JPH05244729A - Method of charging battery - Google Patents

Abstract

PURPOSE:To prevent overcharging and permit efficient charging within a short period of time by a method wherein fuzzy inference is effected from the difference between the ambient temperature and the battery temperature and the increasing rate of a voltage to control the cutting rate of a switching circuit and infer the finishing time of charging. CONSTITUTION:A/D conversion is effected by obtaining the temperature of a battery 1 to be charged by a sensor 5 and obtaining the ambient temperature by another sensor 7 to convert them into voltages through a converter 4. The battery 1 is charged by putting a DC current, obtained by rectifying AC from an AC wiring through a power supply circuit 2, ON/OFF by a switching circuit 6. The terminal voltage of the battery is also converted through an A/D converter 8. A control unit 3 effects the fuzzy inference of a charging current from the temperature of the battery 1, the ambient temperature and the voltage of the battery 1 upon starting charging to obtain the cutting rate of the switching circuit 6 and start charging. The fuzzy inferring is effected by the difference between the battery temperature and the ambient temperature and the increasing rate of the voltage of the battery to control the cutting rate of the switching circuit during charging. At the same time, the finishing time of the charging of the battery is inferred. According to this method, the overcharging of the battery can be prevented and quick charging can be effected efficiently.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a method of charging a battery such as NiCd or Ni hydrogen used in a portable device such as a video camera or a mobile phone.

[0002]

2. Description of the Related Art Conventionally, standard charging (charging in about 12 to 14 hours) and rapid charging (several tens)
There is a method of charging from 5 minutes to 5 hours. This difference is the difference in the supply current for charging, but in the case of quick charging, charging is completed in a short time, but if the completion of charging is not detected promptly, the battery temperature rises rapidly and internal gas This causes an increase in pressure and causes deterioration of the battery.

FIG. 6 shows the relationship between the ambient temperature and the maximum allowable current. Here, CmA is a time rate current in the unit of current during charging, that is, when charging a discharged battery, the current value when charging for 10 hours is 0.1 CmA.
In the following, charging with a current value NCmA is referred to as NC charging, and conversely discharging with a current value NCmA is referred to as NC discharge.

The maximum allowable charging current is determined by
This is because the gas generated inside the battery during charging increases, and the lower the temperature and the higher the charging current, the higher the equilibrium gas pressure. When the gas pressure becomes high, the battery is deteriorated due to breakage of the battery sealing mechanism. FIG. 7 shows the relationship between this gas pressure and temperature. This is because when the temperature becomes low, the gas consumption reaction of the cathode decreases and the gas pressure increases. Therefore, it is necessary to keep the charging current low at low temperatures. Further, when the charging is continued beyond the completion of the charging, the heat generated by the gasification reaction causes a rapid temperature rise of the battery and similarly accelerates the deterioration of the battery.

Although it is best to finish charging the battery in a short time, it is not possible to simply increase the charging current due to the above factors.

The easiest way to overcome this is to stop charging immediately when the battery is fully charged. Conventionally, there is a slight voltage drop when the battery is fully charged. A charging method called a minus delta buoy system that utilizes the characteristic of occurrence (for example, Japanese Patent Laid-Open No. 59-
194640, U.S. Pat. No. 4,354,148, U.S. Pat. No. 4,387,332, etc.) and a method of detecting the state of charge by measuring the change in the heat generation temperature of the battery itself (for example, Japanese Patent Laid-Open No. 59-6731). (See Japanese Patent Publication) and the like were adopted.

[0007]

However, such a conventional method has the following problems.

1) It is originally desirable that the charge allowable current value be changed depending on the ambient temperature.

2) Regarding the increase in gas pressure and the rise in internal temperature, the temperature rise characteristic is slightly behind, and the actual temperature detection delay is added to this. Therefore, an increase in gas pressure is unavoidable to some extent. The effect is particularly great during rapid charging.

3) The battery internal temperature and the battery terminal voltage cannot be uniquely determined as a criterion because they change with the ambient temperature as a parameter.

