Abstract:
In the present invention, when charging both a high-voltage battery and a low-voltage battery by means of electrical power obtained by means of solar generation, by means of prioritizing the charging of the low-voltage battery over the charging of the high-voltage battery, a decrease in charging efficiency of the battery overall is suppressed. The vehicle-mounted power source device charges batteries by means of electrical power obtained by means of solar generation. A solar panel converts sunlight into electrical power. A DC/DC boost converter boosts the power converted by the solar panel. A control unit causes switching in a manner so that the high-voltage battery is charged by the electrical power boosted by the DC/DC boost converter when charging the low-voltage battery by means of the power converted by the solar panel and the amount of accumulated electrical power accumulated at the low-voltage battery is at least a predetermined value.

Description:
TECHNICAL FIELD 
     The present invention relates to a vehicle-mounted power source apparatus that charges a battery with electrical power obtained by solar power generation. 
     BACKGROUND ART 
     In the related art, Patent Literature (hereinafter, referred to as “PTL”) 1 discloses a vehicle-mounted power source apparatus that stores the electrical power obtained by solar power generation in a battery. The vehicle-mounted power source apparatus disclosed in PTL 1 simultaneously supplies the electrical power obtained by solar power generation to two low voltage batteries, that is, a main battery and a sub battery. Unlike a high voltage battery that supplies high-voltage (200V) electrical power for the driving of a vehicle, the main battery and the sub battery supply low-voltage (14.0V or 12.5V) electrical power to the load. 
     In recent years, there has been an increasing demand for a long cruising distance and a short charging time of a high voltage battery in a vehicle that runs on a high voltage battery as a power source, such as an electric automobile. Meanwhile, since the vehicle-mounted power source apparatus disclosed in PTL 1 cannot charge the high voltage battery with electrical power obtained by solar generation, the vehicle-mounted power source apparatus disclosed in PTL 1 cannot sufficiently meet such a demand. 
     In order to meet such a demand, there has been known a vehicle-mounted power source apparatus which charges the high voltage battery for driving of a vehicle, with electrical power obtained by solar power generation. The vehicle-mounted power source apparatus boosts the voltage of electrical power obtained by solar power generation from a low voltage (for example, 12V) to a high voltage (for example, 200V), and stores the electrical power in the high voltage battery. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1 
         Japanese Patent Application Laid-Open No. 2012-56357 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, PTL 1 does not disclose charging both of the low voltage battery and the high voltage battery with electrical power obtained by solar power generation. In a case where both of the low voltage battery and the high voltage battery are simply charged with electrical power obtained by solar power generation, a loss in a booster circuit is large when the booster circuit boosts the voltage of charging electrical power from a low voltage to a high voltage in order to charge the high voltage battery. Thus, the overall charge efficiency of the apparatus decreases. 
     An object of the present invention is to provide a vehicle-mounted power source apparatus that prevents a decrease in the overall charge efficiency of the apparatus by charging a low voltage battery with prior over charging a high voltage battery when charging both of the low voltage battery and the high voltage battery with electrical power obtained by solar power generation. 
     Solution to Problem 
     A vehicle-mounted power source apparatus according to the present invention is a vehicle-mounted power source apparatus that charges a battery with electrical power obtained by solar power generation, the apparatus including: a low voltage battery; a high voltage battery that stores electrical power having a voltage higher than the low voltage battery; a solar panel that converts sunlight into electrical power; a boost section that boosts the voltage of the electrical power obtained through the conversion by the solar panel; and a control section that charges the low voltage battery with the electrical power obtained through the conversion by the solar panel, and that performs switching so as to charge the high voltage battery with the electrical power boosted by the boost section when the amount of electrical power stored in the low voltage battery is equal to or greater than a predetermined value. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to prevent a decrease in the overall charge efficiency of the apparatus by charging a low voltage battery with priority over charging a high voltage battery when charging both of the low voltage battery and the high voltage battery with electrical power obtained by solar power generation. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram illustrating the configuration of a vehicle-mounted power source apparatus according to Embodiment 1 of the present invention; 
         FIG. 2  is a flowchart illustrating an operation of the vehicle-mounted power source apparatus according to Embodiment 1 of the present invention while a vehicle stops; 
         FIG. 3  is a flowchart illustrating an operation of the vehicle-mounted power source apparatus according to Embodiment 1 of the present invention while the vehicle travels; 
         FIG. 4  is a flowchart illustrating an operation of the vehicle-mounted power source apparatus according to Embodiment 2 of the present invention while a vehicle travels; 
         FIG. 5  is a block diagram illustrating the configuration of a vehicle-mounted power source apparatus according to Embodiment 3 of the present invention; 
         FIG. 6  is a flowchart illustrating an operation of the vehicle-mounted power source apparatus according to Embodiment 3 of the present invention while the vehicle stops; 
         FIG. 7  is a flowchart illustrating an operation of the vehicle-mounted power source apparatus according to Embodiment 4 of the present invention while a vehicle stops; and 
         FIG. 8  is a block diagram illustrating the configuration of a vehicle-mounted power source apparatus according to Embodiment 5 of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. 
     (Embodiment 1) 
     &lt;Configuration of Vehicle-Mounted Power Source Apparatus&gt; 
     The configuration of vehicle-mounted power source apparatus  100  according to Embodiment 1 of the present invention will be described with reference to  FIG. 1 . In regard to input and output lines in  FIG. 1 , dotted lines each indicate an input and output line for the transmission of a control signal, and solid lines each indicate an input and output line for the transmission of signals other than the control signal or the delivery of electrical power. 
