JP2928438B2 - Rechargeable battery charging method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging control method for a secondary battery used in portable electronic equipment such as a notebook personal computer.

2. Description of the Related Art In recent years, with the spread of battery-operated electronic devices such as notebook personal computers and portable word processors, there has been a demand for extending the operating time and the life of rechargeable secondary batteries. Nickel-cadmium batteries, nickel-metal hydride batteries, etc. are used as secondary batteries, but when such a secondary battery is charged, it is accurately detected that the battery is fully charged, and if the charging is not stopped, the battery will deteriorate. I will. For this reason, a method for accurately determining the full charge is desired.

[0003]

2. Description of the Related Art FIG. 12 shows a charging voltage curve and a temperature curve of a secondary battery. The vertical axis represents voltage (V) and temperature (° C.), and the horizontal axis represents time (t).

[0004] A charge voltage curve (shown by "a") in FIG. 12 shows that a voltage drop of .DELTA.V (shown by -.DELTA.V) is detected after charging progresses and the charge voltage reaches a peak value (shown by "p"). It is determined that the battery is fully charged. In the detection of -ΔV, the voltage drop can be clearly detected particularly in the case of a nickel-cadmium battery. However, in the case of nickel-metal hydride batteries,
Since the value of the voltage drop is small, there is a possibility that overcharging may occur if the method of detecting -ΔV is used in the same manner, in which case the battery is deteriorated and the life is shortened.

To cope with this, a method of detecting full charge by using a temperature curve of a secondary battery as shown in FIG. 12 is used. This method is used particularly for charging a nickel-metal hydride battery, and incorporates a temperature sensor inside the battery to detect the battery temperature when charging the nickel-metal hydride battery. When the detected temperature is close to full charge, the temperature rise (+ Δ
T) occurs and is detected to determine that the battery is fully charged.

[0006]

The above-described method for detecting the battery temperature has the following problems. Low temperature (for example, 0 ° C) for electronic devices such as notebook computers
When the nickel-metal hydride battery inside the equipment is charged by moving from the state of being left in the environment to the room normal temperature (for example, 25 ° C.) environment before the nickel-metal hydride battery is fully charged, The rise (+ ΔT) may be detected.

[0007] An electronic device is placed near a window or a heating device (for example, CR
If the nickel-metal hydride battery in the electronic device is charged in a state where the nickel-metal hydride battery is placed near the (T display), the temperature rise (ΔT) may be erroneously detected before the nickel-metal hydride battery is fully charged.

[0008] Hard disk and CPU inside electronic equipment
The full charge of the nickel-metal hydride battery cannot be detected normally due to the influence of heat from the battery, and the temperature rises before the battery is fully charged (+ ΔT)
Or the rise in temperature (+ ΔT) cannot be detected.
The possibility of overcharging comes out.

Since the temperature of a nickel-metal hydride battery rises near full charge, even when the temperature rise (+ ΔT) is accurately detected, the battery is overcharged at that time. Also, the charging voltage is measured and the voltage drop at full charge (-ΔV)
As described above, there is a problem that overcharging occurs when charging a nickel-metal hydride battery.

It is an object of the present invention to solve these problems and to provide a secondary battery charging method capable of accurately detecting a fully charged state.

[0011]

FIG. 1 is a block diagram showing the principle of the present invention. In FIG. 1, 1 is a charge controller, 10
Is a voltage detecting means, 11 is a voltage change rate calculating means, 12 is a change rate drop detecting means, 13 is a counting means, 14 is a charging control means, 2 is a storage means having an area for storing each data of 2a and 2b, 2a is an area for storing the voltage values detected this time and the previous time, 2b is an area for storing the change rate composed of the voltage changes of the previous time and this time, and 3 is a secondary battery such as a nickel-cadmium battery or a nickel-metal hydride battery. is there.

The present invention detects the voltage of the charging voltage of the secondary battery, detects that the change in the rate of change drops, and counts each time the detection is performed. Is what you do.

[0013]

When charging power is supplied to the secondary battery, the charging voltage is detected at regular intervals by the voltage detecting means of the charging controller, and the detected voltage value is stored in the storage means. 2a. In the area of the voltage value 2a, not only the voltage value detected this time but also the voltage value detected last time is stored. Next, voltage change rate calculating means 11
Also, it operates at a constant period according to the operation of the voltage detecting means 10 to calculate the voltage change rate. That is, the change (gradient of change) between the previous voltage value and the current voltage value in the voltage value 2a of the storage means 2 is calculated to obtain positive and negative change rates, and the change rate 2b area in the storage means 2 is obtained. Store.

