Patent Publication Number: US-2023158915-A1

Title: Charge control device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application of International Patent Application No. PCT/JP2021/037022 filed on Oct. 6, 2021, which designated the U.S. and claims the benefit of priority from Japanese Patent Application No. 2020-177457 filed in Japan filed on Oct. 22, 2020, the entire disclosure of the above application is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The disclosure described herein relates to a charge control device that controls a charge of a battery. 
     BACKGROUND 
     A charge system is known that includes a vehicle on which a battery and an ECU are mounted, and a charger that charges the battery. 
     SUMMARY 
     A charge control device suppresses an extension of charging time for a battery. 
     A charge control device according to an aspect of the present disclosure includes an acquisition part configured to acquire a detection result of a physical quantity sensor that detects a physical quantity related to charging of a storage battery mounted on a vehicle by external power output from an external power source, a calculation part configured to change a target value of the physical quantity when a charge amount of the storage battery is equal to or greater than a target charge quantity and a difference between the target value of the physical quantity and the detection result is lower than a predetermined value, and an output part configured to output an instruction signal including an instruction to control the external power based on the target value of the physical quantity to the external power supply. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a block diagram showing a charge control system mounted on an electric vehicle; 
         FIG.  2    is a timing chart for explaining changes over time in closed circuit voltage, actual current, and target current when external power is supplied; 
         FIG.  3    is a flowchart for explaining rapid charge processing; 
         FIG.  4    is a flowchart for explaining full charge processing; and 
         FIG.  5    is a flowchart for explaining a modification of full charge processing. 
     
    
    
     DETAILED DESCRIPTION 
     In an assumable example, a charging system is known that includes a vehicle on which a battery and an ECU are mounted, and a charger that charges the battery. The ECU changes a command value output to the charger. The ECU detects a reaction time of the charger to changes in command values. 
     The ECU of the charge system sets a margin for preventing overcharge based on the detected reaction time. The ECU determines a command value related to battery charging after setting the margin based on this margin. Due to the determination of such a command value, the charge time of the battery (storage battery) may be excessively extended depending on a value of the reaction time used to determine the margin. 
     A charge control device suppresses an extension of charging time for a battery. 
     A charge control device according to an aspect of the present disclosure includes an acquisition part configured to acquire a detection result of a physical quantity sensor that detects a physical quantity related to charging of a storage battery mounted on a vehicle by external power output from an external power source, a calculation part configured to change a target value of the physical quantity when a charge amount of the storage battery is equal to or greater than a target charge quantity and a difference between the target value of the physical quantity and the detection result is lower than a predetermined value, and an output part configured to output an instruction signal including an instruction to control the external power based on the target value of the physical quantity to the external power supply. 
     According to this configuration, the external power is controlled based on an actual dynamic response of the external power supply when the charge amount of the storage battery is equal to or greater than the target charge amount. Therefore, it is possible to suppress the extension of the charging time of the storage battery, compared to, for example, a configuration in which the external power is controlled based on a temporary response of the external power supply. 
     The following will describe embodiments for carrying out the present disclosure with reference to the drawings. In each embodiment, parts corresponding to the elements described in the preceding embodiments are denoted by the same reference numerals, and redundant explanation may be omitted. When only a part of the configuration is described in each form, the other forms described above can be applied to the other parts of the configuration. 
     When, in each embodiment, it is specifically described that combination of parts is possible, the parts can be combined. In a case where any obstacle does not especially occur in combining the parts of the respective embodiments, it is possible to partially combine the embodiments, the embodiment and the modification, or the modifications even when it is not explicitly described that combination is possible. 
     First Embodiment 
     A charge control system  100  will be described based on  FIGS.  1  to  4   . The charge control system  100  is mounted on an electric vehicle such as an electric automobile or a hybrid automobile. 
     A charge stand  200  positioned outside the electric vehicle is connected to the charge control system  100 . As a result, DC external power is supplied from the charge stand  200  to the charge control system  100 . In  FIG.  1   , a boundary between the electric vehicle and the outside thereof is shown by a broken line. The charge stand  200  corresponds to an external power supply. 
