JP2013027209A - Protection system of secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protection system capable of constantly monitoring the transition of overcurrent flowing on a charge and discharge paths of a secondary battery.SOLUTION: The protection system of a secondary battery includes: switches (2 and 3) provided to a charge path and a discharge path respectively of a secondary battery, in which plural battery cells are connected in series to each other, to connect and disconnect the charge and discharge paths; a current detection unit (8) that detects a current flowing on the charge and discharge paths; integration units (4, 6 and 7) for obtaining a time integration value of the current detected by the current detection unit; and a control unit (8) that controls the switches to shut off the charge and discharge paths when the current flowing on the charge and discharge path detected by the current detection unit exceeds a threshold value current and when the time integration value obtained by the integration unit exceeds a threshold value time integration value.

Description

  The present invention relates to a secondary battery protection system.

  In a system using a secondary battery, there is a concern that a short circuit or heat generation may occur inside the secondary battery when an abnormal charge / discharge state continues. For this reason, generally, means for preventing an overcurrent during charging or discharging is provided. For example, a secondary battery protection system shown in FIG. 6 disclosed in Patent Document 1 has been proposed.

  In the secondary battery protection system shown in FIG. 6, an overcurrent protection for charging is performed in the charge / discharge path of the secondary battery 1 in which a plurality of battery cells are connected in series between the + terminal 12 and the − terminal 13. An FET (hereinafter referred to as a charge FET) 2, an overcurrent protection FET (hereinafter referred to as a discharge FET) 3 during discharge, a current detection resistor 8 for detecting a charge current or a discharge current as a voltage drop, Is installed. The charge FET 2 is installed so that the forward direction of the parasitic diode is opposite to the charge current, and the discharge FET 3 is installed so that the forward direction of the parasitic diode is opposite to the discharge current. Thereby, both charging current and discharging current can be cut off.

  Furthermore, a control circuit 15 that performs control for preventing overcharge / discharge of the secondary battery 1 is provided. The control circuit 15 is provided with charging / discharging current detecting means 14 for amplifying a minute voltage generated at both ends of the current detecting resistor 8 when a charging current or discharging current flows and detecting it as a charging current or discharging current. ing. Furthermore, in the control circuit 15, when the relative voltage of each battery cell of the secondary battery 1 or its time differential value exceeds a certain value based on the charging current or discharging current detected by the charging / discharging current detecting means 14, Means for controlling on / off of the charge FET 2 and the discharge FET 3 is provided so as to prohibit charging / discharging of the secondary battery 1.

  For example, the control circuit 15 detects the voltages at both ends of each battery cell of the secondary battery 1, and when the relative voltage of the voltages at both ends is smaller than an allowable voltage (for example, 0.3 V), the both ends of the battery cells are detected. When the voltage becomes equal to or higher than a first voltage value (for example, 4.3 V), overcharge protection is performed such that the charging FET 2 is turned off and the charging current is cut off. Further, when the voltage across the battery cell becomes equal to or lower than a second voltage value (for example, 4.0 V), the charging FET 2 is turned on to release the overcharge protection function.

  Regarding the release of the overcharge protection function, a discharge current of a specified current (for example, 0.2 A) or more is allowed for a permissible time in a state where the charging FET 2 is turned off and the supply of the charging current to the secondary battery 1 is cut off (for example, 0.2 A). For example, when the battery flows continuously for 10 ms or more, the overcharge protection function is canceled by switching the charge FET 2 from off to on even if the voltage across the battery cell does not become the second voltage value or less. As described above, when a discharge current exceeding the allowable value continuously flows during the overcharge protection operation, the charge FET 2 is switched from OFF to ON, and charged by the power loss of the parasitic diode corresponding to the discharge current. The FET 2 is prevented from being destroyed.

  Furthermore, if the relative voltage of the voltage across the battery cell exceeds the allowable voltage, both the charge FET 2 and the discharge FET 3 are turned off even if the voltage across the battery cell does not reach the first voltage value. Thus, charging and discharging of the secondary battery 1 are permanently prohibited. As described above, by detecting that the relative voltage is equal to or higher than the allowable voltage, it is possible to detect that the capacity becomes non-uniform due to deterioration of the battery cell or the like and the cell balance is lost. At this time, by prohibiting the use of the secondary battery 1, overcharge of the secondary battery 1 can be prevented in advance.

