JP2009189131A - Charging control circuit, battery pack, and charging system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging control circuit which can control the occurrence of an overvoltage caused by response time of feedback control, and to provide a battery pack and a charging system equipped with it. <P>SOLUTION: A charging control circuit includes a voltage detection circuit 15 for detecting the terminal voltage of secondary batteries 141, 142 and 143, a storage section 215 previously stored with information about a value for reducing a charging current as the time elapses in order to charge the secondary batteries while maintaining the terminal voltage thereof at a fixed level, and a charging control section 212 which performs processing for reducing a charging current, being supplied from a charger 3 to the secondary battery, by a reduction value indicated as the time elapses based on the information about a value for reducing a charging current stored in the storage section 215 subsequently to a time when the terminal voltage of a secondary battery detected by the voltage detection circuit 15 goes above an end-of-charge voltage Vf. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a charging control circuit that controls charging of a secondary battery, a battery pack including the same, and a charging system.

  Conventionally, when charging a secondary battery, first, constant-current charging is performed in which charging is performed at a constant current value, and when the terminal voltage of the secondary battery reaches a preset end-of-charge voltage, the charging is performed. A CCCV (constant current constant voltage) charging method is known in which constant voltage charging is performed by applying a final voltage to a secondary battery and charging at a constant charging voltage (see, for example, Patent Document 1).

  In the CCCV charging method, an open circuit voltage (OCV) when the secondary battery is fully charged, that is, a full charge voltage is set as a charge end voltage. Since the secondary battery has an internal resistance R, when the terminal voltage of the secondary battery becomes the end-of-charge voltage due to constant current charging, the terminal voltage is generated by the charging current I flowing through the internal resistance R. The voltage drop IR is included, and the open-circuit voltage of the secondary battery has not yet reached the charge end voltage (= full charge voltage). Therefore, the secondary battery is not fully charged yet.

  Therefore, when constant voltage charging is further performed, the charging current gradually decreases, the voltage drop IR decreases, and the open-circuit voltage of the secondary battery increases by the amount corresponding to the decrease of the voltage drop IR. Then, when the charging current becomes equal to or less than the charge termination current value set in advance to a very small current value, and the voltage drop IR becomes small enough to be ignored, that is, the open-circuit voltage of the secondary battery becomes substantially equal to the full charge voltage. When the charging is finished, the secondary battery can be fully charged.

In such a CCCV charging method, since it is necessary to switch between a constant current output and a constant voltage output, the constant current power supply circuit or the constant voltage power supply circuit cannot be used as a charger as it is. Therefore, a switching power supply circuit that uses a switching power supply circuit with a variable output current and a charging control circuit that controls the output current of the switching power supply circuit to charge the constant current charging when the constant current charging is performed. When charging at a constant voltage, the charge control circuit monitors the terminal voltage of the secondary battery and performs feedback control to adjust the required current value to the switching power supply circuit so that the terminal voltage matches the end-of-charge voltage. Thus, CCCV charging is performed.
JP-A-6-78471

  However, for example, when performing constant voltage charging while maintaining the terminal voltage of the secondary battery at a constant voltage by the feedback control as described above by a charge control circuit using a microcomputer, if the response time of the feedback loop is long The terminal voltage of the secondary battery may exceed the full charge voltage and become an overvoltage. In order to prevent such overvoltage, the charging voltage may be set lower than the full charging voltage in consideration of the feedback response time. In this case, however, the charging time is extended or the charging capacity is reduced. There was an inconvenience. In order to shorten the response time of the feedback control, for example, a high-speed microcomputer may be used to speed up the charge control circuit. However, there is a disadvantage that the cost increases when the charge control circuit is speeded up.

  The present invention has been made in view of the above circumstances, and provides a charge control circuit capable of suppressing the occurrence of overvoltage caused by the response time of feedback control, and a battery pack and a charge system including the charge control circuit. The purpose is to provide.

  A charge control circuit according to the present invention is a charge control circuit that controls the operation of a charging unit that charges a secondary battery, the voltage detecting unit detecting a terminal voltage of the secondary battery, and a terminal of the secondary battery In order to charge while maintaining the voltage at a constant voltage, current decrease value information indicating a decrease value of the charging current to be decreased as time elapses is stored in advance, and the voltage detection unit detects the current decrease value information After the terminal voltage of the secondary battery becomes equal to or higher than a predetermined reference voltage, the charging is performed based on the decrease value of the charging current indicated as time elapses by the current decrease value information stored in the storage unit. And a charge control unit that performs a current reduction process for reducing a charging current supplied to the secondary battery by the unit.