     The charge control system  100  includes a charge control device  10 , a storage battery  20 , a charger  30 , a in-vehicle device  40 , and a physical quantity sensor  50 . The storage battery  20  of the charge control system  100  is charged with the external power supplied from the charge stand  200 . In the drawing, the storage battery  20  is referred to as SB. The charger  30  is referred to as BC. The in-vehicle device  40  is referred to as VM. The charge stand  200  is referred to as CS. 
     The charge control device  10  is referred to as EVECU. EV is an abbreviation of an Electric Vehicle. ECU is an abbreviation of an Electronic Control Unit. The charge control device  10  controls driving of the charge stand  200 . Thereby, the charge control device  10  controls charging of the storage battery  20 . 
     The storage battery  20  has a plurality of secondary batteries connected in series. A lithium ion battery, for example, can be employed as the secondary batteries. The output power of the storage battery  20  is input to the charger  30  and the in-vehicle device  40 , respectively. 
     The charger  30  is a power converter including an inverter. The charger  30  converts the DC output power input from the storage battery  20  into AC power. This AC power is supplied to a motor (not shown). This motor is connected to the running wheels via a vehicle axle. The charger  30  converts AC power generated by the motor into DC power. This DC power is supplied to the storage battery  20 . 
     The in-vehicle device  40  is a power load of an air conditioner, or the like. When the charge stand  200  is connected to the electric vehicle, the electric vehicle is in a stopping state. At this time, an in-vehicle accessory such as an air conditioner that are driven by a low voltage can be switched between a driving state and a non-driving state. 
     A physical quantity sensor  50  detects a physical quantity associated with charging of the storage battery  20 . The physical quantity sensor  50  has a voltage sensor  51  and a current sensor  52 . The voltage sensor  51  detects the voltage output from the storage battery  20 . The current sensor  52  detects the current flowing through the storage battery  20 . These voltages and currents change when the storage battery  20  is charged. The detection results of the voltage sensor  51  and the current sensor  52  are input to the charge control device  10 . In the drawing, the voltage sensor  51  is referred to as VS. The current sensor  52  is referred to as CS. 
     &lt;OCV, CCV, SOC&gt; 
     The storage battery  20  has an internal resistance. Therefore, there is a difference due to voltage drop according to this internal resistance and the current flowing through the storage battery  20  between the actual output voltage corresponding to the SOC of the storage battery  20  and the output voltage detected by the voltage sensor  51 . 
     Hereinafter, the actual output voltage corresponding to the SOC of the storage battery  20  will be referred to as an open circuit voltage OCV as required. The output voltage detected by the voltage sensor  51  is referred to as a closed circuit voltage CCV. The resistance in the storage battery  20  is referred to as an internal resistance R, and the current that actually flows through the storage battery  20  is referred to as an actual current I. OCV is an abbreviation for Open Circuit Voltage. CCV is an abbreviation for Closed Circuit Voltage. SOC is an abbreviation for State Of Charge. SOC corresponds to the amount of charge. 
     A relationship between the closed circuit voltage CCV and the open circuit voltage OCV is expressed as CCV=OCV±I×R. When the storage battery  20  is discharged, the above relationship is expressed as CCV=OCV−I×R. When the storage battery  20  is charged, the above relationship is expressed as CCV=OCV+I×R. As described above, there is a difference of the voltage drop I×R between the closed circuit voltage CCV and the open circuit voltage OCV regardless of whether the storage battery  20  is discharged or charged. 
     The closed circuit voltage CCV is detected by the voltage sensor  51 , and the closed circuit voltage CCV is higher than the open circuit voltage OCV by the voltage drop I×R when the storage battery  20  is being charged. The actual current I included in the voltage drop can be detected by the current sensor  52 , but the internal resistance R of the storage battery  20  fluctuates due to temperature and aging deterioration. Therefore, it is difficult to calculate the voltage drop I×R with high accuracy. It has become difficult to accurately determine the SOC of the storage battery  20  based on the open circuit voltage OCV. 
