line  18  is provided with a first current sensor  48 , and the power lines of the voltage converter  15  for different phases are each provided with a second current sensor  49  for detecting the current of the corresponding phase. The first current sensor  48  and the second current sensor  49  each consist of a Hall sensor that is not in electrical contact with the circuit to be detected. 
     The FC-side converter  3  has a converter ECU  51  (control unit) that controls the on/off of each switching device  33  in response to a signal from the ECU  8 . The converter ECU  51  forwards a control signal to each switching device  33  via a gate driver  52 . More specifically, the gate driver  52  forwards a drive signal corresponding to the control signal output from the converter ECU  51  to each switching device  33  to drive each switching device  33  accordingly. 
     Each voltage converter  15  boosts the voltage by turning on and off the switching device  33  according to the signal from the converter ECU  51 , and supplies the boosted voltage to the secondary side. The converter ECU  51  determines the number of power converters to be driven, and the on/off phase and the duty ratio of each switching device  33  according to the signal from ECU  8  and the signals from first current sensor  48  and second current sensor  49 . 
     Next, the structure of the FC-side converter  3  is described in the following with reference to  FIGS. 3 to 12 . As shown in  FIGS. 3 and 4 , the outer shell of the FC-side converter  3  is formed by a case  60 . The case  60  has a box-shaped first case  63  including a bottom  61  (first member, mounting portion) consisting of a flat plate and a side wall  62  extending upright from the periphery of the bottom  61  at right angle, and a plate-like second case  64  attached to the free end of the side wall  62  to define a receiving space in cooperation with the first case  63 . In the following description regarding the FC-side converter  3 , the various directions are defined with respect to the case  60 . The direction orthogonal to the bottom  61  is the Z direction (the vertical direction as mounted on the vehicle), the direction toward the second case  64  with respect to the bottom  61  is +Z, and the direction facing away from the +Z is −Z. A first direction orthogonal to the Z direction is defined as X direction (the lateral direction as mounted on the vehicle), and a second direction orthogonal to both the Z direction and the X direction is defined as the Y direction (the fore and aft direction as mounted on the vehicle). The X direction may be +X or −X depending on which way the direction is defined along the X direction. Likewise, the Y direction may be +Y or −Y depending on which way the direction is defined along the Y direction. The case may be made of metallic material such as aluminum. 
     The bottom  61  is formed in a substantially rectangular shape extending along a plane including the X direction and the Y direction, and having a greater width in the X direction than in the Y direction. The side wall  62  includes first and second side walls  66  and  67  extending in the X direction, and third and fourth side walls  68  and  69  extending in the Y direction. The first side wall  66  is disposed on the +Y side with respect to the second side wall  67 , and the third side wall  68  is disposed on the −X side with respect to the fourth side wall  69 . The first side wall  66 , the second side wall  67 , the third side wall  68 , and the fourth side wall  69  are connected to each other to form a frame, and are provided around the periphery of the bottom  61 . The fourth side wall  69  is disposed at a position offset inward with respect to the side edge of the bottom  61  on the +X side. A part of the bottom  61  that protrudes beyond the fourth side wall  69  on the +X side will be referred to as extension  71 . 
     The bottom  61  may be divided into a first region  73  located on the +X side, and a second region  74  located on the −X side. The extension  71  is included in the first region  73 . As shown in  FIG. 4 , the inner surface of the second region  74  is offset from the inner surface of the first region  73  in the outward direction (−Z side) in a step-wise manner. As shown in  FIGS. 4 and 6 , the outer surface of the first region  73  of the bottom  61  is formed with a first recess  75  and a second recess  76  which are recessed inward. The first recess  75  and the second recess  76  extend in the X direction, and the second recess  76  is disposed on the +Y side of the first recess  75 . The first recess  75  and the second recess  76  extend along the −Z side of the fourth side wall  69 , and the end parts of these recesses on the +X side are disposed in the extension  71 . The first recess  75  and the second recess  76  have a certain width in the Y direction. 
