Method and device for supporting determination of deterioration of electrical energy supply medium

Abstract

The present invention provides a battery deterioration determination support device which is small in size, low in power consumption, and capable of greatly shortening a measurement time.　This method supports a deterioration determination by using an electronic circuit to acquire an internal characteristic of an electrical energy supply medium. The method includes: acquiring the internal characteristics of a battery in advance; selecting two or more frequencies required to determine that the battery is satisfactory or unsatisfactory; storing the selected frequencies; performing discharge control based on the selected frequencies; acquiring voltage data and current data by using voltage measurement means and current measurement means; calculating correction voltage data by performing correction processing on the voltage data; calculating resistance data from the correction voltage data and the current data; calculating at least a portion of Cole-Cole plot data from the resistance data; and performing fitting processing by using at least a portion of the Cole-Cole plot data as necessary.

Description

Method and device for supporting determination of deterioration of electric energy supply medium

[0001] The present invention relates to a method for assisting in the determination of deterioration of an electric energy supply medium such as a battery, and more specifically to a method for assisting in the determination of battery deterioration by acquiring the internal characteristics of a battery such as a lithium ion secondary battery, a nickel-metal hydride secondary battery, a solar cell, or a fuel cell.

[0002] In recent years, various methods have been proposed for diagnosing the degradation state of electric energy supply media such as secondary batteries. One of these diagnostic methods employs a Cole-Cole plot or Nyquist plot, in which the horizontal axis represents the real part of the AC impedance of the secondary battery, etc., and the vertical axis represents the imaginary part of the AC impedance of the secondary battery, etc.

[0003] (Explanation of the principle of the Cole-Cole plot) A Cole-Cole plot is a plot of measured values ​​obtained by the AC-IR measurement method, which measures the internal resistance of a battery using an alternating current. Specifically, it is a scatter diagram obtained by measuring the current and voltage values ​​when sine waves of various frequencies are applied to the battery under test, calculating the resistance value including the phase difference from these values, and plotting the real and imaginary parts of the resistance value. Note that in the case of an alternating current, the voltage value V = Vr + Vi × j (where j = (-1) ０．５ ), the current value I is expressed as Ir + Ii × j, and the resistance value R is calculated as a complex number, V / I. As an example, when V = -229.585443703293 - 4195.93748617154i and I = -1.47516371438595 - 5.46385648982277i, the calculation is R = 0.0012072190153994 - 0.000304333685571092i.

[0004] Furthermore, applying a sine wave means charging and discharging the battery being measured. The measurement frequency is set from 0.1 Hz to 1 kHz, and several dozen to a hundred measurements are required. While measurement time is not an issue at high frequencies, for example, a measurement at a frequency of 0.1 Hz takes 10 seconds, so measuring at all planned frequencies takes several minutes to 10 minutes. Furthermore, if noise leveling is performed to reduce noise, additional measurement time is required. For example, if you want to take the average of four measurements, the time required for one measurement will be four times longer than the example above, approximately 20 to 30 minutes.

[0005] An example of generating a Cole-Cole plot from measurement results obtained by an AC-IR meter will be described with reference to Figures 8A and 8B. Figure 8A exemplifies measurement results obtained by an AC-IR meter. Specifically, the figure shows current and voltage measurements made by the AC-IR meter when sine waves of various frequencies are applied to the battery under test. Resistance values ​​(real and imaginary parts) including the phase difference calculated from these measurements are plotted for each frequency. Figure 8B shows a plot of the real and imaginary parts of the resistance values ​​shown in Figure 8A for each frequency. Furthermore, in the Cole-Cole plot shown in Figure 8B, the zero-crossing point (A in the figure) and the change point (depression B in the figure) tend to appear in the same positions for batteries with the same conditions (temperature, battery voltage, etc., the same applies below) and characteristics. Therefore, deviations between these points for batteries under the same conditions and characteristics indicate an abnormality or degradation. This type of determination method can be used, for example, for battery product manufacturing checks.

[0006] (AC-IR Measurement Method) The AC-IR measurement method is a technique for estimating the internal parameter values ​​of a battery by acquiring the battery's AC characteristics. Conventional methods estimate the battery's degradation by determining how much each parameter value deviates from its normal value. While the DC-IR measurement method has also been used in the past, this is a judgment method based on the resistance value measured by measuring the battery's internal resistance using direct current. Because the AC-IR measurement method uses a small current load, it causes less damage to the battery and is said to provide more reliable measurements than the DC-IR measurement method, which only reveals a portion of the battery's characteristics. The AC characteristics obtained by the AC-IR measurement method can be used to understand various reaction states, not only in storage batteries, but also in solar cells, fuel cells, and chemical reactions.

[0007] FIG. 9A conceptually illustrates the physical structure of a lithium-ion secondary battery. In FIG. 9A, the battery 900 includes a positive electrode 910, a negative electrode 920, and an electrolyte 930. In one embodiment, the positive electrode 910 uses an aluminum alloy foil approximately 15 to 30 μm thick as a positive electrode current collector 911, and the negative electrode 920 uses pure copper, such as rolled copper foil or electrolytic copper foil, as a negative electrode current collector 921. Reference numeral 940 denotes a Li compound formed on the negative electrode by decomposition of the electrolyte and additives during the initial charging process of the lithium-ion secondary battery, and is called an SEI (Solid Electrolyte Interphase). Particles without reference numerals in the figure represent various additives. The hexagonal particles 951a and 951b, for example, represent Li+ (ions).

[0008] The physical structure of the secondary battery as shown in Fig. 9A can be considered as an equivalent circuit 950 shown in Fig. 9B. The circuit shown in Fig. 9B includes at least an RC parallel circuit 961 that is an equivalent circuit of the SEI, an RC parallel circuit 962 that is an equivalent circuit of the anode (positive electrode part), and an RC parallel circuit 963 that is an equivalent circuit of the cathode (negative electrode part). In each RC parallel circuit, Ｆ , CPE Ａ , CPE Ｃ9A and 9B, the deterioration state of a secondary battery can be diagnosed using a Cole-Cole plot.