     Therefore, the charge control device  10  first charges the storage battery  20  until the closed circuit voltage CCV reaches the target voltage, as will be described in detail later. After that, the charge control device  10  gradually decreases the actual current I flowing through the storage battery  20  while maintaining the closed circuit voltage CCV at the target voltage. This control minimizes the difference between the closed circuit voltage CCV and the open circuit voltage OCV. The SOC of the storage battery  20  is as close as possible to the SOC when the circuit voltage OCV is the target voltage. 
     &lt;Charge Control Device&gt; 
     As shown in  FIG.  1   , the charge control device  10  has an acquisition part  11 , a storage part  12 , a calculation part  13 , and an output part  14 . In the drawing, the acquisition part  11  is referred to as FS. The storage part  12  is referred to as MU. The calculation part  13  is referred to as OP. The output part  14  is written as OS. 
     Various information is input to the acquisition part  11  from the physical quantity sensor  50  and other various ECUs and various sensors (not shown). That is, the closed circuit voltage CCV and the actual current I are input from the physical quantity sensor  50  to the acquisition part  11 . Various types of information such as battery information including the capacity of the storage battery  20  and vehicle information including the driving state of the electric vehicle are input to the acquisition part  11  from various ECUs and various sensors. In the drawing, the battery information is referred to as BI. The vehicle information is referred to as VI. 
     The storage part  12  is a non-transitional substantive storage medium that non-temporarily stores programs that can be read by a computer or a processor. Various information acquired by the acquisition part  11  and processing results of the calculation part  13  are stored in the storage part  12 . In addition, the storage part  12  stores determination values in advance for the calculation processing by the calculation part  13 . 
     The calculation part  13  has a processor. The calculation part  13  executes various calculation processing based on the information stored in the storage part  12 . The calculation part  13  generates an instruction signal for instructing the operation of the charge stand  200  based on the information stored in the storage part  12 . The instruction signal includes a target voltage that determines the value of the voltage included in the external power output from the charge stand  200  to the storage battery  20 , and a target current that determines the amount of current included in the external power output. The target current corresponds to the target value of the physical quantity. 
     The target voltage is determined according to the capacity of the storage battery  20  mounted on the electric vehicle. The target voltage is determined based on the OCV when the SOC of the storage battery  20  is fully charged. When the closed circuit voltage CCV reaches the target voltage by rapid charge processing, the SOC of the storage battery  20  is expected to reach approximately 80%. The SOC of the storage battery  20  when the closed circuit voltage CCV reaches the target voltage by this rapid charge processing corresponds to the target charge amount. 
     The output part  14  outputs various electric signals including the results of calculation processing performed by the calculation part  13 . The output part  14  outputs the instruction signal generated by the calculation part  13  to the charge stand  200 . The charge stand  200  outputs external power output to the storage battery  20  based on the target voltage and target current included in the instruction signal. 
     &lt;Charge Processing&gt; 
     Next, the charge processing executed by the calculation part  13  will be described with reference to  FIGS.  2  to  4   . The charge processing includes a rapid charge processing and a full charge processing. When the charge stand  200  is electrically connected to the electric vehicle, the calculation part  13  executes the rapid charge processing. After this processing, the calculation part  13  executes the full charge processing. 
     First, based on  FIG.  2   , the rapid charge processing and the full charge processing will be explained. A vertical axis in  FIG.  2    indicates an arbitrary unit, and a horizontal axis indicates a time. The arbitrary unit is referred to as au and the time is referred to as t. The closed circuit voltage CCV and the actual current I of the storage battery  20  are indicated by solid lines. A target voltage is referred to as TV, and a target current is referred to as TC. These target voltage and target current are indicated by dashed lines. 
     At time t 0  in  FIG.  2   , the charge stand  200  is not electrically connected to the electric vehicle. Also, no current flows through the storage battery  20 . Therefore, the target voltage, target current, and actual current I become each zero. Since electric charge is accumulated in the storage battery  20 , the closed circuit voltage CCV has a predetermined value. 
     After a lapse of time from time t 0  to time t 1 , the charging cable of the charge stand  200  is connected to the electric vehicle. At this time, the calculation part  13  starts executing the rapid charge processing. The calculation part  13  outputs an instruction signal including a target voltage and a target current as a control instruction to the charge stand  200 . 
