Battery management method, management device, and battery system

Abstract

To improve the accuracy of impedances obtained from equivalent circuits identified using operational data.SOLUTION: A storage battery management method disclosed herein includes identifying a first equivalent circuit of the storage battery using operating data including battery current data, and obtaining the impedance of the storage battery at one or more operating frequencies of the storage battery on the basis of the first equivalent circuit, and the one or more operating frequencies are obtained by frequency analysis of the current data.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present disclosure relates to a storage battery management method, a management device, and a storage battery system. [Background technology]

[0002] Patent Document 1 discloses identifying an equivalent circuit of a storage battery using operation data including current data of the storage battery. In Patent Document 1, parameters of the equivalent circuit are found by a recursive least squares method. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-156771 A Summary of the Invention

[0004] As a method for measuring the impedance of a storage battery, for example, the AC impedance method is known. In the AC impedance method, AC signals of various frequencies are applied to the storage battery, and a response signal obtained from the storage battery is analyzed to determine the impedance of the storage battery with high accuracy. In the AC impedance method, a frequency sweep is performed to apply AC signals of various frequencies to the storage battery.

[0005] The AC impedance method requires frequency sweeping, which means that the lower the frequency, the longer it takes to measure the impedance.The AC impedance method requires interrupting the operation of the storage battery to measure the impedance, and if the impedance measurement takes a long time, this can cause problems in the operation of the storage battery.

[0006] On the other hand, it is also possible to obtain the impedance of the storage battery from an equivalent circuit identified using operation data of the storage battery as in Patent Document 1. When the impedance is obtained from an equivalent circuit identified using operation data, there is an advantage in that there is no need to interrupt the operation of the storage battery.

[0007] However, the impedance obtained from the equivalent circuit identified using the operational data may have a larger error than the impedance measured by the AC impedance method. Therefore, it is desirable to improve the accuracy of the impedance obtained from the equivalent circuit identified using the operational data.

[0008] One aspect of the present disclosure is a method for managing a storage battery, comprising: identifying a first equivalent circuit of the storage battery using operation data including current data of the storage battery, and acquiring impedance of the storage battery at one or more operating frequencies of the storage battery based on the first equivalent circuit, the one or more operating frequencies being determined by frequency analysis of the current data.

[0009] Another aspect of the present disclosure is a management device for a storage battery. The disclosed device is configured to execute a process including: identifying a first equivalent circuit of the storage battery using operation data including current data of the storage battery; and acquiring impedance of the storage battery at one or more operating frequencies of the storage battery based on the first equivalent circuit. The one or more operating frequencies are obtained by frequency analysis of the current data.

[0010] According to yet another aspect of the present disclosure, there is provided a storage battery system including a storage battery and a management device.

[0011] Further details will be described in the following embodiments. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a configuration diagram of a storage battery system. [Diagram 2]FIG. 2 is a configuration diagram of the management device. [Diagram 3] FIG. 3 is an explanatory diagram showing impedance measurement values ​​obtained by the AC impedance method and identification of an equivalent circuit. [Figure 4] FIG. 4 is a conceptual diagram of impedance acquisition according to the embodiment. [Diagram 5] FIG. 5 is a flowchart of the state analysis process. [Figure 6] FIG. 6 is an explanatory diagram of the first equivalent circuit and parameter estimation for the first equivalent circuit. [Figure 7] FIG. 7 is a Nyquist plot showing the RLS results. [Figure 8] FIG. 8 is a diagram showing current data included in each of a plurality of pieces of operation data and the results of spectrum analysis thereof. [Figure 9] FIG. 9 is a diagram showing impedance at the operating frequency. [Figure 10] FIG. 10 is a diagram showing the complex impedance absolute value and phase at the operating frequency. [Figure 11] FIG. 11 is an explanatory diagram of the second equivalent circuit. [Figure 12] FIG. 12 is a Nyquist diagram showing the impedance of the identified second equivalent circuit and the impedance measured by the AC impedance method. [Figure 13] FIG. 13 is a diagram showing the absolute value of the impedance of the identified second equivalent circuit and the absolute value of the impedance measured by the AC impedance method. [Figure 14] FIG. 14 is a diagram showing the phase of the impedance of the identified second equivalent circuit and the phase of the impedance measured by the AC impedance method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] <1. Overview of storage battery management method, management device, and storage battery system>

[0014] (1) A method for managing a storage battery according to an embodiment preferably includes identifying a first equivalent circuit of the storage battery using operation data including current data of the storage battery, and acquiring impedance of the storage battery at one or more operating frequencies of the storage battery based on the first equivalent circuit. The one or more operating frequencies are preferably determined by frequency analysis of the current data. The present inventors have found that impedance at the operating frequency of the storage battery is reliable even if the impedance is acquired using operation data.

[0015] (2) In order to improve accuracy, it is preferable that a plurality of pieces of data are used as the operation data. That is, it is preferable that the operation data includes at least first operation data including first current data in a first operation of the storage battery, and second operation data including second current data in a second operation different from the first operation. It is preferable that the impedance includes at least a first impedance of the first equivalent circuit identified using the first operation data, and a second impedance of the first equivalent circuit identified using the second operation data. It is preferable that the first impedance is an impedance at one or more first operating frequencies in the first operation. It is preferable that the second impedance is an impedance at one or more second operating frequencies in the second operation. It is preferable that the one or more first operating frequencies are obtained by frequency analysis of the first current data. It is preferable that the one or more second operating frequencies are obtained by frequency analysis of the second current data.