[0009] Furthermore, as shown in Figure 9C, the Cole-Cole plot reveals that the solution resistance, which has the fastest response, appears in the 1 kHz to 300 Hz range, the electric double layer resistance on the electrode surface appears in the 300 Hz to 0.1 Hz range, and the diffusion resistance of the active material inside the electrode appears in the 0.1 Hz or lower range. For this reason, Figure 9D is sometimes used as an alternative equivalent circuit model (simplified equivalent circuit model). This simplified equivalent circuit model also allows the internal characteristic parameters of the battery to be read, enabling the deterioration of the battery to be assessed. As mentioned above, the zero-crossing point (A in Figure 8B) and the change point (depression B in Figure 8B) tend to appear in the same positions for batteries with the same characteristics under the same conditions (temperature, battery voltage, etc.). This also means that AC-IR is sensitive to temperature and SoC (State of Charge).

[0010] Based on such conventional methods, a battery degradation diagnosis system has been proposed that quickly diagnoses the degradation state of a secondary battery while reducing the calculation load on the measuring device (Patent Document 1).

[0011] Specifically, a battery degradation diagnosis system is disclosed that includes a measuring device that measures battery status data related to the state of the electrical characteristics of a secondary battery, and a diagnostic processing device that diagnoses the degradation status of the secondary battery, wherein the diagnostic processing device is equipped with a memory means that pre-stores battery degradation information for identifying the degradation characteristics of the secondary battery, a receiving means that receives the battery status data from the measuring device, a calculation means that, when the receiving means receives the battery status data, calculates the degradation status of the secondary battery corresponding to the battery status data by referring to the battery degradation information stored in the memory means, and a transmission means that transmits the diagnostic result indicating the degradation status of the secondary battery calculated by the calculation means to the measuring device.

[0012] Furthermore, methods and devices for determining the state of a secondary battery that can more accurately determine the state of a secondary battery have been proposed (Patent Documents 2 and 3).

[0013] That is, Patent Document 2 discloses a secondary battery state determination method that acquires a complex impedance measured by applying an AC voltage or an AC current to a secondary battery to be determined, and determines the state of the secondary battery based on the acquired complex impedance, the secondary battery state determination method including: a first capacity deviation determination step that determines the presence or absence of a first capacity deviation based on a comparison between a value of the complex impedance at a predetermined frequency and a first determination value used for determining a negative electrode capacity deviation; and a second capacity deviation determination step that determines the presence or absence of a second capacity deviation based on a comparison between the slope of the complex impedance with respect to the real axis in a diffusion resistance region and a second determination value used for determining a positive electrode capacity deviation when it is determined in the first capacity deviation determination step that the first capacity deviation has not occurred.

[0014] Furthermore, Patent Document 3 discloses a secondary battery state determination method for determining a micro-short circuit prone state, which is a state in which a micro-short circuit is likely to occur in the secondary battery, comprising: an electron transfer resistance measurement step of measuring an electron transfer resistance Rs of the secondary battery by applying a voltage or current of a predetermined frequency or higher to an electrode system of the secondary battery; an electrode distance quality determination step of comparing the electron transfer resistance Rs obtained in the electron transfer resistance measurement step with a preset lower threshold value Rs min; and a secondary battery state determination step of determining that the electrode distance is good and the secondary battery is a good product if the electron transfer resistance Rs is equal to or higher than the lower threshold value Rs min in the electrode distance quality determination step.

[0015] JP 2020-205253 A JP 2019-049479 A JP 2021-174729 A

[0016] However, the conventional AR-IR measurement method has problems such as high cost, high power consumption, and long measurement times, so it has been necessary to judge the quality of a battery based on the battery characteristics measured using DC-IR measurement or simple charging and discharging. For example, regarding high power consumption, the conventional AC-IR measurement method applies a sine wave to the secondary battery, which requires not only discharging but also charging. Not only does charging a battery require a certain amount of power, but increasing the charge / discharge current to improve accuracy requires even more power, resulting in an AC power supply, which increases the size of the device. At the same time, this raises the issue of increased manufacturing costs.

[0017] In addition, with regard to the lengthening of measurement time, since all frequencies must be measured, the accumulation of measurement time in the low frequency band was a particular issue.

[0018] Therefore, a method for supporting deterioration determination of an electric energy supply medium according to one embodiment of the present invention is a method for supporting deterioration determination of an electric energy supply medium by acquiring internal characteristics of the electric energy supply medium using an electronic circuit, the electronic circuit comprising: control means for controlling ON / OFF discharge of the electric energy supply medium; voltage measurement means for measuring the voltage of the ON / OFF controlled electric energy supply medium to acquire voltage measurement data; and current measurement means for measuring the amount of current discharged by the electric energy supply medium, the electronic circuit acquiring a voltage difference between the start and end of measurement for a period associated with the ON / OFF control, and a correction process using correction data obtained by dividing the detected voltage difference by the discharge period in the cycle; a first conversion process for converting the result of the correction process from the time domain to the frequency domain (Fourier transform process) or from the time domain to the complex domain (Laplace transform process); a second conversion process for converting the correction data from the time domain to the frequency domain (Fourier transform process) or from the time domain to the complex domain (Laplace transform process); and a process for offsetting the influence of the correction process by applying the result of the second correction process to the result of the first conversion process.

[0019] The first transformation process is a Fourier transform process, and the second transformation process is characterized in that it generates second corrected transformation data that takes into account a gain coefficient due to the influence of the window function, for the first corrected transformation data that is generated by applying a window function to the correction data generated by the correction process and performing a Fourier transform process.

[0020] Furthermore, the present invention is characterized in that a plurality of frequencies for the ON / OFF control of the discharge are selected and controlled, and the correction is not performed when a relatively high frequency is controlled.

