Patent Publication Number: US-2023155411-A1

Title: Power supply apparatus and inspection method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2021-185688 filed on Nov. 15, 2021. 
     TECHNICAL FIELD 
     The disclosed embodiment relates to a power supply apparatus and an inspection method. 
     BACKGROUND ART 
     A battery control device that backs up a first power supply serving as a main battery with a second power supply serving as a sub-battery when an abnormality occurs in the first power supply is known (see, for example, JP-A-2020-156228). Such a battery control device needs to inspect whether the backup performed by the second power supply is possible, that is, whether electric power can be supplied from the second power supply to a load to which the electric power is to be supplied. 
     SUMMARY OF INVENTION 
     However, when it is inspected whether the backup can be performed by the second power supply, if a discharge amount of the second power supply is large, there is a problem that deterioration of the second power supply progresses. 
     An aspect of the embodiment has been made in view of the above circumstances, and an object thereof is to provide a power supply apparatus and an inspection method capable of inspecting whether the backup performed by the second power supply is possible while preventing deterioration of the second power supply. 
     A power supply apparatus according to an aspect of the embodiment includes a first system, a second system, a connection unit (a connector), a second system switch, and an inspection unit (at least one processor). The first system supplies electric power of a first power supply to a first load. The second system supplies electric power of a second power supply to a second load. The connection unit can connect and disconnect the first system and the second system. The second system switch can connect the second power supply to the second system. The inspection unit performs inspection as to whether electric power can be supplied from the second power supply to the second load. When a voltage of the second power supply is not equal to a voltage of the first power supply, the inspection unit controls the first power supply so that the voltage of the first power supply becomes equal to the voltage of the second power supply, and then conducts the second system switch to perform the inspection by stepping down or stepping up the voltage of the first power supply. 
     The power supply apparatus and the inspection method according to one aspect of the embodiment have an effect of being capable of inspecting whether backup performed by the second power supply is possible while preventing deterioration of the second power supply. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is an illustrative diagram illustrating a configuration example of a power supply apparatus according to an embodiment. 
         FIG.  2    is an illustrative diagram illustrating an operation example of the power supply apparatus according to the embodiment. 
         FIG.  3    is an illustrative diagram illustrating an operation example of the power supply apparatus according to the embodiment. 
         FIG.  4    is an illustrative diagram illustrating an operation example of the power supply apparatus according to the embodiment. 
         FIG.  5    is an illustrative diagram illustrating an operation example of the power supply apparatus according to the embodiment. 
         FIG.  6    is an illustrative diagram illustrating an operation example of the power supply apparatus according to a comparative example. 
         FIG.  7    is an illustrative diagram of an inspection method according to the embodiment. 
         FIG.  8    is an illustrative diagram illustrating an operation example of the power supply apparatus according to the embodiment. 
         FIG.  9    is an illustrative diagram illustrating an operation example of the power supply apparatus according to the embodiment. 
         FIG.  10    is an illustrative diagram of an inspection method according to the embodiment. 
         FIG.  11    is an illustrative diagram of an inspection method according to the embodiment. 
         FIG.  12    is an illustrative diagram of an inspection method according to the embodiment. 
         FIG.  13    is a flowchart illustrating an example of a process executed by an inspection unit according to the embodiment. 
         FIG.  14    is an illustrative diagram of an inspection method according to a modification of the embodiment. 
         FIG.  15    is a flowchart illustrating an example of a process executed by an inspection unit according to the modification of the embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, an embodiment of a power supply apparatus and a power supply control method will be described in detail with reference to the accompanying drawings. The present invention is not limited to the following embodiments. Hereinafter, a power supply apparatus mounted on a vehicle that has an automated driving function and supplying electric power to a load will be described as an example, but the power supply apparatus according to the embodiment may be mounted on a vehicle that does not have the automated driving function. 
     The power supply apparatus according to the embodiment is mounted on an electric vehicle, a hybrid vehicle, or an engine vehicle driven by an internal combustion engine. The power supply apparatus according to the embodiment includes a first power supply and a second power supply. When a power supply failure occurs in the first power supply, the power supply apparatus may be mounted on any apparatus that backs up the first power supply by the second power supply and performs FOP (fail operation). 
     [1. Configuration of Power Supply Apparatus] 
       FIG.  1    is an illustrative diagram illustrating a configuration example of the power supply apparatus according to the embodiment. As illustrated in  FIG.  1   , a power supply apparatus  1  according to the embodiment is connected to a first power supply  10  and an automated driving control device  100 . Further, the power supply apparatus  1  is connected to a first FOP load  101 , a second FOP load  102 , a third FOP load  103 , and a general load  104 , which are examples of a first load, and is connected to the first FOP load  101 , the second FOP load  102 , and the third FOP load  103 , which are examples of a second load. 
     The power supply apparatus  1  includes a first system  110  and a second system  120 . The first system  110  supplies electric power of the first power supply  10  to the first FOP load  101 , the second FOP load  102 , the third FOP load  103 , and the general load  104 , which are examples of the first load, via a first connection device  50 . 
