Patent Publication Number: US-8994212-B2

Title: Electric power supply apparatus

Description:
Priority is claimed on Japanese Patent Application No. 2012-139064, filed on Jun. 20, 2012, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electric power supply apparatus. 
     2. Description of Related Art 
     In the related art, for example, an electric power supply apparatus is known that includes four relays (a first to fourth relay), two rechargeable batteries, and a boost converter, and that connects the two rechargeable batteries to an electric load switching between a series connection state and a parallel connection state, while adjusting a voltage applied to the electric load by the boost converter (for example, refer to Japanese Unexamined Patent Application Publication No. 2012-060838). 
     In addition, in the related art, for example, an electric power supply system is known that includes four switching devices (a first to fourth switching device), two reactors, and two direct current (DC) power supplies, and that connects the two DC power supplies to an electric load switching between a series connection state and a parallel connection state, while adjusting a voltage applied to the electric load (for example, refer to Japanese Unexamined Patent Application Publication No. 2012-070514). 
     SUMMARY OF THE INVENTION 
     In the electric power supply apparatus according to the above related art, the number of components required to configure the apparatus increases, attributed to having the four relays (the first to fourth relay) and the boost converter, which leads to such problems as the apparatus becomes larger and a cost required for a configuration increases. 
     Meanwhile, in the electric power supply system according to the above related art, two switching devices are included in each of electrical conduction paths for the series connection state and the parallel connection state, which leads to such a problem as the electrical conduction loss increases. 
     Moreover, in the electric power supply system according to the above related art, since a total interlinkage magnetic flux of the reactor changes to an increasing tendency corresponding to an increase of a voltage boost rate, the loss increases and a requirement to enlarge the reactor arises. 
     In view of the foregoing, an object of aspects of the present invention is to provide an electric power supply apparatus capable of suitably switching a connection state of a plurality of electric power supplies, while preventing the apparatus from becoming larger and the cost required for a configuration from increasing. 
     In order to achieve the above object, an electric power supply apparatus according to aspects of the present invention adopts one of the configurations described below.
     (1) An aspect of the present invention is an electric power supply apparatus includes: a first electric power supply that is connected between a first node and a second node; a second electric power supply that is connected between a third node and a fourth node; a switch circuit having at least four input terminals, each of which is connected to the first node, the second node, the third node, and the fourth node, and having at least two output terminals; an electric load that is connected between the two output terminals; a reactor that is provided at least any one of between the first electric power supply and one of the first node and the second node, and between the second electric power supply and one of the third node and the fourth node; and a voltage control section that alternately switches between: (A) a series state in which a voltage between both ends of the reactor is increased by connccting the first node with the fourth node, connecting the second node with the a first output terminal, and connecting the third node with a second output terminal, to form a current loop that connects the first electric power supply, the second electric power supply, and the reactor in series with the electric load, and (B) a parallel state in which the voltage between both ends of the reactor is decreased by connecting the first node and the third node with the second output terminal, and connecting the second node and the fourth node with the first output terminal, to connect the first electric power supply and the second electric power supply in parallel with the electric load, and that performs, by the alternate switching, a voltage adjustment control which controls a voltage applied to the electric load to fall within a voltage range between a first voltage that is the voltage, of the first electric power supply or the voltage of the second electric power supply and a second voltage that is the sum of the voltage of the first electric power supply and the voltage of the second electric power supply.   (2) In the aspect of (1) described above, the switch circuit may include a first switch that is connected between the first node and the third node, a second switch that is connected between the first node and the fourth node, and a third switch that is connected between the second node and the fourth node, wherein the voltage control section may alternately switch between the series state and the parallel state, by alternately switching between a first state in which a pair of the first switch and the third switch is closed and the second switch is open, and a second state in which a pair of the first switch and the third switch is open and the second switch is closed.   (3) In the aspect of (1) or (2) described above, the electric power supply apparatus may include an electric motor as the electric load, wherein the voltage control section may include, as an operation mode, a parallel mode that sets the first switch and the third switch to be closed and the second switch to be open, to connect the first electric power supply and the second electric power supply in parallel with the electric motor.   (4) In the aspect of (1) or (2) described above, the electric power supply apparatus may include an electric motor as the electric load, wherein the voltage control section may include, as an operation mode, a series mode that sets the first switch and the third switch to be open and the second switch to be closed, to connect the first electric power supply and the second electric power supply in series with the electric motor.   (5) In the aspect of (1) or (2) described above, the electric power supply apparatus may include an electric motor as the electric load, wherein the voltage control section may include, as operation modes, a parallel mode that sets the first switch and the third switch to be closed and the second switch to be open, to connect the first electric power supply and the second electric power supply in parallel with the electric motor, and a series mode that sets the first switch and the third switch to be open and the second switch to be closed, to connect the first electric power supply and the second electric power supply in series with the electric motor, and may perform the voltage adjustment control when switching between the parallel mode and the series mode.   (6) In the aspect of any one of (1) to (5) described above, the reactor may be provided between the first electric power supply and one of the first node and the second node.   (7) In the aspect of (6) described above, the electric power supply apparatus may include, as the reactor, a second reactor that is provided between the second electric power supply and one of the third node and the fourth node.   (8) In the aspect of (7) described above, a plurality of the reactors may be magnetically coupled.   (9) In the aspect of any one of (1) to (8) described above, the electric power supply apparatus may include a reactor that is provided between the electric load and any one of the two output terminals.   (10) In the aspect of (1) or (2) described above, the electric power supply apparatus may include an electric motor as the electric load, wherein the voltage control section may include, as operation modes, a parallel mode that sets the first switch and the third switch to be closed and the second switch to be open, to connect the first electric power supply and the second electric power supply in parallel with the electric motor, a first constant current mode that makes the first switch closed, the third switch open, and the second switch open, prior to performing the parallel mode, and a second constant current mode that makes the first switch open, the third switch closed, and the second switch open, prior to performing the parallel mode.   

