Abstract:
A vehicle power source device which can improve the accuracy of battery deterioration detection. The vehicle power source device ( 100 ) is provided with: generator ( 110 ) which is in-built in a vehicle; high-voltage first battery ( 120 ) which stores the electricity generated by the generator ( 110 ); DC/DC converter ( 140 ) which is provided between the generator ( 110 ) and the first battery ( 120 ), and electrical component ( 180 ); second battery ( 130 ) which is connected to the first battery ( 120 ) via the DC/DC converter ( 140 ), and which has a lower voltage than the first battery ( 120 ); and power source ECU ( 150 ) which controls the DC/DC converter ( 140 ). If the current drawn from the first battery ( 120 ) satisfies predicted conditions, the power source ECU ( 150 ) increases the output voltage of the DC/DC converter, measures the parameters required to detect the deterioration of the first battery ( 120 ), and determines the deterioration of the first battery ( 120 ).

Description:
TECHNICAL FIELD 
     The present invention relates to a vehicle power supply apparatus used in a car or suchlike vehicle. 
     BACKGROUND ART 
     In recent years, hybrid cars and electric cars have been attracting attention from an environmental protection viewpoint, and their development has progressed rapidly. These cars have a configuration whereby a driving force of driving the wheels is obtained by converting direct current electric power from a power supply having a secondary battery to alternating current electric power, and driving a motor by means of alternating current electric power. Normally, a hybrid car is an electric car that uses both an engine and a motor, and is a kind of electric car in a broad sense. Therefore, for convenience, in this specification the term “electric car” is used in a broad sense that includes a hybrid car unless specifically indicated otherwise. 
     With an electric car of this kind, there is a particular demand for the accuracy of battery deterioration detection to be improved in order to correctly ascertain travel distance, battery life, and so forth. 
     Conventionally, the apparatus described in Patent Literature 1, for example, has been known as a vehicle battery deterioration determination apparatus. In Patent Literature 1, a technology is disclosed whereby when an electrical load connected to a battery is used, a voltage change of a battery voltage detected thereafter is calculated, and battery deterioration determination is performed by comparing the detected voltage change with a predetermined determination value. An electrical load is, for example, an air conditioner, power steering, headlights, brake lights, a radiator fan, or the like. Voltage change is calculated as a change in voltage over a predetermined time (that is, a voltage change trend) or a drop in battery voltage for the electrical load. By means of this configuration, the technology in Patent Literature 1 enables change over time of a battery to be detected accurately as battery deterioration, and the occurrence of starting trouble, stalling, or the like due to a low battery charge to be promptly reported to the driver. 
     CITATION LIST 
     Patent Literature 
     PTL 1 
     Japanese Patent Application Laid-Open No. 2003-214248 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, battery deterioration detection cannot be said to be performed accurately under better conditions with the above conventional battery deterioration determination apparatus. The reason for this is that with an air conditioner, power steering, headlights, or the like as an electrical load, the size of the load is limited to begin with. Consequently, a situation in which battery deterioration can be detected with a high degree of accuracy is not necessarily created merely by calculating a subsequent voltage change of a battery voltage when an electrical load of this kind is used. Therefore, there are certain limits to an improvement in the accuracy of battery deterioration detection. 
     It is an object of the present invention to provide a vehicle power supply apparatus that can further improve the accuracy of battery deterioration detection. 
     Solution To Problem 
     A vehicle power supply apparatus of the present invention has: a generator installed in a vehicle; a high-voltage first battery that is connected to the generator and stores electric power generated by the generator; a DC-DC converter located between electrical equipment, and a node between the generator and the first battery; a second battery that is connected to the first battery via the DC-DC converter, and that has a lower voltage than the first battery; a control section that controls operation of the DC-DC converter so that electric power is supplied to the second battery from the first battery if a condition for which drawing of a current from the first battery is predicted is satisfied; a measurement section that measures a parameter necessary to detect deterioration of the first battery, in synchronization with a control operation on the DC-DC converter by the control section; and a determination section that determines deterioration of the first battery using a measurement result of the measurement section. 
     Advantageous Effects of Invention 
     The present invention can further improve the accuracy of battery deterioration detection 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram showing a configuration of a power supply system that includes a vehicle power supply apparatus according to Embodiment 1 of the present invention; 
         FIG. 2  is a drawing showing examples of conditions for which drawing of a current from the first battery is predicted are satisfied in the power supply system in  FIG. 1 ; 
         FIG. 3  is a main flowchart showing the overall operation of the power supply system in  FIG. 1 ; 
         FIG. 4  is a flowchart showing the contents of the battery state detection processing in  FIG. 3 ; 
         FIG. 5  is a flowchart showing the contents of the battery state control processing in  FIG. 3 ; 
         FIG. 6  is a flowchart showing the contents of the first battery SOC control processing in  FIG. 5 ; 
         FIG. 7  is a flowchart showing the contents of the second battery SOC control processing in  FIG. 5 ; 
         FIG. 8  is a flowchart showing the contents of the regenerative electric power generation control processing in  FIG. 3 ; 
         FIG. 9  is a flowchart showing the contents of the DC-DC converter output control processing in  FIG. 5 ; 
         FIG. 10  is a flowchart showing the contents of the discharge-time deterioration detection processing in  FIG. 3 ; 
         FIG. 11  comprises schematic drawings for explaining the contents of the discharge-time deterioration detection processing in  FIG. 3 ; 
         FIG. 12  is a main flowchart showing the overall operation of a power supply system according to Embodiment 2 of the present invention; 
         FIG. 13  is a flowchart showing the contents of the battery state control processing in  FIG. 12 ; 
         FIG. 14  is a flowchart showing the contents of the first battery SOC control processing in  FIG. 13 ; 
         FIG. 15  is a flowchart showing the contents of the second battery SOC control processing in  FIG. 13 ; 
         FIG. 16  is a flowchart showing the contents of the regenerative electric power generation control and charge-time deterioration detection processing in  FIG. 12 ; and 
         FIG. 17  comprises schematic drawings for explaining the contents of the charge-time deterioration detection processing in  FIG. 16 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Now, embodiments of the present invention will be described in detail using the accompanying drawings. 
     Embodiment 1 
     In Embodiment 1 of the present invention, battery deterioration detection at the time of discharging will be described.  FIG. 1  is a block diagram showing the configuration of a power supply system that includes a vehicle power supply apparatus according to this embodiment. 
