JP2009133675A - Battery pack and method of calculating internal impedance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure exactly an internal impedance of battery cells during actual use. <P>SOLUTION: When a charging current value is at a predetermined current value or higher such as 1 A or higher and a predetermined time has passed from stating the charging such as 2 minutes or longer, a pulsed charging current is supplied to a battery cell 11 and the cell voltage has a pulsed wave shape by repeating ON/OF of a charge control EFT 12a. In this way, an average ΔI<SB>ave</SB>of variation of the charging current and an average ΔV<SB>ave</SB>of variation of the cell voltage are calculated when the charge control EFT 12a undergoes ON/OFF. And the above-described calculated average ΔV<SB>ave</SB>of variation of the cell voltage is divided by the average ΔI<SB>ave</SB>of variation of the charging current, thereby the internal impedance R<SB>1</SB>of the battery cell 11 during charging is calculated. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a battery pack for a secondary battery and a method for calculating the internal impedance of the battery cell.

  In recent years, portable electronic devices such as notebook PCs (Personal Computers), mobile phones, and PDAs (Personal Digital Assistants) have advantages such as light weight, high capacity, ease of detection of remaining capacity, and long cycle life. A battery pack using a lithium ion secondary battery having the above has been widely used.

  Usually, a battery pack deteriorates by repeating charging / discharging, and operation time will become short. Therefore, in such a battery pack, processing for detecting the state of the battery pack such as the full charge capacity, the remaining capacity, and the degree of deterioration is performed.

  The process of detecting the state such as the full charge capacity, remaining capacity, and the degree of deterioration includes, for example, measuring the internal impedance of the battery cell mounted in the battery pack in advance, and the charge / discharge current of the battery cell during actual use. The cell voltage is measured, and the measurement is performed based on these measurement results.

  For example, in Patent Document 1 below, the battery voltage in a state where the operation of the electronic device connected to the battery pack is OFF, and the battery voltage in a state where the electronic device is operating and a constant current load is assumed are described. Describes a technique for determining the degree of deterioration of a battery based on the above.

JP 2005-108491 A

  By the way, it is known that a battery cell generally deteriorates by repeating charge and discharge, and its internal impedance increases. Therefore, in the battery pack that has been repeatedly charged and discharged, the internal impedance at the time of actual use increases from the initial state, and an error occurs in the value of the internal impedance.

  As described above, when an error occurs between the internal impedance in the initial state measured in advance and the internal impedance at the current time, when various state detection processes are performed using the internal impedance in the initial state, Is difficult to detect accurately.

  In order to accurately detect the current state of the battery pack, it is necessary to measure the current internal impedance. The internal impedance at the present time can be calculated based on, for example, the amount of current and voltage fluctuations at the timing when the current and voltage fluctuate.

  However, in this case, there is a problem in that the current internal voltage cannot be accurately measured because fluctuations in current and voltage are not stable.

  Accordingly, an object of the present invention is to provide a battery pack and an internal impedance calculation method capable of accurately measuring the internal impedance of a battery cell during actual use.

In order to solve the above-described problem, a first invention provides a battery pack including one or a plurality of battery cells.
A charge control switch for turning ON / OFF the charging current for the battery cell;
A control unit for controlling the charge control switch,
The control unit
The first charging current and the first cell voltage of the battery cell when the charging control switch is ON, and the second charging current and the second cell voltage of the battery cell when the charging control switch is OFF Measure and
Calculating a fluctuation amount of the charging current based on the first charging current and the second charging current, and a fluctuation amount of the cell voltage based on the first cell voltage and the second cell voltage;
A battery pack characterized in that an internal impedance of a battery cell is calculated based on a fluctuation amount of a charging current and a fluctuation amount of a cell voltage.

In the first invention, the control unit comprises:
It is preferable to measure the internal impedance by controlling ON / OFF of the charge control switch after two minutes or more have elapsed from the start of charging.

In the first invention, the control unit includes:
When the charging current flowing through the battery cell is 1 [A] or more, it is preferable to measure the internal impedance by controlling ON / OFF of the charging control switch.

