JPH0865912A - Battery charger - Google Patents

Abstract

PURPOSE: To provide the charger of a secondary battery where there is neither charge shortage caused by the erroneous judgment of full charge nor overcharge caused by the quick charge of the battery in full charge condition. CONSTITUTION: A temperature differentiator 46 computes the temperature differential value being the temperature rise quantity per the unit time of a secondary battery being sought through a thermistor, an A/D converter 41, and a battery temperature calculator 43, and a second order differentiator 55 seeks the second derivative of the temperature being the variation per unit time of this temperature differential value. When a comparator 54 judges that the temperature differential has reached a set value, a comparator 56 determines the sign of the second derivative of the temperature, including zero. Based on the result of its judgment, a charge controller 50 terminates the quick charge when the second derivative of the temperature is positive at the point of time when the temperature differential value has reached the set value, and performs the control to continue the quick charge when the second derivative of the temperature differential is zero or negative.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for a secondary battery, and more particularly to a charging device suitable for rapid charging of an alkaline secondary battery such as a nickel-cadmium secondary battery or a nickel-hydrogen secondary battery.

[0002]

2. Description of the Related Art In a quick charger for charging a secondary battery in a short time, it is judged that the battery is fully charged, and the rapid charging is terminated. Various methods for determining full charge have been considered, one of which is the temperature differential detection method.
This utilizes the temperature differential of the battery, that is, the temperature rise amount per unit time rapidly increases at the end of charging, and it is determined that the battery is fully charged when the temperature differential reaches a set value, for example, 1 ° C / min. It is a method to do.

By the way, in this temperature differential detection type quick charger, it is usual that the determination of full charge by temperature differential detection is not performed for a fixed time (for example, 5 minutes) from the start of the rapid charge. For example, when a battery used outdoors (eg, 0 ° C.) is brought indoors (eg, 25 ° C.) for quick charging in a cold area such as a ski resort, the battery temperature and the ambient temperature are initially different from each other. Because the temperature difference is large, the amount of temperature rise per minute exceeds 1 ° C. even immediately after the start of charging, and it may be determined that the battery is fully charged even though it is not fully charged. In such a case, the battery is naturally insufficiently charged.

Further, in this temperature differential detection method, the same problem may occur when the battery pack is heated by the heat generated by the charger and the battery temperature rises due to the heat. That is, the amount of heat generated by the charger increases immediately after the start of rapid charging, and the battery pack is affected by the swaying heat, and the amount of temperature rise of the battery per minute exceeds 1 ° C. However, there are cases where it is determined that the battery is fully charged, and in such a case, the battery will be insufficiently charged.

Further, when a battery that has been over-discharged is charged rapidly, the temperature may rise relatively rapidly at the beginning of charging, and the charge may similarly become insufficient. Therefore, for example, a time of 5 minutes is set as the time for the temperature rise of the battery at the start of rapid charging to settle due to these causes, and during this period, the full charge determination is not performed by the temperature differential detection and the temperature differential is reached after 5 minutes have elapsed. Methods of performing detection have been considered. By doing so, it is considered that the temperature rise due to charging can be reliably captured and the full charge can be correctly determined.

However, in this method, when the battery is brought from a low temperature outdoors into a warm room for charging, or when there is swaying heat due to the heat generation of the charger itself, or when the overcharged charger is rapidly charged. In some cases, full charge will not be erroneously determined at the beginning of quick charge, but if the fully charged battery that has already been charged is recharged, it will take 5 minutes after the start of charging. Does not determine full charge, recharge is performed for 5 minutes + 1 minute = 6 minutes despite full charge, which may result in overcharge.

Further, when the temperature differential detection is carried out at 4 ° C./4 minutes instead of 1 ° C./minute, the temperature differential detection time is 5 minutes + the temperature differential detection unit time 4 minutes 9 minutes later. Since the charging is stopped, the battery is overcharged for 9 minutes, the battery temperature rises, for example, 25 ° C. or more, and the deterioration of the battery progresses.

