JP4241540B2 - Battery full charge determination method, charging system and charger - Google Patents

Description

  The present invention relates to a battery full charge determination method, a charging system, and a charger for charging a rechargeable battery.

  Secondary batteries that can be repeatedly used by charging, such as nickel metal hydride batteries, are widely used as power sources for various portable small electronic devices such as mobile phones, notebook computers, and PDAs (Personal Digital Assistance). The demand for nickel metal hydride batteries has increased dramatically with the recent spread of portable small electronic devices.

When charging a nickel-metal hydride battery, it is necessary to terminate the charge and prevent overcharging when the battery is fully charged in order to prevent a decrease in battery performance. For this purpose, it is necessary to accurately detect full charge during charging. As the technology, for example, a minus ΔV detection method, a flat detection method, and the like have been proposed.
The minus ΔV detection method refers to a detection method for detecting full charge using a phenomenon in which the battery voltage suddenly decreases after charging starts and the battery voltage increases to reach a peak voltage. The flat detection method refers to a method of monitoring the rate of increase in battery voltage and detecting full charge when there is no voltage increase beyond a specified level within a certain period of time.

  A technique for detecting full charge by applying the above-described minus ΔV detection method is disclosed in Patent Document 1, for example. That is, in Patent Document 1, the voltage of the battery being charged is periodically measured, the voltage value at the time when the battery voltage starts to drop is detected as the peak voltage value, and the peak voltage value and the voltage value decreased thereafter are And a technique for determining that the battery is fully charged when the voltage width exceeds a certain level.

JP-A-11-250940 (pages 3-4, FIG. 2)

However, with the technique disclosed in Patent Document 1, it is assumed that the voltage drop of the battery voltage in the vicinity of full charge does not occur sufficiently depending on the charging conditions. Therefore, in such a case, full charge cannot be accurately detected, and there is a concern about overcharging.
Further, in the flat detection method, in the case of charging in a high temperature environment or charging an inactivated battery left for a long time, it is assumed that a full charge is erroneously detected during charging. In such a case, there is a concern that the charging may end despite the middle of charging and cannot be fully charged.

  The present invention has been made to solve the above technical problems, and an object of the present invention is to accurately detect full charge of a battery being charged.

For this purpose, the battery full charge determination method to which the present invention is applied measures the voltage value of the battery being charged, detects a flat state in which the change in the voltage value of the battery falls within a predetermined range, It is detected whether or not the duration time of the flat state has reached a predetermined value (C ₁ ). Then, the voltage value of the battery when the flat state voltage value when the flat state duration time reaches the predetermined value (C ₁ ) exceeds the _first voltage value (E ₁ ) and the flat state is detected. And the voltage value at the beginning of charging exceeds the _second voltage value (E ₂ ), the battery is determined to be fully charged. In this case, the second voltage value (E ₂ ) is the voltage value (E ₂ ) after the voltage rise when the voltage value at the beginning of charging and the voltage rise rate per unit time exceeds a specified value. _max ).
Further, the voltage value of the battery being charged is measured, and after the charging time (T) from the beginning of charging reaches a predetermined value (T ₁ ), the battery voltage value changes within a predetermined range. The state is detected, and it is detected whether or not the duration time of the flat state has reached the _first predetermined value (C ₁ ). The battery at the time when the flat state voltage value when the flat state duration time reaches the first predetermined value (C ₁ ) exceeds the _first voltage value (E ₁ ) and the flat state is detected. When the difference between the first voltage value and the voltage value at the beginning of charging does not exceed the second voltage value (E ₂ ), the _second state in which the duration of the flat state is larger than the first predetermined value (C ₁ ). When the predetermined value (C ₂ ) is reached, the battery is determined to be fully charged .

From another point of view, the present invention can be applied to a charging system in which a rechargeable battery is connected to an electronic device for charging. That is, in the charging system to which the present invention is applied, the voltage of the battery being charged is measured by the voltage measuring unit, and the flat state in which the change in the voltage value measured by the voltage measuring unit falls within a predetermined range is detected by the flat detecting unit. Detect with. Further, the flat time duration detected by the flat detecting means is measured by the flat time measuring means. Then, when the duration of the flat state measured by the flat time measuring means reaches a predetermined value (C ₁ ), the voltage value of the flat state detected by the flat detecting means is the first voltage value (E ₁ ). The difference between the peak voltage value of the battery measured by the voltage measuring means at the time when the flat state is detected and the voltage value at the beginning of charging measured by the voltage measuring means is the second voltage value (E ₂ The battery charging is stopped by the charging stop means on condition that the above is exceeded.