     To the outer surface of the first region  73  of the bottom  61  is secured an outer plate member  77  via a gasket so as to close the open ends of the first recess  75  and the second recess  76 . The outer plate member  77  defines an upstream first passage  78  in cooperation with the first recess  75 , and a downstream first passage  79  in cooperation with the second recess  76 . The upstream first passage  78  and the downstream first passage  79  are separated from each other. The outer plate member  77  is provided with a plurality of ribs on an outer surface (facing the −Z side) so as to enhance the cooling of the cooling medium through the first passage. Also, the second region  74  of the bottom  61  is planar in this embodiment, and the outer surface of the outer plate member  77  is substantially flush with the outer surface of second region  74  so that the case  60  may be provided with a simple profile such a rectangular parallelepiped outer profile. The extension  71  of the bottom  61  is provided with an inlet hole  81  (cooling medium inlet) that is passed through from the first recess  75  to the surface of the extension  71  facing the +Z direction, and an outlet hole  82  (cooling medium outlet) passed through from the second recess  76  to the inwardly facing surface of the bottom  61 . 
     As shown in  FIG. 5 , on the −X side of the inner surface of the first region  73 , a planar fastening surface  84  is formed. In the first region  73 , a first communication hole  85  is passed from the first recess  75  through the fastening surface  84 , and a second communication hole  86  is passed from the second recess  76  through the fastening surface  84 . The second communication hole  86  is disposed on the +Y side of the first communication hole  85 . 
     As shown in  FIGS. 3 and 4 , to the fastening surface  84  of the first region  73  is fastened a support plate  88  (second member; inner plate member) which is formed as a plate member having a first surface  88 A (surface facing the −Z side) facing the bottom  61 , and a second surface  88 B (surface facing the +Z side) facing away from the bottom  61 . The support plate  88  is fastened to the fastening surface  84  at the end part of the first surface  88 A on the +X side. The support plate  88  is disposed so as to overlap with the first region  73  in the end part thereof on the +X side, and overlaps with the second region  74  in the remaining part thereof. The support plate  88  opposes the inner surface of the second region  74  in a spaced apart and parallel relationship. The end part of the support plate  88  on the −X side is supported by a projection  89  projecting from the inner surface of the second region  74  toward the +Z side. The end part of the support plate  88  on the −X side may be fastened to the projection  89 . 
     The support plate  88  is internally formed with a second passage  91 . As shown in  FIGS. 4 to 6 , the second passage  91  is provided with a third communication hole  92  opening at an end part of the first surface  88 A of the support plate  88  on the +X side to communicate with the first communication hole  85 , and a fourth communication hole  93  opened at an end part of the first surface  88 A on the +X side to communicate with the second communication hole  86 . The fourth communication hole  93  is disposed on the +Y side of the third communication hole  92 . The second passage  91  extends from the third communication hole  92  to the end part of the support plate  88  on the −X side, and bent back to the +Y side and the +X side before extending to the end part of the support plate  88  on the +X side to be connected to the fourth communication hole  93 . 
     As shown in  FIG. 5 , a pair of annular seal grooves  95  are formed in the fastening surface  84  of the first region  73  so as to surround the first communication hole  85  and the second communication hole  86 , respectively. Each seal groove  95  is provided with a gasket  98  for sealing the connecting part between the first communication hole  85  and the third communication hole  92  or the connecting part between the second communication hole  86  and the fourth communication hole  93 . Each gasket  98  is formed of flexible rubber, and is formed in an annular shape so to extend along the corresponding seal groove  95 . 
     The upstream first passage  78 , the second passage  91 , and the downstream first passage  79  form a medium passage  107  through which the cooling medium flows. The cooling medium may, for example, be water. The inlet hole  81  and the outlet hole  82  are connected to a circulation circuit of the cooling medium via a hose or the like in such a manner that the inlet hole  81  receives a supply of the cooling medium from the circulation circuit, and the outlet hole  82  discharges the cooling medium to the circulation circuit. Thereby, as shown in  FIG. 6 , the cooling medium flows through the inlet hole  81 , the upstream first passage  78 , the first communication hole  85 , the fourth communication hole  93 , the second passage  91 , the fourth communication hole  93 , the second communication hole  86 , the downstream first passage  79 , and the outlet hole  82 , in that order. As shown in  FIG. 4 , the second passage  91  is offset from the upstream first passage  78  and the downstream first passage  79  on the +Z side. 
