JP2001327094A - Charger and charging method for alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the load on a battery by suppressing overcharge, when quick charging is performed by increasing the charging current. SOLUTION: Voltage increase rate is detected, and following control is performed when it exceeds a prescribed level. Charging current is decreased, when the battery temperature exceeds a specified level, and further decreased below a level of 3C when the maximum point of voltage rising rate or a prescribed battery temperature rising rate is detected. When the temperature increase rate exceeds a specified level or the voltage increase rate goes 0, charging operation is stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a charger and a charging method for an alkaline secondary battery such as a nickel-cadmium secondary battery and a nickel-hydrogen secondary battery.

[0002]

2. Description of the Related Art A rapid charging method for an alkaline secondary battery such as a nickel-cadmium secondary battery and a nickel-hydrogen secondary battery is roughly classified into a method of detecting and controlling full charge by a battery voltage and a method of full charge by a battery temperature. There is a method of detecting and controlling charging. A typical method of detecting and controlling the full charge based on the battery voltage is a so-called -ΔV method that detects a decrease in the battery voltage after the full charge, and overcharges the battery without being affected by the ambient temperature. There is an advantage that the amount is small and erroneous detection is small.

The method of detecting and controlling the full charge based on the battery temperature is a method often used for a nickel-hydrogen secondary battery having a relatively small -ΔV. And has the advantage that the amount of overcharge of the battery can be made smaller than that of the -ΔV method.

[0004] Further, as a charging method for eliminating the drawback of the above-mentioned charging method in which an error is caused by the magnitude of the charging current or the ambient temperature and improving the accuracy of detection of the full charge state, the time of the battery voltage change rate Detects the point where the rate of change (the second derivative of the voltage curve) changes from positive to negative, reduces the current, and then detects that the battery voltage change rate becomes 0 or negative, and detects the fully charged state A known method is known (for example, JP-A-4-217826).

Further, in order to prevent overcharging at the time of rapid charging, a method is known in which charging is stopped at a time when a certain gentle slope after the maximum time of the battery voltage change speed is set to a full charge state (for example, see, for example). JP-A-7-240234).

[0006]

The more convenient the battery can be charged in a short time, the more convenient it is. However, for this purpose, it is necessary to increase the charging current. However, when overcharging is performed with a large current, the battery internal pressure rises, gas is released from the safety valve to the outside, and the electrolyte decreases, and the battery is likely to deteriorate faster.

Therefore, it is necessary to detect the full charge state more accurately and stop charging to prevent overcharge. However, in the conventional methods, the full charge state is detected when the charging current is increased. It ’s not early enough to be happy,
In some cases, the burden of overcharging was imposed on the battery.

For example, as a method of detecting the full charge state more accurately and stopping charging accurately, there is a method of shortening the sampling time of the battery voltage as much as possible. When trying to detect a point that turns negative, the battery voltage fluctuation is detected, and the two-time differentiation goes between positive and negative, making it difficult to detect, or when the charging current is as large as 3 C or more. However, there is a problem in that if the user waits for the value to turn negative, the timing for entering the next control is too late.

Accordingly, the present invention is directed to an alkaline secondary battery capable of suppressing overcharging even if the charging current is increased and performing rapid charging, thereby reducing the burden on the battery. It is an object of the present invention to provide a charger and a charging method.

[0010]

According to a first aspect of the present invention, there is provided a charging circuit, switching means for switching a connection between a charging circuit and a battery to be charged, and detecting a battery voltage. An A / D converter for converting into a digital signal;
A charger comprising a control device for controlling the charging circuit and the switching means based on a digital signal input from a D converter, wherein the control device operates to detect a maximum point of a voltage rising rate. A charging circuit for controlling the charging circuit so as to reduce a charging current when a maximum point is detected.

By detecting the maximum point of the voltage rising speed instead of detecting that the time rate of change of the voltage rising speed changes from positive to negative, it is possible to detect a state in which the battery is approaching full charge sooner. By quickly detecting this state and reducing the current, even if rapid charging with a large current is performed, the final fully charged state can be detected more accurately, and overcharging can be performed. It can be suppressed. The “maximum point” does not need to be a strict maximum point, and is preferably the maximum point or a point immediately before the maximum point.

