JP2638647B2 - Battery charging circuit - Google Patents

Description

Description of the Invention [Object of the Invention] (Field of Industrial Application) The present invention relates to a charging circuit for a storage battery, and in particular, controls charging by detecting a minute voltage fluctuation appearing in a terminal voltage waveform of the storage battery at the end of charging. Charging circuit.

(Prior Art) A variety of charging methods for a storage battery (secondary battery) are known. In particular, a method similar to the present invention is disclosed in, for example, Japanese Patent Publication No. 61-5339 (hereinafter referred to as a first conventional example). ).

In this first conventional example, a differentiating circuit responding to a change in terminal voltage corresponding to the amount of charge of the storage battery is connected in parallel to the storage battery, and changes in accordance with the output of the differentiator, that is, the amount of charge of the storage battery. The charging of the storage battery is stopped by detecting that the differential value of the terminal voltage of the storage battery has decreased to the set value. That is, the terminal voltage of the storage battery generally rises rapidly at the end of charging, shows a peak, then falls, and the output of the differentiating circuit also drops.Therefore, it is detected that the output of this differentiating circuit has dropped to the set value. When charging is stopped, for example, appropriate charging can be performed.

However, the charging voltage characteristics of the storage battery vary depending on the type of the storage battery, the charging current, the ambient temperature, and the like. For example, the terminal voltage may not show a peak even at the end of charging when the charged amount substantially reaches the electric capacity of the storage battery. In such a case, in the first conventional example, the output of the differentiating circuit does not decrease to the set value, so that charging cannot be stopped and an overcharge state occurs.

In addition, if the storage battery that has been charged once is recharged by mistake, the output of the differentiating circuit does not drop to the set value and the charging cannot be stopped because the terminal voltage of the storage battery does not drop. turn into. Furthermore, when a plurality of storage batteries are connected in series and charged, it is necessary to change the set value according to the number of storage batteries in series. Further, if the charging voltage characteristics of the individual storage batteries are not uniform, the characteristics of the combined charging voltage become flat, so that even if the charging is completed, the differentiating circuit cannot detect the charging voltage, resulting in an overcharged state. Therefore, when charging a plurality of storage batteries in series, it is necessary to select storage batteries having uniform charging voltage characteristics, and also to consider that the characteristics become gradually uneven due to repetition of charge / discharge cycles.

On the other hand, as another charging method, there is a method in which the peak value of the terminal voltage of the storage battery during charging is detected, and the charging is stopped when the terminal voltage falls below the peak value by a constant value ΔV. As a specific example of this method, for example, Japanese Patent Publication No. 59-37264
(Hereinafter referred to as a second conventional example). this is,
The comparison unit compares the detection voltage of the voltage detection unit that detects a voltage lower than the terminal voltage of the storage battery by a constant voltage (Zener voltage) by the Zener diode with the storage voltage of the storage unit,
When the detected voltage is higher than the storage voltage, the storage voltage is increased to make the storage voltage substantially equal to the detection voltage corresponding to the peak value of the terminal voltage of the storage battery, and the difference between the storage voltage and the detection voltage is calculated. The value amplified by the amplifier is compared by a Zener diode, and when the difference exceeds a predetermined value, charging is stopped.

In the second conventional example, charging is stopped when the voltage obtained by amplifying the difference between the storage voltage and the detection voltage by the arithmetic width unit exceeds the Zener voltage. However, since the Zener voltage changes depending on the ambient temperature, the charging is stopped. Insufficiency may cause the operation time of the device to be short, and conversely, overcharging may significantly impair the performance of the storage battery. In addition, a current integration storage element, which is a type of electrochemical element, is used as a storage element of the storage unit. However, this type of storage element stores data under the influence of self-discharge, leakage current to the outside, and ambient temperature. Since the voltage fluctuates, the same problem as described above occurs.

