JPH10248175A - Method and apparatus for charging secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always enable appropriate charging and repeated charging, by conducting charging under the condition that a secondary battery does not show temperature rise through control that a heavier current is applied in the initial stage of the charging, the point of inflexion of the battery voltage- time curve is detected, and a charging current is reduced after passing the point of inflexion. SOLUTION: A power source section 12 generates a DC voltage for impressing a voltage at the time of charging a secondary battery 20 to be charged. A power control section 14 receives a voltage from the power supply section 12 and controls an output voltage and a duration time depending on the external control signal. A supervising section 16 supervises changes with time of a battery voltage and a charging current of the secondary battery 20 to be charged and generates an output signal by detecting the point of inflexion of a battery voltage time curve. An arithmetic operation driving section 18 drives a power control section 14 by receiving an output signal of the supervising section. Thereby, appropriate charging can always be conducted without allowing temperature rise to give a failure to the secondary battery 20 and the repeated charging can also be enabled without generating a memory effect.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel charging method for a secondary battery and a charging device for a secondary battery for performing the charging method.

In recent years, various types of portable or mobile electric and electronic devices, such as mobile phones, notebook personal computers and other information processing devices, handy terminals, video cameras, rechargeable power tools, compact vacuum cleaners, various transport devices, etc. And batteries as driving sources are indispensable.

As is well known, such batteries include a primary battery that can be discharged only once and a secondary battery that can be charged and discharged many times.

A primary battery widely used as a manganese battery or an alkaline manganese battery is standardized internationally and has an advantage that it can be easily obtained and used. However, since it is a complete consumable, it is uneconomical. is there.

[0005] Lead-acid batteries which can be charged and discharged a number of times and which have been used for a long time for automobile engines and the like have been variously improved over a long history.
The dimensions, capacity, etc. have also been remarkably advanced. However, such a lead storage battery is not suitable as a power source for small-sized mobile devices, for example, portable devices, because of its heavy weight and the use of a dilute sulfuric acid solution as an electrolyte.

[0006] Although small sealed lead-acid batteries in which such a well-known lead-acid storage battery is formed in a small form are also partially adopted, the battery capacity per unit weight is small. At present, nickel-cadmium (Ni) is used as a small secondary battery.
-Cd) batteries, nickel-hydrogen (NiMH) batteries, lithium ion (Li) batteries, and the like are widely used.

[0007] Above all, Ni-Cd batteries have been commercialized in the 1960s and have an overwhelming share. The characteristics of this Ni-Cd battery are (1) sealed type, which does not require replacement fluid, (2) light weight, (3) miniaturization is possible, and standard such as A1, AA, AA, etc. It has the same shape as the standard manganese dry battery and can be replaced as it is. (4) It has little voltage fluctuation and can output a large current. (5) It can be used repeatedly as compared with a manganese dry battery which is a primary battery. Therefore, the cost in use is significantly reduced.

[0008]

2. Description of the Related Art Although it is a small secondary battery having many characteristics as described above, according to standard charging conditions recommended by a battery manufacturer, a current of about 0.1 C is specified for about 10 to 15 hours. . Obviously, such a long charging time is inconvenient in practice and has reduced many features.

Therefore, the charging time is shortened by setting the charging current to be as high as about 0.3 C, and some batteries which can be rapidly charged are set to 30 minutes to 1 hour. Limited to further,
If the charging time is shortened, the temperature becomes extremely high at the end of charging, and there is a risk of shortening the battery life.

In addition, this type of secondary battery has a so-called memory effect in which the effective capacity gradually decreases during repeated incomplete charging, in addition to the remaining capacity, and eventually becomes unusable. Sometimes. Discarding such a secondary battery easily leads to waste of resources and further spoils heavy metal contamination of soil, which is not desirable.

Such a memory effect becomes remarkable by performing the next charging, that is, a so-called additional charging state, before the small secondary battery capacity is completely used up. Before resuming the use of built-in secondary batteries in portable devices,
This occurs in a state where additional charging or additional charging is performed just in case.

In general, in the case of a portable information processing device or a communication device, for example, a power source of a handy terminal or a mobile phone, it is necessary to take a complete discharge procedure in advance every time the secondary battery is charged before use. It is almost impossible from the point of view of trouble.

For example, each time the secondary battery built in the mobile phone is charged before going out, or after the end of use on the day, the supplementary charging is started, the remaining capacity of the secondary battery is checked each time.
Alternatively, it is extremely difficult to perform a complete discharge in advance.
Therefore, the supplementary charging is performed under the condition that the memory effect occurs.

