Patent Publication Number: US-2015085533-A1

Title: Reactor and power converter

Description:
INCORPORATION BY REFERENCE 
     The disclosure of Japanese Patent Application No. 2013-198967 filed on Sep. 25, 2013 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a reactor and a power converter. 
     2. Description of Related Art 
     Japanese Patent Application Publication No. 2005-057925 (JP 2005-057925 A), for example, describes a complex resonant type converter that reduces a coupling coefficient to 0.79, with a gap length of an isolated converter transformer of approximately 1.5 mm. 
     The structure described in JP 2005-057925 A reduces the coupling coefficient by dimensional control of the gap length between coils. 
     SUMMARY OF THE INVENTION 
     However, with the structure described in JP 2005-057925 A, when a current value applied to the coil is increased, leakage flux consequently increases, so the coupling coefficient decreases. In other words, the coupling coefficient changes with a change in the current value applied to the coil. The invention thus provides a reactor and a power converter capable of reducing the amount of change in the coupling coefficient that accompanies a change in the current value applied to the coil. 
     A first aspect of the invention relates to a reactor that includes a magnetic core; a first coil wound around the magnetic core; a second coil wound around the magnetic core; and a magnetic body that is provided between the first coil and the second coil separate from the magnetic core, and that reduces a coupling coefficient between the first coil and the second coil. 
     A second aspect of the invention relates to a power converter that includes a primary side circuit that includes a first reactor including a first magnetic core, a first coil wound around the first magnetic core; a second coil wound around the first magnetic core; and a first magnetic body that is provided between the first coil and the second coil separate from the first magnetic core, and that reduces a coupling coefficient between the first coil and the second coil; and a secondary side circuit that is magnetically coupled to the primary side circuit by a transformer, and includes a second reactor including a second magnetic core, a third coil wound around the second magnetic core; a fourth coil wound around the second magnetic core; and a second magnetic body that is provided between the third coil and the fourth coil separate from the second magnetic core, and that reduces a coupling coefficient between the third coil and the fourth coil. 
     According to the aspects described above, a reactor and a power converter capable of reducing an amount of change in a coupling coefficient that accompanies a change in a current value applied to a coil are able to be obtained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
         FIG. 1  is a block diagram of the structure of a power converter according to a first example embodiment of the invention; 
         FIG. 2  is a perspective view of a reactor according to the first example embodiment of the invention; 
         FIG. 3  is a sectional view at a cross-section along a surface that includes a U-shaped plane of a magnetic core element of the reactor; 
         FIG. 4  is a view of the analysis results of a relationship between a coupling coefficient and current (i.e., current applied to a first coil and a second coil); 
         FIG. 5A  is a view showing the relationship between leakage flux and coupling flux; 
         FIG. 5B  is a view showing the relationship between leakage flux and coupling flux; 
         FIG. 6  is a view of one example of a mounting method of a magnetic body; 
         FIG. 7  is a view of another example of a mounting method of the magnetic body; 
         FIG. 8  is a sectional view of a reactor according to a second example embodiment of the invention; and 
         FIG. 9  is a sectional view of a reactor according to a third example embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, example embodiments of the invention will be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a block diagram of the structure of a power converter  10  according to a first example embodiment of the invention. This power converter  10  may be mounted in a vehicle such as an automobile, and may be used by a system that distributes electric power to on-board loads, for example. 
     The power converter  10  includes, as primary side ports, a first input/output port  60   a  to which a primary side high-voltage system load  61   a  is connected, and a second input/output port  60   c  to which a primary side low-voltage system load  61   c  and a primary side low-voltage system power supply  62   c  are connected, for example. The primary side low-voltage system power supply  62   c  supplies electric power to the primary side low-voltage system load  61   c  that operates on the same voltage system (such as a 12 V system) as the primary side low-voltage system power supply  62   c . Also, the primary side low-voltage system power supply  62   c  supplies electric power that has been stepped up by a primary side converter circuit  20  provided in the power converter  10 , to the primary side high-voltage system load  61   a  that operates on a different voltage system (such as a 48 V system that is higher than the 12 V system) than the primary side low-voltage system power supply  62   c . One specific example of the primary side low-voltage system power supply  62   c  is a secondary battery such as a lead battery. 
