JP2017058176A - Impedance measurement device and method for measuring impedance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an impedance measuring device and a measuring method for reducing a measurement error which occurs when the frequency of a measurement signal given to a measurement target and the frequency of a noise component are close to each other. SOLUTION: A detection signal appearing in a sample to be measured in a state where a measurement signal is not supplied is synchronously detected from two reference signals (synchronous signals) whose phases are orthogonal to each other to measure the noise level of the sample. Do this with multiple measurement frequencies to find a measurement frequency with less noise. A measurement signal with a frequency with less noise is supplied to the sample, and the detection signal is synchronously detected by a reference signal to measure the impedance of the sample. [Selection diagram] Fig. 1

Description

  The present invention relates to an impedance measuring apparatus and an impedance measuring method.

  As a method for measuring the internal impedance of elements constituting an electric circuit, there is an AC impedance measurement method in which an AC signal is applied to a sample to be measured and its electrical response is measured. In this method, the size of the resistance component, capacitance component, and inductance component of the sample can be examined. In addition, it is possible to determine what equivalent circuit these components constitute in the sample, or parameters of the equivalent circuit.

As such an impedance measurement method, a sine wave measurement AC current is supplied from a constant current source to a sample, and a voltage signal appearing on the sample is also referred to as a reference signal (or a reference signal) having the same frequency synchronized with the supplied measurement AC current. There is an impedance measurement method using synchronous detection that reduces the influence of noise components appearing in the sample by performing synchronous detection.
The following prior art documents are available for impedance measurement devices using synchronous detection.

Hereinafter, impedance measurement by synchronous detection will be described with reference to the drawings.
FIG. 6 is a diagram for explaining a conventional impedance measuring apparatus using synchronous detection.
The measurement alternating current i is supplied from the constant current source 10 to the sample 11 (DUT: abbreviation of device under test). Here, the sample 11 is a battery having an internal resistance Rx. The resistor (Rs) 12 is a current detection resistor for detecting the current value of the measurement alternating current i, and is inserted in series with the constant current source 10 and the sample 11. Reference numeral 15 denotes an amplifier that amplifies a detection signal (voltage signal) appearing on the sample 11 in accordance with the measurement alternating current i. Similarly, reference numeral 16 denotes an amplifier that amplifies the voltage signal detected by the current detection resistor (Rs) 12. The voltage detection signal v ₁ amplified by the amplifier 15 is input to the synchronous detector 20 through a band-pass filter (BPF) 17 that passes the measurement frequency. The reference signal v ₂ synchronized with the measurement alternating current i is amplified by the amplifier 16 and input to the synchronous detector 20. The synchronous detector 20 synchronously detects the voltage detection signal v ₁ with the reference signal v ₂ , and the detection output is input to a low-pass filter (LPF) 22 for removing an alternating current component, and the alternating current component is removed. It is input to a digital converter (ADC) 23. The analog-digital converter 23 converts the synchronous detection output into a digital signal. The converted digital signal is input to a calculation device (not shown), and the AC impedance value of the sample 11, the parameters of the equivalent circuit, and the like are calculated. These values are displayed on a display device (not shown) or printed and output. Is done.

Next, with reference to the waveform diagram of FIG. 7, the impedance measurement operation in the impedance measurement apparatus of FIG. 6 will be described.
From the constant current source 10, a sine wave of i = I sin (ω ₁ t) is applied to the sample 11 as a measurement alternating current. At both ends of the specimen 11, a voltage corresponding to the internal resistance R _x is generated in the battery, the voltage is output as v _{1 =} iR _x is amplified by the amplifier 15. Further, v ₂ = iRs corresponding to the current detection resistor R _s is output from the amplifier 16 and is synchronously detected by the synchronous detector 20. Here, v ₁ and v ₂ are
v ₁ = Vsin (ω ₁ t) = IR _x sin (ω ₁ t)
v ₂ = iRs = IR _s sin (ω ₁ t) = k sin (ω ₁ t)
It is. Note that k is a constant (I and Rs are constant).
Synchronous detection output is
v ₁ × v ₂ = kIR _x sin (ω ₁ t) sin (ω ₁ t)
= 1/2 · kIR _x [cos (0) −cos (2ω ₁ t)]
When the AC component is blocked by a low-pass filter, the input of the analog-digital converter 23 is
V _AD = 1/2 · kIR _x cos (0) = 1/2 · kIR _x
Thus, the resistance value Rx of the sample is
R _x = 2 / k · (V _AD / I)
It can ask for.
The waveforms of v ₁ , v ₂ , v ₁ × v ₂ , and v _AD in FIG. 7 are the signal waveforms of signals v ₁ , v ₂ , v ₁ × v ₂ , and v _AD in FIG. 6, respectively.

