Abstract:
The vehicle-mounted power source device comprising: a low-voltage battery; a high-voltage battery; a boost unit that boosts electrical power for charging the high-voltage battery; a solar panel that converts solar light to electrical power; a bi-directional buck-boost unit that boosts/bucks the electrical power converted by the solar panel; and a control unit that performs control in a manner so as to charge the low-voltage battery by means of electrical power of which the voltage has been altered by the buck-boost unit. When the amount of stored electrical power at the low-voltage battery is at least a predetermined value, the control unit performs control in a manner so that the electrical power stored at the low-voltage battery is boosted by the boost unit and the bi-directional buck-boost unit, and the high-voltage battery is charged by means of the boosted electrical power.

Description:
TECHNICAL FIELD 
       [0001]    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 
       [0002]    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. In this respect, the high voltage battery for driving a vehicle may be charged with electrical power obtained by solar power generation. 
         [0003]    When the high voltage battery is charged with the electrical power obtained by solar power generation, a boost DC-DC converter and a relay to boost the voltage of the electrical power to a high voltage need to be driven, however. Thus, when good sunlight is not available, the power consumption for driving a boost DC-DC converter or the like becomes greater than the electrical power obtained by solar power generation. As a result, there is a concern that the high voltage battery may not be charged. 
         [0004]    In Patent Literature (hereinafter, referred to as “PTL”) 1, a configuration is employed in which an electric double-layer capacitor is charged with the electrical power generated by a solar cell, and a charger operation command signal is output to a charger to re-charge a battery with the electrical power in the electric double-layer capacitor when a terminal voltage of the electric double-layer capacitor exceeds a breakdown voltage of a Zener diode. Accordingly, since the charger is in a non-operation state when the terminal voltage is equal to or lower than the breakdown voltage of the Zener diode, it is possible to limit the power consumption in a circuit to the minimum, and to efficiently use energy. 
       CITATION LIST 
     Patent Literature 
     PTL 1 
       [0000]    
       
         Japanese Patent Application Laid-Open No. 10-309002 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0006]    However, in a case where the high voltage battery is charged with boosted electrical power after a low voltage battery (the electric double-layer capacitor in PTL 1) is charged, and when a voltage difference between the low voltage battery and the high voltage battery is large, the efficiency of the boost DC-DC converter deteriorates. That is, there arises a problem in that it is not possible to efficiently charge the high voltage battery with electrical power obtained by solar power generation. 
         [0007]    An object of the present invention is to provide a vehicle-mounted power source apparatus that prevents a decrease in the charge efficiency thereof by using a plurality of boost DC-DC converters when charging a high voltage battery with electrical power obtained by solar power generation. 
       Solution to Problem 
       [0008]    A vehicle-mounted power source apparatus according to the present invention is an 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 boost section that boosts the voltage of the electrical power for charging the high voltage battery; a solar panel that converts sunlight into electrical power; a bidirectional buck-boost section that boosts or steps down the voltage of the electrical power obtained through the conversion by the solar panel; and a control section that makes a control so as to charge the low voltage battery with the electrical power transformed by the bidirectional buck-boost section, in which, when the amount of electrical power stored in the low voltage battery is equal to or greater than a predetermined value, the control section makes a control so as to boost the electrical power stored in the low voltage battery, by the bidirectional buck-boost section and the boost section and to charge the high voltage battery with the boosted electrical power. 
       Advantageous Effects of Invention 
       [0009]    According to the present invention, it is possible to prevent a decrease in the charge efficiency of the apparatus by using a plurality of the boost DC-DC converters when charging the high voltage battery with electrical power obtained by solar power generation. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]      FIG. 1  is a block diagram illustrating the configuration of a vehicle-mounted power source apparatus according to Embodiment 1 of the present invention; and 
           [0011]      FIG. 2  is a flowchart illustrating an operation of the vehicle-mounted power source apparatus according to Embodiment 1 of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0012]    Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. 
       Embodiment 1 
     [Configuration of Vehicle-Mounted Power Source Apparatus] 
       [0013]    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 delivery of electrical power. 
         [0014]    Vehicle-mounted power source apparatus  100  mainly includes solar panel  101 ; protection switch  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 ; protection switch  109 ; low voltage battery  110 ; load  111 ; and control section  112 . 