In order to prevent such a memory effect, a so-called refresh method, in which a standard charge is repeatedly performed after a complete discharge operation is periodically performed, is effective. FIG.
FIG. 9 shows voltage-capacity characteristics when a memory effect occurs in an iCd battery and a NiMH (nickel-hydrogen) battery (solid line) and after refresh (dashed line).

However, in performing such a refresh, consideration must be given to avoid overdischarging, and it is still complicated in terms of the number of steps and time.

In particular, in the case of an assembled battery in which cells are connected in series and parallel, when the cells are overdischarged, the discharge states of the individual cells are different, and the cells that have been discharged earlier are charged to the opposite polarity.
It may be unrecoverable, requiring special consideration.

On the other hand, if the refresh discharge is set shallow to avoid this, some or most of the batteries will be discharged without being refreshed due to variations in the constituent batteries, and the initial effect will be obtained. There may not be.

In the conventional charging method as described above, it is also difficult to end the charging operation in a proper charging state. At present, the state of charge of a small secondary battery cannot be confirmed from outside. Therefore, it is not easy to determine a necessary and sufficient charging end time.

As a method of determining the end of charging of the secondary battery, there are 1 methods. 1. Charge time setting method, Terminal voltage detection method,
3. 3. Battery temperature detection method; A battery voltage change rate detection system (there are several improved systems in addition to the basic system) is known.

1. The charging time setting method controls the charging state of the charging circuit by a timer.
The remaining battery capacity at the start of charging is not uniform, and there is no guarantee that proper charging will be achieved even if charging is stopped for a certain period of time, and often insufficient charging or overcharging.

2. The terminal voltage detection method performs charging with a predetermined charging current, and stops charging when the terminal voltage of the secondary battery reaches a predetermined voltage, that is, a voltage value close to the maximum voltage value at the end of charging. Things.

However, the end-of-charge voltage varies depending on the battery temperature and the charging current. The set voltage for the end-of-charge detection must be set lower to avoid overcharging. Therefore, the detected terminal voltage cannot indicate a true state of charge, and is generally undercharged in many cases.

3. In the battery temperature detection method, the battery temperature is monitored by a temperature detection element incorporated in the battery in advance, and when the temperature reaches a predetermined temperature, the charging current is sequentially reduced, and finally the charging is stopped. It detects the heat of reaction when the gas generated at the end of charging is absorbed by the cathode, but is easily affected by the ambient temperature, and tends to be overcharged at low temperatures and undercharged at high temperatures. Basically, this means that the temperature rise due to overcharge, which is undesirable for the battery itself, is detected, and it is unavoidable that the battery is deteriorated each time it is repeated.

4-1. As shown in FIG. 4, the terminal voltage change rate (ΔV / dt) detection method is used when the battery voltage rises at the end of charging and turns to decrease (ΔV / dt ≦ 0).
Is detected, that is, the rate of change of the slope of, that is, −ΔV, and charging is terminated. Basically, charging is stopped by detecting a voltage drop caused by a rise in battery temperature, and the battery temperature rises inevitably. Note that there are a case where charging reaches a predetermined voltage and charging is completely stopped, and a case where weak charging for maintaining a state (trickle charging) is continued. The charging current curve in FIG. 4B shows a state in which trickle charging is performed.

4-1. The terminal voltage change rate (ΔV / d
t) The detection method detects the rate of change when the temperature reaches the battery voltage at which the temperature rise starts at the end of charging, as shown by the battery voltage curve in FIG. 5A, and charges the battery as shown in FIG. 5B. The current is reduced stepwise. In this case, the type of battery, it is necessary to change the set voltage _{V 1, V 2, V 3} ·· etc. the size or the like.

4-2. The improved second terminal voltage change rate detection method is such that the change rate of the slope of the battery voltage rise in the battery voltage curve of FIG. 6A, that is, ΔV / dt reaches a predetermined value as shown in the enlarged view (C). This is detected, and the current is controlled as shown in FIG. 6 (B). However, the predetermined value in this case is basically to attempt to charge by detecting a change in battery voltage, and it is necessary to change the set value according to the type and capacity of the battery.

Also in this method, the temperature is inevitably increased, and it is necessary to make settings while taking into account the type and capacity of the target battery. This is complicated, and inconvenience due to erroneous operation is likely to occur.

In the conventional various charging methods described above, if the battery is insufficiently charged, the battery performance is not sufficiently exhibited.
It will affect the performance of the onboard equipment.