     According to the aspect of (1) described above, a current loop that connects the first electric power supply, the second electric power supply, and the reactor in series with the electric load is formed, to increase the voltage of both ends of the reactor in the series state that is alternately switched with the parallel state. 
     Thereby, for example, in comparison with a case where a current loop that connects each of the electric power supplies in series only with the reactor is formed, it is possible to suppress an increase of a total interlinkage magnetic flux associated with an increase of a voltage boost rate, to prevent an increase of loss, and to downsize the reactor. 
     According to the aspect of (2) described above, the switch circuit is configured to include three switches of the first switch to the third switch. Thereby, for example, in comparison with a case where the switch circuit includes four or more switches, it is possible to prevent the apparatus from becoming larger, and to prevent the cost required for a configuration from increasing. 
     Moreover, only any one of the first switch to the third switch is included in each of electrical conduction paths for the series state and the parallel state. Thereby, for example, in comparison with a case where a plurality of switches are included in each of electrical conduction paths, it is possible to prevent electrical conduction loss from increasing. 
     According to the aspect of (3) or (4) described above, it is possible to apply a voltage to the electric load including the electric motor, without switching losses of the first switch to the third switch. 
     According to the aspect of (5) described above, it is possible to prevent voltages applied to the first switch to the third switch from increasing, and to suppress switching losses. 
     According to the aspect of (6) described above, at a voltage increasing-decreasing time when the voltage of both ends of the reactor is increased and decreased, only the first electric power supply is made to be charged and to be discharged, and thereby a burden of the charge and discharge operations is assigned only to the first electric power supply. 
     Thereby, it is possible to make the first electric power supply and the second electric power supply as a combination of electric power supplies with different characteristics, which can increase flexibility in the apparatus configuration. 
     According to the aspect of (7) described above, at the voltage increasing-decreasing time when the voltage of both ends of the reactor is increased and decreased, the first electric power supply and the second electric power supply are made equally to be charged and to be discharged, and thereby it is possible to distribute a burden of the charge and discharge operations equally to the first electric power supply and the second electric power supply. 
     Thereby, it is possible to suppress a degradation of the first electric power supply and the second electric power supply. 
     According to the aspect of (8) described above, it is possible to downsize a configuration of a plurality of the reactors, which can reduce the cost required for a configuration. 
     According to the aspect of (9) described above, the single reactor that is provided between the electric load and any one of the two output terminals can make the first electric power supply and the second electric power supply equally to be charged and to be discharged at the voltage increasing-decreasing time when the voltage of both ends of the reactor is increased and decreased. 
     Thereby, it is possible to distribute a burden of the charge and discharge operations equally to the first electric power supply and the second electric power supply, which can suppress a degradation of the first electric power supply and the second electric power supply. 
     According to the aspect of (10) described above, when resolving an unbalance between the voltage of the first electric power supply and the voltage of the second electric power supply, it is possible to prevent an occurrence of charge and discharge operations between the first electric power supply and the second electric power supply that are irrelevant to electric power distribution to the electric load (that is, an occurrence of a state where a current flows from one of the first electric power supply and the second electric power supply with a higher voltage, to the other with a lower voltage, and thereby the voltages of the two converge to be equal). 
     Thereby, it is possible to output a load current equally from the first electric power supply and the second electric power supply, and to perform efficient electric power distribution to the electric load. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a configuration illustration of an electric power supply apparatus according to an embodiment of the present invention. 
         FIG. 2A  is an illustration showing a parallel mode as an operation mode of the electric power supply apparatus according to the embodiment of the present invention. 
         FIG. 2B  is an illustration showing a parallel state as the operation mode of the electric power supply apparatus according to the embodiment of the present invention. 
         FIG. 2C  is an illustration showing a series state as the operation mode of the electric power supply apparatus according to the embodiment of the present invention. 
         FIG. 2D  is an illustration showing a series mode as the operation mode of the electric power supply apparatus according to the embodiment of the present invention. 
         FIG. 3A  is an illustration showing electric potentials of respective nodes in the parallel mode as the operation mode of the electric power supply apparatus according to the embodiment of the present invention. 
         FIG. 3B  is an illustration showing electric potentials of respective nodes in the series mode as the operation mode of the electric power supply apparatus according to the embodiment of the present invention. 
         FIG. 4  is an illustration showing a reactor current I 1 , a second ON duty D 2 , a voltage of both ends of the reactor VL, and an output voltage Vout, in the parallel mode, the parallel state, the series state, and the series mode, as the operation modes of the electric power supply apparatus according to the embodiment of the present invention. 
         FIG. 5A  is an illustration showing the reactor current I 1  in the series state (SB) as the operation mode of the electric power supply apparatus according to the embodiment of the present invention. 
         FIG. 5B  is an illustration showing the reactor current I 1  in the parallel state (PB) as the operation mode of the electric power supply apparatus according to the embodiment of the present invention. 
         FIG. 6  is a flowchart showing an operation of the electric power supply apparatus according to the embodiment of the present invention. 
         FIG. 7  is a configuration illustration of an electric power supply apparatus according to a first modified example of the embodiment of the present invention. 
         FIG. 8  is a configuration illustration of a reactor and a second reactor of the electric power supply apparatus according to the first modified example of the embodiment of the present invention. 
         FIG. 9A  is an illustration showing a parallel mode as an operation mode of the electric power supply apparatus according to the first modified example of the embodiment of the present invention. 
         FIG. 9B  is an illustration showing a parallel state as the operation mode of the electric power supply apparatus according to the first modified example of the embodiment of the present invention. 
         FIG. 9C  is an illustration showing a series state as the operation mode of the electric power supply apparatus according to the first modified example of the embodiment of the present invention. 
         FIG. 9D  is an illustration showing a series mode as the operation mode of the electric power supply apparatus according to the first modified example of the embodiment of the present invention. 
         FIG. 10  is an illustration showing a reactor current I 1 , a second ON duty D 2 , a voltage of both ends of the reactor VL, an output voltage Vout, in the parallel mode, the parallel state, the series state, and the series mode, as the operation modes of the electric power supply apparatus according to the first modified example of the embodiment of the present invention. 
         FIG. 11A  is an illustration showing the reactor current I 1  in the series state as the operation mode of the electric power supply apparatus according to the first modified example of the embodiment of the present invention. 
         FIG. 11B  is an illustration showing the reactor current I 1  in the parallel state as the operation mode of the electric power supply apparatus according to the first modified example of the embodiment of the present invention. 
         FIG. 12A  is an illustration showing a main configuration of the electric power supply apparatus according to the embodiment of the present invention. 
         FIG. 12B  is an illustration showing a main configuration of the electric power supply apparatus according to the embodiment of the present invention. 
         FIG. 13A  is an illustration showing a relationship between a voltage boost rate and a total interlinkage magnetic flux of a reactor in the example, the first modified example, and a comparison example of the embodiment of the present invention. 
         FIG. 13B  is an illustration for explaining the relationship between the voltage boost rate and the total interlinkage magnetic flux of the reactor in the example, the first modified example, and the comparison example of the embodiment of the present invention. 
         FIG. 14  is an illustration showing a change of a reactor current and a voltage of both ends of a reactor in a boost operation in a parallel connection mode according to the comparison example of the embodiment of the present invention. 
         FIG. 15  is an illustration showing a change of the reactor current and the voltage of both ends of the reactor when alternately switching between the series state SB and the parallel state PB in a voltage adjustment control according to the example of the embodiment of the present invention. 
         FIG. 16  is a configuration illustration of an electric power supply apparatus according to a second modified example of the embodiment of the present invention. 
         FIG. 17  is a configuration illustration of an electric power supply apparatus according to a third modified example of the embodiment of the present invention. 
         FIG. 18  is a flowchart showing an operation of an electric power supply apparatus according to a fourth modified example of the embodiment of the present invention. 
         FIG. 19  is a flowchart showing a process of a parallel static control presented in  FIG. 18 . 
         FIG. 20  is a flowchart showing a process of a series static control presented in  FIG. 18 . 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, an electric power supply apparatus according to an embodiment of the present invention will be described with reference to the drawings. 
     An electric power supply apparatus  1  according to this embodiment, for example, as shown in  FIG. 1 , has a configuration of an electric power supply that supplies DC electric power to an inverter  3  which controls driving and regeneration operations of an electric motor (MOT)  2  that generates a driving force to drive a vehicle. 
     The electric power supply apparatus  1  is, for example, configured to include a first electric power supply  11 , a second electric power supply  12 , a switch circuit  13 , a reactor  14 , a first capacitor  15  that is connected to both ends of the first electric power supply  11 , a second capacitor  16  that is connected to both ends of the second electric power supply  12 , a third capacitor  17  that is connected to both ends of a DC side of the inverter  3 , and a control device  18  (voltage control section). 
     The inverter  3  is connected between two output terminals  13   e  and  13   f  of the switch circuit  13 . 
     The first electric power supply  11  is, for example, a battery or the like. A positive terminal of the first electric power supply  11  is connected to a first node A. A negative terminal of the first electric power supply  11  is connected to a second node B. 
     The second electric power supply  12  is, for example, a battery or the like. A positive terminal of the second electric power supply  12  is connected to a third node C. A negative terminal of the second electric power supply  12  is connected to a fourth node D. 
     In addition, for example, a voltage VB 1  that is output from the first electric power supply  11  is set to be equal to a voltage VB 2  that is output from the second electric power supply  12  (VB 1 =VB 2 ). 
     The switch circuit  13  includes a first input terminal  13   a , a second input terminal  13   b , a third input terminal  13   c , and a fourth input terminal  13   d  (four input terminals) that are connected to the first node A, the second node B, the third node C, and the fourth node D, respectively. The switch circuit  13  includes a first output terminal  13   e  and a second output terminal  13   f   1  (two output terminals). 
     The second input terminal  13   b  is shared with the first output terminal  13   e . The third input terminal  13   c  is shared with the second output terminal  13   f.    
     The switch circuit  13  includes, for example, three switching devices (for example, IGBT: Insulated Gate Bipolar mode Transistor), namely a first switching device SW 1 , a second switching device SW 2 , and a third switching device SW 3  that are connected in series. 
