JP5092321B2 - Battery pack and detection method - Google Patents

Description

  The present invention relates to a battery pack for detecting replacement of a battery cell and a detection method.

  In recent years, portable electronic devices such as notebook PCs (Personal Computers), mobile phones, and PDAs (Personal Digital Assistants) have become widespread. Widely used.

  The battery pack in which such a secondary battery is housed is provided with a protection circuit for prohibiting charging / discharging when an abnormality of the secondary battery is detected. Specifically, for example, the voltage, charge / discharge current, temperature, and the like of the secondary battery are measured every predetermined time, and abnormalities such as overcharge, overdischarge, and overcurrent with respect to the secondary battery are detected based on the measurement result. And when these abnormalities are detected, charging / discharging with respect to a secondary battery is prohibited by turning OFF the charging / discharging switch which controls charging / discharging, or fusing a thermal fuse.

  As described above, Japanese Patent Application Laid-Open No. 2004-151867 discloses a technique for melting a secondary fuse and detecting charging / discharging of the secondary battery when an abnormality of the secondary battery is detected.

JP 2000-357540 A

  By the way, the secondary battery deteriorates as charging and discharging are repeated, and the battery capacity decreases. Furthermore, when used for a long time, for example, for several years, the secondary battery may become unusable. In such a case, in order to make the battery capacity of the secondary battery the same as when not in use, it is necessary to replace the battery cell used for the secondary battery.

  However, it is considered that the characteristics of the replaced battery cell and the originally stored battery cell are different. In the above-described protection circuit, the control specifications are determined in accordance with the characteristics of the original battery cell. For this reason, if the battery pack is illegally modified and the battery cell used in the secondary battery is replaced, the protection circuit will not operate normally and an abnormality in the battery pack cannot be detected. However, the battery pack may be in a dangerous state.

  Accordingly, an object of the present invention is to provide a battery pack capable of detecting replacement of a battery cell and a detection method thereof.

  In order to solve the above-described problems, the first invention detects one or a plurality of batteries, a charge / discharge switch that controls charge / discharge currents for the batteries, and the voltage and charge / discharge currents of the batteries. A control unit that calculates the internal resistance of the battery based on the current; and a storage unit that stores the internal resistance calculated by the control unit. The control unit calculates the latest internal resistance calculated when charging the battery. Is compared with the previous internal resistance stored in the storage unit, and if the latest internal resistance is smaller than the previous internal resistance, detection information indicating detection of battery replacement is generated and stored in the storage unit At the same time, the battery pack is controlled such that the charge / discharge switch is turned off, and the latest internal resistance is stored in the storage unit when the latest internal resistance is larger than the previous internal resistance.

  The second aspect of the invention is a calculation step of detecting the voltage and charging / discharging current of one or a plurality of batteries and calculating the internal resistance of the battery based on the voltage and charging / discharging current, and is calculated at the time of charging the battery. The latest internal resistance is compared with the previous internal resistance stored in the storage unit, and if the latest internal resistance is smaller than the previous internal resistance, detection information indicating detection of battery replacement is generated. When the latest internal resistance is larger than the previous internal resistance, the latest internal resistance is stored in the storage unit. And a control step for storing in the detection method.

  As described above, in the first and second inventions, the voltage and current of one or more batteries are detected, the latest internal resistance is calculated based on the voltage and current, the calculated latest internal resistance, Since the previous internal resistance stored in the storage unit is compared, it can be determined whether or not the battery has been replaced.

  This invention calculates the internal resistance of the battery based on the voltage and charge / discharge current of the battery, and compares the latest internal resistance calculated with the previous internal resistance stored in the storage unit. There is an effect that battery replacement can be detected based on the result.

  Hereinafter, an embodiment of the present invention will be described. In the battery pack according to the embodiment of the present invention, the internal resistance value of the secondary battery that increases by repeating charging and discharging is calculated, and whether or not the battery cell has been replaced based on the calculated change in the internal resistance value. I try to judge.

  First, the configuration of an example of a battery pack 1 according to an embodiment of the present invention will be described with reference to FIG. In the battery pack 1, the positive terminal 13 and the negative terminal 14 are connected to the positive terminal and the negative terminal of an external electronic device or a charger, respectively, and the secondary battery 11 is charged / discharged via the circuit board 12.