     Vehicle-mounted power source apparatus  100  is configured to mainly include solar panel  101 ; buck-boost DC-DC converter  102 ; boost DC-DC converter  103 ; relay  104 ; high voltage battery  105 ; protection switch  106 ; low voltage battery  107 ; load  108 ; and control section  109 . 
     Solar panel  101  converts received sunlight into electrical power, and outputs the electrical power to buck-boost DC-DC converter  102 . 
     Buck-boost DC-DC converter  102  stabilizes the voltage value of output electrical power by boosting or bucking the voltage of electrical power received from solar panel  101  according to the control by control section  109 . Buck-boost DC-DC converter  102  outputs electrical power having a stabilized voltage value to boost DC-DC converter  103  and protection switch  106 . 
     Boost DC-DC converter  103  boosts the voltage of electrical power from buck-boost DC-DC converter  102  to a predetermined value (for example, 12V to 400V) according to the control by control section  109 , and outputs the boosted electrical power to relay  104 . At this time, a loss occurs in the electrical power boosted by boost DC-DC converter  103 . 
     Relay  104  switches between ON and OFF states according to the control by control section  109 . When relay  104  is turned on, the electrical power received from boost DC-DC converter  103  is output to high voltage battery  105 , and in contrast, when relay  104  is turned off, the electrical power from boost DC-DC converter  103  is not output to high voltage battery  105 . 
     High voltage battery  105  stores the high-voltage electrical power that is input from boost DC-DC converter  103  via relay  104 . 
     Protection switch  106  switches between ON and OFF states according to the control by control section  109 . When protection switch  106  is turned on, the electrical power from buck-boost DC-DC converter  102  is output to low voltage battery  107 , and in contrast, when protection switch  106  is turned off, the electrical power received from buck-boost DC-DC converter  102  is not output to low voltage battery  107 . 
     Low voltage battery  107  stores the low-voltage electrical power that is input from buck-boost DC-DC converter  102  via protection switch  106 . 
     Load  108  operates on the electrical power from protection switch  106  or electrical power stored in low voltage battery  107 . Load  108  is an accessory for a vehicle such as a car navigation system. 
     Control section  109  controls buck-boost DC-DC converter  102  to switch between the turning on and off of a boost operation and a buck operation, and controls boost DC-DC converter  103  to switch between the turning on and off of a boost operation. Control section  109  monitors the amount of electrical power stored in low voltage battery  107 , and the amount of electrical power stored in high voltage battery  105 . Control section  109  charges low voltage battery  107 , based on a monitoring result, and when the amount of electrical power stored in low voltage battery  107  is equal to or greater than a predetermined value, control section  109  controls relay  104  and protection switch  106  to switch between ON and OFF states in such a manner that high voltage battery  105  is charged. That is, control section  109  stores electrical power produced by solar panel  101  in low voltage battery  107  without boosting the electrical power via boost DC-DC converter  103 , and when the amount of electrical power stored in low voltage battery  107  is equal to or greater than the predetermined value, control section  109  controls relay  104  and protection switch  106  to switch between ON and OFF states in such a manner that electrical power boosted by boost DC-DC converter  103  is stored in high voltage battery  105 . In this manner, vehicle-mounted power source apparatus  100  can prevent a loss from occurring when boost DC-DC converter  103  boosts electrical power produced by solar panel  101 . Here, the charging of high voltage battery  105  or low voltage battery  107  implies that high voltage battery  105  or low voltage battery  107  stores electrical power until the amount of electrical power stored therein reaches a predetermined value. 
     Control section  109  can determine whether the vehicle is traveling or is stopped, based on an ignition signal received from the outside. For example, when the ignition signal to drive a drive section is received, control section  109  determines that the vehicle starts travelling, and then is travelling. When an ignition signal to stop driving the drive section is input, control section  109  determines that the vehicle comes to a stop, and then is stopped. 
     &lt;Operation of Vehicle-Mounted Power Source Apparatus while Vehicle Stops&gt; 
     An operation of vehicle-mounted power source apparatus  100  according to Embodiment 1 of the present invention while the vehicle stops will be described with reference to  FIG. 2 . 
     First, control section  109  determines that the vehicle is stopped, based on an ignition signal, and turns off relay  104  (step ST 201 ). 
     Subsequently, control section  109  determines whether a voltage value VL of low voltage battery  107  is a first threshold value or greater (step ST 202 ). Here, the voltage value VL indicates the amount of electrical power stored in low voltage battery  107 , and increases as the amount of stored electrical power increases. The first threshold value is an upper limit value for the amount of electrical power stored in low voltage battery  107  and is a reference value to determine as to whether or not to stop charging low voltage battery  107 . 
     When control section  109  determines that the voltage value VL is less than the first threshold value (step ST 202 : NO), control section  109  turns on protection switch  106  (step ST 203 ), and the process returns to step ST 202 . Accordingly, vehicle-mounted power source apparatus  100  charges low voltage battery  107  prior to charging high voltage battery  105 . 
     In contrast, when control section  109  determines that the voltage value VL is the first threshold value or greater (step ST 202 : YES), control section  109  turns off protection switch  106  (step ST 204 ). 
     Subsequently, control section  109  turns on the operation of boost DC-DC converter  103  and relay  104  (step ST 205 ). At this time, since a considerable amount of electrical power is stored in low voltage battery  107 , vehicle-mounted power source apparatus  100  starts charging high voltage battery  105 . 
     Control section  109  determines whether the voltage value VL is a second threshold value (the first threshold value&gt;the second threshold value) or less (step ST 206 ). Here, the second threshold value indicates a lower limit value for the amount of electrical power stored in low voltage battery  107 , and is a reference value to determine as to whether or not to start charging low voltage battery  107 . 