  According to this configuration, after the terminal voltage of the secondary battery becomes equal to or higher than the predetermined reference voltage, the charging current flowing through the secondary battery is determined according to the passage of time by the current decrease value information stored in the storage unit. The charging current is decreased based on the decrease value of the charging current indicated by Then, since the current decrease value information indicates the decrease value of the charging current that should be decreased over time in order to charge the terminal voltage of the secondary battery while maintaining the constant voltage, the terminal of the secondary battery Charging is performed while the voltage is maintained at a constant voltage at the reference voltage, that is, constant voltage charging is performed at the reference voltage. In this case, since the charging voltage of the secondary battery is controlled in an open loop, the occurrence of overvoltage due to the response time of feedback control can be suppressed.

  The battery further includes an internal resistance detection unit that detects an internal resistance value of the secondary battery, and the storage unit stores the current decrease value information according to the internal resistance value of the secondary battery, In the current reduction process, the charge control unit is configured such that the secondary charge by the charging unit is based on a charge current reduction value indicated by current reduction value information corresponding to the internal resistance value detected by the internal resistance detection unit. It is preferable to reduce the charging current supplied to the battery.

  In order to charge the battery while maintaining the terminal voltage of the secondary battery at a constant voltage, the decrease value of the charging current that should be decreased with the passage of time changes as the secondary battery deteriorates. Further, when the secondary battery deteriorates, the internal resistance value of the secondary battery increases. That is, the internal resistance value indicates the degree of deterioration of the secondary battery. Therefore, according to this configuration, the charge control unit performs a current reduction process based on the current reduction value information stored in the storage unit corresponding to the internal resistance value of the secondary battery detected by the internal resistance detection unit. As a result of performing constant voltage charging, the influence of deterioration is reduced, and the accuracy of constant voltage charging can be improved.

  The charging control unit further includes a charge cycle counting unit that calculates a cumulative number of charge cycles of the secondary battery, and the charging control unit is configured to base the charging current on the basis of the charging current reduction value indicated by the current reduction value information in the current reduction processing. The amount of decrease in the charging current of the secondary battery may be increased as the cumulative number of charging cycles calculated by the charging cycle counter increases.

  The secondary battery degrades as the cumulative number of charging cycles increases, and the charging current that can maintain the terminal voltage of the secondary battery at a constant voltage decreases. Therefore, by increasing the amount of decrease in the charging current of the secondary battery as the cumulative number of charging cycles increases, the influence of deterioration can be reduced and the accuracy of constant voltage charging can be improved.

  Further, the current decrease value information is a charging current that should be decreased over time in order to charge the secondary battery while maintaining the terminal voltage at a constant voltage according to the number of accumulated charging cycles of the secondary battery. In the current reduction process, the charge control unit is configured to reduce the current decrease value stored in the storage unit according to the cumulative charge cycle number and time elapsed calculated by the charge cycle counting unit. It is preferable that the charging current supplied to the secondary battery by the charging unit is reduced by the reduction value of the charging current indicated by the information.

  According to this configuration, the charge control unit performs the current reduction process based on the current reduction value information stored in the storage unit corresponding to the cumulative charge cycle number of the secondary battery. As a result, the influence of deterioration is reduced and the accuracy of constant voltage charging can be improved.

  Further, a temperature detection unit that detects the temperature of the secondary battery, and a temperature range of the secondary battery detected by the temperature detection unit is set as a temperature range suitable for charging the secondary battery. It is preferable to further include a reference voltage setting unit that sets the reference voltage so that the reference voltage decreases as the temperature increases.

  When the secondary battery is charged at a high temperature, the deterioration is increased, which is not preferable. In addition, from the viewpoint of improving safety, the Battery Association of Japan (BAJ) recommends that the secondary battery charge voltage be reduced at temperatures exceeding the upper limit of the standard temperature range suitable for charging. Yes. Therefore, according to this configuration, when the temperature of the secondary battery exceeds the upper limit of the preferable temperature range, the reference voltage setting unit sets the reference voltage so that the reference voltage is lowered as the temperature is higher. Then, because the constant voltage charging by the reference voltage is performed by the current reduction process of the charging control unit, the higher the temperature of the secondary battery, the lower the charging voltage in the constant voltage charging, thereby improving the safety of the secondary battery. In addition, it is possible to reduce deterioration.

  In addition, a reference voltage setting unit that sets the reference voltage may be further provided such that the reference voltage decreases as the cumulative number of charging cycles calculated by the charge cycle counting unit increases.

  According to this configuration, since the secondary battery deteriorates as the number of accumulated charging cycles increases, the reference voltage decreases as the secondary battery deteriorates. Then, since the constant voltage charging by the reference voltage is performed by the current reduction process of the charging control unit, the charging voltage in the constant voltage charging decreases as the deterioration of the secondary battery progresses, thereby improving the safety of the secondary battery. In addition, it is possible to reduce deterioration.

  The secondary battery is an assembled battery in which a plurality of cells are connected in series, the voltage detection unit detects terminal voltages of the plurality of cells, and the charge control unit is controlled by the voltage detection unit. It is preferable that the current reduction process is performed after the maximum voltage among the detected terminal voltages of each cell becomes equal to or higher than the reference voltage.