In this way, the voltage detection signal at both ends of the sample is synchronously detected with a reference signal having the same phase as the measurement AC current, and the AC component (cos (2ω ₁ t)) is removed by the low-pass filter, so that only the DC component is extracted. Therefore, the effective impedance of the sample to be measured including components other than pure resistance such as a battery can be obtained. Further, since the AC component that appears in the synchronous detection is removed by the low-pass filter, the influence of noise that is AC can be removed, and a minute signal buried in the noise can be extracted.

JP 2007-132806 A

  Since the sample to be measured is an element that constitutes an electric circuit, there is a sample on which noise is superimposed, and the noise affects impedance measurement. For example, a battery equipped in a UPS (uninterruptible power supply) is used as a measurement sample. Since the UPS needs to be constantly operated, the inverter and the converter are operated to perform charging or discharging. For this reason, noise generated from an inverter or a converter is often applied to the battery. Further, since the load is connected, noise often enters from the load side. As described above, when impedance measurement is performed using a UPS battery as a sample, a noise component is detected from the sample to which the measurement alternating current is applied.

  However, there are cases in which noise cannot be completely removed even if synchronous detection is performed using a reference signal having the same phase as the measurement AC current and AC components are removed by a low-pass filter.

When noise having the same frequency as the measurement frequency enters the detection signal as noise, it is superposed on the DC component of the synchronous detection output and cannot be removed by the low-pass filter. Further, if the noise has a frequency close to the measurement frequency, it is difficult to remove all of the noise from the characteristics of the low-pass filter.
For example, when the measurement frequency is 1 kHz and the noise frequency is 1.01 kHz, low AC components that are not direct currents can be removed, but only a small amount cannot be removed. In addition, since the bandpass filter cannot remove noise in the vicinity of the center frequency, which is the measurement frequency, it is difficult to remove noise in the vicinity of the measurement frequency.
For example, the low-pass filter has a frequency characteristic as shown in FIG. 8 and can sufficiently remove a high frequency, but a portion where a low frequency cannot be removed remains.

For this reason, when noise enters the detection signal, a measurement error occurs, and the measured impedance value also varies, resulting in a problem that the measured value is not stable.
The present invention provides an impedance measuring apparatus and a measuring method capable of reducing the measurement error and reducing the influence caused by the noise component having the same frequency as or close to that of the measurement AC current, and enabling stable measurement. Objective.

  A first aspect of the present invention is an impedance measuring apparatus, an AC source that supplies a measurement signal of a predetermined frequency to a sample to be measured, a reference signal generation unit that generates a reference signal synchronized with the measurement signal, and a sample The impedance measurement device includes a synchronous detection unit that synchronously detects a detection signal appearing in the reference signal and a low-pass filter that passes the synchronously detected signal, and the reference signal generation unit does not supply the measurement signal to the sample And a means for generating two reference signals having a predetermined measurement frequency and orthogonal in phase, and the synchronous detection unit uses the two reference signals to detect a detection signal appearing on the sample in a state in which no measurement signal is supplied. Each is provided with means for synchronous detection.

  The synchronous detection unit can include a plurality of bandpass filters having different pass frequencies and a selection unit that selects the plurality of bandpass filters according to the frequency of the measurement signal provided by the AC source.