[0008]

As described above, in the conventional quick charger using the temperature differential detection method, (1) when the battery is brought from a low ambient temperature environment to a high ambient temperature for rapid charging, or (2) ) When the charger itself is overheated and it is affected by heat, or (3) when an over-discharged battery is rapidly charged, a full charge may be erroneously detected immediately after starting charging. May cause insufficient charge.
On the other hand, in order to avoid this problem, if the determination of full charge by temperature differential detection is not performed for a certain period of time after the start of charging, overcharging will occur when recharging the already charged battery, There was a problem that it deteriorates.

The present invention has been made in order to solve the above-mentioned problems of the quick charger by the conventional temperature differential detection method, and there is no shortage of charge due to erroneous determination of full charge, and a fully charged state. It is an object of the present invention to provide a charging device for a secondary battery, which is free from the risk of being overcharged by rapidly charging the battery.

[0010]

In order to solve the above-mentioned problems, the present invention uses both the temperature differential value and the temperature second-order differential value of a secondary battery together to determine full charge, and based on that, a rapid charge is determined. The main point is to control charging.

That is, according to the present invention, in a charging device having a function of rapidly charging a secondary battery, a temperature detecting means for detecting the temperature of the secondary battery and a temperature detected by the temperature detecting means per unit time. Temperature differential detecting means for obtaining a temperature differential value which is the amount of temperature increase, and temperature second differential detecting means for obtaining a temperature second differential value which is the change amount per unit time of the temperature differential value obtained by this temperature differential detecting means, When the temperature differential value obtained by the temperature differential detecting means reaches a set value, the rapid charge is terminated when the second temperature differential value obtained by the temperature second differential detecting means is positive, and the second temperature differential is obtained. When the value is zero or negative, there is provided charge control means for controlling to continue the rapid charge.

[0012]

As described above, according to the present invention, the temperature differential value (dT / d) of the battery is determined in order to determine whether the secondary battery is fully charged during rapid charging.
t) and the temperature second-order differential value (d ² T / dt ² ) are obtained, and the temperature second-order differential value at the time when the temperature differential value reaches the set value is examined. If this temperature second-order differential value is positive, it is regarded as full charge. , Terminate the quick charge. That is, when the condition of dT / dt → set value d ² T / dt ² > 0 is satisfied, the rapid charging is stopped.

On the other hand, when the temperature second-order differential value is zero or a negative value when the temperature differential value reaches the set value, that is, when d ² T / dt ² ≤0, it is determined that the full charge has not been reached. To do.

That is, (1) when the battery is brought from a low ambient temperature environment to a high temperature environment for rapid charging, or (2)
If there is heat due to the heat generated by the charger itself,
Alternatively, (3) when the battery shows a rapid temperature increase immediately after the start of rapid charging, such as when rapidly charging an over-discharged battery, the temperature differential value d
Although T / dt reaches the set value, the temperature rise thereafter becomes gentle, so the temperature second-order differential value d ² T / dt ² shows zero or a negative value. In such a case, even if the condition of dT / dt → set value is satisfied, it is ignored, and rapid charging is continued. During the rapid charging, the temperature differential value and the temperature second-order differential value are constantly detected and determined, and if the above condition of dT / dt → set value and d ² T / dt ² > 0 is satisfied, then the temperature is rapidly changed. Stop charging.

By performing such charging control,
Due to the above-mentioned causes (1) to (3), a secondary battery that is not fully charged is not erroneously determined to be fully charged, and insufficient charging is prevented.

In addition, when rapid charging is started for a fully charged battery, the temperature differential value reaches the set value in a short time due to the rapid increase in the battery temperature, and the temperature second-order differential value becomes a positive value. After the charging is completed, the overcharge amount can be reduced as much as possible.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit configuration diagram of a secondary battery charging device showing an embodiment according to the present invention. In FIG. 1, a battery pack 1 includes a secondary battery (hereinafter, simply referred to as a battery) 2 such as an alkaline secondary battery and a thermistor 3 for temperature measurement arranged near the battery 2 in a housing. is there. FIG.
Shows a state in which the battery pack 1 is set in the charging device 4. A mobile phone or other device in which the battery pack 1 is incorporated may be set in the charging device 4.