[0011]

The present invention has been made in view of the above points, and a first feature thereof is a first membership function indicating the high and low of the ambient temperature of the battery and the battery. To the second member-ship function indicating the magnitude of the charging current with respect to the first step of deriving a first inference result regarding the charging current which is fuzzy inferred, and a third member indicating the level of the battery voltage. A second inference result regarding the charging current which is fuzzy inferred from the correlation between the ship function and the second member ship function;
It consists of a step and a third step of determining an optimum charging current value for the battery from the position of the center of gravity of the logical sum of the first and second inference results.

The second feature is that the correlation between the first membership function indicating the change amount of the battery voltage at each predetermined time and the second membership function indicating the cut rate of the charging current for the battery is obtained. A first step of deriving a first inference result relating to the fuzzy inferred cut rate of the charging current, a third membership function indicating the amount of change in temperature of the battery for each predetermined time, and the second membership. The second step of deriving a second inference result regarding the cut rate of the charging current which is fuzzy inferred from the correlation with the function, and the optimal cutting of the charging current from the position of the center of gravity of the logical sum of the first and second inference results. And the third step of determining the rate.

A third feature is that the charge completion prediction is fuzzy inferred from the correlation between the first membership function related to the voltage when the battery is discharged and the second membership function related to the battery charge completion expected time. A first step of deriving a first inference result regarding time, a third membership function indicating a voltage during charging of the battery, and the second step.
The second step of deriving a second inference result regarding the expected completion time of charging, which is fuzzy inferred from the correlation with the membership function of, and the charging of the battery from the center of gravity position of the logical sum of the first and second inference results. It consists of the third step of determining the expected completion time.

[0014]

Since the present invention is configured as described above, the optimum charging current is set regardless of the battery, and it is possible to prevent the deterioration of the battery which is likely to be caused by quick charging, and the user can set the charging completion time in advance. It is possible to obtain the optimal charging system by presenting it.

[0015]

FIG. 1 shows an embodiment to which the present invention is applied, in which the AC voltage of indoor wiring is converted into a direct current (charging current) suitable for charging a battery (1) to be charged, which is a NiCd battery, for example. A power supply circuit (2) for converting and outputting, a switch means (6) comprising, for example, a switching transistor for controlling the supply of the charging current output from the power supply circuit (2) to the battery (1), A first temperature sensor (5) for detecting the temperature of the battery (1) itself, a second temperature sensor (7) for detecting the ambient temperature of the battery (1), and both temperature sensors (5) Temperature detection voltage conversion circuit (4) that outputs a voltage value corresponding to the detection temperature of (7)
And an A / D converter (8) for analog-digital converting the output of the conversion circuit (4) and the voltage value of the battery (1).
And a control unit (3) which controls the charging current output from the power supply circuit (2) based on the output from the A / D converter (8) and the on / off control of the switch means (6). )
With.

The control unit (3) specifically, based on the voltage value of the battery (1), the temperature of the battery (1) itself and the ambient temperature of the battery (1), a charging current value at the start of charging and The cut rate of the charging current during charging is fuzzy inferred to control the output current value of the power supply circuit (2) and infer the expected charging time.

Next, the decision rules for each of the above fuzzy inferences will be described.

<Rules for determining the charging current value at the start of charging>
First, the rule for determining the charging current will be described. The charging current value is inferred using the ambient temperature and the battery (1) voltage as parameters. Specifically, inference is performed based on the following description.

If ambient temperature is low: charging current is slightly low Ambient temperature is slightly low: charging current is slightly low Ambient temperature is medium: charging current is medium If ambient temperature is slightly high: charging current is slightly High If ambient temperature is high: charging current is slightly high Battery voltage is low: charging current is high Battery voltage is low: charging current is slightly high Battery voltage is medium: charging current is medium If it is a little high: the charging current is a little low. If the battery voltage is high: The charging current is a low temperature is high or low. It is an abstract expression.
However, if you compare it as a numerical value, "high" is
The ambient temperature is 40 ° C or higher, and conversely “low” means −10 ° C or lower.
Temperature set and set in equal intervals and detected by the sensor (7)
It should correspond to the membership function corresponding to. Well
About battery voltage "High" means per battery unit cell
Voltage is 1.3V or more, conversely "low" is 1.2V or less
And divide it into equal parts. Further charging current
About "high" is 0.35C, "low" is 0.05
It is set to C and this space is equally divided.