  According to this configuration, even when an imbalance occurs in a plurality of cells constituting the assembled battery, after the maximum voltage among the terminal voltages of each cell becomes equal to or higher than the reference voltage, the charge control unit Due to the current reduction process, the cell with the maximum terminal voltage is charged at a constant voltage with the reference voltage, and the charge voltage of the other cells is below the reference voltage, so the charge voltage of each cell exceeds the reference voltage and is overcharged. The fear is reduced. In addition, since the same charging current flows in each cell connected in series, when the cell having the largest terminal voltage is charged at a constant voltage with the reference voltage, other cells are also charged and the terminal voltage becomes the reference voltage. Ascend toward. As a result, even when the terminal voltage of each cell is unbalanced, the difference in the terminal voltage of each cell can be reduced and the amount of charge of the entire assembled battery can be increased.

  The battery pack according to the present invention includes the above-described charge control circuit and the secondary battery.

  A charging system according to the present invention includes the above-described charging control circuit, the secondary battery, and the charging unit.

  According to this configuration, after the terminal voltage of the secondary battery becomes equal to or higher than the predetermined reference voltage, the charging current flowing through the secondary battery is determined according to the passage of time by the current decrease value information stored in the storage unit. Is reduced by the decrease value of the charging current shown. Then, since the current decrease value information indicates the decrease value of the charging current that should be decreased over time in order to charge the terminal voltage of the secondary battery while maintaining the constant voltage, the terminal of the secondary battery Charging is performed while the voltage is maintained at a constant voltage at the reference voltage, that is, constant voltage charging is performed at the reference voltage. In this case, since the charging voltage of the secondary battery is controlled in an open loop, the occurrence of overvoltage due to the response time of feedback control can be suppressed.

  According to the charge control circuit, the battery pack, and the charging system having such a configuration, after the terminal voltage of the secondary battery becomes equal to or higher than a predetermined reference voltage, the charging current flowing through the secondary battery is stored in the storage unit. According to the current decrease value information, the charging current is decreased by the decrease value of the charging current indicated as time elapses. Then, since the current decrease value information indicates the decrease value of the charging current that should be decreased over time in order to charge the terminal voltage of the secondary battery while maintaining the constant voltage, the terminal of the secondary battery Charging is performed while the voltage is maintained at a constant voltage at the reference voltage, that is, constant voltage charging is performed at the reference voltage. In this case, since the charging voltage of the secondary battery is controlled in an open loop, the occurrence of overvoltage due to the response time of feedback control can be suppressed.

  Embodiments according to the present invention will be described below with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted.

(First embodiment)
FIG. 1 is a block diagram showing an example of the configuration of a battery pack including a charge control circuit according to the first embodiment of the present invention and a charging system. The charging system 1 shown in FIG. 1 is configured by combining a battery pack 2 and a charging device 3 (charging unit).

  The charging system 1 further includes a load device (not shown) to which power is supplied from the battery pack 2, electronic devices such as portable personal computers, digital cameras, and mobile phones, vehicles such as electric vehicles and hybrid cars, and the like. It may be configured as an electronic device system. In that case, although the battery pack 2 is charged from the charging device 3 in FIG. 1, the battery pack 2 may be attached to the load device and charged through the load device.

  The battery pack 2 includes connection terminals 11, 12, 13, an assembled battery 14 (secondary battery), a current detection resistor 16, a charge control circuit 4, a communication unit 203, and switching elements Q1, Q2. The charging control circuit 4 includes an analog-digital (A / D) converter 201, a control unit 202, a voltage detection circuit 15 (voltage detection unit), and a temperature sensor 17 (temperature detection unit).

  Note that the charging system 1 is not necessarily limited to one configured to be separable into the battery pack 2 and the charging device 3, and one charging control circuit 4 may be configured in the entire charging system 1. Further, the charge control circuit 4 may be shared by the battery pack 2 and the charging device 3.

  The charging device 3 includes connection terminals 31, 32, 33, a control IC 34, and a charging current supply unit 35. The control IC 34 includes a communication unit 36 and a control unit 37. The charging current supply unit 35 is a power supply circuit that supplies a current corresponding to a control signal from the control unit 37 to the battery pack 2 via the connection terminals 31 and 32. The control unit 37 is a control circuit configured using, for example, a microcomputer.

  The battery pack 2 and the charging device 3 are connected to each other by DC high-side connection terminals 11 and 31 that perform power supply, connection terminals 13 and 33 for communication signals, and connection terminals 12 and 32 for power supply and communication signals. Connected. The communication units 203 and 36 are communication interface circuits configured to be able to transmit / receive data to / from each other via the connection terminals 13 and 33.

  In the battery pack 2, the connection terminal 11 is connected to the positive electrode of the assembled battery 14 via the charging switching element Q2 and the discharging switching element Q1. As the switching elements Q1 and Q2, for example, p-channel FETs (Field Effect Transistors) are used. The switching element Q1 has a parasitic diode cathode in the direction of the assembled battery 14. The switching element Q2 has a parasitic diode cathode in the direction of the connection terminal 11.

