JP2552328B2 - Battery charging circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging circuit for a storage battery, and more particularly to a charging circuit that detects minute voltage fluctuations appearing in the terminal voltage waveform of the storage battery at the end of charging and controls charging.

(Prior Art) Various charging methods for storage batteries are known, and as a method particularly similar to the present invention, for example, Japanese Patent Publication No. 61-53.
There is a charging circuit described in Japanese Patent No. 39.

In this known example, a differentiation circuit that responds to a change in the terminal voltage corresponding to the charge amount of the storage battery is connected in parallel to the storage battery, and the output of this differentiation circuit, that is, the terminal of the storage battery that changes corresponding to the charge amount of the storage battery. Detecting that the differential value of the voltage has dropped to the set value, the charging of the storage battery is stopped.

That is, the terminal voltage of the storage battery generally rises rapidly at the end of charging, shows a peak, and then decreases, and the output of the differentiating circuit also decreases accordingly. If charging is stopped when it is detected, proper charging can be performed.

(Problems to be solved by the invention) However, the charging voltage characteristics of the storage battery differ depending on the type of the storage battery, the charging current and the ambient temperature, and the terminal voltage peaks even at the end of charging when the charge amount almost reaches the electric capacity of the storage battery. May not be indicated. In such a case, in the above-mentioned known example, the output of the differentiating circuit does not decrease to the set value, so charging cannot be stopped, and an overcharge state occurs.

Also, if the storage battery that has been fully charged is accidentally recharged, the terminal voltage of the storage battery does not drop, so the output of the differentiation circuit does not drop to the set value, and charging cannot be stopped. It will be charged. Even if you accidentally connect a dry battery, the terminal voltage will not peak and will cause incorrect charging, resulting in rupture or liquid leakage.
This may damage the equipment.

Furthermore, when charging multiple storage batteries in series,
It is necessary to change the set value according to the number of series storage batteries. 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 charging is completed, the differentiating circuit cannot detect it, resulting in an overcharged state. Therefore, in the case of charging a plurality of storage batteries in series, it is necessary to select storage batteries having uniform charging voltage characteristics, and it must also be taken into consideration that the characteristics become gradually uneven due to repeated charge / discharge cycles.

The present invention has been made to solve such conventional problems, and can appropriately control charging regardless of the type of storage battery, charging current, ambient temperature, etc. Does not cause overcharging even when the battery is charged, and when multiple batteries are connected in series for simultaneous charging, overcharging may occur even if the number of batteries connected in series changes or the charging voltage characteristics are not uniform. An object of the present invention is to provide a charging circuit for a storage battery that does not wake up.

(Means for Solving the Problem) The present invention focuses on the fact that a minute voltage fluctuation having a frequency sufficiently higher than the terminal voltage change corresponding to the charge amount occurs in the terminal voltage waveform at the end of charging of the storage battery. A high-pass filter for extracting fluctuations is provided, and when the output of the high-pass filter reaches a set value, the charging of the storage battery is controlled.

(Operation) In the storage batteries such as the sealed nickel-cadmium storage battery, the terminal voltage waveform shows minute voltage fluctuations that were not seen in the early or middle stages of charging until the end of charging. The reason why this phenomenon occurs is that oxygen gas is generated from the anode at the end of charging, the oxygen gas permeates the separator, diffuses toward the cathode side, and reacts with the cathode to absorb the physical gas inside the storage battery. It is considered that the dynamic changes cause changes in characteristics such as internal resistance. The same phenomenon is commonly found not only in the sealed nickel-cadmium storage battery but also in the storage battery of the system in which gas is generated at the end of charging.

Such a minute fluctuation of the terminal voltage at the end of charging of the storage battery always appears even if the charging voltage characteristic changes depending on the type of the storage battery, the charging current, the ambient temperature, etc. Therefore, this minute voltage fluctuation is extracted by the high-pass filter, If the output of the high-pass filter is detected to have decreased to the set value and the charging is controlled, the charging can be surely controlled at the final stage of charging, and overcharging is prevented.

