Patent Publication Number: US-2022231533-A1

Title: In-vehicle backup power supply device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. national stage of PCT/JP2020/018761 filed on May 11, 2020, which claims priority of Japanese Patent Application No. JP 2019-098238 filed on May 27, 2019, the contents of which are incorporated herein. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to an in-vehicle backup power supply device. 
     BACKGROUND ART 
     Conventionally, battery modules formed by a plurality of unit batteries connected in series are used as drive power supplies for electric cars and the like. JP 2014-54143A discloses an example of a power supply device provided with this kind of battery module. 
     In this kind of battery module, the charging capacity of unit batteries depends on the temperature, and the lower the temperature of the unit batteries, the more the internal resistance of the unit batteries increases and the charging capacity decreases. In other words, the lower the temperature of the unit batteries is, the narrower the chargeable regions of the unit batteries are. Due to this characteristic, in an environment in which the temperature of the unit batteries is likely to decrease (e.g., in a cold area or in winter), the substantial charging capacity of the unit batteries is likely to decrease. 
     In view of this problem, in the power supply device of JP 2014-54143A, the temperature of a charging module (battery unit) is raised by performing constant voltage charging and constant current charging, using the power supplied from an external charger to mitigate the problem incurred by a low temperature state. However, the power supply device of the JP 2014-54143A is configured such that an external charger is necessarily required in order to raise the temperature of an assembled battery. 
     In view of this, the present disclosure provides a technique with which it is possible to raise the temperature of a battery unit more effectively with a simpler configuration. 
     SUMMARY 
     An in-vehicle backup power supply device according to the present disclosure is an in-vehicle backup power supply device comprising: a battery unit; a control unit, a first circuit unit, and a second circuit unit. The battery unit includes a plurality of unit batteries connected in series. The voltage conversion unit is provided with a plurality of converters that step up or down a voltage that is input and output the resultant voltage. The control unit is configured to control the voltage conversion unit. The first circuit unit constitutes a power path between the voltage conversion unit and the battery unit. The second circuit unit constitutes a power path between the voltage conversion unit and a load, wherein the battery unit is provided with a plurality of conversion target portions. The conversion target portions are constituted by one of the unit batteries or a plurality of the unit batteries connected in series. The first circuit unit is provided with a plurality of first conductive paths that are conductive paths that connect the highest potential electrodes of the conversion target portions and the respective converters to each other. A plurality of second conductive paths are conductive paths that connect the lowest potential electrodes of the conversion target portions and the respective converters to each other. The second circuit unit is provided with a plurality of third conductive paths that are conductive paths arranged between the converters and a conductive path on the load side. When a first condition is satisfied, the control unit causes the plurality of converters to perform a discharging operation for stepping up or down a potential difference between the first conductive path and the second conductive path as an input voltage and applying an output voltage to the third conductive path. When a second condition is satisfied, the control unit causes one or more of the converters to perform the discharging operation, and the other converter or converters to perform a charging operation for stepping up or down a voltage that is applied to the third conductive path and applying the output voltage between the first conductive path and the second conductive path. 
     Advantageous Effects of Invention 
     According to the present disclosure, it is possible to raise the temperature of a battery unit more effectively with a simpler configuration. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a circuit diagram schematically showing an in-vehicle backup power supply device according to a first embodiment. 
         FIG. 2  is a flowchart showing an operation of the in-vehicle backup power supply device according to the first embodiment. 
         FIG. 3  is a circuit diagram schematically showing an in-vehicle backup power supply device according to a second embodiment. 
         FIG. 4  is a flowchart showing an operation of the in-vehicle backup power supply device according to the second embodiment. 
         FIG. 5  is a circuit diagram schematically showing an in-vehicle backup power supply device according to a third embodiment. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     First, embodiments of the present disclosure will be listed and described. 
     An in-vehicle backup power supply device according to the present disclosure includes a battery unit in which a plurality of unit batteries are connected in series, a voltage conversion unit provided with a plurality of converters that step up or down a voltage that is input and output the resultant voltage, and a control unit configured to control the voltage conversion unit. The in-vehicle backup power supply device includes a first circuit unit constituting a power path between the voltage conversion unit and the battery unit, and a second circuit unit constituting a power path between the voltage conversion unit and a load. The battery unit is provided with a plurality of conversion target portions. A conversion target portion is constituted by the unit battery or a plurality of the unit batteries connected in series. The first circuit unit is provided with a plurality of first conductive paths and a plurality of second conductive paths. The plurality of first conductive paths are conductive paths that connect the highest potential electrodes of the conversion target portions and the respective converters. The plurality of second conductive paths are conductive paths that connect the lowest potential electrodes of the respective conversion target portions and the respective converters. The second circuit unit  31  is provided with a plurality of third conductive paths that are conductive paths arranged between the converters and the conductive paths on the load side. When the first condition is satisfied, the control unit causes the plurality of converters to perform a discharging operation for stepping up or down a potential difference between the first conductive path and the second conductive path as an input voltage and applying an output voltage to the third conductive path. Also, when the second condition is satisfied, the control unit causes one converter to perform the discharging operation. In addition to this, the control unit causes the other converter to perform a charging operation for stepping up or down a voltage that is applied to the third conductive path as an input voltage and applying the output voltage between the first conductive path and the second conductive path. With this configuration, with this in-vehicle backup power supply device, it is possible to raise the temperature of the battery unit by causing one converter to perform the discharging operation from the battery unit, and the other converter to perform the charging operation to the battery unit. In other words, with this in-vehicle backup power supply device, it is possible to raise the temperature of a battery unit more effectively with a simpler configuration without providing a dedicated configuration for raising the temperature of the battery unit. 