     The first connection device  50  includes switches  51 ,  52 ,  53 ,  54 . The switch  51  can connect and disconnect the first system  110  and the first FOP load  101 . The switch  52  can connect and disconnect the first system  110  and the second FOP load  102 . The switch  53  can connect and disconnect the first system  110  and the third FOP load  103 . The switch  54  can connect and disconnect the first system  110  and the general load  104 . 
     The second system  120  supplies electric power of the second power supply  20 , which will be described later, to the first FOP load  101 , the second FOP load  102 , and the third FOP load  103 , which are examples of the second load, via a second connection device  60 . The second connection device  60  includes switches  61 ,  62 ,  63 . The switch  61  can connect and disconnect the second system  120  and the first FOP load  101 . The switch  62  can connect and disconnect the second system  120  and the second FOP load  102 . The switch  63  can connect and disconnect the second system  120  and the third FOP load  103 . 
     The first FOP load  101 , the second FOP load  102 , and the third FOP load  103  are loads for automated driving. For example, the first FOP load  101 , the second FOP load  102 , and the third FOP load  103  may be a steering motor, an electric brake device, an in-vehicle camera, a radar, and the like that operate during the automated driving. The general load  104  includes, for example, a display, an air conditioner, an audio, a video, and various kinds of lights. 
     The first FOP load  101 , the second FOP load  102 , the third FOP load  103 , and the general load  104  are operated by electric power supplied from the power supply apparatus  1 . The automated driving control device  100  is a device that controls automated driving of the vehicle by operating the first FOP load  101 , the second FOP load  102 , and the third FOP load  103 . 
     When the power supply apparatus  1  is mounted on the engine vehicle, the first power supply  10  includes a generator  11  and a lead battery (hereinafter, referred to as a “PbB  12 ”). A battery of the first power supply  10  may be any secondary battery other than the PbB  12 . 
     The generator  11  is, for example, an alternator that converts kinetic energy of a traveling vehicle into electricity to generate electricity. The generator  11  charges the PbB  12  and the second power supply  20  with the generated electric power, and supplies the electric power to the first FOP load  101 , the second FOP load  102 , the third FOP load  103 , and the general load  104 . 
     When the power supply apparatus  1  is mounted on the electric vehicle or the hybrid vehicle, the first power supply  10  includes a DC/DC converter (hereinafter, referred to as “DC/DC”) and the PbB  12 . In this case, the DC/DC is connected to a generator and a high-voltage battery having a voltage higher than that of the PbB  12 , steps down the voltages of the generator and the high-voltage battery, and outputs the stepped-down voltages to the first system  110 . The generator is, for example, the alternator. The high-voltage battery is, for example, a battery for driving a vehicle mounted on the electric vehicle or the hybrid vehicle. 
     The power supply apparatus  1  includes the second power supply  20 , a connection unit  41 , a second system switch  42 , a DC/DC converter (hereinafter referred to as “DC/DC  43 ”), a control unit  3 , a first voltage sensor  7 , a second voltage sensor  70 , and a current sensor  8 . The second power supply  20  is a backup power supply for a case where the electric power cannot be supplied by the first power supply  10 . 
     The second power supply  20  includes a lithium ion battery (hereinafter, referred to as a “LiB  21 ”). A battery of the second power supply  20  may be any secondary battery other than the LiB  21 . The second power supply  20  includes a temperature sensor, a voltage sensor, and a current sensor (not shown). The temperature sensor detects a temperature of the LiB  21  and outputs the temperature to the control unit  3 . The voltage sensor detects a voltage of the LiB  21  and outputs the voltage to the control unit  3 . The current sensor detects a current output from the LiB  21  and a current input to the LiB  21 , and outputs the detected currents to the control unit  3 . 
     The connection unit  41  is a switch provided in an inter-system line  130  that connects the first system  110  and the second system  120 , and capable of connecting and disconnecting the first system  110  and the second system  120 . The second system switch  42  is a switch capable of connecting and disconnecting the second power supply  20  to and from the second system  120 . The DC/DC  43  is connected in parallel with the second system switch  42 , and adjusts the voltage output from the LiB  21  and a voltage input to the LiB  21 . 
     The first voltage sensor  7  is provided in the first system  110 , detects a voltage of the first system  110 , and outputs a detection result to the control unit  3 . The second voltage sensor  70  is provided in the second system  120 , detects a voltage of the second system  120 , and outputs a detection result to the control unit  3 . 
     Specifically, the second voltage sensor  70  includes voltage sensors  71 ,  72 ,  73 . The voltage sensor  71  detects a voltage applied from the second system  120  to the first FOP load  101 , and outputs a detection result to the control unit  3 . The voltage sensor  72  detects a voltage applied from the second system  120  to the second FOP load  102 , and outputs a detection result to the control unit  3 . 
     The voltage sensor  73  detects a voltage applied from the second system  120  to the third FOP load  103 , and outputs a detection result to the control unit  3 . The current sensor  8  detects a current flowing through the second system  120 , and outputs a detection result to the control unit  3 . 
     The voltage sensor  70  may be a single voltage sensor instead of being provided with the voltage sensors for the respective first to third FOP loads  101  to  103 . In this case, the voltage sensor  70  may be provided between a point at which the second system  120  branches to the first to third FOP loads  101  to  103  and a connection point between the second system  120  and the inter-system line  130 . 