     When control section  109  determines that the voltage value VL is the second threshold value or less (step ST 206 : YES), control section  109  turns off the operation of boost DC-DC converter  103  and relay  104  (step ST 207 ), and the process proceeds to step ST 203 . Accordingly, vehicle-mounted power source apparatus  100  starts charging low voltage battery  107 . The second threshold value may not be the lower limit value but may be a value close to the first threshold value (the upper limit value). At this time, since the charging of low voltage battery  107  starts when the voltage value VL is less than the upper limit value, it is possible to preferentially charge low voltage battery  107  with better charge efficiency. 
     In contrast, when determining that the voltage value VL is greater than the second threshold value (step ST 206 : NO), control section  109  determines whether a voltage value VH of high voltage battery  105  is a third threshold value or less (step ST 208 ). Here, the voltage value VH indicates the amount of electrical power stored in high voltage battery  105 , and increases to the extent that the amount of stored electrical power is large. The third threshold value is an upper limit value for the amount of electrical power stored in high voltage battery  105 , and is a reference value to determine as to whether or not to stop charging high voltage battery  105 . 
     When control section  109  determines that the voltage value VH is the third threshold value or less (step ST 208 : YES), the process returns to step ST 205 . Accordingly, vehicle-mounted power source apparatus  100  continuously charges high voltage battery  105 . 
     In contrast, when control section  109  determines that the voltage value VH is greater than the third threshold value (step ST 208 : NO), control section  109  turns off the operation of boost DC-DC converter  103  and relay  104  (step ST 209 ), and ends a charging process. 
     &lt;Operation of Vehicle-Mounted Power Source Apparatus while Vehicle Travels&gt; 
     An operation of vehicle-mounted power source apparatus  100  according to Embodiment 1 of the present invention while the vehicle travels will be described with reference to  FIG. 3 . 
     First, control section  109  determines that the vehicle is travelling, based on an ignition signal, and turns on relay  104  to output electrical power from high voltage battery  105  (step ST 301 ). 
     Subsequently, control section  109  determines whether the voltage value VL of low voltage battery  107  is the first threshold value or greater (step ST 302 ). 
     When determining that the voltage value VL is less than the first threshold value (step ST 302 : NO), control section  109  turns on protection switch  106  (step ST 303 ), and the process returns to step ST 302 . Accordingly, vehicle-mounted power source apparatus  100  charges low voltage battery  107  prior to charging high voltage battery  105 . 
     In contrast, when control section  109  determines that the voltage value VL is the first threshold value or greater (step ST 302 : YES), control section  109  turns off protection switch  106  (step ST 304 ). 
     Subsequently, control section  109  turns on the operation of boost DC-DC converter  103  (step ST 305 ). At this time, since a sufficient amount of electrical power is stored in low voltage battery  107 , vehicle-mounted power source apparatus  100  starts charging high voltage battery  105 . 
     Subsequently, control section  109  determines whether the voltage value VL is the second threshold value (the first threshold value&gt;the second threshold value) or less (step ST 306 ). 
     When control section  109  determines that the voltage value VL is the second threshold value or less (step ST 306 : YES), control section  109  turns off the operation of boost DC-DC converter  103  (step ST 307 ), and the process proceeds to step ST 303 . Accordingly, vehicle-mounted power source apparatus  100  starts charging low voltage battery  107 . 
     In contrast, when determining that the voltage value VL is greater than the second threshold value (step ST 306 : NO), control section  109  determines whether the voltage value VH of high voltage battery  105  is the third threshold value or less (step ST 308 ). 
     When determining that the voltage value VH is the third threshold value or less (step ST 308 : YES), the process returns to step ST 305 . Accordingly, vehicle-mounted power source apparatus  100  continuously charges high voltage battery  105 . 
     In contrast, when determining that the voltage value VH is greater than the third threshold value (step ST 308 : NO), control section  109  turns off the operation of boost DC-DC converter  103  (step ST 309 ), and ends the charging process. 
     &lt;Effects of Embodiment 1&gt; 
     In the embodiment, when both of low voltage battery  107  and high voltage battery  105  are charged with electrical power obtained by solar power generation, switching is performed so that high voltage battery  105  is charged after low voltage battery  107  that requires no boosting (good charge efficiency) is charged. As a result, it is possible to prevent a decrease in the overall charge efficiency of the apparatus. 
     In the embodiment, since both of low voltage battery  107  and high voltage battery  105  are charged with electrical power obtained by solar power generation, it is possible to reliably supply electrical power to load  108  and also to increase the cruising distance of the vehicle and to reduce the charging time of high voltage battery  105 . 
     (Embodiment 2) 
     In this embodiment, while the vehicle travels, low voltage battery  107  is charged after high voltage battery  105  is charged. That is, in a case where high voltage battery  105  is charged while the vehicle stops, it is necessary to turn on relay  104  and to start up a peripheral device for charging, for example, thus consuming electrical power. In contrast, in a case where high voltage battery  105  is charged while the vehicle travels, since relay  104  has already been turned on, and the peripheral device has already been started, it is not necessary to turn on relay  104  or to start up the peripheral device for charging, thus making it possible to prevent a decrease in charge efficiency compared to the case where high voltage battery  105  is charged while the vehicle stops. In the embodiment, taking this factor into consideration, high voltage battery  105  is preferentially charged while the vehicle travels. 