  The overdischarge protection and its release operation are the same as the overcharge protection and its release operation. Further, Patent Document 1 prohibits charging or discharging after a predetermined delay time set to be inversely proportional to the detected current of the charging current or discharging current. For example, when the detected current is 5 A, the delay time is set to 1.0 ms, and when 10 A, the delay time is set to 500 μs.

Japanese Patent No. 3273714

  By the way, in the case of the overcurrent protection of Patent Document 1, the specified current of the charging current or the discharging current and the allowable time thereof are set discretely, for example, even if an abnormal state of the charging current or the discharging current is detected. Since the state transition up to is not monitored, the overcurrent protection at a continuous and appropriate timing of the charging current or discharging current is not achieved. For this reason, in the case of overcurrent protection of patent document 1, there existed a subject that substantial safety was not securable.

  The present invention has been made in order to solve such problems, and its purpose is to improve safety by continuously monitoring the state transition of the current flowing through the charge / discharge path of the secondary battery. It is to provide a secondary battery protection system.

  In order to solve the above-described conventional problems, a secondary battery protection system according to an embodiment of the present invention is provided in a charge / discharge path of a secondary battery in which a plurality of battery cells are connected in series. A switch that conducts and cuts off the path, a current detection unit that detects a current flowing through the charge / discharge path, an integration unit that obtains a time integral value of the current detected by the current detection unit, and a current detection unit that detects the current Control for controlling the switch to cut off the charging / discharging path when the current flowing through the charging / discharging path exceeds a threshold current and the time integration value obtained by the integration unit exceeds the threshold time integration value A unit.

  Here, the “time integral value obtained by the integration unit” represents the sum of the products of the current value in the minute time of the current flowing through the charging / discharging path of the secondary battery and changing every moment and the minute time. The “minute time” may be an infinite time or a finite time. Therefore, “when the current flowing through the charging / discharging path detected by the current detection unit exceeds the threshold current and the time integration value obtained by the integration unit exceeds the threshold time integration value” means an overcurrent When the current (lower limit value) defined as is defined as the threshold current value, and the product of the threshold current value and the time allowed for the current of the threshold current to flow is defined as the threshold time integral value, The time when the current flowing through the charge / discharge path of the secondary battery exceeds the specified current (that is, the time when the overcurrent state is reached) exceeds the allowable time. Therefore, according to this configuration, the state transition of the overcurrent flowing through the charge / discharge path is continuously monitored instead of discretely based on the time integral value of the current flowing through the charge / discharge path of the secondary battery. The safety of the secondary battery protection system can be improved.

In the secondary battery protection system, the current detection unit is a current detection resistor provided in the charge / discharge path, and the integration unit has a frequency component that changes according to a voltage drop of the current detection unit. A voltage-frequency converter that generates a pulse signal having a frequency, a high-pass filter that passes a frequency component of the pulse signal that exceeds the threshold current, and a pulse count of the pulse signal that has passed through the high-pass filter And the control unit is configured to control the switch to cut off the charge / discharge path when the count value of the counter exceeds the threshold time integral value.
It is good.

  According to this configuration, the integration unit and the control unit can be realized by hardware. If these units are implemented in software, there is a possibility that the computer may run out of control, but if these units are implemented in hardware, these possibilities are eliminated, and these units are implemented in software. In comparison, the safety of the secondary battery protection system can be further increased.

  In the secondary battery protection system, the pulse signal output from the voltage-frequency converter may be used in a charge counter that detects a charge amount per unit time charged and discharged by the secondary battery. Good.

  According to this configuration, the above-described control circuit is realized by diverting the voltage-frequency converter necessary for providing a charge counter for the purpose of monitoring the amount of charge per unit time charged / discharged to the secondary battery. Can do.

  ADVANTAGE OF THE INVENTION According to this invention, the protection system of a secondary battery with high safety | security can be provided by continuously monitoring the state transition of the overcurrent which flows through the charging / discharging path | route of a secondary battery.

FIG. 1 is a diagram illustrating a configuration example of a secondary battery protection system according to an embodiment of the present invention. FIG. 2 is a diagram showing a configuration of a comparative example with respect to the embodiment of the present invention shown in FIG. FIG. 3 is a diagram schematically showing the concept of overcurrent protection in a comparative form. FIG. 4 is a diagram showing the time transition of the current flowing through the charging / discharging path of the comparative example. FIG. 5 is a diagram for comparing the operation of the counter in the comparison mode and the operation of the counter in the embodiment of the present invention. FIG. 6 is a diagram showing a configuration of a conventional secondary battery protection system.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same or corresponding elements are denoted by the same reference symbols throughout the drawings, and redundant description thereof is omitted.

