Patent Publication Number: US-10784792-B2

Title: Power conversion device

Description:
TECHNICAL FIELD 
     The present invention relates to a power conversion device that converts power output from an alternating-current power supply or a direct-current power supply to desired direct-current power. 
     BACKGROUND ART 
     Conventionally, a power conversion device is used for charging a low-voltage battery from a high-voltage battery, in an electric car, a hybrid vehicle, or the like. A switch is mounted inside the power conversion device, which is formed by a power semiconductor element of a discrete package or a modularized power semiconductor element (hereinafter, “power module”). The power module switches on/off of the switch by a signal provided from a control circuit to convert a voltage. 
     When a switching element is switched on and off, switching noise is generated in the power module and propagates to the power-supply side and the load side. Therefore, in a case where power is supplied from a commercial power supply installed in a standard home to a power conversion device mounted on a vehicle, for example, noise may propagate to an electric system on the home side. 
     Patent Literature 1 discloses suppressing of noise by grounding a frame of a reactor provided in a power module via an impedance element in order to remove noise. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent Laid-Open Publication No. 2006-238582 
     SUMMARY OF INVENTION 
     However, the conventional example disclosed in Patent Literature 1 does not adjust an impedance between an inductance element and the frame, and does not reduce noise effectively. 
     The present invention has been made in view of such conventional problems. It is an object of the present invention to provide a power conversion device that can reduce noise generated when a switching element is switched on and off. 
     A power conversion device according to an aspect of the present invention includes an inductance element connected to a first power feed bus, a switching element that converts power supplied between the first power feed bus and a second power feed bus by switching, a housing that houses the inductance element and the switching element, and a first impedance element provided between the inductance element and the housing. 
     Advantageous Effects of Invention 
     According to an aspect of the present invention, it is possible to reduce noise generated when a switching element is switched on and off. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a circuit diagram illustrating a configuration of a power conversion device and peripheral devices thereof according to an embodiment of the present invention. 
         FIG. 2  is an explanatory diagram illustrating a cross-section of an inductance element and a second power feed bus of the power conversion device according to a first embodiment. 
         FIG. 3  is a graph representing the level of noise generated in a power conversion device. 
         FIG. 4  is an explanatory diagram illustrating a cross-section of an inductance element and a second power feed bus of a power conversion device according to a modification of the first embodiment. 
         FIG. 5  is an explanatory diagram illustrating a cross-section of an inductance element and a second power feed bus of a power conversion device according to a second embodiment. 
         FIG. 6  is an explanatory diagram illustrating a cross-section of an inductance element and a second power feed bus of a power conversion device according to a modification of the second embodiment. 
         FIG. 7  is an explanatory diagram illustrating a cross-section of an inductance element and a second power feed bus of a power conversion device according to a third embodiment. 
         FIG. 8  is an explanatory diagram illustrating a cross-section of an inductance element and a second power feed bus of a power conversion device according to a fourth embodiment. 
         FIG. 9  is an explanatory diagram illustrating a cross-section of an inductance element and a second power feed bus of a power conversion device according to a fifth embodiment. 
         FIG. 10  is a graph representing a relation between a frequency and an impedance of the power conversion device according to the fifth embodiment. 
         FIG. 11  is an explanatory diagram illustrating a cross-section of an inductance element and a second power feed bus of a power conversion device according to a sixth embodiment. 
         FIG. 12  is an explanatory diagram illustrating a cross-section of an inductance element and a second power feed bus of a power conversion device according to a seventh embodiment. 
         FIG. 13  is an explanatory diagram illustrating a cross-section of an inductance element and a second power feed bus of a power conversion device according to a modification of the seventh embodiment. 
         FIG. 14  is an explanatory diagram illustrating a cross-section of an inductance element and a second power feed bus of a power conversion device according to an eighth embodiment. 
         FIG. 15  is an explanatory diagram illustrating a cross-section of an inductance element and a second power feed bus of a power conversion device according to a ninth embodiment. 
         FIG. 16  is an explanatory diagram illustrating a cross-section of an inductance element and a second power feed bus of a power conversion device according to a tenth embodiment. 
         FIG. 17  is a graph representing a relation between a frequency and an impedance of the power conversion device according to the tenth embodiment. 
         FIG. 18  is a graph representing a relation between an impedance and noise of the power conversion device according to the tenth embodiment. 
         FIG. 19  is an explanatory diagram illustrating a cross-section of an inductance element and a second power feed bus of a power conversion device according to a first modification of the tenth embodiment. 
         FIG. 20  is an explanatory diagram illustrating a cross-section of an inductance element and a second power feed bus of a power conversion device according to a second modification of the tenth embodiment. 
         FIG. 21  is an explanatory diagram illustrating a cross-section of an inductance element and a second power feed bus of a power conversion device according to an eleventh embodiment. 
         FIG. 22  is a graph representing a relation between a frequency and an impedance of the power conversion device according to the eleventh embodiment. 
         FIG. 23  is a graph representing a relation between a frequency and an impedance of a power conversion device according to a first modification of the eleventh embodiment. 
         FIG. 24  is a graph representing a relation between a frequency and an impedance of a power conversion device according to a second modification of the eleventh embodiment. 
         FIG. 25  is a graph representing a relation between a frequency and an impedance of a power conversion device according to a third modification of the eleventh embodiment. 
         FIG. 26  is an enlarged view of a portion “A” illustrated in  FIG. 25 . 
         FIG. 27  is a graph representing a relation between a resistance value of each resistance element and a noise level in the power conversion device according to the eleventh embodiment. 
         FIG. 28  is a circuit diagram illustrating another configuration of a power conversion device. 
         FIG. 29  is a circuit diagram illustrating further another configuration of a power conversion device. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention are described below with reference to the accompanying drawings. 
     Descriptions of First Embodiment 