In order to detect the maximum point of the voltage rise rate, the sampling time of the battery voltage is shortened, preferably 1 second or less, and the comparison point for calculating the rise rate is set to a longer time, preferably sampling. 30 of time
It is preferable to detect by comparing with the sampling data more than twice or more than 30 seconds ago. In the charger of the present invention, after the current is reduced, the full charge state is detected by a conventionally used method or the like, and the charging is stopped or the trickle state is set.

According to a second aspect of the present invention, in the first aspect of the present invention, a battery temperature detecting means is further provided, and the control device operates to detect a temperature rise rate based on the temperature detected by the battery temperature detecting means. If the temperature rising rate exceeds a predetermined value before detecting the maximum point of the voltage rising rate, the charging circuit is controlled so as to reduce the charging current, and the maximum point of the voltage rising rate is detected. An alkaline secondary battery charger characterized in that the charging circuit is controlled so that charging is stopped when the temperature rise rate exceeds a predetermined value later.

By using the control based on the temperature detection together, it is possible to more accurately detect the fully charged state and the state approaching the fully charged state, and it is possible to more accurately prevent overcharge. Further, overcharge can be more effectively prevented for a nickel-metal hydride battery in which a temperature rise is more remarkable than a voltage rise. The predetermined value for reducing the charging current is preferably different from the predetermined value for stopping charging, and the former is preferably increased. This is because the former is for detecting a state approaching full charge, and the latter is for detecting a fully charged state. Further, control for reducing the current by detecting the battery temperature itself may be added. In this case, the current value is preferably set to be larger than the reduced current value.

[0015] In a third aspect of the present invention based on the first or second aspect, the control device detects a voltage rising speed at first, and increases the voltage rising speed when the voltage rising speed reaches a predetermined magnitude. An alkaline secondary battery charger that operates to detect a maximum point of speed.

By doing so, it is possible to omit the control at an unnecessary time, and to reduce the current in a state away from the full charge state due to erroneous detection, which increases the charge time. Can be prevented.

According to a fourth aspect of the present invention, in the first, second or third aspect of the present invention, the control device further comprises the step of determining that a time change rate of the voltage rising rate becomes 0 or less for a predetermined time. An alkaline secondary battery charger characterized in that it is determined that the maximum point of the voltage rising rate has been reached.

In this way, the maximum time change rate can be detected without waiting for the time change rate to become negative especially when the battery voltage sampling time is shortened. The predetermined time can be determined experimentally, for example, and in this case, the predetermined time is set in advance.

In a fifth aspect of the present invention, in the fourth aspect, the comparison reference time for calculating the voltage rising speed is longer than the comparison reference time for calculating the rate of change of the voltage rising speed. Is a charger for an alkaline secondary battery.

By doing so, it is possible to detect the maximum point or immediately before the maximum point. It is preferable that the comparison reference time for calculating the time change rate is the same as the sampling time, or a time length close to this, for example, about several times this.

According to a sixth aspect of the present invention, in the first, second, third, fourth or fifth aspect, the control device further comprises two comparison reference times for detecting a voltage rising speed. A battery charger for an alkaline secondary battery having the above.

When the battery voltage is converted into a digital signal by using an A / D converter, if the sampling time of the battery voltage is shortened, it becomes impossible to calculate the voltage rising speed by comparison with the immediately preceding sampling data. Therefore, it is necessary to compare with the sampling data before a predetermined time. This predetermined time is referred to herein as a comparison reference time,
If this time is as short as possible, it can respond to a rapid change in the battery voltage. However, if it is too short, it may not be possible to determine the voltage rising speed. Therefore, by giving two or more of these reference times, making a judgment with both, and adopting the shorter comparison reference time that enables the judgment,
Faster and more accurate determination can be made.