         [0015]    Solar panel  101  converts received sunlight into electrical power, and outputs the electrical power to buck-boost DC-DC converter  103  via protection switch  102 . 
         [0016]    Protection switch  102  switches between ON and OFF states according to the control by control section  112 . When protection switch  102  is turned on, the electrical power from solar panel  101  is output to buck-boost DC-DC converter  103 , and in contrast, when protection switch  102  is turned off, the electrical power from solar panel  101  is not output to buck-boost DC-DC converter  103 . 
         [0017]    Buck-boost DC-DC converter  103  outputs electrical power with a desired voltage by boosting and stepping down the electrical power that is input from solar panel  101  via protection switch  102 , according to the control by control section  112 . Buck-boost DC-DC converter  103  outputs the transformed electrical power to protection switch  107  and protection switch  109 . 
         [0018]    In the embodiment, buck-boost DC-DC converter  103  is a bidirectional buck-boost DC-DC converter. That is, buck-boost DC-DC converter  103  can boost or step down the electrical power that is input from solar panel  101  via protection switch  102 , and can boost electrical power that is input from low voltage battery  108  via protection switch  107 . The electrical power (the electrical power from low voltage battery  108 ) boosted by buck-boost DC-DC converter  103  is output to boost DC-DC converter  104 . 
         [0019]    Boost DC-DC converter  104  boosts the voltage of the electrical power from buck-boost DC-DC converter  103  to a predetermined value (for example, 50V to 400V) according to the control by control section  112 , and outputs the boosted electrical power to relay  105 . 
         [0020]    At this time, a loss occurs in the electrical power boosted by buck-boost DC-DC converter  103  or boost DC-DC converter  104 . It is known that this loss increases as the degree of boost increases. For example, an electrical power loss associated with boosting further increases when a voltage is boosted by forty times from 10V to 400V compared to when a voltage is boosted by five times from 40V to 200V. 
         [0021]    For this reason, in the embodiment, boosting is performed using two boost DC-DC converters such as buck-boost DC-DC converter  103  and boost DC-DC converter  104 , and thereby an electrical power loss associated with the boosting decreases. That is, when a voltage is boosted by forty times from 10V to 400V, buck-boost DC-DC converter  103  boosts a voltage by five times from 10V to 50V, and boost DC-DC converter  104  boosts a voltage by eight times from 50V to 400V, and thereby it is possible to boost a voltage to a desired voltage value (400V) while preventing a single buck-boost DC-DC converter from performing a high boost operation. Accordingly, it is possible to decrease an electrical power loss associated with boosting, and to prevent a decrease in charge efficiency. 
         [0022]    Relay  105  switches between ON and OFF states according to the control by control section  112 . When relay  105  is turned on, the electrical power from boost DC-DC converter  104  is output to high voltage battery  106 , and in contrast, when relay  105  is turned off, the electrical power from boost DC-DC converter  104  is not output to high voltage battery  106 . 
         [0023]    High voltage battery  106  stores the high-voltage electrical power that is input from boost DC-DC converter  104  via relay  105 . For example, high voltage battery  106  is a lithium-ion cell (400V), and is used as a power source for driving a vehicle equipped with vehicle-mounted power source apparatus  100 . 
         [0024]    Protection switch  107  switches between ON and OFF states according to the control by control section  112 . When protection switch  107  is turned on, the electrical power from buck-boost DC-DC converter  103  is output to low voltage battery  108 , and in contrast, when protection switch  107  is turned off, the electrical power from buck-boost DC-DC converter  103  is not output to low voltage battery  108 . When high voltage battery  106  is charged with electrical power stored in low voltage battery  108 , protection switch  107  is set to be turned on, and thereby the electrical power from low voltage battery  108  is output to buck-boost DC-DC converter  103 . 
         [0025]    Low voltage battery  108  stores the low-voltage electrical power that is input from buck-boost DC-DC converter  103  via protection switch  107 . For example, low voltage battery  108  is a lead-acid battery (10V). 
         [0026]    Protection switch  109  switches between ON and OFF states according to the control by control section  112 . When protection switch  109  is turned on, the electrical power from buck-boost DC-DC converter  103  is output to low voltage battery  110  and load  111 , and in contrast, when protection switch  109  is turned off, the electrical power from buck-boost DC-DC converter  103  is not output to low voltage battery  110  and load  111 . 