     A collector of the first switching device SW 1  (first switch) is connected to the third input terminal  13   c . An emitter of the first switching device SW 1  is connected to the first input terminal  13   a.    
     A collector of the second switching device SW 2  (second switch) is connected to the first input terminal  13   a . An emitter of the second switching device SW 2  is connected to the fourth input terminal  13   d.    
     A collector of the third switching device SW 3  (third switch) is connected to the fourth input terminal  13   d . An emitter of the third switching device SW 3  is connected to the second input terminal  13   b.    
     A diode is connected between the emitter and the collector of each of the first switching device SW 1  the second switching device SW 2 , and the third switching device SW 3 , such that a direction from the emitter toward the collector corresponds to a forward direction of the diode. 
     The switch circuit  13  is, for example, is driven by a pulse-width modulated (pulse width modulation) signal (PWM signal) that is output from the control device  18  and input to a gate of each of the first switching device SW 1 , the second switching device SW 2 , and the third switching device SW 3 . 
     The switch circuit  13 , for example, as shown in  FIG. 2A , sets the first switching device SW 1  and the third switching device SW 3  to be closed (ON) and the second switching device SW 2  to be open (OFF), in a parallel mode PA as an operation mode of the electric power supply apparatus  1 . Thereby, the first electric power supply  11  and the second electric power supply  12  are connected in parallel with the inverter  3 . 
     In addition, the switch circuit  13 , for example, as shown in  FIG. 2D , sets the first switching device SW 1  and the third switching device SW 3  to be open (OFF) and the second switching device SW 2  to be closed (ON), in a series mode SA as an operation mode of the electric power supply apparatus  1 . Thereby, the first electric power supply  11  and the second electric power supply  12  are connected in series with the inverter  3 . 
     The switch circuit  13  alternately switches between a series state SB and a parallel state PB, in a voltage adjustment control that is performed when switching between the parallel mode PA and the series mode SA. 
     In more detail, the switch circuit  13 , for example, as shown in  FIG. 21 , connects the first node A, the third node C, and the second output terminal  13   f , and connects the second node B, the fourth node D, and the first output terminal  13   e . Thereby, it is possible to connect the first electric power supply  11  and the second electric power supply  12  in parallel with the inverter  3  to form the parallel state PB. 
     In addition, the switch circuit  13 , for example, as shown in  FIG. 2C , connects the first node A and the fourth node D, connects the second node B and the first output terminal  13   e , and connects the third node C and the second output terminal  13   f . Thereby, it is possible to form a current loop LSB that connects the first electric power supply  11 , the second electric power supply  12 , and the reactor  14  in series with the inverter  3  to form the series state SB. 
     The switch circuit  13 , for example, in the voltage adjustment control, alternately switches between the series state SB and the parallel state PB, by alternately switching between a first state in which a pair of the first switching device SW 1  and the third switching device SW 3  is closed and the second switching device SW 2  is open, and a second state in which a pair of the first switching device SW 1  and the third switching device SW 3  is open and the second switching device SW 2  is closed. 
     The reactor  14  is provided between the first electric power supply  11  and the first node A. 
     In more detail, a first end of the reactor  14  is connected to the positive terminal of the first electric power supply  11 . A second end of the reactor  14  is connected between the emitter of the first switching device SW 1  and the collector of the second switching device SW 2  of the switch circuit  13 . 
     The first capacitor  15  is connected between the positive terminal and the negative terminal of the first electric power supply  11 . 
     The second capacitor  16  is connected between the positive terminal and the negative terminal of the second electric power supply  12 . 
     The third capacitor  17  is connected between a positive terminal and a negative terminal of the DC side of the inverter  3 . 
     The control device  18  is, for example, configured to include a connection switching control unit  21  and an electric motor control unit  22 . 
     The connection switching control unit  21 , for example, as shown in  FIG. 2A  to  FIG. 2D , controls the switch circuit  13 , in the parallel mode PA and the series mode SA as operation modes of the electric power supply apparatus  1 , and in the series state SB and the parallel state PB that are alternately switched in the voltage adjustment control which is performed when switching between the parallel mode PA and the series mode SA. 
     In more detail, the connection switching control unit  21 , for example, alternately switches between the first state in which the pair of the first switching device SW 1  and the third switching device SW 3  is closed (ON) and the second switching device SW 2  is open (OFF), and the second state in which the pair of the first switching device SW 1  and the third switching device SW 3  is open (OFF) and the second switching device SW 2  is closed (ON). 
     The connection switching control unit  21 , for example, in the parallel mode PA, instructs to set the first switching device SW 1  and the third switching device SW 3  to be closed (ON) and the second switching device SW 2  to be open (OFF), to connect the first electric power supply  11  and the second electric power supply  12  in parallel with the inverter  3 . 
     In addition, the connection switching control unit  21 , for example, in the series mode SA, instructs to set the first switching device SW 1  and the third switching device SW 3  to be open (OFF) and the second switching device SW 2  to be closed (ON), to connect the first electric power supply  11  and the second electric power supply  12  in series with the inverter  3 . 
     Moreover, the connection switching control unit  21 , for example, alternately switches between the series state SB and the parallel state PB, depending on a first ON duty D 1  and a second ON duty D 2  in a period (switching period) of the PWM signal, in the voltage adjustment control when switching between the parallel mode PA and the series mode SA 
     For example, the first ON duty D 1  (=Ton 1 /(Ton 1 +Ton 2 )) and the second ON duty D 2  (=Ton 2 /(Ton 1 +Ton 2 )) are defined by an ON time Ton 1  of the pair of the first switching device SW 1  and the third switching device SW 3  and an ON time Ton 2  of the second switching device SW 2 . 
     The connection switching control unit  21 , for example, alternately switches between the series state SB and the parallel state PB, by alternately switching between the first state in which the pair of the first switching device SW 1  and the third switching device SW 3  is closed (ON) and the second switching device SW 2  is open (OFF), and the second state in which the pair of the first switching device SW 1  and the third switching device SW 3  is open (OFF) and the second switching device SW 2  is closed (ON), depending on the first ON duty D 1  and the second ON duty D 2 . 
     Thereby, the connection switching control unit  21 , for example, controls a voltage that is applied to the inverter  3 , to fall within a voltage range between a first voltage V 1  (=VB 1 , VB 2 ) that is the voltage of the first electric power supply  11  or the voltage of the second electric power supply  12 , and a second voltage V 2  (=VB 1 +VB 2 ) that is the sum of the voltage of the first electric power supply  11  and the voltage of the second electric power supply  12 . 
     The connection switching control unit  21 , for example, in the parallel mode PA shown in  FIG. 2A , forms a current loop LPA 1  that connects the first electric power supply  11  and the first capacitor  15 , the reactor  14 , the first switching device SW 1 , and the inverter  3  and the third capacitor  17 , in series in this order, by setting the second switching device SW 2  to be OFF) and setting the first switching device SW 1  to be ON. 
     Moreover, the connection switching control unit  21  forms a current loop LPA 2  that connects the third switching device SW 3 , the second electric power supply  12 , and the inverter  3  and the third capacitor  17 , in series in this order, by setting the third switching device SW 3  to be ON. 
     In this parallel mode PA, for example, as shown in  FIG. 3A , electric potentials of the first node A and the third node C become equal, electric potentials of the second node B and the fourth node D become equal, and the voltage VB 1  of the first electric power supply  11  and the voltage VB 2  of the second electric power supply  12  that are equal to each other are applied between the positive terminal and the negative terminal of the DC side of the inverter  3 . 
     In addition, the connection switching control unit  21 , for example, in the series mode SA shown in  FIG. 21 , forms a current loop LSA that connects the first electric power supply  11  and the first capacitor  15 , the reactor  14 , the second switching device SW 2 , the second electric power supply  12 , and the inverter  3  and the third capacitor  17 , in series in this order, by setting the second switching device SW 2  to be ON and setting the first switching device SW 1  and the third switching device SW 3  to be OFF. 
     In this series mode SA, for example, as shown in  FIG. 3B , electric potentials of the first node A and the fourth node D become equal, and the sum of the voltage VB 1  of the first electric power supply  11  and the voltage VB 2  of the second electric power supply  12  is applied between the positive terminal and the negative terminal of the DC side of the inverter  3 . 
     In addition, the connection switching control unit  21 , for example, as shown in  FIG. 4 , when switching the parallel mode PA to the series mode SA, first switches the parallel mode PA to the series state SB, next alternately switches between the series state SB and the parallel state PB. At this alternate switching, the first ON duty D 1  (=Ton 1 /(Ton 1 +Tn 2 )) is gradually changed from 100% to 0%, and the second ON duty D 2  (=Ton 2 /(Ton 1 +Ton 2 )) is gradually changed from 0% to 100%. 
     Thereby, the charge and discharge operations of the first electric power supply  11  excite the reactor  14 , which gradually increases a voltage VL of both ends of the reactor  14 . Then, an output voltage Vout applied between the positive terminal and the negative terminal of the DC side of the inverter  3  is increased from the voltage VB 1  of the first electric power supply  11  to the voltage of the sum of the voltage VB 1  of the first electric power supply  11  and the voltage V 132  of the second electric power supply  12  (=VB 1 +VB 2 =2×BV 1 ). Then, after this alternate switching, the state is transferred to the series mode SA. 
     On the other hand, the connection switching control unit  21 , for example, when switching the series mode SA to the parallel mode PA, first switches the series mode SA to the parallel state PB, next alternately switches between the parallel state PB and the series state SB. At this alternate switching, the first ON duty D 1  (=Ton 1 /(Ton 1 +Ton 2 )) is gradually changed from 0% to 100%, and the second ON duty D 2  (=Ton 2 /(Ton 1 +Ton 2 )) is gradually changed from 100% to 0%. 
     Thereby, the charge and discharge operations of the first electric power supply  11  inversely excite the reactor  14 , which gradually decreases the voltage VL of both ends of the reactor  14 . Then, the output voltage Vout applied between the positive terminal and the negative terminal of the DC side of the inverter  3  is decreased from the voltage of the sum of the voltage VB 1  of the first electric power supply  11  and the voltage VB 2  of the second electric power supply  12  (=VB 1 +VB 2 =2×BV 1 ) to the voltage VB 1  of the first electric power supply  11 . Then, after this alternate switching, the state is transferred to the parallel mode PA. 
     The connection switching control unit  21 , for example, in the series state SB shown in  FIG. 2C , forms the current loop LSB that connects the first electric power supply  11  and the first capacitor  15 , the reactor  14 , the second switching device SW 2 , the second electric power supply  12 , and the inverter  3  and the third capacitor  17 , in series in this order. 
     In this case, for example, as shown in  FIG. 4 , a current I 1  that flows through the reactor  14  (reactor current) becomes equal to a current I 2  that flows from the fourth node D through the second electric power supply  12  to the third node C. 
     In this series state SB, a relation between the voltage VB 1  of the first electric power supply  11 , an inductance L of the reactor  14 , the reactor current I 1 , the voltage VB 2  of the second electric power supply  12 , and the output voltage Vout, for example, is as shown in an equation (1) below. 
     Then, the equation (1) below is transformed into, for example, an equation (2) below. In this equation (2), for example, by setting dI 1 =a gradient ΔI 1 P, dt=the second ON duty D 2 , and the voltage VB 1 =the voltage VB 2 , the equation (2) below, for example, is as shown in an equation (3) below. 
     Accordingly, in the series state SB, the reactor current I 1 , as shown, for example, in  FIG. 5A , increases by the gradient ΔI 1 P. 
     