     Power supply system  100  shown in  FIG. 1  has generator  110 , two batteries (first battery  120  and second battery  130 ), two current sensors  122  and  132 , two DC-DC converters  140  and  172 , power supply ECU (Electronic Control Unit)  150 , starter  160 , starter relay  162 , electrically driven compressor  170 , and in-vehicle other general load (electrical equipment)  180 . Of the above configuration elements, two batteries  120  and  130 , two current sensors  122  and  132 , two DC-DC converters  140  and  172 , and power supply ECU  150 , compose a power supply apparatus. Below, starter  160 , electrically driven compressor  170 , and other general load (electrical equipment)  180  are referred to by the generic term “electrical load.” 
     During vehicle deceleration, the rotation of the engine (not shown) is transferred to generator  110 , which generates electric power and outputs regenerated energy electric power. Generator  110  is, for example, a large-capacity (for example, 150 A class) alternator with an IC regulator that is belt-driven by the engine and generates a voltage specified by power supply ECU  150  (for example, a 42 V voltage). It is also possible for generator  110  to be forcibly driven (caused to generate electric power) by means of power supply ECU  150  control as necessary other than during vehicle deceleration (forcible electric power generation). Generator  110  is connected to first battery  120  and two DC-DC converters  140  and  172 . 
     In this embodiment, an alternator is used as generator  110 , but this is not a limitation. For example, it is also possible to use a motor generator as generator  110  instead of an alternator. A motor generator is provided with the functions of both a motor and a generator in a single unit. Also, generator  110  may, for example, be connected by means of a transfer means such as a gear or belt or the like, or directly coupled, to an axle, crank axle, or the like, instead of being belt-driven by the engine. 
     First battery  120  is connected to generator  110  and two DC-DC converters  140  and  172 , recovers and stores regenerated energy generated by generator  110  during vehicle deceleration, and supplies electric power to electric loads (mainly electrically driven compressor  170  and general load  180 ) and second battery  130 . In order to perform regenerated energy recovery efficiently, first battery  120  should preferably be a high-voltage, high-performance battery with a large charging current and excellent chargeability. For example, first battery  120  is a nickel-hydride battery, lithium-ion battery, or the like, and generates a high voltage (for example, 36 V) so as to enable efficient charging with regenerated energy. Using a high-voltage battery makes high-voltage charging possible, and enables regenerated energy recovery to be performed efficiently. First battery  120  functions as the main battery in this system, and, as explained later herein, it is an object of this embodiment to detect deterioration of this main battery (first battery  120 ). 
     Second battery  130  is, for example, a general lead battery with a nominal voltage of 12 V, generates a voltage of 12 to 13 V, and supplies electric power to electrical loads (mainly starter  160  and general load  180 ). Second battery  130  receives and is charged with electric power supplied from generator  110  or first battery  120 . Second battery  130  is connected to DC-DC converter  140 , general load  180 , and starter relay  162 . Second battery  130  is not limited to a lead battery, and, for example, it is possible to use a nickel-hydride battery, lithium-ion battery, or the like instead of a lead battery. 
     Current sensor  122  is a current sensor for measuring the charge/discharge current of first battery  120  in order to detect the state of first battery  120 , and current sensor  132  is a current sensor for measuring the charge/discharge current of second battery  130  in order to detect the state of second battery  130 . 
     DC-DC converter  140 , for example, steps down or steps up an input-side voltage in accordance with a switching operation of an internal power transistor, and supplies the resulting voltage to the output side. In this embodiment, DC-DC converter  140  mainly functions as a step-down DC-DC converter that converts an input direct current voltage (an output voltage of generator  110  or an output voltage of first battery  120 ) to a different, lower direct current voltage, and outputs this lower direct current voltage. For example, DC-DC converter  140  steps down an (input-side—that is, first battery  120 -side) voltage of 36 V to an (output-side—that is, second battery  130 -side) voltage of the order of 12 V. More specifically, for example, DC-DC converter  140  inputs a 36 V voltage as an input voltage and outputs a 12.5 to 14.5 V voltage as an output voltage. The output voltage of DC-DC converter  140  is controlled by power supply ECU  150 . For example, electric power is normally supplied to general load  180  with the output voltage of DC-DC converter  140  controlled at 12.5 V, but when second battery  130  is charged, the output voltage of DC-DC converter  140  is controlled at 14.5 V. That is to say, it is possible for the output voltage of DC-DC converter  140  to be controlled in the range of 12.5 to 14.5 V in order to perform second battery  130  charging control. 
     On the other hand, DC-DC converter  172  mainly functions as a step-up DC-DC converter that converts an input direct current voltage (an output voltage of generator  110  or output voltage of first battery  120 ) to a different, higher direct current voltage, and outputs this higher direct current voltage. For example, if the rated voltage of electrically driven compressor  170  is 200 to 300 V, DC-DC converter  172  steps up a 36 V (input-side—that is, first battery  120 -side) voltage to a 200 to 300 V (output-side—that is, electrically driven compressor  170 -side) voltage. If a higher-voltage (for example, 200 to 300 V) battery is used as first battery  120 , DC-DC converter  172  can be eliminated. 
     Power supply ECU  150  performs overall control of the power supply system  100 . Specifically, for example, power supply ECU  150  controls the on (started)/off (stopped) state and output voltage of each of DC-DC converters  140  and  172 , and also controls the on (started)/off (stopped) state and output of electrically driven compressor  170 . Also, power supply ECU  150  measures the voltage and charge/discharge current of each of batteries  120  and  130 , and calculates state of charge (SOC) of each of batteries  120  and  130  by means of current integration. Furthermore, power supply ECU  150  controls generator  110 . Moreover, power supply ECU  150  detects deterioration of first battery  120  by simultaneously measuring (sampling) the current and voltage of first battery  120  during discharging at predetermined timing and calculating the internal resistance. In addition, power supply ECU  150  performs other controls described later herein. Details of power supply ECU  150  control will be given later herein using flowcharts in  FIG. 3  onward. Power supply ECU  150  comprises a microcomputer, and more specifically, comprises, for example, a CPU (central processing unit), ROM (read only memory) that stores a program, and RAM (random access memory) for program execution. 
     Starter  160  is a motor used when starting (cranking) the engine. Starter  160  is also used during driving to restart the engine from an idling stop state when the vehicle has stopped. Application of a current to starter  160  is performed by turning the ignition (IG) switch (not shown), which is the engine starting switch, to the engine start position (ST position) and turning on starter relay  162 . 
