JP2006038747A - Residual capacity detection method for battery and discharge method for battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect residual capacity when the temperature of a battery is low. <P>SOLUTION: This residual capacity detection method is a method for correcting a residual capacity of a battery detected from an integration value of its discharge current to a low capacity previously set for the residual capacity when a battery voltage falls to a set voltage. If the temperature of the battery is lower than a lowest temperature and the residual capacity of the battery is larger than a determination capacity when the battery voltage falls to the set voltage, the residual capacity is not corrected to the low capacity. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for detecting a remaining capacity by integrating a discharge current, and more particularly, a remaining capacity detecting method for correcting a remaining capacity to a specific capacity when the battery discharge progresses and the battery voltage drops to a set voltage. About.

The remaining capacity of the battery is detected by subtracting the discharge capacity from the fully charged state. The discharge capacity is calculated by integrating the discharge current. The remaining capacity of the battery is expressed by the product of current and time, that is, Ah, or can be expressed as a ratio (%) to the fully charged capacity, where the fully charged capacity (Ah) is 100%. Whichever state is displayed, the remaining capacity is detected by subtracting the discharged capacity from the fully charged state. However, the remaining capacity detected by the integrated value of the discharge current does not always match the correct remaining capacity of the battery. This is because the magnitude and temperature of the discharge current cause an error in detecting the remaining capacity. In order to reduce the error, a method has been developed in which the battery voltage is detected and when the battery voltage reaches a specific set voltage, the remaining capacity is corrected to a specific capacity (see Patent Document 1).
JP-A-5-87896

  Patent Document 1 describes a method of correcting a remaining capacity when a voltage of a battery is detected and the detected voltage becomes a set voltage. However, the method described in this publication has a drawback that the remaining capacity cannot always be corrected correctly. In particular, there is a drawback that the remaining capacity cannot be corrected accurately when the battery temperature is low.

  FIG. 1 shows the characteristic that the battery voltage starts decreasing after the battery of −10 ° C. starts discharging. However, the method shown in this figure is a method of correcting the remaining battery capacity to 10% regardless of the remaining capacity detected by integrating the discharge current when the voltage of the discharged battery drops to 3.1V. is there. As shown in this figure, the battery voltage of a low-temperature battery rapidly decreases when discharging starts. When the battery voltage drops to 3.1V, the remaining capacity is corrected to 10%. Thereafter, the battery voltage rises slightly, but the remaining capacity is corrected to 10%, and thereafter the remaining capacity is gradually reduced by the integrated value of the discharge current. Therefore, the remaining battery capacity detected is indicated by a solid line A. However, since the battery starts discharging from a fully charged state, the correct remaining capacity value does not change as shown by the solid line A in the figure. For this reason, the method described in Patent Document 1 has a drawback that the remaining capacity cannot be accurately detected when the temperature is low.

The present invention has been developed for the purpose of solving this drawback. An important object of the present invention is to provide a battery remaining capacity detection method capable of accurately detecting the remaining capacity even when the battery temperature is low.
Another object of the present invention is to provide a battery discharge method that limits the discharge current to an appropriate maximum discharge current according to the remaining capacity even when the battery temperature is low.

  The battery remaining capacity detection method of the present invention detects the battery discharge capacity by integrating the battery discharge current, calculates the remaining capacity by subtracting the detected discharge capacity, and detects the battery voltage. When the battery voltage drops to the set voltage, the remaining capacity is corrected to a specified low capacity. Furthermore, the remaining capacity detection method of the present invention detects the battery temperature, and when the battery temperature is lower than the minimum temperature and the remaining capacity of the battery is larger than the determination capacity larger than the specific capacity, the battery Even if the voltage drops to the set voltage, the remaining capacity is not reduced, but the remaining capacity is detected by subtracting the discharge capacity. When the battery temperature is lower than the minimum temperature and the remaining capacity of the battery is smaller than the determination capacity, if the battery voltage decreases to the set voltage, the remaining capacity of the battery is corrected to a lower capacity.

