JPH10221418A - Device and method for judging deterioration of battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To judge the deterioration of a battery at a high speed by changing a constant current flowing to the battery in a step-like state and measuring the variation of the transient response of the polarization voltage of the battery and, when the variation becomes larger than a specific value, judging that the battery is deteriorated. SOLUTION: The variation of the transient response of the polarization voltage of a battery is measured while a constant current flowing to the battery is changed in a step-like state. When the variation becomes larger than a prefixed specific value, it is judged that the battery is deteriorated. The period of time during which the constant current is made to flow before the current is changed in the step-like state is made, for example, 10 times longer than the measuring time after changing the current. When, for example, a discharge current pulse is set at 0A after the constant current is made to flow for a fixed period of time, the voltage of the battery becomes a waveform (a). The voltage of the battery immediately after the pulse is set at 0A instantaneously changes by a voltage change (r.I) caused by a pure DC resistance and, thereafter, a voltage change (rη.I) caused by polarization appears. The variation ΔV1 of the polarization voltage which occurs t1 seconds after the discharge current becomes 0A is measured and, when the measured value is larger than the specific value, it is judged that the battery is deteriorated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for judging deterioration of a storage battery at a high speed and a method for judging deterioration using the apparatus.

(2)

2. Description of the Related Art Conventionally, a method of judging the deterioration of a storage battery at a high speed of, for example, about 1 second is mainly a method of applying a DC constant current discharge pulse and observing a drop in the battery voltage at that time (FIG.
(B)) and a method of measuring the AC impedance of the battery by applying an AC signal (FIG. 1 (a)).

[0003] In the former case of discharging with a constant DC current, there is a possibility that wiring resistance and contact resistance existing in the discharge circuit of the battery are included as errors.

When using the latter AC signal, there is a problem that an AC signal source and an AC signal measuring device must be newly provided.

[0005] In principle, the total impedance of L, R, C, and Zf of the equivalent circuit of Fig. 2 is measured by measuring Fig. 1 and it is determined that the impedance has deteriorated when the total impedance exceeds a certain value. Was.

In FIG. 2, E is the superpower of the battery, L is the inductance determined by the shape of the current-carrying part of the storage battery, and R is
Is the resistance of the electrode plate or the electrolyte, C is the capacitance of the electric double layer due to the space charge at the interface between the active material of the electrode and the electrolyte, and Zf is the polarization generated by the movement of the charge or the material at the interface. This is called a resistance component and a capacitance component.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art and provides an apparatus and a method for determining the deterioration of a storage battery at a high speed. That is, except for the influence of an error due to DC resistance in series with the battery, the deterioration of the storage battery is determined at low cost without using an AC signal source or a measuring instrument. (3)

[0008]

SUMMARY OF THE INVENTION According to the present invention, a constant current flowing through a battery is changed in steps to measure a change in the transient response of the polarization voltage of the battery, and this value is equal to or greater than a predetermined value. A battery deterioration determination method characterized in that it is determined that a battery has deteriorated when a voltage fluctuation value has been reached. And the time of the constant current before changing it to the step shape is
10 times or more of the measurement time after the step, preferably 100
It is characterized by being more than double.

The present invention is also a deterioration judging device for realizing the above-described method for judging deterioration of a battery. That is, a means for detecting a battery current, a means for detecting a temporal change in battery voltage, and a means for converting the battery current and the temporal change in battery voltage detected by these two means into a digital signal. And a microcomputer for digitizing the current dependency of the polarization voltage and storing it in advance, and comparing the digitized stored information with a digital signal to determine the deterioration of the battery. This is a battery deterioration determination device.

In addition, a means for detecting the battery temperature is added to the above-mentioned deterioration judging device. On the other hand, the microcomputer quantifies the temperature dependency of the polarization voltage and stores it in advance, and stores the numerically stored information and the detected temperature. A function of comparing the information with the information to determine the deterioration of the battery may be added to the microcomputer.

The means for detecting the time change of the battery voltage is a differential amplifier. The input of the amplifier is a battery voltage having a fixed delay time as a reference value, and a real-time battery voltage is detected. Then, the deterioration of the battery may be determined by comparing with a reference value.