     In the rapid charge processing, the target voltage and target current are substantially constant. In order to realize rapid charge, the target current in the rapid charge processing is set high. This target current is determined according to how fast the storage battery  20  is to be rapidly charged. The target current during the rapid charge processing is hereinafter referred to as the initial target current. This initial target current is included in the instruction signal output from the charge control device  10  to the charge stand  200  at time t 1  shown in  FIG.  2   . 
     The closed circuit voltage CCV fluctuates depending on the resistance of the storage battery  20  and the like, but the target voltage in the rapid charge processing is a value indicating that the SOC of the storage battery  20  is about 80% when the closed circuit voltage CCV is the target voltage. In the present embodiment, the target voltage during the rapid charge processing is equal to the target voltage during the full charge processing. Using the open circuit voltage OCV, the target voltage in the full charge processing is such that the SOC of the storage battery  20  is about 100% when the open circuit voltage OCV is the target voltage. The SOC value of about 100% is a value lower than the SOC of the storage battery  20  in an overcharged state. After time t 1 , the target voltage is included in the instruction signal output from the charge control device  10  to the charge stand  200 . 
     After the elapse of time from time t 1  to time t 2 , the target current becomes the initial target current. Following this processing, the amount of external power supplied from the charge stand  200  to the storage battery  20  increases sharply. The actual current I flowing through the storage battery  20  becomes the initial target current. 
     The SOC of the storage battery  20  increases due to the supply of such external power. Along with this increase, the closed circuit voltage CCV of the storage battery  20  increases. 
     When time t 3  is reached, the closed circuit voltage CCV exceeds the target voltage. When the calculation part  13  detects this condition, it switches from the rapid charge processing to the full charge processing. The calculation part  13  calculates a target current with a current value lower than the initial target current. The calculation part  13  outputs an instruction signal including the target current to the charge stand  200 . Hereinafter, this target current will be referred to as a first target current. 
     After the elapse of time from time t 3  to time t 4 , the target current becomes the first target current. However, the actual current I does not decrease due to the response delay of the charge stand  200 . The closed circuit voltage CCV continues to rise due to the increase in the SOC of the storage battery  20 . 
     At time t 5 , the current amount of the external power output from the charge stand  200  becomes the current amount based on the first target current. Therefore, the actual current I begins to decrease. Along with this decrease, the closed circuit voltage CCV also begins to decrease. 
     After the elapse of time from time t 5  to time t 6 , the closed circuit voltage CCV falls below the target voltage. Upon detecting this condition, the calculation part  13  maintains the target current at the first target current. As a result, the actual current I also becomes constant at the first target current. 
     After time t 5 , the SOC of storage battery  20  continues to improve even if the closed circuit voltage CCV temporarily drops due to a decrease in the amount of current supplied. Therefore, the closed circuit voltage CCV rises again as the SOC of the storage battery  20  improves. 
     After the time t 7  is reached from time t 6 , the closed circuit voltage CCV exceeds the target voltage again. When the calculation part  13  detects this condition, it sets the target current to a second target current whose current value is lower than the previously set first target current. The calculation part  13  outputs an instruction signal including the second target current to the charge stand  200 . 
     After that, at time t 8 , the actual current I begins to decrease due to the response of the charge stand  200  based on the input second target current. Along with this decrease, the closed circuit voltage CCV begins to decrease. 
     After the elapse of time from time t 8  to time t 9 , the closed circuit voltage CCV falls below the target voltage. Upon detecting this condition, the calculation part  13  maintains the target current at the second target current. As a result, the actual current I also becomes constant at the second target current. 
     Hereinafter, although illustration and description are omitted, the target current is gradually decreased according to the actual dynamic response of the charge stand  200  while continuing to charge the storage battery  20  by keeping the closed circuit voltage CCV close to the target voltage. By controlling so, the difference between the closed circuit voltage CCV detected by the voltage sensor  51  and the open circuit voltage OCV corresponding to the actual SOC of the storage battery  20  is minimized. The SOC of the storage battery  20  is brought as close as possible to the SOC when the open circuit voltage OCV is the target voltage. 