     Electrically driven compressor  170  is a compressor driven by an internal motor, and forms part of an air conditioner. The rated voltage of electrically driven compressor  170  is 200 to 300 V, for example, and it has the highest load among in-vehicle electrical loads. In this embodiment, as described later herein, electrically driven compressor  170  having the highest load is used to create a situation in which battery deterioration can be detected with a high degree of accuracy. Since electrically driven compressor  170  is driven by electricity, in many cases it is used as a set together with a regenerative system having a battery that stores regenerated energy. In a system that does not use an electrically driven compressor, other high-load electrical equipment can be used instead of an electrically driven compressor. In a system that uses an electrically driven compressor, other high-load electrical equipment can of course be used together with the electrically driven compressor. 
     General load  180  is, for example, a light or lamp, windshield wipers, audio equipment, a car navigation system, an air conditioner (excluding electrically driven compressor  170 ), or suchlike equipment installed in or on the vehicle. 
     In this embodiment, a regenerative system comprises a plurality of devices—for example, generator  110 , first battery  120  that is the high-voltage main battery (a nickel-hydride battery or lithium-ion battery), step-down DC-DC converter  140 , second battery  130  that is a general lead battery with a 12 V nominal voltage, and electrically driven compressor  170 . 
     Also, in view of the fact that the larger an electrical load the more accurately battery deterioration can be detected, deterioration of first battery  120  is detected with a high degree of accuracy by outputting (discharging) higher electric power from first battery  120  by controlling a plurality of devices (for example, electrically driven compressor  170 /electrical equipment  180  and DC-DC converter  140 ), and at the same time actively (forcibly) creating a situation in which an electrical load is applied. Specifically, first, a situation is actively created for enabling deterioration of first battery  120  to be detected with a high degree of accuracy. For example, when electrically driven compressor  170  is turned on or its power consumption increases, or when electrical equipment (general load)  180 , such as headlights, is turned on, the output voltage of DC-DC converter  140  is increased with the timing synchronized with the power consumption of electrically driven compressor  170  or electrical equipment  180 , provision is made for electric power also to be supplied to second battery  130 , and electric power output from first battery  120  is increased. Then, at the instant at which the electric power output from first battery  120  increases, the current and voltage of first battery  120  are simultaneously measured, the internal resistance of first battery  120  is calculated from the measurement results, and the deterioration of first battery  120  is detected. 
     Here, the timing at which the output voltage of DC-DC converter  140  is increased should be aligned with the timing of power consumption of electrically driven compressor  170  or electrical equipment  180 , and when a condition for which drawing of a current from first battery  120  is predicted is satisfied, the output voltage of DC-DC converter  140  is increased in synchronization with this. A condition for which drawing of a current from first battery  120  is predicted is set beforehand by means of experimentation or the like, for example. Examples of such conditions are as shown in  FIG. 2 , for example. 
     Next, the operation of power supply system  100  having the above configuration will be described using  FIG. 3  through  FIG. 11 . Here,  FIG. 3  is a main flowchart showing the overall operation of power supply system  100  in  FIG. 1 ,  FIG. 4  is a flowchart showing the contents of the battery state detection processing in  FIG. 3 ,  FIG. 5  is a flowchart showing the contents of the battery state control processing in  FIG. 3 ,  FIG. 6  is a flowchart showing the contents of the first battery SOC control processing in  FIG. 5 ,  FIG. 7  is a flowchart showing the contents of the second battery SOC control processing in  FIG. 5 ,  FIG. 8  is a flowchart showing the contents of the regenerative electric power generation control processing in  FIG. 3 ,  FIG. 9  is a flowchart showing the contents of the DC-DC converter output control processing in  FIG. 8 ,  FIG. 10  is a flowchart showing the contents of the discharge-time deterioration detection processing in  FIG. 3 , and  FIG. 11  comprises schematic drawings for explaining the contents of the discharge-time deterioration detection processing in  FIG. 3 . The flowcharts in  FIG. 3  through  FIG. 10  are stored as control programs in a storage apparatus such as ROM, and are executed by a CPU. 
     First, in step S 1000 , power supply ECU  150  determines whether or not the ignition (IG) switch (not shown) has been switched on. Specifically, if the ignition switch has been turned to the engine start position (ST position), power supply ECU  150  determines that the ignition switch has been switched on. If it is determined that the ignition switch has been switched on (S 1000 : YES), the processing flow proceeds to step S 2000 , whereas if it is determined that the ignition switch has not been switched on (S 1000 : NO), the program goes to a standby state. 
     In step S 2000 , power supply ECU  150  starts the engine. Specifically, power supply ECU  150  turns on starter relay  162  and applies a current to starter  160  from second battery  130 . By this means, the engine starts. 
     In step S 3000 , power supply ECU  150  performs battery state detection processing. The contents of this battery state detection processing are as shown in the flowchart in  FIG. 4 . 
     First, in step S 3100 , power supply ECU  150  performs battery measurement. Specifically, power supply ECU  150  measures the first battery  120  current (I 1 ) and voltage (V 1 ), and also measures the second battery  130  current (I 2 ) and voltage (V 2 ). The first battery  120  current (I 1 ) is detected by current sensor  122 , and the second battery  130  current (I 2 ) is detected by current sensor  132 . 
     Then, in step S 3200 , power supply ECU  150  performs battery state calculation. Specifically, for example, power supply ECU  150  performs current sensor  122  detection result (charge/discharge current value) integration and calculates the first battery  120  SOC (hereinafter referred to as “SOC 1 ”), and performs current sensor  132  detection result (charge/discharge current value) integration and calculates the second battery  130  SOC (hereinafter referred to as “SOC 2 ”). In this way, battery SOC calculation can be performed by integrating current flowing into a battery and current flowing out of the battery (so-called Coulomb count processing). The SOC calculation method for batteries  120  and  130  is not limited to Coulomb count processing, and any other known method can also be used. Following this, the control procedure returns to the main flowchart in  FIG. 3 . 
     In step S 4000 , power supply ECU  150  performs battery state control processing. In this battery state control processing, since batteries  120  and  130  will deteriorate more quickly if states of charge SOC 1  and SOC 2  of batteries  120  and  130  fall excessively, states of charge SOC 1  and SOC 2  of batteries  120  and  130  are controlled so as not to become less than or equal to a predetermined value. The contents of this battery state control processing are as shown in the flowchart in  FIG. 5 . 