     In an in-vehicle backup power supply device according to the present disclosure, when the second condition is satisfied, the control unit may cause at least two or more of the plurality of converters to perform an operation for alternately repeating the charging operation and the discharging operation. 
     With this configuration, since the converters do not perform only one of the charging operation and the discharging operation, it is possible to avoid a case in which the unit batteries are overcharged or overdischarged, and the converters can continuously perform both the charging operation and the discharging operation. In this manner, this in-vehicle backup power supply device can favorably raise the temperature of the battery unit. 
     In an in-vehicle backup power supply device according to the present disclosure, in the battery unit, at least one of the plurality of the unit batteries and the plurality of the conversion target portions are arranged side by side along a predetermined direction. The control unit may perform a suppression control for setting an output power in the discharging operation of the converter that corresponds to the unit batteries or the conversion target portions located at the central portion in the predetermined direction to be smaller than an output power at the time of discharging operation of the converters that corresponds to the unit batteries or the conversion target portions located at the two ends in the predetermined direction. 
     With this configuration, it is possible to suppress an excessive increase in temperature of the central portion of the battery unit, and a case in which a difference in temperature occurs between the two sides and the central portion of the battery unit. 
     In an in-vehicle backup power supply device according to the present disclosure, the control unit may perform the suppression control at least in a case in which a temperature at the central portion is higher than a temperature to the outer side of the central portion. 
     With this configuration, it is possible to perform the suppression control only in the case in which a difference in temperature occurs between the outside and the central portion of the battery unit. 
     As shown in  FIG. 1 , an in-vehicle backup power supply device  1  of a first embodiment (hereinafter also referred to as “power supply device  1 ”) includes a battery unit  10 , a voltage conversion unit  11 , and a control unit  12 . Batteries such as lithium-ion batteries formed by a plurality of unit batteries  10 A (cells) are used in the battery unit  10 . The battery unit  10  is used as a power supply for outputting power for driving electromotive devices (e.g., motor) in vehicles such as hybrid cars or electric cars (EV (electric vehicles)). The battery unit  10  has a configuration in which a plurality of unit batteries  10 A configured as lithium ion batteries are connected in series form a module that constitutes one conversion target portion  10 B, and a plurality of the conversion target portions  10 B are connected in series such that they can output a desired output voltage. 
     In the battery unit  10 , for example, a plurality of unit batteries  10 A and a plurality of conversion target portions  10 B are arranged side by side along a predetermined direction (up-down direction in  FIG. 1 ). A power generation device  50  mounted in a vehicle is electrically connected to the electrodes at the two ends of the battery unit  10 , and the battery unit  10  can be charged by the power generation device  50 . The power generation device  50  is configured as a known in-vehicle power generator, and can generate power through rotation of a rotational axis of an engine (not shown). When the power generation device  50  operates, power generated by the power generation device  50  is rectified, and then supplied to the battery unit  10  as DC power. 
     The battery unit  10  is provided with a temperature detection unit  12 A. The temperature detection unit  12 A is formed by a known temperature sensor, for example, and arranged in contact with a surface portion or the like of the battery unit  10  or near the surface portion of the battery unit  10  without being in contact therewith. The temperature detection unit  12 A can output a voltage value indicating the temperature at the position at which it is arranged (i.e., the temperature of the surface or the temperature near the surface of the battery unit  10 ) and input the voltage value to the control unit  12 . 
     The voltage conversion unit  11  includes a plurality of converters  11 A and  11 B. The converters  11 A and  11 B are, for example, configured as known bi-directional step up/down DC-DC converters provided with semiconductor switching elements, inductors, and the like, and step up or down the voltage that is input into them and output the resultant voltage. The converters  11 A and  11 B are electrically connected to the conversion target portions  10 B via a first circuit unit  30 . The first circuit unit  30  forms the power path between the voltage conversion unit  11  and the battery unit. The first circuit unit  30  is provided with first conductive paths  30 A and  30 C, and second conductive paths  30 B and  30 D. The converter  11 A is electrically connected to the highest potential electrode in the conversion target portion  10 B via the first conductive path  30 A. The converter  11 A is electrically connected to the lowest potential electrode in the conversion target portion  10 B via the second conductive path  30 B. The potential difference between the first conductive path  30 A and the second conductive path  30 B is input to the converter  11 A as an input voltage. The converter  11 B is electrically connected to the highest potential electrode in the conversion target portion  10 B via the first conductive path  30 C. The converter  11 B is electrically connected to the lowest potential electrode in the conversion target portion  10 B via the second conductive path  30 D. The potential difference between the first conductive path  30 C and the second conductive path  30 D is input to the converter  11 B as an input voltage. 