       FIG. 1  is a circuit diagram illustrating a configuration of a power conversion device and peripheral devices thereof according to a first embodiment of the present invention. As illustrated in  FIG. 1 , a power conversion device  101  according to the present embodiment is entirely covered by a housing  1  made of metal, such as iron or aluminum. The input side of the power conversion device  101  is connected to a power supply  91  that outputs a direct current via a first power feed bus  93  and a second power feed bus  94 , and the output side thereof is connected to a load  92  via output lines  95  and  96 . Therefore, it is possible to convert a voltage supplied from the power supply  91  into a desired voltage and supply the converted voltage to the load  92 . The power supply  91  is a commercial power supply or a battery installed in a standard home, for example. The load  92  is a battery mounted on an electric car or a hybrid vehicle, for example. 
     A positive terminal of the power supply  91  is connected to the first power feed bus  93 , and a negative terminal thereof is connected to the second power feed bus  94 . 
     An inductance element L 1  connected to the first power feed bus  93  is provided in the housing  1  of the power conversion device  101 . Further, a power module  3  is provided between the first power feed bus  93  and the second power feed bus  94 . 
     The power module  3  includes a switching element Q 1  such as an IGBT (insulated gate bipolar transistor) or a MOSFET, and a diode D 1 . The inductance element L 1  is, for example, a toroidal winding coil or a flat coil. 
     Smoothing capacitors C 100  and C 200  are provided at a preceding stage and a subsequent stage of the power module  3 , respectively. A control input of the switching element Q 1  (for example, a base of an IGBT) is connected to a control circuit  2  that controls on/off of the switching element Q 1 . 
     By controlling on/off of the switching element Q 1  under control by the control circuit  2 , a voltage supplied from the power supply  91  is converted to a different voltage to be supplied to the load  92 . 
       FIG. 2  illustrates an “A-A′” cross-section illustrated in  FIG. 1 . As illustrated in  FIG. 2 , a first impedance element  11  is provided between the inductance element L 1  and the housing  1 . For example, the first impedance element  11  is a capacitance element or a series-connected circuit formed by a capacitance element and a resistance element. 
     In the power conversion device  101  according to the first embodiment, by providing the first impedance element  11 , an impedance between the inductance element L 1  and the housing  1  is made closer to a second stray capacitance that exists between the second power feed bus  94  and the housing  1 . In this manner, noise propagating from the inductance element L 1  to the housing  1  is suppressed, when power is supplied to the load  92  illustrated in  FIG. 1  to drive the load  92 . To “make closer” is a concept including complete match. 
       FIG. 3  is a graph representing noise that propagates to the housing  1  when the switching element Q 1  is switched. In  FIG. 3 , a curve S 1  illustrated with a dotted line represents a change of noise in a case where the first impedance element  11  is not provided, and a curve S 2  illustrated with a solid line represents a change of noise in a case where the first impedance element  11  is provided. As is understood from the graph of  FIG. 3 , noise propagating from the inductance element L 1  to the housing  1  is reduced by providing the first impedance element  11 . 
     In this manner, in the power conversion device according to the first embodiment, an impedance between the inductance element L 1  and the housing  1  can be made higher to become closer to a second stray capacitance existing between the second power feed bus  94  and the housing  1  by providing the first impedance element  11 . Therefore, noise propagating from the inductance element L 1  to the housing  1  can be reduced. 
     Descriptions of Modification of First Embodiment 
     Next, a modification of the first embodiment is described. A power conversion device according to the modification is different in that it uses a planer inductance element L 1   a  and the second power feed bus  94  is formed as a flat wire or a substrate pattern.  FIG. 4  is a cross-sectional view of the inductance element L 1   a  and the second power feed bus  94 . As illustrated in  FIG. 4 , the inductance element L 1   a  and the second power feed bus  94  both have a flat shape. Further, the first impedance element  11  is provided between the inductance element L 1   a  and the housing  1 . The planar inductance element L 1   a  can be formed by a substrate pattern. 
     Also with this configuration, it is possible to reduce noise that propagates from the inductance element L 1   a  to the housing  1 , similarly to the first embodiment described above. Although each of the following embodiments will describe an example in which a toroidal coil is used as the inductance element L 1 , as illustrated in  FIG. 2 , a planar inductance element L 1   a  illustrated in  FIG. 4  can be used. 
     Descriptions of Second Embodiment 
     Next, a second embodiment of the present invention is described.  FIG. 5  is an explanatory diagram illustrating a cross-section of the inductance element L 1  and the second power feed bus  94  of a power conversion device according to the second embodiment. As illustrated in  FIG. 5 , the inductance element L 1  is housed in a frame  4  made of metal, such as iron or aluminum. The frame  4  is fixed to the housing  1  and is in electrical conduction with the housing  1 . The first impedance element  11  is provided between the inductance element L 1  and the frame  4 . That is, the second embodiment is different from the first embodiment described above in that the inductance element L 1  is housed in the frame  4 . Because the frame  4  is provided within the housing  1  and the first impedance element  11  is provided between the inductance element L 1  and the frame  4 , the first impedance element  11  is provided between the inductance element L 1  and the housing  1 . 
     As described above, the inductance element L 1  is housed in the frame  4  in the power conversion device according to the second embodiment. Therefore, noise directly radiated from the inductance element L 1  can be suppressed. Further, by providing the first impedance element  11 , it is possible to increase an impedance between the inductance element L 1  and the frame  4 , so that an impedance between the inductance element L 1  and the housing  1  can be made closer to a second stray capacitance between the second power feed bus  94  and the housing  1 . As a result, noise propagating from the inductance element L 1  to the housing  1  can be reduced. 
     Descriptions of Modification of Second Embodiment 
     Next, a modification of the second embodiment is described.  FIG. 6  is an explanatory diagram illustrating a cross-section of the inductance element L 1  and the second power feed bus  94  of a power conversion device according to the modification of the second embodiment. 
     As illustrated in  FIG. 6 , the modification is different from the second embodiment described above in that a bottom surface of the frame  4  that houses the inductance element L 1  therein and the housing  1  are connected to each other by a wire  5 . That is, the housing  1  and the frame  4  are in conduction with each other by the wire  5 . The housing  1  and the frame  4  are fixed by an insulating body or the like (not illustrated). Even with this configuration, effects identical to those of the second embodiment described above can be achieved. 