[0016] (3) The method of managing a storage battery according to the embodiment preferably further comprises identifying a second equivalent circuit different from the first equivalent circuit by using the impedance. By making the first equivalent circuit and the second equivalent circuit different, appropriate circuit configurations can be adopted for each of them.

[0017] (4) In the method for managing a storage battery according to the embodiment, it is preferable to further include measuring an AC impedance of the storage battery to obtain impedance at a frequency other than the operating frequency. In this case, impedance at more frequencies can be obtained.

[0018] (5) The method for managing a storage battery according to the embodiment preferably further includes identifying a second equivalent circuit different from the first equivalent circuit by using the impedance at the operating frequency and an impedance at a frequency other than the operating frequency. The impedance at the frequency other than the operating frequency is preferably obtained by measuring the AC impedance of the storage battery. In this case, the second equivalent circuit can be identified with higher accuracy.

[0019] (6) The frequency other than the operating frequency is preferably higher than the operating frequency. Since the operating frequency is often low, it is preferable to obtain impedance at a frequency higher than the operating frequency.

[0020] (7) The first equivalent circuit is preferably identified by a recursive least squares method using the operational data. In this case, the first equivalent circuit is easily identified by the recursive least squares method.

[0021] (8) The second equivalent circuit preferably includes two or more RC parallel circuits and a constant phase element connected in series to the two or more RC parallel circuits. Such a second equivalent circuit is novel and suitable for the disclosed method.

[0022] (9) A storage battery management device according to an embodiment is preferably configured to execute a process including: identifying a first equivalent circuit of the storage battery using operation data including current data of the storage battery; and acquiring impedance of the storage battery at one or more operating frequencies of the storage battery based on the first equivalent circuit. The one or more operating frequencies are preferably determined by frequency analysis of the current data. Even if the impedance is acquired using operation data, the impedance at the operating frequency of the storage battery is reliable.

[0023] <2. Examples of storage battery management method, management device, and storage battery system>

[0024] FIG. 1 shows a storage battery system 1 according to an embodiment. The storage battery system 1 includes a storage battery 2 and a management system 3. The storage battery 2 is, for example, a lithium ion battery. The storage battery 2 stores electricity by connecting a charger (not shown) to terminals 4 on both ends of the storage battery 2. The storage battery 2 also discharges the stored electricity to a load (not shown) by connecting the terminals 4 on both ends of the storage battery 2 to the load. Charging or discharging the storage battery is referred to as the "operation" of the storage battery 2. Charging or discharging the storage battery may also be referred to as the "driving" of the storage battery.

[0025] The management system 3 includes a current sensor 5 that measures the current flowing through the storage battery 2, a voltage sensor 6 that measures the terminal voltage of the storage battery 2, and a management device 10. The current sensor 5 outputs measured current data to the management device 10. The voltage sensor 6 outputs measured voltage data to the management device 10. The current and voltage of the storage battery 2 are constantly measured. That is, the management device 10 can constantly acquire the current data and voltage data. The current data and voltage data are used to determine a first equivalent circuit parameter, which will be described later. The current data is also used to determine an operating frequency, which will be described later.

[0026] The management system 3 of the embodiment further includes a temperature sensor 7 for measuring the temperature of the storage battery 2. The temperature sensor 7 outputs temperature data to the management device 10. The temperature sensor 7 measures, for example, the environmental temperature or surface temperature of the storage battery 2. The temperature of the storage battery 2 is constantly measured. In other words, the management device 10 can constantly acquire the temperature data of the storage battery 2. The temperature data is used for temperature correction, which will be described later.

[0027] The management device 10 manages the storage battery 2. The management device 10 is also called a battery management system. The management device 10 acquires current data and voltage data when the storage battery 2 is in operation. Here, when the storage battery 2 is in operation means when the storage battery 2 is being charged or when the storage battery 2 is being discharged. In the embodiment, the current data, voltage data, and temperature data are collectively referred to as operation data. Note that only the current data and voltage data may be referred to as operation data, or only the current data may be referred to as operation data. The operation data may be referred to as charge / discharge data.

[0028] The management device 10 according to the embodiment includes a microcontroller 11 and an impedance measuring device 12. The microcontroller 11 executes processing for managing the storage battery 2. The processing for managing the storage battery 2 includes, for example, estimating the deterioration level of the storage battery 2, estimating the residual value of the storage battery 2, predicting the remaining life of the storage battery 2, or detecting an abnormality in the storage battery 2. The management device 10 according to the embodiment can measure and analyze the state of the storage battery 2 when the storage battery 2 is in operation (operation).

[0029] Moreover, the management system 3 according to the embodiment includes an output device 15 for outputting a result of the processing executed by the management device 10. The output device 15 is, for example, a display for displaying the processing result, or a communication device for transmitting the processing result to an external device.