Japanese Patent Publication No. Sho 60-18177 (hereinafter referred to as a third conventional example) discloses a voltage lower than a terminal voltage of a storage battery by a zener voltage by a first zener diode and a forward voltage of a backflow prevention diode (that is, a peak voltage). An output voltage of a storage circuit constituted by a capacitor storing a corresponding voltage corresponding to a point voltage, and a voltage lower than the terminal voltage by the Zener voltage of the second Zener diode (that is, a voltage corresponding to the terminal voltage of the storage battery after the peak). The comparison circuit compares the output voltage of the detection circuit that outputs the voltage with the output voltage of the detection circuit, and stops charging when the corresponding voltage decreases and the two voltages compared by the comparison circuit match, that is, when the terminal voltage decreases by ΔV. A circuit is disclosed.

Also in the third conventional example, when a Zener diode is used, ΔV fluctuates greatly due to a temperature change, and thus there is a possibility that the battery may be insufficiently charged or overcharged.

Although ΔV is determined by the combination of zener diodes, the zener voltage of a commercially available zener diode is discrete (at intervals of 0.2 to 1 V), and an appropriate ΔV
It is difficult to obtain a combination for obtaining V, and this also causes the same problem as described above. In addition, when the number of serial storage batteries is small, the appropriate ΔV is small.
ΔV in the case of about 3 is about several mV to several tens mV, and it is industrially difficult to obtain such a value by a combination of Zener diodes, so that it is not practical.

Further, in the third conventional example, since a storage circuit having a capacitor and a diode as main elements is used, the storage voltage fluctuates due to leakage of the capacitor itself, leakage from a diode or other components, and the like. It causes shortage and overcharge.

Further, in each of the first, second, and third conventional examples, there was a trouble that the circuit constant had to be changed depending on the number of series storage batteries.

Furthermore, in the second and third conventional examples, the charging is stopped after the peak, so that the battery is overcharged. In particular, in the case of the ultra-rapid charging in which the charging is completed in 30 minutes or less, the deterioration of the battery performance becomes remarkable. There is.

On the other hand, as a conventional example shown in FIG.
No. 29 describes a method of extracting a minute voltage fluctuation of a storage battery, detecting that the minute voltage fluctuation has become a certain value or more, and controlling charging. In this method, the detection circuit may perform a detection operation erroneously due to the influence of noise.
In such a case, charging control is performed even though charging has not been completed due to the influence of noise, resulting in insufficient charging.

(Problems to be Solved by the Invention) As described above, the method of detecting that the output of the differentiating circuit in response to the change in the terminal voltage corresponding to the charge amount of the storage battery has decreased to a set value, and stopping the charging of the storage battery. In the first conventional example, if the terminal voltage does not show a peak even at the end of charging due to the charging voltage characteristics of the storage battery, charging cannot be stopped, resulting in an overcharged state. In addition, when a storage battery that has been charged once is erroneously recharged, overcharge occurs. Further, when a plurality of storage batteries are connected in series and charged, there are drawbacks that the set value needs to be changed according to the number of serial batteries and that storage batteries having uniform charging voltage characteristics must be selected.

A method in which charging is stopped when a value obtained by amplifying a difference between a detection voltage of a voltage detection unit for detecting a terminal voltage of a storage battery and a storage voltage of a storage unit by an arithmetic width unit exceeds a zener voltage (second conventional example) In some cases, undercharging or overcharging may occur due to fluctuations in the temperature characteristics of the Zener voltage or the storage voltage.

A comparison circuit compares a corresponding voltage corresponding to the peak voltage of the terminal voltage of the storage battery with a corresponding voltage corresponding to the terminal voltage after the peak, and stops charging when both voltages match (third conventional method). In the example, too, the use of a zener diode or a storage element in which the storage voltage is likely to fluctuate causes a shortage of charge or overcharge.