       
         
           
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                         ⁢ 
                         
                           
 
                         
                         [ 
                         
                           Equation 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                         ] 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       
                         ⅆ 
                         I 
                       
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                     = 
                     
                       
                         
                           
                             VB 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                           + 
                           
                             VB 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2 
                           
                           - 
                           Vout 
                         
                         L 
                       
                       ⁢ 
                       
                         ⅆ 
                         
                           t 
                           ⁢ 
                           
                             
 
                           
                           [ 
                           
                             Equation 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             3 
                           
                           ] 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       Δ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       I 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       P 
                     
                     = 
                     
                       
                         
                           
                             2 
                             × 
                             VB 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                           - 
                           Vout 
                         
                         L 
                       
                       ⁢ 
                       D 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       2 
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     In addition, the connection switching control unit  21 , for example, in the parallel state PB shown in  FIG. 2B , forms a current loop LPB that connects the first electric power supply  11  and the first capacitor  15 , the reactor  14 , the first switching device SW 1 , and the inverter  3  and the third capacitor  17 , in this order. 
     In this case, for example, as shown in  FIG. 4 , the current I 2  that flows from the fourth node D through the second electric power supply  12  to the third node C becomes zero. 
     In this parallel state PB, a relation between the voltage VB 1  of the first electric power supply  11 , the inductance L of the reactor  14 , the reactor current I 1 , and the output voltage Vout, for example, is as shown in an equation (4) below. 
     Then, the equation (4) below is transformed into, for example, an equation (5) below, and in this equation (5), for example, by setting dI 1 =a gradient ΔI 1 S and dt=the first ON duty D 1  (=1−D 2 ), the equation (5) below, for example, is as shown in an equation (6) below. 
     Accordingly, in the parallel state PB, the reactor current I 1 , as shown, for example, in  FIG. 5B , decreases by the gradient ΔI 1 S. 
     
       
         
           
             [ 
             
               Equation 
               ⁢ 
               
                   
               
               ⁢ 
               4 
             
             ] 
           
         
       
       
         
           
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       VB 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                     = 
                     
                       
                         L 
                         ⁢ 
                         
                           
                             
                               ⅆ 
                               I 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                           
                             ⅆ 
                             t 
                           
                         
                       
                       + 
                       
                         Vout 
                         ⁢ 
                         
                           
 
                         
                         [ 
                         
                           Equation 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           5 
                         
                         ] 
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       
                         ⅆ 
                         I 
                       
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                     = 
                     
                       
                         
                           
                             VB 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                           - 
                           Vout 
                         
                         L 
                       
                       ⁢ 
                       
                         ⅆ 
                         
                           t 
                           ⁢ 
                           
                             
 
                           
                           [ 
                           
                             Equation 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             6 
                           
                           ] 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       Δ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       I 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       S 
                     
                     = 
                     
                       
                         
                           
                             VB 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                           - 
                           Vout 
                         
                         L 
                       
                       ⁢ 
                       
                         ( 
                         
                           1 
                           - 
                           
                             D 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     Then, at the alternate switching between the series state SB and the parallel state PB, as shown, for example, in an equation (7) below, the sum of the gradient ΔI 1 P and the gradient ΔI 1 S becomes zero, and the equation (7) below is transformed into, for example, equations (8) and (9) below. 
     Accordingly, the output voltage Vout is described by the voltage VB 1  of the first electric power supply  11  and the second ON duty D 2 , as shown in the equation (9) below. 
     
       
         
           
             [ 
             
               Equation 
               ⁢ 
               
                   
               
               ⁢ 
               7 
             
             ] 
           
         
       
       
         
           
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       
                         Δ 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         I 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         P 
                       
                       + 
                       
                         Δ 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         I 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         S 
                       
                     
                     = 
                     
                       0 
                       ⁢ 
                       
                         
 
                       
                       [ 
                       
                         Equation 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         8 
                       
                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       
                         
                           
                             
                               2 
                               × 
                               VB 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               1 
                             
                             - 
                             Vout 
                           
                           L 
                         
                         ⁢ 
                         D 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                       
                       + 
                       
                         
                           
                             
                               VB 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               1 
                             
                             - 
                             Vout 
                           
                           L 
                         
                         ⁢ 
                         
                           ( 
                           
                             1 
                             - 
                             
                               D 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                             
                           
                           ) 
                         
                       
                     
                     = 
                     
                       0 
                       ⁢ 
                       
                         
 
                       
                       [ 
                       
                         Equation 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         9 
                       
                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     Vout 
                     = 
                     
                       
                         ( 
                         
                           
                             D 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2 
                           
                           + 
                           1 
                         
                         ) 
                       