[0012]

The measuring method of the present invention utilizes the fact that the capacity of the electric double layer and the capacity component in Zf of FIG. 2 are (4) proportional to the charge capacity of the battery. That is, the deterioration response of the storage battery is determined by measuring the transient response of the polarization voltage.

FIG. 3 is a waveform chart for explaining the polarization voltage measuring method of the present invention. (A) and (b) show a measuring method by discharging, and (c) and (d) show a measuring method by charging.

A measuring method when a discharge current pulse is applied will be described. When the discharge current pulse is caused to flow for a predetermined period of time, for example, 1 second as shown in FIG. That is, the battery voltage immediately after 0 A instantaneously changes by the voltage change (r · I) due to the DC pure resistance, and thereafter, the voltage change (rμ · I) due to polarization appears.

Using such a battery voltage waveform, a change ΔV1 in polarization voltage after t1 seconds immediately after the discharge current becomes 0 A is measured. Is determined to have deteriorated.

The measurement accuracy can be further improved by measuring the change ΔV2 in polarization voltage after t2 seconds immediately after the discharge current becomes 0 A.

FIGS. 3 (c) and 3 (d) show the case where the measurement is performed using the charge pulse, and the principle is the same as the measurement method using the discharge pulse described above. That is, in this case, the change ΔV3 in polarization voltage after t3 seconds immediately after the charging current becomes 0 A is measured, and if this value is equal to or greater than a predetermined value, it is determined that the battery has deteriorated. Similarly, t
By measuring the change ΔV4 in the polarization voltage after 4, the measurement accuracy can be further improved.

Note that the polarization voltage changes ΔV3 and ΔV4 are:
It depends strongly on the waveform of the charging current in (d) (5). Therefore, when the measurement is performed after the set constant current, it is desirable to lengthen the charging current period because the error of the voltage response when the charging current is set to zero becomes small.
For example, there is no practical problem if the measurement time t3 is 0.1 second for a constant current charging period of 1 minute.

The DC charging current does not necessarily have to be a constant current. When viewed in a long time of about 1 minute, it is sufficient that the current is a steady-state current charge that can be regarded as substantially the same pattern being repeated. For example, measurement and comparison may be performed at a point in time when substantially the same current waveform can be considered in a ripple charging waveform such as a waveform in which a commercial full-wave waveform and a switching waveform are superimposed.

Note that the constant current charging period is the measurement time t3, t4
For example, if it is 100 times or more, the measurement error is almost negligible.

FIG. 4 is a graph showing the relationship between Ni and Ni when a charging pulse is used.
4 shows an example of a transient response of a polarization voltage of a Cd battery. The horizontal axis is
The elapsed time is represented on a logarithmic scale with the time when the charging current is set to 0 A as zero. The vertical axis represents the transient response change ΔV of the polarization voltage.

As can be seen from the figure, the change in the polarization voltage of the deteriorated NiCd battery has a larger transient voltage fluctuation as the charging capacity becomes smaller. For example, from 0.1 seconds
If the voltage fluctuation after one second is compared, the difference in the voltage fluctuation is remarkable, so that the deterioration of the NiCd battery can be determined.
In general, a battery in which the amount of change in the polarization voltage per unit time exceeds a predetermined value may be determined as a deteriorated battery.

However, since the polarization voltage has current dependence, temperature dependence, or history dependence, it is necessary to perform measurement under the same conditions in order to eliminate these effects. For example, (6) the measurement is performed under the condition of one current or the same temperature, or the measurement is performed at a battery voltage of about + 10% of the nominal voltage to remove the measurement error due to the measurement condition.

FIG. 5 is a characteristic diagram showing the relationship between the battery temperature and the polarization voltage using the charging current as a parameter for the NiCd battery. The measurement time t3 = 1 second. As can be seen from this figure, the transient response change of the polarization voltage greatly depends on the battery temperature.