         [0027]    Low voltage battery  110  stores the low-voltage electrical power that is input from buck-boost DC-DC converter  103  via protection switch  109 . For example, low voltage battery  110  is a lead-acid battery (12V), and is used as a power source for load  111 . 
         [0028]    Load  111  operates on the electrical power from protection switch  109  or electrical power stored in low voltage battery  110 . For example, load  111  is an accessory for the vehicle such as a car navigation system. 
         [0029]    Control section  112  controls buck-boost DC-DC converter  103  to switch between the turning on and off of a boost operation or a step down operation, and controls a boost operation of boost DC-DC converter  104 , an operation of protection switches  102 ,  107 , and  109 , and an operation of relay  105 . Control section  112  monitors the amount of electrical power stored in low voltage battery  108 , the amount of electrical power stored in high voltage battery  106 , and the amount of electrical power stored in low voltage battery  110 . Control section  112  charges low voltage battery  108 , based on a monitoring result, and when the amount of electrical power stored in low voltage battery  108  is equal to or greater than a predetermined value, control section  112  controls protection switch  102 , buck-boost DC-DC converter  103 , boost DC-DC converter  104 , relay  105 , and protection switch  107  so that high voltage battery  106  is charged. 
         [0030]    That is, first, control section  112  controls boost DC-DC converter  104  to be turned off, protection switch  107  to be turned on, and protection switch  109  to be turned off so that the low voltage battery  108  is charged without boosting the voltage of electrical power from solar panel  101  via boost DC-DC converter  104 . 
         [0031]    When the amount of electrical power stored in low voltage battery  108  is equal to or greater than the predetermined value, control section  112  controls protection switch  102  to be turned off, and buck-boost DC-DC converter  103 , boost DC-DC converter  104 , relay  105 , and protection switch  107  to be turned on so that the high voltage battery  106  is charged with electrical power stored in the low voltage battery  108 . 
         [0032]    When high voltage battery  106  is charged with electrical power stored in low voltage battery  108 , it is possible to boost the voltage of the electrical power stored in low voltage battery  108  via buck-boost DC-DC converter  103  and boost DC-DC converter  104 , and thereby it is possible to boost the voltage to a voltage value required by the high voltage battery in multiple stages. 
         [0033]    Accordingly, in vehicle-mounted power source apparatus  100 , it is possible to decrease a loss when the voltage of electrical power stored in low voltage battery  108  is boosted to the voltage value required by the high voltage battery. 
         [0034]    In addition, since buck-boost DC-DC converter  103  for adjusting the voltage of electrical power from solar panel  101  is used so as to boost the voltage of electrical power stored in low voltage battery  108 , it is not necessary to provide a separate boost DC-DC converter. 
         [0035]    Here, the charging of low voltage battery  108  implies that low voltage battery  108  stores electrical power until the amount of electrical power stored therein reaches a predetermined value. 
         [0036]    Control section  112  can determine whether the vehicle is travelling or is stopped, based on an ignition signal from the outside. For example, when an ignition signal indicates that the vehicle is driven, control section  112  determines that the vehicle is travelling. When an ignition signal indicates that the vehicle is stopped, control section  112  determines that the vehicle is stopped. 
         [0037]    [Operation of Vehicle-Mounted Power Source Apparatus] 
         [0038]    An operation of vehicle-mounted power source apparatus  100  according to Embodiment 1 of the present invention will be described with reference to the flowchart illustrated in  FIG. 2 . A description of this flowchart will be given based on the assumption that protection switches  102  and  107  are turned on, and protection switch  109 , boost DC-DC converter  104 , and relay  105  are turned off (that is, electrical power from solar panel  101  is charged to low voltage battery  108  via protection switch  102 , buck-boost DC-DC converter  103 , and protection switch  107 ). 
         [0039]    First, control section  112  determines whether a voltage value VM of low voltage battery  108  is equal to or greater than a first threshold value (step ST 201 ). Here, the voltage value VM indicates the amount of electrical power stored in low voltage battery  108 , and increases as the amount of stored electrical power is large. The first threshold value is the amount of electrical power (for example, an upper limit value for the amount of electrical power stored in low voltage battery  108 ) suitable for charging high voltage battery  106 , and is a reference value to determine as to whether or not to stop charging low voltage battery  108 . 