                       ⁢ 
                       VB 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     The electric motor control unit  22 , for example, at the driving operation of the electric motor  2  that is a three-phase brushless DC motor or the like, transforms DC electric power that is applied between the positive terminal and negative terminal of the DC side of the inverter  3  into three-phase AC electric power, and distribute each phase of AC currents by sequentially switching conduction to each phase of the electric motor  2 . On the other hand, for example, at the regeneration operation of the electric motor  2 , the electric motor control unit  22  transforms generated AC electric power that is output from the electric motor  2  into DC electric power in synchronization based on a rotation angle of the electric motor  2 . 
     The electric power supply apparatus  1  according to the embodiment of the present invention includes the above configuration, and next, an operation of the electric power supply apparatus  1 , specifically, a process that alternately switches between the series state SB and the parallel state PB will be described. 
     First, for example, in a step S 01  shown in  FIG. 6 , the routine obtains a connection state of the switch circuit  13  corresponding to the operation mode of the electric power supply apparatus  1  (namely, the parallel mode RPA or the series mode SA). 
     Next, in a step S 02 , the routine determines whether there is a request for switching of the connection state of the switch circuit  13  in accordance with switching of the operation mode of the electric power supply apparatus  1  or not. 
     In a case that this determination result is “NO”, the routine proceeds to END. 
     On the other hand, in a case that this determination result is “YES”, the routine proceeds to a step S 03 . 
     Then, in the step S 03 , the routine determines whether the request for switching of the connection state of the switch circuit  13  is a request for switching from the series mode SA to the parallel mode PA or not. 
     In a case that this determination result is “NO”, the routine proceeds to a step S 06  described later. 
     On the other hand, in a case that this determination result is “YES”, the routine proceeds to a step S 04 . 
     Then, in the step S 04 , by alternately switching between the first state in which the pair of the first switching device SW 1  and the third switching device SW 3  is closed and the second switching device SW 2  is open, and the second state in which the pair of the first switching device SW 1  and the third switching device SW 3  is open and the second switching device SW 2  is closed, the first ON duty D 1  is gradually changed from 0% to 100%, and the second ON duty D 2  is gradually changed from 100% to 0%. 
     Next, in a step S 05 , the routine determines whether the first ON duty D 1  is 100% and the second ON duty D 2  is 0% or not. 
     In a case that this determination result is “NO”, the routine returns to the above step S 04 . 
     On the other hand, in a case that this determination result is “YES”, the routine proceeds to END. 
     In addition, in the step S 06 , the routine determines whether the request for switching of the connection state of the switch circuit  13  is a request for switching from the parallel mode PA to the series mode SA or not. 
     In a case that this determination result is “NO”, the routine proceeds to END. 
     On the other hand, in a case that this determination result is “YES”, the routine proceeds to a step S 07 . 
     Then, in the step S 07 , by alternately switching between the first state in which the pair of the first switching device SW 1  and the third switching device SW 3  is closed and the second switching device SW 2  is open, and the second state in which the pair of the first switching device SW 1  and the third switching device SW 3  is open and the second switching device SW 2  is closed, the first ON duty D 1  is gradually changed from 100% to 0%, and the second ON duty D 2  is gradually changed from 0% to 100%. 
     Next, in a step S 08 , the routine determines whether the first ON duty D 1  is 0% and the second ON duty D 2  is 100% or not. 
     In a case that this determination result is “NO” the routine returns to the above step S 07 . 
     On the other hand, in a case that this determination result is “YES”, the routine proceeds to END. 
     (First Modified Example) 
     In addition, in the embodiment described above, considering the electric power supply apparatus  1 , for instance, shown in  FIG. 1  as an example, as the electric power supply apparatus  1  according to a first modified example, for instance, shown in  FIG. 7 , the electric power supply apparatus  1  may include a second reactor  31  that is provided between the fourth node D and the second electric power supply  12 . 
     More specifically, a first end of the second reactor  31  is connected between the emitter of the second switching device SW 2  and the collector of the third switching device SW 3  of the switch circuit  13 , and a second end of the second reactor  31  is connected to the negative terminal of the second electric power supply  12 . 
     In addition, in this first modified example, the reactor  14  and the second reactor  31  are, for example, as shown in  FIG. 8 , may be magnetically coupled by being wound around a common core  32  such that the magnetic paths are shared. 
     In this first modified example, the switch circuit  13 , for example, as shown in  FIG. 9A , in the parallel mode PA as the operation mode of the electric power supply apparatus  1 , sets the first switching device SW 1  and the third switching device SW 3  to be closed (ON) and the second switching device SW 2  to be open (OFF). Thereby, the first electric power supply  11  and the second electric power supply  12  are connected in parallel with the inverter  3 . 
     In addition, the switch circuit  13 , for example, as shown in  FIG. 9D , in the series mode SA as the operation mode of the electric power supply apparatus  1 , sets the first switching device SW 1  and the third switching device SW 3  to be open (OFF) and the second switching device SW 2  to be closed (ON). Thereby, the first electric power supply  11  and the second electric power supply  12  are connected in series with the inverter  3 . 
     Then, the switch circuit  13  alternately switches between the series state SB and the parallel state PB in the voltage adjustment control that is performed when switching between the parallel mode PA and the series mode SA. 
     In more detail, the switch circuit  13 , for example, as shown in  FIG. 9B , connects the first node A, the third node C, and the second output terminal  13   f , and connects the second node B, the fourth node D, and the first output terminal  13   e.    
     Thereby, it is possible to connect the first electric power supply  11  and the second electric power supply  12  in parallel with the inverter  3  to form the parallel state PB in which the voltages of both ends of the reactor  14  and the second reactor  31  are decreased. 
     In addition, the switch circuit  13 , for example, as shown in  FIG. 9C , connects the first node A and the fourth node D, connects the second node B and the first output terminal  13   e , and connects the third node C 1  and the second output terminal  13   f.    
     Thereby, it is possible to form a current loop that connects the first electric power supply  11 , the second electric power supply  12 , the reactor  14 , and the second reactor  31  in series with the inverter  3  to form the series state S 13  in which the voltages of both ends of the reactor  14  and the second reactor  31  are increased. 
     Then, the switch circuit  13 , for example, in the voltage adjustment control, alternately switches between the series state SB and the parallel state PB, by alternately switching between the first state in which the pair of the first switching device SW 1  and the third switching device SW 3  is closed and the second switching device SW 2  is open, and the second state in which the pair of the first switching device SW 1  and the third switching device SW 3  is open and the second switching device SW 2  is closed. 
     In this first modified example, the connection switching control unit  21  of the control device  18 , for example, in the parallel mode PA shown in  FIG. 9A , forms the current loop LPA 1  that connects the first electric power supply  11  and the first capacitor  15 , the reactor  14 , the first switching device SW 1 , and the inverter  3  and the third capacitor  17 , in series in this order, by setting the second switching device SW 2  to be OFF and setting the first switching device SW 1  to be ON. 
     Moreover, the connection switching control unit  21  forms the current loop LPA 2  that connects the third switching device SW 3 , the second electric power supply  12  and the second capacitor  16 , and the inverter  3  and the third capacitor  17 , in series in this order, by setting the third switching device SW 3  to be ON. 
     In addition, the connection switching control unit  21 , for example, in the series mode SA shown in  FIG. 9D , forms the current loop LSA that connects the first electric power supply  11  and the first capacitor  15 , the reactor  14 , the second switching device SW 2 , the second reactor  31 , the second electric power supply  12  and the second capacitor  16 , and the inverter  3  and the third capacitor  17 , in series in this order, by setting the second switching device SW 2  to be ON and setting the first switching device SW 1  and the third switching device SW 3  to be OFF. 
     In addition, the connection switching control unit  21 , for example, as shown in  FIG. 10 , when switching the parallel mode PA to the series mode SA, first switches the parallel mode PA to the series state SB, next alternately switches between the series state SB and the parallel state PB. At this alternate switching, the first ON duty D 1  (=Ton 1 /(Ton 1 +Tn 2 )) is gradually changed from 100% to 0%, and the second ON duty D 2  (=Ton 2 /(Ton 1 +Ton 2 )) is gradually changed from 0% to 100%. 
     Thereby, the charge and discharge operations of the first electric power supply  11  and the second electric power supply  12  excite the reactor  14  and the second reactor  31 , which gradually increases the voltage VL of both ends of the reactor  14  and the voltage of both ends of the second reactor  31 . Then, the output voltage Vout applied between the positive terminal and the negative terminal of the DC side of the inverter  3  is increased from the voltage VB 1  of the first electric power supply  11  to the voltage of the sum of the voltage VB 1  of the first electric power supply  11  and the voltage VB 2  of the second electric power supply  12  (=VB 1 +VB 2 ==2×BV 1 ). Then, after this alternate switching, the state is transferred to the series mode SA. 
     On the other hand, the connection switching control unit  21 , for example, when switching the series mode SA to the parallel mode PA, first switches the series mode SA to the parallel state PB, next alternately switches between the parallel state PB and the series state SB. At this alternate switching, the first ON duty D 1  (=Ton 1 /(Ton 1 +Ton 2 )) is gradually changed from 0% to 100%, and the second ON duty D 2  (=Ton 2 /(Ton 1 +Ton 2 )) is gradually changed from 100% to 0%. 
     Thereby, the charge and discharge operations of the first electric power supply  11  and the second electric power supply  12  inversely excite the reactor  14  and the second reactor  31 , which gradually decreases the voltage V 1 , of both ends of the reactor  14  and the voltage of both ends of the second reactor  31 . Then, the output voltage Vout applied between the positive terminal and the negative terminal of the DC side of the inverter  3  is decreased from the voltage of the sum of the voltage VB 1  of the first electric power supply  11  and the voltage VB 2  of the second electric power supply  12  (=VB 1 +VB 2 =2×BV 1 ) to the voltage VB 1  of the first electric power supply  11 . Then, after this alternate switching, the state is transferred to the parallel mode PA. 
     The connection switching control unit  21 , for example, in the series state SB shown in  FIG. 9C  forms the current loop LSB that connects the first electric power supply  11  and the first capacitor  15 , the reactor  14 , the second switching device SW 2 , the second reactor  31 , the second electric power supply  12  and the second capacitor  16 , and the inverter  3  and the third capacitor  17 , in series in this order. 
     In this case, for example, as shown in  FIG. 10 , the current I 1  that flows through the reactor  14  (reactor current) becomes equal to a current I 2  that flows through the second reactor  31  (second reactor current). 
     In this series state SB, a relation between the voltage VB 1  of the first electric power supply  11 , the inductance L 1  of the reactor  14 , the reactor current I 1 , the inductance L 2  of the second reactor  31 , the second reactor current I 2 , the voltage VB 2  of the second electric power supply  12 , and the output voltage Vout, for example, is as shown in an equation (10) below. 
     Then, the equation (10) below is transformed, for example, by setting the inductance L 1 =the inductance L 2 , into an equation (11) below. In this equation (11), for example, by setting dI 1 =the gradient ΔI 1 P, dt=the second ON duty D 2 , and the voltage VB 1 =the voltage VB 2 , the equation (11) below, for example, is as shown in an equation (12) below. 
     Accordingly, in the series state SB, the reactor current I 1 , as shown, for example, in  FIG. 11A , increases by the gradient ΔI 1 P. 
     