On the other hand, when the secondary battery having a sealed structure is overcharged, the temperature rises, and the electrolyte leaks and a shortage of the electrolyte resulting therefrom, that is, a dry-up phenomenon occurs, resulting in a fatal failure for the secondary battery. May suffer.

[0030]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a battery which can always be properly charged without causing a temperature rise which causes an obstacle to a secondary battery, and which can be repeatedly charged and discharged without causing a memory effect. It is an object of the present invention to provide a charging method for a secondary battery capable of performing the above-described method and a charging device suitable for performing such a method.

[0031]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a battery to be charged so that a variable DC voltage having a maximum value equal to or higher than the terminal voltage of the battery to be charged and which can be reduced by an external control signal has a forward polarity. The inflection point in the battery voltage / time curve of the battery to be charged is detected while applying the corresponding charging current by applying the voltage between the positive and negative terminals, and the applied DC voltage is sequentially controlled in accordance with the detection of the inflection point. Thus, the problem is solved by a method of charging a secondary battery in which charging is performed while reducing charging current.

Further, as shown in FIG. 1, the object of the present invention is to provide a power supply unit 12 for generating a DC voltage for applying a voltage when charging a battery 20 to be charged, and receiving a voltage from the power supply unit 12. A power control unit 14 for controlling an output voltage and a duration according to an external control signal, and monitoring a time change of a battery voltage and a charging current of the battery 20 to be charged, and inflection of the battery voltage / time curve. A monitoring unit 16 that detects points and generates an output signal; and a calculation / drive unit 18 that receives the output signal of the monitoring unit 16 and drives the power control unit 14
Is solved by the charging device 10 for a secondary battery comprising:

In the method for charging a secondary battery according to the present invention,
The DC voltage applied between the positive and negative terminals of the secondary battery can be a continuous voltage or a pulsed voltage. During the charging state, the terminal voltage of the secondary battery to be charged is monitored. In the monitoring, reference is made to required characteristic data, for example, characteristic data suitable for the type of battery, terminal voltage and procedure, etc., stored in the monitoring unit 16 in advance.

By monitoring the charging current, the state of the battery to be charged, in particular, the remaining capacity is measured. An arithmetic process is performed based on the monitoring result, and the magnitude and application time of the subsequent charging voltage are determined according to the result. The charging voltage may be applied either intermittently (pulsed) or continuously.

As shown in the battery voltage-time curve of FIG. 2A and its partially enlarged view (C), the point at which the double differential value is substantially zero (d ² V / dt ² = 0), that is, It is detected that the inflection point has been reached or the inflection point has been substantially reached, and I _1, I _2, I _3, I ₄
As described above, the charging current is reduced according to each inflection point of the voltage of the battery to be charged.

By continuing charging while changing the applied voltage in accordance with the optimum value data thus determined, desired charging can be performed while preventing overcharging, overheating, and the occurrence of the memory effect.

The indication that the temperature of the battery to be charged rises sharply is whether the voltage change rate of the charging voltage-time curve has changed from positive to negative, that is, whether the battery has passed the inflection point, as described above. You can know by. Thus, the inflection point is a point on the curve where the value obtained by double differentiating the time change of the voltage becomes zero when expressed mathematically.

That is, the state in which the downwardly convex voltage-time curve transposes to the upwardly convex curve or the state in which the downwardly convex voltage-time curve is displaced in the opposite direction, that is, after the inflection point is exceeded, the current Suddenly changes, and the temperature rises sharply.

The phenomenon that the inflection point occurs due to the charging voltage-time curve depends on the type and capacity of the secondary battery.
Little difference occurs. Therefore, the charging method according to the present invention and the charging device for performing the method can always perform safe and highly efficient charging.

The inflection point in the terminal voltage-time curve of the battery to be charged is strictly a double differential value d ² V / dt ^{2 of the} voltage change.
Can be easily detected by monitoring the state of. Practically, when the coefficient is equal to or less than a predetermined coefficient k (here, -1>k> 1, and strictly k = 0 is an inflection point) determined by a battery or the like, it is regarded as an inflection point and controlled. be able to.

By taking such considerations into account, efficient charging is performed, and no excessive temperature rise or memory effect occurs during the charging. Therefore, the battery life can be greatly extended, and effective use of resources and suppression of environmental destruction can be achieved.

In this case, the target secondary batteries include nickel-cadmium batteries, nickel-hydrogen batteries, lead-acid batteries,
Examples include nickel-zinc batteries, silver oxide-zinc batteries, silver oxide-cadmium batteries, and various other lithium secondary batteries. As described above, the charging method and the charging device according to the present invention can be widely applied to each of these secondary batteries.