  When measuring the impedance of the sample, the AC source preferably supplies a measurement signal having a frequency with a low noise level appearing on the sample. The sample may be a battery, and the AC source may be a constant current source.

  Another aspect of the present invention is an impedance measurement method, in which a measurement signal having a predetermined frequency is supplied to a sample to be measured, and a detection signal appearing on the sample is synchronously detected with a reference signal synchronized with the measurement signal, and is synchronously detected. The first and second reference signals having a phase orthogonal to the detection signal appearing in the sample in a state in which the measurement signal is not supplied to the sample by extracting the DC component of the measured signal and measuring the AC impedance of the sample The first measurement step for measuring the noise level that appears in the sample in the state where the measurement signal is not supplied is performed with the measurement signal of multiple frequencies, and the measurement signal of the multiple frequencies measured in the first measurement step. The second measurement step of selecting a frequency with a low noise level and supplying a measurement signal to the sample to measure the impedance of the sample is executed. The features.

  In addition, a plurality of bandpass filters that pass detection signals appearing in the sample are provided, and in the first measurement step, a plurality of bandpass filters are selected, a noise level is measured for a measurement signal of a plurality of frequencies, and a second In this measurement step, it is possible to perform impedance measurement of a sample by selecting a band pass filter having a frequency with a low noise level.

  Even if noise having the same frequency as or close to that of the measurement signal is mixed, the noise component can be removed, so that the impedance measurement error can be reduced. In addition, stable measurement can be performed.

It is a figure which shows the structure of the impedance measurement apparatus when calculating | requiring the measurement frequency with a small influence of noise in embodiment of this invention. It is a figure which shows the waveform which appears in each point of FIG. It is a figure which shows the structure of the impedance measuring apparatus when measuring the impedance of a sample with the measurement frequency with a small influence of noise in embodiment of this invention. It is a figure which shows an example of the equivalent circuit of a battery. It is a figure which shows the example of the Cole-Cole plot figure at the time of measuring with the frequency when the influence of noise is large, and selecting and measuring a small frequency. It is a figure which shows the structure of the impedance measuring apparatus using the conventional synchronous detection. It is a figure which shows the signal waveform in FIG. It is a figure which shows the frequency characteristic example of a low-pass filter.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of an impedance measuring apparatus according to an embodiment of the present invention, and illustrates a connection configuration when measuring a noise component.

The constant current source 10 is connected to a sample (DUT) 11 to be measured through a switch SW1. In the present embodiment, the sample 11 is a battery and has _Rx as an internal resistance. A current detection resistor (R _s ) 12 is inserted in a series circuit of the constant current source 10, the switch SW 1, and the sample 11. The switch SW2 is inserted between the constant current source 10 and the switch SW1, and between the sample 11 and the current detection resistor 12. Detection signals of the sample 11, a plurality of band-pass filter via an amplifier _{15 (BPF) 17 1, 17} 2, are input to the · · 17 _n. The switch SW3 selects any _{one of the} bandpass filters 17 _{1 to} 17 _n , and the output thereof is input to both the synchronous detectors 20 and 21. The current detection resistor 12 is connected to the amplifier 16, and the output of the amplifier 16 is input to the synchronous detector 20 and also to the synchronous detector 21 via the phase adjuster 19. The phase adjuster 19 adjusts the phase so that the phase of the output signal of the amplifier 16 is 90 ° with respect to the other reference signal. The detection outputs of the synchronous detectors 20 and 21 are input to a switch SW4, the output of the switch SW4 is input to a low-pass filter (LPF) 22, and the output of the low-pass filter 22 is input to an analog-digital converter (ADC) 23. Is done.

Next, the impedance measurement operation according to this embodiment will be described.
In the present embodiment, first, a first measurement step for measuring the noise level generated in the sample is executed by the measurement frequency, and then the impedance of the sample is measured by the measurement frequency having a small influence of noise by the measured noise level. A second measurement step is performed.