     The power converter  10  is a power converter circuit that has the four input/output ports described above, and performs power conversion between two ports when any two of the four input/output ports are selected. 
     Port powers Pa, Pc, Pb, and Pd are input/output powers (input powers or output powers) of the first input/output port  60   a , the second input/output port  60   c , a third input/output port  60   b , and a fourth input/output port  60   d , respectively. Port voltages Va, Vc, Vb, and Vd are input/output voltages (input voltages or output voltages) of the first input/output port  60   a , the second input/output port  60   c , the third input/output port  60   b , and the fourth input/output port  60   d , respectively. Port currents Ia, Ic, Ib, and Id are input/output currents (input currents or output currents) of the first input/output port  60   a , the second input/output port  60   c , the third input/output port  60   b , and the fourth input/output port  60   d , respectively. 
     The power converter  10  includes a capacitor C 1  provided for the first input/output port  60   a , a capacitor C 3  provided for the second input/output port  60   c , a capacitor C 2  provided for the third input/output port  60   b , and a capacitor C 4  provided for the fourth input/output port  60   d . Some specific examples of the capacitors C 1 , C 2 , C 3 , and C 4  are film capacitors, aluminum electrolytic capacitors, ceramic capacitors, and solid polymer capacitors. 
     The capacitor C 1  is inserted between a terminal  613  on a high-potential side of the first input/output port  60   a , and a terminal  614  on a low-potential side of the first input/output port  60   a  and the second input/output port  60   c . The capacitor C 3  is inserted between a terminal  616  on a high-potential side of the second input/output port  60   c , and the terminal  614  on the low-potential side of the first input/output port  60   a  and the second input/output port  60   c . The capacitor C 2  is inserted between a terminal  618  on a high-potential side of the third input/output port  60   b , and a terminal  620  on a low-potential side of the third input/output port  60   b  and the fourth input/output port  60   d . The capacitor C 4  is inserted between a terminal  622  on a high-potential side of the fourth input/output port  60   d , and the terminal  620  on the low-potential side of the third input/output port  60   b  and the fourth input/output port  60   d.    
     The power converter  10  is a power converter circuit that includes a primary side converter circuit  20  and a secondary side converter circuit  30 . The primary side converter circuit  20  and the secondary side converter circuit  30  are connected together via a primary side magnetic coupling reactor  204  and a secondary side magnetic coupling reactor  304 , and are magnetically coupled by a transformer  400  (a center-tapped transformer). 
     The primary side converter circuit  20  is a primary side circuit that includes a primary side full bridge circuit  200 , the first input/output port  60   a , and the second input/output port  60   c . The primary side full bridge circuit  200  is a primary side power converting portion that includes a primary side coil  202  of the transformer  400 , the primary side magnetic coupling reactor  204 , a primary side first upper arm U1, a primary side first lower arm /U1, a primary side second upper arm V1, and a primary side second lower arm /V1. Here, the primary side first upper arm U1, the primary side first lower arm /U1, the primary side second upper arm V1, and the primary side second lower arm /V1 are all switching elements, each of which includes an N-channel type MOSFET, and a body diode that is a parasitic device of the MOSFET, for example. Diodes may be additionally connected in parallel to the MOSFET. 
     The primary side full bridge circuit  200  includes a primary side positive bus  298  that is connected to the terminal  613  on the high-potential side of the first input/output port  60   a , and a primary side negative bus  299  that is connected to the terminal  614  on the low-potential side of the first input/output port  60   a  and the second input/output port  60   c.    