     As shown in  FIG. 3 , in the first region  73 , the first to fourth reactors  31 A to  31 D are arranged in such a manner that the reactors  31 A to  31 D are arranged side by side in the Y direction with the axial lines thereof extending in the X direction. The first to fourth reactors  31 A to  31 D are arranged in ascending order from the +Y side to the −Y side. The first and second reactors  31 A and  31 B have a common ring-shaped core, and the third and fourth reactors  31 C and  31 D have a common ring-shaped core. 
     As shown in  FIG. 4 , each of the reactors  31 A to  31 D is in contact with the inner surface of the first region  73  of the bottom  61 . The inner surface of the first region  73  is formed with a receiving recess  111  in which the reactors  31 A to  31 D are snugly received so that the contact area between each of the reactors  31 A to  31 D and the inner surface of the first region  73  of the bottom  61  is maximized, and the heat transfer from the reactors  31 A to  31 D to the first region  73  of the bottom  61  is maximized. 
     The secondary side capacitor  35  (smoothing capacitor) is provided on the first surface  88 A of the support plate  88 . The secondary side capacitor  35  is formed in a flat plate shape, and is in contact with the first surface  88 A of the support plate  88 . Further, the secondary side capacitor  35  is in contact with the inner surface of the second region  74  of the bottom  61  at the surface thereof facing away from the support plate  88 . In other words, the secondary side capacitor  35  is disposed in the space defined between the first surface  88 A of the support plate  88  and the inner surface of the second region  74 , and is in contact with both the support plate  88  and the second region  74 . The secondary side capacitor  35  is preferably in surface contact with the support plate  88  and the second region  74 . 
     The power module  37  is formed in a flat rectangular parallelepiped shape, and is placed on and fastened to the second surface  88 B of the support plate  88 . The power module  37  is preferably in surface contact with the second surface  88 B of the support plate  88 . In the power module  37 , the first to fourth switching devices  33 A to  33 D are arranged side by side in the X direction. Specifically, the first switching device  33 A, the second switching device  33 B, the third switching device  33 C, and the fourth switching device  33 D are disposed in that order from the +X side to the −X side. Thus, the power module  37  is formed so as to be larger in width in the X direction than in the Y direction. The power module  37  is disposed on the −X side of the reactors  31 . Preferably, the side edge of the power module  37  on the +Y side is located on the −Y side of the side edge of the first reactor  31 A on the +Y side, and the side edge of the power module  37  on the −Y side is located on the +Y side of the side edge of the first reactor  31 A on the −Y side. In other words, the power module  37  is disposed so as to overlap with the reactors  31  when viewed in the X direction. 
     The edge of the power module  37  on the −Y side is provided with a first positive terminal  41 , a second positive terminal  42 , a third positive terminal  43 , and a fourth positive terminal  44 , in that order from the +X side. The edge of the power module  37  on the +Y side is provided with a negative terminal  46  and a fifth positive terminal  45 , in that order from the +X side to the −X side. 
     On the surface of the power module  37  facing in the +X direction and defined by the mold resin is placed a gate driver  52  which consists of a flat electronic component formed of a printed circuit board and electronic devices to function as a gate drive circuit. The gate driver  52  is fastened to the power module  37 . The power module  37  and the gate driver  52  that are connected to each other jointly form an IPM (Intelligent Power Module). A plurality of pillars  112  project to the +Z side from the periphery of the surface of the power module  37  on the +Z side so as not to interfere with the gate driver  52 . Each pillar  112  extends in the +Z direction beyond the gate driver  52 . 