     The converters  11 A and  11 B are electrically connected to switch elements  52  for switching electrical connection/non-electrical connection between the converters  11 A and  11 B and the load-side conductive path  53  that supplies power to the load  51 , via third conductive paths  31 A and  31 B included in a second circuit unit  31 . The third conductive path  31 A is arranged between the converter  11 A and the load-side conductive path  53  on the load  51  side, and the third conductive path  31 B is arranged between the converter  11 B and the load-side conductive path  53  on the load  51  side. The second circuit unit  31  forms a power path between the voltage conversion units  11  and the load  51 . The switch elements  52  are formed by MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) or the like, for example. The switch elements  52  are electrically connected to the load  51  via the load-side conductive path  53 . 
     When a first condition is satisfied, the converters  11 A and  11 B can be controlled by the control unit  12  and perform a discharging operation for stepping up or down the potential difference between the first conductive paths  30 A and  30 C and the second conductive paths  30 B and  30 D as the input voltage and applying the output voltage to the third conductive paths  31 A and  31 B. That the first condition is satisfied may mean that, for example, an ignition switch (not shown) provided in the vehicle is switched from off to on. 
     When a second condition is satisfied, controlled by the control unit  12 , one converter  11 A or  11 B can perform the discharging operation, and in addition to this, the other converter  11 A or  11 B can perform a charging operation (hereinafter also referred to as “temperature raising operation”) for stepping up/down the voltage applied to the third conductive paths  31 A or  31 B as the input voltage and applying the output voltage between the first conductive paths  30 A and  30 C, or the second conductive paths  30 B and  30 D. Specifically, when the one converter  11 A or  11 B performs the discharging operation, the other converter  11 A or  11 B performs a charging operation based on the output voltage that is output to the third conductive paths  31 A and  31 B, and generates a predetermined potential difference between the first conductive paths  30 A and  30 C and the second conductive paths  30 B and  30 D and outputs the potential difference as the output voltage. That the second condition is satisfied may mean, for example, that the voltage value indicating the temperature of the battery unit  10  that is output from the temperature detection unit  12 A (hereinafter also referred to as “voltage value from the temperature detection unit  12 A”) has reached a predetermined threshold or less (i.e., indicating a predetermined temperature or less). 
     The control unit  12  is constituted mainly by a microcomputer, for example, and includes a computation device such as a CPU (Central Processing Unit), a memory such as a ROM (Read Only Memory) or a RAM (Random Access Memory), an A/D converter and the like. The control unit  12  can grasp the temperature of the battery unit  10  based on a signal from the temperature detection unit  12 A that detects the temperature of the surface or in the vicinity of the surface of the battery unit  10 . 
     The control unit  12  controls the operation of the voltage conversion unit  11  based on the voltage value from the temperature detection unit  12 A. Specifically, when the first condition is satisfied, the control unit  12  performs a control for causing the voltage conversion unit  11  to perform the discharging operation. When the second condition is satisfied, the control unit  12  performs a control for causing the voltage conversion unit  11  to perform the temperature raising operation. 
     Next, the operation of the power supply device  1  will be described. 
     First, the user of the vehicle in which the power supply device  1  is mounted starts a preliminary operation of the vehicle by using a remote controller or the like that can instruct the vehicle to perform a predetermined operation, for example. The preliminary operation is, for example, an operation performed when the ignition switch is off and about to be turned on. The preliminary operation ends when a predetermined condition is satisfied. That the predetermined condition is satisfied may mean, for example, that the voltage value from the temperature detection unit  12 A is greater than the threshold value. In the preliminary operation, as shown in  FIG. 2 , the control unit  12  determines the temperature of the battery unit  10 . First, the control unit  12  determines whether the second condition has been satisfied (step S 1 ). Specifically, the control unit  12  determines whether the voltage value from the temperature detection unit  12 A is the threshold value or less. The threshold value is stored in the ROM of the control unit  12  or the like, for example. Also, if it is determined that the voltage value from the temperature detection unit  12 A is greater than the threshold value (step S 1 : No), the control unit  12  ends the processing and repeats the control shown in the flowchart of  FIG. 2 . 