     A primary side first arm circuit  207  that series-connects the primary side first upper arm U1 to the primary side first lower arm /U1 is attached between the primary side positive bus  298  and the primary side negative bus  299 . This primary side first arm circuit  207  is a primary side first power converter circuit portion (i.e., a primary side U-phase power converter circuit portion) capable of a power converting operation in response to an ON/OFF switching operation of the primary side first upper arm U1 and the primary side first lower arm /U1. Moreover, a primary side second arm circuit  211  that series-connects the primary side second upper arm V1 to the primary side second lower arm /V1 is attached, in parallel to the primary side first arm circuit  207 , between the primary side positive bus  298  and the primary side negative bus  299 . This primary side second arm circuit  211  is a primary side second power converter circuit portion (i.e., a primary side V-phase power converter circuit portion) capable of a power converting operation in response to an ON/OFF switching operation of the primary side second upper arm V1 and the primary side second lower arm /V1. 
     The primary side coil  202  and the primary side magnetic coupling reactor  204  are provided on a bridge portion that connects a midpoint  207   m  of the primary side first arm circuit  207  to a midpoint  211   m  of the primary side second arm circuit  211 . The connections of this bridge portion will now be described in more detail. One end of a primary side first reactor  204   a  of the primary side magnetic coupling reactor  204  is connected to the midpoint  207   m  of the primary side first arm circuit  207 . Also, one end of the primary side coil  202  is connected to the other end of the primary side first reactor  204   a . Moreover, one end of a primary side second reactor  204   b  of the primary side magnetic coupling reactor  204  is connected to the other end of the primary side coil  202 . Then, the other end of the primary side second reactor  204   b  is connected to the midpoint  211   m  of the primary side second arm circuit  211 . The primary side magnetic coupling reactor  204  includes the primary side first reactor  204   a , and the primary side second reactor  204   b  that is magnetically coupled to the primary side first reactor  204   a  by a coupling coefficient k 1 . 
     The midpoint  207   m  is a primary side first intermediate node between the primary side first upper arm U1 and the primary side first lower arm /U1, and the midpoint  211   m  is a primary side second intermediate node between the primary side second upper arm V1 and the primary side second lower arm /V1. 
     The first input/output port  60   a  is a port that is provided between the primary side positive bus  298  and the primary side negative bus  299 . The first input/output port  60   a  includes the terminal  613  and the terminal  614 . The second input/output port  60   c  is a port that is provided between the primary side negative bus  299  and a center tap  202   m  of the primary side coil  202 . The second input/output port  60   c  includes the terminal  614  and the terminal  616 . 
     The center tap  202   m  is connected to the terminal  616  on the high-potential side of the second input/output port  60   c . The center tap  202   m  is an intermediate junction point of a primary side first winding  202   a  and a primary side second winding  202   b  that are formed by the primary side coil  202 . 
     The secondary side converter circuit  30  is a secondary side circuit that includes a secondary side full bridge circuit  300 , the third input/output port  60   b , and the fourth input/output port  60   d . The secondary side full bridge circuit  300  is a secondary side power converting portion that includes a secondary side coil  302  of the transformer  400 , a secondary side magnetic coupling reactor  304 , a secondary side first upper arm U2, a secondary side first lower arm /U2, a secondary side second upper arm V2, and a secondary side second lower arm /V2. Here, the secondary side first upper arm U2, the secondary side first lower arm /U2, the secondary side second upper arm V2, and the secondary side second lower arm /V2 are all switching elements, each of which includes an N-channel type MOSFET, and a body diode that is a parasitic device of the MOSFET, for example. 
     The secondary side full bridge circuit  300  includes a secondary side positive bus  398  that is connected to the terminal  618  on the high-potential side of the third input/output port  60   b , and a secondary side negative bus  399  that is connected to the terminal  620  on the low-potential side of the third input/output port  60   b  and the fourth input/output port  60   d.    