  The secondary battery 11 is a secondary battery such as a lithium ion secondary battery, and is a single battery or an assembled battery in which a plurality of battery cells are connected in series and / or in parallel. In this example, a case where three battery cells are connected in series is shown. The circuit board 12 performs control for preventing overcharge and overdischarge of the battery pack 1 and detection of modification to the battery pack 1. The circuit board 12 mainly includes an MPU (Micro Processing Unit) 21 as a control unit, a memory 22 as a storage unit, a switch circuit 23, a current detection resistor 24, and a thermal fuse 25.

  The MPU 21 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 21 measures the voltage of each of the secondary battery 11 and the battery cells in the secondary battery 11 every predetermined time, and measures the magnitude and direction of the current flowing through the current detection resistor 24 every predetermined time.

  Then, when the voltage of any cell of the secondary battery 11 becomes the overcharge detection voltage based on the measured voltage value and current value and the battery temperature measured by the temperature detection element 26 such as a thermistor, the MPU 21 In addition, when the voltage of the secondary battery 11 becomes equal to or lower than the overdischarge detection voltage, a control signal is sent to the switch circuit 23 to prevent overcharge and overdischarge. Further, the MPU 21 performs control so that the thermal fuse 25 is blown. Here, in the case of a lithium ion battery, the overcharge detection voltage is determined to be 4.2 V ± 0.5 V, for example, and the overdischarge detection voltage is determined to be 2.4 V ± 0.1 V.

  Further, the MPU 21 calculates the internal resistance of the secondary battery 11 based on the measured voltage value and current value. Then, based on the calculated internal resistance, it is determined whether the battery cell used for the secondary battery 11 has been replaced, and the determination result is stored in the memory 22. If it is determined that the battery cell has not been replaced as a result of the determination, the calculated internal resistance value is stored in the memory 22. In addition, the calculation method of an internal resistance value and the detection method of replacement of a battery cell will be described later.

  For example, an EEPROM (Electrically Erasable and Programmable Read Only Memory) that is a nonvolatile memory is used as the memory 22, and when battery cell replacement is detected, detection indicating that battery cell replacement has been detected Information is stored. The memory 22 stores the internal resistance value of the secondary battery 11 calculated by the MPU 21 when the replacement of the battery cell is not detected.

  The switch circuit 23 includes a charge control FET (Field Effect Transistor) 31a and a discharge control FET 31b. When the battery voltage becomes the overcharge detection voltage, the charging control FET 31a is turned off and the charging current is controlled not to flow. Note that after the charge control FET 31a is turned off, only discharge is possible via the parasitic diode 32a.

  Further, when the battery voltage becomes the overdischarge detection voltage, the discharge control FET 31b is turned off and the discharge current is controlled not to flow. Note that after the discharge control FET 31b is turned OFF, only charging is possible via the parasitic diode 32b.

  Next, a battery cell replacement detection method in the battery pack 1 according to the embodiment of the present invention will be described. The secondary battery 11 is usually deteriorated by repeatedly charging and discharging, and the internal resistance of the secondary battery 11 increases as the deterioration progresses. In such a case, when the battery cell used for the secondary battery 11 is replaced with a battery cell having a low degree of deterioration such as an unused product, it is considered that the internal resistance of the secondary battery 11 rapidly decreases. .

  Therefore, in the embodiment of the present invention, the internal resistance of the secondary battery 11 is calculated, and the value of the internal resistance before and after replacement is compared to determine whether or not the battery cell has been replaced.

  The internal resistance of the secondary battery 11 can be calculated at the timing when the voltage and current change rapidly. The timing at which the voltage and current rapidly change is, for example, the timing at which charging or discharging is started. Here, a method of calculating the internal resistance of the secondary battery 11 at the timing when charging is started will be described as an example.

  As a charging method for the secondary battery 11, a constant current constant voltage charging method is generally used. In the constant current constant voltage charging method, as shown in FIG. 2, the secondary battery 11 is charged with a constant current until the voltage of the secondary battery 11 reaches a predetermined voltage, and after the voltage of the secondary battery 11 reaches the predetermined voltage. Charge at a constant voltage. Then, charging ends when the charging current converges to 0 [A].

  In the case of the constant current constant voltage charging method, in the constant current charging region where the voltage of the secondary battery 11 reaches a predetermined voltage immediately after the start of charging, the secondary battery 11 is charged with a constant charging current, and the voltage rapidly increases. To do. The internal resistance in this case can be calculated based on the voltage difference ΔV and the charging current difference ΔI immediately before the start of charging and after a predetermined time has elapsed since the start of charging in the constant current charging region.