  The connection terminal 12 is connected to the negative electrode of the assembled battery 14 via the current detection resistor 16, and the connection terminal 12 is connected from the connection terminal 11 via the switching elements Q 2 and Q 1, the assembled battery 14, and the current detection resistor 16. A current path leading to is configured.

  The current detection resistor 16 converts the charging current and discharging current of the assembled battery 14 into voltage values. The assembled battery 14 is an assembled battery in which a plurality of, for example, three secondary batteries 141, 142, and 143 (cells) are connected in series. The secondary batteries 141, 142, and 143 are secondary batteries such as a lithium ion secondary battery and a nickel hydride secondary battery. The assembled battery 14 may be, for example, a single battery, may be, for example, an assembled battery in which a plurality of secondary batteries are connected in parallel, or is an assembled battery connected in combination of series and parallel. May be.

  The temperature sensor 17 is a temperature sensor that detects the temperatures of the secondary batteries 141, 142, and 143. The temperatures of the secondary batteries 141, 142, and 143 are detected by the temperature sensor 17 and input to the analog / digital converter 201 in the charge control circuit 4. Further, the terminal voltage Vt of the assembled battery 14 and the terminal voltages V1, V2, and V3 of the secondary batteries 141, 142, and 143 are detected by the voltage detection circuit 15, and are sent to the analog-digital converter 201 in the charge control circuit 4. Entered.

  Furthermore, the current value of the charge / discharge current Ic detected by the current detection resistor 16 is also input to the analog-digital converter 201 in the charge control circuit 4. The analog-digital converter 201 converts each input value into a digital value and outputs the digital value to the control unit 202.

  The control unit 202 includes, for example, a CPU (Central Processing Unit) that executes predetermined arithmetic processing, a ROM (Read Only Memory) that stores a predetermined control program, and a RAM (Random Access Memory) that temporarily stores data. And a timer circuit and peripheral circuits thereof. And the control part 202 functions as the protection control part 211, the charge control part 212, the reference voltage setting part 213, and the internal resistance detection part 214 by executing the control program memorize | stored in ROM.

  The storage unit 215 is configured using various nonvolatile storage elements such as the above-described ROM and EEPROM (Electrically Erasable and Programmable Read Only Memory). The storage unit 215 stores current decrease value information indicating a decrease value of the charging current Ic to be decreased with the passage of time in order to charge the terminal voltage Vt of the assembled battery 14 while maintaining the fully charged voltage. Is stored in accordance with the internal resistance value.

  The current decrease value information is obtained by experimentally measuring the decrease value of the charging current over time when constant voltage charging is performed using, for example, a plurality of assembled batteries 14 having different internal resistance values due to deterioration. can get.

  The protection control unit 211 detects an abnormality outside the battery pack 2 such as a short circuit between the connection terminals 11 and 12 and an abnormal current from the charging device 3 from each input value from the analog-digital converter 201 or an abnormality in the assembled battery 14. Detect abnormalities such as excessive temperature rise. Specifically, for example, when the current value detected by the current detection resistor 16 exceeds a preset abnormal current determination threshold, an abnormality based on a short circuit between the connection terminals 11 and 12 or an abnormal current from the charging device 3. For example, when the temperature of the assembled battery 14 detected by the temperature sensor 17 exceeds a preset abnormal temperature determination threshold, it is determined that an abnormality has occurred in the assembled battery 14. If such an abnormality is detected, the protection control unit 211 turns off the switching elements Q1 and Q2, and performs a protection operation for protecting the assembled battery 14 from abnormalities such as overcurrent and overheating.

  In addition, the protection control unit 211 preliminarily detects any of the terminal voltages V1, V2, and V3 of the secondary batteries 141, 142, and 143 detected by the voltage detection circuit 15 in order to prevent the secondary battery from being overdischarged. When the voltage becomes lower than the set discharge inhibition voltage Voff, the switching element Q1 is turned off to prevent the secondary batteries 141, 142, 143 from being deteriorated due to overdischarge. The discharge inhibition voltage Voff is set to 2.50 V, for example.

  In response to each input value from the analog-to-digital converter 201, the charging control unit 212 calculates a voltage value and a current value of a charging current that requires output from the charging device 3, and the communication unit 203 connects to the connection terminal. CCCV (constant current constant voltage) charging is performed by transmitting to charging device 3 via 13 and 32.

  Specifically, the charging control unit 212 first performs constant current charging by supplying a charging current Ic having a preset current value Icc from the charging device 3. As the current value Icc, for example, the nominal capacity value NC of the secondary batteries 141, 142, 143 is discharged with a constant current, and the current value at which the remaining capacity of the secondary batteries 141, 142, 143 becomes zero in 1 hour is 1 It. When (battery capacity (Ah) / 1 (h)) is set, for example, about 0.7 It.