     Descriptions of Third Embodiment 
     Next, a third embodiment of the present invention is described.  FIG. 7  is an explanatory diagram illustrating a cross-section of the inductance element L 1  and the second power feed bus  94  of a power conversion device according to the third embodiment. As illustrated in  FIG. 7 , in the power conversion device according to the third embodiment, the inductance element L 1  is housed in the frame  4 . Further, the first impedance element  11  is provided to cover the inductance element L 1 . The first impedance element  11  is a dielectric body, for example. 
     The frame  4  is provided in the housing  1 , and the first impedance element  11  is provided between the inductance element L 1  and the frame  4 . Further, because the frame  4  and the housing  1  are coupled to each other by a stray capacitance, the first impedance element  11  is provided between the inductance element L 1  and the housing  1 . 
     Further, the housing  1  and the frame  4  are fixed by an insulating body or the like (not illustrated). Because a stray capacitance exists between the frame  4  and the housing  1 , a predetermined electrostatic capacitance exists between the inductance element L 1  and the housing  1 . 
     In this manner, in the power conversion device according to the third embodiment, noise propagating from the inductance element L 1  to the housing  1  can be reduced by making a predetermined electrostatic capacitance described above closer to a second stray capacitance between the second power feed bus  94  and the housing  1 . 
     Descriptions of Fourth Embodiment 
     Next, a fourth embodiment of the present invention is described.  FIG. 8  is an explanatory diagram illustrating a cross-section of the inductance element L 1  and the second power feed bus  94  of a power conversion device according to the fourth embodiment. As illustrated in  FIG. 8 , in the power conversion device according to the fourth embodiment, the first impedance element  11  is provided between the inductance element L 1  and the housing  1 . Further, a second impedance element  12  is provided between the second power feed bus  94  and the housing  1 . 
     By providing the first impedance element  11  and the second impedance element  12 , it is possible to make an impedance between the inductance element L 1  and the housing  1  and an impedance between the second power feed bus  94  and the housing  1  closer to each other. Therefore, it is possible to reduce noise propagating from the inductance element L 1  to the housing  1  and noise propagating from the second power feed bus  94  to the housing  1 . 
     Further, because the first impedance element  11  and the second impedance element  12  are provided, fine adjustment of each impedance can be performed. Therefore, it is possible to match an impedance between the inductance element L 1  and the housing  1  and an impedance between the second power feed bus  94  and the housing  1  more easily. Therefore, it is possible to reduce noise propagating from the inductance element L 1  to the housing  1  and noise propagating from the second power feed bus  94  to the housing  1  with a simple operation. 
     Descriptions of Fifth Embodiment 
     Next, a fifth embodiment of the present invention is described.  FIG. 9  is an explanatory diagram illustrating a cross-section of the inductance element L 1  and the second power feed bus  94  of a power conversion device according to the fifth embodiment. As illustrated in  FIG. 9 , in the fifth embodiment, a first capacitance element C 11  is provided between the inductance element L 1  and the housing  1 . 
     Further, a second capacitance element C 12  is provided between the second power feed bus  94  and the housing  1 . That is, in the fifth embodiment, the first impedance element  11  illustrated in  FIG. 8  is replaced with the first capacitance element C 11  and the second impedance element  12  is replaced with the second capacitance element C 12 . Further, C 01  in  FIG. 9  denotes a first stray capacitance between the inductance element L 1  and the housing  1 , and C 02  denotes a second stray capacitance between the second power feed bus  94  and the housing  1 . 
     In the fifth embodiment, an electrostatic capacitance that is a total of the first stray capacitance C 01  and an electrostatic capacitance of the first capacitance element C 11  and an electrostatic capacitance that is a total of the second stray capacitance C 02  and an electrostatic capacitance of the second capacitance element C 12  are made closer to each other by appropriately setting the electrostatic capacitances of the first capacitance element C 11  and the second capacitance element C 12 . As a result, it is possible to match a voltage applied between the inductance element L 1  and the housing  1  with a voltage applied between the second power feed bus  94  and the housing  1 , so that noise propagating from the inductance element L 1  and the second power feed bus  94  to the housing  1  can be reduced. 
       FIG. 10  is a graph representing a relation between a frequency and an impedance. In  FIG. 10 , a curve S 3  illustrated with a solid line represents a change of impedance between the inductance element L 1  and the housing  1  with respect to a change of frequency. A curve S 4  illustrated with a dotted line represents a change of impedance between the second power feed bus  94  and the housing  1  with respect to a change of frequency. As is understood from the curves S 3  and S 4 , the impedances respectively represented by the curves S 3  and S 4  are substantially matched with each other irrespective of the frequencies thereof. That is, in the power conversion device according to the fifth embodiment, noise propagating to a housing can be reduced even in a case where a frequency of the switching element Q 1  is changed. 
     Descriptions of Sixth Embodiment 
     Next, a sixth embodiment of the present invention is described.  FIG. 11  is an explanatory diagram illustrating a cross-section of the inductance element L 1  and the second power feed bus  94  of a power conversion device according to the sixth embodiment. As illustrated in  FIG. 11 , in the sixth embodiment, the first capacitance element C 11  is provided between the inductance element L 1  and the housing  1 , similarly to the fifth embodiment illustrated in  FIG. 9 . Further, the second capacitance element C 12  is provided between the second power feed bus  94  and the housing  1 . Further, the first stray capacitance C 01  exists between the inductance element L 1  and the housing  1 , and the second stray capacitance C 02  exists between the second power feed bus  94  and the housing  1 . The sixth embodiment is different from the fifth embodiment in that the second power feed bus  94  is formed by a flat wire. 
     In the power conversion device according to the sixth embodiment, an electrostatic capacitance that is a total of the first stray capacitance C 01  and an electrostatic capacitance of the first capacitance element C 11  and an electrostatic capacitance that is a total of the second stray capacitance C 02  and an electrostatic capacitance of the second capacitance element C 12  can be made closer to each other by appropriately setting the electrostatic capacitances of the first capacitance element C 11  and the second capacitance element C 12 , similarly to the fifth embodiment described above. Use of a flat wire as the second power feed bus  94  enables adjustment of the second stray capacitance C 02 . This point is described in detail below. 
     An electrostatic capacitance between the second power feed bus  94  and the housing  1  (the second stray capacitance C 02 ) can be expressed by the following expression (1).
 