Also, when recharging a charged battery,
Since a slight voltage fluctuation occurs due to the generation of gas with a slight time delay after the start of recharging, overcharging is similarly prevented. Further, even if a dry battery that cannot be originally charged is mistakenly connected, a minute voltage fluctuation appears in the terminal voltage waveform due to the generation of gas inside the dry battery, so that charging control is immediately performed and erroneous charging does not occur.

Furthermore, when a plurality (n) of storage batteries are connected in series and charged, during overcharging, a composite of small voltage fluctuations on the terminal voltage waveforms of the individual storage batteries is superimposed on the composite voltage waveform of the n terminal voltages of the storage batteries. However, in that case, a minute voltage fluctuation of the storage battery having the smallest electric capacity first appears. Therefore, using the same charging circuit as in the case of charging one storage battery, charging is controlled when the storage battery having the smallest electric capacity reaches the end of charging, and overcharging does not occur.

(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 source 3, a direct current power source that rectifies an alternating current power source to obtain a direct current, or another relatively large capacity battery is used.

A high-pass filter 4 is further connected to the storage battery 1. The high-pass filter 4 has a capacitor C whose one end is connected to the anode of the storage battery 1 through 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 high-passed. An operational amplifier 5 connected to the output terminal b of the filter 4, and the operational amplifier 5
The active filter is composed of a resistor R connected between the inverting input terminal and the output terminal.

Here, the low cutoff frequency f1 (=
1 / 2πCR) is the terminal voltage V that appears at the end of charging of storage battery 1.
_In order to extract the minute voltage fluctuation of _B , the output corresponding to the terminal voltage change at the time when the increase rate of the terminal voltage change of the storage battery 1 at the end of charging becomes maximum is smaller than the output corresponding to the minute voltage fluctuation. Have been selected for the relationship. More specifically, the terminal voltage V _B of the storage battery 1 at the end of charging
From the time when the increase rate of the maximum, the battery 1 terminal voltage V _B
F1 is 1 / 4t, where t is the time until the maximum
CR is selected to be greater than 1.

The output terminal b of the high pass filter 4 is connected to the input terminal c of the detection circuit 6. The detection circuit 6 is composed of a voltage comparator 7 in this example. The inverting input terminal of the voltage comparator 7 is the input terminal c of the detection circuit 6, and the output terminal is the detection circuit 6.
Are respectively connected to the output terminals d of. The reference voltage Vth is applied to the non-inverting input terminal of the voltage comparator 7.

The output terminal d of the detection circuit 6 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 that is generated when the power is turned on or in association with the operation of a switch or the like is applied. The output terminal Q of the flip-flop 8 is connected to the control terminal of the charging control circuit 2. The charge control circuit 2 is a flip-flop 8
When the output terminal Q of is at a high level, it is in a rapid charge state, and when it is at a low level, it is in a charge control state. In the charge control state, the charging of the storage battery 1 is completely stopped or the charging current is reduced.

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
Becomes a high level, and the battery is in a rapid charge state. In this state, a large current is supplied from the charging power supply 3 to the storage battery 1, and rapid charging is started. In this charging process, the terminal voltage V _B of the storage battery 1 shows a sharp increase in voltage at the initial stage of charging, as shown in FIG. It shows a rapid voltage rise, peaks and then begins to fall.

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,
In the waveform of the terminal voltage V _B of the storage battery 1 at the time when oxygen gas is generated at the end of charging, minute voltage fluctuations as shown in the enlarged view circled in FIG. 2 (a) are intermittent. Appears in. The frequency component of this minute voltage fluctuation is sufficiently higher than the frequency component of the macroscopic change of the terminal voltage V _B corresponding to the change of the charge amount 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.