  When the assembled battery 14 is configured by connecting a plurality of cells in parallel, for example, a current value obtained by multiplying 0.7 It by the number of parallel cells PN is used as the current value Icc. Specifically, the current value Icc is set to 2800 mA at 70% when, for example, the nominal capacity value NC = 2000 mAh and two are in parallel.

  In addition, the charging control unit 212 terminates the charging in which the maximum voltage among the terminal voltages V1, V2, and V3 of the secondary batteries 141, 142, and 143 detected by the voltage detection circuit 15 is set by the reference voltage setting unit 213. After the voltage Vf (reference voltage) or higher, the charging current Ic supplied to the assembled battery 14 by the charging device 3 is stored in correspondence with the internal resistance R of the assembled battery 14 detected by the internal resistance detection unit 214. The current reduction processing is executed by reducing the charging current reduction value indicated by the passage of time by the current reduction value information stored in the unit 215.

  When the charging current Ic flowing through the assembled battery 14 becomes equal to or lower than the charging end current value Ia, the charging control unit 212 determines that the assembled battery 14 is fully charged and ends the charging. The charge end current value Ia is set to about 0.05 It, for example.

  The reference voltage setting unit 213 has a standard temperature range (10 ° C. or more 45 ° C.) in which the temperature t of the assembled battery 14 detected by the temperature sensor 17 is an example of a suitable temperature range suitable for charging the secondary batteries 141, 142, and 143. When the upper limit of (° C. or less) is exceeded, the charge end voltage Vf is set so that the charge end voltage Vf decreases as the temperature t increases. Specifically, for example, if the temperature t is 45 ° C. or lower, the reference voltage setting unit 213 sets the charge end voltage Vf to 4.20 V, which is a full charge voltage, and the temperature t exceeds 45 ° C. to 50 If it is below ℃, the end-of-charge voltage Vf is set to 4.10V, and if the temperature t exceeds 50 ° C and below 60 ° C, the end-of-charge voltage Vf is set to 4.05V.

  When the secondary batteries 141, 142, 143 are lithium ion secondary batteries, the full charge voltage is, for example, the positive electrode potential and the negative electrode when the negative electrode potential of the secondary batteries 141, 142, 143 is substantially 0V. The potential difference from the potential, that is, the terminal voltages V1, V2, V3 of the secondary batteries 141, 142, 143 are used. In the case of a lithium ion secondary battery, the full charge voltage is about 4.2 V when lithium cobaltate is used as the positive electrode active material, and about 4.3 V when lithium manganate is used as the positive electrode active material.

  The internal resistance detection unit 214 detects the internal resistance value R of the assembled battery 14. The detection method of the internal resistance value R is not particularly limited. For example, the internal resistance value is calculated from the change amount ΔI of the current value flowing through the assembled battery 14 and the change amount ΔV of the terminal voltage Vt of the assembled battery 14 at that time. R = ΔV / ΔI can be calculated.

  In the charging device 3, a request from the control unit 202 is received by the communication unit 36 in the control IC 34, and the control unit 37 controls the charging current supply unit 35, and the voltage value according to the request from the control unit 202, The charging current is output from the charging current supply unit 35 at the current value. The charging current supply unit 35 is configured using a switching power supply circuit such as an AC-DC converter or a DC-DC converter, and generates a charging voltage and a charging current instructed by the control unit 37 from, for example, a commercial AC power supply voltage. The battery pack 2 is supplied via the connection terminals 31, 11;

  Next, the operation of the charging system 1 configured as described above will be described. FIG. 2 is an explanatory diagram showing an example of the operation of the charging system 1 shown in FIG. First, the temperature sensor 17 detects the temperature t of the assembled battery 14.

  When the temperature t is 45 ° C. or lower, the reference voltage setting unit 213 sets the charge end voltage Vf to 4.20 V, which is a full charge voltage, and when the temperature t exceeds 45 ° C. and is 50 ° C. or lower, the charge is stopped. If the voltage Vf is set to 4.10 V and the temperature t exceeds 50 ° C. and is 60 ° C. or less, the end-of-charge voltage Vf is set to 4.05 V. FIG. 2 shows an example in which the charge end voltage Vf is set to 4.20V.

  Further, the charge control unit 212 transmits a request signal for requesting the charging current Ic having the current value Icc to the control unit 37 via the communication units 203 and 36. Then, the charging current Ic having the current value Icc is output from the charging current supply unit 35, and the assembled battery 14 is charged with constant current (timing T1).

  Then, the terminal voltage Vt of the assembled battery 14 increases with charging, and the maximum voltage among the terminal voltages V1, V2, and V3 detected by the voltage detection circuit 15, for example, the terminal voltage V1 is the charge end voltage Vf. When the voltage reaches 20 V or more (timing T2), the charging current Ic supplied to the assembled battery 14 by the charging device 3 in response to a request from the charging control unit 212 is detected by the internal resistance detecting unit 214. A current reduction process (timing T2 to T3) is performed in which the current reduction value information stored in the storage unit 215 corresponding to the resistor R is reduced by the charging current reduction value indicated as time elapses.