FIG. 6 shows the constant current charging characteristics of the NiCd battery. Since the battery voltage is relatively stable in the region (A region) where the charge amount is 35 to 85%, a stable polarization voltage can be obtained in this region. Therefore, the temperature and the battery voltage are measured while performing the constant current charging, and when the battery voltage reaches a value corresponding to the region A, the charging current is set to zero, and the change in the movable response of the polarization voltage (ΔV3) is measured. This makes it possible to determine the deterioration of the battery with high accuracy.

FIG. 7 shows the constant current discharge characteristics of the NiCd battery. Since the battery voltage is relatively stable in the region where the discharge amount is 30 to 65% (region B), a stable polarization voltage can be obtained in this region. Therefore, the temperature and the battery voltage are measured while performing the constant current discharge, and when the battery voltage reaches a value corresponding to the region B, the discharge current is set to zero and the transient response change (ΔV1) of the polarization voltage is measured. This makes it possible to determine the deterioration of the battery with high accuracy.

FIG. 8 shows the deterioration judgment circuit of the present invention and NiCd
It is a battery charger. Fig. 3 (c) and (d)
The program is set to measure the waveform as described above and determine the deterioration of the battery. In FIG. 8, the battery pack includes a thermistor and a battery. (7) The thermistor is provided to measure the battery temperature.

In FIG. 8, Amp1 is provided for measuring a charging current. The microcomputer captures the instantaneous value of the charging current through the A / D converter of the microcomputer.

When the charging current waveform is as shown in FIG. 3D, the transient response of the polarization voltage of the battery is measured to determine the deterioration of the battery. Alternatively, the microcomputer of the deterioration judging device may control the charger to make the charging current in a step-like form, form a charging current waveform as shown in FIG. 3D, and execute the battery deterioration measurement.

For measuring the battery voltage, Amp2 and Am3 are used. Amp2 enlarges the battery voltage from 1.2V to 1.6V as compared with the reference voltage of 1.25V and outputs it as 0 to 5V. This is put into an 8-bit A / D converter of the microcomputer. The resolution of the obtained battery voltage is 1.5 mV, but the final bit is considered as an error, and 3 mV is the measurement accuracy of Amp2.

In the present embodiment, the detection accuracy is further improved by two digits in decimal notation using Amp3. The reference voltage of Amp3 consists of an 8-bit D / A converter. The D / A converter output follows the battery voltage with high accuracy and high speed.

The Amp3 makes it possible to measure the battery voltage up to a unit of 80 μV. This makes it possible to detect the transient response of the polarization voltage with high accuracy in real time. When the response value of the polarization voltage per unit time becomes equal to or greater than a specified value, the deterioration is determined.

It is also possible to incorporate the deterioration judgment circuit of the present invention into a microcomputer for battery management on the load side (8). 3 (a) and 3 (b) can be applied to the transient response at that time.

Although the present invention has been described with reference to a NiCd battery, the method of the present invention can be applied to a nickel hydride (NiMH) battery, a Li ion battery, and a sealed lead battery. In addition, the present method is effective for assembled batteries (particularly, series multi-cell batteries).

Further, the battery current step need not be a constant value of DC. If the set value of the transient response of the polarization voltage is measured in advance, a stabilized strain wave current may be used. For example, during charging, a transient response of the polarization voltage between the steady ripple charging state and the charging stop state may be used.

Although the present deterioration determination circuit has been described only when the charging current I is switched to 0 A from when the charging current I is flowing, this is not necessarily the case. If the operation is stabilized, deterioration can be determined even when switching from 0A to constant current charging or when switching from large constant current to small constant current.

If the transient response condition of the battery voltage is stabilized, it is possible to judge the deterioration at the time of switching from the constant charge current to the constant discharge current or the reverse change.

[0038]

According to the method of the present invention, the deterioration of the storage battery can be determined at low cost. A charger using the RFV method can easily add a deterioration determination function. In addition, in the case of a smart battery with an information processing function, the battery voltage and battery current can be viewed, and if the battery temperature can be measured, a function to check the deterioration of the storage battery during operation in a short time can be added.