Thus, FIG. 2A shows the membership function concerning the ambient temperature, FIG. 2B shows the membership function concerning the battery (1) voltage, and FIG. 2C shows the membership function concerning the charging current. Show.

In FIG. 2, for example, the ambient temperature is T (° C.)
Then, if the battery voltage is v (V), from the above-mentioned rule, the conditions are satisfied: if the ambient temperature is medium: the charging current is medium, and if the battery voltage is slightly high: the charging current is slightly low. The area (X) in FIG. 2C is obtained as a logical product from the first condition. Similarly, from the following conditions, the area (Y) in FIG. 2C is obtained as a logical product. As a result, the charging current (medium) corresponding to the position indicated by the barycentric position (G in the arrow) of the logical sum of area (X) and area (Y) is set as the optimum value. (This is called the min-max centroid method) In this example, "high" is charged at 0.35C and low is 0.0
Since it is decided to charge 5C, in the case of the example, it is about 0.1.
It becomes 7C charge.

<Rules for Determining Charging Current Cut Rate during Charging> Next, rules for determining a charging current cut rate will be described. The determination routine is executed by setting a predetermined time interval (several tens of seconds to several minutes) after starting charging with the charging current determined by the above-described rule. The timing of execution will be described later based on the flowchart of FIG.

First, as a parameter, the difference between the temperature of the battery (1) itself and the ambient temperature and the amount of change in the voltage of the battery (1) (actually, the amount of change in voltage for each predetermined time (several tens of seconds to several minutes),
In the following, it will be simply referred to as voltage difference), and based on this, the completion of charging is inferred. Specifically, the membership function is determined based on the following description.

Zero voltage difference: Charge current decrease, Voltage difference slight increase: Charge current slight decrease, Voltage difference increase (+): Current charge current continues Voltage difference decrease (-): Charge stop, Large temperature difference: Charge stop, Temperature difference: Charge current Decrease Temperature difference Slightly: Current charging current continues No temperature difference: Current charging current continues The above "voltage difference increase" means a voltage increase of 0.01 V or more, and such a voltage increase is within the range of normal charging. Indicates. Then, when the charge exceeds about 100%, there is a tendency of saturation, which is "a slight increase in voltage difference (about 0.005 V)". From here, the charging current is gradually reduced. The temperature rise is similar to the tendency of the voltage, but the temperature rise of the battery starts around 100%. When the rise becomes large, charging is stopped. In addition, "large" in the temperature difference
Means 10 ° C. or higher, “presence” means about 7 ° C., “slightly present” means about 3.5 ° C., and “none” means 0 ° C. or lower.

From the above relationships, FIG. 3 (a) shows the membership function relating to the battery voltage difference, FIG. 3 (b) shows the membership function relating to the temperature difference, and FIG. 3 (c) shows the membership function relating to the charge current cut rate. Indicates a function. Here, when the tendency of the decrease of the charging voltage is observed, the correction of the charging current and the stop (completion) of the charging current are determined in relation to the increasing tendency of the surface temperature of the battery. Dynamic determination is possible by observing both the voltage change and temperature change trends.

For example, in the figure, in the pattern of inference of the change of the charging current when the voltage difference v (V) and the temperature difference T (° C.), when the voltage difference is v, the membership function is a function of “slight increase in change”. Then, the area (X) of the pattern of “slight decrease” of the charging current is selected. Regarding the temperature difference T,
The temperature rises hit "none" and "somewhat", but in this case, since they are logical products, the membership function of "none" is selected, and the area (Y) of the pattern "maintain the current state" is selected. (Dotted line α in the figure) As a result, the center of gravity position of the logical sum of area (X) and area (Y) (G in the arrow)
The charging current corresponding to the place indicated by is set as the optimum value. In this case, a slight decrease in charging current is selected.