[0030] The impedance measuring device 12 included in the management device 10 measures the AC impedance of the storage battery 2, for example, by an AC impedance method. The AC impedance method can measure the frequency-dependent impedance of the storage battery 2 with high accuracy. The AC impedance method is also called electrochemical impedance spectroscopy (EIS). Measurement by the AC impedance method is also called AC impedance measurement or EIS measurement.

[0031] In the AC impedance method, AC signals of various frequencies are applied to the storage battery, and a response signal obtained from the storage battery is analyzed to obtain the impedance response of the storage battery. The AC impedance method can be used to estimate the internal state of the battery. In the AC impedance method, a frequency sweep is performed to apply AC signals of various frequencies to the storage battery. The impedance measuring device 12 is configured, for example, as an integrated circuit for impedance measurement separate from the microcontroller 11. The integrated circuit is, for example, an LSI.

[0032] 2 shows details of the management device 10 according to an embodiment. The microcontroller 11 included in the management device 10 is configured by a computer including, for example, a processor 20 and a storage device 30. The processor 20 is, for example, a CPU. The storage device 30 has, for example, a primary storage device. The storage device 30 may include a secondary storage device. The primary storage device is, for example, a RAM. The secondary storage device is, for example, a hard disk drive (HDD) or a solid state drive (SSD). The microcontroller 11 may be configured by a wired logic circuit.

[0033] The storage device 30 stores a computer program 35 for causing the processor 20 to execute processing for managing the storage battery 2. Hereinafter, the processing for managing the storage battery 2 will be referred to as a "state analysis processing 21." The state analysis processing 21 includes acquiring the impedance of the storage battery 2. Since the impedance of the storage battery 2 changes depending on deterioration, temperature, SOC, etc., the state of the storage battery 2 can be analyzed using the acquired impedance.

[0034] The state analysis process 21 according to the embodiment may further include obtaining, from the acquired impedance, parameters of an equivalent circuit (a second equivalent circuit 70 described below) of the storage battery 2. The obtained equivalent circuit parameters may be used for estimating the deterioration level of the storage battery 2, estimating the residual value of the storage battery 2, predicting the remaining life of the storage battery 2, detecting an abnormality in the storage battery 2, or the like.

[0035] The processor 20 reads and executes the computer program 35 from the storage device 30. The computer program 35 has program code for causing the computer to execute the condition analysis process 21.

[0036] The storage device 30 includes a database 31. The database 31 stores data measured by the sensors 5, 6, and 7, data measured by the impedance measuring device 12, data for temperature correction, and results of processing performed by the microcontroller 11. The microcontroller 11 refers to the data stored in the database 31 to execute processing such as the condition analysis process 21.

[0037] The microcontroller 11 according to the embodiment can obtain the impedance of the storage battery 2 from the operation data of the storage battery 2, separately from the impedance measurement by the impedance measuring device 12. Furthermore, the microcontroller 11 according to the embodiment can obtain parameters of an equivalent circuit (a second equivalent circuit 70 described later) of the storage battery 2, using the impedance obtained from the operation data and the impedance obtained by the impedance measuring device 12.

[0038] In general, the impedance measuring device 12 can measure the impedance of the storage battery with high accuracy in a wide frequency range including, for example, a range from 0.1 Hz to 5 kHz by an AC impedance method.

[0039] Figure 3 shows an example of the measured values ​​by the AC impedance method and the equivalent circuit of the storage battery 2. The main elements constituting the internal structure of the storage battery 2 are the electrolyte resistance, the impedance of the electric double layer on the electrode surface, and the diffusion impedance. The internal state of the storage battery 2 changes due to the movement of ions such as Li ions and the precipitation or combination of ions as a result of charging and discharging. The internal state also changes depending on the state of charge (SOC) and temperature.

[0040] Corresponding to the above-mentioned main elements in the storage battery 2, the equivalent circuit shown in FIG. 3 includes R0 corresponding to the electrolyte resistance, an RC parallel circuit corresponding to the negative electrode impedance, an RC parallel circuit corresponding to the positive electrode impedance, and a constant phase element (CPE) corresponding to the diffusion impedance, and each element is connected in series. The RC parallel circuit corresponding to the negative electrode impedance has R1 and C1. The RC parallel circuit corresponding to the negative electrode impedance has R2 and C2.

[0041] In FIG. 3, the measured AC impedance is represented by a Nyquist diagram of AC impedance from 10 kHz to 0.01 Hz. The electrolyte resistance R0, the negative electrode impedance R1, C1, the positive electrode impedance R2, C2, and the diffusion impedance Z CPE Each has a different response speed. Therefore, by using the AC impedance method, the parameters R0, R1, C1, R2, C2, and Z that make up the equivalent circuit shown in Figure 3 are CPE Using this, the internal state of each element of the storage battery 2 can be analyzed.

[0042] In the Nyquist diagram of Figure 3, as viewed from the high frequency side (f->∞), the region up to the intersection with the real axis (Re) corresponds to R0, the semicircle to the right of that corresponds to R1 and C1, the semicircle further to the right corresponds to R2 and C2, and the region lower in frequency than the semicircle corresponding to R2 and C2 (f->0) corresponds to CPE.