[0021] The relatively high frequency is at least 1 Hz or several Hz or more.

[0022] The battery deterioration determination support device according to one embodiment of the present invention has advantageous effects such as being small, consuming little power, and being able to significantly reduce measurement time.

[0023] FIG. 1 is an explanatory diagram illustrating an example of the overall configuration of a system including a battery degradation determination support device according to one embodiment of the present invention. FIG. 1 is an explanatory diagram illustrating an example of measurement of current values ​​in a battery degradation determination support device, etc. according to one embodiment of the present invention. FIG. 2 is an explanatory diagram illustrating an example of measurement of voltage values ​​in a battery degradation determination support device, etc. according to one embodiment of the present invention. FIG. 3 is a flowchart illustrating a measurement procedure in a battery degradation determination support device, etc. according to one embodiment of the present invention. FIG. 4 is a flowchart illustrating a measurement procedure in a battery degradation determination support device, etc. according to one embodiment of the present invention. FIG. 5 is an explanatory diagram illustrating an event that should be addressed by a battery degradation determination support device, etc. according to one embodiment of the present invention. FIG. 6 is an explanatory diagram illustrating an example of a voltage graph used for addressing by a battery degradation determination support device, etc. according to one embodiment of the present invention. FIG. 7 is an explanatory diagram illustrating the state before and after processing by a battery degradation determination support device, etc. according to one embodiment of the present invention. FIG. 8 is an explanatory diagram illustrating the state before and after processing by a battery degradation determination support device, etc. according to one embodiment of the present invention. FIG. 9 is an explanatory diagram illustrating an example of a Cole-Cole plot based on measurement results by a battery degradation determination support device, etc. according to one embodiment of the present invention. FIG. 10 is an explanatory diagram illustrating a comparison between an example of a Cole-Cole plot based on measurements by a battery degradation determination support device, etc. according to one embodiment of the present invention and an example of a Cole-Cole plot based on measurements by a conventional AC-IR measuring instrument. FIG. 11 is an explanatory diagram illustrating example measurement results by an AC-IR measuring instrument. FIG. 1 is an explanatory diagram illustrating an example of generating a Cole-Cole plot from measurement results obtained by an AC-IR measuring instrument; FIG. 2 is an explanatory diagram conceptually illustrating the physical structure of a conventional secondary battery; FIG. 3 is an explanatory diagram illustrating an example of an equivalent circuit based on the physical structure of a conventional secondary battery; FIG. 4 is an explanatory diagram illustrating the properties of an example Cole-Cole plot generated by measuring a conventional secondary battery with an AC-IR measuring instrument; and FIG. 5 is an explanatory diagram illustrating an example of a simple equivalent circuit based on the physical structure of a conventional secondary battery.

[0024] A battery deterioration determination support device according to one embodiment of the present invention will be specifically described below with reference to the drawings. While the term "battery" is used to facilitate understanding of the present invention, the present invention includes "battery" and can be broadly applied to electrical energy supply media that supply electricity or power.

[0025] FIG. 1 shows an example of the overall configuration of a system including a battery deterioration determination support device according to one embodiment of the present invention.

[0026] 1, a system including a battery degradation determination support device 100 according to one embodiment of the present invention includes a control unit 110 having a signal control I / F (111) for transmitting control signals for controlling the ON / OFF of a switch circuit or the like, a current measurement I / F (112), a voltage measurement I / F (113), and an arithmetic processing unit 114 such as a CPU. The system also includes a switch circuit 120, a shunt resistor 130, a resistor (discharge resistor) 140, an A / D converter 150 for digitally converting the resistance value of the shunt resistor 130 (or the value of the current flowing through the shunt resistor 130), and an A / D converter 160 for digitally converting the voltage value of a storage battery 190.

[0027] In one embodiment of the present invention, all of the elements, circuits, and devices except for the storage battery 190 in Fig. 1 can be implemented as a battery deterioration determination support device or system according to the present invention. Also, the control unit 110 can be implemented as a battery deterioration determination support device according to one embodiment of the present invention.

[0028] (Operational Procedure of the Battery Degradation Determination Support Device) The operational features of the battery degradation determination support device according to one embodiment of the present invention are as follows, but are not limited to these. (1) Response characteristics are acquired using a square wave. A square wave includes the fundamental frequency and its higher-order frequency characteristics. For example, by applying a 100 Hz square wave and acquiring its characteristics, it is possible to simultaneously acquire characteristics of 300 Hz, 500 Hz, and higher-order odd-number terms. Acquiring higher-order terms using Fourier transform processing can shorten measurement time. This reduction in measurement time outweighs the increased computational effort required for Fourier transform processing of higher-order terms. (2) Only discharge characteristics are acquired as the response. While conventional AC-IR measurement methods acquire both charge and discharge characteristics, the battery degradation determination support device according to one embodiment of the present invention acquires only discharge characteristics. This feature reduces the power consumption and the complexity associated with larger devices.

[0029] As a result of being equipped with these features, the battery degradation determination support device according to one embodiment of the present invention exhibits the following advantages. (A) Compactness At the time of filing this application, the battery degradation determination support device according to one embodiment of the present invention has been miniaturized to approximately 75.0 mm x 103.0 mm x 50 mm, and further miniaturization is expected. (B) Low power consumption At the time of filing this application, the battery degradation determination support device according to one embodiment of the present invention has been miniaturized to 325 mW. (C) Shortened measurement time The battery degradation determination support device according to one embodiment of the present invention has four measurement points in the frequency band (although not limited to these, in one embodiment, the four points are 0.2 Hz (F1), 1.5 Hz (F2), 12 Hz (F3), and 100 Hz (F4)). As a result, at the time of filing this application, a measurement time of approximately 10 seconds and a communication time of approximately 20 seconds have been achieved (in one embodiment, the communication speed is approximately 100 Kbps and the data format is ASCII; by increasing the communication speed to, for example, 1 Mbps and changing the data format to binary, the communication time can be further shortened.) Furthermore, the measurement points have been improved so that they can be freely selected, and ultimately operation is possible with just two measurement points (in one embodiment, 0.3 Hz and 10 Hz. The limit for higher-order terms is thought to be around 11th to 13th orders. At higher-order frequencies, the plot becomes broadened due to being buried in noise).