The voltage and charging current of the secondary battery 11 immediately before the start of charging are V ₁ [V] and I ₁ [A], and the voltage and charging current of the secondary battery 11 after elapse of a predetermined time t [sec] are V ₂ [ Assuming V] and I ₂ [A], the internal resistance R [Ω] of the secondary battery 11 is calculated based on Equation (1).
R = ΔV / ΔI = (V ₂ −V ₁ ) / (I ₂ −I ₁ ) (1)

  As the timing at which the voltage and current rapidly change, the timing at which charging or discharging ends can be applied, but it is preferable to calculate the internal resistance at the timing at which charging or discharging is started. This is because the internal resistance can be calculated more stably at the timing when charging or discharging is started than when the charging or discharging ends.

The internal resistance R calculated as described above is stored in the memory 22 as the internal resistance R _pre when the battery was last charged. In the next charging, the internal resistance R is calculated as the latest internal resistance R _{new in the same} manner as described above. Then, the internal resistance R _pre stored in the memory 22 is compared with the calculated latest internal resistance R _new .

As a result of the comparison, if R _new is smaller than R _pre , it is determined that the battery cell has been replaced. On the other hand, when R _new is larger than R _pre , it is determined that the battery cell has not been replaced.

  In this way, the latest internal resistance value obtained by calculating the voltage and charging current immediately before the start of charging and after a predetermined time has elapsed from the start of charging, and the internal resistance at the time of previous charging stored in the memory 22 By comparing the value, it is possible to detect whether or not the battery cell has been replaced according to the comparison result.

  Next, a battery cell replacement detection method in the battery pack 1 according to the embodiment of the present invention will be described with reference to the flowchart shown in FIG. Here, it is assumed that the voltage, charge / discharge current, and battery temperature are measured at the start of charging.

  When a charger is connected to the battery pack 1 and charging is started, in step S1, the MPU 21 confirms whether or not detection information indicating that battery cell replacement has been detected is stored in the memory 22, and detection is performed. It is determined whether or not the battery cell has been replaced based on the presence or absence of information. As a result of the determination, if the detection information is not stored in the memory 22 and it is determined that the battery cell is not replaced, the process proceeds to step S2. When the charger is connected to the battery pack 1 for the first time, since the detection information is not stored in the memory 22, it is determined that the battery cell has not been replaced.

In step S2, the MPU 21 measures the voltage, charging current and battery temperature of the secondary battery 11 after a predetermined time has elapsed. In step S3, based on the voltage and charging current of the secondary battery 11 measured in step S2, The latest internal resistance R _new of the secondary battery 11 is calculated.

In step S4, the MPU 21 reads the previous internal resistance R _pre stored in the memory 22 in advance, and compares R _pre with the latest internal resistance R _new calculated in step S3. As a result of the comparison, if R _new is smaller than R _pre , it is determined that the battery cell has been replaced, and the process proceeds to step S5.

  In step S <b> 5, the MPU 21 generates detection information indicating detection of battery cell replacement and stores the detection information in the memory 22. In step S <b> 6, the MPU 21 controls to melt the temperature fuse 25 and prohibits charging / discharging of the secondary battery 11.

  On the other hand, in step S1, if the MPU 21 determines that the detection information is stored in the memory 22 and the battery cell has been replaced, the process proceeds to step S7.

  In step S <b> 7, the MPU 21 controls the switch circuit 23 to prohibit charging / discharging of the secondary battery 11. Specifically, for example, the charge control FET 31a and the discharge control FET 31b provided in the switch circuit 23 are turned off. And the process in step S7 is repeated cyclically, and charging / discharging with respect to the secondary battery 11 is prohibited permanently.

On the other hand, if R _new is larger than R _pre in step S4, it is determined that the battery cell has not been replaced, and the process proceeds to step S8. Note that when R _new is calculated for the first time, R _pre is not stored in the memory 22 and internal resistance cannot be compared, so the process proceeds to step S8. In step S8, the MPU 21 stores the internal resistance R _new calculated in step S3 in the memory 22 as R _pre . Then, the process returns to step S2.

  As described above, in the embodiment of the present invention, the detection information is stored in the memory 22, and it is determined whether the replacement of the battery cell is detected based on the detection information. Even when the battery pack 1 in which the replacement of the battery cell is detected is attached to the electronic device or the like again, it can be detected that the battery cell has been replaced based on the detection information. Can be disabled.

