JP2003090869A - Impedance measuring device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To realize an impedance measuring device capable of measuring impedance at a plurality of frequency points in a short time. An AC signal is supplied to a load device, and the load device discharges a current corresponding to the frequency of the supplied AC signal from the object to be measured. In an impedance measuring apparatus for obtaining an impedance of a measured object based on a flowing current, a waveform generating means for providing a waveform having a plurality of high-frequency components to the load device, a current flowing from the measured object and a An analyzing means for performing an analysis for each component of the waveform based on the voltages at both ends to obtain an impedance is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an impedance measuring device for measuring internal impedance of a battery.

[0002]

2. Description of the Related Art It is common practice to measure the internal impedance of a battery in order to know its performance.
FIG. 8 is a general equivalent circuit diagram of the internal impedance of the battery. The battery is, for example, a fuel cell. The equivalent circuit of the battery is a circuit in which the reaction resistance R and the electric double layer capacity C are connected in parallel, and the solution resistance Rsoln is connected in series to this parallel connection portion. The fuel cell has a structure in which electrodes are arranged so as to face each other in a solution. The reaction resistance R is a resistance applied when a molecule comes out of a solution from an electrode. The electric double layer capacitance C is the capacitance generated by the electrodes. The solution resistance Rsoln is a resistance applied when electric charges move in the solution.

FIG. 9 is a diagram showing a configuration example of a conventional impedance measuring apparatus. In FIG. 9, the frequency response analyzer 10 has a sine wave sweep oscillator 11 and a digital Fourier calculator 12. The sine wave sweep oscillator 11 generates a sine wave signal from an arbitrary low frequency to a high frequency. The sine wave signal generated by the sine wave sweep oscillator 11 is applied to the load device 20. The battery 30 to be measured is connected to the load device 20.

The load device 20 is a sine wave sweep oscillator 1
The battery 30 is discharged with a current amount whose amplitude is proportional to the sine wave signal given by 1. Digital Fourier calculator 1
2, the discharge current and the voltage across the battery at this time are subjected to digital Fourier calculation to obtain the internal impedance of the battery from the gain at each frequency of the sine wave signal and the phase characteristic. The gain here is (amplitude of voltage across battery) /
(Discharge current amplitude). The gain measuring means 121 obtains the gain, and the phase measuring means 122 obtains the phase. The impedance can be obtained from the gain and phase characteristics.

FIG. 10 is a diagram showing an example of measurement results. In FIG. 10, the horizontal axis represents frequency and the vertical axis represents phase and gain. In FIG. 9, A1 and A2 are graphs showing gain and phase, respectively.

In the field of electrochemistry such as batteries, it is common practice to show impedance in a Cole-Cole diagram. FIG. 11 is a Col showing the measurement result of FIG.
It is an e-Cole figure. In the Cole-Cole diagram, the horizontal part represents the real part of impedance and the vertical axis represents the imaginary part. In the arc-shaped graph (the locus taken by impedance) of the Cole-Cole diagram, the real part at the left end where the imaginary part is 0 is Rsoln in the equivalent circuit of FIG. 7, and the size of the real part between the left end and the right end of the arc graph. Is R in the equivalent circuit of FIG. 8, and the maximum value of the imaginary part of the arc-shaped graph is C.
Therefore, all the parameters of the equivalent circuit diagram inside the battery can be known from the Cole-Cole diagram.

In the digital Fourier calculation method, due to its measurement principle, the measured value cannot be obtained unless the signal output from the battery 30 is measured over a period of one cycle or more. If the frequency of the sine wave signal applied to the load device 20 is swept and several points are measured, a longer measurement time is required. In particular, when measuring the internal impedance of a battery, the frequency of the signal to be measured (frequency of the sine wave signal) is often several Hz or less, and the time required for one measurement is the data acquisition time, that is, the measurement. Overwhelmingly depends on the length of the period of the signal of interest. Therefore, there is a problem that the state of the battery may change while sweeping the frequency over a long period of time.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is obtained from an object to be measured by driving the object to be measured with a waveform having a plurality of high frequency components. It is an object of the present invention to realize an impedance measuring device capable of measuring impedance at a plurality of frequency points in a short time by performing an analysis for each component of a waveform to obtain the impedance.

[0009]

The present invention is an impedance measuring device configured as follows.