     The control unit  3  includes a microcomputer having a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and the like, and various circuits. The control unit  3  may be configured with hardware such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA). 
     The control unit  3  includes an inspection unit  31  that functions by the CPU executing a program stored in the ROM using the RAM as a work area, and controls operations of the power supply apparatus  1 . When the power supply apparatus  1  is in normal operation, the control unit  3  brings the switches  51 ,  52 ,  53 ,  54 ,  61 ,  62 ,  63  into a conductive state. 
     The control unit  3  detects a ground fault of the first system  110  or the second system  120  based on the detection results received from the first voltage sensor  7  and the second voltage sensor  70 . A specific example of a method for detecting the ground fault by the control unit  3  will be described later. 
     When the ground fault of the first system  110  or the second system  120  is detected, the control unit  3  notifies the automated driving control device  100  of the fact. When the ground fault of the first system  110  or the second system  120  is detected, the control unit  3  may notify the automated driving control device  100  of a fact that the automated driving is impossible. When the ground fault of the first system  110  or the second system  120  is not detected, the control unit  3  may notify the automated driving control device  100  of a fact that the automated driving is possible. 
     When the ground fault occurs in the first system  110 , the control unit  3  disconnects the connection unit  41 , conducts the second system switch  42 , and supplies electric power from the second power supply  20  to the first FOP load  101 , the second FOP load  102 , and the third FOP load  103 . 
     When the ground fault occurs in the second system  120 , the control unit  3  disconnects the connection unit  41 , and supplies electric power from the first power supply  10  to the first FOP load  101 , the second FOP load  102 , the third FOP load  103 , and the general load  104  in a state where the second system switch  42  is disconnected. 
     Accordingly, even if one of the systems has a ground fault during the automated driving, the power supply apparatus  1  can use the other system, cause the vehicle to perform limp-home traveling to a safe place by the automated driving control device  100 , and stop the vehicle. 
     As described above, when an abnormality occurs in the first power supply  10 , the control unit  3  performs backup by the second power supply  20 , but, for example, when the second system switch  42  is fixed to an off-state, the backup cannot be performed normally. 
     Therefore, the control unit  3  needs to determine whether the backup can be performed by the second power supply  20  (hereinafter, may be referred to as “backup availability determination”). Here, for example, immediately after an ignition switch (IG) is turned on or during a stop of a vehicle waiting for a traffic light, a general control unit turns on the second system switch  42  to supply electric power from the second power supply  20  to the second system  120 , and performs the backup availability determination. 
     Then, the control unit determines that the backup can be performed when electric power is normally supplied from the second power supply  20  to the second system  120 , and determines that the backup cannot be performed when electric power is not supplied from the second power supply  20  to the second system  120 . However, when it is inspected whether the backup can be performed by the second power supply  20 , if a discharge amount of the second power supply  20  is large, there is a problem that deterioration of the LiB  21  in the second power supply  20  progresses. 
     Therefore, the control unit  3  according to the embodiment includes the inspection unit  31  that inspects whether electric power can be supplied from the second power supply  20  to the first FOP load  101 , the second FOP load  102 , and the third FOP load  103 , which are examples of the second load, and prevents the deterioration of the second power supply  20 . 
     When a voltage of the first power supply  10  is not equal to a voltage of the second power supply  20 , the inspection unit  31  controls the first power supply  10  so that the voltage of the first power supply  10  becomes equal to the voltage of the second power supply  20 , and then conducts the second system switch  42  to perform the inspection by stepping down or stepping up the voltage of the first power supply  10 . At this time, the inspection unit  31  steps up or steps down the voltage of the first power supply  10  by controlling the generator  11  of the first power supply  10 . 
     When a minimum necessary current discharged from the second power supply  20  is detected by the current sensor  8  immediately after the voltage of the first power supply  10  equal to the voltage of the second power supply  20  is stepped down, the inspection unit  31  determines that the second system switch  42  is not fixed to the off-state and the backup can be performed. 
     Further, when the current sensor  8  does not detect a current discharged from the second power supply  20  immediately after the voltage of the first power supply  10  equal to the voltage of the second power supply  20  is stepped down, the inspection unit  31  can determine that the second system switch  42  is fixed to the off-state and the backup cannot be performed. 
     In this manner, since the inspection unit  31  performs the inspection of the backup availability determination by discharging the minimum necessary current from the second power supply  20 , it is possible to perform the inspection as to whether electric power can be supplied from the second power supply  20  to the second system  120  while preventing the deterioration of the second power supply  20 . 
     In addition, when a minimum necessary current charged to the second power supply  20  is detected by the current sensor  8  immediately after the voltage of the first power supply  10  equal to the voltage of the second power supply  20  is stepped up, the inspection unit  31  determines that the second system switch  42  is not fixed to the off-state and the backup can be performed. 
     Further, when the current sensor  8  does not a current charged to the second power supply  20  immediately after the voltage of the first power supply  10  equal to the voltage of the second power supply  20  is stepped up, the inspection unit  31  determines that the second system switch  42  is fixed to the off-state and the backup cannot be performed. 
     In this manner, since the inspection unit  31  performs the inspection of the backup availability determination by charging the minimum necessary current to the second power supply  20 , it is possible to perform the inspection as to whether electric power can be supplied from the second power supply  20  to the second system  120  while preventing the deterioration of the second power supply  20 . 