     A support member  115  for supporting the converter ECU  51  is disposed on the +Z side of the gate driver  52 . The support member  115  is formed of an insulating resin material. The support member  115  is formed in a plate shape having a first surface  116  facing the +Z side and a second surface  117  facing the −Z side (a surface facing the bottom  61 ). The support member  115  is fastened to the tip ends of the pillars  112  so that a clearance is defined between the second surface  117  of the support member  115  and the gate driver  52  owing to these pillars  112 . 
     The converter ECU  51  is a flat plate-shaped electronic control unit (ECU) formed of a printed circuit board and devices mounted thereof. The converter ECU  51  is fastened to the upper surface of support member  115  such that the outer surface thereof faces in the +Z direction. 
     The secondary side capacitor  35 , the support plate  88 , the power module  37 , the gate driver  52 , the support member  115 , and the converter ECU  51  are stacked one over another in the Z direction in a +Z side part of the second region  74  of the bottom  61 . 
     As shown in  FIGS. 3 and 8 , the primary side connection portion  23  is provided on the +X side of the outer surface of the first side wall  66 , and the secondary side connection portion  27  is provided on the −X side. Each of the primary side connection portion  23  and the secondary side connection portion  27  is formed in a cylindrical shape opening out toward the +Y side. The primary side connection portion  23  is provided on the +Y side of the reactors  31 , and the secondary side connection portion  27  is provided on the +Y side of the power module  37 . 
     The primary side positive terminal  21  and the primary side negative terminal  22  are provided inside the primary side connection portion  23 . The primary side positive terminal  21  is disposed on the +X side of the primary side negative terminal  22 . The secondary side positive terminal  25  and the secondary side negative terminal  26  are provided inside the secondary side connection portion  27 . The secondary side negative terminal  26  is disposed on the +X side of the secondary side positive terminal  25 . In other words, the primary side positive terminal  21 , the primary side negative terminal  22 , the secondary side negative terminal  26 , and the secondary side positive terminal  25  are arranged on the first side wall  66  in that order from the +X side to the −X side. The primary side positive terminal  21 , the primary side negative terminal  22 , the secondary side negative terminal  26 , and the secondary side positive terminal  25  are each formed in a pin shape. In another embodiment, the primary side positive terminal  21 , the primary side negative terminal  22 , the secondary side negative terminal  26 , and the secondary side positive terminal  25  are each formed in a tubular shape so as to receive a pin-like counterpart terminal. 
     As shown in  FIGS. 3 and 9 , the first to fourth reactors  31 A to  31 D each have a primary side end on the +X side, and a secondary side end on the −X side, with respect to the X direction. The primary side positive terminal  21  is connected to the primary side ends of the first to fourth reactors  31 A to  31 D via a first positive bus bar  121  which is branched in a corresponding manner. The primary side positive line  16  is formed by the first positive bus bar  121 . The first positive bus bar  121  extends from the primary side positive line  16  in the −Y direction, and branches so as to be connected to the primary side ends of the first to fourth reactors  31 A to  31 D at the branched ends thereof. A part of the first positive bus bar  121  may be disposed so as to overlap with the first to fourth reactors  31 A to  31 D when viewed from the Z direction. 
     The secondary side end of the first reactor  31 A is connected to the first positive terminal  41  of the power module  37  via a second positive bus bar  122 . The secondary side end of the second reactor  31 B is connected to the second positive terminal  42  of the power module  37  via a third positive bus bar  123 . The secondary side end of the third reactor  31 C is connected to the third positive terminal  43  of the power module  37  via a fourth positive bus bar  124 . The secondary side end of the fourth reactor  31 D is connected to the fourth positive terminal  44  of the power module  37  via a fifth positive bus bar  125 . The second to fifth positive bus bars  122  to  125  are separated from one another by insulating material  128 . The second to fifth positive bus bars  122  to  125  extend from the secondary side ends of the reactors  31 A to  31 D in the −Y direction, and then extend in the −X direction to be connected to the corresponding positive terminals  41  to  44 . 
     The fifth positive terminal  45  of the power module  37  is connected to the secondary side positive terminal  25  via a sixth positive bus bar  126  which extends from the fifth positive terminal  45  in the +Y direction to be connected to the secondary side positive terminal  25 . 