       
         
           
             [ 
             
               Equation 
               ⁢ 
               
                   
               
               ⁢ 
               10 
             
             ] 
           
         
       
       
         
           
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       VB 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                     = 
                     
                       
                         L 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         
                           
                             
                               ⅆ 
                               I 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                           
                             ⅆ 
                             t 
                           
                         
                       
                       + 
                       
                         L 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         
                           
                             
                               ⅆ 
                               I 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2 
                           
                           
                             ⅆ 
                             t 
                           
                         
                       
                       - 
                       
                         VB 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                       
                       + 
                       
                         Vout 
                         ⁢ 
                         
                           
 
                         
                         [ 
                         
                           Equation 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           11 
                         
                         ] 
                       
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       
                         ⅆ 
                         I 
                       
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                     = 
                     
                       
                         
                           
                             VB 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                           + 
                           
                             VB 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2 
                           
                           - 
                           Vout 
                         
                         
                           2 
                           × 
                           L 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                       
                       ⁢ 
                       
                         ⅆ 
                         
                           t 
                           ⁢ 
                           
                             
 
                           
                           [ 
                           
                             Equation 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             12 
                           
                           ] 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   11 
                   ) 
                 
               
             
             
               
                 
                   
                       
                   
                   ⁢ 
                   
                     
                       Δ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       I 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       P 
                     
                     = 
                     
                       
                         
                           
                             2 
                             × 
                             VB 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                           - 
                           Vout 
                         
                         
                           2 
                           × 
                           L 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                       
                       ⁢ 
                       D 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       2 
                     
                   
                 
               
               
                 
                   ( 
                   12 
                   ) 
                 
               
             
           
         
       
     
     In addition, the connection switching control unit  21 , for example, in the parallel state PB shown in  FIG. 9B , forms a current loop LPB 1  that connects the first electric power supply  11  and the first capacitor  15 , the reactor  14 , the first switching device SW, and the inverter  3  and the third capacitor  17 , in this order. 
     Moreover, the connection switching control unit  21  forms a current loop LPB 2  that connects the third switching device SW 3 , the second reactor  31 , the second electric power supply  12  and the second capacitor  16 , and the inverter  3  and the third capacitor  17 , in this order. 
     In this case, for example, as shown in  FIG. 10 , the current I 1  that flows through the reactor  14  (reactor current) becomes equal to the current I 2  that flows through the second reactor  31  (second reactor current). 
     In this parallel state PB, a relation between the voltage VB 1  of the first electric power supply  11 , the inductance L of the reactor  14 , the reactor current I 1 , the output voltage Vout, for example, is as shown in an equation (13) below. 
     Then, the equation (13) below is transformed into, for example, an equation (14) below, and in this equation (14), for example, by setting dI 1 =the gradient ΔI 1 S and dt=the first ON duty D 1  (=1−D 2 ), the equation (14) below; for example, is as shown in an equation (15) below. 
     Accordingly, in the parallel state PB, the reactor current I 1 , as shown, for example, in  FIG. 11B , decreases by the gradient ΔI 1 S. 
     
       
         
           
             [ 
             
               Equation 
               ⁢ 
               
                   
               
               ⁢ 
               13 
             
             ] 
           
         
       
       
         
           
             
               
                 
                   
                     VB 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   = 
                   
                     
                       L 
                       ⁢ 
                       
                         
                           
                             ⅆ 
                             I 
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                         
                           ⅆ 
                           t 
                         
                       
                     
                     + 
                     
                       Vout 
                       ⁢ 
                       
                         
 
                       
                       [ 
                       
                         Equation 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         14 
                       
                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   13 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       ⅆ 
                       I 
                     
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   = 
                   
                     
                       
                         
                           VB 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                         - 
                         Vout 
                       
                       
                         L 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                       
                     
                     ⁢ 
                     
                       ⅆ 
                       
                         t 
                         ⁢ 
                         
                           
 
                         
                         [ 
                         
                           Equation 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           15 
                         
                         ] 
                       
                     
                   
                 
               
               
                 
                   ( 
                   14 
                   ) 
                 
               
             
             
               
                 
                   
                     Δ 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     I 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     S 
                   
                   = 
                   
                     
                       
                         
                           VB 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                         - 
                         Vout 
                       
                       
                         L 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                       
                     
                     ⁢ 
                     
                       ( 
                       
                         1 
                         - 
                         
                           D 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   15 
                   ) 
                 
               
             
           
         
       
     
     Then, at the alternate switching between the series state SB and the parallel state PB, for example, as shown in an equation (16) below, the sum of the gradient ΔI 1 P and the gradient ΔI 1 S becomes zero, and the equation (16) below is transformed into, for example, equations (17) and (18) below. 
     Accordingly, the output voltage Vout is described by the voltage VB 1  of the first electric power supply  11  and the second ON duty D 2 , as shown in the equation (18) below. 
     