The battery whose remaining capacity is detected is any one of a lithium ion secondary battery, a nickel cadmium battery, and a nickel metal hydride battery.
The low capacity to be corrected when the battery voltage drops to the set voltage is, for example, 5 to 20%.
The determination capacity for determining whether to correct the remaining capacity by comparing the remaining capacity is, for example, 30 to 50%.
Further, the minimum temperature of the battery for determining whether or not the remaining capacity is corrected to a low capacity is set to −5 ° C. to 5 ° C.

  According to the remaining capacity detection method of the present invention, the maximum discharge current is changed according to the remaining capacity of the battery, and the maximum discharge current when the remaining capacity is large is set larger than when the remaining capacity is small. In this method, especially when the battery temperature is lower than the minimum temperature, the maximum discharge current is changed depending on the remaining capacity of the battery, and the maximum discharge current when the remaining capacity is large is set larger than when the remaining capacity is small. The battery can be discharged at maximum current while protecting it.

  The battery discharge method according to claim 8 of the present invention detects the discharge capacity by integrating the discharge current of the battery, calculates the remaining capacity by subtracting the detected discharge capacity, detects the remaining capacity of the battery, When the battery temperature is lower than the minimum temperature, the maximum discharge current is changed according to the remaining capacity of the battery, and the maximum discharge current when the remaining capacity is large is set larger than when the remaining capacity is small.

  The battery remaining capacity detection method of the present invention is characterized in that the remaining capacity can be accurately detected when the battery temperature is low. Even if the battery voltage drops to the set voltage, if the battery temperature is lower than the minimum temperature and the remaining capacity of the battery is larger than the judgment capacity, the remaining capacity is not corrected to a lower capacity. This is because it is possible to eliminate correcting the remaining capacity to an incorrect value when the capacity that can be substantially discharged is lowered.

  The battery discharge method of the present invention changes the maximum discharge current according to the remaining capacity of the battery when the battery temperature is lower than the minimum temperature, and the maximum discharge current when the remaining capacity is large when the remaining capacity is small. It is set larger than Therefore, the discharge current is not unnecessarily limited when the remaining capacity is large at low temperatures.

  Embodiments of the present invention will be described below with reference to the drawings. However, the examples shown below exemplify the remaining capacity detecting method and discharging method of the battery for embodying the technical idea of the present invention, and the present invention describes the remaining capacity detecting method and discharging method as follows. Not specific to the method.

  The remaining capacity detection device 1 shown in FIG. The battery pack 2 includes a remaining capacity detection device 1 and a secondary battery 3. The remaining capacity detection device 1 transmits the detected remaining capacity of the secondary battery 3 to a connected device (not shown) of the battery pack 2 via the connected device communication terminal 4. Further, the remaining capacity detection device 1 outputs a signal indicating a maximum limit current value indicating a maximum current value that can discharge the battery pack 2 from the detected remaining capacity to the connected device via the connected device communication terminal 4.

  The battery pack connection device is an assist bicycle. The battery pack attached to the assist bicycle drives the bicycle by driving the assist bicycle motor. In the battery pack used for this purpose, the discharge current of the battery pack changes due to the driving force for running the bicycle. When the motor drives the bicycle with a strong force, the current discharged to the motor increases. In order to protect the battery pack, the maximum discharge current of the battery is limited. A signal that limits the maximum discharge current of the battery is transmitted from the battery pack to the assist bicycle that is the connected device. The assist bicycle as a connected device controls the discharge current based on the maximum current limit value input from the battery pack. That is, the discharge current is made smaller than the maximum limit current value, and the maximum discharge current is limited to the maximum limit current value. The assist bicycle as the connected device displays the remaining capacity input from the battery pack, and displays the usage time, the travelable distance, and the like based on the remaining capacity. However, the battery pack for calculating the remaining capacity is not always attached to the assist bicycle. The battery pack can be attached to a vehicle such as an automobile, an electric motorcycle, or an electric bicycle, or can be attached to an electric device other than the vehicle.