[0030] (System Configuration Example of Battery Degradation Determination Support Device) The following is an example of a system configuration of a battery degradation determination support device according to one embodiment of the present invention.

[0031] (1) Configuration Example 1 In the case of single-cell measurement, one battery degradation determination support device is used for one storage battery cell. Then, a control device (not shown, which can be realized using existing technology) is prepared to control multiple battery degradation determination support devices, and the multiple battery degradation determination support devices and the control device are interconnected via RS-485 or the like for communication processing. The processed result data may be analyzed in a cloud (not shown).

[0032] Such a configuration has the advantage that the cost of the battery deterioration determination support device can be reduced and an analysis PC or the like is not required.

[0033] (2) Configuration Example 2 Measurements are performed at only the two necessary points, and fitting processing is performed from the data obtained from the measurements. In addition, data in the non-measurement range due to the limited number of measurement points is estimated from the fitting results described above. The fitting processing here is the processing used in Cole-Cole plots, and simulation is performed using an equivalent circuit expressed by a resistor and multiple parallel circuits (RC or RL) directly connected together, and a set of a predetermined number of frequencies. Any known fitting processing can be used for this fitting processing.

[0034] This configuration can meet the need for AC-IR measurements and Cole-Cole plot calculations on battery production lines. Until now, meeting such needs required large equipment costs and the complexity of finding space to install the measuring device and securing an AC power source, but this configuration can be achieved with equipment costs of several tens of thousands of yen, a space the size of a cigarette, and a USB power source.

[0035] In one embodiment of the present invention, fitting processing can be performed assuming the following circuit.

[0036] circuit=R0-p(R1,C1)-p(R2,C2)-p(R3,C3)-p(R4,L4)

[0037] where R0 etc. represent resistors, C1 etc. represent capacitors, L4 is an inductor, "p(R1, C1)" etc. represent parallel connection of the elements in parentheses, and "-" represents series connection. As an example for understanding the present invention, a set of frequencies such as [0.2, 1, 4.5, 7.5, 12.5, 36.5, 61, 97.5, 290, 879, 1465] is used.

[0038] 2A shows an example of current measurement in a battery degradation determination support device according to one embodiment of the present invention. In the figure, the horizontal axis from near zero to near 2000 indicates the current value during the period when discharging is stopped. Similarly, the horizontal axis from near 2000 to near 4000 indicates the current value during the period when discharging is in progress. The waveform shown in the figure is a square wave.

[0039] To be precise, since measurements are taken at approximately 20 points during the discharge period, the sampling points are 20 to 2068, and 2068 to 4116. This means 2048 + 20 and 4096 + 20. The initial value of 20 can be determined as appropriate. In one embodiment of the present invention, it is considered desirable for this value to be around 2-3, or at most 20.

[0040] Figure 2B shows an example of voltage measurement in a battery degradation determination support device according to one embodiment of the present invention. The horizontal axis of voltage in this figure corresponds to the horizontal axis of current in Figure 2A. In Figure 2B, the horizontal axis values ​​from near zero to near 2000 indicate voltage values ​​in the section where discharging is stopped. Similarly, the horizontal axis values ​​from near 2000 to near 4000 indicate voltage values ​​in the section where discharging is in progress. The waveforms shown in this figure indicate voltage values ​​corresponding to the states of discharging stopped and discharging in progress.

[0041] 3A and 3B show a measurement procedure in a battery degradation determination support device or the like according to one embodiment of the present invention. Measurement in a battery degradation determination support device or the like according to one embodiment of the present invention is generally performed in parallel as the flow shown in FIG. 3A and the flow shown in FIG. 3B. More specifically, in one embodiment, steps S304 to S308 in FIG. 3A and steps S351 to S353 in FIG. 3B are performed in parallel.

[0042] (Overview of Measurement Processing) First, an overview of the entire measurement processing, including the measurement circuit and elements, will be described. In the process flows of Figures 3A and 3B, a FET (Field Effect Transistor) is used as the SW (Switching Circuit). In one embodiment, the ON / OFF control of the FET is performed using PWM (Pulse Width Modulation) control, which performs power control using a semiconductor. Control can be performed so that the ON / OFF is repeated a specified number of times.

[0043] Although the present invention is not limited thereto, in one embodiment, sampling of voltage / current values ​​begins immediately before the SW is first turned ON (first) and then OFF, with this point being the starting point. After that, after a predetermined number of ON / OFF control cycles, sampling ends immediately before the end of the final ON cycle, with this point being the end point. For example, if the predetermined number is four and waveforms of four ON / OFF cycles are measured, 4.5 waveforms are actually taken. In this case, the FET is repeatedly processed in the order ON1 / OFF1 / ON2 / OFF2 / ON3 / OFF3 / ON4 / OFF4 / ON5. Measurement begins immediately before the SW is first turned ON (ON1) and then OFF (OFF1), and ends immediately before the SW is last turned OFF (just before the end of ON5). Therefore, the data actually used for measurement is four waveforms.

[0044] Next, the measurement target data is read out at a specified interval using the I2C (Inter-Integrated Circuit) standard (every 10 μs in one embodiment). The read data can also be averaged as needed. In one embodiment of the present invention, both current and voltage are sampled at 4096 points and processed. In one embodiment, the data can be read out once a certain amount of measurement data has been accumulated in the PC. In another embodiment, the data can also be processed by the arithmetic processing unit 114 in the control unit 110. Since the voltage and current are in the form of A / D values, they are converted into voltage and current values.

[0045] Furthermore, since the voltage value gradually decreases due to discharge, the voltage value at the start point and the end point will be different.