In the area of the change rate 2b, the change rate obtained last time is stored together with the change rate obtained this time. Thereafter, when the change rate drop detecting means 12 is activated, the storing means 2
The change rate of the previous time in the area of the change rate 2b is compared with the current change rate, and if it is found that the current change rate is smaller, the counting means 13 is driven to perform +1 counting.

The counting means 13 responds to this by changing the count value to +
1 is done. When the detection output of the change rate drop is sequentially generated by the periodic operation and the count value in the counting means 13 reaches a predetermined value, the output of the count value drives the charge control means 14 as the output of the full charge detection. The charging control means 14 performs control to stop charging.

[0016]

FIG. 2 is a block diagram of an embodiment. In FIG. 2, reference numeral 20 denotes an AC adapter to which AC 100 V is input to generate a DC voltage, reference numeral 21 denotes a secondary battery such as a nickel-metal hydride battery, and reference numeral 22 denotes a DC-DC converter, and a DC voltage from the AC adapter 20 via a diode D1. Is input or when power is not supplied from the AC adapter 20 (when used in a portable destination), a DC voltage from the secondary battery 21 is input via the diode D2, and the output is a data device (not shown). And a charging voltage for charging the secondary battery 21 when the secondary battery 21 is discharged.

Reference numeral 23 denotes a charge controller for controlling charging of the secondary battery, and a control operation is performed by a program in a processing unit 23a having a built-in CPU, RAM, ROM and the like. 23b in the charge controller 23 is a switch control unit, 23c is an A / D converter for charge voltage, and 23d is not essential, but is provided to prevent a situation where full charge cannot be detected due to a change rate of the charge voltage. The A / D converter 23e for detecting the battery temperature outputs the signal of one cell voltage to the A-D converter.
This is an AD converter for performing D-conversion.

Reference numeral 24 denotes a charge switch, which is started by a switch control unit 23b in the charge controller 23,
ON / OFF is controlled according to the end. When the charging voltage is input to the charging voltage A / D converter 23c as it is, the operating voltage becomes higher than the operating voltage of the A / D converter 23c, and the A / D conversion function does not work properly. This is a voltage shift circuit for shifting to a lower level.

In the secondary battery 21, there are provided a temperature sensor 21a composed of a thermistor or the like, and a one-cell voltage generator 21b for outputting a voltage generated by one cell when the secondary battery 21 is composed of a plurality of cells. Have been.

Before explaining the processing operation according to the embodiment, the operation principle of the full charge detection by the charge voltage waveform according to the present invention will be described with reference to FIG. FIG. 3 is an explanatory diagram of the operation principle of the full charge detection. FIG. 12 shows a portion near a full charge of a charging voltage curve when an empty secondary battery is charged at room temperature, and is a curve near a peak of the entire curve shown in FIG. A. When the charging voltage changes according to the charging voltage curve shown in (1), the voltage values of the points a, b, c, d, and e are sequentially detected at a fixed cycle, and the difference from the previous voltage value is obtained at each time point. As a result, the inclination (rate of change) of the tangent to each point is obtained. This change rate is represented by ΔV / Δt (Δt is a fixed time, ΔV is a voltage change value). Corresponds to the first derivative of the curve.

FIG. Is A. Is a voltage change rate curve in which the vertical axis represents the rate of change (ΔV / Δt) at each point determined by the above equation, and the horizontal axis represents time. Corresponds to the time of the same sign. B. According to the voltage change rate curve, the change rates of the points a and b are positive and large numbers, but the change rate decreases at the point c, becomes almost zero at the point d, and further becomes negative at the point e. Is the rate of change of

C. of FIG. Represents the operation of full charge detection by a voltage conversion rate curve, This is a change rate curve similar to that described above. When it is detected that the change rate curve has become smaller than the previous change rate, counting is started, and counting is performed at each falling detection operation in each cycle, so that the count value becomes a constant value. When it becomes full, it will be fully charged. In addition, C. of FIG. The operation cycle of another A. And B. Are shorter than the periods of points a, b, c,.