(1) An AC signal is applied to the load device, and the load device discharges a current according to the frequency of the applied AC signal from the object to be measured. At this time, the voltage across the object to be measured and the object to be measured are measured. In an impedance measuring apparatus for obtaining an impedance of an object to be measured based on a current flowing from the object, a waveform generating means for applying a waveform having a plurality of high frequency components to the load device, a current flowing from the object to be measured and the object to be measured. Based on the voltage across the target, by analyzing for each component of the waveform, the analysis means for obtaining the impedance,
An impedance measuring device comprising:

(2) An AC signal is applied to the load device, and the load device discharges a current corresponding to the frequency of the applied AC signal from the battery. At this time, the voltage across the battery and the current flowing from the battery are also detected. In the impedance measuring device for obtaining the internal impedance of the battery, the waveform generating means for applying a waveform having a plurality of high frequency components to the load device, the current flowing from the battery and the voltage across the battery, An impedance measuring device comprising: an analyzing unit that analyzes each component of a waveform to obtain an impedance.

(3) The impedance measuring device according to (1) or (2), wherein the analyzing means performs analysis by a fast Fourier transform.

(4) The impedance measuring device according to (1) or (2), wherein the waveform generating means is an arbitrary waveform generator that generates a waveform having an arbitrary harmonic component.

(5) The waveform generating means is Ksinx /
The impedance measuring device according to (1) or (2), which generates a waveform defined by x (x is time, K is a constant).

(6) The waveform generating means divides a predetermined frequency range into a predetermined number on a substantially logarithmic scale, and generates a waveform in which sine waves of the divided frequencies are superimposed with the same amplitude. The impedance measuring device according to (1) or (2).

(7) The impedance measuring device according to (1) or (2), wherein the waveform generating means generates a waveform defined by the following equation.

[Equation 3] Here, n: value used to set the number of waveforms to be superimposed m: value used to set the frequency of each waveform to be superimposed v: amplitude of each waveform x: time

(8) The impedance measuring device according to (1) or (2), wherein the waveform generating means generates a waveform defined by the following equation.

[Equation 4] Here, n: a value used to set the number of waveforms to be superimposed m: a value used to set the frequency of each waveform to be superimposed v: amplitude of each waveform x: time INT (a): a value obtained by converting a to an integer

[0018]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. 1 that are the same as those in FIG. 6 are given the same reference numerals. Figure 1
Thus, the frequency response analyzer 40 has an arbitrary waveform generator 50. The arbitrary waveform generator 50 generates not only a single frequency sine wave but also a waveform having a plurality of high frequency components.
By giving the output waveform of the arbitrary waveform generator 50 to the load device 20, the discharge current of the battery is made into a waveform having a plurality of high frequency components. In the digital Fourier calculator 12, the battery discharge current is FFT (Fast Fourier Transform) for each component.
And analyze. The more harmonic components that are superimposed on the output waveform of the arbitrary waveform generator 50, the greater the amount of frequency point data that can be obtained at one time. The analysis means in the claims corresponds to the digital Fourier calculator 12.

FIG. 2 is a diagram showing an example of an output waveform of the arbitrary waveform generator 50. In FIG. 2, the horizontal axis represents time and the vertical axis represents amplitude. In FIG. 2, the arbitrary waveform generator 50 outputs the waveform B3 in which the fundamental wave B1 and the third harmonic wave B2 having the same amplitude are superposed.

FIG. 3 is a diagram showing another example of the waveform output by the arbitrary waveform generator 50. In FIG. 3, the horizontal axis represents time and the vertical axis represents amplitude. FIG. 4 is a diagram showing the signal level of each frequency component included in the waveform of FIG. The horizontal axis of FIG. 4 is frequency,
The vertical axis is the amplitude. In the example of FIG. 3, the output waveform is Ksin.
x / x (x is time, K is a constant). Ksinx / x
As shown in FIG. 4, all the high frequency components are contained in the waveform of the same energy. This has the advantage that the frequency data can be obtained densely at once. This is effective when the battery state changes drastically with time.

The input portion of the frequency response analyzer 40 is S
From the viewpoint of the / N ratio (the ratio of signal to noise) and the effective use of the dynamic range of the A / D converter, it is preferable that the input level is large. Here, the input unit is an input amplifier through which the signal from the battery 30 is input to the frequency response analyzer 40. The A / D converter is provided at the subsequent stage of the input section, A / D-converts the signal input from the input section, and supplies it to the digital Fourier calculator 12. However, in the battery performance test, the AC signal is input for measurement and is an unnecessary disturbance for the battery. When the amplitude level of the input AC signal is large, it may affect the performance of the battery. Therefore, the AC signal is required to be as small as possible.

Ideally, waveforms having more frequency components are superposed and the amplitude of the superposed waveforms is small. The input waveform f (x) is defined as follows. n: a positive integer, φn: the maximum phase amplitude in the nth harmonic occurs when f ′ (x) = 0, so that at this time f (x) is minimized so that each harmonic component Adjust the phase.

