JP2008123961A - Battery pack, battery deterioration measuring device, and battery deterioration measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable to precisely carry out measurement of deterioration of a battery cell in a short time. <P>SOLUTION: In the case of measuring deterioration rate of the battery cell, when a charge current supplied to the battery cell during the time of constant current charging is a first charging current value Ia, a first voltage measuring treatment to obtain a first cell voltage Va is carried out. Then, in the case it changes to a second charge current value Ib lower than the first charge current value Ia, a second voltage measuring treatment to obtain a second cell voltage Vb is carried out. Based on the first cell voltage Va and the second cell voltage Vb obtained like this, the internal resistance of the battery cell is calculated and deterioration judgment treatment to judge the deterioration rate of the battery cell is carried out. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a battery pack incorporating a battery cell such as a secondary battery, which is used as a driving power source for various electronic devices, a battery deterioration measuring device for measuring deterioration of a battery cell in the battery pack, and a battery cell The present invention relates to a battery deterioration measuring method for measuring deterioration.

  Conventionally, for secondary batteries such as lithium ion secondary batteries, appropriate control and protection for charging and discharging are necessary, and a control circuit and a protection circuit are built in a battery pack together with a battery cell. . In that case, as control of charging and discharging by the control circuit, characteristic values such as voltage and current at the time of full charge of the battery cell built in the battery pack are stored in advance and correspond to the stored characteristic values. When a value to be detected is detected, control for stopping charging is performed. Regarding the control at the time of discharging, similarly, the discharge end voltage and the like are stored by the characteristic value of the battery cell, and the discharge is stopped when this voltage is reached.

  By the way, about the battery cell in a battery pack, a characteristic deteriorates by charging and discharging repeatedly. The deterioration state of the battery characteristics can be detected by measuring the internal resistance of the battery cell. As a conventional measurement processing example of the internal resistance of the battery cell, for example, it is known to measure from the difference between the closed voltage and the open voltage of the battery cell and the charging current.

Japanese Patent Application Laid-Open No. 2004-228561 describes a method for determining the battery life by stopping the charging current of the battery and measuring the open-circuit voltage.
JP 2002-230547 A

  By the way, in the process of measuring the deterioration of the battery cell by the above-described method, it is difficult to accurately measure the deterioration of the battery cell in a short time. That is, when charging the battery cell is stopped and the battery cell is opened with respect to the charging circuit and an attempt is made to measure the open circuit voltage, the voltage fluctuation is large immediately after the open circuit, and several hours after the open circuit is opened. There has been a problem that an accurate open-circuit voltage cannot be measured unless it has elapsed. A specific voltage fluctuation example immediately after the open state will be described in comparison with the processing of the present invention in the embodiment described later, but it is difficult to accurately measure the open circuit voltage in a short time. Thus, it has been difficult to measure the internal resistance of the secondary battery in a short time by such a conventional method.

  In view of this point, an object of the present invention is to enable accurate measurement of battery deterioration in a short time.

  In order to solve such a problem, when measuring the deterioration rate of a battery cell, the present invention provides the first charging current supplied during constant current charging to the battery cell when the charging current value is the first charging current value. A first voltage measurement process for obtaining a cell voltage is performed, and a second voltage measurement process for obtaining a second cell voltage when the second charging current value is lower than the first charging current value. Do. Based on the first cell voltage and the second cell voltage obtained in this way, the internal resistance of the battery cell is calculated, and a deterioration determination process for determining the deterioration rate of the battery cell is performed.

  According to the present invention, each of the first cell voltage value and the second cell voltage value is a value measured in a state where a charging current flows to the battery cell, and the first charging used for each measurement. By setting the current value and the second charging current value to a current value having a large difference to some extent, the internal resistance of the battery cell can be accurately calculated. Therefore, according to the present invention, the internal resistance of the battery cell can be accurately calculated without opening the battery cell to the charging circuit.