     When the voltage of the first power supply  10  is equal to the voltage of the second power supply  20 , the inspection unit  31  steps down or steps up the voltage of the first power supply  10  to inspect whether electric power can be supplied from the second power supply  20  to the second system  120 . 
     Accordingly, the inspection unit  31  can perform the inspection of the backup availability determination by discharging the minimum necessary current from the second power supply  20  or charging the second power supply  20  with the minimum necessary current. Therefore, the inspection unit  31  can perform the inspection as to whether electric power can be supplied from the second power supply  20  to the second system  120  while preventing the deterioration of the second power supply  20 . 
     The generator  11  can step up the voltage of the first power supply  10  to a voltage higher than the voltage of the PbB  12 , but cannot step down the voltage of the first power supply  10  to a voltage lower than the voltage of the PbB  12  even when a power generation operation is stopped. 
     Therefore, when the voltage of the first power supply  10  and the voltage of the second power supply  20  cannot be equal to each other, the inspection unit  31  disconnects the connection unit  41 , conducts the second system switch  42 , and inspects whether electric power can be supplied from the second power supply  20  to the second system  120 . 
     Accordingly, even when the voltage of the first power supply  10  and the voltage of the second power supply  20  cannot be equal to each other, the inspection unit  31  can inspect whether electric power can be supplied from the second power supply  20  to the second system  120 . 
     [2. Normal Operation of Power Supply Apparatus] In normal operation in which no ground fault occurs in the first system  110  and the second system  120 , as illustrated in  FIG.  2   , the control unit  3  conducts all the switches  51 ,  52 ,  53 ,  54  of the first connection device  50  and all the switches  61 ,  62 ,  63  of the second connection device  60 . The control unit  3  conducts the connection unit  41  in the state where the second system switch  42  is disconnected, and supplies electric power from the first power supply  10  to the first FOP load  101 , the second FOP load  102 , the third FOP load  103 , and the general load  104 . At this time, the control unit  3  stops operations of the DC/DC  43 .
 
[3. Operation of Power Supply Apparatus when Ground Fault Occurs]
 
     Next, an operation of the power supply apparatus  1  when a ground fault occurs will be described with reference to  FIGS.  3  to  5   . As illustrated in  FIG.  3   , in the power supply apparatus  1 , for example, when a ground fault  202  occurs in the first system  110 , an overcurrent flows toward a ground fault point, and thus the voltage of the first system  110  detected by the first voltage sensor  7  become equal to or less than a ground fault threshold. 
     In the power supply apparatus  1 , when a ground fault  201  occurs in the second system  120  (for example, the second system  120  connected to the third FOP load  103 ), an overcurrent flows toward a ground fault point. Therefore, the voltage of the second system  120  detected by the second voltage sensor  70  becomes equal to or less than the ground fault threshold. 
     Therefore, when the voltage detected by at least one of the first voltage sensor  7  and the second voltage sensor  70  becomes equal to or less than the ground fault threshold, the control unit  3  detects an abnormality of the power supply, disconnects the connection unit  41 , and conducts the second system switch  42  to be in a pre-disconnected state. At this time, the control unit  3  temporarily determines that a ground fault has occurred in the first system  110  or the second system  120 . 
     Thereafter, after the control unit  3  temporarily determines that the ground fault has occurred in the first system  110  or the second system  120 , when the voltage detected by the second voltage sensor  70  is equal to or less than the ground fault threshold, and the voltage detected by the first voltage sensor  7  returns to a value exceeding the ground fault threshold within a predetermined time, the control unit  3  determines that the ground fault  201  occurs in the second system  120 . 
     Then, as illustrated in  FIG.  4   , the control unit  3  disconnects the second system switch  42 , and disconnects all the switches  61 ,  62 ,  63  of the second connection device  60  to bring the second connection device  60  into a final disconnected state. Then, the control unit  3  supplies electric power from the first power supply  10  to the first FOP load  101 , the second FOP load  102 , the third FOP load  103 , and the general load  104 , and notifies the automated driving control device  100  of the fact. 
     Accordingly, the automated driving control device  100  can operate the first FOP load  101 , the second FOP load  102 , the third FOP load  103 , and the general load  104  by the electric power supplied from the first power supply  10  to cause the vehicle to perform the limp-home traveling to a safe place and stop the vehicle. 
     Further, after the control unit  3  temporarily determines that the ground fault has occurred in the first system  110  or the second system  120 , when the voltage detected by the first voltage sensor  7  is equal to or less than the ground fault threshold for the predetermined time or longer, and the voltage detected by the second voltage sensor  70  returns to a value exceeding the ground fault threshold within the predetermined time, the control unit  3  determines that the ground fault  202  occurs in the first system  110 . 
     Thereafter, as illustrated in  FIG.  5   , the control unit  3  disconnects all the switches  51 ,  52 ,  53 ,  54  of the first connection device  50  to bring the first connection device  50  into the final disconnected state, and supplies electric power from the second power supply  20  to the first FOP load  101 , the second FOP load  102 , and the third FOP load  103 . Then, the control unit  3  notifies the automated driving control device  100  of the fact. 