     In the embodiment, since the vehicle-mounted power source apparatus has the same configuration as in  FIG. 1 , the configuration will not be repeatedly described, and an operation of the vehicle-mounted power source apparatus while the vehicle travels will be described using the reference numerals illustrated in  FIG. 1 . In the embodiment, since an operation of the vehicle-mounted power source apparatus while the vehicle stops is the same as in  FIG. 2 , the description of the operation will not be given. 
     &lt;Operation of Vehicle-Mounted Power Source Apparatus while Vehicle Travels&gt; 
     An operation of vehicle-mounted power source apparatus  100  according to Embodiment 2 of the present invention while the vehicle travels will be described with reference to  FIG. 4 . 
     First, control section  109  determines that the vehicle is travelling, based on an ignition signal, and turns on relay  104  to output electrical power from high voltage battery  105  (step ST 401 ). 
     Subsequently, control section  109  determines whether the voltage value VH of high voltage battery  105  is the third threshold value or greater (step ST 402 ). 
     When determining that the voltage value VH is less than the third threshold value (step ST 402 : NO), control section  109  turns on the operation of boost DC-DC converter  103  (step ST 403 ), and the process returns to step ST 402 . Accordingly, vehicle-mounted power source apparatus  100  charges high voltage battery  105  prior to charging low voltage battery  107 . 
     In contrast, when determining that the voltage value VH is the third threshold value or greater (step ST 402 : YES), control section  109  turns off the operation of boost DC-DC converter  103  (step ST 404 ). Accordingly, vehicle-mounted power source apparatus  100  stops charging high voltage battery  105 . 
     Control section  109  turns on protection switch  106  (step ST 405 ). At this time, since a sufficient amount of electrical power is stored in high voltage battery  105 , vehicle-mounted power source apparatus  100  starts charging low voltage battery  107 . 
     Control section  109  determines whether the voltage value VH is a fourth threshold value (the fourth threshold value&lt;the third threshold value) or less (step ST 406 ). Here, the fourth threshold value is a lower limit value for the amount of electrical power stored in high voltage battery  105 , and is a reference value to determine as to whether or not to start charging high voltage battery  105 . 
     When determining that the voltage value VH is the fourth threshold value or less (step ST 406 : YES), control section  109  turns off protection switch  106  (step ST 407 ), and the process returns to step ST 403 . Accordingly, vehicle-mounted power source apparatus  100  starts charging high voltage battery  105 . The fourth threshold value may not be the lower limit value but may be a value close to the third threshold value (the upper limit value). At this time, since the charging of high voltage battery  105  starts when the voltage value VH is less than the upper limit value, it is possible to preferentially charge high voltage battery  105 . 
     In contrast, when determining that the voltage value VH is greater than the fourth threshold value (step ST 406 : NO), control section  109  determines whether the voltage value VL of low voltage battery  107  is the first threshold value or less (step ST 408 ). 
     When control section  109  determines that the voltage value VL is the first threshold value or less (step ST 408 : YES), the process returns to step ST 405 . Accordingly, vehicle-mounted power source apparatus  100  continuously charges low voltage battery  107 . 
     In contrast, when control section  109  determines that the voltage value VL is greater than the first threshold value (step ST 408 : NO), control section  109  turns off protection switch  106  (step ST 409 ), and ends a charging process. 
     &lt;Effects of Embodiment 2&gt; 
     In the present embodiment, when both of low voltage battery  107  and high voltage battery  105  are charged with electrical power obtained by solar power generation, switching is performed so that high voltage battery  105  is charged after low voltage battery  107  that requires no boosting (good charge efficiency) is charged. As a result, it is possible to prevent a decrease in the overall charge efficiency of the apparatus. 
     In the present embodiment, since high voltage battery  105  is preferentially charged while the vehicle travels, it is possible to charge high voltage battery  105  while preventing a decrease in charge efficiency, and to increase the cruising distance of the vehicle compared to the case where high voltage battery  105  is charged while the vehicle stops. 
     In addition, in the embodiment, since both of low voltage battery  107  and high voltage battery  105  are charged with electrical power obtained by solar power generation, it is possible to reliably supply electrical power to load  108 , and also to increase the cruising distance of the vehicle and to reduce the charging time of high voltage battery  105 . 
     (Embodiment 3) 
     In this embodiment, after low voltage battery  107  is charged, low voltage battery  503  is charged, and then high voltage battery  105  is charged with electrical power stored in low voltage battery  503 . That is, there is a problem in that it is necessary to turn on relay  104  and to start up boost DC-DC converter  504  when high voltage battery  105  is charged, thus consuming electrical power. In the embodiment, in order to solve this problem, low voltage battery  503  is charged, and high voltage battery  105  is charged from low voltage battery  503  when low voltage battery  503  stores a predetermined amount of electrical power or higher, and thereby it is possible to reduce an ON time of relay  104  and a start-up time of boost DC-DC converter  504 , and to prevent a decrease in charge efficiency (power consumption during charging). 
     &lt;Configuration of Vehicle-Mounted Power Source Apparatus&gt; 
     The configuration of a vehicle-mounted power source apparatus  500  according to Embodiment 3 of the present invention will be described with reference to  FIG. 5 . In regard to input and output lines in  FIG. 5 , dotted lines each indicate an input and output line for the transmission of a control signal, and solid lines each indicate an input and output line for the transmission of signals other than the control signal or the delivery of electrical power. 
     Compared to the configuration of vehicle-mounted power source apparatus  100  according to Embodiment 1 illustrated in  FIG. 1 , vehicle-mounted power source apparatus  500  illustrated in  FIG. 5  has protection switch  502  and low voltage battery  503  as additional configuration elements, and has buck-boost DC-DC converter  501  in place of buck-boost DC-DC converter  102 , boost DC-DC converter  504  in place of boost DC-DC converter  103 , and control section  505  in place of control section  109 . In  FIG. 5 , the same reference numerals are assigned to portions having the same configurations as in  FIG. 1 , and description thereof will be omitted. 