  The remaining capacity detection device 1 includes a voltage detection unit 5 that detects the voltage of the battery, a temperature detection unit 6 that detects the temperature of the battery, a current detection unit 7 that detects a current flowing through the battery, a voltage detection unit 5 and a temperature. A signal input from the detection unit 6 and the current detection unit 7 is calculated to detect the remaining capacity of the battery, and a remaining capacity calculation unit 8 to detect the maximum limit current value of the battery pack 2 from the remaining capacity and the battery temperature; And a communication processing unit 9 for transmitting the calculated remaining capacity and the maximum limit current value to the connected device. The communication processing unit 9 is connected to the connected device communication terminal 4. The communication processing unit 9 is connected to the connection device via the connection device communication terminal 4 and transmits a signal indicating the remaining capacity and the maximum limit current value to the connection device.

  The battery is a lithium ion secondary battery. However, the battery may be a nickel cadmium battery or a nickel metal hydride battery. In addition, one or a plurality of batteries are connected in series or in parallel.

  The voltage detector 5 detects the voltage of the secondary battery 3 built in the battery pack 2. Since the battery pack 2 shown in the figure has a plurality of secondary batteries 3 connected in series, the voltage detector 5 detects the total voltage of the batteries connected in series. The voltage detector 5 outputs the detected voltage as an analog signal to the remaining capacity calculator 8 or converts the analog signal into a digital signal by an A / D converter and outputs the digital signal to the remaining capacity calculator 8. The voltage detection unit 5 detects the battery voltage at a constant sampling period or continuously, and outputs the detected voltage to the remaining capacity calculation unit 8.

  The temperature detection unit 6 includes a temperature sensor 10 that detects the temperature of the battery built in the battery pack 2. The temperature sensor 10 is in contact with the surface of the battery, or in contact with the battery via a heat conductive material, or is close to the surface of the battery and thermally coupled to the battery to detect the battery temperature. The temperature sensor 10 is a thermistor. However, all elements capable of converting temperature into electrical resistance, such as PTC and varistors, can be used for the temperature sensor 10. The temperature sensor 10 can also be an element that can detect the infrared rays emitted from the battery and detect the temperature without contacting the battery. The temperature detector 6 also outputs the detected battery temperature as an analog signal to the remaining capacity calculator 8, or converts the analog signal into a digital signal using an A / D converter and outputs the digital signal to the remaining capacity calculator 8. The temperature detector 6 detects the battery temperature at a constant sampling period or continuously, and outputs the detected battery temperature to the remaining capacity calculator 8.

  The current detection unit 7 connects a resistance element in series with the battery, detects a voltage induced at both ends of the resistance element, and detects a discharge current flowing through the battery. The resistance element is a low-resistance resistor. However, semiconductors such as transistors and FETs can also be used for the resistance elements. Since the charging current and discharging current of the battery have opposite directions of current flow, the positive and negative polarities induced in the resistance element are reversed. Therefore, it is possible to determine the discharge current based on the polarity of the resistance element and detect the current based on the voltage induced in the resistance element. This is because the current is proportional to the voltage induced in the resistance element. This current detector 7 can accurately detect the discharge current of the battery. However, the current detection unit 7 may be configured to detect a current by detecting a magnetic flux leaking to the outside by a current flowing through the lead wire. The current detection unit 7 also outputs the detected discharge current as an analog signal to the remaining capacity calculation unit 8, or converts the analog signal into a digital signal by an A / D converter and outputs it to the remaining capacity calculation unit 8. The current detection unit 7 detects the discharge current at a constant sampling period or continuously, and outputs the detected discharge current to the remaining capacity calculation unit 8.

  A device that outputs a digital value signal from the voltage detection unit 5, the temperature detection unit 6, and the current detection unit 7 to the remaining capacity calculation unit 8 at a constant sampling period is a digital signal from each detection unit to the remaining capacity calculation unit 8. The digital signal is output to the remaining capacity calculation unit 8 in order.