(Electrostatic capacitance)=ε0·ε r ·( S/d )  (1)
 
     where ε 0  is a permittivity of vacuum, εr is a relative permittivity, S is an opposed area, and d is a distance. 
     Therefore, by changing the opposed area S, it is possible to change the second stray capacitance C 02  between the second power feed bus  94  and the housing  1 . In the sixth embodiment, an electrostatic capacitance between the inductance element L 1  and the housing  1  and the electrostatic capacitance between the second power feed bus  94  and the housing  1  are set by adjusting the opposed area S between the second power feed bus  94  and the housing  1  in addition to the first capacitance element C 11  and the second capacitance element C 12 . Therefore, adjustment of electrostatic capacitances can be easily performed. Accordingly, it is possible to make a voltage applied between the inductance element L 1  and the housing  1  and a voltage applied between the second power feed bus  94  and the housing  1  closer to each other, so that noise propagating to the housing  1  can be reduced. 
     Descriptions of Seventh Embodiment 
     Next, a seventh embodiment of the present invention is described.  FIG. 12  is an explanatory diagram illustrating a cross-section of the inductance element L 1  and the second power feed bus  94  of a power conversion device according to the seventh embodiment. As illustrated in  FIG. 12 , in the seventh embodiment, the first capacitance element C 11  is provided between the inductance element L 1  and the housing  1 , similarly to the fifth embodiment illustrated in  FIG. 9 . Further, the second capacitance element C 12  is provided between the second power feed bus  94  and the housing  1 . Further, the first stray capacitance C 01  exists between the inductance element L 1  and the housing  1 , and the second stray capacitance C 02  exists between the second power feed bus  94  and the housing  1 . The seventh embodiment is different from the fifth embodiment in that the housing  1  near the second power feed bus  94  is formed by a thick portion  7 . 
     In the power conversion device according to the seventh embodiment, an electrostatic capacitance that is a total of the first stray capacitance C 01  and an electrostatic capacitance of the first capacitance element C 11  can be made closer to an electrostatic capacitance that is a total of the second stray capacitance C 02  and an electrostatic capacitance of the second capacitance element C 12  by appropriately setting the electrostatic capacitances of the first capacitance element C 11  and the second capacitance element C 12 . In this case, the second stray capacitance C 02  can be adjusted by changing the thickness of the thick portion  7 . 
     That is, it is possible to change the second stray capacitance C 02  between the second power feed bus  94  and the housing  1  by changing the distance d, as expressed by the expression (1) described above. In the seventh embodiment, an electrostatic capacitance between the inductance element L 1  and the housing  1  is matched with an electrostatic capacitance between the second power feed bus  94  and the housing  1  by adjusting the thickness of the thick portion  7  in addition to the first capacitance element C 11  and the second capacitance element C 12 . Therefore, adjustment of electrostatic capacitances can be easily performed. Although  FIG. 12  illustrates an example in which the thickness of the housing  1  is changed, the distance d can be changed by arranging a conductive plate member on an inner surface of the housing  1 . 
     Accordingly, it is possible to make a voltage applied between the inductance element L 1  and the housing  1  and a voltage applied between the second power feed bus  94  and the housing  1  closer to each other, so that noise propagating to the housing  1  can be reduced. 
     Descriptions of Modification of Seventh Embodiment 
     Next, a modification of the seventh embodiment of the present invention is described.  FIG. 13  is an explanatory diagram illustrating a cross-section of the inductance element L 1  and the second power feed bus  94  of a power conversion device according to the modification of the seventh embodiment. As illustrated in  FIG. 13 , a plate member  6  made of metal is provided on a portion of the inner surface of the housing  1 , which is close to the second power feed bus  94 , in the modification. Therefore, the second stray capacitance C 02  can be adjusted by changing a distance between the second power feed bus  94  and the plate member  6 , similarly to the seventh embodiment described above, so that it is possible to make an electrostatic capacitance that is a total of the inductance element L 1  and the housing  1  and an electrostatic capacitance that is a total of the second power feed bus  94  and the housing  1  closer to each other with a simple operation. 
     Descriptions of Eighth Embodiment 
     Next, an eighth embodiment of the present invention is described.  FIG. 14  is an explanatory diagram illustrating a cross-section of the inductance element L 1  and the second power feed bus  94  of a power conversion device according to the eighth embodiment. As illustrated in  FIG. 14 , in the eighth embodiment, the first capacitance element C 11  is provided between the inductance element L 1  and the housing  1 , similarly to the fifth embodiment illustrated in  FIG. 9 . Further, the second capacitance element C 12  is provided between the second power feed bus  94  and the housing  1 . 
     The eighth embodiment is different from the fifth embodiment in that a second dielectric body  8  is provided between the second power feed bus  94  and the housing  1 . The first stray capacitance C 01  exists between the inductance element L 1  and the housing  1 , and the second stray capacitance C 02  exists between the second power feed bus  94  and the housing  1 . The second stray capacitance C 02  is changed by a permittivity of the second dielectric body  8 . 
     In the power conversion device according to the eighth embodiment, it is possible to make an electrostatic capacitance that is a total of the first stray capacitance C 01  and an electrostatic capacitance of the first capacitance element C 11  and an electrostatic capacitance that is a total of the second stray capacitance C 02  and an electrostatic capacitance of the second capacitance element C 12  closer to each other by appropriately setting the electrostatic capacitances of the first capacitance element C 11  and the second capacitance element C 12 . The second stray capacitance C 02  can be adjusted by changing a permittivity of the second dielectric body  8 . 