In FIG. 3 (c), it is possible to consider, for example, what kind of numerical value represents from the current state maintenance to the stoppage as follows. That is, the rate of decrease with respect to the current charging current is indicated by (%).

Maintain the current state 0 (%) decrease Stop 100 (%) decrease The period is defined on a logarithmic scale. In this way, the range of slight decrease is about 10%, and the range from decrease to stop is 11%.
It can be set to a logarithmic scale of 99% reduction. Applying this as an example, the charging current is reduced by about 5%.

<Rules for Determining Charge Completion Estimated Time> Next,
A method of determining the expected charging time calculated at the start of charging will be described. First, the switch circuit (6) is turned off to form a discharge circuit, and the discharge voltage obtained by correcting the battery voltage during discharge of the battery (1) with the ambient temperature is measured. continue,
The charging circuit is configured by turning on the switch circuit (6), and the voltage of the battery (1) is corrected with the ambient temperature when the charging current suitable for 0.2C is supplied to the battery (1). The measured voltage (charging voltage) is measured. The remaining battery capacity is inferred from the membership function of these two measurement results, and the required charging time (charging completion expected time) is predicted. For example, determine the membership function based on the following description. In addition, here, the discharge voltage was 2 C discharge, and the charge voltage was 0.2 C charge. Further, it is assumed that the charging time required to fully charge the discharged battery is controlled to a maximum of 4 hours.

If the discharge voltage is low: 4 hours charge mode If the discharge voltage is slightly low: 3 hours charge mode If the discharge voltage is slightly high: 2 hours charge mode If the discharge voltage is high: 1 hour charge mode If the charge voltage is low : 4 hours charging mode If the charging voltage is a little low: 3 hours charging mode If the charging voltage is a little high: 2 hours charging mode If the charging voltage is high: 1 hour charging mode "Discharge voltage" here means "high" It is considered that the voltage per unit cell is 1.3 V or more, and conversely, "low" is 1.2 V or less, and the interval is considered to be equally divided. The charging voltage is “high”, which means the voltage per unit cell of the battery is 1.45V.
As described above, conversely, "low" is applied at 1.35 V or less, and it is considered that the interval is equally divided. Of course, the change in voltage value due to temperature is considered to have been corrected.

FIG. 4A shows a membership function relating to the discharge voltage of the battery, FIG. 4B shows a membership function relating to the charging voltage, and FIG. 4C shows a membership function relating to the charging time. For example, when the discharge voltage is slightly higher vo (V) and the charge voltage is slightly lower vi (V), the expected charging completion time is the logical sum of 2 hours charging and 3 hours charging as in the above example, and the charging time is It takes about 2.4 hours at the center of gravity in the figure.

The temperature measurement is further added to the voltage measurement results of the two patterns at the time of charging and discharging, and the remaining battery level is predicted by fuzzy reasoning. A high battery level can be estimated.

Next, these processes will be described with reference to the flow chart shown in FIG. 5 according to the control procedure of the actual battery charging by the control unit (3).

First, in step S1, the switch circuit (6) is turned off to form a discharge circuit, and after a predetermined time, the discharge voltage is measured in step S2. Specifically, it is obtained by correcting the battery voltage value input via the A / D converter (8) with the ambient temperature detected by the second temperature sensor (7). Next, in step S3, the switch circuit (6) is turned on to form a charging circuit, and the power supply circuit (2) supplies a charging current suitable for 0.2 C as a charging current to the battery (1) for charging. Then, the battery voltage at that time is measured in the subsequent S4 step, and the charging voltage is measured by correcting the ambient temperature detected by the second temperature sensor (7). And
In step S5, the estimated charging completion time is inferred based on the above-described rules for determining the estimated charging completion time based on the discharge voltage and the charging voltage measured in steps S2 and S4. The inference result is displayed on, for example, a display unit (not shown).

In the subsequent step S6, the ambient temperature is measured based on the output from the second temperature sensor (7), and the voltage of the battery (1) at this point is measured. Based on the measurement result in step S7. The charging current value at the start of charging is determined by the above-described rule for determining the charging current value at the start of charging, and the voltage value supplied from the power supply circuit (2) to the battery (1) is determined according to the result of this determination.