     Accordingly, the automated driving control device  100  can operate the first FOP load  101 , the second FOP load  102 , and the third FOP load  103  by the electric power supplied from the second power supply  20  to cause the vehicle to perform the limp-home traveling to a safe place and stop the vehicle. 
     Further, in the power supply apparatus  1 , when the first FOP load  101 , the second FOP load  102 , the third FOP load  103 , or the general load  104 , not the ground fault  201  or  202 , temporarily becomes an overload state, the voltages detected by the first voltage sensor  7  and the second voltage sensor  70  may temporarily become equal to or less than the ground fault threshold. 
     In this case, the power supply apparatus  1  disconnects the connection unit  41 , conducts the second system switch  42  to be in a temporary disconnected state, and continuously supplies electric power from the first power supply  10  and the second power supply  20  to the first FOP load  101 , the second FOP load  102 , the third FOP load  103 , and the general load  104 . 
     After it is temporarily determined that the ground fault occurs in the first system  110  or the second system  120 , if the voltages detected by the first voltage sensor  7  and the second voltage sensor  70  both return to values exceeding the ground fault threshold before the predetermined time elapses, the control unit  3  determines that there is no abnormality in the power supplies. Thereafter, in order to return the power supply apparatus  1  to the normal operation illustrated in  FIG.  2   , the control unit  3  disconnects the second system switch  42  and conducts the connection unit  41  again. 
     [4. Inspection of Second System According to Comparative Example] 
     In addition, the power supply apparatus  1  performs operation confirmation of the second system  120  at a timing at which the operation confirmation does not interfere with the automated driving, for example, at the time of activation or at the time of stopping. Here, for example, as illustrated in  FIG.  6   , as an inspection method of the second system  120  according to a comparative example, there is a method of performing inspection by disconnecting the connection unit  41  during the normal operation. 
     In the inspection method according to the comparative example, when a current is detected by the current sensor  8  after the connection unit  41  is disconnected, it can be determined that the second system  120  is normal since electric power is supplied from the second power supply  20  to the second system  120 . In addition, in the inspection method according to the comparative example, when no current is detected by the current sensor  8  after the connection unit  41  is disconnected, it can be determined that an abnormality occurs in the second system  120  since no electric power is supplied from the second power supply  20  to the second system  120 . 
     However, in the inspection method according to the comparative example, since a current corresponding to the voltage of the second power supply  20  flows as an inspection current, the discharge amount inevitably increases. When the discharge amount of the second power supply  20  is large, the deterioration of the second power supply  20  progresses. Therefore, in the inspection method according to the embodiment, whether the backup can be by the second power supply  20  is inspected while preventing the deterioration of the second power supply  20 . 
     [5. Inspection of Second System According to Embodiment] 
     As illustrated in  FIG.  7   , the inspection unit  31  according to the embodiment first detects the voltages of the first power supply  10  and the second power supply  20  at a timing at which the detection does not interfere with the automated driving, such as at the time of activation or at the time of stopping. At this time, the voltage of the first power supply  10  is 16 (V) when the voltage of the generator  11  is 16 (V) and the voltage of the PbB  12  is 13 (V). The voltage of the second power supply  20  is 16 (V) when the voltage of the LiB  21  is 16 (V). 
     When the voltage of the first power supply  10  and the voltage of the second power supply  20  are equal to each other, the inspection unit  31  conducts the second system switch  42 , controls the generator  11 , and performs voltage adjustment to step up or step down the voltage of the first power supply  10 . Thereafter, the inspection unit  31  inspects whether electric power can be supplied from the second power supply  20  to the first FOP load  101 , the second FOP load  102 , and the third FOP load  103 . 
     As illustrated in  FIG.  8   , for example, when the inspection unit  31  steps down the voltage of the first power supply  10  in the state where the second system switch  42  is conducted, the voltage of the first power supply  10  gradually becomes lower than the voltage of the second power supply  20 . That is, a difference voltage between the first power supply  10  and the second power supply  20  gradually increases from 0, and a current corresponding to the difference voltage flows from the second power supply  20  to the second system  120 . This current gradually increases from 0 according to the difference voltage. 
     Therefore, the inspection unit  31  can detect, by the current sensor  8 , a minute current when the current starts to flow from the second power supply  20  to the second system  120  as a current for conduction check. When the conduction check is completed, the inspection unit  31  stops the stepping down of the first power supply  10 . 
     Therefore, when the minimum necessary current discharged from the second power supply  20  is detected by the current sensor  8  immediately after the voltage of the first power supply  10  equal to the voltage of the second power supply  20  is stepped down, the inspection unit  31  determines that the second system switch  42  is not fixed to the off-state and the backup can be performed. 
     Further, when the current sensor  8  does not detect the current discharged from the second power supply  20  immediately after the voltage of the first power supply  10  equal to the voltage of the second power supply  20  is stepped down, the inspection unit  31  determines that the second system switch  42  is fixed to the off-state and the backup cannot be performed. 
     In this manner, since the inspection unit  31  performs the inspection of the backup availability determination by discharging the minimum necessary current from the second power supply  20 , it is possible to perform the inspection as to whether electric power can be supplied from the second power supply  20  to the second system  120  while preventing the deterioration of the second power supply  20 . 