     First, in step S 4100 , power supply ECU  150  performs first battery SOC control processing. In this first battery SOC control processing, state of charge SOC 1  of first battery  120  is controlled within a fixed range. Here, “a fixed range” is decided taking the characteristics of first battery  120  into consideration. For example, in the case of a lithium-ion battery, deterioration progresses more quickly if the SOC is too high or too low, and therefore a lithium-ion battery is normally used in a state in which the SOC is within an appropriate range (for example, 40 to 60%). In this embodiment, the upper limit and lower limit are each narrowed by 5%, and state of charge SOC 1  of first battery  120  is controlled within a range of 45 to 55% (lower limit=45%, upper limit=55%). Also, for example, assuming a case in which first battery  120  is a lithium-ion battery, in order to leave a margin in charging by regenerated electric power, a forcible electric power generation on (started)/off (stopped) state of generator  110  is switched in a range in which state of charge SOC 1  of first battery  120  is 45% or more and less than 50%. The contents of this first battery SOC control processing are as shown in the flowchart in  FIG. 6 . 
     First, in step S 4110 , power supply ECU  150  determines whether or not generator  110  is performing forcible electric power generation. If it is determined that generator  110  is performing forcible electric power generation (S 4110 : YES), the processing flow proceeds to step S 4120 , whereas if it is determined that generator  110  is not performing forcible electric power generation (S 4110 : NO), the processing flow proceeds to step S 4150 . 
     In step S 4120 , power supply ECU  150  further determines whether or not state of charge SOC 1  of first battery  120  is greater than or equal to 50%. If it is determined that state of charge SOC 1  of first battery  120  is less than 50% (S 4120 : NO), the processing flow proceeds to step S 4130 , whereas if it is determined that state of charge SOC 1  of first battery  120  is greater than or equal to 50% (S 4120 : YES), the processing flow proceeds to step S 4140 . 
     In step S 4130 , since state of charge SOC 1  of first battery  120  is less than 50%, power supply ECU  150  continues forcible electric power generation by generator  110 . By this means, first battery  120  is charged with electric power forcibly generated by generator  110 . Following this, the control procedure proceeds to step S 4150 . 
     On the other hand, in step S 4140 , since state of charge SOC 1  of first battery  120  is greater than or equal to 50%, power supply ECU  150  stops forcible electric power generation by generator  110  to leave a margin in charging by regenerated electric power. By this means, charging of first battery  120  with electric power forcibly generated by generator  110  is stopped. Following this, the control procedure proceeds to step S 4150 . 
     In step S 4150 , power supply ECU  150  determines whether or not state of charge SOC 1  of first battery  120  is less than 45%. If it is determined that state of charge SOC 1  of first battery  120  is less than 45% (S 4150 : YES), the processing flow proceeds to step S 4160 , whereas if it is determined that state of charge SOC 1  of first battery  120  is greater than or equal to 45% (S 4150 : NO), the control procedure immediately returns to the flowchart in  FIG. 5 . 
     In step S 4160 , since state of charge SOC 1  of first battery  120  has fallen below 45%, power supply ECU  150  starts forcible electric power generation by generator  110 . By this means, first battery  120  is charged with electric power forcibly generated by generator  110 . Following this, the control procedure returns to the flowchart in  FIG. 5 . 
     Next, in step S 4200 , power supply ECU  150  performs second battery SOC control processing. In this second battery SOC control processing, state of charge SOC 2  of second battery  130  is controlled within a fixed range. Here, “a fixed range” is decided taking the characteristics of second battery  130  into consideration. For example, in the case of a lead battery, deterioration progresses more quickly the greater the fall in the SOC from a fully-charged (100%) state, and therefore a lead battery is normally used in a state close to a fully-charged state (SOC=100%). In this embodiment, for example, assuming a case in which second battery  130  is a lead battery, in order to leave a margin in charging by regenerated electric power, an on (started)/off (stopped) state of forcible charging from first battery  120  to second battery  130  is switched in a range in which state of charge SOC 2  of second battery  130  is 90% or more and less than A % (normally 95%). This forcible charging on (started)/off (stopped) state is switched by controlling the output voltage of DC-DC converter  140 . The contents of this second battery SOC control processing are as shown in the flowchart in  FIG. 7 . 
     First, in step S 4210 , power supply ECU  150  determines whether or not second battery  130  is being forcibly charged. If it is determined that second battery  130  is being forcibly charged (S 4210 : YES), the processing flow proceeds to step S 4220 , whereas if it is determined that second battery  130  is not being forcibly charged (S 4210 : NO), the processing flow proceeds to step S 4250 . 
     In step S 4220 , power supply ECU  150  further determines whether or not state of charge SOC 2  of second battery  130  is greater than or equal to predetermined value A %. Here, “predetermined value A” is normally set to 95 (%), for example. However, when drawing of a current from first battery  120  is predicted (see  FIG. 2 ), for example, predetermined value A is set to 92 (%), and state of charge SOC 2  of second battery  130  is consistently lowered somewhat. By this means, second battery  130  is placed in a state in which it is readily charged at any time (that is, in which the charging current is large), and a discharge current from first battery  120  at the time of deterioration detection of first battery  120  can be made larger. If it is determined that state of charge SOC 2  of second battery  130  is less than A % (S 4220 : NO), the processing flow proceeds to step S 4230 , whereas if it is determined that state of charge SOC 2  of second battery  130  is greater than or equal to A % (S 4220 : YES), the processing flow proceeds to step S 4240 . 
     In step S 4230 , since state of charge SOC 2  of second battery  130  is less than A %, power supply ECU  150  continues forcible charging from first battery  120  to second battery  130 . That is to say, power supply ECU  150  keeps the output voltage of DC-DC converter  140  at 14.5 V. By this means, charging from first battery  120  to second battery  130  is forcibly performed. Following this, the control procedure proceeds to step S 4250 . 
     On the other hand, in step S 4240 , since state of charge SOC 2  of second battery  130  is greater than or equal to A %, power supply ECU  150  stops forcible charging of second battery  130  from first battery  120  to leave a margin in charging by regenerated electric power. That is to say, power supply ECU  150  returns the output voltage of DC-DC converter  140  to 12.5 V. By this means, charging of second battery  130  from first battery  120  is stopped. Following this, the control procedure proceeds to step S 4250 . 
     In step S 4250 , power supply ECU  150  determines whether or not state of charge SOC 2  of second battery  130  is less than 90%. If it is determined that state of charge SOC 2  of second battery  130  is less than 90% (S 4250 : YES), the processing flow proceeds to step S 4260 , whereas if it is determined that state of charge SOC 2  of second battery  130  is greater than or equal to 90% (S 4250 : NO), the control procedure immediately returns to the main flowchart in  FIG. 3 . 