In particular, in the equivalent circuit of FIG.
Focusing on n and R, if the discharge current is subtracted from the battery with a waveform in which the high frequency component is superimposed on the direct current, Rsoln + R can be directly obtained from the direct current component of the measurement result, and R can be directly obtained from the high frequency component. When the impedance is known to some extent, it is possible to simply obtain the Cole-Cole diagram by only one measurement if the frequency components to be superposed are efficiently set.

Further, another example of the waveform output by the above-mentioned arbitrary waveform generator 50 will be described. Cole-Col
In creating an e-diagram, in addition to closely measuring impedance at a given frequency range at once, the data must be collected from the full range of frequencies. That is, Co
In the le-Cole diagram, it is required that the data be plotted at substantially equal intervals.

However, as the frequency of the signal increases linearly, the amount of change in impedance including the reactance component decreases. Therefore, the distribution of the plotted data is biased depending on the frequency. In order to collect data evenly from the desired frequency range, increase the frequency spectrum to be superimposed at once, or change the frequency of the fundamental wave composed of the superimposed waveforms and collect the data in multiple measurements. Must. When the number of waveforms to be superimposed at one time increases, the peak value increases, and the amplitude of each waveform must be reduced, resulting in low resolution of a single spectrum. In addition, measurement from a plurality of times is not desirable from the viewpoint of work efficiency.

Therefore, the input waveform is defined as follows.

[Equation 5] Here, n: value used to set the number of waveforms to be superimposed m: value used to set the frequency of each waveform to be superimposed v: amplitude x: time An example of this waveform will be specifically described with reference to the drawings. .

FIG. 5 is a diagram showing another example of the waveform output by the arbitrary waveform generator 50 described above. In the example of FIG. 5, the output waveform f (x) is

[Equation 6] Is.

In FIG. 5, the horizontal axis represents time and the vertical axis represents amplitude. FIG. 6 is a diagram showing the signal level of each frequency component included in the waveform of FIG. In FIG. 6, the horizontal axis represents frequency and the vertical axis represents amplitude. In the waveform of the example of FIG. 5, frequencies of 20 different orders are included with the same amplitude in the frequency range of 10 Hz to about 800 Hz. Details are as follows.

By setting the amplitude of each waveform to be 0.05, the amplitude of the waveform in FIG. 5 is approximated to 1 and is set to a level suitable for signal processing. This is based on the relationship that the product of the amplitude of each waveform and the number of waveforms is approximately equal to the amplitude of the superimposed waveform. Specifically, the amplitude of the waveform in FIG.
It is 13, and the amount exceeding the target value of 1 can be further reduced to improve the resolution. INT
(a) is a value obtained by converting a into an integer. This is because if the frequency is treated as a real number, high resolution is required for the FFT. By converting the frequency to an integer, if necessary, FF
T may have a relatively low resolution.

Further, the frequency is from 10 Hz to about 800 H
It is divided into 10 on a logarithmic scale every 10 times (one digit of frequency) in the range up to z. In reality, since the frequencies are integerized as described above, the scale is almost logarithmic. Integer conversion is a process of rounding off values such as rounding off fractions. Specifically, 10, 13, 16, 20, 2
5, 32, 40, 50, 63, 79, 100, 130,
160, 200, 250, 320, 400, 500, 6
The frequency is 30,790.

When the impedances at these frequencies are calculated and plotted on the Cole-Cole diagram, the plot becomes almost uniform as shown in FIG. As described above, it is possible to collect data at a substantially uniform interval all at once with sufficient resolution in the frequency range of impedance measurement.

From these facts, if the impedance characteristic is known to some extent, the maximum frequency, the minimum frequency, and the frequency step can be set in advance close to appropriate values, so that the Cole- Cole
It is possible to obtain a figure. For example, the lowest frequency is 10
When the frequency is Hz and the maximum frequency is 10 KHz, the output waveform f (x) is generated based on the following equation.

[Equation 7]

As a result, waveforms of 16 different frequencies from 10 Hz to 10 KHz are superimposed. When actually measured with such a waveform, although the resolution of the Cole-Cole diagram becomes coarse, it is possible to measure at once from 10 Hz to 10 KHz with temporal simultaneity.

When a current is output from a storage battery or the like, the remaining amount decreases, so that the characteristics of the battery change. In such a case, the temporal simultaneity of plot points becomes important. Therefore, it is effective for drawing when it is sufficient to grasp a rough tendency such as battery quality judgment.

In the embodiment, the case where the arbitrary waveform generator is used has been described, but the present invention is not limited to this, and any waveform generating means for generating a waveform having a plurality of harmonic components may be used. Moreover, although the case where the impedance of the battery is measured has been described in the embodiment, the measurement target is not limited to the battery.

[0036]

According to the present invention, the following effects can be obtained.