[0046] Therefore, the voltage values ​​are processed as follows to match the values ​​at the start and end points. First, the difference between the start and end point voltages is found. Next, this difference is added evenly over the discharge period. In the example above, this would be added evenly over only the ON section of four waveforms (addition of correction voltage data). This process results in the voltage at the start and end points matching. Then, for the voltage values, a 4096-point fast Fourier transform (hereinafter referred to as FFT) is performed on the above correction voltage data (this result is referred to as the correction voltage FFT processing result), and for the current values, a 4096-point FFT is performed as is.

[0047] Next, a window function is applied to the voltage-added signal (equally divided correction data) to align the start and end points, and FFT processing is performed. Next, gain correction is performed on the FFT processing result. For example, if a Hanning window is used, the gain is halved, so the result output using the Hanning window is doubled to perform gain correction. Finally, this correction result is added to the correction voltage FFT processing result, and the obtained result is used as the corrected voltage FFT processing result.

[0048] Then, the resistance value is calculated using the corrected voltage FFT processing result and current FFT processing result.

[0049] In other embodiments of the present invention, a general Fourier transform may be used instead of the above-described FFT processing, and may be performed using 1024 points instead of 4096 points. Also, a known alternative Laplace transform process may be used (the same applies to FFT processing hereinafter).

[0050] 3A, when processing for one frequency is started in step S301, the process proceeds to step S302, where SW control is started. Next, the process proceeds to step S303, where the number of repetitions of the waveform to be measured is set. In one embodiment, when four waveforms are to be measured, the number of repetitions is set to four.

[0051] Next, the process proceeds to step S304, where the SW is controlled to be ON. Next, the process proceeds to step S305, where it is determined whether a specified time has elapsed. This time is determined by the frequency, and in the case of processing for a frequency of 0.1 Hz, the specified time here is the 5 seconds of the ON section. If the answer is No in step S305, the process waits in that step until the specified time has elapsed, but if the answer is Yes in that step, the process proceeds to the next step.

[0052] In step S306, the SW is controlled to be OFF. Next, the process proceeds to step S307, where it is determined whether a specified time has elapsed. This time is determined by the frequency, and in the case of processing a frequency of 0.1 Hz, the specified time here is the OFF section of 5 seconds. If the answer is No in step S307, the process waits in that step until the specified time has elapsed, but if the answer is Yes in that step, the process proceeds to the next step.

[0053] In step S308, it is determined whether the number of repetitions of the waveform to be measured has reached the number set in step S303. If the answer is No, the process returns to step S304, but if the answer is Yes, the process proceeds to step S309, where the measurement for one frequency is terminated.

[0054] On the other hand, as a process performed in parallel with the processes from step S304 to step S308, when the process starts at step S351 in FIG. 3B, measurement data is acquired at step S352, voltage values / current values ​​are acquired as data at step S353, and the acquired data is saved at step S354.

[0055] The process in FIG. 3A may be automatically controlled by a microcomputer as PWM processing. In this case, ON / OFF is automatically controlled by the PWM control unit. The only settings that the microcomputer sets are the repetition period and start and stop instructions. Once the repetition period is set and PWM starts, it ends after a predetermined time has passed. This end determination time corresponds to S308. Also, on the measurement side, while ON / OFF control is being performed in S305 to S308, S351 to S354 are repeatedly executed 4096 x N times in this example. N is the number of averages.

[0056] The operating procedure described above is summarized in the table below.

[0057] Taking the second-to-the-bottom (F2) in the table above as an example, the FET is cycled on and off at a 1.531 Hz cycle (actually, it's controlled only on / off / on). On the time axis, it's on for 327.68 ms, off for the next 327.68 ms, and then on for a final 327.68 ms. Measurement begins (for example) about 7.68 ms after the first on and ends 320 ms after the last on. During this time, measurements are taken every 10 us, resulting in 65,536 measurements over 655.36 ms. By averaging 16 of these, we get 4096. This 16 corresponds to the N mentioned above. In other words, steps S351 through S354 are repeated a predetermined number of times, averaging as necessary, until the desired 4096 points (this number can also be freely selected) are obtained.

[0058] Figure 4A illustrates an event that should be addressed by a battery degradation determination support device according to one embodiment of the present invention. Figure 4A shows a situation in which a cycle of discharging (SW control ON section) and discharging stop (SW control OFF section) is repeated just under two times. Note that in the figure, the number of repetitions is set to one, and 4096 sampling points are taken during that cycle (one SW ON / OFF control).

[0059] 4A, it is noteworthy that the voltage at the start of discharge in the second period is slightly lower than the voltage at the start of discharge in the first period (part p in the figure), and that the voltage at the end of the discharge interval in the second period is lower by D than the voltage at the end of the discharge interval in the first period.

[0060] The reason for this periodic voltage drop is due to a decrease in the SoC caused by repeated discharge and discharge stop. The specific symptoms are as follows: In Figure 4A, if the SoC of the battery being measured at time t0 is x%, the SoC is maintained at x% during the discharge stop period from time t0 to time t1. However, when discharge starts at time t1, the SoC gradually decreases during the period until discharge stops at time t2. Then, at time t2, a voltage drop (D) occurs due to the decrease in SoC.

[0061] As mentioned in (Overview of Measurement Processing), this voltage drop (D) is the difference between the voltage value at the start point and the voltage value at the end point, so it needs to be appropriately corrected when performing FFT processing. The reason for this is that when FFT is processed over a finite period, if there is a discrepancy between the values ​​at the start and end of the FFT transformation, unnecessary frequency components will be generated (the problem is that the frequency characteristics of higher-order terms will be calculated). Therefore, both values ​​need to match.