     A secondary side first arm circuit  307  that series-connects the secondary side first upper arm U2 to the secondary side first lower arm /U2 is attached between the secondary side positive bus  398  and the secondary side negative bus  399 . This secondary side first arm circuit  307  is a secondary side first power converter circuit portion (i.e., a secondary side U-phase power converter circuit portion) capable of a power converting operation in response to an ON/OFF switching operation of the secondary side first upper arm U2 and the secondary side first lower arm /U2. Moreover, a secondary side second arm circuit  311  that series-connects the secondary side second upper arm V2 to the secondary side second lower arm /V2 is attached, in parallel to the secondary side first arm circuit  307 , between the secondary side positive bus  398  and the secondary side negative bus  399 . This secondary side second arm circuit  311  is a secondary side second power converter circuit portion (i.e., a secondary side V-phase power converter circuit portion) capable of a power converting operation in response to an ON/OFF switching operation of the secondary side second upper arm V2 and the secondary side second lower arm /V2. 
     The secondary side coil  302  and the secondary side magnetic coupling reactor  304  are provided on a bridge portion that connects a midpoint  307   m  of the secondary side first arm circuit  307  to a midpoint  311   m  of the secondary side second arm circuit  311 . The connections of this bridge portion will now be described in more detail. One end of a secondary side first reactor  304   a  of the secondary side magnetic coupling reactor  304  is connected to the midpoint  307   m  of the secondary side first arm circuit  307 . Also, one end of the secondary side coil  302  is connected to the other end of the secondary side first reactor  304   a . Moreover, one end of a secondary side second reactor  304   b  of the secondary side magnetic coupling reactor  304  is connected to the other end of the secondary side coil  302 . Then, the other end of the secondary side second reactor  304   b  is connected to the midpoint  311   m  of the secondary side second arm circuit  311 . The secondary side magnetic coupling reactor  304  includes the secondary side first reactor  304   a , and the secondary side second reactor  304   b  that is magnetically coupled to the secondary side first reactor  304   a  by a coupling coefficient k 2 . 
     The midpoint  307   m  is a secondary side first intermediate node between the secondary side first upper arm U2 and the secondary side first lower arm /U2, and the midpoint  311   m  is a secondary side second intermediate node between the secondary side second upper arm V2 and the secondary side second lower arm /V2. 
     The third input/output port  60   b  is a port that is provided between the secondary side positive bus  398  and the secondary side negative bus  399 . The third input/output port  60   b  includes the terminal  618  and the terminal  620 . The fourth input/output port  60   d  is a port that is provided between the secondary side negative bus  399  and a center tap  302   m  of the secondary side coil  302 . The fourth input/output port  60   d  includes the terminal  620  and the terminal  622 . 
     The center tap  302   m  is connected to the terminal  622  on the high-potential side of the fourth input/output port  60   d . The center tap  302   m  is an intermediate junction point of a secondary side first winding  302   a  and a secondary side second winding  302   b  that are formed by the secondary side coil  302 . 
     Here, a voltage step-up/down function of the primary side converter circuit  20  will be described. Focusing on the second input/output port  60   c  and the first input/output port  60   a , the terminal  616  of the second input/output port  60   c  is connected to the midpoint  207   m  of the primary side first arm circuit  207  via the primary side first winding  202   a  and the primary side first reactor  204   a  that is series-connected to the primary side first winding  202   a . Also, both ends of the primary side first arm circuit  207  are connected to the first input/output port  60   a , so a voltage step-up/down circuit is attached between the terminal  616  of the second input/output port  60   c  and the first input/output port  60   a.    
     Furthermore, the terminal  616  of the second input/output port  60   c  is connected to the midpoint  211   m  of the primary side second arm circuit  211  via the primary side second winding  202   b  and the primary side second reactor  204   b  that is series-connected to the primary side second winding  202   b . Also, both ends of the primary side second arm circuit  211  are connected to the first input/output port  60   a , so a voltage step-up/down circuit is attached in parallel between the terminal  616  of the second input/output port  60   c  and the first input/output port  60   a . The secondary side converter circuit  30  is a circuit having substantially the same structure as the primary side converter circuit  20 , so two voltage step-up/down circuits are connected in parallel between the terminal  622  of the fourth input/output port  60   d  and the third input/output port  60   b . Therefore, the secondary side converter circuit  30  has a voltage step-up/down function similar to the primary side converter circuit  20 . 