     If it is determined that the voltage value from the temperature detection unit  12 A is the threshold value or less (step S 1 : Yes) (i.e., if the second condition is satisfied), the control unit  12  advances to step S 2  and causes the voltage conversion unit  11  to perform the temperature raising operation. In this manner, the temperature of the conversion target portion  10 B, to which one converter  11 A or  11 B that performs the discharging operation is connected, is raised by the conversion target portion  10 B discharging. Also, the temperature of the conversion target portion  10 B, to which the other converter  11 A or  11 B that performs the charging operation is connected, is raised by the conversion target portion  10 B being charged. At this time, the third conductive paths  31 A and  31 B are electrically connected to the load-side conductive path  53  via the switch elements  52 . In this manner, the third conductive paths  31 A and  31 B of the converters  11 A and  11 B are electrically connected to each other, and power can be exchanged between the converters  11 A and  11 B. Also, a switch (not shown) is provided between a point Pa on the load-side conductive path  53  and the load  51  such that power is not supplied to the load  51  due to this switch being opened in the temperature raising operation. 
     Next, the control unit  12  advances to step S 3  and determines whether the second condition has been satisfied. Specifically, the control unit  12  determines whether the voltage value from the temperature detection unit  12 A is the threshold value or less. If it is determined that the voltage value from the temperature detection unit  12 A is a threshold or less (step S 3 : Yes), the control unit  12  advances to step S 2 . Also, if it is determined that the voltage value from the temperature detection unit  12 A is greater than the threshold value (step S 3 : No), the control unit  12  ends the processing and temperature raising operation, and repeats the control shown in the flowchart of  FIG. 2 . 
     When the control unit  12  causes the voltage conversion unit  11  to perform the temperature raising operation, the control unit  12  causes at least two or more of the plurality of converters  11 A and  11 B to perform an operation for alternately repeating the charging operation and discharging operation. In the first embodiment, when the voltage conversion unit  11  performs the temperature raising operation, the two converters  11 A and  11 B complementarily and alternately repeat the charging operation and the discharging operation. Specifically, when the converter  11 A performs the discharging operation, the converter  11 B performs the charging operation, and when the converter  11 B performs the discharging operation, the converter  11 A performs the charging operation. These operations are alternately repeated. 
     More specifically, first, the switch elements  52  are closed, and the third conductive paths  31 A and  31 B are electrically connected to each other via the load-side conductive path  53 . At this time, the switch (not shown) between the point Pa on the load-side conductive path  53  and the load  51  is opened such that power is not supplied to the load  51 . Then, in the first period, the converter  11 A performs the discharging operation for stepping up or down the potential difference between the first conductive path  30 A and the second conductive path  30 B as the input voltage and applying the output voltage to the third conductive path  31 A. Then, based on the output voltage of the third conductive path  31 B, the converter  11 B generates a predetermined potential difference between the first conductive path  30 C and the second conductive path  30 D and output the potential difference as the output voltage to charge the conversion target portion  10 B. 
     Then, in the second period, the converter  11 B performs the discharging operation for stepping up or down the potential difference between the first conductive path  30 C and the second conductive path  30 D as the input voltage and applying the output voltage to the third conductive path  31 B. Then, based on the output voltage of the third conductive path  31 A, the converter  11 A generates a predetermined potential difference between the first conductive path  30 A and the second conductive path  30 B and outputs the potential difference as the output voltage to charge the conversion target portion  10 B. Note that, the first period and the second period are set so as to not overlap with each other. 
     Due to the control unit  12  causing the converters  11 A and  11 B to alternately repeat the charging operation and the discharging operation, the temperature raising operation can be continued without the battery unit  10  being overcharged or overdischarged. By repeatedly executing the flowchart shown in  FIG. 2 , the control unit  12  periodically compares the voltage value indicating the temperature of the battery unit  10  and the threshold value. If it is determined that the voltage value indicating the temperature of the battery unit  10  is greater than the threshold value (i.e., the second condition is not satisfied), the control unit  12  ends the temperature raising operation performed by the voltage conversion unit  11 . At this time, since a predetermined condition is satisfied, the preliminary operation ends. 
     After the preliminary operation ends, the ignition switch is turned on. Accordingly, the first condition is satisfied. Then, the converters  11 A and  11 B are controlled by the control unit  12  to perform the discharging operation for stepping up or down the potential difference between the first conductive paths  30 A and  30 C and the second conductive paths  30 B and  30 D as the input voltage and applying the output voltage to the third conductive paths  31 A and  31 B. Also, when the first condition is satisfied in the discharging operation, the switch (not shown) is closed, and power is supplied from the load-side conductive path  53  to the load  51 . 
     Next, the effect of this configuration will be illustrated. 