[0043] However, in the impedance measuring device 12 according to the present embodiment, impedance measurement in a low frequency range (for example, a frequency range below 1 Hz) that requires a long time for measurement is omitted, and impedance measurement in a high frequency range (for example, a frequency range of 1 Hz or more) is performed. The impedance measuring device 12 according to the embodiment measures the impedance of the storage battery 2 in the range of 1 Hz to 5 kHz by, for example, sweeping the frequency from 1 Hz to 5 kHz, and outputs the measured value to the microcontroller 11. When impedance is measured in the high frequency range, the frequency sweep for impedance measurement can be completed in a short time. Therefore, impedance measurement in the high frequency range has little effect on the operation of the storage battery 2 even if it is performed while the storage battery 2 is in operation.

[0044] The impedance in the high frequency range (for example, frequencies between 1 Hz and 5 kHz) corresponds to the electrolyte resistance R0, the negative electrode impedance R1, C1, and the positive electrode impedance R2, C2 of the storage battery 2. On the other hand, the impedance in the low frequency range (for example, frequencies below 1 Hz), which takes time in AC impedance measurement, corresponds to the diffusion impedance Z CPE Therefore, if only the impedance measurement in the high frequency range is performed, the electrolyte resistance R0, the negative electrode impedance R1, C1, and the positive electrode impedance R2, C2 of the storage battery 2 can be identified, but the diffusion impedance Z CPE It is difficult to identify.

[0045] Therefore, the microcontroller 11 according to the embodiment obtains the impedance in the low frequency region from the operation data acquired during the operation of the storage battery 2. Since the microcontroller 11 obtains the impedance from the operation data of the storage battery 2, it is possible to obtain the impedance even while the storage battery 2 is in operation.

[0046] That is, in the embodiment, as shown in Fig. 4, the impedance in the low frequency region (first frequency region) of the storage battery 2 is acquired using operation data acquired during operation of the storage battery 2, and the impedance in the high frequency region (second frequency region) of the storage battery 2 is acquired by AC impedance measurement. By combining the impedance in the low frequency region and the impedance in the high frequency region, the impedance in a wide range of frequency regions from the low frequency region to the high frequency region can be obtained. Note that, in the case where the impedance in the high frequency region is not required in the state analysis process 21 of the storage battery 2, only the impedance in the low frequency region may be used.

[0047] 5 shows an example of the procedure of the condition analysis process 21, which includes obtaining impedance in a wide range of frequency regions. In the embodiment, the condition analysis process 21 is executed by the microcontroller 11.

[0048] 5, an equivalent circuit of the storage battery 2 is identified using the operational data. More specifically, in step S101, parameters of the equivalent circuit of the storage battery 2 are estimated by the recursive least squares method. The equivalent circuit identified in step S101 is referred to as a first equivalent circuit 60.

[0049] FIG. 6 shows a first equivalent circuit 60 and a method for estimating parameters of the first equivalent circuit 60. The first equivalent circuit 60 includes an open circuit voltage OCV and internal impedances Ra, Rb, and Cb, which are parameters of the first equivalent circuit 60. OCV represents the electromotive force of the storage battery 2 (storage battery voltage in a no-load state). Ra represents the electrolyte resistance and combined resistance of the electric double layer of the storage battery 2, and Rb and Cb represent the resistance and capacitor representing the diffusion phenomenon inside the electrodes of the storage battery 2. L is the terminal voltage of the storage battery 2, and I is the current flowing through the storage battery 2. In the first equivalent circuit 60, Ra and a parallel circuit of Rb and Cb are connected in series. The first equivalent circuit 60 has a smaller number of parameters than the second equivalent circuit 70 described below, and is preferable because the calculation load for identifying the first equivalent circuit 60 is small. The OCV may be regarded as a constant.

[0050] Terminal voltage u L is approximated by equation (1) shown in FIG. 6. b0 in equation (1) is expressed by equation (1A) in FIG. 6. b1 in equation (1) is expressed by equation (1b) in FIG. 6. a1 in equation (1) is expressed by equation (1C) in FIG. 6. f in equation (1) is expressed by equation (1D) in FIG. 6. Note that in equation (1), the terminal voltage u L and the current I are discrete values. In equation (1), k is a sampling step and is a natural number such as 0, 1, 2, etc. In equations (1B) and (1C), Ts is a sampling period.

[0051] From equation (1), equation (2) shown in Fig. 6 is obtained. φ(k) in equation (2) is represented by equation (2A) in Fig. 6. θ in equation (2) is represented by equation (2B) in Fig. 6.

[0052] The microcontroller 11 derives Ra, Rb, and Cb based on the equation (2) using, for example, the recursive least squares method (RLS). The recursive least squares method is preferably, for example, the least squares method with a forgetting factor. The microcontroller 11 estimates θ in the equation (2) from the current data I(k) and voltage data u(k) included in the operation data by the recursive least squares method. The microcontroller 11 derives Ra, Rb, and Cb, which are parameters of the first equivalent circuit 60, based on the equations (1A), (1B), (1C), and (1D) from b0, b1, a1, and f included in θ. In this way, the first equivalent circuit 60 is identified.