         [0040]    When control section  112  determines that the voltage value VM is less than the first threshold value (step ST 201 : NO), the process returns to step ST 201 . Accordingly, vehicle-mounted power source apparatus  100  continuously charges low voltage battery  108  until the voltage value VM becomes equal to or greater than the first threshold value. 
         [0041]    In contrast, when control section  112  determines that the voltage value VM is equal to or greater than the first threshold value (step ST 201 : YES), control section  112  turns off protection switch  102  (step ST 202 ). Accordingly, vehicle-mounted power source apparatus  100  stops the feeding of electrical power from solar panel  101  to buck-boost DC-DC converter  103 . 
         [0042]    Subsequently, control section  112  turns on boost DC-DC converter  104  and relay  105  (step ST 203 ). Accordingly, vehicle-mounted power source apparatus  100  starts to discharge low voltage battery  108  and to charge high voltage battery  106 . 
         [0043]    Specifically, for example, when low voltage battery  108  is a 10V battery, and high voltage battery  106  is a 400V battery, the control section  112  charges high voltage battery  106  by controlling buck-boost DC-DC converter  103  to boost electrical power by five times from 10V to 50V, the electrical power being input from low voltage battery  108  via protection switch  107 , and controlling boost DC-DC converter  104  to boost the boosted electrical power by eight times from 50V to 400V. A boost ratio between buck-boost DC-DC converter  103  and boost DC-DC converter  104  is preferably set to a value at which an electrical power loss is minimized. 
         [0044]    Subsequently, control section  112  determines whether the voltage value VM is a second threshold value (the first threshold value&gt;the second threshold value) or less (step ST 204 ). Here, the second threshold value indicates the amount of electrical power (a lower limit value for the amount of electrical power stored in low voltage battery  108 ) suitable for confirming completion of the charging of high voltage battery  106 , and is a reference value to determine as to whether or not to stop discharging low voltage battery  108 , and a reference value to determine as to whether or not to stop charging high voltage battery  106 . 
         [0045]    When control section  112  determines that the voltage value VM is greater than the second threshold value (step ST 204 : NO), the process returns to step ST 203 . Accordingly, vehicle-mounted power source apparatus  100  continues to discharge low voltage battery  108  and to charge high voltage battery  106 . 
         [0046]    In contrast, when control section  112  determines that the voltage value VM is the second threshold value or less (step ST 204 : YES), control section  112  turns off boost DC-DC converter  104  and relay  105  (step ST 205 ). Accordingly, vehicle-mounted power source apparatus  100  stops the discharging of low voltage battery  108 , and stops the charging of high voltage battery  106 . 
         [0047]    Subsequently, control section  112  turns on protection switch  102  (step ST 206 ), and charges low voltage battery  108  (process returns to step ST 201 ). 
         [0048]    [Effects of Embodiment 1] 
         [0049]    In the embodiment, when electrical power from solar panel  101  is stored in low voltage battery  108 , and electrical power stored in low voltage battery  108  becomes equal to or greater than the predetermined value, high voltage battery  106  is charged with the electrical power stored in low voltage battery  108 , and thereby 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  106  is charged with the boosted electrical power. 
         [0050]    In the embodiment, the two boost DC-DC converters such as buck-boost DC-DC converter  103  and boost DC-DC converter  104  boost a voltage value of the electrical power stored in low voltage battery  108  up to a voltage value suitable for charging high voltage battery  106 . 
         [0051]    For this reason, even when there is a large voltage difference present between the voltage value of the electrical power stored in low voltage battery  108  and the voltage value suitable for charging high voltage battery  106 , it is possible to decrease an electrical power loss associated with boosting, and to prevent a decrease in charge efficiency. 
         [0052]    Since buck-boost DC-DC converter  103  is a bidirectional boost DC-DC converter, buck-boost DC-DC converter  103  for adjusting the voltage of electrical power from solar panel  101  can be used so as to boost the voltage of electrical power stored in low voltage battery  108 , and it is also possible to reduce costs without providing a separate boost DC-DC converter for multiple stage boosting. 