According to a seventh aspect of the present invention, in the first, second, third, fourth, fifth or sixth aspect of the present invention, the control device further comprises the step of detecting the maximum point of the voltage rising speed. A charger for an alkaline secondary battery, characterized in that the charging circuit is controlled so that a charging current is 3 C or less.

By setting the temperature to 3 C or less, it becomes possible to detect only a change in voltage or temperature due to a temperature rise due to the oxygen gas absorption reaction of the negative electrode, excluding heat generation of the current itself, and to accurately detect a change in charge current after reducing the charging current. Charge can be detected.

In an eighth aspect of the present invention, in the first, second, third, fourth, fifth, sixth or seventh aspect of the invention, the control device further comprises: After detecting the maximum and reducing the charging current, the voltage
The battery charger for an alkaline secondary battery is characterized in that the charging circuit is controlled so that charging is stopped or a trickle charging state is detected when the charging is detected.

According to the ninth invention of the present application, charging is performed with a current larger than 3 C first, and thereafter, the maximum point of the voltage rising speed is detected, and the charging current is reduced to a current of 3 C or less. A charging method for an alkaline secondary battery, characterized in that charging is stopped or a trickle charging state is detected by detecting a fully charged state of the battery.

As described above, the charging time can be reduced by initially charging with a large current, and by detecting the maximum time change rate and reducing the current, it is possible to prevent overcharging due to control being unable to keep up. Further, it is possible to detect an accurate time of full charge.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described together with examples. FIG. 1 is a block diagram showing a schematic configuration of the charger according to the present invention. The charger of the present embodiment includes a charging circuit 3 that rectifies a commercial AC power supply 6 and outputs a predetermined DC current, a switching element 4 that switches between energization and disconnection from the charging circuit 3 to the secondary battery, and a secondary element. An A / D converter 2 for converting a battery terminal voltage into a digital value;
The control device 1 receives the output data from the converter 2 and performs a predetermined charge control operation on the secondary battery.

The control device 1 includes an arithmetic unit 11 composed of a CPU.
And a one-chip microcomputer including a data storage unit 12 and a control output unit 13, and operates according to a program stored in a ROM in advance. The charging circuit 3 is a constant current source, and changes an output current according to a control signal input from the control device 1. The switching element 4 is
The circuit includes a relay, a semiconductor switch, and the like, and turns on and off a circuit in accordance with a control signal input from the control device 1 to control an energization timing. The A / D converter 2 detects the terminal voltage of the secondary battery 5 at a predetermined sampling time, converts this to a digital signal, and inputs the digital signal to the control device 1. In the operation example described below, the sampling time is set to 0.4 seconds, and the bit width when converting to a digital signal is set to 30 mV.

Although the battery charger of this embodiment is not provided with the battery temperature detecting means, for example, when the battery temperature detecting means is provided, the battery temperature is directly or indirectly measured by a temperature sensor or the like. Is input to the control device 1. Then, similarly to the case of voltage detection, control is performed by a microcomputer.

Next, the operation of the battery charger of this embodiment will be described with reference to FIG. 2 showing a flow chart for detecting the maximum value of the battery voltage rising rate, and FIG. 3 showing the detection signal conceptually illustrating the conversion of a digital signal. This will be described with reference to FIGS. When charging is started, the A / D converter 2 takes in the terminal voltage of the secondary battery (FIG. 3A) that changes continuously at a predetermined sampling time, and divides the voltage by a predetermined bit width. Convert to a digital signal (Vn). Since all voltages within the bit width are set to the same voltage, the battery voltage is recognized as a step-like discontinuous voltage change (FIG. 3B).

When the signal Vn is input to the arithmetic unit 11, the signal V _n− input in the arithmetic unit 11 before the comparison reference time (60 seconds in the following operation example) and stored in the data storage unit 12. _The voltage increase speed ΔVn is calculated by subtracting ₆₀ from the current value, and further, whether or not this value is equal to or greater than a predetermined value Vth is compared. In the following operation example, Vth is set to 3. In other words, it is determined whether or not a change of three bits has occurred, that is, whether or not the voltage rise rate is 90 mV / min or more.