Further, the second invention provides a first charging current and a first cell voltage of the battery cell when the charging control switch for turning on / off the charging current for one or a plurality of battery cells is ON, and the charging control switch. Measuring the second charging current and the second cell voltage of the battery cell when is OFF
Calculating a fluctuation amount of the charging current based on the first charging current and the second charging current, and a fluctuation amount of the cell voltage based on the first cell voltage and the second cell voltage;
An internal impedance calculation method for calculating an internal impedance of a battery cell based on a fluctuation amount of a charging current and a fluctuation amount of a cell voltage.

  As described above, in the first and second inventions, the first charging current and the first cell of the battery cell when the charge control switch for turning ON / OFF the charging current for one or a plurality of battery cells is ON. The voltage, the second charging current when the charging control switch is OFF, and the second cell voltage of the battery cell are measured, and the fluctuation amount of the charging current is determined based on the first charging current and the second charging current. And calculating a variation amount of the cell voltage based on the first cell voltage and the second cell voltage, and calculating an internal impedance of the battery cell based on the variation amount of the charging current and the variation amount of the cell voltage. Therefore, the internal impedance during actual use can be accurately calculated.

  The present invention measures the charge current and cell voltage when the charge control switch is turned on, and the charge current and cell voltage when the charge control switch is turned off. Since the internal impedance of the battery cell is measured based on the fluctuation amount of the charging current and the fluctuation amount of the cell voltage, there is an effect that the internal impedance of the battery cell can be accurately measured.

  BEST MODE FOR CARRYING OUT THE INVENTION The best mode of the present invention will be described below. The correspondence relationship between the disclosed invention and one embodiment is exemplified as follows.

  The battery pack according to claim 1 is a charge control switch (for example, FIG. 1) for turning on / off a charging current for the battery cell in a battery pack (for example, the battery pack 1 in FIG. 1) including one or a plurality of battery cells. 1 switch circuit 5) and a control unit (for example, MPU 3 in FIG. 1) for controlling the charge control switch, and the control unit has a first charging current when the charge control switch is ON. And the first cell voltage of the battery cell, the second charging current when the charge control switch is OFF, and the second cell voltage of the battery cell are measured (for example, step S3 and FIG. 4). Step S4), fluctuation amount of the charging current based on the first charging current and the second charging current, and fluctuation of the cell voltage based on the first cell voltage and the second cell voltage. (For example, step S5 of FIG. 4), and the internal impedance of the battery cell is calculated based on the amount of fluctuation of the charging current and the amount of fluctuation of the cell voltage (for example, step S6 of FIG. 4). And

  5. The internal impedance calculation method according to claim 4, wherein a first charging current and a first cell of the battery cell when a charge control switch for turning ON / OFF a charging current for one or a plurality of battery cells is ON. The voltage, the second charging current when the charging control switch is OFF, and the second cell voltage of the battery cell are measured (for example, step S3 and step S4 in FIG. 4), and the first charging is performed. A variation amount of the charging current based on the current and the second charging current and a variation amount of the cell voltage based on the first cell voltage and the second cell voltage are calculated (for example, step S5 in FIG. 4). The internal impedance of the battery cell is calculated based on the fluctuation amount of the charging current and the fluctuation amount of the cell voltage (for example, step S6 in FIG. 4).

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an example of a battery pack 1 according to an embodiment of the present invention. The battery pack 1 includes an assembled battery 2, an MPU (Micro Processing Unit) 3 as a control unit, a memory 4, a switch circuit 5, a cutoff circuit 6, an FET (Field Effect Transistor) 7, a current detection resistor 8, and a positive terminal 9 And the negative electrode terminal 10 are connected to the positive terminal and the negative terminal of an external electronic device or charger, respectively, and charging / discharging of the assembled battery 2 is performed.

  The assembled battery 2 is a secondary battery such as a lithium ion secondary battery, and is an assembled battery in which a plurality of battery cells are connected in series and / or in parallel. In this example, a case will be described in which two battery cells 11a and 11b (hereinafter simply referred to as a battery cell 11 as appropriate unless otherwise distinguished) are connected in series.