  Next, a first modification of the embodiment of the present invention will be described. In the first modification of the embodiment of the present invention, it is determined whether or not the battery cell has been replaced based on the change in the battery temperature in addition to the change in the internal resistance value.

  It is known that the internal resistance of the secondary battery 11 usually decreases as the battery temperature increases. Therefore, for example, even when the internal resistance decreases, the decrease in the internal resistance may be caused by an increase in battery temperature when the voltage and current of the secondary battery are measured.

Therefore, when calculating the internal resistance R of the secondary battery 11, the MPU 21 stores the battery temperature T of the secondary battery 11 measured by the temperature detection element 26 in the memory 22 in advance as T _pre . Further, when the latest internal resistance R _new is calculated, the latest battery temperature T _new is measured. Then, the previous internal resistance R _pre stored in the memory 22 is compared with the calculated latest internal resistance R _new, and when the internal resistance value of the secondary battery 11 decreases, it is further stored in the memory 22. The previous battery temperature T _pre is compared with the latest battery temperature T _new, and it is determined whether or not the battery cell has been replaced according to the comparison result.

  Hereinafter, a battery cell replacement detection method in the battery pack 1 according to the first modification of the embodiment of the present invention will be described with reference to the flowchart shown in FIG. In addition, about the process similar to one Embodiment mentioned above, the code | symbol same as the flowchart shown in FIG. 3 is attached | subjected, and detailed description is abbreviate | omitted.

  When a charger is connected to the battery pack 1 and charging is started, in step S1, the MPU 21 determines whether or not the battery cell has been replaced based on the presence or absence of detection information stored in the memory 22, and the result of the determination If it is determined that the battery cell has not been replaced, the process proceeds to step S2.

In step S2, the MPU 21 measures the voltage, charging current and battery temperature of the secondary battery 11 after a predetermined time has elapsed. In step S3, based on the voltage and charging current of the secondary battery 11 measured in step S2, The latest internal resistance R _new of the secondary battery 11 is calculated.

In step S4-1, the MPU 21 reads the previous internal resistance R _pre stored in advance in the memory 22, and compares R _pre with the latest internal resistance R _new calculated in step S3. As a result of the comparison, if R _new is smaller than R _pre , the process proceeds to step S4-2.

In step S4-2, the MPU 21 reads the previous battery temperature T _pre stored in advance in the memory 22, and compares T _pre with the latest battery temperature T _new measured in step S2. If T _new is smaller than T _{pre as} a result of the comparison, it is determined that the battery cell has been replaced, and the process proceeds to step S5.

  In step S5, the MPU 21 generates detection information and stores it in the memory 22. In step S6, the MPU 21 performs control so that the temperature fuse 25 is melted and charging / discharging of the secondary battery 11 is prohibited. Then, the process proceeds to step S7.

  On the other hand, in step S1, if the MPU 21 determines that the detection information is stored in the memory 22 and the battery cell has been replaced, the process proceeds to step S7.

  In step S <b> 7, the MPU 21 controls the switch circuit 23 to prohibit charging / discharging of the secondary battery 11. And the process in step S7 is repeated cyclically, and charging / discharging with respect to the secondary battery 11 is prohibited permanently.

On the other hand, if R _new is greater than R _pre in step S4-1, it is determined that the battery cell has not been replaced, and the process proceeds to step S8. In step S4-2, if T _new is larger than T _pre , it is determined that the battery cell has not been replaced, and the process proceeds to step S8.

In step S8, the MPU 21 stores the internal resistance R _new calculated in step S3 as R _pre in the memory 22, and stores the battery temperature T _new measured in step S2 as T _pre in the memory 22. Then, the process returns to step S2.

  Thus, by comparing the previous internal resistance and the latest internal resistance, and comparing the previous battery temperature and the latest battery temperature, it is possible to more accurately determine whether or not the battery cell has been replaced.

  Next, a second modification of the embodiment of the present invention will be described. In the second modification of the embodiment of the present invention, as shown in FIG. 5, a discharge circuit is provided on the circuit board 12 ′ of the battery pack 1 ′, and the internal resistance can be calculated even during discharge by the discharge circuit. I did it. In the following, the same parts as those of the battery pack 1 described in the embodiment of the present invention are denoted by the same reference numerals as those shown in FIG.

  The discharge circuit 41 is a constant current or constant resistance discharge circuit and is connected to the secondary battery 11. In the discharge circuit 41, a discharge current flows from the secondary battery 11 under the control of the MPU 21 and consumes the electric power stored in the secondary battery 11.