     An in-vehicle backup power supply device  1  according to the present disclosure includes; a battery unit  10  in which a plurality of unit batteries  10 A are connected in series, a voltage conversion unit  11  provided with a plurality of converters  11 A and  11 B that step up or down a voltage that is input and output the resultant voltage, and a control unit  12  configured to control the voltage conversion unit  11 . The in-vehicle backup power supply device  1  further includes a first circuit unit  30  constituting a power path between the voltage conversion unit  11  and the battery unit  10 , and a second circuit unit  31  constituting a power path between the voltage conversion unit  11  and a load  51 . The battery unit  10  is provided with a plurality of conversion target portions  10 B. A conversion target portion  10 B is constituted by the unit battery  10 A or a plurality of the unit batteries  10 A connected in series. The first circuit unit  30  is provided with a plurality of first conductive paths  30 A and  30 C and a plurality of second conductive paths  30 B and  30 D. The plurality of first conductive paths  30 A and  30 C are conductive paths that connect the highest potential electrodes of the conversion target portions  10 B and the respective converters  11 A and  11 B. The plurality of second conductive paths  30 B and  30 D are conductive paths that connect the lowest potential electrodes of the respective conversion target portions  10 B and the respective converters  11 A. The second circuit unit  31  is provided with a plurality of third conductive paths  31 A and  31 B that are conductive paths arranged between the converters  11 A and the conductive paths on the load  51  side. When the first condition is satisfied, the control unit  12  causes the plurality of converters  11 A and  11 B to perform a discharging operation for stepping up or down a potential difference between the first conductive path  30 A and  30 C and the second conductive path  30 B and  30 D as an input voltage and applying an output voltage to the third conductive path  31 A and  31 B. Also, when the second condition is satisfied, the control unit  12  causes one converter  11 A or  11 B to perform the discharging operation. In addition to this, the control unit  12  causes the other converter  11 A or  11 B to perform a charging operation for stepping up or down a voltage that is applied to the third conductive path  31 A and  31 B as an input voltage and applying the output voltage between the first conductive path  30 A and  30 C and the second conductive path  30 B and  30 D. 
     In this manner, the in-vehicle backup power supply device  1  causes the one converter  11 A or  11 B to perform the discharging operation from the battery unit  10 . In addition to this, the in-vehicle backup power supply device  1  can raise the temperature of battery unit  10  by causing the other converter  11 A or  11 B to perform the charging operation on the battery unit  10 . In other words, with the in-vehicle backup power supply device  1 , it is possible to raise the temperature of a battery unit  10  more effectively with a simpler configuration without providing a dedicated configuration for raising the temperature of the battery unit  10 . 
     When the second condition is satisfied, the control unit  12  of the in-vehicle backup power supply device  1  according to the present disclosure causes the plurality of converters  11 A and  11 B to alternately repeat the charging operation and the discharging operation. 
     With this configuration, a situation in which the converters  11 A and  11 B perform only one of the charging operation or the discharging operation can be prevented. For this reason, it is possible to avoid a case in which the unit batteries  10 A are overcharged or overdischarged, and the converters  11 A and  11 B can continuously perform both the charging operation and discharging operation. Accordingly, the in-vehicle backup power supply device  1  can favorably raise the temperature of the battery unit  10 . 
     Second Embodiment 
     Next, an in-vehicle backup power supply device  2  (hereinafter referred to as “power supply device  2 ”) according to a second embodiment will be described with reference to  FIGS. 3 and 4 . The power supply device  2  is different from that of the first embodiment in that the converters  111 A,  111 B,  111 C,  111 D,  111 E, and  111 F (hereinafter also referred to as “converters  111 A to  111 F”) are provided in correspondence with the respective unit batteries  10 A. The same constituent elements are given the same reference numerals and the description of their structure, operation, and effect will be omitted. 
     The battery unit  110  of the power supply device  2  according to the second embodiment is formed by the plurality of unit batteries  10 A connected in series. In the battery unit  110 , the plurality of unit batteries  10 A are arranged side by side along a predetermined direction. 
     The battery unit  110  is provided with a plurality of temperature detection units  12 A,  12 B, and  12 C. Specifically, the temperature detection unit  12 A is arranged in a predetermined direction in which the unit batteries  10 A are arranged, in contact with the surface portion of a central portion  10 D of the battery unit  110  or in the vicinity of the surface portion of a central portion  10 D without contact. The temperature detection unit  12 B is arranged in contact with the surface portion of one end  10 C or in the vicinity of the surface portion of the one end  10 C without contact. The temperature detection unit  12 C is arranged in contact with the surface portion of the other end  10 C or in the vicinity of the surface portion of the other end  10 C without contact. 
     The voltage conversion unit  111  includes the converters  111 A to  111 F. The converters  111 A to  111 F are provided in correspondence with the respective unit batteries  10 A. The converters  111 A to  111 F are electrically connected to the respective unit batteries  10 A via the first circuit unit  130 . The first circuit unit  130  is provided with first conductive paths  130 A,  130 C,  130 E,  130 G,  130 J, and  130 L (hereinafter also referred to as “first conductive paths  130 A to  130 L”) and second conductive paths  130 B,  130 D,  130 F,  130 H,  130 K, and  130 M (hereinafter also referred to as “second conductive paths  130 B to  130 M”). The first conductive paths  130 A to  130 L respectively and electrically connects the high potential electrode of the unit batteries  10 A to the converters  111 A to  111 F that correspond to the unit batteries  10 A. The second conductive path  130 B to  130 M electrically connect the low potential electrodes of the unit batteries  10 A and the converters  111 A to  111 F that correspond to the respective unit batteries  10 A. 