When the voltage does not exceed Vth, only the above operation is repeated. However, when the voltage exceeds Vth, it is calculated before a predetermined comparison reference time (0.4 seconds in the following operation example), and the data is stored in the data storage unit 12. Is subtracted from the ΔV _n−60 stored in the step S1 to calculate the time rate of change Δ ² Vn of the voltage rising rate ΔVn, and the operation starts to detect the time rate of change of the voltage rising rate.

As described above, the detection of the time rate of change is not performed until the voltage rising rate becomes a certain value or more, in order to prevent erroneous detection before entering a sharp voltage rising period at the end of charging. It is. At the point L in FIG. 3D, the time change rate Δ
² Vn is 0, and if such processing is not performed, it may be judged that the end of charging has been approached at this point and the current may be reduced, but the rate of voltage increase may increase at the end of charging. In this manner, malfunction is prevented by detecting the maximum point of the voltage rising speed when the voltage rising speed reaches a predetermined value. In this figure, the maximum point detecting operation starts from the point K in FIG.

Although omitted in the flowchart of FIG. 2,
A predetermined number of times (in the following operation example, 1
It is also determined whether the detection has been performed continuously (0 times), and the process proceeds to the time change rate calculation step only after the detection is continuously performed a predetermined number of times.
This is to prevent erroneous detection due to noise.

Next, when the time change rate Δ ² Vn is calculated, it is compared whether this value is smaller than a predetermined value ΔVth. By changing the magnitude of ΔVth, the timing of the switching of the charging current can be changed. Depending on the comparison reference time for calculating Δ ² Vn and the sampling time, the timing of the switching becomes earlier with a larger value. In the following operation example, ΔVth is set to 1 (bit), and Δ ² V
By setting in this way together with shortening the comparison reference time for n calculation, it is possible to detect the maximum point of the voltage rising speed or the vicinity immediately before it. That is, it is detected whether or not the time rate of change of the voltage rising speed has become 0 or less during the predetermined time.

If it is smaller than ΔVth, the number of times satisfying this condition is counted. If the count becomes a predetermined number or more (five or more in the following operation example), the arithmetic unit outputs the current to the control output unit 13 at the timing of current reduction. The control output unit 13 inputs a signal notifying that there is
The charging circuit 3 receives the input of this signal to reduce the current, and preferably reduces the current to 3 C or less. In addition,
The count is accumulated when the condition of less than ΔVth is continuously satisfied, but is reset when the condition is not continuous. This is to prevent erroneous detection due to noise.

In FIG. 3D, since the time rate of change Δ ² Vn changes from a positive value to a negative value at once, a detection signal as the maximum value is output when the voltage rise rate exceeds the maximum value. This is because, in this figure, the sampling time is very short in order to make the figure easy to understand, and in fact, the sampling time is shortened. It is possible to detect that Δ ² Vn becomes 0 at a point, and it is possible to accurately detect the maximum point of the voltage rising speed.

For example, as shown in FIG. 4, the time rate of change of the voltage rising rate is gradually increased, but becomes close to 0 before and after the maximum point. For this reason, by making the comparison reference time sufficiently short, for example, by comparing with a value immediately before the sampling time is made sufficiently short, Δ ² Vn can be made only 0, 1, −1, Where the rate of change is large, 1 appears at short time intervals, and where the rate of time change is small, it appears at long time intervals. Therefore, by utilizing this, it is possible to detect immediately before the maximum point by detecting that 0 is detected for a predetermined time (point P in the figure). That is, the comparison reference time and the predetermined time for detecting 0 may be appropriately adjusted.

By performing the above operation, the maximum point of the voltage rising speed is detected, and when the maximum point is detected, the charging current is reduced. After that, when detecting that the voltage rising rate is 0 or negative, the control device 1 operates so as to stop charging or to set a trickle charging state,
The charger of this example operates so that the secondary battery 5 is charged while preventing the overcharge state.