  FIG. 3 is an explanatory diagram illustrating an example of current decrease value information stored in the storage unit 215 illustrated in FIG. 1. In FIG. 3, the vertical axis indicates the current decrease value, and the horizontal axis indicates the elapsed time after the maximum value of each cell voltage reaches the charge end voltage Vf. The current decrease value Id1 indicates a current decrease value when the assembled battery 14 is not deteriorated and therefore the internal resistance R is a small resistance value R1. The current decrease value Id2 indicates a current decrease value at the resistance value R2 in which the assembled battery 14 deteriorates and the internal resistance R increases. The current decrease value Id3 indicates a current decrease value when the deterioration of the assembled battery 14 further proceeds and the internal resistance R becomes a resistance value R3 larger than the resistance value R2.

  In the storage unit 215, current curves such as current decrease values Id1, Id2, and Id3 are stored, for example, as a data table or an arithmetic expression of a quadratic function.

  FIG. 2 shows an example in which the assembled battery 14 is not deteriorated and the resistance value of the internal resistance R of the assembled battery 14 detected by the internal resistance detection unit 214 is R1. When the resistance value of the internal resistance R is R1, after the timing T2, the charging control unit 212 reduces the charging current Ic from the current decrease value Id1 shown in FIG. Is sent as a request value.

  FIG. 4 shows an example in which the assembled battery 14 is deteriorated and the resistance value of the internal resistance R of the assembled battery 14 detected by the internal resistance detection unit 214 is R2. When the resistance value of the internal resistance R is R2, the charging control unit 212 reduces the charging current Ic to the control unit 37 as time passes by the charging control unit 212 after time T2. Is sent as a request value.

  Then, in accordance with a control signal from the control unit 37, the charging current supply unit 35 supplies the charging current Ic during the period of timing T2 to T3 shown in FIG.

  In this case, the current decrease value information indicates a decrease value of the charging current Ic that should be decreased with the passage of time in order to charge the secondary battery while maintaining the terminal voltage at the full charge voltage. When the charging current Ic is decreased according to Id1, the terminal voltage V1 reaching the charging end voltage Vf is charged while being maintained at the charging end voltage Vf. As a result, the secondary battery 141 is charged at a constant voltage. The

  As a result, the secondary battery 141 is charged at a constant voltage by controlling the charging current in an open loop, so that an overvoltage caused by the response time of the control loop as in the case of performing feedback control does not occur.

  Only the terminal voltages V2 and V3 that have not yet reached the charge end voltage Vf gradually increase so as to approach the charge end voltage Vf, and the secondary batteries 142 and 143 are also charged until they are substantially fully charged. Thereby, even if the characteristics and the charging depth of the secondary batteries 141, 142, and 143 vary and the terminal voltages V1, V2, and V3 are different, the terminals of the secondary batteries 141, 142, and 143 Recharge a secondary battery having a low terminal voltage until the terminal voltage reaches substantially the end-of-charge voltage Vf, that is, substantially fully charged, while reducing the possibility of overcharging the voltage exceeding the end-of-charge voltage Vf. Can do.

  In addition, in order to charge the secondary battery while maintaining the terminal voltage at the full charge voltage, the decrease value of the charging current Ic that should be reduced as time elapses changes with the deterioration of the secondary battery. Further, when the secondary battery deteriorates, the internal resistance R increases. That is, the internal resistance R indicates the degree of deterioration of the secondary battery.

  Therefore, the charging control unit 212 determines the current at the timings T2 to T3 based on the current decrease value information stored in the storage unit 215 corresponding to the internal resistance R of the assembled battery 14 detected by the internal resistance detection unit 214. Since the reduction process is executed, the accuracy of constant voltage charging in the secondary battery 141 having the highest terminal voltage can be improved.

  FIG. 5 shows an example in which the end-of-charge voltage Vf is set to 4.10 V by the reference voltage setting unit 213 when the temperature t detected by the temperature sensor 17 exceeds 45 ° C. and is 50 ° C. or less. Show.

  When the end-of-charge voltage Vf is set to 4.10 V, after the terminal voltage V1 becomes 4.10 V or higher (timing T2), the assembled battery 14 is charged by the charging device 3 in response to a request from the charging control unit 212. The charging current Ic supplied to is indicated by the current decrease value information stored in the storage unit 215 corresponding to the internal resistance R of the assembled battery 14 detected by the internal resistance detection unit 214 as time elapses. As a result of the decrease of the charging current, the secondary battery 141 is charged at a constant voltage of 4.10 V, and the terminal voltages of the secondary batteries 142 and 143 are also suppressed to 4.10 V or less (timing T2 to T3). .