     Vehicle-mounted power source apparatus  500  is configured to mainly include solar panel  101 ; relay  104 ; high voltage battery  105 ; protection switch  106 ; low voltage battery  107 ; load  108 ; buck-boost DC-DC converter  501 ; protection switch  502 ; low voltage battery  503 ; boost DC-DC converter  504 ; and control section  505 . 
     Buck-boost DC-DC converter  501  stabilizes a voltage value of output electrical power by boosting or bucking the voltage of electrical power from solar panel  101  according to the control by control section  505 . Buck-boost DC-DC converter  501  outputs electrical power having a stabilized voltage value to protection switch  106 , protection switch  502 , and boost DC-DC converter  504 . 
     Protection switch  502  switches between ON and OFF states according to the control by control section  505 . Protection switch  502  switches between the following two patterns according to the control by control section  505 . In a first pattern, when protection switch  502  is turned on, electrical power from buck-boost DC-DC converter  501  is output to low voltage battery  503 , and in contrast, when protection switch  502  is turned off, electrical power from buck-boost DC-DC converter  501  is not output to low voltage battery  503 . In a second pattern, when protection switch  502  is turned on, electrical power from low voltage battery  503  is output to boost DC-DC converter  504 , and in contrast, when protection switch  502  is turned off, electrical power from low voltage battery  503  is not output to boost DC-DC converter  504 . 
     Low voltage battery  503  stores the low-voltage electrical power that is input from buck-boost DC-DC converter  501  via protection switch  502 . 
     Boost DC-DC converter  504  boosts the voltage of the electrical power from buck-boost DC-DC converter  501 , or the voltage of the electrical power from protection switch  502  to a predetermined value according to the control by control section  505 , and outputs the boosted electrical power to relay  104 . At this time, a loss occurs in the electrical power boosted by boost DC-DC converter  504 . When starting up, boost DC-DC converter  504  consumes electrical power. 
     Control section  505  controls buck-boost DC-DC converter  501  to switch between the turning on and off of a boost operation and a buck operation, and controls boost DC-DC converter  504  to switch between the turning on and off of a boost operation. Control section  505  monitors the amount of electrical power stored in low voltage battery  107 , the amount of electrical power stored in high voltage battery  105 , and the amount of electrical power stored in low voltage battery  503 . Control section  505  charges low voltage battery  107 , based on a monitoring result, and when the amount of electrical power stored in low voltage battery  107  is equal to or greater than a predetermined value, control section  505  charges low voltage battery  503 . When the amount of electrical power stored in low voltage battery  503  is equal to or greater than a predetermined value, control section  505  controls relay  104 , protection switch  106  and protection switch  502  to switch between ON and OFF states in such a manner that high voltage battery  105  is charged. 
     That is, first, control section  505  controls relay  104 , protection switch  106 , and protection switch  502  to switch between ON and OFF states in such a manner that electrical power from solar panel  101  is stored in low voltage battery  107  without being boosted by boost DC-DC converter  504 , and low voltage battery  107  is charged. When the amount of electrical power stored in low voltage battery  107  is equal to or greater than the predetermined value, control section  505  controls relay  104 , protection switch  106 , and protection switch  502  to switch between ON and OFF states in such a manner that electrical power from solar panel  101  is stored in low voltage battery  503  without being boosted by boost DC-DC converter  504 , and low voltage battery  503  is charged. When the amount of electrical power stored in low voltage battery  503  is equal to or greater than the predetermined value, control section  505  controls relay  104 , protection switch  106 , and protection switch  502  to switch between ON and OFF states in such a manner that high voltage battery  105  is charged. Accordingly, in vehicle-mounted power source apparatus  500 , it is possible to immediately charge high voltage battery  105  from low voltage battery  503 , to reduce a start-up time of boost DC-DC converter  504 , relay  104 , and the like, and to prevent a decrease in charge efficiency (electrical power consumption during charging). Here, the charging of low voltage battery  503  implies that low voltage battery  503  stores electrical power until the amount of electrical power stored therein reaches a predetermined value. 
     Control section  505  can determine whether the vehicle is travelling or is stopped, based on an ignition signal from the outside. Control section  505  determines an operation state of the vehicle based on an ignition signal in the same manner as performed by control section  109 . Thus, a description using a specific example will not be given. 
     Relay  104  switches between ON and OFF states according to the control by control section  505 . When relay  104  is turned on, the electrical power from boost DC-DC converter  504  is output to high voltage battery  105 , and in contrast, when relay  104  is turned off, the electrical power from boost DC-DC converter  504  is not output to high voltage battery  105 . 
     Protection switch  106  switches between ON and OFF states according to the control by control section  505 . When protection switch  106  is turned on, the electrical power from buck-boost DC-DC converter  501  is output to low voltage battery  107 , and in contrast, when protection switch  106  is turned off, the electrical power from buck-boost DC-DC converter  501  is not output to low voltage battery  107 . 
     &lt;Operation of Vehicle-Mounted Power Source Apparatus while Vehicle Stops&gt; 
     An operation of vehicle-mounted power source apparatus  500  according to Embodiment 3 of the present invention while the vehicle stops will be described with reference to  FIG. 6 . 
     First, control section  505  determines that the vehicle is stopped, based on an ignition signal, and turns off protection switch  502  and the operation of boost DC-DC converter  504  (step ST 601 ). 
     Subsequently, control section  505  determines whether the voltage value VL of low voltage battery  107  is the first threshold value or greater (step ST 602 ). 