The voltage and discharge current of the secondary battery 11 immediately before the start of discharge are V ₃ [V] and I ₃ [A], and the voltage and charge current of the secondary battery 11 after a predetermined time t [sec] have elapsed are V ₄ [ Assuming that V] and I ₄ [A], the internal resistance R [Ω] of the secondary battery 11 is calculated based on Equation (2).
R = ΔV / ΔI = (V ₄ −V ₃ ) / (I ₄ −I ₃ ) (2)

The internal resistance R calculated as described above is stored in the memory 22 as the previous internal resistance R _pre as in the case of charging. In the next discharge, the internal resistance R is calculated as the latest internal resistance R _{new in the same} manner as described above. Then, the internal resistance R _pre stored in the memory 22 is compared with the calculated latest internal resistance R _new .

  As described above, since the internal resistance can be calculated even when discharging is performed by the discharge circuit 41, by providing the discharge circuit 41, an opportunity to detect whether or not the battery cell has been replaced can be increased.

  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 the embodiment of the present invention, the lithium ion secondary battery has been described as an example. However, the present invention is not limited to this example, and can be applied to a secondary battery such as a nickel cadmium storage battery. Further, the present invention can be applied not only to secondary batteries but also to primary batteries such as alkaline manganese batteries, physical batteries such as solar batteries, and fuel cells.

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 which shows an example of the charge characteristic by a constant current constant voltage charge system. It is a flowchart which shows the flow of a process of the detection method of the battery cell replacement | exchange in the battery pack by one Embodiment of this invention. It is a flowchart which shows the flow of a process of the detection method of the battery cell replacement | exchange in the battery pack by the 1st modification of one Embodiment of this invention. It is a block diagram which shows the structure of an example of the battery pack by the 2nd modification of one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1 'Battery pack 11 Secondary battery 12, 12' Circuit board 13 Positive electrode terminal 14 Negative electrode terminal 21 MPU
22 Memory 23 Switch circuit 24 Current detection resistor 25 Thermal fuse 26 Temperature detection element 31a Charge control FET
31b Discharge control FET
32a, 32b Parasitic diode 41 Discharge circuit

Claims (5)

One or more batteries;
A charge / discharge switch for controlling a charge / discharge current for the battery;
A controller that detects the voltage of the battery and the charge / discharge current, and calculates an internal resistance of the battery based on the voltage and the charge / discharge current;
A storage unit that stores the internal resistance calculated by the control unit;
The control unit
When charging the battery, compare the calculated latest internal resistance with the previous internal resistance stored in the storage unit,
When the latest internal resistance is smaller than the previous internal resistance, detection information indicating detection of battery replacement is generated and stored in the storage unit, and the charge / discharge switch is turned off. Control
When the latest internal resistance is larger than the previous internal resistance, the battery pack stores the latest internal resistance in the storage unit. The battery pack according to claim 1,
The control unit
A battery pack, wherein when the detection information is stored in the storage unit, it is determined that the battery has been replaced, and the charge / discharge switch is controlled to be turned off. The battery pack according to claim 1,
A temperature detection unit for detecting the temperature of the battery;
The control unit
When the latest internal resistance is smaller than the previous internal resistance, the latest temperature detected by the temperature detection unit is compared with the previous temperature stored in the storage unit,
When the latest temperature is lower than the previous temperature, the detection information is generated and stored in the storage unit, and the charge / discharge switch is controlled to be turned off.
The battery pack, wherein the latest temperature is further stored in the storage unit when the latest temperature is higher than the previous temperature. The battery pack according to claim 1,
It further has a discharge circuit that consumes the power stored in the battery,
When the control unit controls the discharge circuit to discharge the battery, the control unit determines whether the battery has been replaced by comparing the latest internal resistance with the previous internal resistance. Battery pack featuring. A calculation step of detecting a voltage and a charge / discharge current of one or a plurality of batteries, and calculating an internal resistance of the battery based on the voltage and the charge / discharge current;
When charging the battery, compare the latest internal resistance calculated with the previous internal resistance stored in the storage unit,
When the latest internal resistance is smaller than the previous internal resistance, detection information indicating detection of battery replacement is generated and stored in the storage unit, and charging / discharging current for controlling the charging / discharging current for the battery is controlled. Control to turn off the discharge switch,
And a control step of storing the latest internal resistance in the storage unit when the latest internal resistance is greater than the previous internal resistance.

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