  When the secondary battery is charged at a high temperature, the deterioration is increased, which is not preferable. In addition, from the viewpoint of improving safety, the battery association of Japan (BAJ) reduces the charging voltage of secondary batteries at temperatures exceeding the standard temperature range (10 ° C to 45 ° C) suitable for charging. It is recommended that Therefore, when the reference voltage setting unit 213 causes the temperature t of the assembled battery 14 to exceed the standard temperature range (10 ° C. or higher and 45 ° C. or lower) suitable for charging, the higher the temperature t, the lower the charge end voltage Vf. The charge end voltage Vf is set so that the charge voltage is lowered. Thereby, deterioration can be reduced, improving the safety | security of a secondary battery.

  When the charge current Ic detected by the current detection resistor 16 becomes equal to or less than the charge end current value Ia, the charge control unit 212 requests the control unit 37 via the communication units 203 and 36 to end the charge. Is sent. Then, the charging current supply unit 35 sets the charging current Ic to zero and the charging operation ends (timing T3).

(Second Embodiment)
Next, a battery pack provided with a charge control circuit according to a second embodiment of the present invention and a charging system will be described. FIG. 6 is a block diagram showing an example of the configuration of the battery pack 2a including the charging control circuit 4a according to the second embodiment of the present invention and the charging system 1a. The charging system 1a shown in FIG. 1 is configured by combining a battery pack 2a and a charging device 3.

  The charge control circuit 4a shown in FIG. 6 differs from the charge control circuit 4 shown in FIG. 1 in the following points. That is, the charge control circuit 4a shown in FIG. 6 is different in that the control unit 202a does not include the internal resistance detection unit 214 but includes a charge cycle number counting unit 216 instead. Further, the operation of the charging control unit 212a is different.

  Further, the current decrease value information stored in the storage unit 215 is obtained according to the passage of time in order to charge the battery while maintaining the terminal voltage of the assembled battery 14 at a constant voltage according to the cumulative number of charging cycles of the assembled battery 14. The decrease value of the charging current to be decreased is shown. Since the other configuration is the same as that of the charging system 1 shown in FIG. 1, the description thereof is omitted, and the characteristic points of the present embodiment will be described below.

  The charging cycle number counting unit 216 calculates the cumulative number of charging cycles of the assembled battery 14. Specifically, the charging cycle number counting unit 216 calculates the accumulated charge amount by, for example, integrating the charging current Ic of the assembled battery 14 detected by the current detection resistor 16. Then, the charge cycle number counting unit 216 divides the accumulated charge amount by the battery capacity of the assembled battery 14 to thereby calculate the accumulated charge cycle number of the assembled battery 14. Note that the charge cycle number counting unit 216 may calculate the accumulated discharge charge amount by integrating the discharge current instead of the charge current Ic to obtain the accumulated charge charge amount.

  The internal resistance R of the assembled battery 14 tends to increase according to cycle deterioration, and there is a correlation between the internal resistance R and the cumulative charge cycle number. Therefore, by using the cumulative charge cycle number of the assembled battery 14 instead of the internal resistance R, it is possible to perform the same control as the charge control circuit 4 shown in FIG.

  Therefore, after the timing T2, the charging control unit 212a performs charging indicated by the current decrease value information stored in the storage unit 215 according to the cumulative charging cycle number calculated by the charging cycle number counting unit 216 and the passage of time. By reducing the charging current supplied to the assembled battery 14 by the charging device 3 by the decrease value of the current, the charging cycle counter 216 has made a coefficient based on the decrease value of the charging current indicated by the current decrease value information. As the cumulative number of charging cycles increases, the amount of decrease in the charging current of the battery pack 14 is increased.

  Thus, for example, when the cumulative charge cycle number becomes 300 cycles, the maximum value of the charge current during the current reduction process is reduced from, for example, 0.7 It to 0.5 It, and the cumulative charge cycle number becomes 500 cycles. In this case, the maximum value of the charging current during the current reduction process is reduced from 0.5 It to 0.3 It, for example.

  Then, since there is a correlation between the cumulative number of charging cycles and the internal resistance value R, as a result, the secondary battery 141 having the highest terminal voltage is the same as in the charging system 1 shown in FIG. Charge current is controlled in an open loop and constant voltage charging is performed. As a result, an overvoltage due to the response time of the control loop as in the case of performing feedback control does not occur. In addition, since it is not necessary to stop charging or change the charging current in order to detect the internal resistance value R, the possibility of increasing the charging time for detecting the internal resistance value R is reduced.

  Note that the storage unit 215 is not limited to the example in which the current decrease value information corresponding to the cumulative charge cycle number of the assembled battery 14 is stored. For example, the storage unit 215 has a current decrease when the assembled battery 14 is new. The value information is stored in advance, and the charge control unit 212a is stored in the storage unit 215 using a predetermined function, for example, a quadratic function, according to the cumulative charge cycle number calculated by the charge cycle number counting unit 216. The current decrease value information may be corrected and used.