     An electrode between two unit batteries  10 A connected in series is electrically connected to the second conductive path that is connected to the converter that corresponds to the high potential unit battery  10 A, and to the first conductive path that is connected to the converter that corresponds to the low potential unit battery  10 A. The second conductive path  130 B connected to the converter  111 A that corresponds to the high potential unit battery  10 A and the first conductive path  130 C connected to the converter  111 B that corresponds to the low potential unit battery  10 A are electrically connected to the electrode between the unit batteries  10 A for example. The potential difference between the first conductive path and the second conductive path is input to the converters as the input voltage. The potential difference between the first conductive path  130 A and the second conductive path  130 B is input to the converter  111 A as the input voltage, for example. 
     The converters  111 A to  111 F are electrically connected to the switch elements  52  for switching conduction/non-conduction to the load  51  via the third conductive paths  131 A,  131 B,  131 C,  131 D,  131 E, and  131 F (hereinafter also referred to as “third conductive paths  131 A to  131 F”) included in the second circuit unit  131 . 
     Next, the operation of the power supply device  2  will be described. 
     First, the user of the vehicle in which the power supply device  2  is mounted starts a preliminary operation of the vehicle by using a remote controller or the like that can instruct the vehicle to operate, for example. As shown in  FIG. 4 , in the preliminary operation, the control unit  12  determines the temperature of the battery unit  110 . First, the control unit  12  determines whether the second condition is satisfied (step S 11 ). Specifically, the control unit  12  determines whether the voltage values indicating the temperatures of the battery unit  110  that are input from the temperature detection units  12 A,  12 B, and  12 C (hereinafter also referred to as “voltage values from the temperature detection units  12 A,  12 B, and  12 C”) are a threshold value or less. 
     If it is determined that at least one of the voltage values from temperature detection units  12 A,  12 B, or  12 C is the threshold value or less (step S 11 : Yes) (i.e., if the second condition is satisfied), the control unit  12  advances to step S 12  and causes the voltage conversion unit  111  to perform the temperature raising operation. At this time, the third conductive paths  131 A to  131 F are electrically connected to the load-side conductive path  53  via the switch elements  52 . In this manner, the third conductive paths  131 A to  131 F of the converters  111 A to  111 F are electrically connected to each other, and power can be exchanged between the converters  111 A to  111 F. Also, a switch (not shown) is provided between the load-side conductive path  53  and the load  51  such that power is not supplied from the load-side conductive path  53  to the load  51  in the temperature raising operation. 
     When the control unit  12  causes the voltage conversion unit  111  to perform the temperature raising operation, the control unit  12  causes the plurality of converters  111 A to  111 F to perform an operation for alternately repeating the charging operation and discharging operation. 
     For example, first, the switch elements  52  are closed, and the third conductive paths  131 A to  131 F are electrically connected to each other via the load-side conductive path  53 . Then, the switch (not shown) between the load-side conductive path  53  and the load  51  is opened such that power is not supplied to the load  51 . Then, in the first period, the converters  111 A,  111 B and  111 C perform the discharging operation for stepping up or down the potential difference between the first conductive paths  130 A,  130 C, and  130 E and the second conductive paths  130 B,  130 D, and  130 F as the input voltage and applying the output voltage to the third conductive paths  131 A,  131 B, and  131 C. In addition to this, based on the output voltage of the third conductive paths  131 D,  131 E, and  131 F, the converters  111 D,  111 E, and  111 F generate a predetermined potential difference between the first conductive paths  131 G,  131 J, and  131 L and the second conductive paths  130 H,  130 K, and  130 M and output the potential difference as the output voltage. In this manner, the unit batteries  10 A that correspond to the converters  111 D,  111 E, and  111 F are charged. 
     In the second period, the converters  111 D,  111 E, and  111 F perform the discharging operation for stepping up or down the potential difference between the first conductive paths  130 G,  130 J, and  130 L and the second conductive paths  130 H,  130 K, and  130 M as the input voltage and applies the output voltage to the third conductive paths  131 D,  131 E, and  131 F. In addition to this, based on this output voltage of the third conductive paths  131 A,  131 B, and  131 C, the converters  111 A,  111 B, and  111 C generate a predetermined potential difference between the first conductive paths  130 A,  130 C, and  130 E and the second conductive paths  130 B,  130 D, and  130 F and output the potential difference as the output voltage. In this manner, the unit batteries  10 A that correspond to the converters  111 A,  111 B, and  111 C are charged. Note that, the first period and the second period are set so as to not overlap with each other. 