     The primary side negative terminal  22  is connected to the secondary side negative terminal  26  and the negative terminal  46  of the power module  37  via a branched negative bus bar  127 . The negative line  18  is formed by the negative bus bar  127 . The negative bus bar  127  extends from the primary side negative terminal  22  to the −X side and the −Y side to be connected to the negative terminal  46 , and branches from a lengthwise intermediate point thereof to extend in the +Y direction therefrom to be connected to the secondary side negative terminal  26 . 
     The first current sensor  48  is provided on the negative bus bar  127 . The second current sensor  49  is provided on the second to fifth positive bus bars  122  to  125 . The second current sensor  49  is disposed behind the power module  37 . As shown in  FIG. 7 , a first reactor temperature sensor  131  is provided between the first reactor  31 A and the second reactor  31 B to detect the temperature of the first reactor  31 A and the second reactor  31 B. A second reactor temperature sensor  132  is provided between the third reactor  31 C and the fourth reactor  31 D to detect the temperature of the third reactor  31 C and the fourth reactor  31 D. In addition, a capacitor temperature sensor  133  is provided on the secondary side capacitor  35  to detect the temperature of the secondary side capacitor  35 . The third side wall  68  is provided with a connector  134  for external connection. 
     As shown in  FIGS. 7 and 10 , a wire harness  137  is formed by tying together some of a signal line  48 L of the first current sensor  48 , a signal line  49 L of the second current sensor  49 , a signal line  131 L of the first reactor temperature sensor  131 , a signal line  132 L of the second reactor temperature sensor  132 , a signal line  133 L of the capacitor temperature sensor  133 , a signal line  134 L of the external connection connector  134 , a signal line  121 L extending from the first positive bus bar  121 , a signal line  126 L extending from the sixth positive bus bar  126 , and a signal line  127 L extending from the negative bus bar  127 . The wire harness  137  is branched into a number of terminal ends which are connected to connectors  138  provided on an edge part of the converter ECU  51 . The signal lines  121 L,  126 L, and  127 L forward the voltage signals of the bus bars  121 ,  126 , and  127  to the converter ECU  51 , and the converter ECU  51  acquires the voltages on the primary side and the secondary side of the FC-side converter  3 . 
     As shown in  FIG. 11 , a plurality of reinforcing ribs  141  project from the first surface  116  and the second surface  117  of the support member  115 . A receiving groove  142  for receiving the wire harness  137  is formed between the adjacent reinforcing ribs  141  on the upper surface of the support member  115 . The receiving groove  142  opens toward the +Z side, and extends in the direction along the surface of the support member  115 . The receiving groove  142  extends in the X direction, and is provided with a first end  143  that reaches and extends through the side edge of the support member  115  on the −X side and opens toward the −X side and a second end  144  that reaches and extends through the side edge of the support member  115  on the +X side and opens toward the +X side. The receiving groove  142  is further provided with a branch portion  145  branching toward the +Y side from a central point thereof with respect to the X direction. A third end  146  forming the end of the branch portion  145  on the +Y side reaches the front edge of the support member  115  and opens toward the +Y side. 
     The receiving groove  142  has at least one curved portion  148  at an intermediate part thereof in the lengthwise direction. In particular, the receiving groove  142  is curved instead of being linear. In the present embodiment, the intermediate part of the receiving groove  142  with respect to the X direction is offset to the +Y side with respect to the first end  143  and the second end  144  thereof. The presence of the bend in the receiving groove  142  can improve the bending stiffness of the support member  115 . If the receiving groove  142  were formed so as to extend linearly, a weakened part owing to the absence of the reinforcing ribs  141  would extend linearly so that the support member  115  would be prone to bending deformation with the receiving groove  142  serving as a valley or a ridge for such bending deformation. By thus providing the curved portion  148  in the receiving groove  142 , the weakened portion is prevented from lining up in a straight line, and the bending stiffness of the support member  115  can be improved. 