Now, in FIG. 3 (a), the terminal voltage at the end of charging
From the time ta to increase rate is the maximum of V _B, when the time until the time tb when the terminal voltage V _B is the maximum value Vp and t1 (sec),
The maximum value f2 (Hz) of the frequency component of the macroscopic change of the terminal voltage V _{B at} the end of charging has a period of about 4t as shown by the broken line.
Since it is 1, it is roughly expressed by the following equation (1).

f2 = 1 / 4t1 (1) In addition, the time from the time when the rate of increase of the differential value dV _B / dt with respect to the time change of the terminal voltage V _B of the storage battery 1 becomes maximum to the time when dV _B / dt becomes the maximum, Let t2 be the maximum value f3 of the frequency component of the macroscopic change of the terminal voltage V _{B at} the end of charging.
(Hz) is roughly expressed by the following equation (2).

f3 = 1 / 4t2 (2) By the way, the frequency component of the distorted wave is generally displayed by a trigonometric function, but since the frequency does not change even if the trigonometric function is differentiated, the formulas (1) and (2) are It is usually almost the same.
The maximum frequency component of the macroscopic change in the terminal voltage V _B of the storage battery 1 may be obtained by the equation (1) that is easy to calculate, but depending on the type of the storage battery 1, the ambient temperature and the history of charging / discharging, FIG. ), The terminal voltage V _B of the storage battery 1 at the end of charging
Sometimes does not show a peak, and in such a case, it can be obtained by the equation (2).

Therefore, the low cutoff frequency f1 of the high pass filter 4 is
If it is selected higher than the frequencies f2 and f3 shown in the formula (1) or (2), the output of the high-pass filter 4 corresponds to a macroscopic change at the time when the rising rate of the terminal voltage V _B of the storage battery 1 becomes maximum. The output corresponding to the frequency component of the minute voltage fluctuation is larger than the output. That is, the high-pass filter 4 can extract the latter frequency component of the minute voltage fluctuation.

The maximum values f2, f3 of the frequency component of the macroscopic change of the terminal voltage V _B of the storage battery 1 and the frequency component of the minute voltage fluctuation change depending on the type of the storage battery 1, the ambient temperature, the charging current, the charge / discharge history, and the like. However, f2 and f3 are approximately 0.001 Hz or less, and the frequency components of minute voltage fluctuations have a difference of approximately one digit or more within the range of approximately 0.01 to 10 Hz. By setting the value close to the geometric mean value of both to the low cutoff frequency f1 of the high-pass filter 4, even if the frequency components of f2, f3 and the minute voltage fluctuation fluctuate to some extent, the frequency component of the minute voltage fluctuation can be extracted.

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 the detection circuit 6 and compared with the reference voltage Vth by the voltage comparator 7. The output of the voltage comparator 7 becomes low level when the output of the high-pass filter 4 exceeds Vth as shown in FIG. 2 (c), and the flip-flop 8 is reset. Since the output terminal Q of the flip-flop 8 is at a low level in the reset state, the charge control circuit 2 is in the charge control state and either stops charging the storage battery 1 or reduces 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 charging is controlled when the output of the high-pass filter 4 reaches the set value given by the reference voltage Vth. Thus, the storage battery 1 can always be charged to an appropriate amount without overcharging. That is, while the charging voltage characteristics vary depending on the type of storage battery, charging current, ambient temperature, etc., the minute voltage fluctuations described above are a phenomenon that always appears at the end of charging. If charging is controlled by detecting it, 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.

Similarly, even if you try to charge by connecting dry batteries,
Similarly, since gas is generated and a minute voltage fluctuation occurs, charge control can be performed, and thus erroneous charge can be prevented.

Furthermore, when multiple 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 storage batteries is controlled at that time, so the electric capacity A storage battery with a small charge will not be 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.

The present invention is not limited to the above-described embodiment. For example, in FIG. 1, the high-pass filter 4 is composed of an active filter composed of a resistor, a capacitor and an operational amplifier, but other types of active filters may be used. It may be a passive filter that does not use a filter or a digital filter. Further, a bandpass filter in which a lowpass filter function is added to a highpass filter may be used in order to prevent erroneous operation due to the frequency of the AC power supply and stabilize the operation.

Further, although the detection circuit 6 is composed of only the voltage comparator 7 in FIG. 1, it may be structured as shown in FIGS. 4 to 10. FIG. 4 shows an example in which the rectifier circuit 11 is inserted before the inverting input terminal of the voltage comparator 7. Although the rectifier circuit 11 shows a half-wave rectifier circuit using one diode in the figure, it may be a full-wave rectifier circuit, an ideal diode circuit combining a diode and an operational amplifier, or an absolute value circuit. It may be.