The charging device 4 is constructed as follows. The charging device 4 has a commercial AC power source 5 (for example, 100V)
Power from is input and filter 6 for noise removal
After being converted into a direct current by the rectifying / smoothing circuit 7 via, the signal is supplied to the primary side of the transformer 8. On the primary side of the transformer 8,
A switching transistor 9 composed of a power MOS transistor is connected via a resistor 10. The switching transistor 9 is a PWM (pulse width modulation) circuit 1
It is switched by the output of 1. As a result, a pulse current flows in the primary side of the transformer 8 and energy is transmitted to the secondary side of the transformer 8. The output generated on the secondary side of the transformer 8 is converted into a direct current by the rectifying and smoothing circuit 12,
It is supplied as a charging current to the battery 2 through the quick charging transistor 13 or the series circuit of the trickle charging transistor 14 and the resistor 15 and further through the backflow prevention diode 16. The output of the rectifying / smoothing circuit 12 is also supplied to the light emitting element 18 of the photocoupler 17, and the output of the light receiving element 19 of the photocoupler 17 is input to the PWM circuit 11.

The microcontroller 20 is mainly composed of a microcomputer, and controls the rapid charging transistor 13, the trickle charging transistor 14, the photo coupler 17, and the LED 31. This microcontroller 20 has a voltage at the connection point between the resistor 21 and the thermistor 3 (hereinafter referred to as the thermistor voltage).
Vt and a voltage Vb obtained by dividing the voltage VB of the battery 2 by the resistors 22 and 23 (hereinafter, referred to as a battery voltage division value) Vb are input.

The resistors 24-29 and the operational amplifier 30 are
It is provided for controlling the charging current to be constant. The inverting input terminal of the operational amplifier 30 receives the terminal voltage of the resistor 24 that is inserted in series in the charging path and detects the charging current via the resistor 27, and the non-inverting input terminal of + 5V.
A voltage (reference voltage) obtained by dividing the power supply voltage of 2 by the resistors 25 and 26 is input via the resistor 28. Operational amplifier 30
A resistor 29 is connected between the inverting input terminal and the output terminal, and the gain of the operational amplifier 30 is determined by the resistors 27 and 29. The output terminal of the operational amplifier 30 is connected to the side of the light emitting element 18 of the photocoupler 17 opposite to the side connected to the output terminal of the rectifying / smoothing circuit 12. With such a configuration, feedback control is performed so that the inverting input terminal and the non-inverting input terminal of the operational amplifier 30 have the same potential.

For example, when the charging current of the battery 2 is large and the terminal voltage of the current detecting resistor 24 is large, the inverting input terminal of the operational amplifier 30 has a higher potential than the non-inverting input terminal, so that the operational amplifier 30 has a higher potential. Output voltage decreases, and the current flowing through the light emitting element 18 increases. As a result, the output pulse width of the PWM circuit 11, that is, the on-time width of the switching transistor 9 is shortened, the energy transmitted to the secondary side of the transformer 8 is reduced, and the charging current is reduced.

On the contrary, when the charging current of the battery 2 is small,
Since the inverting input terminal of the operational amplifier 30 has a lower potential than the non-inverting input terminal thereof, the output voltage of the operational amplifier 30 increases and the current flowing through the light emitting element 18 decreases, so that the PWM
The output pulse width of the circuit 11, that is, the on-time width of the switching transistor 9 increases, and the energy transmitted to the secondary side of the transformer 8 increases, so that the charging current increases.

In this way, the resistance 2 depending on the charging current
Feedback control is performed so that the terminal voltage of No. 4 and the reference voltage obtained by the resistors 25 and 26 become equal to each other, and the charging current is subjected to constant current control.