[0053] Fig. 7 is a Nyquist diagram showing the impedance of the first equivalent circuit 60 identified using the operation data of the storage battery 2. Fig. 7 shows Nyquist diagrams of the impedance A obtained from the first operation data, the impedance B obtained from the second operation data, and the impedance C obtained from the third operation data. Fig. 7 also shows the measured value of the impedance of the storage battery 2 measured by the AC impedance method as a reference value. Here, the measured value of the impedance of the storage battery 2 measured by the AC impedance method is considered to be a true value.

[0054] The impedance A is obtained from the parameters Ra, Rb, and Cb of the first equivalent circuit 60 identified using the first operational data. The impedance B is obtained from the parameters Ra, Rb, and Cb of the first equivalent circuit 60 identified using the second operational data. The impedance C is obtained from the parameters Ra, Rb, and Cb of the first equivalent circuit 60 identified using the third operational data.

[0055] As shown in Fig. 7, the impedances A, B, and C obtained from the operation data of the storage battery 2 are not constant but differ for each piece of operation data. Furthermore, the impedances A, B, and C obtained from the operation data of the storage battery 2 may have a large error from the impedance of the storage battery 2 measured by the AC impedance method. Note that, since the first equivalent circuit 60 shown in Fig. 6 has only one RC parallel circuit, the Nyquist diagram is roughly a semicircle.

[0056] The inventors have found that the impedances A, B, and C obtained from the operation data of the storage battery 2 are not constant but differ for each piece of operation data due to differences in the waveform of the current I of the storage battery 2. FIG. 8 shows the current data (current waveform) included in each piece of operation data and the results of spectrum analysis of each piece of current data. As shown in FIG. 8, the first current data included in the first operation data, the second current data included in the second operation data, and the third current data included in the third operation data each have a different current waveform. In other words, the current data each have a different frequency component.

[0057] The main frequency component of each current data is called the operating frequency. The main frequency component is, for example, a frequency whose power or amplitude is equal to or greater than a predetermined threshold value when the current data included in the operating data is subjected to frequency analysis. In each current data, there may be one operating frequency or multiple operating frequencies. Frequency analysis is also called spectrum analysis.

[0058] Here, the operating frequency obtained by frequency analysis of the first current data is referred to as the first operating frequency, the operating frequency obtained by frequency analysis of the second current data is referred to as the second operating frequency, and the operating frequency obtained by frequency analysis of the third current data is referred to as the third operating frequency.

[0059] The inventors have found that even for impedances A, B, and C obtained using operational data, the impedance values ​​at each operational frequency are close to the AC impedance measurement values ​​considered to be true values, as shown in Figs. 9 and 10.

[0060] 9, among the impedance A obtained from the first operation data, the first impedance at each of the three first operating frequencies is indicated by an * mark on the impedance A. Furthermore, among the impedance B obtained from the second operation data, the second impedance at one second operating frequency is indicated by an X mark on the impedance B. Furthermore, among the impedance C obtained from the third operation data, the third impedance at each of the two third operating frequencies is indicated by an ◯ mark on the impedance C.

[0061] Since the Nyquist diagrams of impedances A, B, and C are semicircular, depending on the frequency, impedances A, B, and C may be far from the AC impedance measurement value considered to be the true value, but the * mark, × mark, and ◯ mark corresponding to each operating frequency are all close to the AC impedance measurement value considered to be the true value.

[0062] 10 also shows |Z| and θ at each operating frequency, where |Z| indicates the absolute value of the complex impedance Z, and θ is the phase of the complex impedance Z in the complex plane.

[0063] In FIG. 10, |Z| and θ at each of the three first operating frequencies are indicated by an * mark. Also, |Z| and θ at one second operating frequency are indicated by an X mark. Furthermore, |Z| and θ at each of the three third operating frequencies are indicated by an ◯ mark. Also, in FIG. 10, |Z| and θ obtained from AC impedance measurement values ​​considered to be true values ​​are shown as curves. It can be seen from FIG. 10 that the * mark, the X mark, and the ◯ mark corresponding to each operating frequency are all close to |Z| and θ obtained from AC impedance measurement values ​​considered to be true values.

[0064] From the above, it can be seen that even though the impedances A, B, and C (see Figure 9) may have a large error from the true value, the impedances at each operating frequency have a small error from the true value and are reliable. Therefore, among the impedances A, B, and C obtained from the operating data, the impedances at the operating frequencies are close to the AC impedance measurement values ​​that are considered to be true values.

[0065] By utilizing the above, the microcontroller 11 according to the embodiment obtains a highly accurate impedance while using the operation data. Returning to Fig. 5, as described above, the microcontroller 11 identifies the first equivalent circuit 60 from the operation data including the current data, and obtains the parameters of the first equivalent circuit 60 (step S101). Furthermore, the microcontroller 11 performs a frequency analysis (spectral analysis) of the current data to obtain the operation frequency (step S102).

[0066] It is preferable that the identification of the first equivalent circuit 60 (step S101) and the calculation for obtaining the operating frequency (step S102) are each performed multiple times. For example, the current data (first current data) and voltage data (first voltage data) acquired in a first time period are set as the first operation data. The microcontroller 11 can identify the first equivalent circuit 60 from the first operation data, and can obtain one or more first operating frequencies from the current data included in the first operation data.