[0062] A common approach to addressing discrepancies between the signal values ​​at the start and end points is to apply a window function to make the start and end points zero and match them. In other words, the window function is applied with a function that increases the center value and approaches zero at the periphery, eliminating the gaps at both ends by "deeming them to be zero." This approach only works when the signal characteristics are contained in the center. For example, it does not work well when important signals are contained in large amounts at the start and end points, as important information is lost. In the case of transient responses, applying a window function will eliminate much of the response signal obtained near the start and end points, so a signal processing method that does not use a window function must be introduced.

[0063] Based on the above considerations, in one embodiment of the present invention, the following correction process is performed to make the voltage value at the start point and the voltage value at the end point coincident with each other.

[0064] (Correction Process) (1) The difference between the start point voltage and the end point voltage is calculated (D).

[0065] (2) The voltage difference D calculated in (1) above is added evenly throughout the discharge period. Specifically, correction voltage data is added evenly only to the ON section of the waveform (one waveform in FIG. 4) for the number of repetitions (one in FIG. 4).

[0066] (3) For the voltage value, 4096-point FFT processing is performed on the above-mentioned correction voltage data to obtain the correction voltage FFT processing result.

[0067] (4) For the current value, 4096-point FFT processing is performed on the data acquired without correction, and the corrected result is used.

[0068] (5) To align the start point and end point, a window function is applied to the voltage-added signal (equal division correction data), and FFT processing is performed.

[0069] (6) Gain correction is performed on the result of FFT processing. For example, if a Hanning window is used, the gain is halved, so the result output using the Hanning window is doubled to perform gain correction.

[0070] (7) The result of the correction performed in (6) above is subtracted from the result of the corrected voltage FFT processing, and the result obtained is set as the corrected voltage FFT processing result.

[0071] (8) The corrected voltage FFT processing results and current FFT processing results are used to calculate the resistance value, which is a complex impedance consisting of a real resistance part (R) and an imaginary resistance part (X) for each frequency.

[0072] From another perspective, the above processes (1) to (8) can be divided into a (battery transient response processing phase) and a (post-processing phase), in which case they can also be explained as follows.

[0073] (Battery transient response processing phase) (A1) The cell voltage immediately before the FET is turned off for the first time (time t0) is set to V0 (the voltage at the start of FFT). At this time, since the time from the start of FFT to the first discharge stop is short, it can be assumed that there is no change in the SoC at this time (the cell voltage around this time is constant at V0).

[0074] (A2) The time that the FET was turned off ends (a little after time t1), and the FET is turned on again (discharge begins). Then, the cell voltage begins to decrease rapidly. If the cell voltage at the end of the FFT (time t2) is V1, then if the SoC does not fluctuate due to discharge, V1 should be higher. It is unclear whether this voltage value is higher or lower than V0, but we will assume it is V0 here.

[0075] (A3) Then, the difference (V1-V0) is proportionally subtracted from immediately after the FET is turned on (in the figure, the time when the voltage starts to drop a little after time t1), and a correction is applied so that the cell voltage becomes V0 at the end of the FFT (time t2). In this way, when applying the FFT, the values ​​at the start and end points can be matched.

[0076] As described above, it is assumed that the voltage is V0 at time t0 and that this value does not change until the discharge stops (because the time between these two is short). At this time, D = V0 - V1. In one embodiment of the present invention, this D is proportionally subtracted. Theoretically, there are 2048 points, but in actual measurement, if the time between t0 and the end of the discharge is 1 ms, 100 points are required (because it takes 10 us to measure one point), so 1948 points are effectively proportionally divided.

[0077] (Post-processing phase) (B1) For the results of FFT processing, FFT processing is performed on a certain voltage drop from immediately after the FET is turned on until the end of the FFT. At this time, a window function is applied to points where the start point and end point do not coincide.

[0078] (B2) In one embodiment of the present invention, but not limited to this, the function applied is a simple voltage drop function (a function in which the voltage decreases linearly over time).

[0079] As described above, the measurement and correction embodiments have been explained from various angles. Below, supplementary explanations will be added to further deepen understanding.

[0080] [Supplementary Note 1] The significance of matching the voltages at the start and end points As mentioned above, the correction process involves matching the voltages at the start and end points, which means that the difference in the discharge period is divided equally to "match" them. Further examples of this process are given below (1-1) to (1-4).

[0081] (1-1) First, let the starting voltage be V0, the ending voltage be V1, and the intermediate voltage be Vx. Let t0, t1, and tx be the times at each voltage. Let 0, 4095, and Cx be the sample numbers, respectively.

[0082] (1-2) When the discharge is stopped, the intermediate voltage Vx rises from V0 to Vx. When the discharge starts at time tx, the intermediate voltage Vx drops to V1.

[0083] (1-3) Here, Vd = V0 - V1 (since the SoC decreases due to discharge, V0 > V1 can be set). In one embodiment of the present invention, 4096 points are acquired, but 20 to 30 samples from t0 to the end of discharge are also acquired, and these data are included in the 4096 points. Therefore, the end point time is 20 to 30 samples before the second discharge stop.

[0084] (1-4) If the number of samples in the section from Vx to V1 is S (= 4095 - Cx), the voltage at time ti is corrected as V = Vi + Vd / S * (Ci - Cx). Also, if ti = tx, it is corrected as Vi = Vx + Vd / S * (Cx - Cx) = Vx, and if ti = t1, it becomes Vi = V1 + Vd / S * (C1 (= 4095) - Cx) = V1 + Vd = V1 + V0 - V1 = V0, and the voltages at the start and end points are combined.

[0085] [Supplement 2] Necessity of processing to offset the influence of the difference When processing to match the voltages of the start point and end point is performed as explained in Supplement 1, processing to offset the influence of the difference is required. This is explained using examples in (2-1) to (2-3).

[0086] (2-1) The process in Supplementary Note 1 is a method of proportionally adding the difference in the second discharge period. However, the voltage value proportionally added in this way is not the original voltage. It is merely a measure to avoid the occurrence of errors in higher-order terms when FFT processing is performed.