  The MPU 3 controls each unit using a RAM (Random Access Memory) (not shown) as a work memory according to a program stored in advance in a ROM (Read Only Memory) (not shown). The MPU 3 measures the voltage of the battery cells 11a and 11b every predetermined time, and measures the magnitude and direction of the current flowing through the current detection resistor 6 every predetermined time.

  The MPU 3 controls the switch circuit 5 based on the measured voltage value and current value. The switch circuit 5 is turned off when the voltage of any one of the battery cells 11a and 11b becomes an overcharge detection voltage or when the voltage of any battery cell becomes equal to or lower than the overdischarge detection voltage. This prevents overcharge and overdischarge. Here, in the case of a lithium ion battery, the overcharge detection voltage per battery cell is determined to be, for example, 4.2 V ± 0.05 V, and the overdischarge detection voltage is determined to be 2.5 V ± 0.1 V. Details of the switch circuit 5 will be described later.

  Further, the MPU 3 controls the cutoff circuit 6 based on the measured voltage value of each battery cell 11. The MPU 3 supplies a control signal to the FET 7 when the voltage of any battery cell becomes equal to or higher than the overcharge detection voltage, turns the FET 7 ON, and causes the current to flow through the cutoff circuit 6. Cut off charge / discharge current.

  Further, the MPU 3 controls the switch circuit 5 during charging to repeatedly turn on / off the charging current. And based on the fluctuation amount of the charging current at this time and the fluctuation amount of the voltage of each battery cell 11, the internal impedance of each battery cell 11 is measured. A method for measuring the internal impedance during charging will be described later.

  Furthermore, the MPU 3 includes a communication terminal 14 and a communication terminal 15, and when the battery pack 1 is connected to an external electronic device, the MPU 3 is connected to a communication terminal provided in the external electronic device, whereby the external electronic device To be able to communicate with. As a communication method used for communication between the battery pack 1 and an external electronic device, for example, SMBus (System Management Bus) can be used.

  The memory 4 is a nonvolatile memory such as an EEPROM (Electrically Erasable and Programmable Read Only Memory), for example, and stores, for example, an internal impedance value in an initial state of each battery cell 11 measured in the manufacturing process in advance. . In addition, the memory 4 stores in advance characteristic data indicating the correspondence between the voltage of each battery cell 11 in an unloaded state, that is, the open circuit voltage (OCV) of the battery cell 11 and the discharge depth. The memory 4 is not limited to this example, and may be provided in the MPU 3, for example.

  The switch circuit 5 includes a charge control FET 12a, a discharge control FET 12b, and parasitic diodes 13a and 13b, and is controlled by the MPU 3. The charge control FET 12a is turned off when the battery voltage becomes the overcharge detection voltage, and is controlled by the MPU 3 so that the charge current does not flow in the current path of the assembled battery 2. Note that after the charge control FET 12a is turned off, only discharge is possible via the parasitic diode 13a. The discharge control FET 12b is turned off when the battery voltage becomes the overdischarge detection voltage, and is controlled by the MPU 3 so that the discharge current does not flow in the current path of the assembled battery 2. Note that after the discharge control FET 12b is turned off, only charging is possible through the parasitic diode 13b.

  The interruption circuit 6 is, for example, a fuse element having a built-in heater resistor. When an overcurrent flows, the interruption circuit 6 is melted by the overcurrent Joule heat that flows through the fuse circuit 2 and interrupts the current path of the assembled battery 2. Further, when the voltage of one of the battery cells 11a or 11b of the assembled battery 2 becomes equal to or higher than the overcharge detection voltage, the FET 7 is turned on and a current flows through the heater resistance. Have been to.

  Next, various processing methods in the battery pack 1 according to the embodiment of the present invention will be described. In one embodiment of the present invention, the deterioration rate and remaining capacity of the battery cell 11 are calculated using the internal impedance of the battery cell 11 in the initial state where the initial charge is not performed and the internal impedance during actual use. Various processes are performed.

  First, a method for measuring the internal impedance of the battery cell 11 in the initial state will be described. The internal impedance of the battery cell 11 in the initial state is calculated based on, for example, the fluctuation amount of the charging current when the charging current is fluctuated and the fluctuation amount of the voltage of the battery cell 11 (hereinafter appropriately referred to as the cell voltage). be able to.

