Impedance measurement device for secondary battery, impedance measurement method for secondary battery, and impedance measurement program for secondary battery

Abstract

To suppress a decrease in SOC of a secondary battery while suppressing a decrease in reliability of a measurement value of impedance due to a random error, in an impedance measurement device of the secondary battery.SOLUTION: An impedance measuring device (10) measures an impedance of a secondary battery (41,42) on the basis of a measurement value of an alternating current flowing from the secondary battery and a measurement value of a voltage fluctuation between terminals of the secondary battery in response to the alternating current. The impedance measurement device shortens the measurement time for measuring the alternating current and the voltage fluctuation as the magnitude of the correlation parameter correlated with the magnitude of the impedance changes in a direction in which the impedance increases.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a device for measuring the impedance of a secondary battery. [Background technology]

[0002] There is a method for measuring the impedance of a secondary battery and estimating the SOH (State Of Health) of the secondary battery based on the measured impedance value (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6019368 Summary of the Invention [Problem to be solved by the invention]

[0004] The impedance of a secondary battery is measured based on the AC current flowing from the battery and the voltage fluctuation between the battery's terminals in response to the AC current. Here, the measured AC current and voltage fluctuation values ​​contain random errors. The random errors arise, for example, from the random motion of electrons in semiconductors included in the circuit that measures the AC current and voltage fluctuation. Generally, the random errors become smaller as the measurement time for measuring the AC current and voltage fluctuations becomes longer. However, extending the measurement time for the AC current and voltage fluctuations increases the discharge time of the secondary battery, resulting in a decrease in the SOC (State of Charge) of the secondary battery.

[0005] The present invention has been made to solve the above-mentioned problems, and its main object is to suppress a decrease in the SOC of a secondary battery while suppressing a decrease in the reliability of impedance measurements due to random errors in an impedance measuring device for a secondary battery. [Means for solving the problem]

[0006] The first means for solving the above problem is: An impedance measuring device (10) for measuring the impedance of a secondary battery (41, 42) based on a measured value of an AC current flowing from the secondary battery and a measured value of a voltage fluctuation between terminals of the secondary battery in response to the AC current, The measurement time for measuring the AC current and the voltage fluctuation is shortened as the magnitude of the correlation parameter correlated with the magnitude of the impedance changes in the direction in which the impedance increases.

[0007] According to the above configuration, the impedance measuring device measures the impedance of the secondary battery based on a measured value of the AC current flowing from the secondary battery and a measured value of the voltage fluctuation between the terminals of the secondary battery in response to the AC current.

[0008] Generally, the random error contained in the measured values ​​of AC current and voltage fluctuations decreases as the measurement time for measuring AC current and voltage fluctuations increases. Here, the inventors of the present application focused on the S / N ratio, which is the ratio between the magnitude of impedance (S: Signal) and the random error (N: Noise). The inventors of the present application considered that even if the measurement time is shortened, the reliability of the measured impedance value will not decrease as long as the S / N ratio does not decrease.

[0009] In this regard, the impedance measuring device shortens the measurement time for measuring the AC current and the voltage fluctuation as the magnitude of the correlation parameter correlated with the magnitude of the impedance changes in the direction of increasing the impedance. In other words, the device allows for an increase in random error as the impedance increases. Therefore, even if the measurement time for the AC current and the voltage fluctuation is shortened, a decrease in the S / N ratio can be suppressed. Therefore, the impedance measuring device can suppress a decrease in the SOC of the secondary battery while suppressing a decrease in the reliability of the impedance measurement value due to random error. Note that the correlation parameter includes not only various parameters correlated with the magnitude of the impedance but also the impedance itself.

[0010] The second method is An impedance measurement method for measuring impedance of a secondary battery (41, 42) based on a measurement value of an AC current flowing from the secondary battery and a measurement value of a voltage fluctuation between terminals of the secondary battery in response to the AC current, comprising: The measurement time for measuring the AC current and the voltage fluctuation is shortened as the magnitude of the correlation parameter correlated with the magnitude of the impedance changes in the direction in which the impedance increases.