     Next, a reactor of the invention will be described. The reactor described below is able to preferably be used in the power converter  10  described above. For example, the reactor may be used as the primary side magnetic coupling reactor  204 , or as the secondary side magnetic coupling reactor  304 . In the description below, the reactor will be described as one that forms the primary side magnetic coupling reactor  204 , as an example. 
       FIG. 2  is a perspective view of a reactor  70 A according to one example embodiment (a first example embodiment) of the invention.  FIG. 3  is a sectional view of the reactor  70 A (i.e., a sectional view in a direction in which a cross-section of magnetic core elements  72   a  and  72   b  is U-shaped). 
     The reactor  70 A includes a magnetic core  72 , a first coil  80 , a second coil  90 , and a magnetic body  100 . 
     The magnetic core  72  may be made of any suitable magnetic material (such as material that includes iron oxide such as ferrite). In the example shown in  FIG. 2 , the magnetic core  72  includes two magnetic core elements  72   a  and  72   b . These magnetic core elements  72   a  and  72   b  are both U-shaped cores, and are arranged facing each other in a manner in which a slot  72   c  is formed. In this structure, identical parts are able to be used for these magnetic core elements  72   a  and  72   b . The magnetic core  72  may be formed by combining a U-shaped core with an I-shaped core, or it may be a ring-shaped core. Also, the magnetic core  72  may be a core that is formed by punching, or it may be a laminated core. 
     The first coil  80  is wound around a first leg portion  73   a  of the magnetic core  72 , in a manner passing through the slot  72   c . In this case, the first leg portion  73   a  defines a first axis around which the first coil  80  is wound. The second coil  90  is wound around a second leg portion  73   b  of the magnetic core  72 , in a manner passing through the slot  72   c . The second leg portion  73   b  defines a second axis around which the second coil  90  is wound. In the description below, the X direction corresponds to a direction parallel to the first axis and the second axis. 
     The first coil  80  and the second coil  90  are typically made of the same material. The first coil  80  and the second coil  90  are each preferably formed by flat wire having a rectangular cross-section that is able to handle a larger current than thin round wire having a round cross-section. However, the first coil  80  and the second coil  90  may also each be formed by thin round wire having a round cross-section. Also, the first coil  80  and the second coil  90  may each have a single-layer winding structure, or a multi-layer winding structure. 
     The magnetic body  100  may be made of any suitable magnetic material (such as material that includes iron oxide such as ferrite). The magnetic body  100  is provided between the first coil  80  and the second coil  90  in a Y direction. The Y direction is a perpendicular to an extending direction (i.e., the X direction) of the first leg portion  73   a  (and the second leg portion  73   b ) in a U-shaped plane of the magnetic core elements  72   a  and  72   b . The magnetic body  100  has a function of reducing the coupling coefficient between the first coil  80  and the second coil  90 . The shape of the magnetic body  100  may be any suitable shape and is not limited to having the function of reducing the coupling coefficient between the first coil  80  and the second coil  90 . In the example shown in  FIG. 2 , the magnetic body  100  is a flat plate-shaped member (a flat plate in which the Y direction is a normal line), and is arranged in the slot  72   c  of the magnetic core  72 . When the magnetic body  100  is a flat plate-shaped member, the plate thickness may be approximately 0.1 mm, for example. The extending range of the magnetic body  100  in a Z direction is arbitrary. For example, the magnetic body  100  may extend inside the slot  72   c  between both end surfaces of the magnetic core  72  in the Z direction (see  FIG. 2 ), or may extend in a manner protruding out in the Z direction from both end surfaces of the magnetic core  72  in the Z direction, or may extend in a manner staying further to the inside in the Z direction than both end surfaces of the magnetic core  72  in the Z direction. 