     In step S 4260 , since state of charge SOC 2  of second battery  130  has fallen below 90%, power supply ECU  150  starts forcible charging of second battery  130  from first battery  120 . That is to say, power supply ECU  150  raises the output voltage of DC-DC converter  140  to 14.5 V. By this means, electric power is supplied to second battery  130  from first battery  120 , and second battery  130  is forcibly charged with this electric power. Following this, the control procedure returns to the main flowchart in  FIG. 3 . 
     In step S 5000 , power supply ECU  150  performs regenerative electric power generation control. The contents of this regenerative electric power generation control are as shown in the flowchart in  FIG. 8 . 
     First, in step S 5100 , power supply ECU  150  determines whether or not the vehicle speed is greater than or equal to a predetermined value (for example, 10 km/h) and the vehicle is decelerating. Here, determining whether or not the vehicle speed is greater than or equal to a predetermined value is to determine whether or not the current vehicle speed is suitable for regenerative electric power generation—that is, whether or not kinetic energy necessary for regenerative electric power generation is available in the vehicle. Regenerated energy is obtained by converting kinetic energy of the vehicle to electrical energy, and if the vehicle speed is low, the kinetic energy is low. Thus, a regenerated energy amount cannot be expected. Whether or not the vehicle is decelerating is determined, for example, based on vehicle speed information, or based on the degree of brake pedal depression (whether the brake pedal is being depressed). If it is determined that the vehicle speed is greater than or equal to the predetermined value (10 km/h) and the vehicle is decelerating (S 5100 : YES), the processing flow proceeds to step S 5200 , and if this is not the case—that is, if the vehicle speed is less than the predetermined value (10 km/h) or the vehicle is not decelerating (that is, the vehicle is accelerating, traveling at a constant speed, idling, or the like)—(S 5100 : NO), the control procedure immediately returns to the main flowchart in  FIG. 3 . 
     In step S 5200 , power supply ECU  150  determines whether or not state of charge (SOC 1 ) of first battery  120  is less than or equal to a predetermined value (for example, 55%). This predetermined value (55%) is the above upper limit. If it is determined that state of charge (SOC 1 ) of first battery  120  exceeds the predetermined value (55%) (S 5200 : NO), the processing flow proceeds to step S 5300 , whereas if it is determined that state of charge (SOC 1 ) of first battery  120  is less than or equal to the predetermined value (55%) (S 5200 : YES), the processing flow proceeds to step S 5400 . 
     In step S 5300 , power supply ECU  150  stops electric power generation by generator  110 . Following this, the control procedure returns to the main flowchart in  FIG. 3 . 
     On the other hand, in step S 5400 , power supply ECU  150  performs electric power generation control on generator  110 . Specifically, power supply ECU  150  sets and outputs an output instruction value to generator  110  to a target value. Here, a “target value” is a voltage necessary to charge first battery  120 , and in the case of a 36 V lithium-ion battery, for example, this target value is 42 V. 
     Then in step S 5500 , power supply ECU  150  performs output control on DC-DC converter  140 . The contents of this output control are as shown in the flowchart in  FIG. 9 . 
     First, in step S 5510 , power supply ECU  150  determines whether or not state of charge SOC 2  of second battery  130  is less than 100%. If it is determined that state of charge SOC 2  of second battery  130  is less than 100% (S 5510 : YES), the processing flow proceeds to step S 5520 , whereas if it is determined that state of charge SOC 2  of second battery  130  is greater than or equal to 100% (S 5510 : NO), the processing flow proceeds to step S 5530 . 
     In step S 5520 , since second battery  130  is not in a fully-charged (SOC 2 =100%) state, power supply ECU  150  raises the output voltage of DC-DC converter  140  to 14.5 V, higher than the initial value (12.5 V). By this means, regenerated electric power generated by generator  110  charges not only first battery  120  but also second battery  130 . Following this, the control procedure returns to the main flowchart in  FIG. 3 . 
     On the other hand, in step S 5530 , since second battery  130  is in a fully-charged (SOC 2 =100%) state, power supply ECU  150  returns the output voltage of DC-DC converter  140  to the initial value (12.5 V). The reason for this is that a lead battery will deteriorate more quickly if excessively charged. Following this, the control procedure returns to the main flowchart in  FIG. 3 . 
     Next, in step S 6000 , power supply ECU  150  performs discharge-time deterioration detection processing. This discharge-time deterioration detection processing is as shown in the flowchart in  FIG. 10 . 
     First, in step S 6100 , power supply ECU  150  determines whether or not drawing of a current from first battery  120  is predicted. This determination is made, for example, by determining whether or not a predetermined condition shown in  FIG. 2  is satisfied. For example, in the example shown in  FIG. 2 , with regard to electrically driven compressor  170 , if the temperature inside the vehicle rises by a certain temperature (for example, 5° C.) or more in a certain time (for example, one minute), it is predicted that the user will turn on the air conditioner (if the air conditioner is off) or increase the output of the air conditioner (if the air conditioner is on), and drawing of a current from first battery  120  occurs through the air conditioner actually being turned on or the air conditioner output actually being increased subsequently. Apart from electrically driven compressor  170 , drawing of a current from first battery  120  is also predicted if a condition such as shown in  FIG. 2  is satisfied for electrical equipment  180  with comparatively high power consumption (such as headlights, power steering, brake lights, or windshield wipers, for example). If it is determined that drawing of a current from first battery  120  is predicted (S 6100 : YES), the processing flow proceeds to step S 6200 , whereas if it is determined that drawing of a current from first battery  120  is not predicted (S 6100 : NO), the control procedure immediately returns to the main flowchart in  FIG. 3 . 
     In step S 6200 , power supply ECU  150  further determines whether or not state of charge SOC 2  of second battery  130  is less than or equal to 95%. The reason for this is to determine whether or not second battery  130  (a lead battery) is in a state in which it readily absorbs electric power (that is, readily receives a supply of electric power). If it is determined that state of charge SOC 2  of second battery  130  is less than or equal to 95% (S 6200 : YES), the processing flow proceeds to step S 6300 , whereas if it is determined that state of charge SOC 2  of second battery  130  exceeds 95% (S 6200 : NO), the control procedure immediately returns to the main flowchart in  FIG. 3 . 
     In step S 6300 , power supply ECU  150  performs output increase control of DC-DC converter  140 . Specifically, power supply ECU  150  raises (increases) the output voltage of DC-DC converter  140  from the initial value (12.5 V) to 14.5 V. By this means, electric power is supplied from first battery  120  not only to electrically driven compressor  170  or electrical equipment  180 , but also to second battery  130 , and supplying power to second battery  130  is started in line with (that is, in synchronization with) the timing of the start of power consumption by electrically driven compressor  170  or electrical equipment  180 . Thus, a situation in which greater electric power is output (discharged) from first battery  120  is forcibly (actively) created. For example, as shown schematically in  FIG. 11  (A), greater electric power (a larger current) is output when the output voltage of DC-DC converter  140  is increased in addition to driving of electrically driven compressor  170  than when only electrically driven compressor  170  is driven. 