     When control section  505  determines that the voltage value VL is less than the first threshold value (step ST 602 : NO), control section  505  turns on protection switch  106  (step ST 603 ), and the process returns to step ST 602 . Accordingly, vehicle-mounted power source apparatus  500  charges low voltage battery  107  prior to charging high voltage battery  105 . 
     In contrast, when control section  505  determines that the voltage value VL is the first threshold value or greater (step ST 602 : YES), control section  505  turns off protection switch  106  and turns on protection switch  502  (step ST 604 ). Accordingly, vehicle-mounted power source apparatus  500  charges low voltage battery  503  prior to charging high voltage battery  105 . 
     Control section  505  determines whether the voltage value VL is the second threshold value or less (step ST 605 ). 
     When determining that the voltage value VL is the second threshold value or less (step ST 605 : YES), control section  505  turns off protection switch  502  (step ST 606 ), and the process returns to step ST 603 . Accordingly, vehicle-mounted power source apparatus  500  stops charging low voltage battery  503 , and starts charging low voltage battery  107 . 
     In contrast, when determining that the voltage value VL is greater than the second threshold value (step ST 605 : NO), control section  505  determines whether a voltage value VM of low voltage battery  503  is a fifth threshold value or greater (step ST 607 ). Here, the voltage value VM indicates the amount of electrical power stored in low voltage battery  503 , and increases as the amount of stored electrical power increases. The fifth threshold value indicates the amount of stored electrical power suitable for charging high voltage battery  105  (an upper limit value for the amount of electrical power stored in low voltage battery  503 ), and is a reference value to determine as to whether or not to stop charging low voltage battery  503 . 
     When control section  505  determines that the voltage value VM is less than the fifth threshold value (step ST 607 : NO), the process returns to step ST 604 . Accordingly, vehicle-mounted power source apparatus  500  continuously charges low voltage battery  503 . 
     In contrast, when control section  505  determines that the voltage value VM is the fifth threshold value or greater (step ST 607 : YES), control section  505  turns off buck-boost DC-DC converter  501  (step ST 608 ). Accordingly, vehicle-mounted power source apparatus  500  stops charging low voltage battery  503 . 
     Subsequently, control section  505  turns on the operation of boost DC-DC converter  504  and relay  104  (step ST 609 ). Accordingly, vehicle-mounted power source apparatus  500  starts discharging low voltage battery  503 , and starts charging high voltage battery  105 . 
     Control section  505  determines whether the voltage value VM is a sixth threshold value (the fifth threshold value&gt;the sixth threshold value) or less (step ST 610 ). Here, the sixth threshold value indicates the amount of stored electrical power (for example, a lower limit value for the amount of electrical power stored in low voltage battery  503 ) suitable for confirming completion of the charging of high voltage battery  105 , and is a reference value to determine as to whether or not to stop discharging low voltage battery  503 , and a reference value to determine as to whether or not to stop charging high voltage battery  105 . 
     When control section  505  determines that the voltage value VM is greater than the sixth threshold value (step ST 610 : NO), the process returns to step ST 609 . Accordingly, vehicle-mounted power source apparatus  500  continues to discharge low voltage battery  503  and to charge high voltage battery  105 . 
     In contrast, when determining that the voltage value VM is the sixth threshold value or less (step ST 610 : YES), control section  505  turns off the operation of boost DC-DC converter  504  and relay  104  (step ST 611 ). Accordingly, vehicle-mounted power source apparatus  500  stops discharging low voltage battery  503 , and stops charging high voltage battery  105 . 
     Subsequently, control section  505  turns on the operation of buck-boost DC-DC converter  501  (step ST 612 ), and charges low voltage battery  503 . 
     The operation of vehicle-mounted power source apparatus  500  while the vehicle travels is the same as that illustrated in  FIG. 6  except that relay  104  is turned on in a step following step ST 601 , and the controlling of relay  104  to be turned off in step ST 611  is omitted, and thereby a description thereof will be omitted. 
     &lt;Effects of Embodiment 3&gt; 
     In the embodiment, when all of low voltage batteries  107  and  503 , and high voltage battery  105  are charged with electrical power obtained by solar power generation, switching is performed so that high voltage battery  105  is charged after low voltage batteries  107  and  503  that require no boosting are charged. As a result, it is possible to prevent a decrease in the overall charge efficiency of the apparatus. 
     In the embodiment, since high voltage battery  105  is charged with electrical power stored in low voltage battery  503 , it is possible to prevent a decrease in charge efficiency compared to when electrical power from solar panel  101  is boosted in each case, and high voltage battery  105  is charged with the boosted electrical power. 
     In the embodiment, since low voltage battery  107  is charged prior to low voltage battery  503 , it is possible to reliably supply electrical power to load  108 . 
     In addition, in the embodiment, since both of low voltage battery  107  and high voltage battery  105  are charged with electrical power obtained by solar power generation, it is possible to reliably supply electrical power to load  108  and also to increase the cruising distance of the vehicle and to reduce the charging time of high voltage battery  105 . 
     &lt;Variation of Embodiment 3&gt; 
     In the embodiment, low voltage battery  107  is charged prior to high voltage battery  105  while the vehicle travels; however, high voltage battery  105  may be charged prior to low voltage battery  107 . 
     (Embodiment 4) 
     In this embodiment, after low voltage battery  503  is charged, high voltage battery  105  is charged with electrical power stored in low voltage battery  503 . 