  Further, the reference voltage setting unit 213 may set the end-of-charge voltage Vf so that the end-of-charge voltage Vf decreases as the cumulative number of charge cycles calculated by the charge cycle counting unit 216 increases.

  The present invention relates to a charging control circuit that controls charging of a secondary battery in a battery-mounted device such as a portable personal computer, a digital camera, an electronic device such as a mobile phone, a vehicle such as an electric vehicle or a hybrid car, and the like. The battery pack and the charging system provided can be suitably used.

It is a block diagram which shows an example of a structure of the battery pack provided with the charge control circuit which concerns on 1st Embodiment of this invention, and a charging system. It is explanatory drawing which shows an example of operation | movement of the charging system shown in FIG. It is explanatory drawing which shows an example of the electric current reduction value information memorize | stored in the memory | storage part shown in FIG. It is explanatory drawing which shows an example of operation | movement of a charging system when an assembled battery deteriorates and internal resistance increases. It is explanatory drawing which shows an example of operation | movement of the charging system when the temperature of an assembled battery becomes high. It is a block diagram which shows an example of a structure of the battery pack provided with the charge control circuit which concerns on 2nd Embodiment of this invention, and a charging system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Charging system 2 Battery pack 3 Charging apparatus 4 Charging control circuit 14 Assembly battery 15 Voltage detection circuit 16 Current detection resistance 17 Temperature sensor 31 Connection terminal 35 Charging current supply part 141,142,143 Secondary battery 201 Analog-digital converter 202 Control Unit 211 protection control unit 212 charge control unit 213 reference voltage setting unit 214 internal resistance detection unit 215 storage unit 216 charge cycle number counting unit Ia charge end current value Id1, Id2, Id3 current decrease value Vf charge end voltage

Claims (9)

A charge control circuit for controlling the operation of a charging unit for charging a secondary battery,
A voltage detector for detecting a terminal voltage of the secondary battery;
In order to charge the secondary battery while maintaining the terminal voltage at a constant voltage, a storage unit in which current decrease value information indicating a decrease value of the charging current to be decreased with the passage of time is stored in advance,
After the terminal voltage of the secondary battery detected by the voltage detection unit becomes equal to or higher than a predetermined reference voltage, the charging current indicated by the current decrease value information stored in the storage unit as time elapses A charge control circuit, comprising: a charge control unit that performs a current reduction process for reducing a charge current supplied to the secondary battery by the charging unit based on a decrease value of the charging unit. An internal resistance detector for detecting an internal resistance value of the secondary battery;
In the storage unit,
The current decrease value information is stored according to the internal resistance value of the secondary battery,
The charge controller is
In the current reduction process, the charge supplied to the secondary battery by the charging unit based on the reduction value of the charging current indicated by the current reduction value information corresponding to the internal resistance value detected by the internal resistance detection unit The charge control circuit according to claim 1, wherein the current is reduced. A charge cycle counting unit for calculating a cumulative charge cycle number of the secondary battery;
The charge controller is
In the current reduction process, the amount of decrease in the charging current of the secondary battery as the cumulative number of charging cycles increased by the charging cycle counting unit increases based on the charging current reduction value indicated by the current reduction value information. The charge control circuit according to claim 1, wherein the charge control circuit is increased. The current decrease value information is:
In accordance with the cumulative number of charging cycles of the secondary battery, indicating a decrease value of the charging current to be reduced over time in order to charge the terminal voltage of the secondary battery while maintaining a constant voltage,
The charge controller is
In the current reduction process, according to the cumulative charge cycle number and time elapsed calculated by the charge cycle counting unit, only the decrease value of the charge current indicated by the current decrease value information stored in the storage unit, Reducing the charging current supplied to the secondary battery by the charging unit;
The charge control circuit according to claim 3. A temperature detector for detecting the temperature of the secondary battery;
When the temperature of the secondary battery detected by the temperature detection unit exceeds the upper limit of a suitable temperature range set as a temperature range suitable for charging the secondary battery, the reference voltage increases as the temperature increases. The charge control circuit according to claim 1, further comprising a reference voltage setting unit that sets the reference voltage so as to be low. The reference voltage setting part which sets the said reference voltage is further provided so that the said reference voltage may become low, so that the accumulation charge cycle coefficient by the said charge cycle counting part increases. The charge control circuit described in 1. The secondary battery is
A battery pack in which a plurality of cells are connected in series,
The voltage detector is
Detecting a terminal voltage of each of the plurality of cells;
The charge controller is
The current reduction process is performed after the maximum voltage among the terminal voltages of each cell detected by the voltage detection unit becomes equal to or higher than the reference voltage. The charge control circuit according to item. The charge control circuit according to any one of claims 1 to 7,
A battery pack comprising the secondary battery. The charge control circuit according to any one of claims 1 to 7,
The secondary battery;
A charging system comprising: the charging unit.

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