Further, in each of the first to third conventional examples, there is a trouble that the circuit constant has to be changed according to the number of series of storage batteries, and in addition, in the second and third conventional examples, charging is stopped after a peak. Therefore, particularly in the case of ultra-rapid charging, the battery performance may be significantly degraded due to overcharging.

A method of extracting minute voltage fluctuations of a storage battery and detecting that the minute voltage fluctuations are equal to or more than a certain value to control charging (fourth conventional example) is similar to the first to third conventional examples. Although there is no problem, it may be erroneously detected that the minute voltage fluctuation has exceeded a certain value due to the influence of noise. In such a case, charging control is performed even though charging is not completed. As a result, the battery becomes insufficiently charged.

The present invention has been made in order to solve such a conventional problem, and it is possible to appropriately control charging regardless of the type of the storage battery, charging current and ambient temperature, and to erroneously charge a storage battery in a fully charged state. If multiple batteries are connected in series and charging is performed at the same time without overcharging, even if the number of batteries connected in series changes or the charging voltage characteristics are not uniform, overcharging does not occur. It is another object of the present invention to provide a charging circuit for a storage battery that does not have a fear of insufficient charging due to charge control being performed under the influence of noise.

[Means for Solving the Problems] In order to solve the above-described problems, the present invention provides a terminal device having a sufficiently high frequency due to a terminal voltage change corresponding to a charged amount in a terminal voltage waveform at the end of charging of a storage battery. Focusing on the occurrence of voltage fluctuations, extracting this minute voltage fluctuation, shaping it into a pulse signal, and controlling charging by the output of a counting means for counting this pulse signal. .

(Operation) In a storage battery such as a sealed nickel-cadmium storage battery, a minute voltage fluctuation which is not seen in the initial stage or in the middle of charging appears in the terminal voltage waveform at the end of charging. The reason for this phenomenon is that oxygen gas is generated from the anode at the end of charging, and this oxygen gas permeates through the separator and diffuses to the cathode side, reacts with the cathode and is absorbed in the storage battery. It is considered that a minute change in voltage is caused by a chemical change or a chemical reaction.

Such a small change in the terminal voltage at the end of charging of the storage battery always appears even if the charge voltage characteristics change due to the type of the storage battery, the charging current, the ambient temperature, and the like. If the extracted minute voltage fluctuation is converted into a pulse signal and input to the counting means, the charging is controlled when the counting means reaches a preset count value, so that the charge control is surely performed at the end of charging. Is performed, and overcharging is prevented.

Also, when recharging a charged battery,
Since the gas is generated with a slight time delay after the start of recharging, a minute voltage fluctuation occurs, so that overcharging is similarly prevented.

On the other hand, when a plurality (n) of storage batteries are connected in series and charged, at the time of overcharging, the synthesis of minute voltage fluctuations in the terminal voltage waveform shape of each storage battery is superimposed on the composite voltage waveform of the n battery terminal voltages. However, in that case, a minute voltage fluctuation of the storage battery having the smallest electric capacity appears first. Therefore, the storage battery 1
Using the same charging circuit as in the case of performing book charging, charging is controlled when the storage battery with the smallest electric capacity reaches the end of charging, so that overcharging does not occur.

Furthermore, since the number of pulse signals obtained by shaping the minute voltage fluctuation is counted and charging is continued until the counted value reaches a predetermined value, even if noise is mixed, the counted value only slightly increases. Insufficient charging due to erroneous charging control due to noise, such as a method of controlling charging when the amplitude of a signal exceeds a certain value, can be avoided.

(Embodiment) FIG. 1 shows a charging circuit for a storage battery according to an embodiment of the present invention. The storage battery 1 is connected to a charging power supply 3 via a charging control circuit 2. The charging control circuit 2 includes a switching circuit that controls a charging current. As the charging power supply 3, a DC power supply that rectifies an AC power supply to obtain a DC power, or another relatively large-capacity battery is used.