FIG. 2A shows an example state of the charging current, and FIG. 2B shows an example state of the cell voltage of the battery cell 11. As shown in FIG. 2A, when charging is performed with a predetermined charging current, the charging current is reduced after a predetermined time has elapsed. Then, as shown in FIG. 2B, the cell voltage immediately before the charging current is reduced and the cell voltage after the charging current is reduced are measured. In this case, assuming that the fluctuation amount of the charging current is ΔI and the fluctuation amount of the cell voltage is ΔV, the internal impedance R ₀ of the battery cell 11 in the initial state is calculated based on the formula (1).
R ₀ = ΔV / ΔI (1)

When a plurality of battery cells 11 are connected in series, the internal impedance is measured for each battery cell 11 using the above-described formula (1). Then, the internal impedance value R ₀ of each battery cell 11 and the maximum internal impedance value R _0max among the internal impedances of each battery cell 11 are stored in the memory 4.

  For example, when the cell voltage of the battery cell 11 is measured in the MPU 3, the analog measurement value is converted into the digital measurement value by an A / D (Analog / Digital) converter provided in the MPU 3. Measurement errors occur during this conversion. When the variation amount ΔV of the cell voltage is large, the influence of the measurement error on the variation amount ΔV is small. However, when the variation amount ΔV of the cell voltage is small, the influence of the measurement error on ΔV is large. That is, when the variation amount ΔI of the charging current is small, the variation amount ΔV of the cell voltage is small, so that the influence due to the measurement error becomes large and the internal impedance cannot be calculated accurately.

  In particular, since the internal impedance value of the battery cell 11 in the initial state is smaller than the internal impedance value when the battery cell 11 is deteriorated by repeated charging and discharging, the charging current fluctuation amount ΔI and the cell voltage fluctuation amount ΔV are small. The calculated internal impedance value is greatly affected by the measurement error. Therefore, when changing the charging current, it is preferable to set a relatively large fluctuation amount, for example, the fluctuation amount of the charging current to 1 [A] or more in order to reduce the influence of the measurement error.

  Further, when the battery temperature of the battery cell 11 fluctuates, the internal impedance value also fluctuates. For example, it is preferable to correct the internal impedance value based on the battery temperature. In this case, for example, a temperature correction coefficient for correcting the internal impedance value to the internal impedance value at the reference battery temperature according to the battery temperature is stored in the memory 4 in advance. And it is good to measure battery temperature using the temperature sensor etc. which are not shown in figure for measuring battery temperature, and to correct an internal impedance value using a temperature correction coefficient based on the measured battery temperature.

  Next, a method for measuring the internal impedance of the battery cell 11 during actual use will be described. As described in the background art section, the internal impedance of the battery cell 11 at the time of actual use can be calculated, for example, at a timing when the current and voltage change rapidly. The timing at which the current and voltage change suddenly is, for example, the timing at which charging or discharging is started. At this time, the internal impedance of the battery cell 11 is calculated based on the fluctuation amount of the charging / discharging current and the fluctuation amount of the cell voltage immediately after the start of charging / discharging.

  However, in this case, since the fluctuation amount of the charge / discharge current and the cell voltage is not stable, the internal impedance of the battery cell 11 cannot be measured accurately.

  In addition, a method of measuring the internal impedance during the discharge is conceivable. In this case, for example, the load fluctuates depending on the use state of the external device connected to the battery pack 1, and the discharge is performed. Since the current and the cell voltage are not stable, the internal impedance of the battery cell 11 cannot be measured accurately.

  Therefore, in the embodiment of the present invention, the internal impedance of the battery cell 11 is measured based on the variation amount of the cell voltage and the charging current when the charging current is varied in pulses during charging. The internal impedance of the battery cell 11 during charging is the average value of the fluctuation amount of the charging current when the charging current for the battery cell 11 is repeatedly turned on / off during charging, and the cell voltage of the battery cell 11 that fluctuates at this time. It can be calculated based on the average value of the fluctuation amount.