(Embodiment)
[Configuration example]
FIG. 1 is a diagram illustrating a configuration example of a secondary battery protection system according to an embodiment of the present invention.

  In the secondary battery protection system shown in FIG. 1, in the charge / discharge path of the secondary battery 1 in which a plurality of battery cells are connected in series between a positive terminal 12 and a negative terminal 13, an overcurrent protection for charging is provided. An FET (hereinafter referred to as a charge FET) 2, a diode 20 connected in parallel with the charge FET 2 so that a discharge current flows in a forward direction, and an FET for overcurrent protection during discharge (hereinafter referred to as a discharge FET) 3), a diode 30 connected in parallel with the discharge FET 3 so that the charging current flows in the forward direction, and a current detection resistor 8 for detecting the charging current or the discharging current. .

  Furthermore, in the secondary battery protection system shown in FIG. 1, an overcurrent protection circuit 50 for preventing overcharge / discharge of the secondary battery 1 is provided. The overcurrent protection circuit 50 is a one-chip integrated circuit including a VF (Voltage Frequency) converter 4, a charge counter (also called a coulomb counter) 5, a high-pass filter 6, a counter 7, and a drive control circuit 11. It is realized as an integrated circuit.

  In the secondary battery protection system shown in FIG. 1, the charge or discharge state of the secondary battery 1 is managed by detecting the amount of charge charged to or discharged from the secondary battery 1. When a current flows through the current detection resistor 8 by charging or discharging the secondary battery 1, the voltage drop generated at both ends of the current detection resistor 8 is frequency-converted by the VF converter 4, and a signal having the frequency component is a charge counter. 5 is input. Here, if the charging current or discharging current increases, the output frequency of the VF converter 4 and thus the count value of the charge counter 5 increase as the voltage across the current detection resistor 8 increases. Conversely, if the charging current or discharging current decreases, the output frequency of the VF converter 4 and thus the count value of the charge counter 5 decrease as the voltage across the current detection resistor 8 decreases. Therefore, the amount of charge per unit time charged / discharged to / from the secondary battery 1 can be indirectly detected from the amount of change in the count value of the charge counter 5 (the integrated value of the charging current or discharging current and time).

  The output of the VF converter 4 is input to the high-pass filter 6 in addition to the charge counter 5. The high-pass filter 6 extracts a frequency component equal to or higher than a predetermined cutoff frequency corresponding to the threshold current of the charging current or discharging current from the output of the VF converter 4 and inputs a signal having the frequency component to the counter 7. . The counter 7 counts the number of pulses of a signal having a frequency component equal to or higher than a predetermined cutoff frequency output from the high-pass filter 6. When the counter 7 indicates that the delay time corresponding to the amount of current flowing through the current detection resistor 8 has elapsed, the counter 7 has detected that the drive control circuit 11 has detected an overcurrent state. Is output so as to output an overcurrent detection signal. That is, the delay time is set so as not to react to an instantaneous overcurrent, and this delay time is varied according to the amount of current flowing through the current detection resistor 8.

  The drive control circuit 11 is configured to perform switching control of the charge FET 2 and the discharge FET 3 at the timing when the overcurrent detection signal is received from the counter 7. Specifically, the charge FET 2 and the discharge FET 3 are both turned on to protect the diodes 20 and 30 when the secondary battery 1 is charged and discharged. In the case of overcharge protection, only the charge FET 2 is turned off. In the case of overdischarge protection, only the discharge FET 3 is turned off. Further, the drive control circuit 11 is configured to execute the setting of a predetermined threshold value of the high-pass filter 6 and the adjustment of the output time of the overcurrent detection signal of the counter 7 together. That is, switching control of the charge FET 2 and the discharge FET 3 is executed using the output of the VF converter 4 for managing the charge / discharge state.

  In addition to the above configuration, for example, the amount of current flowing through the current detection resistor 8 may be detected by digital processing using an analog / digital converter. However, the overcurrent protection system is preferably configured with hardware as described above from the viewpoint of safety.