The microcontroller 20 controls by software processing using a microcomputer. FIG. 2 shows a functional block diagram of the microcontroller 20.

In FIG. 2, the thermistor voltage Vt and the battery voltage divided value Vb are converted into digital values by the A / D converters 41 and 42, respectively, and then the battery temperature calculation unit 4
3 and the battery voltage detector 44, respectively, to obtain the battery temperature TB and the battery voltage VB. The output of the battery temperature calculation unit 43 is input to the battery temperature determination unit 45 and the temperature differential calculation unit 46. The battery temperature determination unit 45 determines in what temperature range the battery voltage is.
The temperature differential calculation unit 46 calculates the temperature differential of the battery, that is, the amount of temperature rise per unit time.

The output of the temperature differential calculation section 46 is input to the temperature differential value determination section 54. The temperature differential value determination unit 54 compares the temperature differential value obtained by the temperature differential calculation unit 46 with a set value (reference temperature differential value), for example, 1.0 ° C./minute to determine the magnitude.

The output of the temperature differential calculation unit 46 is also input to the temperature second-order differential calculation unit 55. Temperature second derivative calculation unit 55
Is a change amount of the temperature differential value obtained by the temperature differential calculating section 46 per unit time, that is, a temperature second-order differential value.

The output of the second temperature differential calculating section 55 is input to the second temperature differential value determining section 56. The temperature second-order differential value determination unit 56 determines whether the positive or negative of the temperature second-order differential value obtained by the temperature second-order differential calculation unit 55 includes zero.

On the other hand, the output of the battery voltage detection unit 44 is input to the battery state determination unit 47. The battery state determination unit 47
It is determined from the battery voltage whether or not the battery 2 is normal. The output of the A / D converter 41 is also input to the battery pack set detection unit 48. Battery pack set detector 48
Is for detecting whether or not the battery pack 1 is set in the charging device 4.

A / D converter 41, battery temperature determination unit 45,
The outputs of the battery state determination unit 47, the battery pack set detection unit 48, the temperature differential value determination unit 54, and the temperature second-order differential value determination unit 56 are input to the charging control unit 50, and the charging control unit 50 rapidly determines based on these outputs. Fast charge control signal 51 to the charging transistor 13, trickle charging transistor 1
4 to generate a trickle charge control signal 52 and a charge start signal 53. The charge start signal 53 is supplied to one end of the resistor 28 in FIG.

Further, the charge control unit 50 causes the temperature differential calculation unit 46 and the temperature second-order differential calculation unit 55 to perform the temperature differential and the temperature differential calculation based on the output (timer value) of the timer 49 for measuring the elapsed time from the start of the rapid charge. Unit time information 57 (for example, information of 1 minute in this example) at the time of obtaining the second derivative is supplied. Further, the timer 49 also counts time as a quick charge time timer and a trickle charge time timer according to an instruction from the charge control unit 50.

Next, the operation of this embodiment will be described with reference to the flow charts shown in FIGS. First, the thermistor voltage Vt is read via the A / D converter 41 (step 101). When the battery pack 1 is set in the charging device 4, the thermistor voltage Vt decreases from + 5V until then due to the partial pressure of the thermistor 3 and the resistor 21.
Here, the thermistor voltage Vt is a predetermined value (for example, 4.8).
V) or less, the battery pack set detection unit 48 detects that the battery pack 1 is set in the charging device 4 (step 102).

When the set of the battery pack 1 is detected in step 102, the battery temperature calculator 43 converts the thermistor voltage Vt into temperature data to calculate the battery temperature TB (step 103), and then the battery temperature determiner 4
According to 5, it is determined whether the battery temperature TB is in the range of 0 ° C. or higher and 40 ° C. or lower (step 104). When the battery temperature TB falls within the range of 0 ° C. ≦ TB ≦ 40 ° C., the trickle charge control signal 52 subsequently output from the charge control unit 50 becomes “L” level, and the trickle charge transistor 14 is turned on. Then, trickle charging is performed (step 105). Thereafter, the battery voltage division value Vb is read via the A / D converter 42 (step 106), the battery voltage VB is obtained by the battery voltage detecting unit 44, and the battery voltage VB is further obtained by the battery state determining unit 47.
It is determined from B that the battery 2 is normal (step 1
07). Specifically, the battery voltage VB per unit cell is 1.
When 0V ≦ VB ≦ 1.7V, the battery 2 is judged to be normal. Here, if the battery 2 is not normal, the process ends and rapid charging is not performed.