FIG. 4 is a processing flow of the full charge detection. This process is executed at regular intervals during the charge control in the processing unit 23a of the charge controller 23 in FIG. When the process starts, the charging voltage of the secondary battery 21 in FIG.
A voltage is detected from the output that has been A / D converted by the D conversion unit 23c (S1 in FIG. 4). This voltage value is stored in a buffer (provided in the RAM) in the processing unit 23a. next,
The voltage change rate (same as the change value) is calculated (S2 in FIG. 4). This voltage change rate is calculated using the current A / D conversion value stored in the battery and the last A / D conversion value obtained by detecting the previous cycle operation and also stored in the buffer. -The previous A / D conversion value. The obtained voltage change rate is also set as the current change rate in the buffer (S3 in FIG. 4).

Next, the change in the rate of change is calculated (S
4). This calculation uses the previous change rate and the current change rate stored in the buffer in advance, calculates “current change rate−previous change rate”, and uses the result to determine whether the current change rate is smaller than the previous change rate. It is determined (S5). That is, it is determined whether the result of the above calculation is negative, and in the case of YES, the count value of the full charge counter (a specific area allocated to the RAM in the processing unit 23a in FIG. 2) is incremented by 1 (FIG. 4). S8). Thereafter, it is determined whether or not the full charge counter value has reached 3 (S9), and if it has reached, the charging is stopped as a full charge state (S10), and the process is terminated.

In S5, if the current change rate does not become smaller than the previous change rate, the full charge counter is set to "0".
(S6). If "0", the process ends. If not, the full charge counter is decremented by one (S6).
7), end the processing. The reason why the full charge counter is decremented by one is to prevent false detection of full charge by decreasing the value of the full charge counter when the change rate increases after the change rate decreases due to noise or the like.

When charging a secondary battery such as a nickel-cadmium battery or a nickel-metal hydride battery, if the remaining battery is more than half as shown in FIG. 3 instead of an empty secondary battery, or if the environmental temperature is high, FIG. 5 shows the state when the battery is charged.

FIG. 5 shows the curves when the gradient of the charging voltage change rate does not become positive. In the case where the remaining battery charge is large or the charging is performed at a high temperature as shown in FIG. And a charging voltage change rate curve (change of ΔV / Δt with respect to time t) as shown in FIG. B. of FIG. In the case shown in FIG. 5, the change (gradient) of the voltage change rate changes from positive to negative. As shown in (2), the change in the voltage change rate does not become positive, but starts counting from the time when it starts to become negative, and when it becomes +3, the full charge is detected by the processing of FIG.

The processing flow of the full charge detection shown in FIG. 4 is executed at a cycle (Δt) corresponding to the charging speed. However, since the charging voltage does not change much in a short time, the cycle is set to 2 minutes (1
20 seconds), and the detection process is performed. However, in this cycle, if there is a possibility that the detection of the full charge is shifted from the point of the actual full charge state and becomes overcharged, the accuracy of the full charge state detection shown in FIG. A method can be used.

In the example of FIG. 6, “dt” is set to 2 minutes, and 2
The voltage change “dV / dt” at each minute interval is obtained. By shifting such a voltage change by 30 seconds, the time indicated by the mark ● is set as the starting point, and the time indicated by the mark ○ is set as the calculation execution time.
DV1 / dt, dV2 / dt, dV3
/ Dt and dV4 / dt are obtained, and the accuracy can be improved by using these values. In this case, the processing flow of the full charge detection in FIG. 4 is executed at intervals of 30 seconds.

FIG. 7 is an overall processing flow of the charge control. This processing flow is executed by the charge controller shown in FIG. 2, and the full charge detection processing shown in FIG. 4 is partially executed. In the overall charge control, a charge characteristic used for detecting a full charge of the secondary battery shown in FIG. 8 is used.

FIG. Is the characteristic of the voltage change rate curve from the start of charging to full charge. As shown in the figure, the charge voltage change rate at the start of charging and near full charge is smaller than before, so it is necessary to distinguish between the two. . Therefore, the detection of the full charge is not performed until a certain time (time t1 in FIG. 8A) from the start of charging. This time t1 is, for example, 5
Minutes. Further, after a fixed time t1 from the start of charging, the full charge detection is performed after the charging voltage change rate becomes larger than the previous time.

FIG. FIG. 7 is a diagram showing voltage curves near the start of charging of a battery with a large remaining battery (battery capacity close to full charge) and an empty battery (discharged battery). An empty battery is shown by a solid line, and a battery with a large remaining battery is shown by a dotted line. As shown in the figure, in the case of a fully charged battery, a fixed time (t1) from the start of charging.
Since the voltage difference between the battery voltage after the lapse of time and the battery voltage after the lapse of the time t2 is + ΔV2 or more, when this state is detected, it can be determined that the battery is fully charged.