     Further, for example, when the inspection unit  31  steps up the voltage of the first power supply  10  in the state where the second system switch  42  is conducted, the voltage of the first power supply  10  gradually becomes larger than the voltage of the second power supply  20 . That is, the difference voltage between the first power supply  10  and the second power supply  20  gradually increases from 0, and a current corresponding to the difference voltage flows from the first power supply  10  to the second power supply  20  as a charging current. This current gradually increases from 0 according to the difference voltage. 
     Therefore, as illustrated in  FIG.  9   , the inspection unit  31  can detect, by the current sensor  8 , a minute current when the current starts to flow from the first power supply  10  to the second power supply  20  as a charging current for conduction check. When the conduction check is completed, the inspection unit  31  stops the stepping up of the first power supply  10 . 
     Therefore, when a minimum necessary charging current flowing from the first power supply  10  to the second power supply  20  is detected by the current sensor  8  immediately after the voltage of the first power supply  10  is stepped up, the inspection unit  31  determines that the second system switch  42  is not fixed to the off-state and the backup can be performed. 
     Further, when the current sensor  8  does not detect the current flowing from the first power supply  10  to the second power supply  20  immediately after the voltage of the first power supply  10  is stepped up, the inspection unit  31  determines that the second system switch  42  is fixed to the off-state and the backup cannot be performed. 
     In this manner, since the inspection unit  31  performs the inspection of the backup availability determination by charging the minimum necessary current in the second power supply  20 , it is possible to perform the inspection as to whether electric power can be supplied from the second power supply  20  to the second system  120  while preventing the deterioration of the second power supply  20 . 
     As illustrated in  FIG.  10   , when the voltages are detected, the voltage of the first power supply  10  and the voltage of the second power supply  20  may not be equal to each other. For example, when the voltage of the first power supply  10  is lower than the voltage of the second power supply  20 , the inspection unit  31  steps up the voltage of the first power supply  10  while disconnecting the second system switch  42 , and performs the voltage adjustment such that the voltage of the first power supply  10  and the voltage of the second power supply  20  become equal to each other. 
     Thereafter, the inspection unit  31  conducts the second system switch  42 , steps down the voltage of the first power supply  10 , and inspects whether electric power can be supplied from the second power supply  20  to the first FOP load  101 , the second FOP load  102 , and the third FOP load  103 . 
     Accordingly, since the inspection unit  31  can create a same state as the state illustrated in  FIG.  8   , by discharging the minimum necessary current from the second power supply  20 , it is possible to perform the inspection as to whether electric power can be supplied from the second power supply  20  to the second system  120  while preventing the deterioration of the second power supply  20 . 
     The inspection unit  31  may perform the voltage adjustment so that the voltage of the first power supply  10  and the voltage of the second power supply  20  become equal to each other, then conduct the second system switch  42 , step up the voltage of the first power supply  10 , and inspect whether electric power can be supplied from the second power supply  20  to the second system  120 . 
     Accordingly, since the inspection unit  31  can create a same state as the state illustrated in  FIG.  9   , by charging the minimum necessary charging current to the second power supply  20 , it is possible to perform the inspection as to whether electric power can be supplied from the second power supply  20  to the second system  120  while preventing the deterioration of the second power supply  20 . 
     As illustrated in  FIG.  11   , when the voltages are detected, the voltage of the first power supply  10  may be higher than the voltage of the second power supply  20 . In this case, when the voltage of the LiB  21  is higher than the voltage of the PbB  12 , the inspection unit  31  steps down the voltage of the generator  11  and performs the voltage adjustment so that the voltage of the first power supply  10  and the voltage of the LiB  21  become equal to each other. 
     Thereafter, the inspection unit  31  conducts the second system switch  42 , steps down the voltage of the first power supply  10 , and inspects whether electric power can be supplied from the second power supply  20  to the first FOP load  101 , the second FOP load  102 , and the third FOP load  103 . At this time, the inspection unit  31  may conduct the second system switch  42 , step up the voltage of the first power supply  10 , and inspect whether electric power can be supplied from the second power supply  20  to the first FOP load  101 , the second FOP load  102 , and the third FOP load  103 . 
     As illustrated in  FIG.  12   , when the voltages are detected, the voltage of the LiB  21  may be lower than the voltage of the PbB  12 . In this case, even when the inspection unit  31  controls the generator  11 , the inspection unit  31  cannot step down the voltage of the first power supply  10  to the voltage of the second power supply  20 . 
     Therefore, when the voltage of the LiB  21  is lower than the voltage of the PbB  12 , the inspection unit  31  disconnects the connection unit  41  and then conducts the second system switch  42  in the same manner as the inspection method according to the comparative example illustrated in  FIG.  6   . Then, the inspection unit  31  inspects whether electric power can be supplied from the second power supply  20  to the first FOP load  101 , the second FOP load  102 , and the third FOP load  103 . 
     [6. Process Executed by Inspection Unit] 
     Next, a process executed by the inspection unit  31  will be described with reference to  FIG.  13   .  FIG.  13    is a flowchart illustrating an example of the process executed by the inspection unit  31  according to the embodiment. The inspection unit  31  starts the process illustrated in  FIG.  13    at a timing at which the process does not interfere with the automated driving, for example, at the time of activation or at the time of stopping. At this time, the connection unit  41  is conducted, and the second system switch  42  is disconnected. 