When it is determined in step 107 that the battery 2 is normal, the timer 49 is started (step 108), the elapsed time from the charging start time is measured, and the timer value of the timer 49 (charging start time Information 57) is input to the temperature differential calculation unit 46, the temperature rise amount per unit time, that is, the temperature differential value is obtained by the temperature differential calculation unit 46, and the temperature second differential calculation unit 55 calculates the temperature second differential. Value is required (Step 1
09). Then, when the quick charge control signal 51 output from the charge control unit 50 becomes “L” level, the quick charge transistor 13 is turned on, and the charge start signal 53 becomes “L” level. Rapid charging is performed (step 110). During this time, LED3
1 is controlled by the microcontroller 20 and lights up to indicate that quick charging is being performed. Further, during this rapid charging, the charging current is kept constant by the above-mentioned feedback control.

During this rapid charging, the temperature differential calculating unit 46 causes the temperature differential value of the battery temperature TB, that is, a unit time (for example, 1
The temperature rise amount per minute) is constantly calculated (step 109), and it is determined whether or not this temperature differential value is a set value, for example, 1.0 ° C./minute or more (step 111). , 1.0 ° C./min or more, the process proceeds to step 112, and otherwise returns to step 109.

In step 112, it is judged whether or not the temperature second-order differential value calculated in step 109 is> 0, that is, the positive and negative values thereof include zero. Here, if the temperature second-order differential value> 0 (positive), it is determined that the battery 2 is fully charged, and the process proceeds to step 113. If not, that is, when the temperature second-order differential value ≦ 0 (zero or negative). Returns to step 109.

When it is determined in step 112 that the battery 2 is fully charged, the quick charge control signal 51 is set to the "H" level to end the quick charge (step 11).
3). At this time, at the same time, the charge start signals 53 are both set to the “H” level, and the feedback to the PWM circuit 11 for keeping the rapid charging current constant is stopped. Although not shown in FIG. 1, the quick charge start signal 5
It is assumed that the PWM circuit 11 works so that the output voltage of the rectifying / smoothing circuit 12 becomes a constant voltage when 3 becomes the “H” level. The constant voltage output of the rectifying / smoothing circuit 12 is the trickle charging current, the microcontroller 20 and the LED.
Used as an energy source to 31.

Here, FIG. 4 which is a characteristic process of the present invention.
The meaning of the process of step 112 in step 1 will be described with reference to FIG. 5, the battery voltage VB when a current of I = 1.0 C Amperes 0-50 minutes as fast-charge current, battery temperature TB, the temperature differential value dT / dt and the temperature second order differential value d ²
The time change of T / d ² t is shown. Note that trickle charging is performed after 50 minutes.

In FIG. 5, areas 401 and 402 are shown in FIG.
The area where the temperature differential value is determined to be 1.0 ° C./minute or more in step 111 of FIG. Where region 4
Since the temperature second-order differential value 404 in 01 is a negative value, the determination result in step 112 is NO, and step 10
Return to 9. That is, the quick charge is continued.

Here, in the area 401, (1) when the battery temperature TB suddenly rises due to the swaying heat of the charging device, (2) when the battery 2 is brought outdoors from a cold state and brought into a high temperature room, When the battery temperature TB suddenly rises due to the start of charging, or (3) the battery temperature TB suddenly rises due to the rapid charging of an over-discharged battery, the temperature differential value is the set value (1.0 ° C / Even if it is more than min), since the temperature second-order differential value is negative, there is no erroneous determination of full charge, rapid charge continues, and there is no shortage of charge.