Further, when the present invention is viewed from another viewpoint, the present invention can be applied to a battery charger that can be charged. In other words, the charger to which the present invention is applied receives the voltage value of the battery being charged, detects a flat state where the change in the voltage value of the battery is within a predetermined range, and detects the flat state by the flat detection unit. The duration of the detected flat state is measured by the flat time measuring means. Then, when the duration of the flat state measured by the flat time measuring means reaches a predetermined value (C ₁ ), the voltage value of the flat state detected by the flat detecting means is the first voltage value (E ₁ ). The charge stopping means stops charging the battery on condition that the difference between the voltage value in the flat state and the voltage value at the beginning of charging exceeds the second voltage value (E ₂ ).

  According to the present invention, since full charge can be accurately detected for a battery being charged, overcharging and uncharging at the completion of charging can be suppressed.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a control block diagram of the main part of a portable mini-disc device (hereinafter abbreviated as MD) according to the present embodiment.
The MD 10 includes a current limit circuit 11, a constant voltage circuit 12, a battery voltage amplifier circuit 13, a full charge detection circuit 14, a transistor control circuit 15, and a timer 16. The MD 10 includes a transistor 17 and a diode 18 and is connected to a nickel metal hydride battery 20 to be charged.
The current limit circuit 11 is a circuit for maintaining the charging current at 500 mA by monitoring the charging current and sending a control signal to the transistor control circuit 15. The constant voltage circuit 12 is a circuit for monitoring the output voltage and keeping the output constant by sending a control signal to the transistor control circuit 15 when no battery is inserted. The battery voltage amplification circuit 13 is a circuit that amplifies the battery voltage by 6 times so that the full charge detection circuit 14 can reliably monitor the fluctuation of the battery voltage.
The full charge detection circuit 14 is a circuit that detects a full charge by monitoring an increase value of the battery voltage and a charging time. The full charge detection circuit 14 sends a control signal to the transistor control circuit 15 when full charge is detected, thereby stopping the charge. The transistor control circuit 15 keeps the charging current constant or stops charging via the transistor 17 according to control signals from the current limit circuit 11, the constant voltage circuit 12, the full charge detection circuit 14 and the timer 16. Circuit. The timer 16 is for measuring time from the start of charging, and stops measuring time after detecting full charge.

Next, control contents from the start of charging to full charge detection will be described with reference to FIG.
FIG. 2 is a flowchart showing control during charging.
As shown in FIG. 2, when charging of the nickel metal hydride battery 20 is started, the full charge detection circuit 14 records the start voltage E ₀ of the nickel metal hydride battery 20, resets the voltage peak value E _max , and a flat detection counter. C is reset (S101).
Here, the voltage peak value E _max is a voltage value that is updated when the full-charge detection circuit 14 monitors the battery voltage E being charged and the voltage rises more than a specified value. Specifically, when the voltage rises above the specified level, the battery voltage E after the voltage increase is stored in a storage means (not shown), and when the voltage rises above the specified level thereafter, it is replaced with the voltage after the voltage increase. And remember. “Voltage increase above the specified value” here refers to a case where the voltage increase rate per unit time is calculated and the value of the voltage increase rate is equal to or greater than a predetermined value.
The flat detection counter C is for measuring the elapsed time during which the voltage peak value E _max is not updated during charging, and is measured by the full charge detection circuit 14.

After the reset or the like is performed, measurement of the battery voltage E of the nickel metal hydride battery 20 is started by the full charge detection circuit 14 (S102), and the charging time counter is added in the timer 16 to thereby charge time T. Measurement is started (S103).
Next, it is determined whether or not the battery voltage E of the nickel metal hydride battery 20 is less than the first voltage value E ₁ mV (S104). When the battery voltage E of the nickel metal hydride battery 20 is less than the _first voltage value E ₁ mV (E <E ₁ ), the process returns to step 102. When the battery voltage E of the nickel metal hydride battery 20 is not less than the first voltage value E ₁ mV (E ≧ E ₁ ), the flat detection counter C is activated (S105).
Thereafter, it is determined whether or not the voltage peak value E _max has been updated (S106). When the voltage peak value Emax is updated, the flat detection counter C is reset (S107), and the process returns to step 105. When the voltage peak value E _max is not updated, the flat detection counter C is added (S108).