     As shown in  FIG. 12 , the wire harness  137  extends from the first end  143  to the second end  144  through the receiving groove  142 , and extends further from the second end  144  of the receiving groove  142  to the +Z side to be connected to the connectors  138  provided at the edge of the converter ECU  51 . 
     As shown in  FIG. 7 , the receiving groove  142  is provided with a groove cover  151  which covers at least a part of the wire harness  137 . The groove cover  151  is coupled to the support member  115  by means of locking claws or screws. The groove cover  151  retains the wire harness  137  in the receiving groove  142 , and prevents the wire harness  137  from being dislodged from the receiving groove  142 . 
     Owing to this arrangement, the wire harness  137  is disposed along the support member  115  as it extends along a space defined between the support member  115  and the converter ECU  51 . 
     The FC-side converter  3  may be disposed in any orientation when mounted to the vehicle. The FC-side converter  3  may be disposed, for example, so that the bottom  61  extends horizontally or vertically. 
     The effect of the FC-side converter  3  according to the present embodiment is discussed in the following. In the FC-side converter  3 , the power module  37  and the secondary side capacitor  35  are stacked in the Z direction via the support plate  88 . Since an AC magnetic flux is generated inside each reactor  31  by the current passing through the FC-side converter  3 , the reactor  31  needs to have a magnetic path having an appropriate cross sectional area so that the reactor  31  is not magnetically saturated by the magnetic flux. In this case, even if there are severe restrictions such as the need for a high electric capacity, and a small available floor area (footprint) of each reactor  31 , an adequate cross sectional area for the magnetic flux can be ensured by making the thickness of the reactor to be greater than either the power module  37  or the secondary side capacitor  35 . Therefore, the space efficiency of the FC-side converter  3  can be enhanced by stacking the power module  37  and the secondary side capacitor  35  one over the other, and arranging the reactors  31  separately therefrom. 
     For the given magnetic characteristics of each reactor  31 , the floor area of the reactor  31  can be limited by increasing the thickness of the reactor  31  so as to ensure an adequate cross area for the magnetic flux. Thereby, the space efficiency of the FC-side converter  3  can be optimized. For instance, the floor area of the reactors  31  can be limited even further by making the thickness of the reactors  31 A to  31 D in the Z direction to be greater than the combined thickness of the power module  37 , the support plate  88 , and the secondary side capacitor  35  in the Z direction. 
     In addition, since the secondary side capacitor  35 , the power module  37 , the gate driver  52 , and the converter ECU  51  are stacked in the Z direction in the second region  74 , the floor area of the bottom  61  of the case  60  can be further reduced. Further, the outer profile of the second case  64  can be made flat by making the combined thickness of the reactors  31  and the upstream first passage  78  (downstream first passage  79 ) to be substantially the same as the combined thickness of the secondary side capacitor  35 , the support plate  88 , the power module  37 , the support member  115 , and the converter ECU  51 . In particular, the external shape of the case formed by the first case  63  and the second case  64  can be made substantially rectangular. 
     In addition, since the second passage  91  is formed in the support plate  88  which is remote from the second region  74  of the bottom  61 , and the power module  37  and the secondary side capacitor  35  are provided on the respective two surfaces of the support plate  88 , all of the power module  37  and the secondary side capacitor  35  can be favorably cooled without increasing the floor area. 
     Since the second region  74  of the bottom  61  does not have a passage through which the cooling medium flows, the second region  74  may be made thinner than the first region  73  so that the receiving space formed on the inner side (+Z side) of the second region  74  can be widened without causing the bottom  61  of the case  60  to protrude outward (−Z side). 
     Since the wire harness  137  is wired between the converter ECU  51  and the support member  115 , clips that are required for securing the wire harness  137  can be partially omitted. In addition, since the signal lines are wired by using the space created between the converter ECU  51  and the support member  115 , each device therein can be integrated at high density so that the FC-side converter  3  can be made highly compact. 