[0043]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 3 shows a secondary battery charger 10 suitable for carrying out the charging method according to the present invention.
FIG. 3 is a schematic block diagram illustrating a configuration example of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals.

FIG. 3 shows a monitoring unit 1 among the basic elements of FIG.
6 and the operation / drive unit 18 are disclosed according to a specific configuration example. The monitoring unit 16 includes a voltage detection unit 16V that detects a terminal voltage of the battery 20 to be charged, and a current detection unit 16A that detects a charging current. Other conditions are comprehensively monitored.

The monitoring section 16 has a main storage section 16M for storing data necessary for executing a series of charging operations. The data stored in the main storage unit 16M includes:
Based on the charging capacity of the battery to be charged 20 at that time, a temporal relationship of charging current, a temperature characteristic, and the like are included.

The monitoring section 16 is provided with an inflection point detecting section. The inflection point detection unit includes a circuit 1 for detecting a voltage change rate.
6d, a temporary storage unit 16T, and a comparison unit 16C. The voltage signal detected by the voltage detector 16V at predetermined time intervals is detected as a double differential value in the voltage change rate detection circuit 16d.

The double differential value thus detected is temporarily stored in the temporary storage section 16T. The accumulated value and the voltage value detected by sampling the voltage value at successive predetermined time intervals, for example, every 15 seconds, and obtaining the average over a period of about 1 to 2 minutes by continuously performing the sampling several times are used. The multiple differential values are sequentially compared in the comparison circuit 16C, and it is detected that the comparison result is equal to or less than the predetermined coefficient value k. That is, when the double differential value of the voltage change of the terminal voltage-time curve becomes equal to or less than the predetermined coefficient value k, an output signal corresponding to (d ² V / dt ² ≦ k) is generated.
The coefficient k in this case varies depending on the type and capacity of the secondary battery, but as described above, −1>k> 1, and k = 0.
Is the exact inflection point.

The signal detected as an inflection point by the monitoring section 16 is applied to an operation / drive section 18 composed of a microcomputer or the like, subjected to a desired operation process, and then applied as a drive signal to the power control section 14. Supplied to As a result, the optimal applied voltage is supplied from the power control unit 14 to the battery 20 to be charged. The operation / drive unit 18
Has a drive unit 18D and a calculation unit 18T.

The power supply unit 12 is, as described above,
It has a maximum voltage higher than the terminal voltage of 0 and generates a DC voltage suitable for the battery to be charged. This voltage can be changed according to the type of the battery to be charged, the battery configuration, the capacity, and the like.

The DC output of the power supply unit 12 is
The power control unit 14 is controlled as an intermittent voltage or a continuous voltage having a peak value equal to or higher than the voltage of the battery to be charged. When this DC voltage is used as the intermittent voltage, it is desirable that the peak value of the DC voltage is at least 1.3 times or more the terminal voltage of the battery to be charged. this is,
It is important for quick charging of a secondary battery and for eliminating or preventing a memory effect.

However, if such a high voltage is continuously applied for a long time, a severe charging current is given to the secondary battery, which causes overheating of the battery and physical destruction of the electrodes. is necessary.

In the secondary battery charging apparatus according to the present invention, hardware constituted by a combination of a microcomputer, a memory, a register, a sensor, and the like known in the art, software for controlling the hardware, Can be easily configured by appropriately combining.

The types of batteries that can be charged in the charging method according to the present invention include nickel-cadmium batteries, nickel-hydrogen batteries, lead-acid batteries, and nickel-cadmium batteries as described above.
Examples include zinc batteries, silver oxide-zinc batteries, silver oxide-cadmium batteries, and various other lithium secondary batteries.

[0054]

According to the method for charging a secondary battery according to the present invention,
Focusing on the fact that many of the charging actions of the above-mentioned batteries are endothermic reactions, a large current is passed at the beginning of charging, and
It is characterized in that the inflection point of the time curve is detected, the charging current is controlled to be reduced after passing through the inflection point, and the rechargeable battery is charged under the condition that the temperature does not rise.

Therefore, according to the present invention, it is possible to charge the battery for a short time, and since the state of the battery is constantly monitored, excessive temperature rise and overcharging do not occur, thereby extending the battery life. Can be.

In the method of charging a secondary battery according to the present invention,
As described above, charging can be performed in a charging time of about 1/3 of that of the related art. Therefore, it is also advantageous for charging portable devices.