Then, it is determined whether or not the flat detection counter C is less than a _first threshold value (predetermined value) C ₁ minutes (S109). When the flat detection counter C is less than the _first threshold C ₁ (C <C ₁ ), the process returns to step 102. When the flat detection counter C is not less than the first threshold C ₁ (C ≧ C ₁ ), it is further determined whether or not the charging time T is equal to or greater than the threshold T ₁ (S110). That is, when the charging time T is not longer than the threshold (predetermined time) T ₁ minutes (T <T ₁ ), it is determined that the battery is fully charged (S111), and charging is terminated or stopped (hereinafter simply referred to as “end”) ( S112), the process is terminated. Further, when the charging time T is equal to or longer than the threshold value T ₁ (T ≧ T ₁ ), the process proceeds to step 113.
In step 113, it is determined whether or not the rising voltage ΔE (ΔE = E _max −E ₀ ) from the beginning of charging is less than the second voltage value E ₂ mV. That is, when the rising voltage ΔE is not less than the second voltage value E ₂ mV (ΔE ≧ E ₂ ), it is determined that the battery is fully charged (S111), and after the charging is finished (S112), the process is finished. When the rising voltage ΔE is less than the _second voltage value E ₂ mV (ΔE <E ₂ ), the process proceeds to step 114.
In step 114, the flat detection counter C is determined greater than the first threshold value C ₁ second threshold whether (a value greater than the predetermined value) C less than ₂ minutes. That is, when the flat detection counter C is not less than the second threshold value C ₂ (C ≧ C ₂ ), it is determined that the battery is fully charged (S111), and after the charging is finished (S112), the process is finished. When the flat detection counter C is less than the _second threshold C ₂ (C <C ₂ ), the process returns to step 102.

Next, the voltage increase of the nickel metal hydride battery 20 during charging will be described with reference to FIGS.
FIG. 3 is a graph for explaining the transition of the voltage rise in the case of low current charging, and FIG. 4 is a graph showing the transition of the voltage rise in the present embodiment. FIG. 5 is a graph showing a transition of voltage increase when a fully charged battery is charged in the present embodiment, and FIG. 6 is a voltage increase when charging a fully charged battery in the present embodiment. It is a graph which shows transition of. 3 to 6, the vertical axis represents the battery voltage (mV) and the horizontal axis represents the charging time (minutes).
For example, charging with a large current of 1 A increases the amount of heat generated by charging, which is not preferable for the MD 10. Therefore, for example, it is conceivable to design the battery so as to charge with a low current of 0.5C or less. Here, “C” is a symbol used to represent the charge / discharge rate.
However, when such a low current charge is performed, as shown in FIG. 3, the voltage drop of the battery voltage after full charge does not occur sufficiently, and it changes substantially flat (see the portion 3a in FIG. 3). In addition, when a battery with a small remaining capacity is charged with a low current, a point at which the battery voltage flattenes in the initial stage of charging appears (see part 3b in FIG. 3). Such a phenomenon at the initial stage of charging becomes conspicuous in an inert battery or charging in a high temperature environment.
Therefore, in the conventional minus ΔV detection method focusing on the voltage drop after full charge, and in the conventional flat detection method mainly focusing on the voltage rise of the battery voltage being flat, the change in the battery voltage is shown in FIG. In such a case, there is a risk of false detection of full charge detection.

In order to prevent such erroneous detection, this embodiment is configured as described above. That is, in the present embodiment, as shown in FIG. 4, the conditions for full charge detection are as follows: (1) battery voltage E does not increase for the first threshold C ₁ or more (flat detection), (2) battery The voltage E is set to three, that is, the first voltage value E ₁ mV or more, and (3) the increase of the battery voltage E is the second voltage value E ₂ mV or more. If all three conditions are satisfied, the battery being charged is determined to be fully charged, and charging is terminated.
In the present embodiment, the following two methods are used to cope with erroneous detection for charging a fully charged battery. That is, as shown in FIG. 5, the first method is only when the flat detection of (1) is performed when the charging time T from the start of charging is less than the threshold T ₁ minute, and the above (2) and Even if the condition of (3) is not satisfied, it is determined that the battery being charged is fully charged, and charging is terminated.
In the second method, as shown in FIG. 6, the charging time T is the threshold T after ₁ minute from the start of charging, satisfies the above (1) and (2), when not satisfied (3) above, Only when the increase in the battery voltage E in the above (1) is continued for the second threshold C ₂ (C ₂ > C ₁ ) or more, it is determined that the battery being charged is fully charged, and the charging is terminated. Is.