According to the first aspect of the invention, the object to be measured is driven by the waveform having a plurality of high frequency components, and the impedance is obtained by analyzing each component of the waveform obtained from the object to be measured. Thereby, the impedances at a plurality of frequency points can be measured in a short time. Also,
The simultaneity of data at each frequency can be secured.

According to the second aspect of the invention, the battery is driven by the waveform having a plurality of high frequency components, and the impedance is obtained by analyzing each component of the waveform obtained from the battery. Thereby, the internal impedance of the battery at a plurality of frequency points can be measured in a short time. Further, it is possible to secure the simultaneity of data at each frequency.

According to the third aspect of the present invention, the analysis means performs the analysis by the fast Fourier transform, so that the analysis time can be shortened.

According to the fourth aspect of the invention, since the waveform generating means is an arbitrary waveform generator, impedance at an arbitrary frequency point can be measured.

According to the fifth aspect of the invention, the waveform generating means generates a waveform defined by Ksinx / x,
All high-frequency components are included in the analysis result with equal energy. As a result, the frequency data can be obtained densely at one time, which is effective when the battery state changes drastically with time.

In the inventions according to claims 6 to 8,
Divide the range of frequencies by almost a logarithmic scale, calculate the impedance at these frequencies, and calculate the Cole-Col.
Plot on the e diagram. As a result, data can be collected at once at substantially equal intervals in the desired frequency range of impedance measurement. If the impedance characteristic is known to some extent, the maximum frequency, the minimum frequency, and the frequency step can be set close to appropriate values in advance. This makes it possible to collect effective data for drawing when it is sufficient to grasp a general tendency such as quality judgment.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a waveform used for impedance measurement in the present invention.

FIG. 3 is a diagram showing another example of a waveform used for impedance measurement in the present invention.

FIG. 4 is a diagram showing signal levels of respective frequency components included in the waveform of FIG.

FIG. 5 is a diagram showing another example of a waveform used for impedance measurement in the present invention.

6 is a diagram showing the signal level of each frequency component included in the waveform of FIG.

7 is a Cole-C showing a measurement result based on the waveform of FIG.
It is an ole figure.

FIG. 8 is an equivalent circuit diagram of the internal impedance of the battery.

FIG. 9 is a diagram showing a configuration example of a conventional impedance measuring apparatus.

FIG. 10 is a diagram showing an example of measurement results.

11 is a Cole-Cole diagram showing the measurement result of FIG. 9;

[Explanation of symbols]

12 Digital Fourier calculator 20 load device 30 batteries

Claims (8)

[Claims] 1. An AC signal is applied to a load device, and the load device discharges a current according to the frequency of the applied AC signal from the object to be measured. At this time, the voltage across the object to be measured and the object to be measured. In an impedance measuring device for obtaining the impedance of a measured object based on the current flowing from the waveform measuring means, a waveform generating means for applying a waveform having a plurality of high frequency components to the load device, a current flowing from the measured object and the measured object An impedance measuring device for analyzing each component of the above-mentioned waveform based on the voltage between both ends of the to obtain an impedance. 2. An AC signal is applied to the load device, and the load device discharges a current corresponding to the frequency of the applied AC signal from the battery. At this time, the voltage across the battery and the current flowing from the battery are used. In the impedance measuring device for determining the internal impedance of the battery, the waveform generating means for applying a waveform having a plurality of high frequency components to the load device, and the waveform based on the current flowing from the battery and the voltage across the battery. An impedance measuring device comprising: an analyzing unit that analyzes the impedance of each component to determine the impedance. 3. The impedance measuring apparatus according to claim 1 or 2, wherein the analyzing means performs analysis by a fast Fourier transform. 4. The impedance measuring apparatus according to claim 1, wherein the waveform generating means is an arbitrary waveform generator that generates a waveform having an arbitrary harmonic component. 5. The waveform generating means is Ksinx / x
The impedance measuring device according to claim 1 or 2, wherein a waveform defined by (x is time and K is a constant) is generated. 6. The waveform generating means divides a predetermined frequency range into a predetermined number on a substantially logarithmic scale, and generates a waveform in which sine waves of the divided frequencies are superimposed with the same amplitude. The impedance measuring device according to claim 1 or 2. 7. The impedance measuring device according to claim 1 or 2, wherein the waveform generating means generates a waveform defined by the following equation. [Equation 1] Here, n: value used to set the number of waveforms to be superimposed m: value used to set the frequency of each waveform to be superimposed v: amplitude of each waveform x: time 8. The impedance measuring device according to claim 1 or 2, wherein the waveform generating means generates a waveform defined by the following equation. [Equation 2] Here, n: a value used to set the number of waveforms to be superimposed m: a value used to set the frequency of each waveform to be superimposed v: amplitude of each waveform x: time INT (a): a value obtained by converting a to an integer