     That is, it is possible to change the second stray capacitance C 02  between the second power feed bus  94  and the housing  1  by changing the relative permittivity εr, as expressed by the expression (1) described above. In the eighth embodiment, an electrostatic capacitance between the inductance element L 1  and the housing  1  is matched with an electrostatic capacitance between the second power feed bus  94  and the housing  1  by adjusting the relative permittivity εr of the second dielectric body  8  in addition to the first capacitance element C 11  and the second capacitance element C 12 . Therefore, adjustment of electrostatic capacitances can be easily performed. 
     Descriptions of Ninth Embodiment 
     Next, a ninth embodiment of the present invention is described.  FIG. 15  is an explanatory diagram illustrating a cross-section of the inductance element L 1  and the second power feed bus  94  of a power conversion device according to the ninth embodiment. As illustrated in  FIG. 15 , in the ninth embodiment, the first capacitance element C 11  is provided between the inductance element L 1  and the housing  1 , similarly to the fifth embodiment illustrated in  FIG. 9 . Further, the second capacitance element C 12  is provided between the second power feed bus  94  and the housing  1 . 
     The ninth embodiment is different from the fifth embodiment in that a first dielectric body  9  is provided between the inductance element L 1  and the housing  1  and the second dielectric body  8  is provided between the second power feed bus  94  and the housing  1 . The first stray capacitance C 01  exists between the inductance element L 1  and the housing  1 , and the second stray capacitance C 02  exists between the second power feed bus  94  and the housing  1 . The first stray capacitance C 01  is changed by a permittivity of the first dielectric body  9 , and the second stray capacitance C 02  is changed by a permittivity of the second dielectric body  8 . 
     In the power conversion device according to the ninth embodiment, an electrostatic capacitance that is a total of the first stray capacitance C 01  and an electrostatic capacitance of the first capacitance element C 11  and an electrostatic capacitance that is a total of the second stray capacitance C 02  and an electrostatic capacitance of the second capacitance element C 12  are made closer to each other by appropriately setting the electrostatic capacitances of the first capacitance element C 11  and the second capacitance element C 12 . In this case, the first stray capacitance C 01  and the second stray capacitance C 02  can be adjusted by changing permittivities of the first dielectric body  9  and the second dielectric body  8 . 
     That is, it is possible to change the first stray capacitance C 01  and the second stray capacitance C 02  by changing the relative permittivity εr in the expression (1) described above. In the ninth embodiment, an electrostatic capacitance between the inductance element L 1  and the housing  1  is matched with an electrostatic capacitance between the second power feed bus  94  and the housing  1  by adjusting the relative permittivity εr of the first dielectric body  9  and that of the second dielectric body  8  in addition to the first capacitance element C 11  and the second capacitance element C 12 . Therefore, adjustment of electrostatic capacitances can be easily performed. 
     Descriptions of Tenth Embodiment 
     Next, a tenth embodiment of the present invention is described.  FIG. 16  is an explanatory diagram illustrating a cross-section of the inductance element L 1  and the second power feed bus  94  of a power conversion device according to the tenth embodiment. As illustrated in  FIG. 16 , in the tenth embodiment, a series-connected circuit formed by the first capacitance element C 11  and a first resistance element R 11  is provided between the inductance element L 1  and the housing  1 . Further, the second capacitance element C 12  is provided between the second power feed bus  94  and the housing  1 . 
     The first stray capacitance C 01  exists between the inductance element L 1  and the housing  1 , and the second stray capacitance C 02  exists between the second power feed bus  94  and the housing  1 . 
     In the power conversion device according to the tenth embodiment, a combined impedance of the first stray capacitance C 01  and the series-connected circuit formed by the first capacitance element C 11  and the first resistance element R 11  (hereinafter, this combined impedance is referred to as “first impedance”) is made closer to a combined impedance of the second stray capacitance C 02  and an electrostatic capacitance of the second capacitance element C 12  (hereinafter, this combined impedance is referred to as “second impedance”) by appropriately setting a resistance value of the first resistance element R 11 , an electrostatic capacitance of the first capacitance element C 11 , and the electrostatic capacitance of the second capacitance element C 12 . 
     Further, a resonance frequency (referred to as “first resonance frequency”) exists between the inductance element L 1  and the housing  1  because of existence of the first capacitance element C 11 , the first stray capacitance C 01 , and the inductance element L 1 . Therefore, in a case where the first resistance element R 11  is not provided, a first impedance is reduced at a first resonance frequency, so that a difference between the first impedance and a second impedance is enlarged, causing generation of noise. In the present embodiment, reduction of the first impedance is prevented by providing the first resistance element R 11 . This point is described in detail below. 
       FIG. 17  is a graph representing a relation between a frequency and an impedance. A curve Z 2  (solid line) illustrated in  FIG. 17  represents a change of a second impedance Z 2  between the second power feed bus  94  and the housing  1 . 
     A curve Z 0  (alternate long and short dash line) represents a change of the first impedance in a case where the first resistance element R 11  is not provided in  FIG. 16 , that is, the inductance element L 1  and the housing  1  are connected to each other by the first capacitance element C 11 . As represented by the curve Z 0 , a first resonance frequency f 0  exists between the inductance element L 1  and the housing  1 , at which the impedance is significantly reduced. 
     The first resonance frequency f 0  described above can be expressed by the following expression (2). 
     