[0067] Similarly, the current data (second current data) and voltage data (second voltage data) acquired in a second time period different from the first time period are set as second operation data. Then, the microcontroller 11 identifies the first equivalent circuit 60 from the second operation data, and obtains one or more second operating frequencies from the current data included in the second operation data. Furthermore, the current data (third current data) and voltage data (third voltage data) acquired in a third time period different from the first time period and the second time period are set as third operation data. The microcontroller 11 identifies the first equivalent circuit 60 from the third operation data, and obtains one or more third operating frequencies from the current data included in the third operation data.

[0068] The microcontroller 11 calculates a first impedance (first complex impedance) of the storage battery 2 at one or more first operating frequencies from the parameters Ra, Rb, and Cb of the first equivalent circuit 60 identified using the first operation data (step S103). The calculation of the first impedance is performed based on the first equivalent circuit 60 shown in FIG. 6. For example, the microcontroller 11 calculates the impedance Z based on the first equivalent circuit 60 using the formula Z=Ra+Rb / (1+jωRbCb). Here, ω is an angular frequency and is 2πf. In this calculation, the first operating frequency is used as f. Through this calculation, for example, the first impedance shown by the mark * in FIG. 9 is acquired.

[0069] Furthermore, the microcontroller 11 calculates a second impedance (second complex impedance) of the storage battery 2 at each of one or more second operating frequencies from the parameters Ra, Rb, and Cb of the first equivalent circuit 60 identified using the second operation data (step S103). The calculation of the second impedance is performed based on the first equivalent circuit 60 shown in Fig. 6. Through this calculation, for example, the second impedance shown by the cross in Fig. 9 is acquired.

[0070] Furthermore, the microcontroller 11 calculates a third impedance (third complex impedance) of the storage battery 2 at each of one or more third operating frequencies from the parameters Ra, Rb, and Cb of the first equivalent circuit 60 identified using the third operation data (step S103). The calculation of the third impedance is performed based on the first equivalent circuit 60 shown in Fig. 6. Through this calculation, for example, the third impedance shown by the circle in Fig. 9 is acquired.

[0071] In this way, by using a plurality of pieces of operation data, it is possible to obtain impedance at many operating frequencies. Note that since the operating frequency of the storage battery 2, which is a DC power source, is generally low, the impedance obtained in step S103 is an impedance within a low frequency range (for example, a frequency range from 0.01 Hz to 1 Hz). Such an impedance in a low frequency range corresponds to the diffusion impedance of the storage battery. In other words, the microcontroller 11 according to the embodiment can accurately obtain the diffusion impedance by using the operation data.

[0072] In the above description, a plurality of pieces of operation data are used to obtain the impedance at the operation frequency. However, only one piece of operation data may be used to obtain the impedance at the operation frequency. For example, when there are many operation frequencies of the current data included in one piece of operation data, the impedance at many operation frequencies can be obtained even by using only one piece of operation data. For example, in FIG. 9, since there are three first operation frequencies of the first current included in the first operation data, the impedance at each of the three first operation frequencies can be obtained from one piece of first operation data.

[0073] Next, the microcontroller 11 performs temperature correction of the impedance Z calculated in step S103 to improve accuracy (step S104). For example, temperature correction of the high frequency component (Ra) of the impedance Z is performed as the temperature correction of the impedance Z. For the temperature correction of Ra, for example, reference data for temperature correction of Ra is stored in the database 31, and the microcontroller 11 corrects the high frequency component (Ra) of the impedance Z to a value at a predetermined temperature (for example, 25° C.) using the temperature data and the reference data. Note that if the effect of temperature on the impedance Z can be ignored, the temperature correction may be omitted.

[0074] After the temperature correction, the impedance at the operating frequency is used, for example, by the microcontroller 11 to obtain an approximation curve (step S106). The obtained approximation curve indicates the impedance in the low frequency region. Furthermore, the microcontroller 11 identifies the second equivalent circuit 70 (see FIG. 11) using the obtained approximation curve (impedance in the low frequency region) and the impedance in the high frequency region measured by the impedance measuring device 12 (step S106).

[0075] FIG. 11 shows a second equivalent circuit 70 according to the embodiment. The second equivalent circuit 70 has a larger number of parameters than the first equivalent circuit 60, and is a model with higher accuracy than the first equivalent circuit 60. The second equivalent circuit 70 is similar to the equivalent circuit shown in FIG. 3. That is, the second equivalent circuit 70 includes R0 corresponding to the electrolyte resistance, a first RC parallel circuit corresponding to the negative electrode impedance, a second RC parallel circuit corresponding to the positive electrode impedance, and a constant phase element (CPE) corresponding to the diffusion impedance, and each element is connected in series. The RC parallel circuit corresponding to the negative electrode impedance has R1 and C1. The RC parallel circuit corresponding to the negative electrode impedance has R2 and C2. The number of RC parallel circuits may be three or more.

[0076] As described above, the impedance measuring device 12 measures the impedance in a high frequency range (for example, a frequency of 1 Hz or more and 5 kHz or less). Then, the microcontroller 11 identifies the electrolyte resistance R0, the negative electrode impedances R1 and C1, and the positive electrode impedances R2 and C2 in the second equivalent circuit 70 from the impedance in the high frequency range.