In FIG. 5, a peak-to-peak detection circuit 12 for outputting the difference between the maximum value and the minimum value of the output of the high-pass filter 4 is inserted before the inverting input terminal of the voltage comparator 7. In this way, the input level of the voltage comparator 7 is doubled and the detection accuracy is improved.

FIG. 6 shows an integrating circuit between the rectifier circuit 11 and the voltage comparator 7.
This is an example in which 13 is inserted, and FIG. 7 is an example in which an integrating circuit 13 is inserted between the peak-to-peak detection circuit 12 and the voltage comparator 7. When configured as shown in FIGS. 6 and 7,
Malfunction due to noise or vibration when supplying current by contacting the power supply terminal of the charging circuit to the terminal of the storage battery
It is possible to prevent malfunction caused by a change in output of the high-pass filter 4 caused by a change in contact resistance due to impact.

In FIG. 8, a peak detection circuit 14 for detecting and holding the peak of the output of the high pass filter 4 is inserted in front of the inverting input terminal of the voltage comparator 7. This peak detection circuit
By providing 14, since only the change in the peak value of the output of the high pass filter 4 is input to the voltage comparator 7, it is easier for the voltage comparator 7 to detect that the output of the high pass filter 4 exceeds the reference voltage Vth. it can. In this case, once the output of the high-pass filter 4 exceeds the reference voltage Vth, the output of the voltage comparator 7 maintains the low level state, so the flip-flop 8 in FIG. 1 can be omitted.

FIG. 9 is a peak detection circuit combining FIG. 8 and FIG.
A rectifier circuit 11 is inserted in front of 14, and
The figure shows a combination of FIG. 8 and FIG. 5 in which the peak-to-peak detection circuit 12 is inserted before the peak detection circuit 14.

If a filter for preventing malfunction due to noise, vibration, or shock is inserted between the terminal of the storage battery 1 and the peak detection circuit 12 in FIGS. 8 and 10, reliability is further improved.

Further, in FIG. 1, the high-pass filter 4 and the detection circuit 6
Although and were directly connected, it is also possible to improve the detection sensitivity by inserting an amplifier between both circuits.

Further, the charging control according to the present invention can be carried out in combination with a conventional charging control method such as timer control, voltage control, temperature control or the like.

(Effect of the Invention) According to the present invention, a minute voltage fluctuation component, which is a frequency component higher than the terminal voltage change corresponding to the charge amount, which appears in the terminal voltage waveform at the end of charging of the storage battery is detected by the high pass filter, and this high pass filter The configuration that controls the charging of the storage battery by detecting when the output of the filter has reached the set value ensures the end of charging regardless of changes in the charging voltage characteristics due to the type of storage battery, charging current, ambient temperature, etc. It is possible to detect and control charging, and it is possible to prevent the life of the storage battery from being shortened due to overcharging.

Also, if the storage battery after charging is mistakenly charged, it goes into the charge control state immediately, so overcharging is prevented, and even if you try to charge the dry cell by mistake, it immediately goes into the charge control state and prevents incorrect charging. To be done.

Furthermore, when a plurality of storage batteries are connected in series and charged, the charging of all storage batteries is controlled at the time when a minute voltage fluctuation of the storage batteries with a small electric capacity appears at the end of charging, so that a storage battery with a small electric capacity is used. There is no need to select a storage battery having a uniform charging voltage characteristic without being overcharged.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a charging circuit for a storage battery according to an embodiment of the present invention, FIGS. 2 and 3 are voltage waveform diagrams for explaining the operation of the embodiment, and FIGS. The figure is a diagram showing another configuration example of the detection circuit in the present invention. 1 ... Storage battery, 2 ... Charging control circuit, 3 ... Charging power source, 4 ... High-pass filter, 5 ... Detection circuit.

Claims (1)

(57) [Claims] 1. A high-pass filter for extracting a minute voltage fluctuation that appears in a terminal voltage waveform at the end of charging of a storage battery and has a frequency component higher than the terminal voltage change corresponding to the charge amount, and the output of this high-pass filter is set to a set value. A storage battery charging circuit comprising: a detection unit that detects that the storage battery has reached and a charging control unit that controls the charging of the storage battery by the output of the detection unit.