  FIG. 3 shows a state of an example of the charging current and cell voltage of the battery cell 11 when the charging current is turned ON / OFF during charging. As shown in FIG. 3A, by repeatedly turning ON / OFF the charge control FET 12a, a pulsed charging current is supplied to the battery cell 11, and the cell voltage of the battery cell 11 is pulsed as shown in FIG. 3B. It becomes the waveform. As a result, the cell voltage fluctuates stably.

In such a case, based on the average value of the charging current when the charging control FET 12a is in the ON state and the average value of the charging current when the charging control FET 12a is in the OFF state, the average value of the fluctuation amount of the charging current ΔI _ave is calculated. Further, based on the average value of the cell voltage when the charge control FET 12a is in the ON state and the average value of the cell voltage when the charge control FET 12a is in the OFF state, the average value ΔV _ave of the fluctuation amount of the cell voltage is calculated. To do.

The internal impedance R ₁ of the battery cell 11 during charging is based on Equation (2) using the average value ΔI _ave of the fluctuation amount of the charging current and the average value ΔV _ave of the cell voltage fluctuation amount calculated as described above. Is calculated.
R ₁ = ΔV _ave / ΔI _ave (2)

When a plurality of battery cells 11 are connected in series, the internal impedance of each battery cell 11 is calculated using the above equation (2), as in the case of calculating the internal impedance of the battery cell 11 in the initial state. Measure. Then, the internal impedance value R ₁ of each battery cell 11 and the maximum value R _1max of the internal impedance value are stored in the memory 4.

  In addition, when measuring the internal impedance of the battery cell 11 during charging, in order to reduce the influence due to the measurement error of the cell voltage by the A / D converter of the MPU 3, as in the case of calculating the internal impedance in the initial state, This is preferably performed when the charging current is not less than a relatively large current value, for example, 1 [A] or more.

  In addition, when the cell voltage of the battery cell 11 is low, the voltage is not stable and the cell voltage value may vary, so it is difficult to accurately measure the internal impedance of the battery cell 11. It is. In order to accurately measure the internal impedance of the battery cell 11, the cell voltage rises to some extent after a predetermined time has elapsed since the start of charging, and the amount of fluctuation in the cell voltage when the charge / discharge FET 12a is repeatedly turned on / off is stable. It is necessary to calculate the internal impedance. Therefore, when calculating the internal impedance of the battery cell 11 during charging, it is preferable that the predetermined voltage elapses from the start of charging, for example, two minutes or more from the start of charging, and the cell voltage is stable.

  Furthermore, when calculating the internal impedance during charging, it is preferable to perform temperature correction using the temperature correction coefficient stored in the memory 4 as in the case of the internal impedance in the initial state.

  The flow of processing for measuring the internal impedance of the battery cell 11 during actual use (during charging) will be described with reference to the flowchart shown in FIG. Unless otherwise specified, the following processing is performed under the control of the MPU 3. The battery pack 1 is connected to, for example, an external charger, and charging of the battery pack 1 is started to start a series of processes.

  In step S1, it is determined whether or not the charging current for the battery cell 11 is 1 [A] or more and two or more minutes have elapsed since the start of charging. If it is determined that the charging current is 1 [A] or more and two minutes or more have elapsed from the start of charging, the process proceeds to step S2. On the other hand, if both conditions are not satisfied, the process returns to step S1.

  Further, in step S1, only one of the conditions is determined among the determination of whether or not the charging current is 1 [A] or more and the determination of whether or not two minutes have elapsed since the start of charging. May be. In this case, it is more preferable to determine whether or not two minutes or more have elapsed since the start of charging.

  In step S2, the charge control FET 12a is turned ON / OFF repeatedly. In step S3, the charge current and the cell voltage for the battery cell 11 when the charge control FET 12a is ON are measured, and the average values are calculated. In step S4, the charging current and the cell voltage for the battery cell 11 when the charging control FET 12a is OFF are measured, and the average values are calculated.

In step S5, the charging current fluctuation amount ΔI _ave is calculated based on the charging current when the charging control FET 12a is ON and OFF. Further, the cell voltage fluctuation amount ΔV _ave is calculated based on the cell voltage when the charge control FET 12a is ON and OFF.