       
         
           
             [ 
             
               Equation 
               ⁢ 
               
                   
               
               ⁢ 
               16 
             
             ] 
           
         
       
       
         
           
             
               
                 
                   
                     
                       Δ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       I 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       P 
                     
                     + 
                     
                       Δ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       I 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       S 
                     
                   
                   = 
                   
                     0 
                     ⁢ 
                     
                       
 
                     
                     [ 
                     
                       Equation 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       17 
                     
                     ] 
                   
                 
               
               
                 
                   ( 
                   16 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       
                         
                           
                             2 
                             × 
                             VB 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                           - 
                           Vout 
                         
                         
                           2 
                           × 
                           L 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                       
                       ⁢ 
                       D 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       2 
                     
                     + 
                     
                       
                         
                           
                             VB 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                           - 
                           Vout 
                         
                         
                           L 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                       
                       ⁢ 
                       
                         ( 
                         
                           1 
                           - 
                           
                             D 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2 
                           
                         
                         ) 
                       
                     
                   
                   = 
                   
                     0 
                     ⁢ 
                     
                       
 
                     
                     [ 
                     
                       Equation 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       18 
                     
                     ] 
                   
                 
               
               
                 
                   ( 
                   17 
                   ) 
                 
               
             
             
               
                 
                   Vout 
                   = 
                   
                     
                       2 
                       × 
                       VB 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                     
                       2 
                       - 
                       
                         D 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   18 
                   ) 
                 
               
             
           
         
       
     