This embodiment is effective for low current charging (0.5 C or less) of a nickel metal hydride battery mainly used for portable small electronic devices. In addition, this embodiment is effective for charging in a state where a rise in battery voltage cannot be expected so much, such as charging of a nickel metal hydride battery in a high temperature environment. Furthermore, this embodiment is effective in a state where a rise in battery voltage cannot be expected so much, such as charging of an inactive nickel-metal hydride battery that has not been used for a long period of time.
Thus, according to the method for determining full charge in the present embodiment, stable full charge detection is always realized by using the battery voltage E, the charge time T, and the flat detection counter C that are increased by charging. Can do. In addition, stable full charge detection can always be performed even in a state where there is a possibility that full charge may be erroneously detected in a conventional flat detection under a high temperature environment or an inactivated battery.

Here, as an example of specific numerical values, the first voltage value E ₁ = 1450 mV, the second voltage value E ₂ = 80 mV, the first threshold value C ₁ = 15 minutes, and the second threshold value C ₂ = 25 minutes, threshold T ₁ = 50 minutes. These numerical values are determined through experiments, and different values are adopted if conditions differ.

Various modifications of the present embodiment can be considered. For example, in the present embodiment, the case where the nickel metal hydride battery in the MD 10 is charged has been described, but the same applies to the case where the nickel metal hydride battery removed from the MD 10 is charged by a charger (not shown) alone. Can do.
Moreover, when charging the nickel metal hydride battery in MD10, it can be employed not only when charging by connecting a power cord directly to the main body of MD10, but also when charging via a charging stand (cradle). .

  In addition, after determining that the battery is fully charged and finishing charging, always charge with a small current to compensate for capacity loss due to discharging, and always perform trickle charging to keep the battery fully charged. Is also possible. Further, when it is determined that the battery is fully charged, it may be possible to perform float charging in which the current passes through a bypass circuit in the charger and the burden on the battery is zero.

  Further, in the present embodiment, the charging of the nickel metal hydride battery 20 has been described. However, it may be applied to other rechargeable secondary batteries.

It is a control block diagram of the principal part of the portable minidisc apparatus concerning this Embodiment. It is a flowchart which shows the control during charge. It is a graph for demonstrating transition of the voltage rise in the case of low current charge. It is a graph which shows transition of the voltage rise in this Embodiment. It is a graph which shows transition of the voltage rise at the time of charging the fully charged battery in this Embodiment. It is a graph which shows transition of the voltage rise at the time of charging the fully charged battery in this Embodiment.

Explanation of symbols

10 ... MD, 14 ...... full-charge detection circuit, 16 ... timer, 20 ... NiMH batteries, C ... flat detection counter, C ₁ ... first threshold, C ₂ ... second threshold, E ... battery voltage, E ₀ ... start voltage, E ₁ ... first voltage value, E ₂ ... second voltage value, E _max ... voltage peak value, ΔE ... rising voltage, T ... charging time, T ₁ ... threshold value

Claims (6)