  The remaining capacity calculation unit 8 integrates the discharge current of the battery to detect the discharge capacity, and subtracts the detected discharge capacity to calculate the remaining capacity of the battery. For example, when a battery having a full charge capacity of 1000 mAh is discharged by 500 mAh, the remaining capacity is 50%. Therefore, as the fully charged battery is discharged, the remaining capacity gradually decreases as shown by the solid line B in FIG. Further, the remaining capacity calculation unit 8 corrects the remaining capacity detected from the discharge capacity with the voltage of the battery. For example, as shown in FIG. 3, when the battery voltage input from the voltage detection unit 5 drops to the set voltage, the remaining capacity is corrected to a low capacity that is specified in advance. The set voltage and the low capacity are stored in the memory 11 connected to the remaining capacity calculation unit 8. FIG. 3 shows the characteristics of the lithium ion secondary battery, where the set voltage is 3.1 V / cell and the low capacity is 10%. Accordingly, when the voltage of the discharged battery is reduced to the set voltage of 3.1 V / cell, the remaining battery capacity detected by calculating the discharge current is corrected to 10%.

  In the method of correcting the remaining capacity to a low capacity when the voltage of the discharged battery reaches the set voltage, the correction of the remaining capacity becomes inaccurate when the battery temperature is very low. FIG. 1 shows a specific example thereof. This figure shows the discharge characteristics of a fully charged battery having a temperature of −10 ° C. As shown in this figure, when a cryogenic battery is discharged, the discharge starts and the voltage rapidly decreases in a short time. In this figure, the battery voltage has dropped to 3V. Thus, when the battery voltage becomes lower than the set voltage, if the remaining capacity is corrected to 10% of the low capacity, the correct remaining capacity cannot be detected.

  The remaining capacity calculation unit 8 determines whether or not to correct the remaining capacity from the battery temperature and the remaining capacity when the battery voltage drops to the set voltage in order to prevent the above-described adverse effects. Even if the battery voltage drops to the set voltage of 3.1 V / cell, if the battery temperature is lower than the preset minimum temperature of 0 ° C., the remaining capacity of the battery is set in advance. Only when the remaining capacity is smaller than 40%, the remaining capacity is corrected to a low capacity, and when the remaining capacity is larger than 40% of the determination capacity, the remaining capacity is not corrected to a low capacity. That is, it is assumed that the remaining capacity detected from the discharge current is correct.

  The memory 11 stores a minimum temperature and a determination capacity. The minimum battery temperature for determining whether or not to correct to a low capacity can be set in the range of -5 ° C to 5 ° C. If the minimum temperature is too high or too low, the remaining capacity cannot be corrected accurately. The determination capacity can be set in a range of 30 to 50%. However, if the determination capacity is too large or too small, the remaining capacity cannot be accurately corrected. Therefore, the minimum temperature and the determination capacity are set to values that can correct the remaining capacity most accurately in consideration of the type and size of the battery.

  The remaining capacity calculation unit 8 corrects the remaining capacity to a lower capacity regardless of the remaining capacity of the battery when the battery voltage is lower than the set voltage and the battery temperature is higher than the minimum temperature. In FIG. 3, the battery voltage becomes lower than the set voltage at the beginning of the discharge of the battery. At this time, the battery temperature is lower than the minimum temperature of 0 ° C., but the remaining capacity detected from the discharge current is the judgment capacity. Therefore, the remaining capacity is not corrected to 10% of the low capacity. When the battery voltage decreases to the set voltage of 3.1 V / cell while the discharge of the battery progresses and the discharge capacity becomes 1400 mAh to 1600 mAh, the temperature of the battery is higher than the minimum temperature of 0 ° C. The remaining capacity is corrected to 10% of the low capacity. In the figure, the temperature of the battery is higher than the minimum temperature of 0 ° C. at this time. However, even if the battery temperature at this time is lower than the minimum temperature of 0 ° C., the remaining capacity of the battery is 40% of the determination capacity. Therefore, the remaining capacity is corrected to 10% of the low capacity.