     In addition, in the example and the first modified example of the embodiment described above, the reactor  14  may be provided between the first electric power supply  11  and the second node B 3 . 
     Also, in the first modified example of the embodiment described above, the second reactor  31  may be provided between the second electric power supply  12  and the third node C. 
     As described above, the electric power supply apparatus  1  according to the example and the first modified example of the embodiment of the present invention, for example, as shown in  FIGS. 12A and 12B , includes the first electric power supply  11  that is connected between the first node A and the second node B, the second electric power supply  12  that is connected between the third node C and the fourth node D, the switch circuit  13  having four input terminals  13   a ,  13   b ,  13   c , and  13   d  which are connected to the first node A, the second node B, the third node C, and the fourth node D, respectively, and two output terminals  13   e  and  13   f , the electric load that consists of the inverter  3  and that is connected between the two output terminals  13   e  and  13   f , and the reactor  14  that is provided between the first electric power supply  11  and one of the first node A and the second node B. 
     In addition, the electric power supply apparatus  1  alternately switches between the series state SB in which the voltage between both ends of the reactor  14  is increased by connecting the first node A with the fourth node D, connecting the second node  13  with the first output terminal  13   e , and connecting the third node C with the second output terminal  13   f , to form the current loop that connects the first electric power supply  11 , the second electric power supply  12 , and the reactor  14  in series with the electric load, and the parallel state PB in which the voltage between both ends of the reactor  14  is decreased by connecting the first node A and the third node C with the second output terminal  13   f , and connecting the second node  1 B and the fourth node D with the first output terminal  13   e , to connect the first electric power supply  11  and the second electric power supply  12  in parallel with the electric load. 
     According to the electric power supply apparatus  1  of the example and the first modified example of this embodiment, it is possible to finely tune the voltage applied to the inverter  3  corresponding to a load of the electric motor  2  that is the electric load, and thereby a desired power performance can be obtained. In addition, it is possible to prevent the applied voltage from being excessive, and thereby a driving efficiency of the electric motor  2  and the inverter  3  can be improved. 
     Moreover, by configuring the switch circuit  13  to include three switching devices, i.e. the first switching device SW 1 , the second switching device SW 2 , and the third switching device SW 3 , it is possible to prevent electric power supply apparatus  1  from being larger and prevent the cost required for a configuration from increasing, compared to a case in which, for example, four or more switching devices are included. 
     Furthermore, in each of the current loops LPA 1 , LPA 2 , LSA, LPB, LPB 1 , LPB 2 , and LSB that are formed in the parallel mode PA, the series mode SA, the parallel state PB, and the series state SB, one switching device is only included in each of the electrical conduction paths. Thereby, it is possible to prevent the electrical conduction loss from increasing, compared to a case in which, for example, a plurality of switching devices are included in the electrical conduction path. 
     In addition, when alternately switching between the series state SB and the parallel state PB in the voltage adjustment control for switching between the parallel mode PA and the series mode SA, in comparison with, for example, a case where a current loop that connects each of the electric power supplies in series only with the reactor is formed, it is possible to suppress the increase of the total interlinkage magnetic flux associated with the increase of the voltage boost rate, to prevent the increase of the loss, and to downsize the reactor  14  and the second reactor  31 . 
     For example, as shown in  FIGS. 13A and 13B , when a switching operation between a voltage boost operation in the parallel connection mode and a voltage boost operation in the series connection mode of the electric power supply system according to the above Japanese Unexamined Patent Application Publication No. 2012-070514 is considered as a comparison example, in this comparison example the total interlinkage magnetic flux at a peak current of the reactor changes to an increasing tendency corresponding to an increase of the voltage boost rate. 
     On the other hand, according to the example and the first modified example of the embodiment of the present invention described above, the total interlinkage magnetic flux at a peak current of the reactor changes to an decreasing tendency when the voltage boost rate exceeds about 1.5. Thereby, compared to the comparison example, it is possible to suppress a change of a maximum magnetic flux and the loss of the reactor  14  and the second reactor  31 , and to downsize the converter. 
     Specifically, when considering the electric power supply apparatus  1  as an electric power supply for vehicles, in most cases a required voltage boost rate falls within a range of 1.5 to 2, and thus applicability to the vehicles can be improved. 
     In addition, in the voltage boost operation in the parallel connection mode of the comparison example, for example, as shown in  FIG. 14  (A) to (C), a current loop that connects a single electric power supply (a voltage=V 1 ) in series with a reactor (R), and a current loop that connects the single electric power supply (a voltage=V 1 ) and the reactor (R) in series with an output section (an output voltage=Vout) are switched with a duty D and a duty (1−D), respectively. Thereby; a total interlinkage magnetic flux (=cV 0 ×time) at a peak current of the reactor (R) becomes the voltage V 1 ×the duty D. 
     On the other hand, when alternately switching between the series state SB and the parallel state PB in the voltage adjustment control according to the example of the embodiment, for example, as shown in  FIG. 15  (A) to (C), the total interlinkage magnetic flux (=the voltage V 0  of both ends of the reactor  14 ×time) at a peak current of the reactor  14  becomes a voltage (=VB 1 +VB 2 −Vout)×the second ON duty D 2 . 
     In addition, in the electric power supply apparatus  1  according to the example and the first modified example of the embodiment of the present invention, a closed state and an open state of the pair of the first switching device SW 1  and the third switching device SW 3 , and the second switching device SW 2  are fixed, in the parallel mode and the series mode as operation modes of the electric power supply apparatus  1 . Thereby, it is possible to apply a voltage to the inverter  3  and the electric motor  2  that are the electric load and drive them without switching losses. 
     In addition, in the electric power supply apparatus  1  according to the example of the embodiment of the present invention, the reactor  14  is included between the first electric power supply  11  and one of the first node A and the second node B, and thus at the voltage increasing-decreasing time when the voltage of both ends of the reactor  14  is increased and decreased, only the first electric power supply  11  is made to be charged and to be discharged, and thereby a burden of the charge and discharge operations is assigned only to the first electric power supply  11 . 
     Thereby, it is possible to make the first electric power supply  11  and the second electric power supply  12  as a combination of electric power supplies with different characteristics, and increase flexibility in the apparatus configuration. 
     In addition, in the electric power supply apparatus  1  according to the first modified example of the embodiment of the present invention, the second reactor  31  is included between the second electric power supply  12  and one of the third node C and the fourth node D, and thus at the voltage increasing-decreasing time when the voltages of both ends of the reactor  14  and the second reactor  31  are increased and decreased, the first electric power supply  11  and the second electric power supply  12  are made equally to be charged and to be discharged, and thereby it is possible to distribute the burden of the charge and discharge operations equally to the first electric power supply  11  and the second electric power supply  12 . 
     Thereby, it is possible to suppress a degradation of the first electric power supply  11  and the second electric power supply  12 . 
     Moreover, in the electric power supply apparatus  1  according to the first modified example of the embodiment of the present invention, the reactor  14  and the second reactor  31  are magnetically coupled, and thereby it is possible to downsize the reactor  14  and the second reactor  31 . 
     (Second Modified Example, Third Modified Example) 
     In addition, in the embodiment described above, for example, in place of the reactor  14 , as the electric power supply apparatus  1  according to a second modified example, for instance, shown in  FIG. 16 , or as the electric power supply apparatus  1  according to a third modified example, thr instance, shown in  FIG. 17 , a third reactor  41  or a fourth reactor  42  that is provided between the inverter  3  as the electric load and any one of the two output terminals  13   e  and  13   f , may be included. 
     According to these second and third modified examples, the single reactor (specifically, the third reactor  41  or the fourth reactor  421 ) makes it possible to charge and discharge equally the first electric power supply  11  and the second electric power supply  12  equally at the voltage increasing-decreasing time when the voltage of both ends of the reactor is increased and decreased. 
     Thereby, it is possible to distribute the burden of the charge and discharge operations equally to the first electric power supply  11  and the second electric power supply  12 , and it is possible to suppress a degradation of the first electric power supply  11  and the second electric power supply  12 . 
     (Fourth Modified Example) 
     In addition, in the embodiment described above, the first switching device SW 1  and the third switching device SW 3  are set to be closed (ON) and the second switching device SW 2  is set to be open (OFF) in the parallel mode PA, but the present invention is not limited hereto. For example, in a case where the series mode SA is switched to the parallel mode PA or the like, a constant current control for resolving an unbalance between the voltage VB 1  of the first electric power supply  11  and the voltage VB 2  of the second electric power supply  12  may be further performed. 
     An operation of the electric power supply apparatus  1  according to the fourth modified example of this embodiment described above, specifically, a process that alternately switches between the series state SB and the parallel state PB will be described below. 
     First, for example, in a step S 01  shown in  FIG. 18 , the routine obtains a connection state of the switch circuit  13  corresponding to the operation mode of the electric power supply apparatus  1  (namely, the parallel mode PA or the series mode SA). 
     Next, in a step S 02 , the routine determines whether there is a request for switching of the connection state of the switch circuit  13  in accordance with switching of the operation mode of the electric power supply apparatus  1  or not. 
     In a case that this determination result is “NO”, the routine proceeds to END. 
     On the other hand, in a case that this determination result is “YES”, the routine proceeds to a step S 03 . 
     Then, in the step S 03 , the routine determines whether the request for switching of the connection state of the switch circuit  13  is a request for switching from the series mode SA to the parallel mode PA or not. 
     In a case that this determination result is “NO”, the routine proceeds to a step S 06  described later. 
     On the other hand, in a case that this determination result is “YES”, the routine proceeds to a step S 04 . 
     Then, in the step S 04 , by alternately switching between the first state in which the pair of the first switching device SW 1  and the third switching device SW 3  is closed and the second switching device SW 2  is open, and the second state in which the pair of the first switching device SW 1  and the third switching device SW 3  is open and the second switching device SW 2  is closed, the first ON duty D 1  is gradually changed from 0% to 100%, and the second ON duty D 2  is gradually changed from 100% to %0%. 
     Next, in a step S 05 , the routine determines whether the first ON duty D 1  is 100% and the second ON duty D 2  is 0% or not. 
     In a case that this determination result is “NO”, the routine returns to the above step S 04 . 
     On the other hand, in a case that this determination result is “YES”, the routine proceeds to a step S 11 . In this step S 11 , a parallel static control is performed, and the routine proceeds to END. 
     In addition, in the step S 06 , the routine determines whether the request for switching of the connection state of the switch circuit  13  is a request for switching from the parallel mode PA to the series mode SA or not. 
     In a case that this determination result is “NO”, the routine proceeds to END. 
     On the other hand, in a case that this determination result is “YES”, the routine proceeds to a step S 07 . 
     Then, in the step S 07 , by alternately switching between the first state in which the pair of the first switching device SW 1  and the third switching device SW 3  is closed and the second switching device SW 2  is open, and the second state in which the pair of the first switching device SW 1  and the third switching device SW 3  is open and the second switching device SW 2  is closed, the first ON duty D 1  is gradually changed from 100% to 0%, and the second ON duty D 2  is gradually changed from 0% to 100%. 
     Next, in a step S 08 , the routine determines whether the first ON duty D 1  is 0% and the second ON duty D 2  is 100% or not. 
     In a case that this determination result is “NO”, the routine returns to the above step S 07 . 
     On the other hand, in a case that this determination result is “YES”, the routine proceeds to a step S 12 . In this step S 12 , a series static control is performed, and the routine proceeds to END. 
     The parallel static control in the above step S 11  will be described below. 
     First, for example, in a step S 21  shown in  FIG. 19 , the routine determines whether the reactor current I 1  is greater than a load current I 0  (that is, a current that flows between the positive terminal and the negative terminal of the DC side of the inverter  3 ) or not. 
     In a case that this determination result is “NO”, the routine proceeds to a step S 23  described later. 
     On the other hand, in a case that this determination result is “YES”, the routine proceeds to a step S 22 . 
     Then, in the step S 22 , as an unbalanced state where the voltage VB 1  of the first electric power supply  11  is higher than the voltage VB 2  of the second electric power supply  12  has been arising, a current flow from the first electric power supply  11  to the second electric power supply  12  is cut off, by setting the first switching device SW 1  to be closed (ON), the third switching device SW 3  to be open (OFF), and the second switching device SW 2  to be open (OFF). 
     Thereby, the voltage VB of the first electric power supply  11  is decreased by a current consumption at the electric load. Thus, the reactor current I 1  and the load current I 0  converge to be equal to each other, the voltage VB 1  of the first electric power supply  11  and the voltage VB 2  of the second electric power supply  12  converge to be equal to each other, and the unbalanced state converges to a state where the first electric power supply  11  and the second electric power supply  12  equally output the load current I 0 . 
     Then, in the step S 23 , the routine determines whether a current I 2  (that is, a current I 2  that flows from the fourth node D through the second electric power supply  12  to the third node C) is greater than the load current I 0  or not. 
     In a case that this determination result is “NO”, the routine proceeds to a step S 25  described later. 
     On the other hand, in a case that this determination result is “YES”, the routine proceeds to a step S 24 . 
     Then, in the step S 24 , as an unbalanced state where the voltage VB 2  of the second electric power supply  12  is higher than the voltage VB 1  of the first electric power supply  11  has been arising, a current flow from the second electric power supply  12  to the first electric power supply  11  is cut off, by setting the first switching device SW 1  to be open (OFF), the third switching device SW 3  to be closed (ON), and the second switching device SW 2  to be open (OFF). 
     Thereby, the voltage VB 2  of the second electric power supply  12  is decreased by a current consumption at the electric load. Thus, the current I 2  and the load current I 0  converge to be equal to each other, the voltage VB 1  of the first electric power supply  11  and the voltage VB 2  of the second electric power supply  12  converge to be equal to each other, and the unbalanced state converges to a state where the first electric power supply  11  and the second electric power supply  12  equally output the load current I 0 . 
     Then, in the step S 25 , the first switching device SW 1  and the third switching device SW 3  is set to be closed (ON) and the second switching device SW 2  is set to be open (OFF), and the routine proceeds to RETURN. 
     The series static control in the above step S 12  will be described below. 
     For example, in a step S 31  shown in  FIG. 20 , the first switching device SW 1  and the third switching device SW 3  are set to be open (OFF), and the second switching device SW 2  is set to be closed (ON), and the routine proceeds to RETURN. 
     According to this fourth modified example, when resolving an unbalance between the voltage VB 1  of the first electric power supply  11  and the voltage VB 2  of the second electric power supply  12 , it is possible to prevent an occurrence of charge and discharge operations between the first electric power supply  11  and the second electric power supply  12  that are irrelevant to electric power distribution to the electric load (that is, an occurrence of a state where a current flows from one of the first electric power supply  11  and the second electric power supply  12  with a higher voltage, to the other with a lower voltage, and thereby the voltages VB 1 , VB 2  of the two converge to be equal). 
     Thereby, it is possible to perform efficient electric power distribution to the electric motor  2  and the inverter  3  that are the electric load. 
     In addition, in the embodiment described above, for example, an inverter for a generator that is connected in parallel with the inverter  3 , and a generator controlled by this inverter for a generator may be included. 
     While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary examples of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the scope of the present invention. Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims.