Patent Publication Number: US-2023134343-A1

Title: Vehicle power supply system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2021-177230 filed on Oct. 29, 2021, the entire disclosure of which is incorporated by reference herein. 
     BACKGROUND 
     The present disclosure relates to a vehicle power supply system. 
     Some vehicles are equipped with computers capable of performing grid computing (see, e.g., Patent Document 1). In an example of Japanese Unexamined Patent Publication No. 
     2020-160661, a signal indicating permission to participate in the grid computing is transmitted to a management server according to user&#39;s vehicle engine OFF operation or power OFF operation. 
     SUMMARY 
     In Japanese Unexamined Patent Publication No. 2020-160661, device power consumption management (particularly, power consumption reduction) is not taken into consideration much. 
     An object of the present aspect is to reduce power consumption in a vehicle. 
     In order to achieve the object, in the technique disclosed herein, a vehicle power supply system includes a first secondary battery, a second secondary battery whose output voltage is lower than that of the first secondary battery, a DC power supply unit configured to convert an input AC voltage into a DC voltage to output the DC voltage, a battery pack configured to receive the DC power output from the DC power supply unit and charge the first secondary battery, a first step-down circuit configured to step down an input DC voltage to output the stepped-down DC voltage, a second step-down circuit configured to step down an input DC voltage to output the stepped-down DC voltage, and a control device configured to control the battery pack. The first secondary battery is connected to an input port of the first step-down circuit and an input port of the second step-down circuit via the battery pack. An output port of the first step-down circuit is connected to a computer, and the first step-down circuit is provided separately from the computer. An output port of the second step-down circuit is connected to the second secondary battery. 
     According to the above-described aspect, the power is distributed by the control device and the battery pack; therefore, power consumption in a vehicle can be reduced. Further, the first step-down circuit and the computer are provided separately; therefore, the degree of freedom in vehicle design is improved. 
     The control device may have a control mode of controlling the battery pack to supply the output of the DC power supply unit to the first secondary battery. 
     According to the above-described aspect, the first secondary battery can be charged with the power from the DC power supply unit. 
     The control device may have a control mode of controlling the battery pack to supply the output of the DC power supply unit to the computer. 
     According to the above-described aspect, the power from the DC power supply unit can be supplied to the computer. 
     The control device may have a control mode of supplying the power of the second secondary battery to the computer in a case where the power of the second secondary battery is equal to or greater than a predetermined value. 
     According to the above-described aspect, the power from the second secondary battery can be supplied to the computer. 
     The control device may have a control mode of supplying the power of the second secondary battery to the computer in a case where the power of the second secondary battery is equal to or greater than the predetermined value. 
     According to the above-described aspect, the second secondary battery can be charged with the power from the first secondary battery. 
     According to the present disclosure, power consumption in the vehicle can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a diagram showing, as an example, a configuration of a system of an embodiment. 
         FIG.  2    is a diagram for describing the concept of grid computing. 
         FIG.  3    is a block diagram showing, as an example, a configuration (an excerpt) of a vehicle. 
         FIG.  4    is a block diagram showing a configuration of a charging control unit etc. 
         FIG.  5    is a table for describing power control in a case where the vehicle is connected to a normal charger. 
         FIG.  6    is a table for describing the power control in a case where the vehicle is not connected to the normal charger. 
     
    
    
     DETAILED DESCRIPTION 
     [Embodiment] 
     Hereinafter, a vehicle power supply system according to the present embodiment will be described with reference to the drawings. The vehicle power supply system of the present embodiment is mounted on a vehicle. The vehicle is connected to a system  1  (described later). Thus, the system  1  will be described. Note that the same or corresponding parts are denoted by the same reference characters in the drawings, and the description thereof will not be repeated. 
     «System  1 » 
       FIG.  1    shows, as an example, a configuration of the system  1  in the present embodiment. The system  1  includes a plurality of vehicles  10 , a plurality of user terminals  20 , a client server  30 , a facility server  40 , and a management server  50 . 
     The client server  30  is owned by a client. The client requests the management server  50  to calculate job data. Examples of such a client include a company, a research institution, an educational institution, etc. The facility server  40  is owned by a facility. A user visits the facility. 
     The user can make a reservation for visiting the facility. Examples of such a facility include a stadium, a theater, a supermarket, a restaurant, an accommodation, a store, etc. The management server  50  manages operation (e.g., job assignment) of the system  1  in which grid computing is built. The management server  50  is owned by a business operator operating the system  1 . 
     These components can communicate with each other via a communication network  5 . Each vehicle  10  is equipped with an arithmetic unit  105  (trip computer). Note that a plurality of client servers  30  may be provided in the system  1 . Similarly, a plurality of facility servers  40  may be provided in the system  1 . 
     [Grid Computing] 
       FIG.  2    is a diagram for describing the concept of grid computing. As shown in  FIG.  2   , in the system  1 , grid computing is built by the plurality of arithmetic units  105 . In the system  1 , a process (a grid computing process) of causing an available one of the plurality of arithmetic units  105  to process the job data is performed. 
     Note that when the computing power of the arithmetic unit  105  is required in the vehicle  10 , the arithmetic unit  105  enters an operating state. That is, the computing power of the arithmetic unit  105  is utilized. For example, when the computing power of the arithmetic unit  105  is required for controlling travelling of the vehicle  10 , the arithmetic unit  105  enters the operating state. 
     On the other hand, when the computing power of the arithmetic unit  105  is no longer necessary in the vehicle  10 , the arithmetic unit  105  enters a stop state. That is, in the vehicle  10 , the computing power of the arithmetic unit  105  is not utilized. 
     Here, in the vehicle  10 , when the computing power of the arithmetic unit  105  is unnecessary, the computing power of the arithmetic unit  105  is provided to the grid computing process. With this configuration, the computing power of the arithmetic unit  105  can be effectively utilized. 
     [Vehicle] 
     The vehicle  10  (a computer system) is owned by the user. The user drives the vehicle  10  in some cases. In this example, the vehicle  10  is a four-wheeled motor vehicle. Examples of the vehicle  10  include an electric vehicle, a plug-in hybrid motor vehicle, etc. 
       FIG.  3    is a block diagram showing, as an example, a configuration (an excerpt) of the vehicle.  FIG.  4    is a block diagram showing a configuration of a charging control unit  200  (see  FIG.  3   ) etc. As shown in  FIGS.  3  and  4   , the vehicle  10  includes an actuator  11 , a sensor  12 , a motor  13 , a battery pack  201  (including a first secondary battery  14  described later), a second secondary battery  15 , an inverter circuit  16 , an input unit  101 , an output unit  102 , a communication unit  103 , a storage unit  104 , the arithmetic unit  105 , a DC/DC converter  109 , a cooling device  108 , the charging control unit  200 , a power control unit  202 , a heater  203 , an electrical system  205 , a drive/steering system  206 , and a cooling/heating system  207 . 
     The inverter circuit  16  converts an input DC voltage into an AC voltage having a predetermined frequency and a predetermined voltage, and outputs the AC voltage. The output (the three-phase AC voltage) of the inverter circuit  16  is supplied to a motor (the motor  13 ) for driving the vehicle. 
     The voltage of the second secondary battery  15  is 12 V. The power of the second secondary battery  15  is supplied to a computer (e.g., a central control unit  105   b  described later) etc. 
     The actuator  11  includes, for example, a steering actuator, a braking actuator, etc. Examples of the braking actuator include a brake. Examples of the steering actuator include a steering. 
     The sensor  12  acquires various types of information used for controlling the vehicle  10 . Examples of the sensor  12  include an external camera, an internal camera, a radar, a vehicle speed sensor, an acceleration sensor, a yaw rate sensor, an accelerator position sensor, a steering sensor, a brake hydraulic sensor, etc. The external camera images the outside of the vehicle. The internal camera images the inside of the vehicle. The radar searches outside the vehicle. 
     The input unit  101  inputs information and data. Examples of the input unit  101  include an operation unit operated to input information according to the operation, a camera inputting an image indicating information, a microphone inputting sound indicating information, etc. Examples of the operation unit include an operation button and a touch sensor of a car navigation device etc. The information and data input to the input unit  101  are transmitted to the arithmetic unit  105 . 
     The output unit  102  outputs information and data. Examples of the output unit  102  include a display unit outputting an image indicating information, a speaker outputting sound indicating information, etc. Examples of the display unit include a display of a car navigation device. Examples of the speaker include a speaker of a car navigation device. 
     The communication unit  103  transmits and receives information and data. The information and data received by the communication unit  103  are transmitted to the arithmetic unit  105 . In the present embodiment, the user can provide (transmit) an instruction on an operation mode (described later) in the case of connection with a normal charger to the communication unit  103 . In this example, the user can send the instruction from the user terminal  20  to the communication unit  103  via wireless communication. 
     The storage unit  104  stores information and data. 
     The battery pack  201  includes the first secondary battery  14  and a battery heater  201   a.  The voltage of the first secondary battery  14  is hundreds of volts (e.g., 200 V). The output voltage of the first secondary battery  14  is higher than the output voltage of the second secondary battery  15 . The power of the first secondary battery  14  is input to the inverter circuit  16 . The first secondary battery  14  may be normally charged, or may be rapidly charged. 
     The battery heater  201   a  is a heater for adjusting the temperature of the first secondary battery  14 . The battery heater  201   a  receives the power supplied from the first secondary battery  14 . 
     The cooling device  108  cools the arithmetic unit  105  and the first secondary battery  14 . Specifically, the cooling device  108  cools the first secondary battery  14  with water. The cooling device  108  also air-conditions the inside of the vehicle (the inside of a room). In other words, the cooling device  108  has a water cooling function and an air-conditioning function. Using these functions, the cooling device  108  cools part of the arithmetic unit  105  with water, and cools another part of the arithmetic unit  105  with air. 
     In order to implement the water cooling function and the air-conditioning function, the cooling device  108  includes a condenser, an evaporator, a chiller, a pump, etc. (any of these components is not shown). Operation of the cooling device  108  is controlled by the arithmetic unit  105 . 
     The arithmetic unit  105  includes a plurality of control units (computers). In this example, the arithmetic unit  105  includes, as the control units, a video media control unit  105   a  (non trip computer), the central control unit  105   b,  and a driving assist unit  105   e  (see  FIG.  4   ). Note that although the video media control unit  105   a  is a computer forming the arithmetic unit  105 , the video media control unit  105   a  is independently shown in  FIG.  4    for the sake of convenience in illustration. 
     Some of these computers are allowed to participate in the grid computing, and the other computers are not allowed to participate in the grid computing. Power is supplied from the second secondary battery  15  to the central control unit  105   b  and the driving assist unit  105   e.    
     The video media control unit  105   a  (the computer) includes a media processing unit (MPU). The MPU is a device including a processor for processing image data. Note that the video media control unit  105   a  may allow the user to select whether or not the video media control unit  105   a  is attached upon, e.g., purchase of the vehicle  10 . 
     When the MPU executes a predetermined program, the video media control unit  105   a  processes video captured by the internal camera and video (image data) captured by the external camera. For example, the MPU can automatically edit the image data by executing the program. Note that the video media control unit  105   a  communicates, in some cases, with the central control unit  105   b  and the driving assist unit  105   e  via a local area network (e.g., Ethernet). 
     The MPU is a processor having a relatively high computing power. The video media control unit  105   a  (the MPU) is allowed to participate in the grid computing. 
     An electronic component of the video media control unit  105   a  is cooled by the cooling device  108 . For example, a predetermined semiconductor element forming the video media control unit  105   a  is cooled with water by the cooling device  108 . Cold air is injected from the cooling device  108  into a housing that houses the video media control unit  105   a.  In other words, the video media control unit  105   a  is cooled with air by the cooling device  108 . 
     The video media control unit  105   a  can control the cooling device  108  by executing the program. The video media control unit  105   a  can adjust the capacity of the cooling device  108  to cool the video media control unit  105   a  itself. 
     The central control unit  105   b  includes one or more central processing units (CPUs). The central control unit  105   b  controls the vehicle  10  by the CPUs executing a predetermined program while the vehicle  10  is traveling. In principle, the central control unit  105   b  does not operate the vehicle  10  while the vehicle  10  is parked. 
     For example, the central control unit  105   b  controls the driving actuator (the motor  13 ) according to various types of information obtained by the sensor  12 . The central control unit  105   b  also controls the cooling device  108  (e.g., control of air-conditioning in the vehicle). The central control unit  105   b  is not allowed to participate in the grid computing. Note that, e.g., the CPUs of the central control unit  105   b  are cooled by the cooling device  108  as in the video media control unit  105   a.    
     The driving assist unit  105   e  includes one or more CPUs. The driving assist unit  105   e  controls each function in preventive driving assistance in such a manner that the CPUs execute a predetermined program. In principle, the driving assist unit  105   e  does not operate while the vehicle  10  is parked. 
     For example, the driving assist unit  105   e  causes the vehicle  10  to follow a preceding vehicle, evaluate a status relating to an advanced emergency braking system, and controls the brake. The driving assist unit  105   e  is not allowed to participate in the grid computing. 
     A component group including the second secondary battery  15 , the inverter circuit  16 , the video media control unit  105   a,  the DC/DC converter  109 , the charging control unit  200 , the battery pack  201 , and the power control unit  202  may also be referred to as a vehicle power supply system. 
     The charging control unit  200  manages charging of the first secondary battery  14 , for example. The charging control unit  200  is connected to the normal charger during normal charging. The normal charger is, for example, a commercial power supply. The commercial power supply is, for example, a single-phase 100V or 200V AC power supply. 
     The charging control unit  200  includes, as components, a power distribution control unit  105   c  (a control device) and a power conversion device  106  (a DC power supply unit). Each component of the charging control unit  200  is housed in a single housing. Each component of the charging control unit  200  may be mounted on the same substrate. 
     The power conversion device  106  is connected to the normal charger upon normal charging. The power conversion device  106  converts an input AC voltage into a DC voltage, and outputs the DC voltage. Operation of the power conversion device  106  is controlled by the power distribution control unit  105   c.  The power conversion device  106  includes a rectifier  106   a,  an inverter circuit  106   b,  a transformer  106   c,  and a rectifier  106   d.    
     The rectifier  106   a  (an AC/DC converter) rectifies an AC voltage input from the normal charger, and outputs a DC voltage. The rectifier  106   a  may include a diode bridge circuit, for example. 
     The inverter circuit  106   b  (a DC/AC converter) converts the DC voltage output from the rectifier  106   a  into an AC voltage having predetermined voltage and frequency. The output of the inverter circuit  106   b  is input to the transformer  106   c.    
     The transformer  106   c  (a booster) boosts the AC voltage output from the inverter circuit  106   b.  The output voltage of the transformer  106   c  is hundreds of volts (e.g., about 200 V). The output of the transformer  106   c  is input to the rectifier  106   d.    
     The rectifier  106   d  (an AC/DC converter) converts the AC voltage output from the transformer  106   c  into a DC voltage. The output voltage of the rectifier  106   d  is a DC voltage (e.g., 200 V) suitable for charging the first secondary battery  14 . The rectifier  106   d  may include a diode bridge circuit, for example. 
     The power conversion device  106  converts an AC voltage input via an input port into a specified DC voltage, and outputs the DC voltage to an output port (specifically, an output port of the rectifier  106   d ). Control of (instruction for) the power conversion device  106  is performed by the power distribution control unit  105   c.    
     The first secondary battery  14  is connected to an output port of the power conversion device  106 . The power conversion device  106  can control ON/OFF of a power supply to the first secondary battery  14 . Such ON/OFF control is performed by the power distribution control unit  105   c.    
     A DC/DC converter  107  is a step-down circuit (a first step-down circuit). The DC/DC converter  107  includes at least one input port and a plurality of output ports. A voltage output via each output port is 12 V. The DC/DC converter  107  may control the magnitude of power at each output port. The power at the output port of the DC/DC converter  107  is zero (i.e., an OFF state) in some cases. 
     The input port of the DC/DC converter  107  is connected to the output port of the power conversion device  106  and the first secondary battery  14  via a bus  21  in the battery pack  201 . In the present embodiment, a destination to which the power of the DC/DC converter  107  is supplied includes the video media control unit  105   a,  the power distribution control unit  105   c,  and the power control unit  202 . 
     Here, in the present embodiment, the DC/DC converter  107  is provided outside the video media control unit  105   a.  That is, the DC/DC converter  107  and the video media control unit  105   a  are provided separately. 
     The DC/DC converter  109  is a step-down circuit (a second step-down circuit). The first secondary battery  14  is connected to an input port of the DC/DC converter  109  via the bus  21  in the battery pack  201 . A voltage output via an output port of the DC/DC converter  109  is 12 V. The DC/DC converter  109  can control ON/OFF of the output. The second secondary battery  15  is connected to the output port of the DC/DC converter  109 . 
     The power control unit  202  includes a CPU. The power control unit  202  monitors the first secondary battery  14  and controls a relay in the battery pack  201  in such a manner that the CPU executes a predetermined program, for example. For example, the power control unit  202  also checks and diagnoses the temperature, current, voltage, etc. of a cell of the first secondary battery  14 . Moreover, the power control unit  202  also controls the DC/DC converter  109 . Specifically, the power control unit  202  switches ON/OFF of the output of the DC/DC converter  109 . Note that the first secondary battery  14 , the DC/DC converter  109 , and the video media control unit  105   a  are connected to each other via a line formed in the battery pack  201 . 
     The heater  203  is a heater for air-conditioning the inside of the vehicle. The heater  203  receives the power supplied from the first secondary battery  14 . The electrical system  205 , the drive/steering system  206 , the cooling/heating system  207 , etc. are electrical components provided in the vehicle  10 . These electrical components receive the power supplied from the second secondary battery  15 . 
     «Operation Example (Power Control Example)» 
     Power control in the vehicle  10  (the computer system) will be described for each of a case where the vehicle  10  is connected to the normal charger and a case where the vehicle  10  is not connected to the normal charger. 
     &lt;Case where Vehicle  10  is Connected to Normal Charger&gt; 
     When the vehicle  10  is connected to the normal charger, power is supplied from the normal charger to the charging control unit  200  (more precisely, the power conversion device  106 ). In the vehicle  10 , the following three modes can be selected as the operation mode in a case where the vehicle  10  is connected to the normal charger. 
     (1) A mode (a first mode) in which the first secondary battery  14  is charged, but the video media control unit  105   a  does not participate in the grid computing. 
     (2) A mode (a second mode) in which both charging of the first secondary battery  14  and participation of the video media control unit  105   a  in the grid computing are performed. 
     (3) A mode (a third mode) in which the first secondary battery  14  is not charged, but the video media control unit  105   a  participates in the grid computing. 
       FIG.  5    is a table for describing the power control in a case where the vehicle  10  is connected to the normal charger (abbreviated as “CHARGER” in the drawing). In  FIG.  5   , an on board charger (OBC) means the charging control unit  200  (the same also applies to other drawings). Moreover, in  FIG.  5   , a circle mark means a state in which a corresponding device operates, and a cross mark means a state in which a corresponding device is stopped. Further, “MPU COMPUTATION” means that the video media control unit  105   a  participates in the grid computing (the same also applies to other drawings). 
     In  FIG.  5   , “POWER STATE OF SECOND SECONDARY BATTERY” being “HIGH” means that the second secondary battery  15  is in a power state in which power can be supplied to the video media control unit  105   a  (the MPU). “POWER STATE OF SECOND SECONDARY BATTERY” being “LOW” means that the second secondary battery  15  is in a power state in which power cannot be supplied to the video media control unit  105   a  (the MPU). 
     [First Mode] 
     In the first mode, the first secondary battery  14  is charged. In the first mode, the power from the normal charger is supplied to the first secondary battery  14 . Specifically, in the first mode, the power distribution control unit  105   c  controls the power conversion device  106  such that the output of the power conversion device  106  is supplied to the first secondary battery  14 . 
     In the first mode, the charging control unit  200  operates (see  FIG.  5   ). In other words, the power is supplied to the charging control unit  200 . In the first mode, no power is supplied to the video media control unit  105   a.  In the present embodiment, the power control unit  202  controls, e.g., the relay in the battery pack  201  to stop a power supply to the video media control unit  105   a.  Note that in this case, the power control unit  202  may control the DC/DC converter  107  to stop a power supply to the video media control unit  105   a.    
     [Second Mode] 
     Charging of First Secondary Battery  14   
     In the second mode, the first secondary battery  14  is charged. In the second mode, the power from the normal charger is supplied to the first secondary battery  14 . Specifically, in the second mode, the power distribution control unit  105   c  controls the power conversion device  106  such that the output of the power conversion device  106  is supplied to the first secondary battery  14 . In this manner, the first secondary battery  14  is charged. While the first secondary battery  14  is being charged, the power control unit  202  transmits information such as the voltage of the first secondary battery  14  to the power distribution control unit  105   c.    
     Power Supply to MPU 
     In the second mode, the power is supplied to the video media control unit  105   a  (the 
     MPU). In the second mode, a power supply source for the video media control unit  105   a  varies according to whether the power state of the second secondary battery  15  (the 12 V battery) is “HIGH” or “LOW.” For example, in a case where the power state of the second secondary battery  15  is “HIGH,” the power is directly supplied from the second secondary battery  15  to the video media control unit  105   a.    
     In a case where the power state of the second secondary battery  15  is “LOW,” the power obtained from the normal charger is supplied to the video media control unit  105   a . Specifically, the power distribution control unit  105   c  controls the power control unit  202  (controls, e.g., the relay in the battery pack  201  or the DC/DC converter  107 ) such that the output of the power conversion device  106  is input to the video media control unit  105   a.    
     The video media control unit  105   a  includes the DC/DC converter  107 . The DC/DC converter  107  steps down the output voltage (the DC voltage) of the power conversion device  106  to a voltage suitable for the video media control unit  105   a.  The DC/DC converter  107  supplies the DC voltage generated as described above to the video media control unit  105   a.  In this manner, the video media control unit  105   a  is allowed to participate in the grid computing. 
     As described above, in the second mode, the charging control unit  200  (the OBC) operates. In other words, the power is supplied to the charging control unit  200 . In the second mode, the power is also supplied to the video media control unit  105   a  and the power control unit  202 . In the second mode, the control can be made such that no power is supplied to a device unnecessary for operation of the charging control unit  200 , the power control unit  202 , and the video media control unit  105   a.    
     [Third Mode] 
     In the third mode, the first secondary battery  14  is not charged. 
     In the third mode, the power is supplied to the video media control unit  105   a  and a device for operating the video media control unit  105   a.  Also in the third mode, a power supply source for the video media control unit  105   a  varies according to whether the power state of the second secondary battery  15  is “HIGH” or “LOW.” In a case where the power state of the second secondary battery  15  is “HIGH,” the power is supplied from the second secondary battery  15  to the video media control unit  105   a.  In a case where the power state of the second secondary battery  15  is “LOW,” the power obtained from the normal charger is supplied to the video media control unit  105   a.    
     Specifically, in a case where the power state of the second secondary battery  15  is “HIGH,” the power distribution control unit  105   c  controls the power control unit  202  such that the output of the power conversion device  106  is input to the DC/DC converter  107 . The DC/DC converter  107  steps down the output voltage (the DC voltage) of the power conversion device  106  to a voltage suitable for the video media control unit  105   a.    
     The DC/DC converter  107  supplies the DC voltage generated as described above to the video media control unit  105   a.  In this manner, the video media control unit  105   a  is allowed to participate in the grid computing. 
     In the third mode, in a case where the power state of the second secondary battery  15  is “LOW,” the power distribution control unit  105   c  and the power conversion device  106  operate in the charging control unit  200  (the OBC). That is, part of the charging control unit  200  operates. Moreover, in a case where the power state of the second secondary battery  15  is “LOW,” the power is supplied to the power control unit  202  and the DC/DC converter  107 . 
     On the other hand, in a case where the power state of the second secondary battery  15  is “HIGH,” operation of the charging control unit  200  is not necessary in principle. Note that in some cases, the power distribution control unit  105   c  operates in the charging control unit  200  for the sake of convenience in power management. That is, part of the charging control unit  200  operates in some cases. 
     &lt;Case where Vehicle  10  is not Connected to Normal Charger&gt; 
     While the vehicle  10  is travelling, the vehicle  10  is not connected to the normal charger. In addition, while the vehicle  10  is parked, the vehicle  10  is not connected to the normal charger in some cases. In the vehicle  10 , the following three modes (fourth to sixth modes) can be selected as the operation mode in a case where the vehicle  10  is not connected to the normal charger. 
     (1) A mode (the fourth mode) in which the second secondary battery  15  (the 12 V battery) is charged, but the video media control unit  105   a  does not participate in the grid computing. 
     (2) A mode (the fifth mode) in which both charging of the second secondary battery  15  and participation of the video media control unit  105   a  in the grid computing are performed. 
     (3) A mode (the sixth mode) in which the second secondary battery  15  is not charged, but the video media control unit  105   a  participates in the grid computing. 
       FIG.  6    is a table for describing the power control in a case where the vehicle  10  is not connected to the normal charger. Also in  FIG.  6   , an OBC means the charging control unit  200 . Also in  FIG.  6   , a circle mark means a state in which a corresponding device operates, and a cross mark means a state in which a corresponding device is stopped. 
     [Fourth Mode] 
     In the fourth mode, the second secondary battery  15  is charged with the power of the first secondary battery  14 . Specifically, in the fourth mode, the power control unit  202  causes the DC/DC converter  109  (the second step-down circuit) to operate. 
     The DC/DC converter  109  steps down the DC voltage (e.g., 200 V) supplied from the first secondary battery  14  to a DC voltage (e.g., 12 V) suitable for charging the second secondary battery  15 . The DC/DC converter  109  supplies the DC voltage to the second secondary battery  15 . In this manner, the second secondary battery  15  is charged. 
     As described above, in the fourth mode, it is not necessary to operate the charging control unit  200  in order to charge the second secondary battery  15 . 
     [Fifth Mode] 
     In the fifth mode, the second secondary battery  15  is charged with the power of the first secondary battery  14 . Also in the fifth mode, the control similar to that in the fourth mode is performed to charge the second secondary battery  15 . That is, also in the fifth mode, the power control unit  202  causes the DC/DC converter  109  (the second step-down circuit) to operate. The DC/DC converter  109  supplies the generated DC voltage to the second secondary battery  15 . 
     In the fifth mode, a power supply source for the video media control unit  105   a  varies according to whether the power state of the second secondary battery  15  is “HIGH” or “LOW.” In a case where the power state of the second secondary battery  15  is “HIGH,” the power of the second secondary battery  15  is directly supplied to the video media control unit  105   a.    
     In a case where the power state of the second secondary battery  15  is “LOW,” the power of the first secondary battery  14  is supplied to the video media control unit  105   a . Specifically, the power distribution control unit  105   c  controls the power control unit  202  such that the output of the first secondary battery  14  is input to the DC/DC converter  107 . 
     The DC/DC converter  107  steps down the DC voltage input from the first secondary battery  14  to a DC voltage suitable for operation of the video media control unit  105   a.  As described above, the DC voltage generated by the DC/DC converter  107  is supplied to the video media control unit  105   a.  In this manner, the video media control unit  105   a  is allowed to participate in the grid computing. 
     In the fifth mode, it is not necessary to operate the charging control unit  200  in order to charge the second secondary battery  15 . In addition, it is not necessary to operate the charging control unit  200  in order to supply the power to the video media control unit  105   a.    
     [Sixth Mode] 
     In the sixth mode, the power is supplied to the video media control unit  105   a  and a device for operating the video media control unit  105   a.  Also in the sixth mode, a power supply source for the video media control unit  105   a  varies according to whether the power state of the second secondary battery  15  is “HIGH” or “LOW.” In a case where the power state of the second secondary battery  15  is “HIGH,” the power of the second secondary battery  15  is directly supplied to the video media control unit  105   a.    
     In a case where the power state of the second secondary battery  15  is “LOW,” the first secondary battery  14  is used to supply the power to the video media control unit  105   a.  Specifically, the power distribution control unit  105   c  controls the power control unit  202  such that the output of the first secondary battery  14  is input to the DC/DC converter  107 . 
     The DC/DC converter  107  steps down the DC voltage input from the first secondary battery  14  to a DC voltage suitable for operation of the video media control unit  105   a.  As described above, the DC voltage generated by the DC/DC converter  107  is supplied to the video media control unit  105   a.  In this manner, the video media control unit  105   a  is allowed to participate in the grid computing. 
     In the sixth mode, it is not necessary to operate the charging control unit  200  in order to charge the second secondary battery  15 . In addition, it is not necessary to operate the charging control unit  200  in order to supply the power to the video media control unit  105   a.    
     &lt;Advantages of Embodiment&gt; 
     As described above, in the present embodiment, a control of distributing the power to the secondary batteries  14 ,  15  and the video media control unit  105   a  (the MPU) can be made. In the case of charging the second secondary battery  15  with the power of the first secondary battery  14 , it is not necessary to activate the charging control unit  200 . That is, the components of the charging control unit  200  are activated as necessary. According to the present embodiment, power consumption in the vehicle can be reduced. 
     The DC/DC converter  107  and the video media control unit  105   a  are provided separately. Since the video media control unit  105   a  and the DC/DC converter  107  are arranged separately, the degree of freedom in vehicle design is improved. 
     [Other Embodiments] 
     The computer participating in the grid computing is not limited to the video media control unit  105   a  (a first computer). In addition to the video media control unit  105   a,  other computers may be allowed to participate in the grid computing. 
     In the first to third modes, part or the entirety of the process performed by the power distribution control unit  105   c  may be performed by the video media control unit  105   a.  For example, if the video media control unit  105   a  performs the entirety of the process performed by the power distribution control unit  105   c,  the power distribution control unit  105   c  is not necessarily provided. 
     In the above-described embodiment, the DC/DC converters  107 ,  109  are provided separately, but may be provided as a common converter. In this case, the DC/DC converter steps down the DC voltage input from the first secondary battery  14 , and supplies the stepped-down DC voltage to the second secondary battery  15  and the video media control unit  105   a.    
     The above-described embodiments may be implemented in combination, as necessary. The above-described embodiments are merely examples in nature, and are not intended to limit the scope, applications, or use of the technique disclosed herein.