     &lt;Rapid Charge Processing&gt; 
     Next, a rapid charge processing will be described based on  FIG.  3   . When the charging cable of the charge stand  200  is connected to the electric vehicle, the calculation part  13  starts executing this rapid charge processing. 
     In step S 10 , the calculation part  13  outputs an instruction signal including the target voltage and the initial target current to the charge stand  200 . These target voltage and initial target current may be calculated based on the performance of the storage battery  20 , the stored SOC, and the like when executing this rapid charge processing. Alternatively, the target voltage and the initial target current may be stored in the storage part  12  in advance. After outputting the instruction signal to the charge stand  200 , in the calculation part  13 , the process proceeds to step S 20 . 
     When proceeding to step S 20 , the calculation part  13  acquires the detection result of the physical quantity sensor  50  input to the acquisition part  11 . That is, the calculation part  13  acquires the closed circuit voltage CCV and the actual current I of the storage battery  20 . After this process, in the calculation part  13 , the process proceeds to step S 30 . 
     When proceeding to step S 30 , the calculation part  13  compares the closed circuit voltage CCV acquired in step S 20  with the target voltage included in the instruction signal in step S 10 . When the closed circuit voltage CCV is equal to or higher than the target voltage, in the calculation part  13 , the process proceeds to step S 40 . When the closed circuit voltage CCV is lower than the target voltage, in the calculation part  13 , the process returns to step S 10 . The calculation part  13  repeats steps S 10  to S 30  until the closed circuit voltage CCV becomes equal to or higher than the target voltage. 
     When proceeding to step S 40 , the calculation part  13  determines that the rapid charge has been completed. Then, the calculation part  13  ends the rapid charge processing and starts executing the full charge processing. This rapid charge processing corresponds to the processing from time t 1  to time t 3  in the example shown in  FIG.  2   . The full charge processing described below corresponds to the processing after time t 3 . 
     &lt;Full Charge Processing&gt; 
     In step S 110  shown in  FIG.  4   , the calculation part  13  acquires the closed circuit voltage CCV and the actual current I of the storage battery  20 . After this process, in the calculation part  13 , the process proceeds to step S 120 . 
     When proceeding to step S 120 , the calculation part  13  compares the closed circuit voltage CCV obtained in step S 110  with the target voltage included in the output instruction signal. When the closed circuit voltage CCV is equal to or higher than the target voltage, in the calculation part  13 , the process proceeds to step S 130 . When the closed circuit voltage CCV is lower than the target voltage, in the calculation part  13 , the process returns to step S 110 . The calculation part  13  repeats steps S 110  to S 120  until the closed circuit voltage CCV becomes equal to or higher than the target voltage. 
     When proceeding to step S 130 , the calculation part  13  calculates a difference value by subtracting the target current from the actual current I acquired in step S 110 . Then, the calculation part  13  determines whether or not this difference value is lower than a predetermined current. When the difference value is lower than the predetermined current, the calculation part  13  permits the reduction of the target current, and proceeds to step S 140 . When the difference value is equal to or greater than the predetermined current, the calculation part  13  prohibits the reduction of the target current, and proceeds to step S 150 . This prohibition of reduction of the target current corresponds to unchanged the target value of the physical quantity. 
     The predetermined current is determined based on the performance of the charge stand  200 , the detection accuracy of the current sensor  52 , and the like. The performance of the charge stand  200  includes the responsiveness of the charge stand  200 , the stability of changes over time in the current and voltage supplied from the charge stand  200 , and the like. Therefore, the calculation part  13  may calculate the performance of the charge stand  200 , for example, during the rapid charge processing, and determine the predetermined current based on the calculation result. Alternatively, the designer of the charge control device  10  may preliminarily calculate a predetermined current according to the performance of various charge stands  200  connected to the electric vehicle, and store it in the storage part  12 . A predetermined current corresponds to a predetermined value. The actual current I corresponds to the physical quantity. 