The storage battery 1 is further connected to a high-pass filter 4 constituting a minute voltage fluctuation extraction circuit. The high-pass filter 4 has a capacitor C having one end connected to the anode of the storage battery 1 via the input terminal a, an inverting input terminal connected to the other end of the capacitor C, a non-inverting input terminal grounded, and an output terminal connected to the high-pass filter. It comprises an active filter comprising an operational amplifier 5 connected to the output terminal b of the filter 4 and a resistor R connected between the inverting input terminal and the output terminal of the operational amplifier 5. Here, reducing the cut-off frequency as the high-pass filter 4 may extract a small voltage fluctuation of the terminal voltage V _B appearing at the end of charging of the storage battery 1 is selected.

The output terminal b of the high-pass filter 4 is connected to the input terminal c of the shaping circuit 6. The shaping circuit 6 is a circuit for shaping a minute voltage fluctuation, which is an output signal of the high-pass filter 4, into a pulse signal in order to ensure the operation of the counting circuit 9, and is constituted by a voltage comparator 7 in this example. .
The inverting input terminal of the voltage comparator 7 is connected to the input terminal c of the shaping circuit 6, and the output terminal is connected to the output terminal d of the shaping circuit 6. The reference voltage Vth is applied to the non-inverting input terminal of the voltage comparator 7. The output terminal d of the shaping circuit 6 is connected to the input terminal of the counting circuit 9.

The output terminal f of the counting circuit 9 is connected to the reset terminal R of the flip-flop 8. To the set terminal S of the flip-flop 8, a start pulse generated when the power is turned on or when the switch or the like moves is applied. The output terminal Q of the flip-flop 8 is connected to the control terminal of the charging control circuit 2 and the reset terminal g of the counting circuit 9.

The charge control circuit 2 enters the fast charge state when the output terminal Q of the flip-flop 8 is at a high level, and enters the charge control state when the output terminal Q is at a low level. In the charging control state, the charging of the storage battery 1 is completely stopped or the charging current is reduced.
The counting circuit 9 is in a counting state when the output terminal Q of the flip-flop 8 is at a high level, and is in a reset state when the output terminal Q is at a low level.

Next, the operation of the charging circuit of FIG. 1 will be described with reference to the voltage waveform diagram of FIG.

When a start pulse generated at power-on of the charging circuit or in conjunction with a switch operation is applied to the set terminal S of the flip-flop 8, the output terminal Q of the flip-flop 8
Is at a high level, the charge control circuit 2 is in a quick charge state, and the counter circuit 9 is in a count state. In this state, the charging power source 3
Supplies a large current to the storage battery 1 to start rapid charging.

In this charging process, the terminal voltage V _B of the battery 1 and the second
As shown in FIG. 7A, the voltage rises sharply at the beginning of charging, rises gently during the middle stage of charging, and at the end of charging, the voltage again rises sharply, reaches a peak, and then starts falling. At the end of charging, oxygen gas is generated from the anode of the storage battery 1, so that in the case of a sealed storage battery, the internal pressure P increases as shown by the broken line in FIG. 2 (a).

Here, the waveform of the terminal voltage V _B of the battery 1 at the time the oxygen gas is reacted to absorb the generated cathode at the end of charging is illustrated in an enlarged view surrounded by ○ in Fig. 2 (a) Such minute voltage fluctuations appear intermittently. Frequency component of the small voltage fluctuation is sufficiently higher than the frequency components of the macroscopic change in the terminal voltage V _B corresponding to a change in the amount of charge of the storage battery 1. The level of the minute voltage fluctuation is small at the beginning of the fluctuation, but the level of the minute voltage fluctuation increases as the charging proceeds further and the amount of generated oxygen gas increases.

This output terminal b of the high-pass filter 4 so that the output appears corresponding to the minute voltage variation of FIG. 2 (b) the terminal voltage of the battery 1 as shown in V _B. The output of the high-pass filter 4 is input to a shaping circuit 6 and compared with a reference voltage Vth by a voltage comparator 7. The output of the voltage comparator 7 appears pulse signal respond to small voltage fluctuation of the terminal voltage V _B of the battery 1 as shown in FIG. 2 (c) is, and is supplied to an input terminal e of the counting circuit 9.