     In the embodiment, since the vehicle-mounted power source apparatus has the same configuration as in  FIG. 5 , the configuration will not be repeatedly described, and an operation of the vehicle-mounted power source apparatus while the vehicle stops will be described using the reference numerals illustrated in  FIG. 5 . 
     &lt;Operation of Vehicle-Mounted Power Source Apparatus while Vehicle Stops&gt; 
     An operation of vehicle-mounted power source apparatus  500  according to Embodiment 4 of the present invention while the vehicle stops will be described with reference to  FIG. 7 . 
     First, control section  505  determines that the vehicle is stopped, based on an ignition signal, and turns off protection switch  106  and the operation of boost DC-DC converter  504  (step ST 701 ). 
     Subsequently, control section  505  turns on protection switch  502  (step ST 702 ). Accordingly, vehicle-mounted power source apparatus  500  charges low voltage battery  503  prior to charging high voltage battery  105 . 
     Subsequently, control section  505  determines whether the voltage value VM of low voltage battery  503  is the fifth threshold value or greater (step ST 703 ). 
     When control section  505  determines that the voltage value VM is less than the fifth threshold value (step ST 703 : NO), control section  505  repeats step ST 703 . Accordingly, vehicle-mounted power source apparatus  500  continuously charges low voltage battery  503 . 
     In contrast, when control section  505  determines that the voltage value VM is the fifth threshold value or greater (step ST 703 : YES), control section  505  turns off buck-boost DC-DC converter  501  (step ST 704 ). Accordingly, vehicle-mounted power source apparatus  500  stops charging low voltage battery  503 . 
     Subsequently, control section  505  turns on the operation of boost DC-DC converter  504  and relay  104  (step ST 705 ). Accordingly, vehicle-mounted power source apparatus  500  starts discharging low voltage battery  503  and starts charging high voltage battery  105 . 
     Subsequently, control section  505  determines whether the voltage value VM is the sixth threshold value or less (step ST 706 ). 
     When control section  505  determines that the voltage value VM is greater than the sixth threshold value (step ST 706 : NO), the process returns to step ST 705 . Accordingly, vehicle-mounted power source apparatus  500  continues to discharge low voltage battery  503  and to charge high voltage battery  105 . 
     In contrast, when determining that the voltage value VM is the sixth threshold value or less (step ST 706 : YES), control section  505  turns off the operation of boost DC-DC converter  504  and relay  104  (step ST 707 ). Accordingly, vehicle-mounted power source apparatus  500  stops discharging low voltage battery  503  and stops charging high voltage battery  105 . 
     Subsequently, control section  505  turns on the operation of buck-boost DC-DC converter  501  (step ST 708 ), and ends the charging process. 
     When the amount of electrical power stored in low voltage battery  107  is the second threshold value (the reference value to determine as to whether or not to start charging low voltage battery  107 ) or less, preferably, control section  505  stops the operation illustrated in  FIG. 7 , and stores electrical power in low voltage battery  107 . 
     The operation of vehicle-mounted power source apparatus  500  while the vehicle travels is the same as that illustrated in  FIG. 7  except that relay  104  is turned on in a step following step ST 701 , and the controlling of relay  104  to be turned off in step ST 707  is omitted, and thereby description thereof will be omitted. 
     &lt;Effects of Embodiment 4&gt; 
     In the present embodiment, when both of low voltage battery  503  and high voltage battery  105  are charged with the electrical power obtained by solar power generation, switching is performed so that high voltage battery  105  is charged after low voltage battery  503  that requires no boosting is charged. As a result, it is possible to prevent a decrease in the overall charge efficiency of the apparatus. 
     In the embodiment, since high voltage battery  105  is charged with electrical power stored in low voltage battery  503 , it is possible to prevent a decrease in charge efficiency compared to when electrical power from solar panel  101  is boosted, and high voltage battery  105  is charged with the boosted electrical power. 
     &lt;Variation of Embodiment 4&gt; 
     In the embodiment, low voltage battery  503  is charged prior to high voltage battery  105  while the vehicle travels; however, high voltage battery  105  may be charged prior to low voltage battery  503 . 
     (Embodiment 5) 
     This embodiment is characterized in that, when high voltage battery  105  is charged with electrical power stored in low voltage battery  803 , the charging and the discharging of low voltage battery  803  are performed via different paths. 
     &lt;Configuration of Vehicle-Mounted Power Source Apparatus&gt; 
     The configuration of vehicle-mounted power source apparatus  800  according to Embodiment 5 of the present invention will be described with reference to  FIG. 8 . In regard to input and output lines in  FIG. 8 , dotted lines each indicate an input and output line for the transmission of a control signal, and solid lines each indicate an input and output line for the transmission of signals other than the control signal or the delivery of electrical power. 
     Compared to the configuration of vehicle-mounted power source apparatus  100  according to Embodiment 1 illustrated in  FIG. 1 , vehicle-mounted power source apparatus  800  illustrated in  FIG. 8  has protection switch  802 , low voltage battery  803 , and protection switch  804  as additional configuration elements, and has buck-boost DC-DC converter  801  in place of buck-boost DC-DC converter  102 , boost DC-DC converter  805  in place of boost DC-DC converter  103 , and control section  806  in place of control section  109 . In  FIG. 8 , the same reference numerals are assigned to portions having the same configurations as in  FIG. 1 , and description thereof will be omitted. 
     Vehicle-mounted power source apparatus  800  is configured to mainly include solar panel  101 ; relay  104 ; high voltage battery  105 ; protection switch  106 ; low voltage battery  107 ; load  108 ; buck-boost DC-DC converter  801 ; protection switch  802 ; low voltage battery  803 ; protection switch  804 ; boost DC-DC converter  805 ; and control section  806 . 