Further, since the memory effect does not occur even by so-called additional charging, in the case of emergency, the above-mentioned 15 to
The charging may be performed for a fraction of the charging time of 20 minutes, for example, 5 minutes, and the additional charging may be performed after the charging is completed.

The charging method according to the present invention is applied to a small-sized
The present invention is not limited to portable secondary batteries. The above-mentioned various secondary batteries are sufficiently applicable to large-sized secondary batteries such as battery forklifts, electric carts, and other transportation devices, and electric vehicle power supplies. At present, even in applications where charging takes several hours when not in use, such as at night, charging in a fraction of a fraction is possible, which is also useful for energy saving.

The biggest problems of electric vehicles that do not exceed the prototype stage at present are that small and lightweight batteries cannot be obtained, battery capacity is limited and long-distance traveling cannot be performed, and charging time cannot be shortened. , Etc. In the field of large-capacity batteries such as electric vehicles, application of an alkaline storage battery that is superior to a conventional lead battery in capacity-to-weight ratio and capacity-to-volume ratio is expected. The present invention provides a useful technique as a charging technique for these batteries. Therefore, there is a possibility of quick charging in a battery stand or the like.

According to the present invention, the life of the battery can be greatly extended, the effective use of resources can be promoted, and the amount of battery disposal can be reduced, thereby contributing to the prevention of environmental destruction.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram showing a basic configuration of a charging device for a secondary battery according to the present invention.

FIG. 2 is an explanatory view showing a time change of a battery voltage and a current waveform in a method of charging a secondary battery according to the present invention, and FIG. 2 (C) is a partially enlarged view.

FIG. 3 is a block diagram illustrating a configuration of an embodiment of a charging device for a secondary battery according to the present invention.

FIG. 4 is an explanatory diagram showing a time change of a battery voltage and a current waveform in a first method of charging a secondary battery according to the related art.

FIG. 5 is an explanatory diagram showing a time change of a battery voltage and a current waveform in a second method of charging a secondary battery according to the related art.

FIG. 6 is an explanatory diagram showing a time change of a battery voltage and a current waveform in a third method of charging a secondary battery according to the related art;
FIG. (C) is a partially enlarged view.

FIG. 7 is a diagram showing voltage-capacity characteristics when a memory effect occurs in a NiCd battery and a NiMH battery according to the related art and after refresh.

[Explanation of symbols]

 Reference Signs List 10 charging device 12 power supply unit 14 power control unit 16 monitoring unit 16A current detection unit 16V voltage detection unit 16d voltage change rate detection unit (circuit for obtaining voltage change rate) 16M storage unit 16T temporary storage unit (temporary storage circuit) 16C comparison unit (Comparison circuit) 18 Operation / drive section 18T Calculation section 18D drive section 20 Battery to be charged

Claims (4)

[Claims] 1. A charging method in which a variable DC voltage having a maximum value equal to or higher than a terminal voltage of a battery to be charged and reduced by an external control signal is applied between positive and negative terminals of the battery to be charged so as to have a forward polarity. While supplying the current, the inflection point in the battery voltage-time curve of the battery to be charged is detected, and the applied DC voltage is sequentially controlled in accordance with the detection of the inflection point, thereby reducing the charging current and performing the charging. Performing a method for charging a secondary battery. 2. The inflection point is detected by monitoring a double differential value of a voltage change in a battery voltage-time curve of a battery to be charged, and issued when the double differential value changes from positive to negative. The method for charging a secondary battery according to claim 1, wherein the charging is performed by a signal. 3. A power supply unit for generating a DC voltage for applying a voltage when charging a battery to be charged, receiving a voltage from the power supply unit, and controlling an output voltage and a duration according to an external control signal. A power control unit that monitors a battery voltage and a charging current of the battery to be charged over time, detects an inflection point of the battery voltage / time curve, and generates an output signal. And a calculating / driving unit for receiving the output signal and driving the power control unit. 4. An inflection point detecting section in the monitoring section, wherein a circuit for calculating a battery voltage change rate of the battery to be charged at predetermined time intervals, and a temporary storage circuit for temporarily storing the previously obtained voltage change rate. A comparison circuit for sequentially comparing the accumulated value stored in the storage circuit with the next voltage change rate generated after a predetermined time, wherein a difference between the preceding and following voltage change rates is positive. The charging device for a secondary battery according to claim 3, wherein when it changes to a negative value, it is determined that the point is an inflection point, and the calculation / drive unit is controlled according to the determination result.