When the number of pulse signals input to the input terminal e reaches the preset value n, the counting circuit 9 sets the output terminal f to a high level as shown in FIG. 2 (d) and resets the flip-flop 8. State. Since the output terminal Q of the flip-flop 8 is at the low level in the reset state, the charge control circuit 2 is in the charge control state, and performs control to stop charging the storage battery 1 or reduce the charging current.

In this way, the minute voltage fluctuation appearing in the terminal voltage waveform at the end of charging of the storage battery 1 is detected by the high-pass filter 4, and the number of pulse signals generated each time the output exceeds the reference voltage Vth is counted by the counting circuit 9. By controlling the charging when the number reaches n, the storage battery 1 can always be charged to an appropriate amount without causing overcharging.
In other words, while the charging voltage characteristics vary depending on the type of storage battery, charging current, ambient temperature, and the like, the above-described minute voltage fluctuation is a phenomenon that always appears at the end of charging. If charging is controlled by detection, overcharging will not occur.

In addition, even if an attempt is made to recharge a charged storage battery by mistake, oxygen gas is generated as in the last stage of charging, and a slight voltage fluctuation occurs, and charge control can be performed. Is possible.

On the other hand, when a plurality of storage batteries are connected in series and charged, a minute voltage fluctuation of the storage battery with the smallest electric capacity appears first at the end of charging, and the charging of all the storage batteries is controlled at that time. There is no possibility that the storage battery having a small value becomes overcharged. Therefore, when a plurality of storage batteries are connected in series and charged simultaneously, it is possible to save the trouble of selecting storage batteries having uniform charging voltage characteristics as in the related art.

Further, even if noise enters during the rapid charging, charging is continued until the count value of the counting circuit 9 reaches n. Therefore, malfunction such as charging control immediately due to noise does not occur, and shortage of charging is avoided. Can be.

The present invention is not limited to the above embodiment. For example, in FIG. 1, the high-pass filter 4 is constituted by an active filter including a resistor, a capacitor and an operational amplifier, but another resistor is connected in series with the capacitor. The operation may be stabilized, and another type of active filter, a passive filter without an operational amplifier, or a digital filter may be used. Further, instead of a simple high-pass filter, a band-pass filter having a function of a low-pass filter added to the high-pass filter may be used to prevent malfunction due to the frequency of the AC power supply and stabilize the operation.

Further, in FIG. 1, the shaping circuit 6 is constituted only by the voltage comparator 7, but may be constituted as shown in FIG. 3 to FIG.

FIG. 3 shows a rectifier circuit before the inverting input terminal of the voltage comparator 7.
This is an example in which 11 is inserted. The rectifier circuit 11 is a half-wave rectifier circuit using one diode in the figure, but may be a full-wave rectifier circuit, an ideal diode circuit combining a diode and an operational amplifier, or an absolute value circuit. You may.

FIG. 4 shows that a peak-to-peak detection circuit 12 for outputting a difference between the maximum value and the minimum value of the output of the high-pass filter 4 is inserted in front of the inverting input terminal of the voltage comparator 7. By doing so, the input level of the voltage comparator 7 is doubled, and the detection accuracy is improved.

FIG. 5 shows an integrating circuit between the rectifier circuit 11 and the voltage comparator 7.
This is an example in which 13 is inserted. FIG. 6 shows an example in which an integrating circuit 13 is inserted between the peak-to-peak detecting circuit 12 and the voltage comparator 7. When configured as shown in FIGS. 5 and 6,
To prevent malfunction due to noise or malfunction due to a change in output of the high-pass filter 4 caused by a change in contact resistance due to vibration or shock when a supply terminal of a charging circuit is connected to a terminal of the storage battery 1 to supply current. Can be.