       
         
           
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     In the present embodiment, reduction of the first impedance at the first resonance frequency f 0  is suppressed by providing the first resistance element R 11 . 
     Specifically, the resistance value of the first resistance element R 11  is set to a value that is larger than an impedance Z 0 ( f   0 ) at the frequency f 0  and is smaller than the second impedance Z 2 ( f   0 ). That is, the resistance value of the first resistance element R 11  is set in a range expressed by the following expression (3).
 
 Z 0( f 0)≤ R 11≤ Z 2( f 0)  (3)
 
     where Z 0  is an impedance by the inductance element L 1 , the first capacitance element C 11 , and the first stray capacitance C 01 , and Z 2  is an impedance by the second power feed bus  94 , the second capacitance element C 12 , and the second stray capacitance C 02 . In the following descriptions, an element and a numerical value of that element are denoted by the same sign. For example, the resistance value of the resistance element R 11  is denoted by the same sign R 11 . 
     As a result, the first impedance at the first resonance frequency f 0  can be made higher than the lowest point of the impedance Z 0 . Further, by making the resistance value R 11  closer to Z 2 ( f   0 ), a change of the first impedance with respect to a frequency becomes a change as illustrated by a curve Z 1  (dotted line) in  FIG. 17 , so that the change of the first impedance can be made closer to the curve Z 2 . 
     That is, the resistance value of the first resistance element R 11  is set to be equal to or lower than an impedance between the second power feed bus  94  and the housing  1  at the first resonance frequency f 0  and be higher than an impedance between the inductance element L 1  and the housing  1  in a case where the first resistance element R 11  is not included. Preferably, the resistance value of the first resistance element R 11  is set to match with the impedance between the second power feed bus  94  and the housing  1  at the first resonance frequency f 0 . 
     Therefore, at the first resonance frequency f 0 , it is possible to prevent rapid reduction of the first impedance, so that noise propagation to the housing  1  can be reduced without being influenced by a change of frequency. 
       FIG. 18  is a graph representing an effect of suppressing noise that propagates to the housing  1  at the first resonance frequency f 0 . The horizontal axis represents a magnitude of the first resistance element R 11 , and the vertical axis represents a noise level. As is understood from  FIG. 18 , by setting the resistance value R 11  in a range from Z 0 ( f   0 ) to Z 2 ( f   0 ) (that is, a range expressed by the expression (3) described above), the noise level can be reduced, and the effect of suppressing noise can be increased as R 11  becomes closer to Z 2 ( f   0 ). 
     In this manner, in the tenth embodiment, a series-connected circuit formed by the first capacitance element C 11  and the first resistance element R 11  is provided between the inductance element L 1  and the housing  1 . Therefore, even in a case where the first resonance frequency f 0  exists between the inductance element. L 1  and the first capacitance element C 11 , it is possible to prevent reduction of the first impedance at the first resonance frequency by setting the resistance value of the first resistance element R 11  in the range of the expression (3) described above. Consequently, it is possible to make a voltage applied between the inductance element L 1  and the housing  1  and a voltage applied between the second power feed bus  94  and the housing  1  closer to each other, so that noise propagating to the housing  1  can be reduced. 
     In particular, noise can be reduced more effectively by matching the resistance value R 11  with the impedance Z 2 ( f   0 ) between the second power feed bus  94  and the housing  1  at the first resonance frequency f 0 . 
     Descriptions of First Modification of Tenth Embodiment 
     Next, a first modification of the tenth embodiment is described.  FIG. 19  is an explanatory diagram illustrating a cross-section of the inductance element L 1  and the second power feed bus  94  of a power conversion device according to the first modification of the tenth embodiment. 
     As illustrated in  FIG. 19 , the inductance element L 1  is housed in the frame  4  made of metal, such as iron or aluminum. The frame  4  is connected to the housing  1  by the wire  5 . A series-connected circuit formed by the first resistance element R 11  and the first capacitance element C 11  is provided between the inductance element L 1  and the frame  4 . 
     According to this configuration, the inductance element L 1  is housed in the frame  4 , thereby suppressing noise directly radiated from the inductance element L 1 . Further, by providing the first resistance element R 11  and the first capacitance element C 11  within the frame  4 , it is possible to make an impedance between the inductance element L 1  and the frame  4  higher, so that an impedance between the inductance element L 1  and the housing  1  can be made closer to an electrostatic capacitance between the second power feed bus  94  and the housing  1  (an electrostatic capacitance that is a total of the second capacitance element C 12  and the second stray capacitance C 02 ). 
     Further, by appropriately setting the resistance value of the first resistance element R 11  similarly to the tenth embodiment described above, reduction of the first impedance at the first resonance frequency f 0  can be prevented, and noise propagating from the inductance element L 1  to the housing  1  can be suppressed. 
     Descriptions of Second Modification of Tenth Embodiment 
     Next, a second modification of the tenth embodiment is described.  FIG. 20  is an explanatory diagram illustrating a cross-section of the inductance element L 1  and the second power feed bus  94  of a power conversion device according to the second modification of the tenth embodiment. 
     As illustrated in  FIG. 20 , the inductance element L 1  is housed in the frame  4  made of metal, such as iron or aluminum. A series-connected circuit formed by the first resistance element R 11  and the first capacitance element C 11  is provided between the inductance element L 1  and the frame  4 . Further, the frame  4  and the housing  1  are insulated from each other. The first stray capacitance C 01  exists between the frame  4  and the housing  1 . 
     Also in the second modification, the inductance element L 1  is housed in the frame  4 , similarly to the first modification described above. Therefore, noise directly radiated from the inductance element L 1  can be suppressed. Further, by providing the first resistance element R 11  and the first capacitance element C 11  within the frame  4 , an impedance between the inductance element L 1  and the frame  4  can be increased. As a result, it is possible to make an impedance between the inductance element L 1  and the housing  1  closer to an electrostatic capacitance between the second power feed bus  94  and the housing  1  (the electrostatic capacitance that is a total of the second capacitance element C 12  and the second stray capacitance C 02 ). 
     Further, by appropriately setting the resistance value of the first resistance element R 11  similarly to the tenth embodiment described above, reduction of the first impedance at the first resonance frequency f 0  can be prevented, and noise propagating from the inductance element L 1  to the housing  1  can be suppressed. 
     Descriptions of Eleventh Embodiment 
     Next, an eleventh embodiment of the present invention is described.  FIG. 21  is an explanatory diagram illustrating a cross-section of the inductance element L 1  and the second power feed bus  94  of a power conversion device according to the eleventh embodiment. As illustrated in  FIG. 21 , in the eleventh embodiment, a series-connected circuit formed by the first capacitance element C 11  and the first resistance element R 11  is provided between the inductance element L 1  and the housing  1 . Further, a series-connected circuit formed by a second resistance element R 12  and the second capacitance element C 12  is provided between the second power feed bus  94  and the housing  1 . 
     In the power conversion device according to the eleventh embodiment, a first impedance between the inductance element L 1  and the housing  1  and a second impedance between the second power feed bus  94  and the housing  1  are made closer to each other by appropriately setting a resistance value of the first resistance element R 11 , an electrostatic capacitance of the first capacitance element C 11 , a resistance value of the second resistance element R 12 , and an electrostatic capacitance of the second capacitance element C 12 . 
     A method of setting the resistance values of the first resistance element R 11  and the second resistance element R 12  is described below.  FIG. 22  is a graph representing a relation between a frequency and an impedance. A curve Z 11 ( f ) illustrated in  FIG. 22  represents an impedance between the inductance element L 1  and the housing  1  in a case where the first resistance element R 11  is not provided (first impedance), and a curve Z 21 ( f ) represents an impedance between the second power feed bus  94  and the housing  1  in a case where the second resistance element R 12  is not provided (second impedance). 
     Further, a curve Z 10 ( f ) represents an impedance of the inductance element L 1 , and a curve Z 20 ( f ) represents an impedance of the second power feed bus  94 . Because the curve Z 10 ( f ) only represents an inductance, the impedance increases with increase of a frequency. As for the curve Z 20 ( f ), the impedance is reduced with increase of a frequency, because of existence of a stray capacitance. 
     Meanwhile, the impedance Z 11 ( f ) and the impedance Z 21 ( f ) have resonance frequencies, respectively. Although it is desirable that both resonance frequencies match with each other, the resonance frequencies are different in many cases. Here, it is assumed that the resonance frequency of the impedance Z 11 ( f ) is a first resonance frequency f 1  and the resonance frequency of the impedance Z 21 ( f ) is a second resonance frequency  2 . 
     Therefore, as illustrated in  FIG. 22 , Z 11 ( f ) and Z 21 ( f ) each have characteristics in which the impedance is rapidly reduced at the first resonance frequency f 1  or the second resonance frequency  2 . In the present embodiment, resistance values of the first resistance element R 11  and the second resistance element R 12  are set in such a manner that reduction of the first impedance and the second impedance is suppressed at the respective resonance frequencies f 1  and f 2 . 
     A range of the resistance value R 11  and a range of the resistance value R 12  are set as expressed by the following expressions (4) and (5).
 