  According to the present invention, it is possible to accurately calculate the internal resistance of the battery cell while keeping the battery cell connected to the charging circuit, and to accurately calculate the deterioration rate of the battery cell based on the accurate internal resistance. Judgment is possible. In this case, since the measurement can be performed while the battery cell is in the closed state connected to the charging circuit, it is not necessary to leave the battery cell in the open state for a long time as in the conventional case, and accurate measurement can be performed in a short time.

Hereinafter, an example of an embodiment of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a block diagram illustrating a configuration example of the battery pack 20 of the present example and the charging device 10 connected to the battery pack 20. The battery pack 20 is used as a drive power source for various electronic devices such as personal computer devices. A plurality of (six in this case) secondary battery cells 31 to 36 are built in the battery pack 20. Here, lithium ion secondary batteries are used as the secondary battery cells 31 to 36. Moreover, in FIG. 1, it is set as the so-called 2 parallel 3 series cell structure which made 6 cells 2 pieces parallel, and connected 3 sets in series. The six battery cells 31 to 36 basically have the same characteristics and capacity. The number of cells incorporated in the battery pack 20 is an example, and is not limited to six as shown in FIG. 1, and the connection state is also limited to the connection configuration as shown in FIG. Not.

  The charging device 10 includes a power plug 11 for obtaining a commercial AC power source. The commercial AC power source supplied from the power plug 11 is transformed and rectified in the charging circuit 12 to obtain a DC low voltage power source. Is used to obtain a charging current for charging the battery cell. The positive terminal 13 and the negative terminal 14, which are output terminals of the charging circuit 12, are connected to the positive terminal 21 and the negative terminal 22 of the battery pack 20, respectively, and supply charging current to the battery cells 31 to 36 in the battery pack 20. To do.

  In this case, when a charging current is supplied from the charging device 10 to the battery pack 20, the charging in the constant voltage charging mode and the charging in the constant current charging mode can be performed. Furthermore, at the time of charging in the constant voltage charging mode, the charging current can be varied in a plurality of stages, and a charging current varying process for measuring the deterioration rate of the battery cell described later is possible. As a configuration for changing the charging current in a plurality of stages, for example, a configuration for performing trickle charging may be used. That is, for example, when the battery voltage is low, in order to safely charge the secondary battery cell, when the charging device is configured to perform trickle charging (preliminary charging) with a small current, the small current You may utilize the charge in for measuring the deterioration rate of the battery cell mentioned later. Such processing for reducing the received current to a small current can be performed by transmitting data for setting a charging current value from the battery pack 20 side to the charging device 10 side. Specifically, for example, a command to temporarily set the trickle charging mode is sent from the battery pack 20 side to the charging device 10 side, and the charging current variable processing for measuring the deterioration rate of the battery cell is performed. It is possible to send a command to return to the charging mode.

  The charging device 10 includes communication terminals 15 and 16 and is configured to perform charging while communicating with a central control unit (CPU) 27 on the battery pack 20 side. That is, when the battery pack 20 is connected to the charging apparatus 10, the positive terminal 13 and the negative terminal 14 of the charging apparatus 10 are connected to the positive terminal 21 and the negative terminal 22 of the battery pack 20, and the charging apparatus 10 communication terminals 15 and 16 are connected to the communication terminals 23 and 24 of the battery pack 20, and the charging circuit 12 receives a command from the central control unit 27 on the battery pack 20 side. The charging current is supplied based on the state (mode).

  In the example of FIG. 1, the charging device 10 is illustrated as a single charging device. However, for example, the charging device 10 is connected to the main body side of an electronic device (such as a personal computer device) to which the battery pack 20 is connected. A corresponding circuit may be incorporated.

  Next, the configuration of the battery pack 20 will be described. As already described, the connection configuration of the cells in the battery pack 20 is a two-parallel three-series cell configuration, and the positive electrode terminal 21 of the battery pack 20 is a field effect transistor (FET) 25, 26 for charge / discharge control. Is connected to the positive electrodes of the battery cells 31 and 32. The negative electrodes of the battery cells 31 and 32 are connected to the positive electrodes of the battery cells 33 and 34, and the negative electrodes of the battery cells 33 and 34 are connected to the negative electrode terminal 22 of the battery pack 20 via the current detection resistor 37. It is. The two field effect transistors 25 and 26 for charge / discharge control have connection directions opposite to each other. The discharge control is performed by turning on / off one transistor 25 and the charge is controlled by turning on / off the other transistor 26. . The two field effect transistors 25 and 26 for charge / discharge control are turned on / off by the control of the charge / discharge control unit 29.