  That is, when the discharged battery voltage drops to the set voltage, when the battery temperature is lower than the minimum temperature, the remaining capacity is reduced only when the remaining capacity detected from the discharge current is smaller than the judgment capacity. When the remaining capacity is larger than the determination capacity, the remaining capacity is not corrected to a lower capacity. When the battery voltage drops to the set voltage and the battery temperature is higher than the set temperature, the battery is corrected to a low capacity regardless of the remaining capacity.

FIG. 4 shows a flowchart in which the remaining capacity calculation unit 8 corrects the remaining capacity to a low capacity when the voltage of the battery to be discharged becomes lower than the set voltage. In the flowchart of this figure, the remaining capacity is corrected by the following steps.
[Step of n = 1]
In this step, the remaining capacity calculation unit 8 determines whether or not the battery voltage is lower than the set voltage. If the battery voltage is not lower than the set voltage, this step is looped.
[Step of n = 2]
When the battery voltage becomes lower than the set voltage, it is determined in this step whether or not the battery temperature is lower than the minimum temperature. If it is higher than the set temperature, jump to the step of n = 4 and correct the remaining dose to a low volume.
[Step n = 3]
When the battery voltage is lower than the set voltage and the battery temperature is lower than the minimum temperature, in this step, it is determined whether or not the remaining capacity of the battery is smaller than the judgment capacity, and if the remaining capacity is smaller than the judgment capacity, In step n = 4, the remaining capacity is corrected to a low capacity. If the remaining capacity is larger than the determination capacity, the process jumps to the step n = 1 without correcting the remaining capacity to a low capacity.
[Step n = 4]
The battery voltage is lower than the set voltage and the battery temperature is higher than the minimum temperature, the battery voltage is lower than the set voltage, the battery temperature is lower than the minimum temperature, and the remaining capacity is smaller than the judgment capacity The remaining battery capacity is corrected to a low capacity in this step.

  Further, the remaining capacity calculation unit 8 transmits a maximum discharge current signal, which is a signal indicating the maximum discharge current of the battery pack 2, to the connected device according to the detected remaining capacity of the battery. The connected device sets the maximum current for discharging the battery pack 2 to a current specified by the maximum discharge current signal, and controls the battery pack 2 to be discharged with a current smaller than this current. The maximum discharge current of the battery pack 2 is calculated by the remaining capacity calculation unit 8 based on the remaining capacity of the battery. As shown in FIG. 5, the remaining capacity calculation unit 8 changes the maximum discharge current according to the remaining capacity of the battery. The maximum discharge current is set to be large when the remaining capacity is large and small when the remaining capacity is small, that is, the maximum discharge current when the remaining capacity is large is set to be larger than that when the remaining capacity is small. is doing. That is, the battery pack 2 stores a function or table for specifying the maximum discharge current from the remaining capacity in the memory 11. The function shown in FIG. 5 is a linear function that linearly changes the maximum discharge current according to the remaining capacity. The memory 11 can also store the maximum discharge current in a stepwise manner according to the remaining capacity, and stores the maximum discharge current with respect to the remaining capacity as a table. When the remaining capacity is detected, the remaining capacity calculation unit 8 detects the maximum discharge current of the battery pack 2 from the remaining capacity using a function or table stored in the memory 11 and outputs a maximum discharge current signal to the setting device. Output.