  The diodes 20 and 30 may be realized by parasitic diodes of the charge FET2 and the discharge FET3, or may be diodes of discrete elements or diode-connected transistors.

[Composition of comparison form]
In order to facilitate understanding of the operational effects of the present embodiment, the present embodiment will be described below in comparison with the comparative embodiment.

  FIG. 2 is a diagram showing a configuration of a comparative example with respect to the embodiment of the present invention shown in FIG. In the comparative form shown in FIG. 2, overcurrent detection comparators 9A, 9B, and 9C are connected to one end of the current detection resistor 8. The overcurrent detection comparators 9A, 9B, 9C are constituted by, for example, a differential amplifier in which one end of the current detection resistor 8 is connected to the non-inverting input terminal and each reference power supply is connected to the inverting input terminal. Yes. In other words, the overcurrent detection comparator 9 detects that an overcharge / discharge exceeding a certain threshold occurs when the voltage at one end of the current detection resistor 8 exceeds the voltage of each reference power supply. To do. In the reference power supplies used for the overcurrent detection comparators 9A, 9B, and 9C, different voltages are set so that overcurrents in different states can be detected. For example, the overcurrent detection comparator 9A detects 1 mA as an abnormal current of the discharge current, the overcurrent detection comparator 9B detects 10 mA as another abnormal current of the discharge current, and the overcurrent detection comparator 9C detects 100 mA as another abnormal current of the discharge current. The voltage of each reference power supply is set so that it can be done.

  In the comparative form shown in FIG. 2, counters 10A, 10B, and 10C are connected to the output terminals of the overcurrent detection comparators 9A, 9B, and 9C. The counters 10A, 10B, and 10C are configured to count the time during which an overcurrent exceeding a certain threshold value flows based on the outputs of the overcurrent detection comparators 9A, 9B, and 9C. The drive control circuit 11 is configured to turn off the charge FET 2 and / or the discharge FET 3 when a certain period of time has passed based on the outputs of the counters 10A, 10B, and 10C. . In addition to the above configuration, an overcurrent detection comparator and a counter may be separately provided so that an abnormal current of the charging current can be detected.

[Contrast between this embodiment and comparative embodiment]
In the case of the comparison form shown in FIG. 2, a discrete overcurrent state is detected using three overcurrent detection comparators 9A, 9B, 9C and three counters 10A, 10B, 10C. That is, by defining the states of the three charge / discharge paths based on the amount of current flowing through the charge / discharge paths, and determining that these states are dangerous on the system when a certain time has elapsed, Alternatively, the discharge FET 3 is switched from on to off. This ensures the safety of the system.

  FIG. 3 is a diagram schematically showing the concept of overcurrent protection in a comparative form. As shown in FIG. 3, with respect to the current flowing through the charge / discharge path, detection point A (specified current A, allowable time A), detection point B (specified current B, allowable time B), detection point C (specified current C, An allowable time C) is defined. At the detection point A, the largest specified current A compared to the other specified currents B and C and the shortest allowable time A compared to the other allowable times B and C are defined. That is, at the detection point A, the allowable time A in which the current more than the specified current A is allowed to flow is the shortest, and it is determined whether the system is in the most dangerous state. Can do. Similarly, an allowable time B for the specified current B is defined at the detection point B, and an allowable time C for the specified current C is defined at the detection point C. Therefore, in the case of the comparative example, the state transition of the overcurrent is discretely monitored at the three detection points A, B, and C, and safety is not substantially ensured.

  FIG. 4 is a diagram showing a time transition of the current flowing through the charging / discharging path of the comparative form. The specified currents A, B, and C shown in FIG. 4 are the specified currents to be monitored defined in FIG. In FIG. 4, the time during which the current exceeding the specified current A flows (overcurrent time) is expressed as T1, the time when the current exceeding the specified current B flows (overcurrent time) is expressed as T2, and the current exceeding the specified current C The time (overcurrent time) during which is flowing is represented as T3. Here, when a current transition occurs such that “overcurrent time T1 <allowable time A, overcurrent time T2 <allowable time B, and overcurrent time T3 <allowable time C”, detection points A and B , C are not satisfied, and switching control of the charge FET 2 and / or the discharge FET 3 for overcurrent protection cannot be performed. Therefore, for example, when an abnormal state exists in which an overcurrent time T1 in which a current that oscillates between the specified currents A to C flows and a current greater than the specified current A flows exists, the overcurrent Switching control of the charge FET 2 and / or the discharge FET 3 for protection cannot be performed, and safety is significantly reduced.