  Moreover, the charge / discharge control part 29 is set as the structure which measures the cell voltage of each battery cell 31-36. That is, one end of the resistor 38 is connected to the connection point on the positive electrode side of the battery cells 31 and 32 connected in parallel. In addition, one end of a resistor 39 is connected to a connection point between the negative electrode side of the battery cells 31 and 32 and the positive electrode side of the battery cells 33 and 34. In addition, one end of the resistor 40 is connected to a connection point between the negative electrode side of the battery cells 33 and 34 and the positive electrode side of the battery cells 35 and 36. Furthermore, one end of the resistor 41 is connected to the connection point on the negative electrode side of the battery cells 35 and 36.

  And the voltage obtained by the other end of each resistor 38,39,40,41 is measured by the charging / discharging control part 29, and it is set as the structure which judges the cell voltage of each battery cell. Here, the cell voltage is measured in units of two battery cells connected in parallel. In the following description, the voltage of two battery cells connected in parallel is referred to as a cell block voltage. The measured cell voltage data is sent to the central control unit 27. In the central control unit 27, the voltage across the current detection resistor 37 is also measured, and the current flowing through the resistor 37 is also measured.

  Then, the central control unit 27 determines each cell voltage sent from the charge / discharge control unit 29 and the charge current detected by the voltage across the current detection resistor 37, and monitors the charge state and the discharge state. .

  A memory 28 is connected to the central control unit 27. The memory 28 is composed of, for example, a nonvolatile memory. The memory 28 stores data relating to the characteristics of the battery cells 31 to 36 prepared in the battery pack 20. That is, characteristics such as a cell voltage when the battery cell is fully charged, a discharge end voltage, an allowable charging current, and a discharging current are stored. Further, data necessary for determining the deterioration rate of the battery cell and data of a calculation formula necessary for calculating the deterioration rate are also stored. When the deterioration rate is determined, stored data of the determined deterioration rate (or data of the full charge amount determined from the deterioration rate) is updated as needed. Details of the deterioration rate determination process will be described later.

  When the central control unit 27 determines the deterioration rate of the battery cells 31 to 36, the full charge amount of the battery cell is reduced based on the deterioration rate. By reducing the full charge amount of the battery cell, when the central control unit 27 detects that the reduced full charge amount is reached at the time of charging, the charge control field effect transistor 26 is turned off to perform charging. Control to stop is performed. In addition, when the deterioration rate of the battery cells 31 to 36 is determined to be a deterioration rate that is equal to or lower than a predetermined threshold, data indicating battery deterioration is communicated. The battery may be output to the outside via the terminals 23 and 24, and a display unit or the like on the connected electronic device side may be notified of battery deterioration and displayed to prompt the user to replace the battery.

  In the configuration of FIG. 1, a protection circuit such as a fuse in the battery pack is omitted. However, a general fuse with a heating temperature resistor or the like is arranged as a protection circuit for this type of battery pack, so that the battery cell The battery pack may not be used by fusing the fuse when an abnormality occurs.

Next, with reference to the flowchart of FIG. 2, an example of a battery cell internal resistance measurement process performed when the battery pack 20 of the present example is charged will be described. The internal resistance measurement process of this example is executed by the control and determination of the central control unit 27.
Here, it is assumed that the voltage of the battery cell before the start of charging is a relatively low voltage, and charging is performed in the constant current charging mode. Charging is started in the constant current mode, and a constant current having a current value Ia is supplied from the charging device 10 to the battery pack 20. When charging at this constant current is started, the voltage of each cell block detected by the charge / discharge control unit 29 is judged when 20 minutes or more have elapsed from the start of charging in that state, and each cell block voltage is It is determined whether or not the predetermined range is set (step S11). In this example, it is determined whether or not the cell block voltage exceeds 3.9V and is less than 4.15V. This voltage range is a voltage range selected from a cell voltage (cell block voltage) at full charge and a discharge end voltage. If it is within this voltage range after 20 minutes from the start of charging, it can be said that it is a relatively stable constant current charging state.