  In addition, such a method of regulating the maximum discharge current is particularly effective at low temperatures. That is, in general, when a battery is discharged at a low temperature, the battery voltage tends to be lower than that at room temperature. When the discharge current is large at a low temperature, the discharge stop voltage (for example, 2.7 V / cell) May fall below. Actually, the battery cannot be used even though the remaining battery capacity is present. Therefore, conventionally, for example, in a power-assisted bicycle, when the temperature is low, information (limit current value or the like) for limiting the current is transmitted to the main body according to the temperature, and the current is limited on the main body (FIG. 5). In the conventional current value in the above, the discharge stop voltage was not reduced below. In this conventional case, since the current is limited only by the temperature, there is a drawback in that the assist force of the electrically assisted bicycle is limited to a certain level regardless of the state where the remaining battery capacity is almost fully charged. On the other hand, as described above, a method of limiting the maximum discharge current based on the remaining capacity is useful. In particular, it is useful to detect the battery temperature and use it at a low temperature. As the low temperature, for example, the minimum battery temperature to be determined can be set in the range of −5 ° C. to 5 ° C. as in the above-described embodiment. When the temperature is lower than the minimum temperature, the maximum discharge current is limited by the function shown in FIG. Therefore, in a state where the remaining battery capacity is sufficient, even if the limit current value is slightly increased, the discharge stop voltage is not lowered, and the discharge current is not unnecessarily limited, and the discharge current can be maximized. It becomes possible. For example, in the case of a battery-assisted bicycle, when the remaining battery capacity is sufficient, the limit current value can be increased and the assist force can be increased.

It is a graph which shows the voltage characteristic which discharges a low-temperature lithium ion secondary battery. It is a block diagram of the battery pack incorporating the remaining capacity calculation device used for the remaining capacity detection method of the present invention. 6 is a graph showing characteristics for correcting a remaining capacity of a battery discharged by a method according to an embodiment of the present invention. It is a flowchart figure which shows the process in which the remaining capacity calculating apparatus of FIG. 3 calculates remaining capacity. It is a graph which shows the characteristic which changes the maximum discharge current with remaining capacity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Remaining capacity detection apparatus 2 ... Pack battery 3 ... Secondary battery 4 ... Connection apparatus communication terminal 5 ... Voltage detection part 6 ... Temperature detection part 7 ... Current detection part 8 ... Remaining capacity calculation part 9 ... Communication processing part 10 ... Temperature Sensor 11 ... Memory

Claims (8)

The battery discharge current is integrated by integrating the discharge current of the battery, the remaining capacity is calculated by subtracting the detected discharge capacity, the battery voltage is detected, and when the detected battery voltage drops to the set voltage, the remaining capacity is A battery remaining capacity detection method for correcting to a specified low capacity,
If the battery temperature is detected, the battery temperature is lower than the minimum temperature, and the remaining battery capacity is greater than the judgment capacity that is larger than the specified capacity, the remaining capacity is maintained even if the battery voltage drops to the set voltage. The battery capacity is reduced to the set voltage when the battery temperature is lower than the minimum temperature and the remaining battery capacity is lower than the judgment capacity. Then, the remaining capacity detection method of a battery characterized by correct | amending the remaining capacity of a battery to low capacity.   The battery remaining capacity detection method according to claim 1, wherein the battery is any one of a lithium ion secondary battery, a nickel cadmium battery, and a nickel metal hydride battery.   The battery remaining capacity detection method according to claim 1, wherein the low capacity is 5 to 20%.   The battery remaining capacity detection method according to claim 1, wherein the determination capacity is 30 to 50%.   The battery remaining capacity detection method according to claim 1, wherein the minimum temperature is -5C to 5C.   The method for detecting the remaining capacity of a battery according to claim 1, wherein the maximum discharging current is changed according to the remaining capacity of the battery, and the maximum discharging current when the remaining capacity is large is set larger than when the remaining capacity is small. .   The maximum discharge current is changed according to the remaining capacity of the battery when the battery temperature is lower than the minimum temperature, and the maximum discharge current when the remaining capacity is large is set larger than that when the remaining capacity is small. 6. The battery remaining capacity detection method described in 6.   The discharge capacity of the battery is integrated to detect the discharge capacity, and the remaining capacity is calculated by subtracting the detected discharge capacity to detect the remaining capacity of the battery.When the battery temperature is lower than the minimum temperature, the remaining battery capacity is A method for discharging a battery, wherein the maximum discharge current is changed depending on the capacity, and the maximum discharge current when the remaining capacity is large is set larger than when the remaining capacity is small.

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