First, the measurement operation in the first noise level measurement step will be described.
The switch SW1 is turned off and the switch SW2 is turned on. Then, from the constant current source 10, and designated arbitrarily be measured with frequency _{f (sin (ω i t)} ) is applied to measure alternating current to the current detection resistor 12, the sample 11, the measurement alternating currents Do not apply. The voltage signal appearing in the current detection resistor 12 is amplified by the amplifier 16, and the output signal is branched and one of the signals is directly input to the synchronous detector 20 as a reference signal. The other reference signal of the branched output is converted into a reference signal whose phase is 90 ° different from that of the one reference signal by the phase adjuster 19, and is input to the other synchronous detector 21.
A detection signal that appears in the sample in a state where no alternating current for measurement is applied is amplified by the amplifier 15 and input to a plurality of bandpass filters 17 _{1 to} 17 _n having different pass frequencies, and the constant current source 10 is switched by the switch SW3. The output of the bandpass filter 17 _i that passes the input measurement frequency is selected and the output is input to both the synchronous detectors 20 and 21. The outputs of the synchronous detectors 20 and 21 are sequentially selected by the switch SW4 and input to the low-pass filter 22. The low-pass filter 22 removes the AC component through the low-pass filter 22 of the outputs of the synchronous detectors 20 and 21 sequentially selected by the switch SW4 and outputs it to the analog-digital converter 23.

Here, in the state where the measurement alternating current is not applied to the sample 11, the detection signal appearing on the sample 11 is a noise component. By synchronously detecting this detection signal through the band-pass filters 17 _{1 to} 17 _n , The noise level for each measurement frequency can be measured.

Hereinafter, measurement of noise levels occurring at both ends of the sample 11 will be described using equations.
Reference signals v ₂ and v ₃ are generated by setting a measurement frequency with the constant current source 10 and referring to the synchronous detection. v ₃ is given 90 ° (π / 2) by the phase adjuster 19 as a phase difference from v ₂ .
v ₂ = IR _s sin (ω _N t) (same phase as measurement AC current i N is 1 to n)
v ₃ = IR _s sin (ω _N t + 90 °) · (phase difference of 90 ° from measurement AC current i)
The signal after passing through the band pass filter 17 _i having the measurement frequency sin (ω _N t) as the center frequency in the band pass filter 17 is v _{1 ′,} which is detected from both ends of the sample 11. In the band pass filters 17 _{1 to} 17 _n , a band pass filter suitable for the measurement frequency is selected by the switch SW 3 and v ₁ is passed.

Where v ₁ ′ is
v ₁ ′ = G _BPF V _x cos (ω _x t + θ + θ _BPF )
G _BPF is the gain of the bandpass filter, Vx is the voltage of the noise generated by the sample (Rx), θ is the phase angle of the noise, and θ _BPF is the phase angle generated by the bandpass filter.
By synchronously detecting v ₁ ′ with v ₂ and v ₃ with the synchronous detectors 20 and 21,
Detection output _{v 1} '× _{v 2,} the detection output _{v 1} of the synchronous detector 21' of the synchronous detector 20 × _{v 3} is expressed as follows.
v ₁ '× v ₂ = 1/2 · G _BPF v _x IR _s {cos (ω _x t + θ + θ _BPF −ω _N t
_{)} - cos (ω x t} + θ + θ BPF + ω N t)
v ₁ '× v ₃ = 1/2 · G _BPF v _x IR _s {cos (ω _x t + θ + θ _BPF −ω _N t
-90 °)} - cos (ω x t + θ + θ BPF + ω N t + 90 °)
By passing the synchronously detected v ₁ ′ × v ₂ and v ₁ ′ × v ₃ through the low-pass filter 22, the measurement frequency component is removed and the noise component remains. The result of the analog-digital conversion is all noise and becomes a component that cannot be removed by the band pass filter and the low pass filter.
The square root of the sum of squares of v ₁ ′ × v ₂ and v ₁ ′ × v ₃ subjected to synchronous detection is the noise level.