After that, in step S8, the amount of change in the voltage of the battery (1) and the temperature difference between the temperature of the battery (1) itself and the ambient temperature at that time are measured at predetermined time intervals, and the above measurement is performed in step S9. Based on the result, the charge current cut rate is inferred according to the above-described rule for determining the charge current cut rate during charging, and in the inference result, the cut rate is 0%, that is, when the charge current does not need to be changed,
The processing is returned to the S8 step. If the inference result is not 0% and the charging current needs to be changed, the process proceeds to step S10.

In step S10, it is determined whether or not the charging current cut rate inferred in step S9 is 100%, and if it is determined to be 100%, the charging is terminated.
On the other hand, if it is determined that the charging current cut rate is less than 100%, the process proceeds to step S11, and the charging current value is changed according to the charging current cut rate inferred in step S9.

In the present embodiment, the temperature difference used for inferring the charging current cut rate is the difference between the temperature of the battery (1) itself and the ambient temperature, but this temperature difference is the battery (1) itself at a predetermined time interval. It is also possible to set the temperature rise degree of.

[0039]

As described above, according to the present invention, the parameters (voltage, temperature, etc.) related to battery charging are sequentially measured, and the desired condition is inferred and determined from the result by using fuzzy inference. The optimal battery charging can be realized in time, and the time required for it can be inferred.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an apparatus to which the present invention is applied.

FIG. 2 is a schematic diagram showing a membership function relating to an ambient temperature, a battery voltage and a charging current according to the present embodiment.

FIG. 3 is a schematic diagram showing a membership function regarding a voltage difference, a temperature difference, and a charging current cut rate in the present embodiment.

FIG. 4 is a schematic diagram showing a membership function relating to a discharge voltage, a charge voltage, and an estimated charging completion time according to the present embodiment.

FIG. 5 is a flowchart showing the operation of this embodiment.

FIG. 6 is a graph showing the maximum allowable charging current of a battery.

FIG. 7 is a graph showing the relationship between battery overcharge current and equilibrium gas pressure.

[Explanation of symbols]

 1 Battery to be Charged 2 Power Supply Circuit 3 Control Unit 4 Temperature Detection Voltage Conversion Circuit 5 First Temperature Sensor 6 Switch Circuit 7 Second Temperature Sensor

Claims (3)

[Claims] 1. A charging current which is fuzzy inferred from a correlation between a first membership function indicating a high and low ambient temperature of a battery and a second membership function indicating a magnitude of a charging current for the battery. A first step of deriving a first inference result, and a second step of fuzzy inference based on the correlation between the third membership function indicating the level of the battery voltage and the second membership function.
Second step of deriving the inference result of the above, and the above first and second
And a third step of determining an optimum charging current value for the battery from the position of the center of gravity of the logical sum of the inference result of 1. 2. A charge fuzzy inferred from a correlation between a first membership function indicating a change amount of a battery voltage for each predetermined time and a second membership function indicating a cut rate of a charging current for the battery. A first step of deriving a first inference result regarding the current cut rate, and a correlation between the third membership function indicating the amount of change in temperature of the battery at predetermined time intervals and the second membership function. A second step of deriving a second inference result relating to a more fuzzy inference of the charging current cut rate, and a step of determining an optimal cutting rate of the charging current from the barycentric position of the logical sum of the first and second inference results. A method of charging a battery, which comprises three steps. 3. A first charge-completion expected time, which is fuzzy inferred from a correlation between a first membership function relating to the voltage when the battery is discharged and a second membership function relating to the battery charge-completion expected time. First step of deriving an inference result, and second inference regarding the expected charging completion time, which is fuzzy inferred from the correlation between the third membership function indicating the voltage when the battery is charged and the second membership function. A battery charging method comprising: a second step of deriving a result; and a third step of determining an expected charging completion time of the battery from the position of the center of gravity of the logical sum of the first and second inference results.