     Then, in step S 6400 , power supply ECU  150  performs simultaneous current and voltage measurement for first battery  120 . At this time, as shown schematically in  FIG. 11(A) , for example, power supply ECU  150  can simultaneously measure the current and voltage of first battery  120  at the instant at which electric power output from first battery  120  increases. The measurement of current and voltage is performed for at least two points. 
     In step S 6500 , power supply ECU  150  performs deterioration determination. Specifically, power supply ECU  150  calculates internal resistance r by means of equation 1 below, using the currents and voltages of a plurality of points measured in step S 6400 . Internal resistance r is one indicator of battery deterioration. For example, as shown schematically in  FIG. 11(B) , if current and voltage are taken as coordinate axes and measured currents and voltages of a plurality of points are plotted on the coordinate plane, the gradient of a linear approximation is internal resistance r. Solving equation 1 using measured values (−100 A, 30 V) and (−300 A, 28 V) of two points shown in FIG. 11 gives a value of 0.01Ω for internal resistance r. While solving equation 1 for internal resistance r requires measurements for at least two points, measurements for three or more points may be used in order to improve the accuracy of deterioration determination.
 
 E+rI=V    (Equation 1)
 
where E: Electromotive force
         r: Internal resistance   I: Current   V: Voltage       

     Power supply ECU  150  compares calculated internal resistance r with a predetermined determination value, and determines whether or not there is deterioration of first battery  120 . The determination result is stored in a storage apparatus such as RAM, and is also reported to the user. Following this, the control procedure returns to the main flowchart in  FIG. 3 . 
     Next, in step S 7000 , power supply ECU  150  determines whether or not the ignition (IG) switch has been switched off. If it is determined that the ignition switch has been switched off (S 7000 : YES), the processing flow proceeds to step S 8000 , whereas if it is determined that the ignition switch has not been switched off (S 7000 : NO), the processing flow returns to step S 3000 . 
     In step S 7000 , power supply ECU  150  stops the engine, Specifically, power supply ECU  150  outputs a control signal that stops the engine to an engine ECU (not shown) that controls engine operation. By this means, the engine stops. 
     Thus, according to this embodiment, greater electric power can be output (discharged) from first battery  120  by controlling a plurality of devices (for example, electrically driven compressor  170 /electrical equipment  180  and DC-DC converter  140 ) and actively (forcibly) creating a situation in which an electrical load is applied simultaneously. 
     Consequently, deterioration of first battery  120  can be detected with a high degree of accuracy. 
     Embodiment 2 
     In Embodiment 2 of the present invention, battery deterioration detection at the time of charging will be described, The configuration of a power supply system of this embodiment is identical to the configuration of a power supply system that includes the vehicle power supply apparatus according to Embodiment 1 shown in  FIG. 1 , In this embodiment, battery state control, regenerative electric power generation control, and battery deterioration detection by power supply ECU  150  differ from those in Embodiment 1. 
     The operation of power supply system  100  having the above configuration will now be described using  FIG. 12  through  FIG. 17 . Here,  FIG. 12  is a main flowchart showing the overall operation of the power supply system in  FIG. 1 ,  FIG. 1   3  is a flowchart showing the contents of the battery state control processing in  FIG. 12 ,  FIG. 14  is a flowchart showing the contents of the first battery SOC control processing in  FIG. 13 ,  FIG. 15  is a flowchart showing the contents of the second battery SOC control processing in  FIG. 13 ,  FIG. 16  is a flowchart showing the contents of the regenerative electric power generation control and charge-time deterioration detection processing in  FIG. 12 , and  FIG. 17  comprises schematic drawings for explaining the contents of the charge-time deterioration detection processing in  FIG. 16 . 
     Steps in  FIG. 12  common to  FIG. 2  are assigned the same reference signs as in  FIG. 2 , and detailed descriptions thereof are omitted here. The operations in S 1000 , S 2000 , S 3000 , S 6000 , and S 7000  in  FIG. 12  are common to  FIG. 2 . 
     In step S 4000 A, power supply ECU  150  performs battery state control processing. In this battery state control processing, since batteries  120  and  130  will deteriorate more quickly if states of charge SOC 1  and SOC 2  of batteries  120  and  130  fall excessively, states of charge SOC 1  and SOC 2  of batteries  120  and  130  are controlled so as not to become less than or equal to a predetermined value. The contents of this battery state control processing are as shown in the flowchart in  FIG. 13 . 
     First, in step S 4100 A, power supply ECU  150  performs first battery SOC control processing. In this first battery SOC control processing, state of charge SOC 1  of first battery  120  is controlled within a fixed range. Here, “a fixed range” is decided taking the characteristics of first battery  120  into consideration. For example, in the case of a lithium-ion battery, deterioration progresses more quickly if the SOC is too high or too low, and hence a lithium-ion battery is normally used in a state in which the SOC is within an appropriate range (for example, 40 to 60%). In this embodiment, the upper limit and lower limit are each narrowed by 5%, and state of charge SOC 1  of first battery  120  is controlled within a range of 45 to 55% (lower limit=45%, upper limit=55%). Also, for example, assuming a case in which first battery  120  is a lithium-ion battery, in order to leave a margin in charging by regenerated electric power, on (started)/off (stopped) state of a forcible electric power generation of generator  110  is switched in a range in which state of charge SOC 1  of first battery  120  is 45% or more and less than A % (normally 50%, for example). The contents of this first battery SOC control processing are as shown in the flowchart in  FIG. 14 . 
     First, in step S 4110 A, power supply ECU  150  determines whether or not generator  110  is performing forcible electric power generation. If it is determined that generator  110  is performing forcible electric power generation (S 4110 A: YES), the processing flow proceeds to step S 4120 A, whereas if it is determined that generator  110  is not performing forcible electric power generation (S 4110 A: NO), the processing flow proceeds to step S 4150 A. 