In step S6, the internal impedance R ₁ during actual use is calculated based on the above-described equation (1) using the charging current fluctuation amount ΔI _ave and the cell voltage fluctuation amount ΔV _ave calculated in step S5. In step S <b> 7, the internal impedance R ₁ during charging is stored in the memory 4. When the internal impedance during charging is already stored in the memory 4, the internal impedance value is updated. When the plurality of battery cells 11 are connected in series, the maximum value R _1max of the internal impedance is also stored in the memory 4.

  Thus, by repeatedly turning ON / OFF the charge / discharge FET 12a and supplying a pulsed charging current to the battery cell 1, the cell voltage of the battery cell 11 fluctuates in a stable state. The internal impedance can be measured accurately.

  Next, a method for calculating the deterioration rate of the battery cell 11 using the measured internal impedance of the battery cell 11 will be described. It is known that the battery cell 11 usually deteriorates by repeated charge and discharge, and its internal impedance increases compared to the initial state. When the battery cell 11 deteriorates and the internal impedance increases, the battery pack 1 may be in a dangerous state due to heat generated by the internal impedance during charging.

  Therefore, it has been conventionally performed to determine the degree of deterioration of the battery cell by utilizing the fact that the internal impedance increases as the deterioration of the battery cell 11 progresses. For example, as a method for detecting the deterioration of the battery cell, a method is conceivable in which a predetermined threshold is set for the internal impedance value and the degree of deterioration of the battery cell is determined based on the relationship between the threshold and the internal impedance value. More specifically, for example, a plurality of threshold values are set for the internal impedance value, and the degree of deterioration is determined stepwise based on the relationship between the set threshold values and the internal impedance value.

  However, the internal impedance of the battery cell varies depending on the type of battery cell and the material used. Moreover, even if they are the same type, there are individual differences depending on manufacturing lots and the like, and a slight difference occurs in the value of internal impedance. Therefore, for example, when the internal impedance value exceeds a predetermined threshold, it cannot be determined that different types of battery cells or battery cells using different materials are similarly deteriorated.

  Therefore, in the embodiment of the present invention, a deterioration rate indicating how much the battery cell 11 has deteriorated from the initial state is calculated based on the internal impedance in the initial state and the internal impedance during actual use (during charging). Like to do.

The deterioration rate is calculated based on Expression (3) using the maximum internal impedance value R _{0max in} the initial state of the battery cell 11 and the current internal impedance maximum value R _1max measured during charging.
Deterioration rate = (R _1max −R _0max ) / R _0max × 100 [%] (3)

For example, when the maximum value R _1max of the internal impedance measured during charging is twice the maximum value R _0max of the internal impedance in the initial state, the deterioration rate is 100 [%].

  Thus, by calculating the deterioration rate using the internal impedance in the initial state and the internal impedance during actual use, it is possible to prevent the battery pack 1 from entering a dangerous state.

  Next, a method for calculating the remaining capacity of the battery cell 11 will be described. In the embodiment of the present invention, the remaining capacity of the battery cell 11 is calculated based on the depth of discharge indicating the ratio of the discharge capacity to the full charge capacity of the battery cell 11.

  The depth of discharge of the battery cell 11 is the open circuit voltage of the battery cell 11 that is a voltage in a no-load state where no load is connected to the battery pack 1, and the depth of discharge indicating the ratio of the discharge capacity to the full charge capacity of the battery cell 11. Can be obtained based on characteristic data indicating the relationship. In this example, characteristic data indicating the relationship between the open circuit voltage of the battery cell 11 and the depth of discharge is stored in the memory 4 in advance, and the open circuit voltage calculated based on the cell voltage, the charging current, and the internal impedance of the battery cell 11 is used. Based on this, the depth of discharge is determined.

  FIG. 5 shows an example of the relationship between the open circuit voltage of the battery cell 11 and the depth of discharge. The horizontal axis indicates the discharge depth [%] of the battery cell 11, and the vertical axis indicates the open circuit voltage of the battery cell 11. When the depth of discharge is 0 [%], it indicates that the battery cell 11 is not discharged, that is, is in a fully charged state. Further, when the depth of discharge is 100 [%], it indicates that the battery cell 11 is completely discharged, that is, a complete discharge state. According to the characteristic data shown in FIG. 5, for example, when the open circuit voltage of the battery cell 11 is 3700 [mV], the discharge depth is about 80 [%], and the remaining capacity of the battery cell 11 is the full charge capacity. It can be seen that it is about 20%.