     The closed circuit voltage CCV becomes to be equal to or higher than the target voltage when the rapid charge processing is finished and the full charge processing is started. At the same time, the difference value is lower than the predetermined current. Therefore, when the full charge processing is started, the calculation part  13  proceeds from step S 120  to step S 130 . In the calculation part  13 , the process proceeds from step S 130  to step S 140 . 
     When proceeding to step S 140 , the calculation part  13  reduces the target current included in the instruction signal output to the charge stand  200 . Then, in the calculation part  13 , the process proceeds to step S 160 . 
     When proceeding to step S 160 , the calculation part  13  determines whether or not the actual current I is lower than a determination current. When the actual current I is lower than the determination current, the calculation part  13  terminates the full charge processing. The calculation part  13  cuts off the electrical connection between the charge stand  200  and the storage battery  20  to terminate charging of the storage battery  20 . If the actual current I is greater than or equal to the determination current, the calculation part  13  determines that the storage battery  20  is not fully charged. At this time, in the calculation part  13 , the process returns to step S 110 . 
     The determination current is a determination value for determining whether or not the difference between the closed circuit voltage CCV detected by the voltage sensor  51  and the open circuit voltage OCV corresponding to the actual SOC of the storage battery  20  has become as small as possible. This determination current is a finite value close to OA. The value of the determination current can be appropriately determined by the manufacturer of the electric vehicle or the user of the electric vehicle. 
     When the rapid charge processing is finished and the full charge processing is started, the actual current I used for determination in step S 160  does not reflect the decrease in the target current in step S 140 . Therefore, the calculation part  13  returns from step S 160  to step S 110 . Then, the calculation part  13  executes the processing from step S 110  again. 
     The calculation part  13  acquires the actual current I in step S 110 , but the reduction in the target current in step S 140  is not necessarily reflected in this actual current I. This is because there is a delay in the response of the charge stand  200  with respect to changes in the target current. 
     Due to this response delay, the closed circuit voltage CCV and actual current I detected in step S 110  immediately after the target current is reduced are almost different from the closed circuit voltage CCV and the actual current I detected in step S 110  before the target current is reduced. 
     Therefore, as a result of the charge stand  200  responding to the reduced target current, as long as the actual current I follows this target current and the difference between the actual current and the target current does not become smaller than the predetermined current, the calculation part  13  advances from step S 130  to step S 150 . 
     When proceeding to step S 150 , the calculation part  13  starts measuring a waiting time. The measurement of the standby time is started when it is first determined in step S 130  that the difference value is equal to or greater than the predetermined current. The measurement of the standby time is started when the reduction of the target current is prohibited. After this process, in the calculation part  13 , the process proceeds to step S 170 . 
     When proceeding to step S 170 , the calculation part  13  determines whether or not the waiting time has become equal to or longer than an expected response time. This expected response time is a time in which a reliable response is expected in the charge stand  200  regardless of the type of charge stand  200 . The calculation part  13  may calculate the expected response time of the charge stand  200  connected to the electric vehicle, for example, during the rapid charge processing. 
     When the standby time is equal to or longer than the expected response time, the calculation part  13  determines that a reduction instruction of the target current to the charge stand  200  is delayed, and the process proceeds to step S 180 . When the waiting time is less than the expected response time, the calculation part  13  returns to step S 110 . At this time, the calculation part  13  repeats steps S 110  to S 120 , or steps S 110  to S 130 , steps S 150 , and steps S 170 . The calculation part  13  enters a standby state. 
     When the charge stand  200  normally responds to the decrease in the target current while the calculation part  13  is in the standby state, the actual current I changes to follow the target current. An actual current I corresponding to the reduced target current is detected in step S 110 . When the difference between the actual current I and the target current becomes smaller than the predetermined current, in the calculation part  13 , the process proceeds from step S 130  to step S 140 . In this step S 140 , the calculation part  13  reduces the target current again. By executing the processing described above, the target current is gradually decreased. The calculation part  13  resets the standby time when decreasing the target current again. 