     As illustrated in  FIG.  13   , at an inspection timing, the inspection unit  31  first detects the voltages of the first power supply  10  and the second power supply  20  (step S 101 ), and determines whether the voltage of the first power supply  10  and the voltage of the second power supply  20  are equal to each other (step S 102 ). 
     When the inspection unit  31  determines that the voltage of the first power supply  10  and the voltage of the second power supply  20  are equal to each other (step S 102 , Yes), the inspection unit  31  conducts the second system switch  42  (step S 103 ) and issues a step-down instruction to the generator  11  (step S 104 ). 
     Then, the inspection unit  31  determines whether backup electric power can be supplied from the second power supply  20  to the second system  120  (step S 105 ). At this time, when a current is detected by the current sensor  8 , the inspection unit  31  determines that the backup electric power can be supplied. When the current sensor  8  does not detect the current, the inspection unit  31  determines that the backup electric power cannot be supplied. Thereafter, the inspection unit  31  cancels the instruction of the generator  11  to stop the generator  11  (step S 106 ), disconnects the second system switch  42  (step S 107 ), and ends the process. 
     When the inspection unit  31  determines in step S 102  that the voltage of the first power supply  10  and the voltage of the second power supply  20  are not equal to each other (step S 102 , No), the inspection unit  31  determines whether the voltage of the first power supply  10  is lower than the voltage of the second power supply  20  (step S 108 ). 
     When the inspection unit  31  determines that the voltage of the first power supply  10  is lower than the voltage of the second power supply  20  (step S 108 , Yes), the inspection unit  31  issues a step-up instruction to the generator  11  (step S 109 ), and proceeds the process to step S 111 . Further, when the inspection unit  31  determines that the voltage of the first power supply  10  is higher than the voltage of the second power supply  20  (step S 108 , No), the inspection unit  31  issues the step-down instruction to the generator  11  (step S 110 ), and proceeds the process to step S 111 . 
     In step S 111 , the inspection unit  31  determines whether the voltage of the first power supply  10  can be made equal to the voltage of the second power supply  20 . When the inspection unit  31  determines that the voltage of the first power supply  10  can be equal to the voltage of the second power supply  20  (step S 111 , Yes), the inspection unit  31  proceeds the process to step S 103 . 
     When the inspection unit  31  determines that the voltage of the first power supply  10  cannot be equal to the voltage of the second power supply  20  (step S 111 , No), the inspection unit  31  disconnects the connection unit  41  (step S 112 ), conducts the second system switch  42  (step S 113 ), and proceeds the process to step S 105 . The above-described embodiment is an example, and various modifications are possible. Hereinafter, an inspection method and an example of a process executed by the inspection unit  31  according to a modification of the embodiment will be described. 
     [7. Inspection of Second System According to Modification of Embodiment] 
     The inspection unit  31  according to the modification controls the first power supply  10  such that the voltage of the first power supply  10  is equal to the voltage of the second power supply  20 , and when a voltage difference between the first power supply  10  and the second power supply  20  is within a predetermined voltage difference, the inspection unit  31  conducts the second system switch  42 . Then, the inspection unit  31  inspects whether electric power can be supplied from the second power supply  20  to the first FOP load  101 , the second FOP load  102 , and the third FOP load  103 . 
     For example, as illustrated in  FIG.  14   , when the voltages are detected, if the voltage of the first power supply  10  is lower than the voltage of the second power supply  20 , the inspection unit  31  issues the step-up instruction to the generator  11  so that the voltage of the first power supply  10  becomes equal to the voltage of the second power supply  20 . 
     Then, when the voltage difference between the first power supply  10  and the second power supply  20  becomes equal to or less than the predetermined voltage difference before the voltage of the first power supply  10  becomes equal to the voltage of the second power supply  20 , the inspection unit  31  cause the generator  11  to end the stepping up. At this time, the voltage of the first power supply  10  is lower than the voltage of the second power supply  20  by the predetermined voltage difference. 
     Therefore, the inspection unit  31  can discharge a small current from the second power supply  20  to the second system  120  by conducting the second system switch  42  in this state. Then, the inspection unit  31  can inspect whether electric power can be supplied from the second power supply  20  to the first FOP load  101 , the second FOP load  102 , and the third FOP load  103  based on whether the current sensor  8  detects the current. 
     Accordingly, the inspection unit  31  can inspect whether electric power can be supplied from the second power supply  20  to the second system  120  without stepping down the voltage of the first power supply  10  after stepping up the voltage of the first power supply  10  until the voltage of the first power supply  10  becomes equal to the voltage of the second power supply  20  once. 
     If the voltage of the first power supply  10  is higher than the voltage of the second power supply  20 , the inspection unit  31  issues the step-down instruction to the generator  11  so that the voltage of the first power supply  10  becomes equal to the voltage of the second power supply  20 . Then, when the voltage difference between the first power supply  10  and the second power supply  20  becomes equal to or less than the predetermined voltage difference before the voltage of the first power supply  10  becomes equal to the voltage of the second power supply  20 , the inspection unit  31  cause the generator  11  to end the stepping down. At this time, the voltage of the first power supply  10  is higher than the voltage of the second power supply  20  by the predetermined voltage difference. Therefore, the inspection unit  31  can charge a small current from the first power supply  10  to the second power supply  20  by conducting the second system switch  42  in this state. Then, the inspection unit  31  can inspect whether electric power can be supplied from the second power supply  20  to the first FOP load  101 , the second FOP load  102 , and the third FOP load  103  based on whether the current sensor  8  detects the current. 