 Z 11( f 1)≤ R 11≤ Z 21( f 1)  (4).
 
 Z 21( f 2)≤ R 12≤ Z 11( f 2)  (5).
 
     Specifically, the range of the resistance value R 11  is set to a range denoted by a sign q 1  in  FIG. 22 , and the range of the resistance value R 12  is set to a range denoted by a sign q 2 . 
     By setting the resistance value of the first resistance element R 11  to be in the range expressed by the expression (4) described above, it is possible to suppress reduction of the impedance of the curve Z 11 ( f ) in  FIG. 22  at the first resonance frequency f 1 . Similarly, by setting the resistance value of the second resistance element R 12  to be in the range expressed by the expression (5) described above, it is possible to suppress reduction of the impedance of the curve Z 21 ( f ) at the second resonance frequency f 2 . 
     That is, when a resonance frequency by the second power feed bus  94  and an electrostatic capacitance of the second capacitance element C 12  is assumed as the second resonance frequency f 2 , the resistance value of the second resistance element R 12  is set to be higher than the impedance Z 21 ( f   2 ) between the second power feed bus  94  and the housing  1  and be lower than the impedance Z 11 ( f   2 ) between the inductance element L 1  and the housing  1 , at the second resonance frequency f 2  in a case where the second resistance element R 12  is not included. 
     Therefore, by providing the resistance elements R 11  and R 12 , it is possible to suppress reduction of the first impedance and the second impedance at the first resonance frequency f 1  and the second resonance frequency f 2 , and to prevent generation of noise. 
       FIG. 27  is a characteristic diagram illustrating a relation between a resistance value and a noise level, in which the horizontal axis represents a resistance value and the vertical axis represents a noise level. By setting the resistance values R 11  and R 12  as expressed by the expressions (4) and (5) described above, the resistance values are values in a range denoted by a sign X 1 . Therefore, the noise level can be reduced. 
     As described above, in the eleventh embodiment, a series-connected circuit formed by the first capacitance element C 11  and the first resistance element R 11  is provided between the inductance element L 1  and the housing  1 , and a series-connected circuit formed by the second capacitance element C 12  and the second resistance element R 12  is provided between the second power feed bus  94  and the housing  1 . Therefore, it is possible to suppress reduction of the first impedance and the second impedance at the first resonance frequency f 1  and the second resonance frequency f 2 , so that noise propagating to the housing  1  can be reduced. 
     Further, by setting the resistance values R 11  and R 12  as expressed by the expressions (4) and (5) described above, it is possible to suppress reduction of the impedance at the first resonance frequency f 1  and the second resonance frequency f 2 , so that noise propagating to the housing  1  can be reduced. 
     Descriptions of First Modification of Eleventh Embodiment 
     Next, a first modification of the eleventh embodiment is described. In the first modification, each of the resistance values of the resistance elements R 11  and R 12  described above is set to a value expressed by the following expression (6).
 
 R 11, R 11≈{ Z 21( f 1)+ Z 11( f 2)}/2  (6).
 
     This setting is described below with reference to a graph illustrated in  FIG. 23 .  FIG. 23  is a graph representing the first impedance Z 11 ( f ) and the second impedance Z 21 ( f ), in which a difference between the first resonance frequency f 1  and the second resonance frequency  12  illustrated in  FIG. 22  is emphasized in order to facilitate understanding. Each of R 11  and R 12  obtained by the expression (6) described above is a resistance value denoted by a sign q 3 . That is, R 11  and R 12  are an average value between Z 21 ( f   1 ) and Z 11 ( f   2 ). 
     That is, each of the resistance values of the first resistance element R 11  and the second resistance element R 12  is set to an average value between the impedance Z 21 ( f   1 ) between the second power feed bus  94  and the housing  1  at the first resonance frequency f 1  and the impedance Z 11 ( f   2 ) between the inductance element L 1  and the housing  1  at the second resonance frequency f 2 . 
     Therefore, by setting the resistance values of the first resistance element R 11  and the second resistance element R 12  as expressed by the expression (6), it is possible to suppress reduction of the impedance of the curve Z 11 ( f ) at the first resonance frequency f 1 . Similarly, it is possible to suppress reduction of the impedance of the curve Z 21 ( f ) at the second resonance frequency f 2 . 
     By setting the resistance values R 11  and R 12  as expressed by the expression (6) described above, the resistance values can be a resistance value denoted by a sign X 2  in  FIG. 27 , so that an effect of reducing the noise level can be maximized. Therefore, it is possible to suppress reduction of the first impedance and the second impedance at the first resonance frequency f 1  and the second resonance frequency f 2 , so that noise propagating to the housing  1  can be reduced. 
     Descriptions of Second Modification of Eleventh Embodiment 
     Next, a second modification of the eleventh embodiment is described. In the second modification, resistance values of the first resistance element R 11  and the second resistance element R 12  are set in ranges expressed by the following expressions (7a) and (7b), respectively.
 