  If it is determined in step S11 that the value is within a certain range, the process proceeds to the internal resistance measurement process of this example. First, an accurate value of the current charging current value Ia is measured and stored in the memory 28 (step S12). Then, in the state where the charging current is supplied, the voltage (closed circuit voltage) Va of each cell block is measured and stored in the memory 28 (step S13).

  Next, a command is sent from the central control unit 27 in the battery pack 20 to the charging circuit 12 side of the charging device 10, and the charging current value is changed from the current value Ia to the current value Ib that is about 1/3 of the current value Ia. (Step S14). The reduced current value Ib may be a charging current value prepared by the charging device 10 for trickle charging. Thereafter, the charging current is measured, and an accurate value of the supplied charging current value Ib is measured and stored in the memory 28 (step S15). Then, with the charging current supplied, the voltage (closed circuit voltage) Vb of each cell block is measured and stored in the memory 28 (step S16). When the measurement so far is finished, a command is sent from the central control unit 27 in the battery pack 20 to the charging circuit 12 side of the charging apparatus 10, and the charging current value is returned to the original current value Ia (step S17). It should be noted that only the time required for measuring the charging current value Ib and the voltage Vb of the cell block is sufficient after the charging current value Ib is changed in step S14 until the charging current value Ia is returned in step S17.

  In the central control unit 27, the internal resistance for each cell block is calculated using each data stored in the memory 28 (step S18). A calculation formula for calculating the internal resistance will be described later. And the deterioration rate of the battery cell which comprises each cell block is calculated from the calculated internal resistance value (step S19). When the deterioration rate of the battery cell is calculated, the data in the memory 28 about the full charge amount of each battery cell is updated based on the deterioration rate (step S20).

  FIG. 3 is a diagram showing an example of changes in charging current and cell voltage when such processing is performed. However, FIG. 3 is a diagram showing the concept of the change state, and the time axis of the horizontal axis in FIG. 3 does not always coincide with the real time. FIG. 3A shows an example of the charging current, and FIG. 3B shows an example of the cell voltage (charging voltage). First, at timing t1, charging is started at the charging current value Ia, and at timing t2 when a predetermined time has elapsed, the charging current value is changed to Ib. The charging current value Ib is reduced by a predetermined current ΔI so as to be about 1/3 of the current value Ia.

  Then, as shown in FIG. 3B, the cell voltage Va immediately before changing the charging current from the current value Ia to the current value Ib is measured, and the cell voltage Vb at the current value Ib is further measured. When the measurement of the cell voltage Vb is completed, as shown in FIG. 3A, the charging current is returned to the current value Ia at the timing t3, and the charging in the original state is resumed. Thereafter, charging is continued until the central control unit 27 determines that the battery is fully charged. However, the constant current charging at the current value Ia may be performed up to a certain cell block voltage, and thereafter, another charging mode such as constant voltage charging may be used.

  Next, an example of internal resistance calculation processing for each cell block in step S18 of the flowchart of FIG. 2 will be described. In the process described with reference to the flowchart of FIG. 2, two charging current values Ia and Ib and cell block voltages Va and Vb during charging are measured. Since the cell block voltages Va and Vb are cell voltages in a state where a charging current is supplied, they are closed circuit voltages (that is, voltages not in an open state). Using the charging current values Ia and Ib and the cell block voltages Va and Vb, the central control unit 27 calculates the internal resistance Imp of each cell block by the following arithmetic expression.

[Equation 1]
(Va−Vb) / (Ia−Ib) = Imp

  The deterioration rate is calculated by the following equation, assuming that the internal resistance of each cell block in the initial state is Imp NEW.

[Equation 2]
Imp / Imp NEW = Deterioration rate

  Since the deterioration rate can be calculated in this way, the full charge amount of each of the battery cells 31 to 36 built in the battery pack 20 can be accurately measured. Moreover, in this example, the internal resistance can be accurately measured in a short time.