Here, the overall processing flow of the charging control shown in FIG. 7 will be described. First, the process waits for a mask time at the start of charging (S1 in FIG. 7). This processing is performed in accordance with the process shown in FIG.
This is because the erroneous detection of full charge is performed until the time t1 from the start of charging shown in FIG.
When the mask time elapses, voltage detection is performed (S2), and it is determined whether or not a sharp voltage rise has occurred using the detected voltage (S3). If there is a sharp rise (the voltage difference is + ΔV2 or more), B. in FIG. Full charge control (charging is stopped) based on the characteristics shown in (1) that the battery is fully charged.
(S9). If there is no sharp rise, the voltage change rate is calculated (S4).

Next, full charge detection is determined using the voltage change rate obtained by the calculation (S5). In this determination process, the process using the full charge counter in S5 to S9 in FIG. 4 is performed, and when it is determined that the battery is fully charged, the full charge control is performed (S9 in FIG. 7, S10 in FIG. 4). Corresponding to). If no full charge is detected in step S5,
Monitoring temperature where battery temperature is predetermined (for example, 50 ° C)
Is determined (S6 in FIG. 7), and if it is higher, it is determined that the battery is fully charged and charging is stopped (S9).

In this determination, when the full charge is not detected in S3 and S5, when the temperature rise of the battery becomes higher than the monitoring temperature, the battery is prevented from being overcharged and the battery is prevented from being deteriorated. This is performed in order to suppress adverse effects on peripheral devices due to a rise in temperature. In the configuration shown in FIG. 2, this temperature rise is caused by the output of the temperature sensor 21a in the secondary battery 21 being used for the temperature A of the charge controller 23.
It can be detected by monitoring the output of the -D converter 23c.

If the battery temperature is not high, it is determined whether the voltage detected this time is lower than the voltage detected last time (S7 in FIG. 7). This determination corresponds to a case in which a full charge is detected when it is detected that the charge voltage has dropped (−ΔV) in the charge voltage curve of the secondary battery (see FIG. 12). If a drop in the charging voltage is not detected, it is further determined whether or not the charging time has exceeded a preset charging time (S8 in FIG. 7), and if it has, charging is stopped. The charging time is set in advance to a time statistically obtained by an actual charging operation.

Although not included in the processing flow of FIG.
In addition, the full charge can be determined using the characteristics shown in FIGS. FIG. 9 shows a charging voltage, a charging voltage curve, and a voltage change rate curve. The vertical axis represents voltage (V) and voltage change rate (ΔV / Δt), the horizontal axis represents time (t), and the solid line represents the charging voltage curve. The dotted line represents the voltage change rate curve. As shown in this figure, the detected voltage at a fixed time (t1) from the start of charging is compared with the detected voltage immediately after that, and when the difference becomes a fixed voltage (+ ΔV1), the charging voltage change rate becomes It can be determined that the battery is fully charged when it becomes smaller than before.

FIG. 10 shows the relationship between the battery capacity and the charging voltage. The vertical axis represents the battery voltage (V), the horizontal axis represents the battery capacity (Q), and the maximum capacity of the battery is taken as 100%. Unit. As shown in this curve, the voltage becomes higher as the capacity (charge amount) of the secondary battery is closer to full charge, and a voltage at which full charge can be determined is V1 (this is referred to as a full charge determination reference voltage). When a new battery is installed, the installed secondary battery is charged at the full charge determination reference voltage (V1).
If it is higher, it can be determined that the battery capacity is close to full charge.

Next, a method of obtaining the full charge judgment reference voltage (V1) used for judging full charge shown in FIG. 10 will be described with reference to the configuration of the above embodiment (FIG. 2) and FIG. FIG.
Reference numeral 1 denotes a configuration in which a secondary battery such as a nickel hydrogen battery has a plurality of cells connected in series. A configuration for taking out the voltage of one cell inside the battery is provided, and this configuration is a one-cell voltage generation unit 21b in FIG. 2, and the voltage for one cell generated from this (referred to as v1) is charged to the charge controller 2
3 is inputted to the A / D converter 23e, and the one-cell voltage value converted into the digital value is supplied to the processor 23a.