     Here, the operation in which the charging operation and the discharging operation of the converter  111 A,  111 B, and  111 C and the converter  111 D,  111 E, and  111 F are alternately repeated is performed, but the combination of the converters that alternately repeats the charging operation and the discharging operation is not limited to this. For example, a configuration is also possible in which the converters  111 A, and  111 B,  111 C,  111 D,  111 E, and  111 F are combined with each other, or the converter  111 A, and  11 B, and  111 C,  111 D,  111 E, and  111 F are combined with each other, and the like. 
     Next, the control unit  12  advances to step S 13  and determines whether a predetermined temperature condition has been satisfied. Specifically, the control unit  12  may compare a voltage value at a central portion with voltage values at the two end portions. The voltage value at the central portion is a voltage value from the temperature detection unit  12 A arranged in the central portion  10 D of the battery unit  110  in a predetermined direction in which the unit batteries  10 A are arranged when the control unit  12  causes the voltage conversion unit  111  to perform the temperature raising operation. The voltage values at the two end portions are voltage values from the temperature detection units  12 B and  12 C arranged at the two ends  10 C of the battery unit  110 . 
     When performing the temperature raising operation, since, in the predetermined direction in which the unit batteries  10 A are arranged, the contact area of the central portion  10 D with ambient air is smaller than that of the two ends  10 C of the battery unit  110 , the temperature of the central portion  10 D is more likely to increase. When the control unit  12  causes the voltage conversion unit  111  to perform the temperature raising operation, for example, the control unit  12  compares the voltage value at the central portion with the voltage values at the two end portions and checks the difference between the central voltage value and the voltage values at the two end portions. If the predetermined temperature condition according to which the voltage value at the central portion is greater than the voltage values at the two end portions and the difference between these values are greater than a predetermined threshold is satisfied (step S 13 ; Yes), the control unit  12  advances to step S 14  to perform a suppression control. The suppression control is a control for setting the output power to the third conductive path  131 B,  131 C,  131 D, and  131 E in the discharging operation performed by the converters  111 B,  111 C,  111 D, and  111 E that correspond to the unit batteries  10 A in the central portion  10 D, smaller than the output power in the discharging operation performed by the converters  111 A and  111 F that correspond to the unit batteries  10 A at the two ends  10 C. 
     If the voltage value at the central portion is not greater than the voltage values at the two end portions, or the difference between the voltage value at the central portion and the voltage values at the two end portions is a predetermined threshold or less (step S 13 : No) (i.e., a predetermined temperature condition is no longer satisfied), the control unit  12  stops the suppression control (step S 15 ). 
     Also, if the predetermined temperature condition is satisfied, then the control unit  12  may perform the suppression control as below in accordance with the difference between the voltage value at the central portion and the voltage values at the two end portions. For example, if the predetermined temperature condition is satisfied and the difference between the voltage value at the central portion and the voltage values at the two end portions increases, the control unit  12  may decrease the output power to be output to the third conductive paths  131 B to  131 E in the discharging operation performed by the converters  111 B to  111 E that correspond to the unit batteries  10 A in the central portion  10 D. Also, if a predetermined temperature condition is satisfied and the difference between the voltage value at the central portion and the voltage values at the two end portions decreases, the control unit  12  may increase the output power to be output to the third conductive paths  131 B to  131 E in the discharging operation performed by the converters  111 B to  111 E that correspond to the unit batteries  10 A of the central portion  10 D. 
     Next, the control unit  12  advances to step S 16  and determines whether a second condition is satisfied. Specifically, if it is determined that all the voltage values from the temperature detection units  12 A,  12 B, and  12 C are greater than the threshold value (step S 16 : No) (i.e., the second condition is not satisfied), the control unit  12  ends the temperature raising operation performed by the voltage conversion unit  111 . At this time, the preliminary operation ends. Also, if it is determined at least one of the voltage values from the temperature detection units  12 A,  12 B, or  12 C is the threshold value or less (step S 16 : Yes) (i.e., the second condition is satisfied), the control unit  12  advances to step S 12 . 
     After ending the preliminary operation, the control unit  12  turns on the ignition switch. Accordingly, the first condition is satisfied. The control unit  12  causes the converters  111 A to  111 F to perform the discharging operation for stepping up or down the potential difference between the first conductive paths  130 A to  130 L and the second conductive paths  130 B to  130 M as the input voltage and applying the output voltage to the third conductive paths  131 A to  131 F. Also, when the first condition is satisfied in the discharging operation, the switch (not shown) is closed, and thus power is supplied from the load-side conductive path  53  to the load  51 . 
     Next, the effect of this configuration will be illustrated. 
     In the battery unit  110  of the in-vehicle backup power supply device  2  according to the present disclosure, the plurality of unit batteries  10 A are arranged side by side along a predetermined direction. The control unit  12  sets the output voltage to be output to the third conductive paths  131 B to  131 E in the discharging operation performed by the converters  111 B to  111 E that correspond to the unit batteries  10 A located at the central portion  10 D in a predetermined direction of the battery unit  110 , smaller than the output voltage to be output by the converters  111 A and  111 F that correspond to the unit batteries  10 A located at the two ends  10 C in a predetermined direction of the battery unit  110 . 