[Brief description of the drawings]

 (9)

FIG. 1 is a prior art battery deterioration determination circuit, (a) is a method of applying a discharge pulse and observing a decrease in battery voltage at that time;
(B) is a method of measuring an AC impedance of a battery by applying an AC signal.

FIG. 2 is an equivalent circuit of a battery deterioration determination circuit.

FIGS. 3A and 3B are waveform diagrams for explaining a method of measuring a polarization voltage according to the present invention, wherein FIGS.
(D) shows a measuring method by charging.

FIG. 4 is an example of a transient response of a polarization voltage of a NiCd battery when a charging pulse is used.

FIG. 5 is a characteristic diagram showing a relationship between a battery temperature and a polarization voltage using a charging current as a parameter for a NiCd battery.

FIG. 6 shows a constant current charging characteristic of a NiCd battery.

FIG. 7 shows constant current discharge characteristics of a NiCd battery.

FIG. 8 shows a deterioration determination circuit and a NiCd battery charger of the present invention.

[Explanation of symbols]

 E Electromotive force of battery L Inductance of battery R Resistance of electrode plate and electrolyte C Capacity of electric double layer Zf Faraday impedance Amp1 Charge current measurement amplifier (9) Amp2 Battery voltage measurement amplifier Amp3 Battery voltage measurement amplifier

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[Procedure amendment]

[Submission date] March 26, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction contents]

In FIG. 2, E is the electromotive force of the battery, L
Is the inductance determined by the shape of the energized part of the storage area,
R is the opposition of the electrode plate or the electrolyte, C is the capacity of the electric double layer due to the space charge at the interface between the active material of the electrode and the electrolyte, Zf is the polarization generated by the movement of the charge or the material at the interface, and the Faraday impedance. It is what is called a scan, which is a resistor component and a capacitance component.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction contents]

A measuring method when a discharge current pulse is applied will be described. When the discharge current pulse is caused to flow for a predetermined period of time, for example, 1 second as shown in FIG. That is, the battery voltage immediately after 0 A changes instantaneously by the voltage change (r · I) due to the DC pure resistance, and thereafter, the voltage change (r η · I) due to polarization appears.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0030

[Correction method] Change

[Correction contents]

[0030] The battery voltage measurement using the Amp2 and Am p 3. The battery voltage 1.2 to 1.6 V is enlarged as compared with the reference voltage 1.25 V of Amp 2 and output as 0 to 5 V.
This is put into an 8-bit A / D converter of the microcomputer. Although the resolution of the obtained battery voltage is 1.5 mV, the final bit is considered to be an error, and 3 mV is the measurement accuracy of Amp2. ────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] March 26, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Name of invention

[Correction method] Change

[Correction contents]

Patent application title: Battery Deterioration Determining Apparatus and Deterioration Determining Method

Claims (5)

[Claims] 1. A method according to claim 1, wherein a constant current flowing through the battery is changed in a stepwise manner, and a transient response change of the polarization voltage of the battery is measured. Battery deterioration determination method for determining 2. The method for determining deterioration of a battery according to claim 1, wherein the time of the constant current before the stepwise change is 10 times or more of the measurement time after the step. Method. 3. A means for detecting a battery current, a means for detecting a temporal change in a battery voltage, and a means for converting a temporal change in a battery current and a battery voltage detected by these means into a digital signal. And a microcomputer that digitizes and stores in advance the current dependency of the polarization voltage, compares the digitized storage information with the digital signal, and determines deterioration of the battery. Deterioration determination device. 4. The battery deterioration judging device according to claim 3, further comprising means for detecting a battery temperature, digitizing the temperature dependency of the polarization voltage and storing the numerical value in advance, and storing the digitized storage information and the temperature. A battery deterioration judging device, comprising: a microcomputer for comparing the information with the microcomputer to judge the deterioration of the battery. 5. The battery deterioration judging device according to claim 3, wherein the means for detecting a temporal change in the battery voltage is a differential amplifier, wherein the differential amplifier has a constant delay time. A battery deterioration determination device characterized in that a battery deterioration determination is performed by detecting and comparing a real-time battery voltage with reference to a reference value.