Next, a specific operation example will be described.
FIG. 4 is an operation explanatory diagram showing a change in battery voltage, a change in battery temperature and a change in charge current value when a nickel-cadmium secondary battery is charged by the charger according to the present invention, and FIG. FIG. 9 is an operation explanatory diagram showing a change in battery voltage, a change in battery temperature, and a change in a charging current value when a secondary battery is charged by the charger according to the present invention.

The charger used in this operation example has a battery temperature detecting means comprising a thermistor in addition to the configuration of the above charger, and the control device detects a battery temperature rising speed, and this value is equal to or more than a predetermined value. In this case, a program for controlling the charging circuit so as to reduce the charging current in the case of is installed. When the battery voltage rise rate is 0 or the temperature rise rate is equal to or more than a predetermined value, the switching element is turned off to control the charging current to be 0. Further, when the temperature rising speed exceeds a predetermined value before detecting the maximum point of the voltage rising speed, the charging circuit is controlled so as to reduce the charging current. Furthermore, the battery has a function of reducing the current when the battery temperature becomes equal to or higher than a predetermined temperature, and the charger used in the case of the nickel-hydrogen secondary battery described below has a temperature of 42 ° C. When it exceeds, an operation to reduce the current is performed. This absolute temperature detection is a control for preventing the battery from overheating, and a value smaller than the temperature is set so as not to exceed the limit temperature of the battery during charging.

In the present charger, the sampling time is 0.4 seconds, and the bit width at the time of converting to a digital signal is 3 seconds.
0 mV, and two types of comparison reference times for calculating the temperature rise speed, 60 seconds and 30 seconds, are set. Based on each comparison reference time, similar control processing is performed in parallel in the control device. It is to be performed in. 60
If the control signal is issued at a different time from the second and 30 seconds, or if the control signal is output from only one of them, the control is performed by the earlier signal. In order to quickly respond to such a change, the control signal for 30 seconds is prioritized. The comparison reference time for calculating the rate of change of the voltage rising speed is set to 0.4 seconds.

As the predetermined value used for the determination at the temperature rising rate, two values of 2 ° C./minute and 1 ° C./minute are prepared. When the maximum point of the voltage rising rate is detected, the current becomes small. The predetermined value serving as a criterion before the determination is set at 2 ° C./min, and the predetermined value after the current is reduced is set at 1 ° C./min. When the detection of the temperature rise rate is used in this way, the predetermined value serving as a criterion before the maximum point of the voltage rise rate is detected and the current is reduced is a larger value, and the predetermined value after the current is reduced is reduced. The predetermined value may be a smaller value. This is because, after the current is reduced, the temperature rise rate is reduced, and this is more accurately detected to prevent overcharging. Also, the determination of the temperature rising speed before the current becomes small is performed for the same purpose as the detection of the maximum point of the voltage rising speed.

Further, the charging current at the start of charging is 10 amps, the charging current after the maximum point of the voltage rising rate is detected, and the temperature rising rate is 2 ° C./sec before the maximum point of the voltage rising rate is detected. The charging current in the case of exceeding the minute is set to be 3 amps. Thus, these set currents should be the same. Further, the charging current when the battery temperature becomes equal to or higher than the predetermined value before the maximum point of the voltage increasing speed and the predetermined value of the temperature increasing speed are detected is set to 6 amps. This current is preferably set to be larger than the former in order to increase the charging speed.

In the operation explanatory diagram of FIG. 5, a nickel-cadmium secondary battery having a battery voltage of 12 V and a nominal capacity of 1900 mA is used. In this case, the current control operation based on the temperature rising speed and the temperature was not performed, and only the current controlling operation based on the voltage rising speed was performed. The charging time was about 19 minutes. Compared to the conventional method of performing constant current charging at 10 amps and detecting the time point at which the battery voltage rise rate becomes zero to stop charging, the time until the end of charging is increased by about 2 minutes.
The battery temperature after the completion of charging was about 5 ° C. lower than in the conventional case, and the cycle life was extended.