[0087] (2-2) Therefore, after the final FFT processing, it is necessary to restore this correction amount. The result of the addition processing is a straight line where Vd is zero from t0 to tx and decreases linearly from tx to t1. However, even if this is subjected to FFT processing, the desired result will not be obtained because it is a straight line.

[0088] (2-3) Therefore, a window function is applied to the voltage graph data shown in FIG. 4B to perform FFT processing, and then a gain is applied to calculate the influence, which is then subtracted from the voltage FFT to return to a state where there was no influence.

[0089] [Supplementary Note 3] The significance of not performing correction processing at high frequencies. The frequency of the characteristic to be determined varies depending on the battery or discharger being measured, but measurements are typically made by dividing the frequency range from approximately 0.1 Hz to 1 kHz into 100 parts. In contrast, the battery degradation determination support device according to one embodiment of the present invention measures four points in the frequency band (although not limited to these, in one embodiment, the four points are 0.2 Hz (F1), 1.5 Hz (F2), 12 Hz (F3), and 100 Hz (F4)). Furthermore, no correction processing is performed for frequencies above 10 Hz, and the technical justification for this is as follows.

[0090] In other words, if a 100Hz rectangular wave of one wavelength is input, it will be ON for only 0.005 seconds in real time (to be precise, it will be ON for 0.01 seconds, since it goes ON / OFF / ON → end). How much does the SoC decrease during this time? There is almost no decrease (see the slight voltage drop at part p in Figure 4A).

[0091] In fact, when measured at 100 Hz, the starting voltage was 3.26431 V, while the ending voltage was 3.26400 V. During this time, there was a voltage drop of approximately 0.00031 V, but the effect of this drop on the FFT processing was negligible.

[0092] Furthermore, in one embodiment, the actual measured values ​​at frequencies less than 100 Hz were as follows: when measured at 12 Hz, the starting voltage was 3.26393 V and the end voltage was 3.26393 V, when measured at 1.5 Hz, the starting voltage was 3.26294 V and the end voltage was 3.26256 V, when measured at 0.2 Hz, the starting voltage was 3.26050 V and the end voltage was 3.25943 V.

[0093] Although it can be determined that either of these has little effect on FFT processing, in one embodiment of the present invention, it is acceptable to not perform correction processing for frequencies of at least 1 Hz or a few Hz or higher. For example, the ON time at 1 Hz is 0.5 seconds, and for this length of time, the effect of a decrease in SoC is considered to be small.

[0094] [Supplementary Note 4] Significance of Calculating Parameters by Fitting: The battery degradation determination support device according to one embodiment of the present invention measures four frequencies: 0.2 Hz (F1), 1.5 Hz (F2), 12 Hz (F3), and 100 Hz (F4). Based on these measurements, higher-order terms (first, third, fifth, etc.) are calculated. Meanwhile, for slower frequencies, 0.2 Hz, 0.6 Hz, 1.0 Hz, 1.4 Hz, etc. are obtained, but under the above conditions, frequencies below 0.2 Hz are not obtained. For faster frequencies, 300 Hz, 500 Hz, and 700 Hz can be obtained, based on a reference frequency of approximately 100 Hz. However, at frequencies up to, for example, 2 kHz or 3 kHz, the gain becomes too small, resulting in fluctuations due to noise.

[0095] Therefore, the above-mentioned fitting process is performed, and the circuit used at this time is: circuit=R0-p(R1, C1)-p(R2, C2)-p(R3, C3)-p(R4, L4).

[0096] By substituting the values ​​of the fitting results into the circuit described above and numerically shifting the frequency outside the measurement range, the values ​​of the higher-order terms can be calculated. Although not limited to this, in one embodiment of the present invention, only two points, 0.5 Hz and 20 Hz, are measured, and the gap is filled to some extent with higher-order terms before parameter calculations are performed by fitting, making it possible to create a Cole-Cole plot sufficient for determining the deterioration of the battery being measured.

[0097] The extent to which the aforementioned 0.2 Hz can be increased is likely to depend on the battery characteristics. 0.2 Hz refers to the FET ON / OFF cycle of 0.2 Hz, which requires 5 seconds per cycle. To create an accurate Cole-Cole plot useful for assessing battery degradation, it may be desirable to measure at 0.1 Hz, but this would require 10 seconds. If the fitting results are not significantly different, processing from 0.5 Hz can significantly reduce the processing time to 2 seconds, often resulting in greater overall convenience. In this case, it is acceptable to perform the fitting at 0.5 Hz, then fill in the higher-order terms (1.5 Hz, 7.5 Hz, etc.), perform further fitting, calculate the parameters, and then generate a Cole-Cole plot including the lower-speed range (e.g., 0.1 Hz).

[0098] 5A and 5B show the state before and after processing by a battery degradation determination support device or the like according to one embodiment of the present invention. FIG. 5A shows an example of a voltage measurement before processing by a battery degradation determination support device or the like according to one embodiment of the present invention, and FIG. 5B shows an example of the result of performing correction processing by a battery degradation determination support device or the like according to one embodiment of the present invention on the voltage measurement example shown in FIG. 5A . As shown in FIG. 5B , it can be seen that the difference D between the start and end voltages observed in the voltage measurement example shown in FIG. 5A is raised to zero relative to the overall voltage during the discharging period by the above-described voltage correction processing. Furthermore, the above-described FFT processing is performed on the corrected voltage values ​​shown in FIG. 5B . In other words, if calculations are performed under the assumption that the start and end points coincide and this waveform is repeated, the problem of high-frequency abnormal data being calculated will not occur.

[0099] (Example of a Cole-Cole Plot) Figure 6 shows an example of a Cole-Cole plot based on the measurement results obtained by a battery degradation determination support device according to one embodiment of the present invention. In Figure 6, plots a1 to a4 are measurement points for first-order terms. Furthermore, as shown by the scattering of the plots in the r1 region, the plots tend to vary as the order increases. The plots in the r1 region can be derived by arithmetic operations as higher-order terms. The plots in the r2 region can be derived by arithmetic operations as higher-order terms of a4, and here, 3rd, 5th, 7th, and 9th orders are shown. Higher-order terms can also be derived, but because they overlap with the high-frequency first-order term a3, they are not shown here.