     Buck-boost DC-DC converter  801  stabilizes a voltage value of output electrical power by boosting or bucking the voltage of electrical power from solar panel  101  according to the control by control section  806 . Buck-boost DC-DC converter  801  outputs electrical power having a stabilized voltage value to protection switch  106 , protection switch  802 , and protection switch  804 . 
     Protection switch  802  switches between ON and OFF states according to the control by control section  806 . When protection switch  802  is turned on, the electrical power from buck-boost DC-DC converter  801  is output to low voltage battery  803 , and in contrast, when protection switch  802  is turned off, the electrical power from buck-boost DC-DC converter  801  is not output to low voltage battery  803 . 
     Low voltage battery  803  stores the low-voltage electrical power that is input from buck-boost DC-DC converter  801  via protection switch  802 . 
     Protection switch  804  switches between ON and OFF states according to the control by control section  806 . When protection switch  804  is turned on, the electrical power from buck-boost DC-DC converter  801  is output to boost DC-DC converter  805 , and in contrast, when protection switch  804  is turned off, the electrical power from buck-boost DC-DC converter  801  is not output to boost DC-DC converter  805 . Boost DC-DC converter  805  boosts the voltage of the electrical power that is input from buck-boost DC-DC converter  801  via protection switch  804 , or the voltage of the electrical power acquired from low voltage battery  803  to a predetermined value according to the control by control section  806 , and outputs the boosted electrical power to relay  104 . At this time, a loss occurs in the electrical power boosted by boost DC-DC converter  805 . 
     Control section  806  controls buck-boost DC-DC converter  801  to switch between the turning on and off of a boost operation and a buck operation, and controls boost DC-DC converter  805  to switch between the turning on and off of a boost operation. Control section  806  monitors the amount of electrical power stored in low voltage battery  107 , the amount of electrical power stored in high voltage battery  105 , and the amount of electrical power stored in low voltage battery  803 . Control section  806  charges low voltage battery  803 , based on a monitoring result, and when the amount of electrical power stored in low voltage battery  803  is equal to or greater than a predetermined value, control section  806  controls relay  104 , protection switch  106 , protection switch  802 , and protection switch  804  to switch between ON and OFF states in such a manner that high voltage battery  105  is charged with electrical power stored in low voltage battery  803 . 
     That is, first, control section  806  controls relay  104 , protection switch  106 , protection switch  802 , and protection switch  804  to switch between ON and OFF states in such a manner that electrical power from solar panel  101  is stored in low voltage battery  803  without being boosted by boost DC-DC converter  805 , and low voltage battery  803  is charged. When the amount of electrical power stored in low voltage battery  803  is equal to or greater than the predetermined value, control section  806  turns off protection switch  802  and protection switch  804  and turns on boost DC-DC converter  805  and relay  104  in such a manner that high voltage battery  105  is charged from low voltage battery  803 . Accordingly, high voltage battery  105  is charged from low voltage battery  803  via boost DC-DC converter  805  and relay  104 . At this time, protection switch  802  and protection switch  804  are turned off, and protection switch  106  is turned on, and thereby electrical power generated by solar panel  101  can be supplied to low voltage battery  107  and load  108  while high voltage battery  105  is charged from low voltage battery  803 . Here, the charging of low voltage battery  803  implies that low voltage battery  803  stores electrical power until the amount of electrical power stored therein reaches a predetermined value. 
     Control section  806  can determine whether the vehicle is travelling or is stopped, based on an ignition signal from the outside. Control section  806  determines an operation state of the vehicle based on an ignition signal in the same manner as performed by control section  109 , and thereby a description of a specific example will not be given. 
     Relay  104  switches between ON and OFF states according to the control by control section  806 . When relay  104  is turned on, the electrical power from boost DC-DC converter  805  is output to high voltage battery  105 , and in contrast, when relay  104  is turned off, the electrical power from boost DC-DC converter  805  is not output to high voltage battery  105 . 
     Protection switch  106  switches between ON and OFF states according to the control by control section  806 . When protection switch  106  is turned on, the electrical power from buck-boost DC-DC converter  801  is output to low voltage battery  107 , and in contrast, when protection switch  106  is turned off, the electrical power from buck-boost DC-DC converter  801  is not output to low voltage battery  107 . 
     &lt;Effects of Embodiment 5&gt; 
     In the embodiment, boost DC-DC converter  805  directly acquires electrical power stored in low voltage battery  803  without going through protection switch  802 . Accordingly, in the embodiment, in addition to the effects of Embodiment 3, electrical power generated by solar panel  101  can be supplied to low voltage battery  107  and load  108  while high voltage battery  105  is charged from low voltage battery  803 , and it is possible to efficiently use the generated electrical power, and to prevent a decrease in charge efficiency. 
     &lt;Variation Common to all Embodiments&gt; 
     In Embodiments 1 to 5, each battery is charged by storing electrical power until the amount of electrical power stored therein reaches a predetermined value; however, each battery may be charged by storing electrical power for a predetermined amount of time. 
     The disclosure of Japanese Patent Application No. 2012-252094, filed on Nov. 16, 2012, including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     INDUSTRIAL APPLICABILITY 
     The vehicle-mounted power source apparatus according to the present invention is suitable for storing electrical power obtained by solar power generation in a battery. 
     REFERENCE SIGNS LIST 
     
         
           100  Vehicle-mounted power source apparatus 
           101  Solar panel 
           102  Buck-boost DC-DC converter 
           103  Boost DC-DC converter 
           104  Relay 
           105  High voltage battery 
           106  Protection switch 
           107  Low voltage battery 
           108  Load 
           109  Control section