A battery full charge determination method for determining full charge of a battery to be charged,
Measure the voltage value of the battery being charged,
Detecting a flat state in which a change in the voltage value of the battery falls within a predetermined range;
Detecting whether the duration of the flat state has reached a predetermined value (C ₁ );
The voltage of the battery when the flat state voltage value when the flat state duration time reaches a predetermined value (C ₁ ) exceeds the _first voltage value (E ₁ ) and the flat state is detected. The difference between the voltage value at the beginning of charging and the voltage value at the beginning of charging is the voltage value after the voltage increase when the voltage value at the beginning of charging and the voltage increase rate per unit time exceeds a specified value ( A battery full charge determination method that determines that the battery is fully charged when a _second voltage value (E ₂ ) that is a difference from E _max ) is exceeded. A battery full charge determination method for determining full charge of a battery to be charged,
Measure the voltage value of the battery being charged,
After the charging time (T) from the beginning of charging reaches a predetermined value (T ₁ ), a flat state where the change in the voltage value of the battery falls within a predetermined range is detected,
When the duration of the flat state reaches the _first predetermined value (C ₁ ), the voltage value of the flat state exceeds the _first voltage value (E ₁ ) and the flat state is detected. After the voltage rise when the difference between the voltage value of the battery and the voltage value at the beginning of charging is a voltage rise at which the voltage value at the beginning of charging and the value of the voltage rise rate per unit time exceed a specified value When the second voltage value (E ₂ ), which is the difference from the voltage value (E _max ), is not exceeded,
A full charge of the battery that determines that the battery is fully charged when the duration of the flat state reaches a _second predetermined value (C ₂ ) that is greater than the first predetermined value (C ₁ ) Judgment method. In a charging system that charges a rechargeable battery by connecting it to an electronic device,
Voltage measuring means for measuring the voltage of the battery being charged;
Flat detection means for detecting a flat state in which a change in the voltage value measured by the voltage measurement means falls within a predetermined range;
Flat time measuring means for measuring the duration of the flat state detected by the flat detecting means;
When the duration of the flat state measured by the flat time measuring means reaches a predetermined value (C ₁ ), the voltage value of the flat state detected by the flat detecting means is the first voltage value (E ₁ ) and the difference between the peak voltage value of the battery measured by the voltage measuring means at the time when the flat state is detected and the initial voltage value measured by the voltage measuring means is the charge A second voltage value (E ) that is a difference between the voltage value at the beginning of the start and the voltage value (E _max ) after the voltage increase when the voltage increase rate exceeds a specified value per unit time. ₂ ) A charging system comprising: charging stopping means for stopping charging of the battery on the condition that it exceeds ( ₁ ). In a charging system that charges a rechargeable battery by connecting it to an electronic device,
Voltage measuring means for measuring the voltage of the battery being charged;
Flat detection means for detecting a flat state in which the change in the voltage value measured by the voltage measurement means falls within a predetermined range after the charging time (T) from the beginning of charging reaches a predetermined value (T ₁ ). When,
Flat time measuring means for measuring the duration of the flat state detected by the flat detecting means;
When the duration of the flat state measured by the flat time measuring means reaches a _first predetermined value (C ₁ ), the voltage value of the flat state detected by the flat detecting means is the first voltage. The difference between the voltage value of the battery measured by the voltage measuring unit at the time when the flat state is detected and the value (E ₁ ) is detected and the voltage value at the beginning of charging measured by the voltage measuring unit is A second voltage value that is a difference between the voltage value at the beginning of the charge and the voltage value (E _max ) after the voltage rise when the voltage rise rate exceeds a specified value per unit time. In the case where (E ₂ ) is not exceeded, the battery is charged on condition that the duration of the flat state has reached a _second predetermined value (C ₂ ) that is greater than the first predetermined value (C ₁ ). Stop charging to stop Charging system, including the door. Flat detection means for detecting a flat state in which the voltage value of the battery being charged is input and the change in the voltage value of the battery falls within a predetermined range;
Flat time measuring means for measuring the duration of the flat state detected by the flat detecting means;
When the duration of the flat state measured by the flat time measuring means reaches a predetermined value (C ₁ ), the voltage value of the flat state detected by the flat detecting means is the first voltage value (E ₁ ) and the difference between the voltage value in the flat state and the voltage value at the beginning of charging is higher than the specified voltage value at the beginning of charging and the voltage increase rate per unit time. A charging stop means for stopping charging of the battery on the condition that the _second voltage value (E ₂ ), which is a difference from the voltage value (E _max ) after the voltage rise at that time , is exceeded . When the voltage value of the battery being charged is input and the charging time (T) from the beginning of charging reaches a predetermined value (T ₁ ), the battery voltage value changes within a predetermined range. Flat detection means for detecting;
Flat time measuring means for measuring the duration of the flat state detected by the flat detecting means;
When the duration time of the flat state measured by the flat time measuring means reaches a _first predetermined value (C ₁ ), the voltage value of the flat state detected by the flat detecting means is the first voltage. The difference between the voltage value at the time of exceeding the value (E ₁ ) and detecting the flat state and the voltage value at the beginning of charging is the voltage value at the beginning of charging and the voltage increase rate per unit time. When the second voltage value (E ₂ ), which is the difference from the voltage value after the voltage increase (E _max ) when there is a voltage increase exceeding the specified value, does not exceed the second voltage value (E ₂ ), the duration of the flat state is And a charging stop means for stopping charging of the battery on condition that a _second predetermined value (C ₂ ) larger than the first predetermined value (C ₁ ) has been reached .

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