[0077] Furthermore, the microcontroller 11 determines the remaining diffusion impedance Z CPE is identified by an approximation curve obtained from the impedance at the operating frequency. CPE is Z CPE =1 / (Q(jω) α ) is expressed by the constant phase element Z CPE In the formula, Q represents the length of the portion representing the diffusion impedance in the Nyquist diagram (the portion extending almost linearly from the inflection point (△ mark) diagonally upward to the right in FIG. 9 ), and α represents the gradient of the linearly extending portion.

[0078] When approximating the impedance at the operating frequency, the approximation curve is Z CPE =1 / (Q(jω) α ) formula. That is, the above Z CPE The approximate curve can be obtained by using the least squares method to find the Q and α that minimize the error with the impedance at the operating frequency, with Q and α as variables. Once the approximate curve is obtained, the diffusion impedance Z CPE The approximate curve is identified as Z CPE =1 / (Q(jω) α ) and calculate the approximate curve by Z CPE =1 / (Q(jω) α ) can be fitted to the impedance at the operating frequency without obtaining an approximate curve. CPE =1 / (Q(jω) α) Alternatively, if the impedance at the operating frequency spans a sufficiently wide frequency range, the entire second equivalent circuit 70 may be identified using only the impedance at the operating frequency.

[0079] From the above, the parameters R0, R1, C1, R2, C2, and Z of the second equivalent circuit 70 corresponding to a wide frequency range are obtained. CPE In the second equivalent circuit 70, a constant phase element is connected in series to two RC parallel circuits connected in series, and therefore, the second equivalent circuit 70 is suitable for the state analysis according to the embodiment.

[0080] The parameters R0, R1, C1, R2, C2, and Z of the second equivalent circuit 70 identified as above CPE may change due to changes in the state of the storage battery 2. Therefore, the parameters R0, R1, C1, R2, C2, Z of the second equivalent circuit 70 may also be CPE By obtaining the fluctuation of the impedance, it is possible to analyze the deterioration of the storage battery 2 and estimate the SOC of the storage battery (step S107). In this embodiment, since the impedance is obtained by utilizing the operation data, the operation of the storage battery 2 is less disturbed and the state analysis can be performed with high accuracy.

[0081] The method of obtaining the approximation curve is not limited to the least squares method. For example, the approximation curve may be obtained using an artificial intelligence configured to output appropriate approximation curve parameters when the impedance at the operating frequency is given as an input. Such an artificial intelligence may be, for example, a neural network trained to output appropriate approximation curve parameters when the impedance at the operating frequency is given as an input. The artificial intelligence may also output parameters of the second equivalent circuit 70 when the impedance at the operating frequency is given as an input.

[0082] Now, the approximation curve obtained from the impedance at the operating frequency in step S106 is obtained as an approximation curve of the impedance (marked with *, marked with ×, and marked with ◯) at each of the multiple operating frequencies in, for example, the absolute value |Z|-frequency plane of the complex impedance and the phase θ-frequency plane of the complex impedance in Fig. 10. The approximation curve may be obtained as an approximation curve of the impedance (marked with *, marked with ×, and marked with ◯) at each of the multiple operating frequencies in the complex plane shown in Fig. 9.

[0083] When calculating the approximate curve, the more the number of impedances at the operating frequency (number of * marks, x marks, and o marks), the higher the accuracy of the approximate curve. The approximate curve may be calculated only from the impedances at the operating frequency (* marks, x marks, and o marks), but to further increase the accuracy of the approximate curve, the impedances measured by the AC impedance method (△ marks in Figures 9 and 10) may also be used.

[0084] Of the impedances measured by the AC impedance method, the impedance used to obtain the approximate curve is preferably an impedance at a frequency other than the operating frequency. Since the operating frequency is generally low, it is more preferable that the frequency other than the operating frequency is a frequency higher than the operating frequency. When the impedance measuring device 12 measures the AC impedance by performing a frequency sweep in a frequency range from 1 Hz to 5 kHz by the AC impedance method, for example, an impedance at 1 Hz, which is the lowest frequency in the frequency range from 1 Hz to 5 kHz (indicated by a triangle in Figs. 9 and 10), can be used. Of the impedances measured by the AC impedance method, one or more impedances may be used to obtain the approximate curve.

[0085] If an approximation curve is obtained using not only the impedance at the operating frequency (marked with *, ×, and ◯) but also the impedance measured by the AC impedance method (marked with △), the approximation curve will be closer to the true value (the curve to the left of the △ in Fig. 10). In addition, the approximation curve is advantageous in that it is easier to maintain continuity with the impedance in the frequency range from 1 Hz to 5 kHz measured by the AC impedance method (the curve to the right of the △ in Fig. 10).

[0086] The frequency (position of △) other than the operating frequency is preferably a frequency corresponding to an inflection point occurring when moving from a portion corresponding to the diffusion impedance to a higher frequency region in a Nyquist diagram drawn on a complex plane as shown in Fig. 9. As shown in Fig. 9, the Nyquist diagram of impedance measurements by the AC impedance method has an inflection point (△ mark in Fig. 9) at a certain frequency (e.g., 1 Hz), and extends from the inflection point in an almost straight line obliquely upward to the right in the complex plane. The portion extending from the inflection point in an almost straight line obliquely upward to the right corresponds to the diffusion impedance. Therefore, the diffusion impedance can be accurately represented by obtaining an approximation curve using the impedance (△ mark) of the frequency corresponding to the inflection point as well.