  Here, the calculation method of the open circuit voltage of the battery cell 11 is demonstrated. Since the open circuit voltage of the battery cell 11 is the battery voltage of the battery cell itself and does not include the voltage increase due to the internal impedance of the battery cell 11, the voltage increase due to the internal impedance from the cell voltage during charging (closed voltage; CCV). Can be calculated by subtracting. The voltage increase due to the internal impedance can be calculated by multiplying the internal impedance calculated as described above by the charging current.

Accordingly, when the open circuit voltage value is OCV, the cell voltage value is CCV, the charging current value is I _chg , and the internal impedance value is R _1max , the open circuit voltage value OCV of the battery cell 11 is calculated based on Equation (4). .
OCV = CCV−R ₁ × I _chg (4)

  Next, based on the characteristic data indicating the relationship between the depth of discharge and the open circuit voltage shown in FIG. 5, the depth of discharge corresponding to the open circuit voltage of the battery cell 11 calculated as described above is obtained. A value obtained by subtracting the discharge depth [%] from 100 [%] indicates the ratio of the remaining capacity of the battery cell 11 to the full charge capacity.

  Thus, the full charge capacity of the battery cell 11 is obtained by using the discharge depth obtained based on the open circuit voltage of the battery cell 11 using the characteristic data indicating the relationship between the open circuit voltage of the battery cell 11 and the discharge depth. The ratio of the remaining capacity to can be calculated. At this time, since the open circuit voltage does not depend on the degree of deterioration of the battery cell 11, even when the deterioration of the battery cell 11 progresses and the internal impedance increases, the remaining capacity of the battery cell 11 is not affected by the internal impedance value. It can be calculated accurately.

  In this example, the ratio of the remaining capacity to the full charge capacity of the battery cell 11 is calculated. However, a specific value of the remaining capacity is calculated by measuring the full charge capacity of the battery cell 11 in advance. can do. For example, the full charge capacity of the battery cell 11 is measured in advance during the manufacturing process and stored in the memory 4. As a method for measuring the full charge capacity, a conventionally known method can be used.

Then, by using the full charge capacity of the battery cell 11 and the obtained depth of discharge, the remaining capacity of the battery cell 11 can be calculated based on Expression (5).
Remaining capacity = full charge capacity × (100 [%] − discharge depth [%]) / 100 (5)

  As described above, in the embodiment of the present invention, various processes such as the calculation of the deterioration rate and the remaining capacity can be performed by using the calculated internal impedance value of the battery cell 11. The replacement of the battery cell 11 mounted on the pack 1 can also be detected. As described above, the internal impedance value of the battery cell 11 is degraded by repeated charge and discharge. When the battery cell 11 deteriorates, the internal impedance value usually increases compared to the initial state.

  In such a case, when the battery cell is replaced with a new one such as an unused product, it is considered that the internal impedance value of the battery cell rapidly decreases as compared with the immediately preceding internal impedance value. Therefore, in one embodiment of the present invention, it is possible to determine whether or not the battery cell has been replaced by detecting a change in the internal impedance value.

  Specifically, for example, every time the internal impedance is measured, the immediately preceding internal impedance value stored in the memory 4 is compared with the currently measured internal impedance value. As a result of the comparison, if the current internal impedance value is larger than the immediately previous internal impedance value, it is determined to be normal. On the other hand, when the current internal impedance value is smaller than the previous internal impedance value, it is determined that the battery cell 11 has been replaced.

  It is known that the internal impedance value of the battery cell 11 decreases as the battery temperature increases. Therefore, when the internal impedance value at the present time decreases, it cannot be determined whether the decrease in the internal impedance value is due to the replacement of the battery cell 11 or due to the increase in the battery temperature. .

  Therefore, in such a case, for example, the temperature is corrected with respect to the internal impedance value using a temperature correction coefficient, and the current internal impedance value is corrected to the internal impedance value at the reference battery temperature. Can be ignored.