       FIG. 4  is a view of the analysis results of a relationship between a coupling coefficient and current (i.e., current applied to the first coil  80  and the second coil  90 ).  FIGS. 5A and 5B  are views illustrating the relationship between leakage flux and coupling flux when the second coil  90  is energized.  FIG. 5A  is a view of a case of a comparative example, and  FIG. 5B  is a view of a case with the example embodiment.  FIG. 4  is a view showing the analysis results based on CAE (computer-aided engineering) analysis by the inventor.  FIG. 4  is also a view showing the analysis results of the comparative example for comparison. The comparative example is formed without the magnetic body  100 . That is, the comparative example has the same structure of the reactor  70 A minus the magnetic body  100 . The coupling coefficient indicates the percentage at which magnetic flux generated by one coil links to the other coil. Here, the relationship between the leakage flux and the coupling flux when the second coil  90  is energized is described. The relationship between the leakage flux and the coupling flux when the first coil  80  is energized is essentially the same. 
     With the comparative example, when a relatively low current is applied to the second coil  90 , coupling flux is generated, as shown in the frame format in  FIG. 5A . At this time, with the comparative example, there is an air gap between the first coil  80  and the second coil  90  in the Y direction, as shown in  FIG. 5A , so the leakage flux that flows through this air gap is small (shown in a frame format by the dotted line). Therefore, with the comparative example, the coupling coefficient is relative high (approximately 96%), as shown in  FIG. 4 . 
     On the other hand, with the example embodiment, when a relatively low current is applied to the second coil  90 , coupling flux and leakage flux are generated, as shown in the frame format in  FIG. 5B . With the example embodiment, the magnetic body  100  is provided between the first coil  80  and the second coil  90  in the Y direction, as shown in  FIG. 5B , so the magnetic body  100  forms a magnetic path such that the leakage flux increases. Therefore, with this example embodiment, the coupling coefficient is relatively low (approximately 90%), as shown in  FIG. 4 . In this way, with the example embodiment, the coupling coefficient in the low current region is able to be reduced compared to the comparative example, by providing the magnetic body  100  between the first coil  80  and the second coil  90  in the Y direction. This kind of low coupling coefficient is especially preferable when the primary side magnetic coupling reactor  204  is to have a current filter function. 
     Also, with the comparative example, when the current applied to the second coil  90  is increased, the percentage of magnetic flux (leakage flux) that passes through the air gradually increases (the percentage of magnetic flux flowing through the magnetic core  72  gradually decreases), so the coupling coefficient decreases, as shown in  FIG. 4 . For example, with the example shown in  FIG. 4 , the coupling rate changes (i.e., decreases) by more than 1% when the current is increased to the maximum value (see the dotted line) of the usage range. 
     On the other hand, with the example embodiment, when the current applied to the second coil  90  is increased, the percentage of magnetic flux that flows through the magnetic core  72  and the percentage of magnetic flux that flows through the magnetic body  100  both increase, so the coupling coefficient remains substantially constant, as shown in  FIG. 4 . That is, the increase in the percentage of leakage flux of the magnetic core  72  is cancelled out by the decrease in the percentage in the magnetic flux flowing through the magnetic body  100 , so the coupling coefficient remains substantially constant. As a result, with the example embodiment, the coupling coefficient is able to be made constant from the low current region to the high current region (throughout the entire region of the usage range). The term “constant” here means not strictly constant, but rather that fluctuation is kept within a range of less than 1% (see  FIG. 4 ). 
     The characteristics shown in  FIG. 4  rely on the makeup of the magnetic core  72  (e.g., the current value at the time of magnetic saturation), the magnetic saturation characteristic of the magnetic body  100  (e.g., the current value at the time of magnetic saturation), and the amount of clearance A (see  FIG. 3 ) in the X direction between the magnetic core  72  and the magnetic body  100 , and the like. Therefore, characteristics (i.e., the relationship between current and the coupling coefficient) such as the coupling coefficient being constant throughout the entire region of the usage range may also be realized by adjusting the amount of clearance A, for example. The magnetic body  100  becomes saturated faster (i.e., the current value at the time of magnetic saturation becomes lower) the smaller the clearance A is in the X direction between the magnetic core  72  and the magnetic body  100 . 