[0087] Furthermore, the impedance in the high frequency range measured by the impedance measuring device 12 may be subject to temperature compensation (step S105). In temperature compensation of the impedance in the high frequency range, the impedance itself may be temperature compensated, or the parameters of the second equivalent circuit 70 representing the impedance may be temperature compensated. Furthermore, for a relatively high frequency impedance among the impedances measured by the impedance measuring device 12, the second equivalent circuit parameters representing the impedance (for example, R0, R1, C1 of the second equivalent circuit 70) may be temperature compensated. Furthermore, for a relatively low frequency impedance among the impedances measured by the impedance measuring device 12 (the impedance represented by R2, C2), the impedance itself may be temperature compensated.

[0088] For temperature compensation of the impedance measured by the impedance measuring device 12, for example, reference data for the temperature compensation is stored in the database 31. The microcontroller 11 compensates the impedance or parameter to a value at a predetermined temperature (for example, 25°C) using the temperature data and the reference data. Note that if the effect of temperature on the impedance can be ignored, the temperature compensation may be omitted.

[0089] FIG. 12 shows the impedance of the second equivalent circuit 70 identified by the method according to the embodiment. FIG. 13 shows the absolute value |Z| of the impedance of the second equivalent circuit identified by the method according to the embodiment, and FIG. 14 shows the phase θ of the impedance of the second equivalent circuit identified by the method according to the embodiment. In FIG. 12, FIG. 13, and FIG. 14, the impedance measurement value Z by the AC impedance method, which is regarded as a true value, or a value based on the impedance measurement value (|Z|, θ) is also shown. The error of θ was 0.72°, and the error of |Z| was 1.9%.

[0090] 12, 13, and 14, it can be seen that the second equivalent circuit 70 is identified with high accuracy by the method according to the embodiment. In addition, since the impedance can be obtained with high accuracy, it can be seen that the second equivalent circuit 70 is an equivalent circuit model suitable for the method according to the embodiment.

[0091] <3. Notes> The present invention is not limited to the above-described embodiment, and various modifications are possible. [Explanation of symbols]

[0092] 1: Battery storage system 2: Battery 3: Management system 4: Terminal 5: Current sensor 6: Voltage sensor 7: Temperature sensor 10: Management device 11: Microcontroller 12: Impedance measuring device 15: Output device 20: Processor 21: Status analysis processing 30: Storage device 31: Database 35: Computer Programs 60: First equivalent circuit 70: Second equivalent circuit

Claims

1. identifying a first equivalent circuit for the battery using operational data including current data for the battery; Obtaining impedance of the storage battery at one or more operating frequencies of the storage battery based on the first equivalent circuit. Prepare for this. The one or more operating frequencies are obtained by subjecting the current data to frequency analysis. How to manage storage batteries.

2. The operational data includes: First operation data including first current data during a first operation of the storage battery; second operation data including second current data in a second operation different from the first operation; At least The impedance is a first impedance of the first equivalent circuit identified using the first operational data; a second impedance of the first equivalent circuit identified using the second operational data; and At least the first impedance is an impedance at one or more first operating frequencies in the first operation; the second impedance is an impedance at one or more second operating frequencies in the second operation; the one or more first operating frequencies are obtained by subjecting the first current data to frequency analysis; The one or more second operating frequencies are obtained by subjecting the second current data to a frequency analysis. The method for managing the storage battery according to claim 1 .

3. Using the impedance, identify a second equivalent circuit that is different from the first equivalent circuit. The storage battery management method according to claim 1 or 2, further comprising:

4. The impedance at a frequency other than the operating frequency is obtained by measuring an AC impedance of the storage battery. A method for managing a storage battery according to any one of claims 1 to 3.

5. Identifying a second equivalent circuit different from the first equivalent circuit using the impedance at the operating frequency and the impedance at a frequency other than the operating frequency. Further, The impedance at the frequency other than the operating frequency is obtained by measuring the AC impedance of the storage battery. A method for managing a storage battery according to any one of claims 1 to 3.

6. The frequency other than the operating frequency is higher than the operating frequency. The storage battery management method according to claim 4 or 5.

7. The first equivalent circuit is identified by a recursive least squares method using the operational data. A method for managing a storage battery according to any one of claims 1 to 6.

8. The second equivalent circuit includes two or more RC parallel circuits and a constant phase element connected in series to the two or more RC parallel circuits. The method for managing the storage battery according to claim 3 or 5.

9. identifying a first equivalent circuit for the battery using operational data including current data for the battery; Obtaining impedance of the storage battery at one or more operating frequencies of the storage battery based on the first equivalent circuit. The method is configured to perform a process comprising: The one or more operating frequencies are obtained by subjecting the current data to frequency analysis. A battery management device.

10. A storage battery, A storage battery system comprising: the management device according to claim 9.

Images