On the other hand, the current battery voltage (V) generated from all the cells of the secondary battery shown in FIG. 11 is converted into a digital value by the A / D converter 23c through the voltage shift circuit 25 of FIG. It is supplied to the processing unit 23a. By dividing this battery voltage V by the voltage v1 for one cell, the number of cells (n) of the secondary battery 21 can be known. The number n of cells is multiplied by a full charge determination reference voltage per cell (which can be obtained in advance according to the specifications of the secondary battery) to obtain a full charge determination reference voltage V1 (for all cells) of the secondary battery (for all cells). 10 (see FIG. 10).

[0041]

According to the present invention, when charging a secondary battery, it is possible to normally detect a full charge regardless of whether the battery is an empty battery or a battery having a remaining capacity near full charge. This makes it possible to prevent battery deterioration due to overcharge of the secondary battery (particularly nickel-metal hydride battery) and heat generation due to overcharge.

[Brief description of the drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is a configuration diagram of an embodiment.

FIG. 3 is an explanatory diagram of the operation principle of full charge detection.

FIG. 4 is a processing flow of full charge detection.

FIG. 5 is each curve when the slope of the charging voltage change rate is not positive.

FIG. 6 is an explanatory diagram of a method for improving the accuracy of detection of a fully charged state.

FIG. 7 is an overall processing flow of charge control.

FIG. 8 is a diagram showing charging characteristics used for detecting a full charge of a secondary battery.

FIG. 9 is a diagram showing a charging voltage, a charging voltage curve, and a voltage change rate curve.

FIG. 10 is a diagram showing the relationship between battery capacity and charging voltage.

FIG. 11 is a diagram showing a configuration of a secondary battery in which a plurality of cells are connected in series.

FIG. 12 is a diagram showing a charging voltage curve and a temperature curve of a secondary battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Charge controller 10 Voltage detection means 11 Voltage change rate calculation means 12 Change rate drop detection means 13 Counting means 14 Charge control means 2 Storage means 2a Voltage value 2b Change rate 3 Secondary battery

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Shuichi Kano 4-49 Fukami Nishi, Yamato-shi, Kanagawa Prefecture PF Yamato Factory Co., Ltd. (56) References JP-A-4-217826 (JP, A) Hei 4-190640 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) H01M 10/42-10/48

Claims (4)

(57) [Claims] 1. A charging system for a secondary battery used as a power source of a portable electronic device, comprising: a voltage controller for detecting a charging voltage of the secondary battery by a charge controller for controlling charging of the secondary battery; Charge control means for controlling the supply or stop of the charging voltage to the battery, and storage means for storing the voltage value detected by the voltage detection means.
Find the difference from the previous voltage value stored in the storage means
The rate of change in voltage is calculated and stored in the storage means.
The calculation means and the newly calculated voltage change rate
When it detects that it has fallen below the rate of change, it counts +1 and
If the descent is not detected, the counting means for counting -1 is driven.
Change rate drop detecting means and counting means are predetermined.
A charging method for a secondary battery, wherein the charging control means is driven to be in a fully charged state when it is detected that a numerical value has been reached . 2. The method according to claim 1, wherein a period (T) of the detection operation of the rate-of-change drop of the charging voltage includes:
Each of the multiple (n) detection operations is executed for a fixed time (T
/ n) The secondary battery is characterized in that it detects each of the plurality of detected change rates in the storage means and detects a drop in the change rate by maintaining the respective cycles while shifting each of the detected cycles. Charging method. 3. The method according to claim 1, wherein the charging voltage is not detected until a predetermined time (t1) has elapsed after charging of the secondary battery is started, and the charging voltage value detected after the predetermined time is equal to the previous voltage. A charging method for a secondary battery, wherein the charging control means is driven when the voltage is equal to or more than a fixed voltage (+ ΔV1) from the value, and the battery is in a fully charged state. 4. The rechargeable battery according to claim 1, further comprising: a one-cell voltage generator for generating a voltage for one cell inside the secondary battery, wherein the charge controller controls a voltage from the one-cell voltage generator and a current battery voltage. The number of cells constituting the secondary battery is determined based on the above, and a full charge determination reference voltage is set according to the number of cells. If the voltage detected at the start of charging of the secondary battery is higher than the full charge determination reference voltage, And charging the secondary battery by stopping the charging by driving the charging control means assuming that there is a charging capacity close to full charge.