       FIG. 6  is a view of an example of a mounting method of the magnetic body  100 . 
     In the example shown in  FIG. 6 , the magnetic body  100  is integrally formed (insert molded) with a bobbin  110 . A resin portion of the bobbin  110  includes a first coil retaining portion  112 , a second coil retaining portion  114 , a base portion  116 , and a covering portion  118 . The first coil retaining portion  112  and the second coil retaining portion  114  stand erect on the base portion  116  in a manner extending in the X direction. The first coil retaining portion  112  and the second coil retaining portion  114  both have a hollow cylindrical shape. Through-holes  116   a  and  116   b  corresponding to the hollow portions of the first coil retaining portion  112  and the second coil retaining portion  114  are formed in the base portion  116 . The covering portion  118  covers the magnetic body  100 . The first coil  80  and the second coil  90  are wound around the outer peripheries of the first coil retaining portion  112  and the second coil retaining portion  114 , respectively. Also, the first leg portion  73   a  and the second leg portion  73   b  of the magnetic core  72  are inserted into the hollow portions of the first coil retaining portion  112  and the second coil retaining portion  114 , respectively. 
     Only one bobbin  110  may be used in one reactor  70 A, or two bobbins  110  may be used in one reactor  70 A. When two bobbins  110  are used, the two bobbins  110  may be arranged opposing one another with the base portions  116  aligned in the X direction. In this case, the magnetic core elements  72   a  and  72   b  are both attached from both sides of the two bobbins  110  in the X direction. 
       FIG. 7  is a view of another example of the mounting method of the magnetic body  100 . 
     The magnetic body  100  may be affixed to either one of the coils, i.e., the first coil  80  or the second coil  90 , by adhesive or tape or the like. In the example shown in  FIG. 7 , the magnetic body  100  is affixed to the outer peripheral surface of the first coil  80  (i.e., the outer peripheral surface opposing the second coil  90  in the Y direction). Insulating layers  121  and  122  are formed on both surfaces of the magnetic body  100  in the Y direction. The insulating layers  121  and  122  may be formed by applying a resin coating or tape-like insulating material having a thickness of 10 μm or more, for example. If the magnetic body  100  is affixed to the outer peripheral surface of the first coil  80  with tape, the insulating layer  121  may be omitted. 
       FIG. 8  is a sectional view of a reactor  70 B according to another example embodiment (a second example embodiment) of the invention, and corresponds to  FIG. 3  of the first example embodiment described above. 
     The reactor  70 B differs from the reactor  70 A in the first example embodiment described above, in terms of the arrangement of the first coil  80  and the second coil  90 . Accordingly, the manner in which the magnetic body  100  is arranged differs from that of the first example embodiment described above. The other structure may be the same as it is in the first example embodiment. 
     More specifically, the first coil  80  is wound around the second leg portion  73   b  of the magnetic core  72  in a manner passing through the slot  72   c . The second coil  90  is also wound around the second leg portion  73   b  of the magnetic core  72  in a manner passing through the slot  72   c . The first coil  80  and the second coil  90  are wound around the same axis, separated in the X direction. In the example shown in  FIG. 8 , the first coil  80  and the second coil  90  are wound around the second leg portion  73   b  of the magnetic core  72 , but they may also be wound around the first leg portion  73   a.    
     The magnetic body  100  is provided between the first coil  80  and the second coil  90  in the X direction. In the example shown in  FIG. 8 , the magnetic body  100  is similarly arranged inside the slot  72   c  of the magnetic core  72 . The magnetic body  100  has a flat plate shape with the X axis being a normal line. The magnetic body  100  has a function of reducing the coupling coefficient between the first coil  80  and the second coil  90 , as described in the first example embodiment described above. 
     The reactor  70 B according to the second example embodiment is also able to obtain effects similar to those obtained by the reactor  70 A according to the first example embodiment described above. That is, with the second example embodiment, a change in the coupling coefficient with respect to a change in the energizing current is able to be suppressed, while the coupling coefficient is reduced, by providing the magnetic body  100  between the first coil  80  and the second coil  90 . As a result, the coupling coefficient is able to be made constant from the low current region to the high current region (i.e., throughout the entire region of the usage range). 
     In the second example embodiment as well, characteristics (the relationship between the current and the coupling coefficient) such as the coupling coefficient being constant throughout the entire region of the usage range may also be realized by adjusting the amount of clearance  42  (clearance in the Y direction between the magnetic body  100  and the magnetic core  72 ), for example. 
       FIG. 9  is a sectional view of a reactor  70 C according to yet another example embodiment (a third example embodiment) of the invention, and corresponds to  FIG. 3  in the first example embodiment described above. 
     The reactor  70 C differs from the reactor  70 A in the first example embodiment described above mainly in that a magnetic core  720  is formed by an E-shaped core. Accordingly, the manners in which the first coil  80 , the second coil  90 , and the magnetic body  100  are arranged are different than they are in the first example embodiment described above. The other structure may be the same as it is in the first example embodiment. 
     The magnetic core  720  includes two magnetic core elements  720   a  and  720   b . The magnetic core elements  720   a  and  720   b  are both E-shaped cores, and are arranged facing each other in a manner in which two slots  720   c  and  720   d  are formed. In this structure, identical parts are able to be used for these magnetic core elements  720   a  and  720   b . The magnetic core  720  may also be formed by combining an E-shaped core with an I-shaped core (i.e., the magnetic core  720  may be an EI-shaped core). Also, the magnetic core  720  may be a core that is formed by punching, or it may be a laminated core. 
     The first coil  80  and the second coil  90  are wound around a center leg portion  730  of the magnetic core  720 , in a manner passing through the two slots  720   c  and  720   d . The first coil  80  and the second coil  90  are wound around the same axis, separated in the X direction. 
     The magnetic body  100  is provided between the first coil  80  and the second coil  90  in the X direction. In the example shown in  FIG. 9 , the magnetic body  100  is similarly arranged in the slots  720   c  and  720   d  of the magnetic core  720 . In the example shown in  FIG. 9 , the magnetic body  100  has a flat plate shape with the X direction being a normal line. The magnetic body  100  has a function of reducing the coupling coefficient between the first coil  80  and the second coil  90 , as described in the first example embodiment described above. 
     The reactor  70 C according to the third example embodiment is also able to obtain effects similar to those obtained by the reactor  70 A according to the first example embodiment described above. That is, with the third example embodiment, a change in the coupling coefficient with respect to a change in the energizing current is able to be suppressed, while the coupling coefficient is reduced, by providing the magnetic body  100  between the first coil  80  and the second coil  90 . As a result, the coupling coefficient is able to be made constant from the low current region to the high current region (i.e., throughout the entire region of the usage range). 
     In the third example embodiment as well, characteristics (the relationship between the current and the coupling coefficient) such as the coupling coefficient being constant throughout the entire region of the usage range may also be realized by adjusting the amount of clearance  43  (clearance in the Y direction between the magnetic body  100  and the magnetic core  720 ), for example. 
     Heretofore, various example embodiments have been described in detail, but they are not limited to the specific example embodiments. Various modifications and changes are also possible. Also, all or a plurality of the constituent elements of the example embodiments described above may be combined. 
     For example, the reactors  70 A and  70 B according to the example embodiments described above may be used not only as magnetic coupling reactors in the power converter  10  having the structure illustrated, but also as magnetic coupling reactors in a power converter having another structure. Also, the reactors  70 A and  70 B according to the example embodiments described above may also be used as transformers.