Here, the fact that the internal resistance of the battery cell can be measured in a short time by the processing of this example will be described in comparison with the case of measuring the internal resistance of the battery cell by measuring the conventional open-circuit voltage.
FIG. 4A shows a characteristic example in the case of measuring from the difference between the closed voltage and the open voltage of the battery cell and the charging current, which has been conventionally known, as described in the background art section. As shown in FIG. 4A, the charging current is cut off in a state where the battery is charged with a constant current, charged to a certain degree and becomes the cell voltage V11. By cutting off the charging current and bringing the battery cell into an open state (that is, a state where the battery cell is not in a closed state), the cell voltage rapidly decreases to the voltage V12. However, after that, the cell voltage gradually decreases from the voltage V12 over time, and after several hours (for example, 2 hours) have passed since the charging current was cut off, the cell voltage finally becomes stable.

  FIG. 4B shows an equivalent circuit inside each cell. Thus, the circuit inside the cell can be shown by a series circuit of the resistor R1 and the parallel circuit of the capacitor C1 and the resistor R2. In this equivalent circuit, when the battery cell changes from a closed state to an open state, a voltage drop due to the resistor R1 appears immediately after the charging current is cut off. The voltage drop due to the resistor R1 is a drop from the voltage V11 to the voltage V12 shown in FIG.

  On the other hand, the capacitor C1 shown in the equivalent circuit starts discharging when the charging current is interrupted, and the voltage gradually decreases while the discharging is being performed. This voltage drop is performed over several hours, for example.

  FIG. 5 (a) shows an example of characteristics when measuring the internal resistance of the battery cell in this example. As shown in FIG. 5A, the charging current is reduced to about 1/3 in a state where the battery is charged with a constant current and charged to some extent to become the cell voltage V21. With this decrease in charging current, the voltage drops to the cell voltage V22, but the lowered cell voltage V22 is maintained.

  The cell voltage V22 thus lowered is maintained in a constant state as shown in the equivalent circuit shown in FIG. 5B even when the charging current decreases, the charging current continues to be supplied. This is because the discharge from the capacitor C1 in the equivalent circuit does not occur, and only a drop due to the resistor R1 occurs.

An example of actual measurement is shown in FIG. 6A as an example of voltage / current change in the conventional process shown in FIG. 4 (that is, when the battery cell is changed from a closed state to an open state). FIG. 6B shows an example of voltage / current change when measuring the internal resistance in the processing of this example shown.
As shown in FIG. 6A, when the charging current Ix in the conventional process is cut off, the cell voltage Vx drops sharply at the time of cutting, and then gradually decreases over a long period of time as shown by the inclined straight line α. .

  On the other hand, in the case of this example, as shown in FIG. 6B, when the charging current Iy is decreased, the cell voltage Vy rapidly decreases at the time of change, and then as shown by the horizontal straight line β. The voltage value can be maintained, and an accurate cell voltage can be measured in a short time. In the example of FIG. 6B, the cell voltage is stabilized at a constant cell voltage in about 100 seconds after the charging current is reduced.

  By performing the processing of this example in this way, the internal resistance of the battery cell can be accurately measured in a short time during charging, the deterioration rate of the battery cell can be accurately calculated in a short time, and the deterioration rate can be calculated. It is possible to accurately determine the remaining charge in consideration.

  In addition, as a small charging current used for measuring the internal resistance of the battery cell, the charging current for trickle charging provided in the charging device is used, so that the internal resistance of the battery cell can be accurately measured using the existing charging device. Measurement can be performed, and it is not necessary to prepare a special configuration for changing the charging current on the charging device side, and measurement can be easily performed using an existing charging device.

  In the embodiment described above, a secondary battery constituted by a lithium ion secondary battery is used as a cell incorporated in the battery pack. However, other secondary battery cells such as a nickel hydride secondary battery are used. In the built-in battery pack, the present invention can also be applied when the deterioration rate is determined from the internal resistance.