 Z 21( f 1)≤ R 11≤ Z 11( f 2)  (7a).
 
 Z 21( f 1)≤ R 12≤ Z 11( f 2)  (7b).
 
     This setting is described below with reference to a graph illustrated in  FIG. 24 .  FIG. 24  is a graph representing the first impedance Z 11 ( f ) and the second impedance Z 21 ( f ), in which a difference between the first resonance frequency f 1  and the second resonance frequency  12  illustrated in  FIG. 22  is emphasized. R 1  and R 2  respectively set by the expressions (7a) and (7b) described above are in a range denoted by a sign q 4  in  FIG. 24 . 
     That is, the resistance values of the first resistance element R 11  and the second resistance element R 12  are set to resistance values between the impedance Z 11 ( 12 ) between the inductance element L 1  and the housing  1  at the second resonance frequency  12  in a case where the first resistance element R 11  is not included, and the impedance Z 21 ( f   1 ) between the second power feed bus  94  and the housing  1  at the first resonance frequency f 1  in a case where the second resistance element R 12  is not included. 
     By setting the resistance values R 11  and R 12  as expressed by the expressions (7a) and (7b) described above, the respective resistance values R 11  and R 12  are in a range denoted by a sign X 3  in  FIG. 27 , and a noise level can be reduced. As a result, it is possible to make a voltage generated between the inductance element L 1  and the housing  1  and a voltage generated between the second power feed bus  94  and the housing  1  closer to each other, so that noise propagating to the housing  1  can be reduced. 
     Descriptions of Third Modification of Eleventh Embodiment 
     Next, a third modification of the eleventh embodiment is described. In the third modification, each of the resistance values of the first resistance element R 11  and the second resistance element R 12  (assumed as “Rr”) is set to a value expressed by the following expression (8).
 
 Rr=R 11, R 12={ Z 10( f 12)+ Z 20( f 12)}/2  (8)
 
     where f 12  is a frequency of an intersection of the curve Z 11 ( f ) and the curve Z 21 ( f ) as illustrated in  FIG. 25 . That is, the frequency f 12  is an intermediate frequency between the first resonance frequency f 1  and the second resonance frequency f 2 . 
     This setting is described below with reference to a graph illustrated in  FIG. 25 .  FIG. 25  is a graph representing the first impedance Z 11 ( f ) and the second impedance Z 21 ( f ), in which a difference between the first resonance frequency f 1  and the second resonance frequency f 2  illustrated in  FIG. 22  is emphasized. In addition,  FIG. 26  is an enlarged view of a portion “A” in  FIG. 25 . Each of the resistance values R 11  and R 12  set by the expression (8) described above is a value denoted by a sign q 5  in  FIG. 26 . 
     That is, the intermediate frequency f 12  between the first resonance frequency f 1  and the second resonance frequency f 2  is set, and the resistance values of the first resistance element R 11  and the second resistance element R 12  are set to a resistance value between an impedance Z 10 ( f   2 ) between the inductance element L 1  and the housing  1  in a case where the first impedance element is not provided, and an impedance Z 20 ( f   12 ) between the second power feed bus  94  and the housing  1  in a case where the second impedance element is not provided, at the intermediate frequency f 12 . 
     In this manner, each of the resistance values of the first resistance element R 11  and the second resistance element R 12  is set to an intermediate value between Z 10 ( f   12 ) and Z 20 ( f   12 ) at the frequency f 12 . Therefore, the resistance values R 11  and R 12  (=Rr) are a value X 4  in  FIG. 27 , so that an effect of reducing the noise level can be maximized. 
     Accordingly, it is possible to make a voltage generated between the inductance element L 1  and the housing  1  and a voltage generated between the second power feed bus  94  and the housing  1  closer to each other, so that noise propagating to the housing  1  can be reduced. 
     Other Embodiments 
     In each of the embodiments described above, an example has been described in which power is converted by using the power module  3  formed by the switching element Q 1  and the diode D 1  as illustrated in  FIG. 1 . However, the present invention is not limited to the embodiments. For example, a rectifier circuit  31  formed by a diode-bridge circuit can be provided at a preceding stage of the smoothing capacitor C 100  as illustrated in  FIG. 28 . In a case where power supplied from the power supply  91  is alternating-current power, the alternating-current power can be rectified to be supplied to the power module  3 . 
     Further, a power conversion device can be configured to include a power module  3   a  including four switching elements, a control circuit  34  that controls the power module  3   a , a transformer  35 , and a rectifier circuit  33  including four diodes at a subsequent stage of the inductance element L 1  as illustrated in  FIG. 29 . Also with this configuration, noise can be reduced by providing the first impedance element between the inductance element L 1  and the housing  1 . 
     Although the power conversion device according to the present invention has been described above based on the embodiments as illustrated in the drawings, the present invention is not limited to those, and configurations of respective parts can be replaced by arbitrary configurations having identical functions thereto. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  housing 
               2 ,  34  control circuit 
               3 ,  3   a  power module 
               4  frame 
               5  wire 
               6  plate member 
               7  thick portion 
               8  second dielectric body 
               9  first dielectric body 
               11  first impedance element 
               12  second impedance element 
               31 ,  33  rectifier circuit 
               35  transformer 
               91  power supply 
               92  load 
               93  first power feed bus 
               94  second power feed bus 
               95 ,  96  output line 
               101  power conversion device 
             L 1  inductance element 
             L 1   a  planer inductance element 
             C 01  first stray capacitance 
             C 02  second stray capacitance 
             C 11  first capacitance element 
             C 12  second capacitance element 
             C 100 , C 200  smoothing capacitor 
             D 1  diode 
             f 0  first resonance frequency 
             f 1  first resonance frequency 
             f 12  intermediate frequency 
             f 2  second resonance frequency 
             L 1  inductance element 
             L 1   a  planer inductance element 
             Q 1  switching element 
             R 11  first resistance element 
             R 12  second resistance element