     In step S 4120 A, power supply ECU  150  further determines whether or not state of charge SOC 1  of first battery  120  is greater than or equal to A %. Here, “predetermined value A” is normally set to 50 (%), for example. However, since regenerated energy increases in proportion to an increase in vehicle speed, provision is made for the value of predetermined value A to be lowered in preparation for regenerated energy at the time of the next vehicle deceleration. For example, settings such as 50% for a vehicle speed of 60 km/h or less, 49% for a vehicle speed of 80 km/h or less, 48% for a vehicle speed of 100 km/h or less, and so forth, may be made. If it is determined that state of charge SOC 1  of first battery  120  is less than A % (S 4120 A: NO), the processing flow proceeds to step S 4130 A, whereas if it is determined that state of charge SOC 1  of first battery  120  is greater than or equal to A % (S 4120 A: YES), the processing flow proceeds to step S 4140 A. 
     In step S 4130 A, since state of charge SOC 1  of first battery  120  is less than A %, power supply ECU  150  continues forcible electric power generation by generator  110 . By this means, first battery  120  is charged with electric power forcibly generated by generator  110 . Following this, the control procedure proceeds to step S 4150 A. 
     On the other hand, in step S 4140 A, since state of charge SOC 1  of first battery  120  is greater than or equal to A %, power supply ECU  150  stops forcible electric power generation by generator  110  to leave a margin in charging by regenerated electric power. By this means, charging of first battery  120  with electric power forcibly generated by generator  110  is stopped. Following this, the control procedure proceeds to step S 4150 A. 
     In step S 4150 A, power supply ECU  150  determines whether or not state of charge SOC 1  of first battery  120  is less than 45%. If it is determined that state of charge SOC 1  of first battery  120  is less than 45% (S 4150 A: YES), the processing flow proceeds to step S 4160 A, whereas if it is determined that state of charge SOC 1  of first battery  120  is greater than or equal to 45% (S 4150 A: NO), the control procedure immediately returns to the flowchart in  FIG. 13 . 
     In step S 4160 A, since state of charge SOC 1  of first battery  120  has fallen below 45%, power supply ECU  150  starts forcible electric power generation by generator  110 . By this means, first battery  120  is charged with electric power forcibly generated by generator  110 . Following this, the control procedure returns to the flowchart in  FIG. 13 . 
     Next, in step S 4200 A, power supply ECU  150  performs second battery SOC control processing. In this second battery SOC control processing, state of charge SOC 2  of second battery  130  is controlled within a fixed range. Here, “a fixed range” is decided taking the characteristics of second battery  130  into consideration. For example, in the case of a lead battery, the greater the fall in the SOC from a fully-charged (100%) state, the more quickly deterioration progresses, and therefore a lead battery is normally used in a state close to a fully-charged state (SOC=100%). In this embodiment, for example, assuming a case in which second battery  130  is a lead battery, in order to leave a margin in charging by regenerated electric power, an on (started)/off (stopped) state of forcible charging from first battery  120  to second battery  130  is switched in a range in which state of charge SOC 2  of second battery  130  is 90% or more and less than 95%. This forcible charging on (started)/off (stopped) state is switched by controlling the output voltage of DC-DC converter  140 . The contents of this second battery SOC control processing are as shown in the flowchart in  FIG. 15 , 
     First, in step S 4210 A, power supply ECU  150  determines whether or not second battery  130  is being forcibly charged. If it is determined that second battery  130  is being forcibly charged (S 4210 A: YES), the processing flow proceeds to step S 4220 A, whereas if it is determined that second battery  130  is not being forcibly charged (S 4210 A: NO), the processing flow proceeds to step S 4250 A. 
     In step S 4220 A, power supply ECU  150  further determines whether or not state of charge SOC 2  of second battery  130  is greater than or equal to 95%, If it is determined that state of charge SOC 2  of second battery  130  is less than 95% (S 4220 A: NO), the processing flow proceeds to step S 4230 A, whereas if it is determined that state of charge SOC 2  of second battery  130  is greater than or equal to 95% (S 4220 A: YES), the processing flow proceeds to step S 4240 A. 
     In step S 4230 A, since state of charge SOC 2  of second battery  130  is less than 95%, power supply ECU  150  continues forcible charging from first battery  120  to second battery  130 . That is to say, power supply ECU  150  keeps the output voltage of DC-DC converter  140  at 14.5 V. By this means, charging from first battery  120  to second battery  130  is forcibly performed. Following this, the control procedure proceeds to step S 4250 A. 
     On the other hand, in step S 4240 A, since state of charge SOC 2  of second battery  130  is greater than or equal to 95%, power supply ECU  150  stops forcible charging of second battery  130  from first battery  120  to leave a margin in charging by regenerated electric power. That is to say, power supply ECU  150  returns the output voltage of DC-DC converter  140  to 12.5 V. By this means, charging of second battery  130  from first battery  120  is stopped. Following this, the control procedure proceeds to step S 4250 A. 
     In step S 4250 A, power supply ECU  150  determines whether or not state of charge SOC 2  of second battery  130  is less than 90%. If it is determined that state of charge SOC 2  of second battery  130  is less than 90% (S 4250 A: YES), the processing flow proceeds to step S 4260 A, whereas if it is determined that state of charge SOC 2  of second battery  130  is greater than or equal to 90% (S 4250 A: NO), the control procedure immediately returns to the main flowchart in  FIG. 12 . 
     In step S 4260 A, since state of charge SOC 2  of second battery  130  has fallen below 90%, power supply ECU  150  starts forcible charging of second battery  130  from first battery  120 . That is to say, power supply ECU  150  raises the output voltage of DC-DC converter  140  to 14.5 V. By this means, electric power is supplied to second battery  130  from first battery  120 , and second battery  130  is forcibly charged with this electric power. Following this, the control procedure returns to the main flowchart in  FIG. 12 . 
     In step S 5000 A, power supply ECU  150  performs regenerative electric power generation control and charge-time deterioration detection. The contents of this regenerative electric power generation control and charge-time deterioration detection are as shown in the flowchart in  FIG. 16 . 
     First, in step S 5050 A, power supply ECU  150  determines whether or not the vehicle speed is greater than or equal to a predetermined value (for example, 10 km/h) and the vehicle is decelerating. Here, determining whether or not the vehicle speed is greater than or equal to a predetermined value is to determine whether or not the current vehicle speed is suitable for regenerative electric power generation that is, whether or not kinetic energy necessary for regenerative electric power generation is available in the vehicle. Regenerated energy is obtained by converting kinetic energy of the vehicle to electrical energy, and if the vehicle speed is low the kinetic energy is low. Thus, a regenerated energy amount cannot be expected. Whether or not the vehicle is decelerating is determined, for example, based on vehicle speed information, or based on the degree of brake pedal depression (whether the brake pedal is being depressed). If it is determined that the vehicle speed is greater than or equal to the predetermined value (10 km/h) and the vehicle is decelerating (S 5050 A: YES), the processing flow proceeds to step S 5100 A, and if this is not the case—that is, if the vehicle speed is less than the predetermined value (10 km/h) or the vehicle is not decelerating (that is, the vehicle is accelerating, traveling at a constant speed, idling, or the like)—(S 5050 A: NO), the control procedure immediately returns to the main flowchart in  FIG. 12 . 