Then, when the rapid charge progresses and the temperature differential value becomes 1.0 ° C./min or more as shown in a region 402 50 minutes after the start of the rapid charge, the temperature second-order differential value 406
Indicates a positive value, so it is determined that the battery is fully charged.
Rapid charging is stopped (step 113).

When the rapid charging is stopped in this way, the microcontroller 20 starts the timer 49 and keeps the trickle charge control signal 52 at the "L" level during the period for counting the trickle charge timer value (for example, 10 hours) to set the trickle charge control signal 52 to "L" level. Trickle charging is performed by turning on the charging transistor 14 (step 114). Then, when the trickle charge timer value times out, all charging operations are stopped.

[0043]

As described above, according to the present invention, the temperature differential value and the temperature second-order differential value of the battery are calculated to determine the full charge when the secondary battery is rapidly charged. When the temperature second-order differential value at the time of reaching the set value is examined, if the temperature second-order differential value is positive, it is regarded as full charge and the quick charge is terminated,
On the other hand, when the temperature differential value reaches the set value and the temperature second-order differential value is zero or a negative value, it is judged that the full charge has not been reached and rapid charging is continued, so that the indoor environment can be changed from a low temperature environment. When a battery pack is brought in for quick charging, when there is swaying heat due to the heat generated by the charger itself, or when an overdischarged charger is quickly charged, fully charge a battery that is not fully charged. There is no shortage of charge due to the erroneous determination that the battery is fully charged, and it is possible to prevent overcharging due to accidentally rapidly charging a fully charged battery.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a secondary battery charging device according to an embodiment of the present invention.

FIG. 2 is a functional block diagram of the microcontroller in FIG.

FIG. 3 is a diagram showing a part of a flowchart for explaining the operation of the embodiment.

FIG. 4 is a view showing another part of the flowchart for explaining the operation of the embodiment.

FIG. 5 is a diagram showing a time change of a battery voltage, a battery temperature, a charging current, a temperature differential value, and a temperature second-order differential value at the time of rapid charging for explaining the operation of the embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Battery pack 2 ... Secondary battery 3 ... Thermistor 4 ... Charging device 5 ... Commercial AC power supply 6 ... Filter 7 ... Rectification smoothing circuit 8 ... Transformer 9 ... Switching transistor 11 ... Pulse width modulation circuit 12 ... Rectification smoothing circuit 13 ... Rapid Charge transistor 14 ... Trickle charge transistor 16 ... Backflow prevention diode 17 ... Photocoupler 20 ... Microcontroller 30 ... Operational amplifier 32 ... Discharge transistor 41 ... A / D converter 42 ... A / D converter 43 ... Battery temperature Calculation unit 44 ... Battery voltage detection unit 45 ... Battery temperature determination unit 46 ... Temperature differential calculation unit 47 ... Battery state determination unit 48 ... Battery pack set detection unit 49 ... Timer 50 ... Charge control unit 51 ... Rapid charge control signal 52 ... Trickle Charge control signal 53 ... Charge start signal 54 ... Temperature differential value determination unit 55 ... Temperature second floor Min calculator 56 ... temperature second-order differential value determination unit

Claims (1)

[Claims] 1. A charging device having a function of rapidly charging a secondary battery, comprising temperature detecting means for detecting the temperature of the secondary battery, and a temperature rise per unit time of the temperature detected by the temperature detecting means. A temperature differential detecting means for obtaining a temperature differential value which is an amount, and a temperature second differential detecting means for obtaining a temperature second differential value which is an amount of change per unit time of the temperature differential value obtained by the temperature differential detecting means, When the temperature differential value obtained by the differential detecting means reaches the set value, the rapid charging is terminated when the second temperature differential value obtained by the temperature second differential detecting means is positive, and the second temperature differential value is reached. Is a zero or a negative value, a charging control means for controlling to continue the rapid charging is provided.