  When it is determined that the battery cell 11 has been replaced in this way, it is preferable to prohibit charging / discharging of the battery cell 11 by turning off the charge / discharge control FET or by fusing the fuse element of the interruption circuit 6. In addition, a command to stop charging / discharging may be transmitted to the external electronic device connected to the battery pack 1 via the communication terminals 14 and 15, and charging / discharging may be stopped on the electronic device side.

  As described above, by periodically measuring the internal impedance of the battery cell 11 at the start of charging and comparing the measurement results, for example, the battery pack 1 can be used when the battery cell 11 is illegally replaced. Can be banned.

  In one embodiment of the present invention, by calculating the internal impedance of each battery cell 11 in actual use more accurately, the above-described deterioration rate and remaining capacity of the battery cell 11 can be calculated, and the battery cell 11 can be replaced. Various processes such as detection can be performed accurately.

  The embodiment of the present invention has been described above. However, the present invention is not limited to the embodiment of the present invention described above, and various modifications and applications can be made without departing from the gist of the present invention. Is possible. In this example, a case where a plurality of battery cells 11a and 11b are connected in series is described. However, the present invention is not limited to this. For example, a block in which a plurality of battery cells are connected in parallel (hereinafter referred to as a cell block as appropriate). However, the present invention is also applicable to the case where they are connected in series.

  However, in this case, since the battery cells constituting the cell block are connected in parallel and the internal impedance value of each battery cell cannot be measured, the internal impedance value is measured for each cell block unit, and the memory 4 is stored. Various processes are performed using the internal impedance value of the cell block stored in the memory 4 and the voltage and charging current of the cell block.

It is a block diagram which shows the structure of an example of the battery pack by one Embodiment of this invention. It is a basic diagram for demonstrating the measuring method of the internal impedance of the battery cell in an initial state. It is a basic diagram for demonstrating the measuring method of the internal impedance of the battery cell at the time of actual use (during charge). It is a flowchart for demonstrating the flow of the process which measures the internal impedance of the battery cell at the time of actual use (during charge). It is a basic diagram which shows an example of the relationship between the discharge depth of a battery cell, and an open circuit voltage.

Explanation of symbols

1 battery pack 2 assembled battery 3 MPU
4 Memory 5 Switch circuit 6 Cutoff circuit 7 FET
8 Current detection resistor 9 Positive terminal 10 Negative terminal 11a, 11b Battery cell 12a Charge control FET
12b Discharge control FET
14,15 Communication terminal

Claims (4)

In a battery pack comprising one or more battery cells,
A charge control switch for turning ON / OFF the charging current for the battery cell;
A control unit for controlling the charge control switch,
The control unit
A first charging current when the charge control switch is ON and a first cell voltage of the battery cell, a second charging current when the charge control switch is OFF and a second cell voltage of the battery cell Measure the cell voltage and
Calculating a fluctuation amount of the charging current based on the first charging current and the second charging current, and a fluctuation amount of the cell voltage based on the first cell voltage and the second cell voltage;
A battery pack characterized in that the internal impedance of the battery cell is calculated based on the fluctuation amount of the charging current and the fluctuation amount of the cell voltage. The battery pack according to claim 1,
The control unit
A battery pack characterized by measuring the internal impedance by controlling ON / OFF of the charge control switch after two minutes or more have elapsed from the start of charging. The battery pack according to claim 1,
The control unit
A battery pack, wherein the internal impedance is measured by controlling ON / OFF of the charge control switch when a charging current flowing through the battery cell is 1 [A] or more. A first charge current when a charge control switch for turning on / off a charge current for one or a plurality of battery cells is ON, a first cell voltage of the battery cell, and a case where the charge control switch is OFF Measuring a second charging current and a second cell voltage of the battery cell;
Calculating a fluctuation amount of the charging current based on the first charging current and the second charging current, and a fluctuation amount of the cell voltage based on the first cell voltage and the second cell voltage;
An internal impedance calculation method, wherein the internal impedance of the battery cell is calculated on the basis of the fluctuation amount of the charging current and the fluctuation amount of the cell voltage.

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