In FIG. 1, a normal voltage comparator 7 is used for the shaping circuit 6. However, when a voltage comparator with a hysteresis characteristic is used, a case where noise of a minute amplitude is superimposed on the output of the minute voltage fluctuation extracting circuit is shown. Malfunction can also be prevented.

In FIG. 1, the high-pass filter 4 and the shaping circuit 6 are directly connected.
It is also possible to increase the input level of, and to facilitate shaping.

Although FIG. 1 shows an example in which a high-pass filter is used as the minute voltage fluctuation extracting circuit, a similar effect can be obtained by using a differentiating circuit that captures the slope of the voltage fluctuation.

Further, in FIG. 1, the pulse signal from the shaping circuit 6 is counted by the counting circuit 9, and the charging is controlled when the accumulated pulse number reaches a preset value n after the rapid charging is started. Alternatively, a reset pulse may be applied to the reset terminal g of the counting circuit 9 at regular intervals, and charging may be controlled when the number of pulses generated within the constant time reaches n.

Further, a gate circuit may be inserted between the output terminal d of the shaping circuit 6 and the input terminal e of the counting circuit 9 to limit the number of pulse signals input to the counting circuit 9.

In addition, the present invention can be variously modified and implemented without departing from the gist.

[Effects of the Invention] According to the present invention, a minute voltage fluctuation, which is a frequency component higher than a terminal voltage change corresponding to a charged amount and appears in a terminal voltage waveform at the end of charging a storage battery, is detected, and this minute voltage fluctuation is detected. It is shaped into a pulse signal and counted, and by detecting that the count value has reached a set value, the charging of the storage battery is controlled, so that the charging voltage characteristics depending on the type of storage battery, charging current, ambient temperature, etc. Charging can be controlled by reliably detecting the end of charging irrespective of the change, and it is possible to prevent the life of the storage battery from being shortened due to overcharging.

In addition, if the storage battery is incorrectly charged after the completion of charging, the battery immediately enters the charge control state to prevent overcharging. Even if the battery is erroneously charged, the battery immediately enters the charge control state to prevent overcharging. Is done.

Furthermore, when a plurality of storage batteries are connected in series and charged, there is an advantage that a storage battery having a small electric capacity does not become overcharged at the end of charging, and it is not necessary to select storage batteries having uniform charging voltage characteristics. is there.

Further, in the present invention, unlike the method of controlling charging when the amplitude of the minute voltage fluctuation becomes equal to or more than a certain value, the charging is continued until the number of pulse signals obtained by shaping the minute voltage fluctuation reaches a predetermined value. Even if it does, the count value only slightly increases, and the charge control is hardly affected by noise.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a charging circuit for a storage battery according to one embodiment of the present invention, FIG. 2 is a voltage waveform diagram for explaining the operation of the embodiment, and FIGS. FIG. 9 is a circuit diagram illustrating another configuration example of the shaping circuit according to the present invention. DESCRIPTION OF SYMBOLS 1 ... Storage battery, 2 ... Charging control circuit, 3 ... Charging power supply, 4 ... High-pass filter (small voltage fluctuation extraction means), 6 ... Shaping circuit, 9 ... Counting circuit.

Claims (2)

(57) [Claims] 1. A minute voltage fluctuation extracting means for extracting a minute voltage fluctuation of a frequency component higher than a terminal voltage change corresponding to a charge amount appearing in a terminal voltage waveform appearing in a terminal voltage waveform at the end of charging of a storage battery; Shaping means for shaping the voltage fluctuation into a pulse signal; counting means for counting the pulse signal output from the shaping means; and charging of the storage battery when the count value of the pulse signal by the counting means reaches a predetermined value. And a charge control means for controlling the charging time. 2. The storage battery charging circuit according to claim 1, wherein said minute voltage fluctuation extracting means is a high-pass filter or a differentiation circuit, and said shaping means includes a voltage comparator.