  The reason why synchronous detection is performed with the reference signal as orthogonal phases is that the phase of noise is unknown, and if detection is performed with only one phase, the level is reduced by the phase of noise. An accurate noise level can be measured by performing synchronous detection on the same detection signal using a reference signal having an orthogonal phase.

An example in which the noise level is measured by changing the measurement frequency is shown in FIG. Of (a) is 2, a case where the measurement frequency and f1, the reference signal v an output synchronous detection at ₂ V _{AD_v1 '× v2} of the output of the low pass _filter, the reference signal v ₃ the output synchronous detection V _{AD — v1 ′ × v2} .
Figure 2 (a) is a case where the frequency of the noise is equal to the measured frequency f _1, the output of the low-pass filter, an example in which the DC component of the noise is output. 2 (b) is, if the frequency of the noise is close to the measurement frequency f _2, the output of the low-pass filter, also appeared AC component. FIG. 2C shows a case where the noise frequency is considerably distant from the measurement frequency f _3, and the output of the low-pass filter is almost zero level.

Thus, the noise level is measured by sequentially changing the measurement frequency from the constant current source 10 and switching the corresponding bandpass filters 17 _{1 to} 17 _n .
Here, regarding the switching of the band-pass filter, when switching the band-pass filter corresponding to the switching of the measurement frequency of the constant current source 10, the band-pass filter may be manually switched sequentially corresponding to a plurality of set frequencies. It is also possible to switch with.
Then, when measuring the impedance by applying a measurement alternating current to the sample 11, in the example of FIG. 2, a frequency having a low noise level is selected while avoiding f ₁ and f ₂ having a high noise level.

Next, a measurement alternating current is applied to the sample 11 to measure the impedance of the sample 11. At this time, a measurement frequency with a small influence of noise obtained by noise measurement is selected, and as shown in FIG. 3, the switch SW1 is turned on, the switch SW2 is turned off, and the switch SW3 is connected to the bandpass filters 17 _{1 to} 17 _n . Among them, a bandpass filter that passes the measurement frequency is selected, a measurement alternating current is supplied from the constant current source 10 to the sample 11, and the impedance of the sample is measured in the same manner as in the conventional method.

  As described above, first, the noise level appearing on the sample 11 is measured for each measurement frequency, and the impedance of the sample can be measured at a measurement frequency with a low noise level, that is, with a small influence of noise.

(Effects of the present invention)
In the present invention, even when noise appears in the sample 11 to be measured, the measurement error can be reduced because the impedance can be measured at a measurement frequency with a low noise level and a small influence of noise. In addition, since the measurement value is less likely to vary due to noise, the output is stable and the measurement time can be shortened.
Furthermore, even for a sample such as a UPS battery in which noise is superimposed on a detection signal, it is possible to select and measure a frequency that is less affected by noise.

An example will be described in which the impedance of a battery such as a battery is measured to obtain a Cole-Cole plot diagram for evaluating the characteristics of the battery.
The equivalent circuit of FIG. 4 is a diagram illustrating an example of an equivalent circuit of a battery. One model of an equivalent circuit of a battery can be represented by a circuit in which a series circuit of an inductance L1 and a resistor Rs and a parallel circuit of a resistor R1 and a capacitance C1 are connected. At this time, in the low frequency region, the current flowing through the resistor Rs and the resistor R1 is large. When the frequency is high, the impedance portion occupied by the inductance L1 is large and the impedance of the capacitance C1 is small.

About such an equivalent circuit, the change in the impedance of the battery according to the frequency is drawn on the plane composed of the real part and the imaginary part of the impedance, which is a Cole-Cole plot diagram.
In the Cole-Cole plot diagram, the impedance of the battery is measured by scanning the frequency applied to the measurement sample from the constant current source. At this time, when the impedance is measured while changing the load with the battery load device, or when the UPS battery is measured, if the impedance value to be measured varies due to the influence of noise, as shown in FIG. Therefore, there is a possibility that an accurate Cole-Cole plot diagram cannot be drawn.
In the present invention, since the impedance of the battery can be measured by selecting a measurement frequency with a small noise influence, the number of frequencies that can be measured may be reduced, but the influence of the noise can be reduced. By using it, it is possible to draw a smooth Cole-Cole plot as shown in FIG.