     In step S 5100 A, power supply ECU  150  determines whether or not state of charge (SOC 1 ) of the first battery  120  is less than or equal to a predetermined value (for example, 55%). This predetermined value (55%) is the above upper limit. If it is determined that state of charge (SOC 1 ) of first battery  120  exceeds the predetermined value (55%) (S 5100 A: NO), the processing flow proceeds to step S 5150 A, whereas if it is determined that state of charge (SOC 1 ) of first battery  120  is less than or equal to the predetermined value (55%) (S 5100 A: YES), the processing flow proceeds to step S 5200 A. 
     In step S 5150 A, power supply ECU  150  stops electric power generation by generator  110 . Following this, the control procedure returns to the main flowchart in  FIG. 12 . 
     On the other hand, in step S 5200 A, power supply ECU  150  performs electric power generation control on generator  110 . Specifically, power supply ECU  150  sets and outputs an output instruction value to generator  110  to a target value. Here, a “target value” is a voltage necessary to charge first battery  120 . In the case of a 36 V lithium-ion battery, for example, this target value is 42 V. 
     Then, in step S 5250 A, power supply ECU  150  determines whether or not regenerated electric power generated by generator  110  is greater than or equal to a predetermined value (for example, regenerated electric power of generated current of 100 A). If generated regenerated electric power is low, electric power with which first battery  120  is charged is also low, and accurate deterioration detection cannot be expected. Regenerated electric power generated by generator  110  depends on the vehicle speed. If it is determined that generated regenerated electric power is greater than or equal to the predetermined value (S 5250 A: YES), the processing flow proceeds to step S 5300 A, whereas if it is determined that generated regenerated electric power is less than the predetermined value (S 5250 A: NO), the control procedure immediately returns to the main flowchart in FIG,  12 . 
     In step S 5300 A, power supply ECU  150  determines whether or not state of charge SOC 2  of second battery  130  is greater than or equal to 95%. The reason for this is to determine whether or not it is possible to supply electric power to electrical equipment  180  from second battery  130  when DC-DC converter  140  is temporarily stopped. If it is determined that state of charge SOC 2  of second battery  130  is greater than or equal to 95% (S 5300 A: YES), the processing flow proceeds to step S 5350 A, whereas if it is determined that state of charge SOC 2  of second battery  130  is less than 95% (S 5300 A: NO), the control procedure immediately returns to the main flowchart in  FIG. 12 . 
     In step S 5350 A, power supply ECU  150  stops electrically driven compressor  170 . By this means, supplying regenerated energy generated by generator  110  to electrically driven compressor  170  is stopped. 
     Then, in step S 5400 A, power supply ECU  150  stops DC-DC converter  140 . By this means, supplying regenerated energy generated by generator  110  to electrical equipment  180  and second battery  130  is stopped. In this state, all regenerated energy generated by generator  110  is supplied to first battery  120 . 
     Next, in step S 5450 A, power supply ECU  150  performs simultaneous current and voltage measurement for first battery  120 . At this time, as shown schematically in  FIG. 17(A) , for example, power supply ECU  150  can simultaneously measure the current and voltage of first battery  120  at the instant at which charging electric power to first battery  120  increases. The measurement of current and voltage is performed for at least two points. 
     Then, in step S 5500 A, power supply ECU  150  starts electrically driven compressor  170 . 
     Next, in step S 5550 A, power supply ECU  150  starts DC-DC converter  140 . 
     Then, in step S 5600 A, power supply ECU  150  performs deterioration determination. Specifically, power supply ECU  150  calculates internal resistance r by means of equation 1 below, using the currents and voltages of a plurality of points measured in step S 5450 A. Internal resistance r is one indicator of battery deterioration. For example, as shown schematically in  FIG. 17(B) , if current and voltage are taken as coordinate axes and measured currents and voltages of a plurality of points are plotted on the coordinate plane, the gradient of a linear approximation is internal resistance r. Solving equation 1 using measured values (50 A, 39 V) and (150 A, 40 V) of two points shown in  FIG. 17  gives a value of 0.01Ω for internal resistance r. While solving equation 1 for internal resistance r requires measurements for at least two points, measurements for three or more points may be used in order to improve the accuracy of deterioration determination.
 
 E+rI=V    (Equation 1)
 
where E: Electromotive force
         r: Internal resistance   I: Current   V: Voltage       

     Power supply ECU  150  compares calculated internal resistance r with a predetermined determination value, and determines whether or not there is deterioration of first battery  120 . The determination result is stored in a storage apparatus such as RAM, and is also reported to the user. Following this, the control procedure returns to the main flowchart in  FIG. 12 . 
     Thus, according to this embodiment, during vehicle deceleration, the operation of other devices (for example, electrically driven compressor  170 , DC-DC converter  140 , and so forth) can be temporarily stopped, and first battery  120  can be charged in a concentrated fashion with regenerated energy generated by generator  110 . Consequently, deterioration of first battery  120  can be detected with a high degree of accuracy. 
     In this embodiment, current and voltage are measured simultaneously and internal resistance is calculated as parameters for detecting battery deterioration, but the present invention is not limited to this. For example, provision may also be made for the gradient of voltage change or a drop in battery voltage to be calculated at the instant at which main battery output increases, using the method described in Patent Literature 1. 
     The disclosures of Japanese Patent Application No. 2010-081978, filed on Mar. 31, 2010, and Japanese Patent Application No. 2010-081979, filed on Mar. 31, 2010, including the specifications, drawings and abstracts, are incorporated herein by reference in their entirety. 
     INDUSTRIAL APPLICABILITY 
     A vehicle power supply apparatus according to the present invention is suitable for use as a vehicle power supply apparatus that can further improve the accuracy of battery deterioration detection. 
     REFERENCE SIGNS LIST 
     
         
           100  Power supply system 
           110  Generator 
           120 ,  130  Battery 
           122 ,  132  Current sensor 
           140 ,  172  DC-DC converter 
           150  Power supply ECU 
           160  Starter 
           162  Starter relay 
           170  Electrically driven compressor 
           180  General load (electrical equipment)