     When the process proceeds to step S 180  because the standby time is longer than the expected response time, the calculation part  13  forcibly reduces the target current included in the instruction signal that continues to be output to the charge stand  200 . After this process, in the calculation part  13 , the process proceeds to step S 160 . 
     The reduction amount of the target current in step S 180  and the reduction amount of the target current in step S 140  may be the same or different. In the present embodiment, the reduction amount of target current in step S 180  is lower than the reduction amount of target current in step S 140 . The forcible reduction of the target current in step S 180  is not reflected in the timing chart shown in  FIG.  2   . 
     &lt;Operation and Effects&gt; 
     As described above, when the closed circuit voltage CCV of the storage battery  20  becomes equal to or higher than the target voltage and the SOC of the storage battery  20  becomes equal to or higher than the target SOC during rapid charge processing, the calculation part  13  executes the full charge processing. 
     In the full charge processing, the calculation part  13  changes (decreases) the target current to be included in the instruction signal output to the charge stand  200 . After that processing, when the difference between the actual current I and the target current becomes lower than the predetermined current, the calculation part  13  determines that the charge stand  200  has reduced the amount of current contained in the external power supplied to the storage battery  20  in accordance with the decrease in target current. Each time this determination is established, the calculation part  13  gradually decreases the target current. 
     Thus, the calculation part  13  reduces the target current during the full charge processing based on the actual dynamic response of the charge stand  200  during the full charge processing. Therefore, for example, compared to a configuration that reduces the target current during the full charge processing based on the temporary response of the charge stand  200  before the full charge processing, a rapid decrease in the target current during the full charge processing is suppressed. As a result, extension of the charge time of the storage battery  20  during the full charge processing is suppressed. Moreover, the voltage state of the storage battery  20  during the full charge processing is stabilized. 
     After decreasing the target current, the calculation part  13  forcibly decreases the target current if the difference between the actual current I and the target current does not become equal to or less than a predetermined current even after the expected response time has elapsed. By doing so, it is possible to prompt the charge stand  200  to respond. It is possible to facilitate the reduction of the actual current I. 
     (Modifications) 
     In the present embodiment, an example is shown in which the actual current I is used as the physical quantity for determining the responsiveness of the charge stand  200 . However, the closed circuit voltage CCV can be used as the physical quantity for determining the responsiveness of the charge stand  200 . 
     In the case of this modification, the calculation part  13  executes the full charge processing shown in  FIG.  5   . This full charge processing executes step S 190  shown in  FIG.  5    instead of step S 130  of the full charge processing shown in  FIG.  4   . 
     In step S 190 , the calculation part  13  detects the time change of the closed circuit voltage CCV based on the closed circuit voltage CCV detected in the repeated step S 110 . This time change of the closed circuit voltage CCV is, for example, a value obtained by subtracting the closed circuit voltage CCV at time t 2  from the closed circuit voltage CCV at time t 3  shown in  FIG.  2   . 
     When the response of the charge stand  200  to the instruction signal is delayed, the time change of the closed circuit voltage CCV remains large. However, when the charge stand  200  responds to the instruction signal, it is expected that the time change of the closed circuit voltage CCV will become small. 
     Therefore, when the time change of the closed circuit voltage CCV is lower than a predetermined voltage, the calculation part  13  determines that the actual current I changes following the target current, and the process proceeds to step S 140 . When the time change of the closed circuit voltage CCV is equal to or greater than the predetermined voltage, the calculation part  13  determines that the actual current I does not follow the target current, and the process proceeds to step S 150 . 
     The predetermined voltage is determined based on the performance of the charge stand  200 , the detection accuracy of the voltage sensor  51 , and the like, in the same manner as the predetermined current. In this modification, the predetermined voltage corresponds to the predetermined value. The closed circuit voltage CCV corresponds to the physical quantity. 
     Although the present disclosure has been described in accordance with the embodiments, it is understood that the present disclosure is not limited to the above embodiments or structures. To the contrary, the present disclosure is intended to cover various modification and equivalent arrangements. In addition, while various combinations and modes are described in the present disclosure, other combinations and modes including only one element, more elements, or less elements therein are also within the scope and spirit of the present disclosure.