  In contrast, in the present embodiment, the state transition of the overcurrent flowing through the charging / discharging path of the secondary battery 1 is continuously monitored using the output of the VF converter 4 for managing the charging / discharging state. Yes. Specifically, for example, the above-mentioned specified current C is defined as a current (lower limit value: threshold current value) defined as an overcurrent, and the above-described allowable time is defined as a time during which the current of the threshold current value is allowed to flow. C is defined, and the product of the defined current C and the allowable time C is defined as the threshold time integral value. In this case, the specified current C and the allowable time C are set from the viewpoint of protection of the charge FET 2 and the discharge FET 3, but are not limited thereto.

  FIG. 5 is a diagram for comparing the operations of the counters 10A, 10B, and 10C in the comparison mode with the operations of the counter 7 in the embodiment of the present invention. In the case of the counters 10A, 10B, and 10C in the comparative form, the count operation is started at the timing of the detection points A, B, and C, and the count frequency and the counted overcurrent times T1, T2, and T3 are constant. .

  On the other hand, in the case of the counter 7 in this embodiment, when the current flowing through the current detection resistor 8 exceeds the allowable current C, the counter 7 starts counting, and thereafter, according to the amount of current flowing through the current detection resistor 8. The time required for one count varies. For example, if the amount of current increases, the time required for one count is shortened accordingly, and if the amount of current decreases, the time required for one count increases. When the total count reaches the count set in correspondence with the above-described threshold time integral value, the charge FET 2 and / or the discharge FET 3 are switched from on to off.

  As described above, according to the embodiment of the present invention, for example, the delay time T required for overcurrent detection automatically varies so as to match the amount of current allowed for the charge FET 2 and the discharge FET 3. Therefore, the current flowing on the charging / discharging path can be continuously monitored, and protection taking into account the elapsed time of the overcurrent can be achieved. Further, according to the embodiment of the present invention, it is not necessary to provide a plurality of comparators for detecting an overcurrent state as in the comparative embodiment, so that the hardware to be mounted can be reduced, resulting in low consumption. Electricity can be achieved.

  From the foregoing description, many modifications and other embodiments of the present invention are obvious to one skilled in the art. Accordingly, the foregoing description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details of the structure and / or function may be substantially changed without departing from the spirit of the invention.

  INDUSTRIAL APPLICABILITY The present invention is useful as a secondary battery protection system that improves safety by continuously monitoring the state transition of overcurrent flowing through the charge / discharge path of the secondary battery.

1 Secondary battery 2 Charging FET
3 Discharge FET
4 VF Comparator 5 Charge Counter 6 High-Pass Filter 7 Counter 8 Current Detection Resistors 9A, 9B, 9C Overcurrent Detection Comparator 10A, 10B, 10C Counter 11 Drive Control Circuit 12 + Terminal 13 −Terminal 50 Overcurrent Protection Circuit

Claims (3)

A switch that is provided in a charge / discharge path of a secondary battery in which a plurality of battery cells are connected in series, and that conducts and blocks the charge / discharge path;
A current detection unit for detecting a current flowing through the charge / discharge path;
An integration unit for obtaining a time integral value of the current detected by the current detection unit;
When the current flowing through the charging / discharging path detected by the current detection unit exceeds a threshold current and the time integration value obtained by the integration unit exceeds the threshold time integration value, the charging / discharging path is interrupted. A control unit for controlling the switch,
A secondary battery protection system comprising: The current detection unit is a current detection resistor provided in the charge / discharge path,
The integration unit includes a voltage-frequency converter that generates a pulse signal having a frequency component that changes in accordance with a voltage drop of the current detection unit, and a high frequency band that passes the frequency component of the pulse signal that exceeds the threshold current. A pass filter, and a counter that counts the number of pulses of the pulse signal that has passed through the high-pass filter,
2. The secondary battery according to claim 1, wherein the control unit is configured to control the switch to cut off the charge / discharge path when a count value of the counter exceeds the threshold time integral value. 3. Protection system.   The secondary battery protection according to claim 2, wherein the pulse signal output from the voltage-frequency converter is used in a charge counter that detects a charge amount per unit time charged and discharged to the secondary battery. system.

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