  Although the above embodiment has been described with reference to an example in which an AC constant current is supplied from the constant current source 11 to the sample and the impedance is measured, impedance measurement using a voltage is also possible. For example, an AC constant voltage may be supplied from a voltage source to the sample and the impedance may be measured by synchronous detection. When the object to be measured is a battery, it is preferable to perform impedance measurement with a constant current. However, for example, in the case of a capacitor that is incorporated in an electric circuit and may cause noise, impedance measurement with constant voltage AC may be used. .

10 Constant current source
11 Sample (DUT)
12 Resistance for current detection (Rs)
15,16 amplifiers 17, 17 ₁ to 17 _N bandpass filter (BPF)
19 Phase adjuster 20, 21 Synchronous detector 22 Low pass filter (LPF)
23 Analog to digital converter SW1 to SW4 switch

Although the above embodiment has been described with reference to an example in which an AC constant current is supplied from the constant current source 11 to the sample and the impedance is measured, impedance measurement using a voltage is also possible. For example, an AC constant voltage may be supplied from a voltage source to the sample and the impedance may be measured by synchronous detection. When the measurement target is a battery, it is preferable to perform impedance measurement with a constant current. However, for example, in the case of a capacitor that is incorporated in an electric circuit and may cause noise, impedance measurement with an AC constant voltage may be used. .

Claims (6)

An AC source that supplies a measurement signal of a predetermined frequency to the sample to be measured;
A reference signal generator for generating a reference signal synchronized with the measurement signal;
A synchronous detector for synchronously detecting a detection signal appearing in the sample with the reference signal;
An impedance measuring device comprising: a low-pass filter that passes a synchronously detected signal;
The reference signal generator is
Means for generating two reference signals having a predetermined measurement frequency and orthogonal in phase without supplying a measurement signal to the sample;
The synchronous detector is
An impedance measuring apparatus comprising: means for synchronously detecting a detection signal appearing on a sample in a state where no measurement signal is supplied, using the two reference signals. The impedance measuring device according to claim 1,
The synchronous detector is
A plurality of band pass filters with different pass frequencies;
An impedance measuring apparatus comprising: selection means for selecting the plurality of bandpass filters according to a frequency of a measurement signal provided by the AC source. The impedance measuring device according to claim 1 or 2,
When the impedance measurement of the sample is performed, the AC source supplies a measurement signal having a frequency with a low noise level appearing on the sample. The impedance measuring device according to any one of claims 1 to 3,
The impedance measurement apparatus, wherein the sample is a battery, and the alternating current source is a constant current source. A measurement signal having a predetermined frequency is supplied to a sample to be measured, a detection signal appearing on the sample is synchronously detected with a reference signal synchronized with the measurement signal, and a direct current component of the synchronously detected signal is extracted to obtain an alternating current of the sample. An impedance measurement method for measuring impedance,
The detection level that appears in the sample when no measurement signal is supplied to the sample is subjected to synchronous detection with the first and second reference signals having orthogonal phases, and the noise level that appears in the sample when no measurement signal is supplied Performing a first measurement step to measure multiple frequency measurement signals,
Executing a second measurement step of selecting a frequency having a low noise level from the measurement signals of a plurality of frequencies measured in the first measurement step and supplying the measurement signal to the sample to measure the impedance of the sample. Impedance measuring method characterized by this. The impedance measuring method according to claim 5,
A plurality of band-pass filters that pass detection signals appearing on the sample;
In the first measurement step, a plurality of band-pass filters are selected and a noise level is measured for a measurement signal of a plurality of frequencies,
The impedance measurement method characterized in that in the second measurement step, the impedance measurement of the sample is performed by selecting a bandpass filter having a low noise level.