         [0053]    [Variation of Embodiment 1] 
         [0054]    In this embodiment, control section  112  determines whether a voltage value VH of high voltage battery  106  is equal to or greater than a third threshold value, and when the voltage value VH is equal to or greater than the third threshold value, control section  112  may stop the charging of high voltage battery  106  and low voltage battery  108  (that is, turning off boost DC-DC converter  104  and protection switch  107 ), and supply electrical power from solar panel  101  to low voltage battery  110  and load  111  (that is, turning on protection switch  109 ). 
         [0055]    Here, the voltage value VH indicates the amount of electrical power stored in high voltage battery  106 , and increases as the amount of stored electrical power increases. The third threshold value is an upper limit value for the amount of electrical power stored in high voltage battery  106 , and is a reference value to determine as to whether or not to stop charging high voltage battery  106 . 
         [0056]    Since the charging of high voltage battery  106  stops when the amount of electrical power stored in high voltage battery  106  reaches the upper limit value, it is possible to prevent high voltage battery  106  from being overcharged, and to efficiently use electrical power from solar panel  101  without waste. 
         [0057]    As described above, when the amount of electrical power stored in high voltage battery  106  reaches the upper limit value, electrical power from solar panel  101  may be supplied to low voltage battery  110  and load  111 . Instead of that, first, electrical power from solar panel  101  may be supplied to low voltage battery  110  and load  111 , and when the voltage value VL of low voltage battery  110  reaches the upper limit value for the amount of electrical power stored in low voltage battery  110 , the charging of high voltage battery  106  (low voltage battery  108 ) may be started. 
         [0058]    Accordingly, low voltage battery  110  not requiring the boosting of the electrical power (having a small electrical power loss associated with boosting) is preferentially charged, and thereby it is possible to further decrease an electrical power loss associated with boosting, and to prevent a decrease in charge efficiency. 
         [0059]    The prioritization for charging low voltage battery  110  and high voltage battery  106  (low voltage battery  108 ) may be determined based on whether the vehicle equipped with vehicle-mounted power source apparatus  100  is travelling or stopped. For example, when the vehicle is travelling, high voltage battery  106  (low voltage battery  108 ) is preferentially charged, and in contrast, when the vehicle is stopped, low voltage battery  110  is preferentially charged. 
         [0060]    That is, since high voltage battery  106  is charged when the vehicle is stopped, it is necessary to turn on relay  105  and to start up the peripheral devices for charging, and electrical power is consumed; however, since relay  105  has already been turned on, and the peripheral devices have already been started up when the vehicle is travelling, it is possible to prevent a decrease in charge efficiency when high voltage battery  106  is charged while the vehicle is travelling compared to when high voltage battery  106  is charged while the vehicle is stopped. 
         [0061]    For this reason, when the vehicle is travelling, high voltage battery  106  may be preferentially charged. 
         [0062]    In contrast, since it is possible to prevent load  111  from consuming electrical power from low voltage battery  110  when electrical power is supplied to low voltage battery  110  and load  111  while the vehicle is travelling compared to when low voltage battery  110  is charged while the vehicle is stopped, low voltage battery  110  and load  111  may be preferentially charged while the vehicle is travelling. 
         [0063]    In the embodiments, buck-boost DC-DC converter  103  is preferably a maximum power point tracking (MPPT) apparatus. 
         [0064]    Accordingly, even when the vehicle equipped with vehicle-mounted power source apparatus  100  is partially shaded while travelling, it is possible to charge low voltage battery  108  and the like with the maximum electrical power amount from solar panel  101 . 
         [0065]    The disclosure of Japanese Patent Application No. 2012-251755, filed on Nov. 16, 2012, including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
       INDUSTRIAL APPLICABILITY 
       [0066]    The vehicle-mounted power source apparatus is suitable for storing electrical power obtained by solar power generation in the batteries. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           100  vehicle-mounted power source apparatus 
           101  solar panel 
           102  protection switch 
           103  buck-boost DC-DC converter 
           104  boost DC-DC converter 
           105  relay 
           106  high voltage battery 
           107  protection switch 
           108  low voltage battery 
           109  protection switch 
           110  low voltage battery 
           111  load 
           112  control section