     With this configuration, it is possible to avoid a case in which the temperature of the central portion  10 D of the battery unit  110  excessively increases and suppress a case in which a difference in temperature occurs between the two ends  10 C and the central portion  10 D of the battery unit  110 . 
     In the in-vehicle backup power supply device  2  according to the present disclosure, the control unit  12  performs the suppression control in the case where the temperature of the central portion  10 D is higher than the temperature at the outside thereof. 
     With this configuration, it is possible to perform the suppression control only in the case in which there is a difference in temperature between the two ends  10 C and the central portion  10 D of the battery unit  110 . 
     Third Embodiment 
     Next, an in-vehicle backup power supply device  3  (hereinafter also referred to as “power supply device  3 ”) according to a third embodiment will be described with reference to  FIG. 5 . The power supply device  3  is different from the first embodiment in that no temperature detection unit is provided. The same constituent elements as the first embodiment are given the same reference numerals, and the description of their structure, operation, and effect will be omitted. 
     First, the user of the vehicle in which the power supply device  3  is mounted starts a preliminary operation of the vehicle by using a remote controller or the like that can instruct the vehicle to perform a predetermined operation, for example. For example, in the preliminary operation, the control unit  12  causes the voltage conversion unit  11  to perform the temperature raising operation. Also, the temperature of the conversion target portion  10 B to which one converter  11 A or  11 B that performs the discharging operation is connected is raised by the conversion target portion  10 B discharging. Also, the temperature of the conversion target portion  10 B to which the other converter  11 A or  11 B that performs the charging operation is connected is raised by the conversion target portion  10 B being charged. At this time, the third conductive paths  31 A and  31 B are electrically connected to the load-side conductive path  53  via the switch elements  52 . In this manner, the third conductive paths  31 A and  31 B of the converters  11 A and  11 B are electrically connected to each other, and power can be exchanged between the converters  11 A and  11 B. Also, a switch (not shown) is provided between the load-side conductive path  53  and the load  51  such that power is not supplied to the load  51  due to this switch being opened in the temperature raising operation. 
     Next, the control unit  12  determines whether a predetermined time has elapsed since the temperature raising operation started. If it is determined that a predetermined time has not elapsed since the temperature raising operation started, the control unit  12  continues the temperature raising operation. If it is determined that a predetermined time has elapsed since the temperature raising operation started, the control unit  12  ends the temperature raising operation. At this time, since a predetermined condition is satisfied, the preliminary operation ends. 
     The operation of the converters  11 A and  11 B of the voltage conversion unit  11  in the temperature raising operation in the third embodiment is similar to that of the first embodiment. In the power supply device  3 , due to the control unit  12  causing the converters  11 A and  11 B to alternately repeat the charging operation and the discharging operation, the temperature raising operation can be continued without the battery unit  10  being overcharged or overdischarged. 
     After ending the preliminary operation, the control unit turns on the ignition switch. Accordingly, the first condition is satisfied. The control unit  12  causes the converters  11 A and  11 B to perform the discharging operation for stepping up or down the potential difference between the first conductive paths  30 A and  30 C and the second conductive paths  30 B and  30 D as the input voltage and applying the output voltage to the third conductive paths  31 A and  31 B. Also, when the first condition is satisfied in the discharging operation, the switch (not shown) is closed, and thus power is supplied from the load-side conductive path  53  to the load  51 . 
     Other Embodiments 
     The configuration is not limited to the embodiments described using the above description and the drawings, and for example, the following embodiments are also encompassed within the technical scope of the present invention. 
     Although in the second embodiment, a configuration of the converter  111 A that corresponds to the unit battery  10 A is illustrated, a configuration is also possible in which, in the battery unit in which a plurality of the conversion target portions formed by a plurality of unit batteries are arranged in series, the operation of the converters that correspond to the respective conversion target portions may be controlled as in the second embodiment. 
     In the second embodiment, based on the voltage value from a plurality of temperature detection units  12 A, the output voltage from the converters  111 B,  111 C,  111 D, and  111 E in the central portion  10 D to the third conductive paths  131 B,  131 C,  131 D, and  131 E is suppressed. On the other hand, a configuration is also possible in which the output voltage to the third conductive path from the converters located in the center of the central portion is set smaller than the output voltage to the third conductive path from the converters located at the outside of the central portion. 
     If there are three or more converters, in the temperature raising operation, a converter that does not perform any operation may also be present, in addition to the converter that performs the discharging operation and the converter that performs the charging operation. 
     The embodiments disclosed herein should be construed to be exemplary in all aspects, and not be restrictive. The present invention is not limited to the embodiments disclosed herein, but defined in the claims, and intended to include all modifications within the meaning and the scope equivalent thereof.