Abstract:
An object is to miniaturize device size in a vehicle mounted converter. The vehicle mounted converter includes a plurality of inductors, a switching unit for switching current path, an external power acquisition unit for acquiring alternating current power from a power generation source provided separately from the mounted vehicle, and a switching means for switching a circuit connection state to a connection state of either a boost connection state for connecting one end of the inductors to a path to a battery for vehicle drive power supply and connecting the switching unit to the other end of the inductors, or a charging connection state for connecting one end of one of the plurality of inductors to the path to the battery, disconnecting one end of the remaining inductors from the path to the battery and connecting to the external power acquisition unit, and connecting the other end of the inductors to the switching unit.

Description:
PRIORITY INFORMATION 
     This application claims priority to Japanese Patent Application No. 2009-066682 filed on Mar. 18, 2009, which is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a vehicle mounted converter including a plurality of inductors for performing switching of currents flowing to the inductors. 
     2. Description of Related Art 
     Hybrid automobiles and electric automobiles traveling by the driving force of a motor are widely used. These motor driven vehicles include a battery for supplying the driving power to the motor and a booster converter for boosting a battery voltage and outputting the boosted voltage to a motor drive circuit. 
     The booster converter includes inductors and switching circuits for switching currents flowing to the inductors. The inductors generate an induced electromotive force by switching of the currents. The booster converter outputs to the motor drive circuit a boosted voltage where the induced electromotive force has been added to an input voltage. As a result, the booster converter can output a voltage higher than the battery voltage to the motor drive circuit. 
     In recent years, external charging devices for vehicle mounting have been developed for charging a battery by supplying power to the battery from a commercial power supply receptacle or other external power supply device. However, when mounting an external charging device in addition to a battery and booster converter to a vehicle, there was a problem with the increase in size of the system. 
     For example, Japanese Patent Laid-Open Publication No. Hei 8-308255 discloses a device for performing external charging using part of a vehicle mounted inverter, which performs direct current to alternating current conversion. An external charging circuit using part of the inverter is configured in this device and the addition of a large inductor is considered necessary. 
     The present invention solves this problem, namely, by miniaturizing the device size for a vehicle mounted power supply device having an external charging function. 
     SUMMARY OF THE INVENTION 
     The present invention is a vehicle mounted converter including a plurality of inductors; a switching unit for switching a current path; an external power acquisition unit for acquiring alternating current power from a power generating source provided separately from a mounted vehicle; and a switching means for switching a connection state of inductors, the switching unit, and the external power acquisition unit to a connection state of either a boost connection state for connecting one end of each inductor to a path to a battery for vehicle drive power supply and connecting the other end of each inductor to the switching unit, or a charging connection state for connecting one end of one of the plurality of inductors to the path to the battery, disconnecting one end of remaining inductors from the path to the battery and connecting to the external power acquisition unit, and connecting the other end of each inductor to the switching unit; wherein the switching unit, when the switching means sets the connection state to the boost connection state, outputs from the vehicle mounted converter a voltage based on an induced electromotive force generated at the inductors in accordance with current path switching and an output voltage of the battery; when the switching means sets the connection state to the charging connection state, converts an alternating current voltage output from the external power acquisition unit to a direct current voltage on the basis of current path switching and applies the direct current voltage thereof to the battery. 
     Furthermore, in the vehicle mounted converter relating to the present invention, it is preferable to include a drive circuit for controlling the drive motor of the mounted vehicle, wherein the switching means connects the drive circuit to the switching unit so that a voltage based on induced electromotive force generated at the inductors and the output voltage of the battery is output to the drive circuit when the connection state is set to the boost connection state; and disconnects the drive circuit from the switching unit when the connection state is set to the charging connection state. 
     Furthermore, the present invention is a vehicle mounted converter including a plurality of inductors; a switching unit for switching a current path; an external power acquisition unit for acquiring alternating current power from a power generation source provided separately from the mounted vehicle; and a switching means for switching the connection state of the inductors, the switching unit, and the external power acquisition unit to a boost connection state for connecting one end of each inductor to a path to a battery for vehicle drive power supply and connecting the other end of each inductor to the switching unit, or to a charging connection state for disconnecting one end of each inductor from the path to the battery, connecting one end of one of the plurality of inductors to the external power acquisition unit as well as connecting the other end thereof to a front-stage section of the switching unit, and further connecting the remaining inductors to the switching unit so that a magnetically coupled circuit is formed for magnetically coupling the front-stage section and a back-stage section of the switching unit; wherein the switching unit outputs a voltage based on induced electromotive force generated at the inductors in accordance with current path switching and an output voltage of the battery when the switching means sets the connection state to the boost connection state; and converts an alternating current voltage output from the external power acquisition unit to a direct current voltage based on current path switching and applies the direct current voltage thereof from the back-stage section to the battery when the switching means sets the connection state to the charging connection state. 
     Furthermore, in the vehicle mounted converter relating to the present invention, it is preferable to further include a drive circuit for controlling a drive motor of the mounted vehicle connected to the back-stage section, wherein when the switching means sets the connection state to the boost connection state, a voltage based on induced electromotive force generated at the inductors and the output voltage of the battery is output from the switching unit to the drive circuit. 
     According to the present invention, device size can be miniaturized for a vehicle mounted power supply device having an external charging function. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a configuration of a hybrid vehicle drive system relating to a first embodiment. 
         FIG. 2  shows an example configuration of a switching device. 
         FIG. 3  shows a circuit configuration of a three-phase multiphase converter in an external charging mode. 
         FIG. 4  shows a configuration of a hybrid vehicle drive system relating to an application example of the first embodiment. 
         FIG. 5  shows a circuit configuration of a four-phase multiphase converter relating to an application example in the external charging mode. 
         FIG. 6  shows a configuration of a hybrid vehicle drive system relating to a second embodiment. 
         FIG. 7  shows a circuit configuration of a six-phase multiphase converter in the external charging mode. 
         FIG. 8  shows a configuration of a hybrid vehicle drive system relating to an application example of the second embodiment. 
         FIG. 9  shows a circuit configuration of a seven-phase multiphase converter relating to an application example in the external charging mode. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a configuration of a hybrid vehicle drive system  10  relating to the first embodiment of the present invention. The hybrid vehicle drive system  10  includes a switching three-phase multiphase converter  12 . The switching three-phase multiphase converter  12  charges a battery  14  for vehicle drive power supply on the basis of power obtained from an external power supply device, such as a commercial power supply, or boosts and outputs the output voltage of the battery  14  to a drive circuit  20 . Furthermore, the drive circuit  20 , a drive motor  22 , and a power generation motor  24  are provided, where the drive circuit  20  performs direct current to alternating current conversion and transfers power between the switching three-phase multiphase converter  12  and the drive motor  22  as well as the power generation motor  24 . 
     The switching three-phase multiphase converter  12  has a configuration where inductors are connected to connection nodes between the switching devices connected at the top and bottom. The switching three-phase multiphase converter  12  operates in either a boost mode for boosting the output voltage of the battery  14  or an external charging mode for charging the battery  14  on the basis of power obtained from an external power supply device. 
     An input capacitor  16  is connected in parallel with both ends of the battery  14 . To the positive electrode of the battery  14  is connected one end of a relay switch RS 1 , one end of a relay switch RS 2 , and one end of an inductor L 3 . 
     The other ends of the relay switches RS 1  and RS 2  are respectively connected to one end of inductors L 1  and L 2 . The other end of the inductor L 1  is connected to the connection node between the switching devices S 1  and S 2 , and the other end of the inductor L 2  is connected to the connection node between the switching devices S 3  and S 4 . Furthermore, the other end of the inductor L 3  is connected to the connection node between the switching devices S 5  and S 6 . 
     One end of the switching device S 1  opposite to the switching device S 2  side, one end of the switching device S 3  opposite to the switching device S 4  side, and one end of the switching device S 5  opposite to the switching device S 6  side are connected in common to one end of a relay switch RS 3 . The other end of the relay switch RS 3  is connected to the drive circuit  20 . 
     One end of the switching device S 2  opposite to the switching device S 1  side, one end of the switching device S 4  opposite to the switching device S 3  side, and one end of the switching device S 6  opposite to the switching device S 5  side are connected in common to the negative electrode of the battery  14  and to a relay switch RS 4 . The other end of the relay switch RS 4  is connected to the drive circuit  20 . To the drive circuit  20  are connected the drive motor  22  and the power generation motor  24 . 
     An output capacitor  18  is connected between the common connection node of the switching devices S 1 , S 3 , and S 5  and the common connection node of the switching devices S 2 , S 4 , and s 6 . 
     A single-phase power supply plug  26  is connected between the connection node of the relay switch RS 1  and the inductor L 1  and the connection node of the relay switch RS 2  and the inductor L 2 . 
     The switching devices S 1  to S 6  and the relay switches RS 1  to RS 4  are controlled to turn on or off by a controller  28 . Semiconductor devices, such as insulated gate bipolar transistors (IGBT), other common bipolar transistors, field effect transistors, and so forth, can be used for the switching devices S 1  to S 6 . The same applies to other switching devices described hereinafter. When using IGBTs as the switching devices, the IGBTs are connected at the connected positions of the switching devices so that the collector terminals are on the upper side in  FIG. 1  and the emitter terminals are on the lower side. Then, between the collector terminal and the emitter terminal of each IGBT is connected a diode so that the anode terminal is on the emitter terminal side. In this case, a current in the direction of emitter terminal to collector terminal flows through the diode due to the diode being forward biased.  FIG. 2  shows that an IGBT  32  and a diode  34  shown on the right side can be used as a switching device  30  shown on the left side. 
     An operation of the boost mode will be described. In the boost mode, the controller  28  turns on the relay switches RS 1  to RS 4 . Then, the next control is performed so that a voltage, which is the output voltage of the battery  14  that has been boosted, is output as the output voltage of the switching three-phase multiphase converter  12  to the drive circuit  20 . 
     Of the two switching devices connected at the top and bottom, when the upper switching device is turned off and the lower switching device is turned on, current flows from the positive electrode of the battery  14  to the lower switching device via the inductor connected to the upper and lower switching devices. When the lower switching device is turned off in this state, an induced electromotive force is generated at the inductor. At this time, by turning on the upper switching device, a voltage where the induced electromotive force has been added to the output voltage of the battery  14  is applied to both ends of the output capacitor  18  and the drive circuit  20 . 
     When the voltage where the induced electromotive force has been added to the output voltage of the battery  14  is greater than or equal to the voltage between terminals of the output capacitor  18 , the output capacitor  18  is charged or the charged voltage of the output capacitor  18  is maintained. As a result, a voltage higher than the output voltage of the battery  14  can be output to the drive circuit  20 . 
     When the voltage where the induced electromotive force has been added to the output voltage of the battery  14  is lower than the voltage between terminals of the output capacitor  18 , current flows from the output capacitor  18  and the drive circuit  20  to the battery  14  and the input capacitor  16  via the upper switching device that is on and the inductor connected thereto. As a result, the battery  14  and the input capacitor  16  can be charged. The input capacitor  16  reduces the ripple component included in the output voltage of the battery  14  due to charging and discharging. 
     On the basis of this principle, the controller  28  controls the switching devices S 1  to S 6  so that a voltage where the inductor induced electromotive force has been added to the output voltage of the battery  14  is applied to the output capacitor  18  and the voltage between terminals of the output capacitor  18  is output to the drive circuit  20 . The induced electromotive force generated at each inductor can be adjusted by varying the switching timing of each switching device. 
     The controller  28  adjusts the switching timing of each switching device in accordance with travel control so that a direct current voltage is output from the switching three-phase multiphase converter  12  to the drive circuit  20  in accordance with travel control of the mounted vehicle. 
     This embodiment has a configuration using three pairs of switching devices connected at the top and bottom. As a result, compared to the case using one or two pairs of upper and lower switching devices, the ripple component included in the direct current voltage that is output to the drive circuit  20  can be reduced. 
     The drive circuit  20  includes an inverter for performing direct current to alternating current conversion based on switching. The drive circuit  20  performs direct current to alternating current conversion between the switching three-phase multiphase converter  12  and the drive motor  22 . In accordance with the magnitude relationship between the output voltage of the switching three-phase multiphase converter  12  and the voltage between terminals of the drive motor  22 , the drive circuit  20  converts the direct current power, which the switching three-phase multiphase converter  12  outputs, to alternating current power and supplies the alternating current power thereof to the drive motor  22 . Furthermore, in accordance with the magnitude relationship between the output voltage of the switching three-phase multiphase converter  12  and the voltage between terminals of the drive motor  22 , the generated power from the drive motor  22  is converted to direct current power and the direct current power thereof is supplied to the switching three-phase multiphase converter  12 . 
     Similarly, the drive circuit  20  performs direct current to alternating current conversion between the switching three-phase multiphase converter  12  and the power generation motor  24 . In accordance with the magnitude relationship between the output voltage of the switching three-phase multiphase converter  12  and the voltage between terminals of the power generation motor  24 , the drive circuit  20  converts the direct current power, which the switching three-phase multiphase converter  12  outputs, to alternating current power, and outputs the alternating current power thereof to the power generation motor  24 . Furthermore, in accordance with the magnitude relationship between the output voltage of the switching three-phase multiphase converter  12  and the voltage between terminals of the power generation motor  24 , the generated power from the power generation motor  24  is converted to direct current power and the direct current power thereof is supplied to the switching three-phase multiphase converter  12 . 
     The drive motor  22  drives the mounted vehicle or performs regenerative dynamic braking. The power generation motor  24  performs power generation depending on the engine drive power or starting of the engine. 
     Next, an operation of the external charging mode will be described. The controller  28  controls the relay switches RS 1  to RS 4  to turn off. This results in the circuit configuration shown in  FIG. 3 . The same reference numerals have been applied to parts identical to those shown in  FIG. 1 . 
     The single-phase power supply plug  26  is inserted into a single-phase power supply receptacle. One electrode of the single-phase power supply plug  26  is connected to one end of the inductor L 1  on the relay switch RS 1  side and the other electrode of the single-phase power supply plug  26  is connected to one end of the inductor L 2  on the relay switch RS 2  side. 
     From the single-phase power supply plug  26  and via the inductors L 1  and L 2  a single-phase alternating current voltage is applied between a connection node A of the switching devices S 1  and S 2  and a connection node B of the switching devices S 3  and S 4 . The controller  28  operates the switching devices S 1  to S 4  as a single-phase inverter. Namely, PWM (Pulse Width Modulation) control is performed for the switching devices S 1  to S 4 , rectification and boosting of the alternating current voltage between connection nodes A and B are performed, and the resulting obtained direct current voltage is applied to the output capacitor  18 . 
     When the voltage between electrodes of the single-phase power supply plug  26  is V sin(ωt) (where V is voltage amplitude, ω is angular frequency, and t is time), for example, the controller  28  controls the switching devices S 1  to S 4  so that the voltage between terminals of the inductor L 1  based on the single-phase power supply plug  26  side and the voltage between terminals of the inductor L 2  based on the connection node B side become (½)B cos(ωt) (where B is voltage amplitude). Since current flowing through each inductor is an integral value of the terminal voltage, current flowing out from one end and flowing into another end of the single-phase power supply plug  26  at this time has the same phase as the voltage between electrodes of the single-phase power supply plug  26 . As a result, the power factor between electrodes of the single-phase power supply plug  26  can be set as 1 and the withstand voltage and the withstand current of each part of the switching three-phase multiphase converter  12  can be suppressed to necessary minimum values. Furthermore, due to the induced electromotive force of the inductors L 1  and L 2 , a voltage higher than the voltage amplitude between electrodes of the single-phase power supply plug  26  can be applied to the output capacitor  18 . 
     The controller  28  performs the next control so that the voltage between terminals of the output capacitor  18  drops and the input capacitor  16  and the battery  14  are charged by the voltage after the drop. 
     When the switching device S 6  is turned on and the switching device S 5  is turned off, current flows from the positive electrode of the battery  14  to the switching device S 6  via the inductor L 3 . When the switching device S 6  is turned off in this state, an induced electromotive force is generated at the inductor L 3 . At this time, when a voltage where the induced electromotive force of the inductor L 3  has been added to the output voltage of the battery  14  is lower than the voltage between terminals of the output capacitor  18 , turning on the switch S 5  causes electric charge to be discharged from the output capacitor  18  via the inductor L 3  to the input capacitor  16  and the battery  14  so that the input capacitor  16  and the battery  14  can be charged. 
     On the basis of this principle, the controller  28  controls the switching devices S 5  and S 6  so that electric charge is discharged from the output capacitor  18  to the input capacitor  16  and the battery  14  thereby charging the input capacitor  16  and the battery  14 . As a result, the switching three-phase multiphase converter  12  can obtain alternating current power from the external power supply device and charge the battery  14 . 
     According to this configuration, the inductors L 1  and L 2 , which are used as boost inductors in the boost mode, can be used as power factor improvement and boost inductors in the external charging mode. Furthermore, the inductor L 3 , which is used as a boost inductor in the boost mode, can be used as a voltage drop inductor in the external charging mode. As a result, parts used in the boost mode can be used in the external charging mode so that the size of the system can be miniaturized. 
     Next, an application example of the first embodiment will be described.  FIG. 4  shows a configuration of a hybrid vehicle drive system  36  relating to the application example. The same reference numerals have been applied to parts identical to those shown in  FIG. 1  and the descriptions thereof will be omitted. 
     The hybrid vehicle drive system  36  includes a switching four-phase multiphase converter  38 . The switching four-phase multiphase converter  38  adds an inductor L 4 , a relay switch RS 5 , and switching devices SA 1  and SA 2  to the switching three-phase multiphase converter  12  of  FIG. 1  and enables the charging of the battery  14  with three-phase alternating current in the external charging mode. 
     One end of the relay switch RS 5  is connected to the positive electrode of the battery  14 . The other end of the relay switch RS 5  is connected to one end of the inductor L 3 . The other end of the inductor L 3  is connected to the connection node between the switching devices S 5  and S 6 . 
     One end of the inductor L 4  is connected to the positive electrode of the battery  14 . The other end of the inductor L 4  is connected to the connection node between the switching devices SA 1  and SA 2 . One end of the switching device SA 1  opposite to the switching device SA 2  side is connected to a common connection node of the switching devices S 1 , S 3 , and S 5 . One end of the switching device SA 2  opposite to the switching device SA 1  side is connected to a common connection node of the switching devices S 2 , S 4 , and S 6 . 
     A three-phase power supply plug  40  is connected to the connection node between the relay switch RS 1  and the inductor L 1 , the connection node between the relay switch RS 2  and the inductor L 2 , and the connection node between the relay switch RS 5  and the inductor L 3 . 
     When using IGBTs as switching devices SA 1  and SA 2 , the IGBTs are connected at the connected positions of the switching devices so that the collector terminals are on the upper side in  FIG. 4  and the emitter terminals are on the lower side. Then, between the collector terminal and the emitter terminal of each IGBT is connected a diode so that the anode terminal is on the emitter terminal side. 
     An operation in the boost mode will be described. In the boost mode, a controller  42  controls the relay switches RS 1  to RS 5  to turn on. 
     The controller  42  controls the switching devices S 1  to S 6 , SA 1 , and SA 2  so that a voltage where the inductor induced electromotive force has been added to the output voltage of the battery  14  is applied to the output capacitor  18  and the drive circuit  20  based on the same control principle with respect to the switching devices connected at the top and bottom in the switching three-phase multiphase converter  12 . The induced electromotive force generated at each inductor can be adjusted by varying the switching timing of each switching device. 
     The controller  42  adjusts the switching timing of the switching devices in accordance with travel control so that a direct current voltage in accordance with travel control of the mounted vehicle is output from the switching four-phase multiphase converter  38  to the drive circuit  20 . 
     This embodiment has a configuration using four pairs of switching devices connected at the top and bottom. As a result, compared to the case using less than four pairs of upper and lower switching devices, the ripple component included in the direct current voltage that is output to the drive circuit  20  can be reduced. 
     The drive circuit  20  performs direct current to alternating current conversion and power transfers between the switching four-phase multiphase converter  38  and the drive motor  22  as well as the power generation motor  24 . 
     Next, an operation of the external charging mode will be described. The controller  42  controls the relay switches RS 1  to RS 5  to turn off. This results in the circuit configuration shown in  FIG. 5 . The same reference numerals have been applied to parts identical to those shown in  FIG. 4 . 
     The three-phase power supply plug  40  is inserted into a three-phase power supply receptacle. A first electrode of the three-phase power supply plug  40  is connected to one end of the inductor L 1  on the relay switch RS 1  side and a second electrode of the three-phase power supply plug  40  is connected to one end of the inductor L 2  on the relay switch RS 2  side. Furthermore, a third electrode of the three-phase power supply plug  40  is connected to one end of the inductor L 3  on the relay switch RS 5  side. 
     A three-phase alternating current voltage is applied from the three-phase power supply plug  40  via the inductors L 1 , L 2 , and L 3  to the connection node A between the switching devices S 1  and S 2 , the connection node B between the switching devices S 3  and S 4 , and a connection node C between the switching devices S 5  and S 6 . The controller  42  operates the switching devices S 1  to S 6  as a three-phase inverter. Namely, PWM control of the switching devices S 1  to S 6  is performed and interphase voltages mutually between the connection nodes A, B, and C are rectified and boosted so that the resulting direct current voltage is applied to the output capacitor  18 . 
     When the voltages with respect to the neutral point voltage of the first to third electrodes of the three-phase power supply plug  40  are V sin(ωt), V sin(ωt+120°), and V sin(ωt+240°), respectively, for example, the controller  42  controls the switching devices S 1  to S 6  so that currents flowing into the first to third electrodes are I sin(ωt), I sin(ωt+120°), and I sin(ωt+240°), respectively (where I is current amplitude). As a result, the power factor between electrodes of the three-phase power supply plug  40  can be set to 1 and the withstand voltage and the withstand current of each part of the switching four-phase multiphase converter  38  can be suppressed to necessary minimum values. Furthermore, due to the induced electromotive force of the inductors L 1  to L 3 , a voltage higher than the voltage amplitude between electrodes of the three-phase power supply plug  40  can be applied to the output capacitor  18 . 
     Similar to the control with respect to the switching three-phase multiphase converter  12  of  FIG. 3 , the controller  42  controls the switching devices SA 1  and SA 2  so that electric charge is discharged from the output capacitor  18  to the input capacitor  16  and the battery  14  thereby charging the input capacitor  16  and the battery  14 . Here, the inductor L 4  of  FIG. 5  has the same function as the inductor L 3  of  FIG. 3 . As a result, the switching four-phase multiphase converter  38  can obtain three-phase alternating current power from the external power supply device and charge the battery  14 . 
     According to this configuration, the inductors L 1  to L 3 , which are used as boost inductors in the boost mode, can be used as power factor improvement and boost inductors in the external charging mode. Furthermore, the inductor L 4  used as a boost inductor in the boost mode can be used as a voltage drop inductor in the external charging mode. As a result, parts used in the boost mode can be used in the external charging mode so that the size of the system can be miniaturized. 
       FIG. 6  shows a configuration of a hybrid vehicle drive system  44  relating to a second embodiment of the present invention. The hybrid vehicle drive system  44  includes a switching six-phase multiphase converter  46 . The switching six-phase multiphase converter  46  charges the battery  14  based on the electric power obtained from the external power supply device, such as a commercial power supply, or boosts and outputs the output voltage of the battery  14  to the drive circuit  20 . The same reference numerals have been applied to parts identical to those shown in  FIG. 1  and the descriptions thereof will be omitted. 
     The switching six-phase multiphase converter  46  has a configuration where inductors are connected to the connection nodes between the switching devices connected at the top and bottom. The switching six-phase multiphase converter  46  operates in either a boost mode for boosting the output voltage of the battery  14  or an external charging mode for charging the battery  14  on the basis of power obtained from an external power supply device. 
     Relay switches SW 1  to SW 4  have one end connected to the positive electrode of the battery  14 . To the other ends of the relay switches SW 1  and SW 2  are connected one end of the inductor L 1  and one end of the inductor L 2 , respectively. To the other end of the relay switch SW 3  are connected one end of the inductor L 3  and one end of the inductor L 4  and to the other end of the relay switch SW 4  are connected one end of an inductor L 5  and one end of an inductor L 6 . 
     The other end of the inductor L 1  is connected to the connection node between the switching devices S 1  and S 2  and the other end of the inductor L 2  is connected to the connection node between the switching devices S 3  and S 4 . Furthermore, the other end of the inductor L 3  is connected to the connection node between the switching devices S 5  and S 6  and the other end of the inductor L 4  is connected to the connection node between switching device S 7  and S 8 . Moreover, the other end of the inductor L 5  is connected to the connection node between switching devices S 9  and S 10  and the other end of the inductor L 6  is connected to the connection node between switching devices S 11  and S 12 . 
     One end of the switching device S 1  opposite to the switching device S 2  side, one end of the switching device S 3  opposite to the switching device S 4  side, one end of the switching device S 5  opposite to the switching device S 6  side, and one end of the switching device S 7  opposite to the switching device S 8  side are connected in common to one end of the relay switch SW 7 . The other end of the relay switch SW 7  is connected to the drive circuit  20 . 
     One end of the switching device S 2  opposite to the switching device S 1  side, one end of the switching device S 4  opposite to the switching device S 3  side, one end of the switching device S 6  opposite to the switching device S 5  side, and one end of the switching device S 8  opposite to the switching device S 7  side are connected in common to one end of a relay switch SW 6 . The other end of the relay switch SW 6  is connected to the negative electrode of the battery  14  and to the drive circuit  20 . 
     A front-stage output capacitor  18 - 1  is connected between a common connection node of the switching devices S 1 , S 3 , S 5 , and S 7  and a common connection node of the switching devices S 2 , S 4 , S 6 , and S 8 . 
     One end of the switching device S 9  opposite to the switching device S 10  side and one end of the switching device S 11  opposite to the switching device S 12  side are connected to the drive circuit  20 , one end of a relay switch SW 5 , and one end of a relay switch SW 7 . The other end of the relay switch SW 5  is connected to the positive electrode of the battery  14 . 
     One end of the switching device S 10  opposite to the switching device S 9  side and one end of the switching device S 12  opposite to the switching device S 11  side are connected to the negative electrode of the battery  14  and to the drive circuit  20 . 
     A back-stage output capacitor  18 - 2  is connected between a common connection node of the switching devices S 9  and S 11  and a common connection node of the switching devices S 10  and S 12 . 
     The single-phase power supply plug  26  is connected between a connection node of the relay switch SW 1  and the inductor L 1  and a connection node of the relay switch SW 2  and the inductor L 2 . 
     The inductors L 3  and L 5  magnetically couple so that when current flows toward a switching device through one inductor, an induced electromotive force is generated at the other inductor causing current to flow toward a switching device. The inductors L 4  and L 6  magnetically couple so that when current flows toward a switching device through one inductor, an induced electromotive is generated at the other inductor causing current to flow toward a switching device. 
     The switching devices S 1  to S 12  and the relay switches SW 1  to SW 7  are controlled to turn on or off by a controller  48 . When using IGBTs for the switching devices, the IGBTs are connected at the connected positions of the switching devices so that the collector terminals are on the upper side in  FIG. 6  and the emitter terminals are on the lower side. Then, between the collector terminal and the emitter terminal of each IGBT is connected a diode so that the anode terminal is on the emitter terminal side. 
     An operation of the boost mode will be described. In the boost mode, the controller  48  controls the relay switches SW 1  to SW 4 , SW 6 , and SW 7  to turn on and the relay switch SW 5  to turn off. 
     The controller  48  controls the switching devices S 1  to S 12  so that a voltage where the inductor induced electromotive force has been added to the output voltage of the battery  14  is applied to the front-stage output capacitor  18 - 1 , the back-stage output capacitor  18 - 2 , and the drive circuit  20  based on the same control principle with respect to the switching devices connected at the top and bottom in the switching three-phase multiphase converter  12  of  FIG. 1 . The induced electromotive force generated at each inductor can be adjusted by varying the switching timing of each switching device. 
     The controller  48  adjusts the switching timing of the switching devices in accordance with travel control so that a direct current voltage in accordance with travel control of the mounted vehicle is output from the switching six-phase multiphase converter  46  to the drive circuit  20 . 
     This embodiment has a configuration using six pairs of switching devices connected at the top and bottom. As a result, compared to the case using less than six pairs of upper and lower switching devices, the ripple component included in the direct current voltage that is output to the drive circuit  20  can be reduced. 
     The drive circuit  20  performs direct current to alternating current conversion and power transfers between the switching six-phase multiphase converter  46  and the drive motor  22  as well as the power generation motor  24 . 
     Next, an operation of the external charging mode will be described. The controller  48  controls the relay switches SW 1  to SW 4 , SW 6 , and SW 7  to turn off and SW 5  to turn on. This results in the circuit configuration shown in  FIG. 7 . The same reference numerals have been applied to parts identical to those shown in  FIG. 6 . In the external charging mode, the switching six-phase multiphase converter  46  is divided into parts in a stage before inductor L 3 +L 4  and parts in a stage after inductor L 5 +L 6 . 
     The single-phase power supply plug  26  is inserted into a single-phase power supply receptacle. One electrode of the single-phase power supply plug  26  is connected to one end of the inductor L 1  on the relay switch SW 1  side and the other electrode of the single-phase power supply plug  26  is connected to one end of the inductor L 2  on the relay switch SW 2  side. The drive circuit  20  is connected to the right side of the battery  14  in  FIG. 7 . 
     Similar to the embodiment shown in  FIG. 3 , the controller  48  operates the switching devices S 1  to S 4  as a single-phase inverter. As a result, an alternating current voltage between connection nodes A and B is rectified and boosted and the direct current voltage after rectification and boosting is applied to the front-stage output capacitor  18 - 1 . 
     The primary-side inductor L 3 +L 4  is connected between a connection node D of the switching devices S 5  and S 6  and a connection node E of the switching devices S 7  and S 8 . 
     The primary-side inductor L 3 +L 4  has inductors L 3  and L 4  connected in series. The secondary inductor L 5 +L 6  is connected between a connection node F of the switching devices S 9  and S 10  and a connection node G of the switching devices S 11  and S 12 . The secondary inductor L 5 +L 6  has the inductors L 5  and L 6  connected in series. 
     The controller  48  operates the switching devices S 5  to S 8  as a single-phase inverter. Namely, PWM control is performed for the switching devices S 5  to S 8 , the voltage between terminals of the front-stage output capacitor  18 - 1  is converted to an alternating current voltage, and the alternating current voltage thereof is applied to the primary-side inductor L 3 +L 4 . The magnetic coupling of the primary-side inductor L 3 +L 4  and the secondary-side inductor L 5 +L 6  causes an alternating current voltage to be generated at the secondary-side inductor L 5 +L 6  and the alternating current voltage thereof is applied between the connection node F and the connection node G. 
     The controller  48  operates the switching devices S 9  to S 12  as a single-phase inverter. Namely, PWM control of the switching devices S 9  to S 12  is performed, the alternating current voltage applied from the secondary-side inductor L 5 +L 6  to between the connection node F and the connection node G is rectified, and the direct current voltage after rectification is applied to the back-stage output capacitor  18 - 2 , the input capacitor  16 , and the battery  14 . As a result, the switching six-phase multiphase converter  46  can obtain power from the external power supply device and charge the battery  14 . 
     According to this configuration, the inductors L 1  and L 2 , which are used as boost inductors in the boost mode, can be used as power factor improvement and boost inductors in the external charging mode. As a result, parts used in the boost mode can be used in the external charging mode so that the size of the system can be miniaturized. 
     Furthermore, in the external charging mode, on the basis of the magnetic coupling of the primary-side inductor L 3 +L 4  and the secondary-side inductor L 5 +L 6 , the front-stage section and the back-stage section are coupled and electrically insulated. This makes it possible to avoid an application of a high voltage to the front-stage section, and during the handling of the single-phase power supply plug  26  in the front-stage section to avoid shortening of the system life, such as due to contact between parts being applied with high voltages. 
     Next, an application example of the second embodiment will be described.  FIG. 8  shows a configuration of a vehicle drive system  50  relating to the application example. The same reference numerals have been applied to parts identical to those shown in  FIG. 6  and the descriptions thereof will be omitted. 
     The hybrid vehicle drive system  50  includes a switching seven-phase multiphase converter  52 . The seven-phase multiphase converter  52  adds an inductor L 7 , a relay switch SW 8 , and switching devices SA 3  and SA 4  to the switching six-phase multiphase converter  46  of  FIG. 6  and makes charging of the battery  14  possible with three-phase alternating current power in the external charging mode. 
     One end of the relay switch SW 8  is connected to the positive electrode of the battery  14 . The other end of the relay switch SW 8  is connected to one end of the inductor L 7 . The other end of the inductor L 7  is connected to a connection node between the switching devices SA 3  and SA 4 . 
     One end of the switching device SA 3  opposite to the switching device SA 4  side is connected to a common connection node of the switching devices S 1 , S 3 , S 5 , and S 7 . One end of the switching device SA 4  opposite to the switching device SA 3  side is connected to a common connection node of the switching devices S 2 , S 4 , S 6 , and S 8 . 
     The three-phase power supply plug  40  is connected to the connection node of the relay switch SW 1  and the inductor L 1 , the connection node of the relay switch SW 2  and the inductor L 2 , and the connection node of the relay switch SW 8  and the inductor L 7 . 
     When using IGBTs as the switching devices SA 3  and SA 4 , the IGBTs are connected at the connected positions of the switching devices so that the collector terminals are on the upper side in  FIG. 8  and the emitter terminals are on the lower side. Then, between the collector terminal and the emitter terminal of each IGBT is connected a diode so that the anode terminal is on the emitter terminal side. 
     An operation of the boost mode will be described. In the boost mode, a controller  54  controls the relay switches SW 1  to SW 4  and SW 6  to SW 8  to turn on and SW 5  to turn off. 
     The controller  54  controls the switching devices S 1  to S 12 , SA 3 , and SA 4  so that a voltage where the inductor induced electromotive force has been added to the output voltage of the battery  14  is applied to the front-stage output capacitor  18 - 1 , the back-stage output capacitor  18 - 2 , and the drive circuit  20  based on the same control principle with respect to the switching devices connected at the top and bottom in the switching six-phase multiphase converter  46  of  FIG. 6 . The induced electromotive force generated at each inductor can be adjusted by varying the switching timing of each switching device. 
     The controller  54  adjusts the switching timing of the switching devices in accordance with travel control so that a direct current voltage in accordance with travel control of the mounted vehicle is output from the switching seven-phase multiphase converter  52  to the drive circuit  20 . 
     This embodiment has a configuration using seven pairs of switching devices connected at the top and bottom. As a result, compared to the case using less than seven pairs of upper and lower switching devices, the ripple component included in the direct current voltage that is output to the drive circuit  20  can be reduced. 
     The drive circuit  20  performs direct current to alternating current conversion and power transfers between the switching seven-phase multiphase converter  52  and the drive motor  22  as well as the power generation motor  24 . 
     Next, an operation in the external charging mode will be described. The controller  54  controls the relay switches SW 1  to SW 4  and SW 6  to SW 8  to turn off and SW 5  to turn on. This results in the circuit configuration shown in  FIG. 9 . The same reference numerals have been applied to parts identical to those shown in  FIG. 8 . 
     The three-phase power supply plug  40  is inserted into a three-phase power supply receptacle. The first electrode of the three-phase power supply plug  40  is connected to one end of the inductor L 1  on the relay switch SW 1  side and the second electrode of the three-phase power supply plug  40  is connected to one end of the inductor L 2  on the relay switch SW 2  side. Furthermore, the third electrode of the three-phase power supply plug  40  is connected to one end of the inductor L 7  on the relay switch SW 8  side. 
     A three-phase alternating current voltage is applied from the three-phase power supply plug  40  via the inductors L 1 , L 2 , and L 7  to the connection node A of the switching devices S 1  and S 2 , the connection node B of the switching devices S 3  and S 4 , and a connection node H of the switching devices SA 3  and SA 4 . The controller  54  operates the switching devices S 1  to S 4 , SA 3 , and SA 4  as a three-phase inverter. As a result, interphase voltages mutually between the connection nodes A, B, and H are rectified and boosted so that the resulting direct current voltage is applied to the front-stage output capacitor  18 - 1 . 
     When the voltages with respect to the neutral point voltage of the first to third electrodes of the three-phase power supply plug  40  are V sin(ωt), V sin(ωt+120°), and V sin(ωt+240°), respectively, for example, the controller  54  controls the switching devices S 1  to S 4 , SA 3 , and SA 4  so that currents flowing into the first to third electrodes are I sin(ωt), I sin(ωt+120°), and I sin(ωt+240°), respectively. As a result, the power factor between electrodes of the three-phase power supply plug  40  can be set to 1 and the withstand voltage and the withstand current of each part of the switching seven-phase multiphase converter  52  can be suppressed to necessary minimum values. Furthermore, due to the induced electromotive force of the inductors L 1 , L 2 , and L 7 , a voltage higher than the voltage amplitude between electrodes of the three-phase power supply plug  40  can be applied to the front-stage output capacitor  18 - 1 . 
     Similar to the control with respect to the switching six-phase multiphase converter  46  of  FIG. 7 , the controller  54  operates the switching devices S 5  to S 8  as a single-phase inverter and the switching devices S 9  to S 12  as a single-phase inverter. As a result, the switching seven-phase multiphase converter  52  can obtain the three-phase alternating current voltage from the external power supply device and charge the battery  14 . 
     According to this configuration, the inductors L 1 , L 2 , and L 7 , which are used as boost inductors in the boost mode, can be used as power factor improvement and boost inductors in the external charging mode. 
     Furthermore, in the external charging mode, on the basis of the magnetic coupling of the primary-side inductor L 3 +L 4  and the secondary-side inductor L 5 +L 6  the front-stage section and the back-stage section are coupled and electrically insulated. This makes it possible to avoid an application of a high voltage to the front-stage section, and during the handling of the single-phase power supply plug  26  in the front-stage section to avoid a shortening of the system life, such as due to contact between parts being applied with high voltages. 
     Examples using the switching multiphase converter relating to embodiments of the present invention in hybrid vehicle drive systems were described in the aforementioned. The switching multiphase converter relating to the embodiments of the present invention can be used in electric automobiles. In this case, it is not absolutely necessary to use the power generation motor  24  and the drive circuit  20  may have a configuration for direct current to alternating current conversion and power transfers between the switching multiphase converter and the drive motor  22 . 
     Further, among the relay switches employed in the above-described embodiments, those provided in the capacitor discharge path may be additionally provided with a discharge circuit using a resistor.