[0100] 7 shows a comparison between an example Cole-Cole plot based on measurements using a battery degradation determination support device according to one embodiment of the present invention and an example Cole-Cole plot based on measurements using a conventional AC-IR measuring device. In the figure, the plots concentrated on side A are the Cole-Cole plot (○ plot) for Battery 1 (a good battery) based on measurements using a conventional AC-IR measuring device, and the Cole-Cole plot (△ plot) for Battery 1 based on measurements using a battery degradation determination support device according to one embodiment of the present invention. Furthermore, the plots concentrated on side B are the Cole-Cole plot (○ plot) for Battery 2 (a deteriorated battery) based on measurements using a conventional AC-IR measuring device, and the Cole-Cole plot (△ plot) for Battery 2 based on measurements using a battery degradation determination support device according to one embodiment of the present invention.

[0101] Both measurements using a conventional AC-IR measuring instrument and measurements using a battery degradation determination support device according to one embodiment of the present invention show the characteristics of a good battery and a deteriorated battery in the same way, indicating that measurements using a battery degradation determination support device according to one embodiment of the present invention are in no way inferior to measurements using a conventional AC-IR measuring instrument.

[0102] That is, a person skilled in the art can observe a Cole-Cole plot based on measurements made using a battery degradation determination support device according to one embodiment of the present invention and make an accurate battery degradation determination in the same manner as in the past.

[0103] The battery deterioration determination support device according to one embodiment of the present invention has been described above based on specific examples. However, embodiments of the present invention can also be embodied as a method or program for implementing a system or device, or as a storage medium on which a program is recorded (for example, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a CD-RW, a magnetic tape, a hard disk, or a memory card).

[0104] Furthermore, the implementation form of the program is not limited to application programs such as object code compiled by a compiler or program code executed by an interpreter, but may also be in the form of a program module incorporated into an operating system.

[0105] Furthermore, it is not necessary for all processing of the program to be performed solely by the CPU on the control board, but rather, the program can be configured so that part or all of it is performed by another processing unit (such as a DSP) implemented on an expansion board or expansion unit added to the board as needed.

[0106] All of the features described in this specification (including the claims, abstract, and drawings) and / or all steps of any disclosed method or process may be combined in any combination, except combinations in which these features are mutually exclusive.

[0107] Furthermore, each feature described in this specification (including the claims, abstract, and drawings) may be replaced by alternative features serving the same, equivalent, or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each disclosed feature is only one example of a generic series of identical or equivalent features.

[0108] Furthermore, the present invention is not limited to the specific configuration of any of the above-described embodiments, but extends to any novel feature or combination thereof described in this specification (including the claims, abstract, and drawings), or any novel method or process step or combination thereof described.

[0109] REFERENCE SIGNS LIST 10 Battery deterioration determination support device 110 Control unit 111 Signal control I / F 112 Current measurement I / F 113 Voltage measurement I / F 120 Switch circuit, switching circuit

Claims

1. A method for assisting in the determination of deterioration of an electric energy supply medium by acquiring internal characteristics of the electric energy supply medium using an electronic circuit, the electronic circuit comprising: control means for controlling the ON / OFF of discharge of the electric energy supply medium; voltage measurement means for measuring the voltage of the ON / OFF controlled electric energy supply medium to acquire voltage measurement data; and current measurement means for measuring the amount of current discharged by the electric energy supply medium, wherein the electronic circuit: acquires a voltage difference between the start and end of measurement for a cycle associated with the ON / OFF control, and performs a correction process using correction data obtained by proportionally dividing the acquired voltage difference by the discharge period in the cycle; performs a first conversion process on the result of the correction process, which converts from the time domain to the frequency domain (Fourier transform process) or from the time domain to the complex domain (Laplace transform process); and performs a second conversion process on the correction data, which converts from the time domain to the frequency domain (Fourier transform process) or from the time domain to the complex domain (Laplace transform process). a process for correcting the influence of the correction process by applying a result of the second correction process to a result of the first conversion process.

2. The method according to claim 1, wherein the first transformation process is a Fourier transform process, and the second transformation process is a process for generating second corrected transformation data that takes into account a gain coefficient due to the influence of the window function, for the first corrected transformation data generated by the correction process and performing a Fourier transform process by applying a window function to the correction data generated by the correction process.

3. The method according to claim 1 or 2, characterized in that a plurality of frequencies are selected for the ON / OFF control of the discharge and the control is performed, and the correction is not performed when a relatively high frequency is controlled.

4. The method of claim 3, wherein the relatively high frequency is at least 1 Hz or several Hz or more.

5. A method for assisting in the determination of deterioration of an electric energy supply medium by acquiring the internal characteristics of the electric energy supply medium using an electronic circuit, comprising: acquiring the internal characteristics of a battery in advance; selecting two or more frequencies required for determining whether the battery is good or bad; storing the selected frequencies; performing discharge control based on the selected frequencies; acquiring voltage data and current data using a voltage measurement means and a current measurement means; performing a correction process on the voltage data to calculate corrected voltage data; calculating resistance data from the corrected voltage data and current data; calculating at least some Cole-Cole plot data from the resistance data; performing a fitting process using the at least some Cole-Cole plot data; and providing support for determining deterioration by comparing each parameter value calculated as a result of the fitting process with a predetermined threshold value.

6. The method according to claim 5, further comprising the step of generating a Cole-Cole plot based on the parameter values ​​calculated as a result of the fitting.

7. The method according to claim 5 or 6, characterized in that two frequencies necessary for determining whether the battery is good or bad are selected, and for the lower frequency value, a higher frequency is selected as long as it does not affect the parameter calculation by the fitting.

8. Apparatus for carrying out the method according to any one of claims 1 to 7.

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