     Since the support member  115  is formed of an insulating material, the converter ECU  51  and the gate driver  52  can be arranged in layers while being insulated from each other. Thereby, the converter ECU  51  and the gate driver  52  can be integrated at high density so that the FC-side converter  3  can be made highly compact. 
     The receiving groove  142  is formed between the reinforcing ribs  141  on the upper surface of the support member  115 , and the wire harness  137  is wired in the receiving groove  142 . Therefore, the wire harness  137  is buried in the support member  115  so that the total thickness of the support member  115  can be minimized. In addition, since the wire harness  137  can be held in position by being received in the receiving groove  142 , clips required for fixing the wire harness  137  can be partially omitted. 
     Further, since each end of the receiving groove  142  reaches the corresponding edge of the support member  115 , the wire harness  137  can enter the receiving groove  142  from the edge of the support member  115  so that the converter ECU  51  can be disposed even closer to support member  115 . 
     According to the foregoing arrangement of the first to fourth reactors  31 A to  31 D, the first to fourth switching devices  33 A to  33 D, the primary side connection portion  23 , and the secondary side connection portion  27 , in the FC-side converter  3  essentially consisting of a step-up type multiphase converter, the lengths of the first positive bus bar  121  and the negative bus bar  127  through which the largest current flows can be minimized so that the loss can be minimized. In the FC-side converter  3 , the largest current flows in the region of the primary side positive line  16  ranging from the primary side positive terminal  21  to the part thereof branching into the first to fourth reactors  31 A to  31 D which are connected in parallel to one another. In the negative line  18 , the largest current flows in the region ranging from the primary side negative terminal  22  to the part thereof branching into the first to fourth switching devices  33 A to  33 D. In the secondary side positive line  17  and the secondary side of the negative line  18 , the voltage is increased so the current is decreased. Therefore, the loss can be reduced most efficiently by shortening the lengths of the first positive bus bar  121  and the negative bus bar  127 . 
     Since the secondary side connection portion  27  is disposed on the +Y side of the power module  37 , the distance between the negative terminal  46  of the power module  37  and the secondary side negative terminal  26  can be minimized. Thereby, the negative bus bar  127  can be shortened, and the loss can be minimized. 
     In the first side wall  66 , since the primary side positive terminal  21 , the primary side negative terminal  22 , the secondary side negative terminal  26 , and the secondary side positive terminal  25  are arranged in that order from the +X side, the distance between the negative terminal  22  and the secondary side negative terminal  26  can be minimized so that the length of the negative bus bar  127  can be reduced even further. It should be noted that that this arrangement is not essential for the present invention, and the order of the primary side positive terminal  21 , the primary side negative terminal  22 , the secondary side negative terminal  26 , and the secondary side positive terminal  25  may be changed in other embodiments. 
     Since the first to fourth reactors  31 A to  31 D have the primary side on the +X side and the secondary side on the −X side, the loss can be minimized by reducing the lengths of the second to fifth positive bus bars  122  to  125  connecting the first to fourth reactors  31 A to  31 D to the fourth positive terminals  41  to  44  of the power module  37 , respectively. 
     Although the present invention has been described in terms of a specific embodiment, the present invention is not limited by such an embodiment, but can be modified in various ways without departing from the spirit of the present invention. For example, the number of reactors  31  can be changed. Moreover, the signal lines contained in the wire harness  137  can be changed suitably. A smoothing primary side capacitor may be connected between the primary side positive line  16  and the negative line  18 . 
     In the above embodiment, the first to fourth reactors  31 A to  31 D had the primary side end on the +X side and the secondary side end on the −X side. In an alternate embodiment, the first to fourth reactors  31 A to  31 D have the primary side end on the −X side and the secondary side end on the +X side. When the secondary side end is provided on the +X side of the first to fourth reactors  31 A to  31 D, the lengths of the second to fifth positive bus bars  122  to  125  are longer as compared to the case where the second side end is provided on the −X side of the first to fourth reactors  31 A to  31 D. However, since the current flowing through the second to fifth positive bus bars  122  to  125  is smaller than that of the first positive bus bar  121 , the increase in the loss is minimal.