  In the above-described embodiment, the control unit in the battery pack calculates the internal resistance of the battery and determines the deterioration rate. However, if the cell voltage and the charging current data are obtained, the charging circuit The battery cell deterioration rate may be calculated on the side. When the charging circuit is built in the main body of an electronic device such as a personal computer device, for example, a program for calculating an internal resistance for executing the processing shown in the flowchart of FIG. An additional process may be performed.

It is a block diagram which shows the structural example of the battery pack by the example of one embodiment of this invention, and the charging circuit connected to it. It is a flowchart which shows the example of a measurement process by the example of one embodiment of this invention. It is a characteristic view which shows the example of a waveform change at the time of the measurement by one embodiment of this invention. It is explanatory drawing which shows the example in the case of measuring the internal resistance of a battery cell as an open state. It is explanatory drawing which shows the example of a measurement of the internal resistance of the battery cell by the example of one embodiment of this invention. It is a characteristic view which shows the example of a voltage change by the example of one embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Charger, 11 ... Power plug, 12 ... Charging circuit, 13 ... Positive electrode terminal, 14 ... Negative electrode terminal, 15, 16 ... Communication terminal, 20 ... Battery pack, 21 ... Positive electrode terminal, 22 ... Negative electrode terminal, 23, 24 ... Communication terminal, 25, 26 ... Field effect transistor (FET) for charge / discharge control, 27 ... Central control unit (CPU), 28 ... Memory, 29 ... Charge / discharge controller, 31, 32, 33, 34, 35, 36 ... Battery cell, 37 ... Current detection resistor, 38, 39, 40, 41 ... Cell voltage detection resistor

Claims (6)

A battery cell;
A charge / discharge control switch for controlling charging and / or discharging of the battery cell;
A voltage measuring unit for measuring the voltage of the battery cell;
A current measuring unit for measuring a charging current of the battery cell;
A battery pack including a control unit that controls the charge / discharge control switch and determines a measurement result of the voltage measurement unit and the current measurement unit;
The control unit obtains a first cell voltage from a voltage value measured by the voltage measurement unit when a charging current supplied during constant current charging to the battery cell is a first charging current value, When the second charging current value is lower than the first charging current value, a second cell voltage is obtained from the voltage value measured by the voltage measuring unit, and the first cell voltage and the second cell voltage are obtained. A battery pack characterized in that an internal resistance of the battery cell is calculated on the basis of the cell voltage and a deterioration rate of the battery cell is determined. The battery pack according to claim 1, wherein
Provided with a plurality of battery cells as the electronic cell, a battery pack configuration in which the plurality of battery cells are arranged in parallel or in series,
The voltage measurement of the battery cell in the said voltage measurement part is measured for every block of a predetermined cell unit, The battery pack characterized by the above-mentioned. The battery pack according to claim 1, wherein
The control unit calculates a remaining charge amount of the battery cell based on a determination of a deterioration rate of the battery cell, and controls charge or discharge based on the calculated remaining charge amount. pack. The battery pack according to claim 1, wherein
The control unit instructs the charging device connected to the battery pack to set a trickle charging mode, and changes the first charging current value to the second charging current value. Battery pack. In a battery deterioration measuring device that measures the deterioration of battery cells,
A voltage measuring unit for measuring the voltage of the battery cell;
A current measuring unit for measuring a charging current of the battery cell;
When the charging current supplied during constant current charging to the battery cell is a first charging current value, a first cell voltage is obtained from the voltage value measured by the voltage measuring unit, and the first charging is performed. When the second charging current value is lower than the current value, a second cell voltage is obtained from the voltage value measured by the voltage measuring unit, and the first cell voltage and the second cell voltage are obtained. And a control unit that calculates an internal resistance of the battery cell and determines a deterioration rate of the battery cell. In a battery deterioration measuring method for measuring battery cell deterioration,
A first voltage measurement process for obtaining a first cell voltage when a charging current supplied during constant current charging to the battery cell is a first charging current value;
A second voltage measurement process for obtaining a second cell voltage when the second charging current value is lower than the first charging current value;
A deterioration determination process for calculating an internal resistance of the battery cell based on the first cell voltage and the second cell voltage and determining a deterioration rate of the battery cell is performed. How to control the pack.

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