In the operation explanatory diagram of FIG. 6, a nickel-hydrogen secondary battery having a battery voltage of 12 V and a nominal capacity of 3000 mA is used. In this case, a current control operation is performed by detecting a temperature rise because the battery temperature first exceeds 42 ° C., and the charging current is switched from 10 amps to 6 amps. Thereafter, the maximum point of the voltage increasing rate is detected. It has been switched to 3 amps. The charging time was about 25 minutes. Compared with the conventional method of performing constant current charging at 10 amps and detecting the time point at which the battery voltage rise rate becomes zero to stop charging, the time until the end of charging is slightly longer. The voltage was lower than in the conventional case, and the cycle life was extended.

[0048]

According to the present invention, overcharging can be suppressed even when rapid charging is performed by increasing the charging current, and the battery is easy to use, which can reduce the burden on the battery. A charger and a charging method for an alkaline secondary battery can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a charger for an alkaline secondary battery and a charger of a charging method according to the present invention.

FIG. 2 is a flowchart for detecting a maximum value of a battery temperature rising speed.

FIG. 3 is an explanatory diagram of a detection signal.

FIG. 4 is an explanatory diagram of a detection signal.

FIG. 5 is an operation explanatory diagram when a nickel-cadmium secondary battery is charged.

FIG. 6 is an operation explanatory diagram when a nickel-hydrogen secondary battery is charged.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Control apparatus 2 A / D converter 3 Charging circuit 4 Switching element 5 Secondary battery

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H02J 7/04 H02J 7/04 L

Claims (9)

[Claims] 1. A charging circuit, switching means for switching connection between a charging circuit and a battery to be charged, an A / D converter for converting a detected battery voltage into a digital signal, and the A / D converter And a controller that controls the charging circuit and the switching means based on the digital signal input from the controller, wherein the controller operates to detect the maximum point of the voltage rising speed, and A battery charger for an alkaline secondary battery, wherein the charger circuit is controlled so as to reduce a charging current when detecting a battery. 2. A battery temperature detecting means, wherein the control device operates to detect a temperature rising rate based on the temperature detected by the battery temperature detecting means, and detects a maximum point of the voltage rising rate before detecting the maximum point. When the temperature rising speed exceeds a predetermined value, the charging circuit is controlled to reduce the charging current, and when the temperature rising speed exceeds the predetermined value after detecting the maximum point of the voltage rising speed, 2. The charger for an alkaline secondary battery according to claim 1, wherein the controller controls the charging circuit so as to stop charging. 3. The control device according to claim 1, wherein the control device detects a voltage rising speed at first, and detects a maximum point of the voltage rising speed when the voltage rising speed becomes a predetermined magnitude. Item 3. The charger for an alkaline secondary battery according to Item 1 or 2. 4. The control device according to claim 1, wherein the controller determines that the maximum point of the voltage rising speed has been reached when the time rate of change of the voltage rising speed has become 0 or less for a predetermined time. 4. The charger for an alkaline secondary battery according to 2 or 3. 5. The charger for an alkaline secondary battery according to claim 4, wherein the comparison reference time for calculating the voltage rising rate is longer than the comparison reference time for calculating the rate of change of the voltage rising rate. . 6. The alkaline secondary battery according to claim 1, wherein the control device has two or more comparison reference times for detecting a voltage rising speed. Battery charger. 7. The control device according to claim 1, wherein the control device controls the charging circuit so that the charging current becomes 3 C or less when a maximum point of the voltage rising speed is detected. 7. The charger for an alkaline secondary battery according to claim 4, 4, 5, or 6. 8. The control device detects the maximum point of the voltage rising speed and reduces the charging current.
The charging circuit is controlled so that charging is stopped or a trickle charging state is detected when the charging becomes negative.
The charger for an alkaline secondary battery according to the above. 9. First, charging is performed with a current larger than 3C, thereafter, the maximum point of the voltage rising speed is detected, the charging current is reduced so as to be a current of 3C or less, and then the battery is fully charged. A charging method for an alkaline secondary battery, wherein charging is stopped or trickle charging is detected.