     [8. Process Executed by Inspection Unit According to Modification of Embodiment] 
     Next, a process executed by the inspection unit  31  according to a modification will be described with reference to  FIG.  15   .  FIG.  15    is a flowchart illustrating an example of the process executed by the inspection unit  13  according to the modification of the embodiment. 
     As illustrated in  FIG.  15   , at the inspection timing, the inspection unit  31  first detects the voltages of the first power supply  10  and the second power supply  20  (step S 201 ), and determines whether the voltage of the first power supply  10  and the voltage of the second power supply  20  are equal to each other (step S 202 ). 
     When the inspection unit  31  determines that the voltage of the first power supply  10  and the voltage of the second power supply  20  are equal to each other (step S 202 , Yes), the inspection unit  31  conducts the second system switch  42  (step S 203 ) and issues a step-down instruction to the generator  11  (step S 204 ). 
     Then, the inspection unit  31  determines whether backup electric power can be supplied from the second power supply  20  to the second system  120  (step S 205 ). Thereafter, the inspection unit  31  cancels the instruction of the generator  11  to stop the generator  11  (step S 206 ), disconnects the second system switch  42  (step S 207 ), and ends the process. The processing of steps S 201  to S 207  up to this point are the same as the processing of steps S 101  to S 107  shown in  FIG.  13   . 
     When the inspection unit  31  according to the modification determines in step S 202  that the voltage of the first power supply  10  and the voltage of the second power supply  20  are not equal to each other (step S 202 , No), the inspection unit  31  determines whether the voltage of the first power supply  10  is lower than the voltage of the second power supply  20  (step S 208 ). 
     When the inspection unit  31  determines that the voltage of the first power supply  10  is not lower than the voltage of the second power supply  20  (step S 208 , No), the inspection unit  31  issues the step-down instruction to the generator  11  (step S 209 ), and determines whether the voltage difference between the first power supply  10  and the second power supply  20  is equal to or less than the predetermined voltage difference (step S 210 ). 
     When the inspection unit  31  determines that the voltage difference between the first power supply  10  and the second power supply  20  is equal to or less than the predetermined voltage difference (step S 210 , Yes), the inspection unit  31  conducts the second system switch  42  (step S 215 ), and proceeds the process to step S 205 . When the inspection unit  31  determines that the voltage difference between the first power supply  10  and the second power supply  20  is not equal to or less than the predetermined voltage difference (step S 210 , No), the inspection unit  31  determines whether a certain time has elapsed after the step-down instruction is issued in step S 209  (step S 211 ). 
     When the inspection unit  31  determines that the certain time has not elapsed (step S 211 , No), the inspection unit  31  returns the process to step S 209 . When the inspection unit  31  determines that the certain time has elapsed (step S 211 , Yes), the inspection unit  31  determines that the voltage of the PbB  12  is higher than the voltage of the LiB  21  by the predetermined voltage difference or more, determines that the voltage of the first power supply  10  cannot be stepped down any more, disconnects the connection unit  41  (Step S 212 ), and proceeds the process to step S 205 . 
     When the inspection unit  31  determines that the voltage of the first power supply  10  is lower than the voltage of the second power supply  20  (step S 208 , Yes), the inspection unit  31  issues the step-up instruction to the generator  11  (step S 213 ). Then, the inspection unit  31  determines whether the voltage difference between the first power supply  10  and the second power supply  20  is equal to or less than the predetermined voltage difference (step S 214 ). 
     When the inspection unit  31  determines that the voltage difference between the first power supply  10  and the second power supply  20  is equal to or less than the predetermined voltage difference (step S 214 , Yes), the inspection unit  31  proceeds the process to step S 215 . Further, when the inspection unit  31  determines that the voltage difference between the first power supply  10  and the second power supply  20  is not equal to or less than the predetermined voltage difference (step S 214 , No), the inspection unit  31  proceeds the process to step S 213 . 
     Additional effects and modifications can be easily derived by those skilled in the art. Therefore, broader aspects of the present invention are not limited to the specific details and the representative embodiments shown and described above. Therefore, various modifications can be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and equivalents of the claims. 
     REFERENCE SIGNS LIST 
     
         
           1  power supply apparatus 
           10  first power supply 
           11  generator 
           12  PbB 
           20  second power supply 
           21  LiB 
           3  control unit 
           31  inspection unit 
           41  connection unit 
           42  second system switch 
           43  DC/DC 
           50  first connection device 
           60  second connection device 
           51  to  54 ,  61  to  63  switch 
           7  first voltage sensor 
           70  second voltage sensor 
           71  to  73  voltage sensor 
           8  current sensor 
           100  automated driving control device 
           101  first FOP load 
           102  second FOP load 
           103  third FOP load 
           104  general load 
           110  first system 
           120  second system 
           130  inter-system line