[0011] According to the above steps, the impedance measuring method for a secondary battery can achieve the same effects as the first means.

[0012] The third method is an impedance measurement program that causes a computer (20) to execute a process of measuring the impedance of a secondary battery (41, 42) based on a measured value of an AC current flowing from the secondary battery (41, 42) and a measured value of a voltage fluctuation between terminals of the secondary battery in response to the AC current, The computer is caused to execute a process of shortening the measurement time for measuring the AC current and the voltage fluctuations as the magnitude of a correlation parameter correlated with the magnitude of the impedance changes in the direction in which the impedance increases.

[0013] According to the above process, in a program that causes a computer to execute the process, it is possible to achieve the same effects as the first means. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 2 is a circuit diagram showing the battery module and the monitoring IC according to the first embodiment. [Figure 2] 4 is a time chart showing the discharge current from a battery. [Figure 3] 10 is a graph showing the frequency of impedance measurements when the measurement time is short. [Figure 4] 10 is a graph showing the frequency of impedance measurements when the measurement time is long. [Figure 5] A graph showing the concept of maintaining a constant S / N ratio. [Figure 6] 4 is a flowchart showing the procedure for measuring impedance according to the first embodiment. [Figure 7] 10 is a graph showing the relationship between the magnitude of impedance and measurement time. [Figure 8] FIG. 10 is a circuit diagram showing a battery module and a monitoring IC according to a second embodiment. [Figure 9] 10 is a flowchart showing the procedure for measuring impedance according to the second embodiment. [Figure 10] 10 is a graph showing the relationship between temperature and measurement time. [Figure 11] FIG. 10 is a block diagram showing a modified example of the monitoring IC. DETAILED DESCRIPTION OF THE INVENTION

[0015] (First embodiment) Hereinafter, a first embodiment embodied in an impedance measuring device for a secondary battery applied to a power supply system of a vehicle (for example, a hybrid vehicle or an electric vehicle) will be described with reference to the drawings.

[0016] As shown in FIG. 1, the impedance measuring device 10 includes a current limiting resistor 11, an FET 12, a shunt resistor 13, a monitoring IC 20, and the like.

[0017] A plurality of battery modules 41 are connected in series to form an assembled battery. The assembled battery has a terminal voltage of, for example, 100 V or more, and is electrically connected to a motor (corresponding to a rotating electric machine) via an inverter. The battery module 41 is formed by connecting a plurality of battery cells 42 in series. The battery cells 42 (corresponding to secondary batteries) can be, for example, lithium iron phosphate ion batteries (LFP batteries), lithium ion storage batteries, or nickel-metal hydride storage batteries. Each battery cell 42 is a storage battery having an electrolyte and a plurality of electrodes.

[0018] A series connection of a current limiting resistor 11, a FET 12, and a shunt resistor 13 is connected in parallel to the battery module 41. The current limiting resistor 11 (corresponding to a resistor) is a resistor that limits the current when a discharge current flows from the battery module 41. The FET 12 (corresponding to a switching element) is, for example, an N-channel MOSFET. The opening and closing of the FET 12 is controlled by the monitoring IC 20. The shunt resistor 13 (corresponding to a current sensor) is used to measure the current flowing through the series connection and the battery module 41 (i.e., the battery cell 42).

[0019] The monitoring IC 20 (corresponding to a computer) is primarily composed of a microcomputer equipped with a CPU, ROM, RAM, an input / output interface, etc. The monitoring IC 20 includes a current measurement unit 21, a voltage response measurement unit 22, and an impedance measurement unit 23. The monitoring IC 20 executes installed programs to realize the functions of the current measurement unit 21, the voltage response measurement unit 22, and the impedance measurement unit 23. These functions may be realized by electronic circuits, which are hardware, or by both hardware and software. The monitoring IC 20 measures the state of charge (SOC) and state of health (SOH) of each battery cell 42. The monitoring IC 20 measures the impedance of each battery cell 42 and inputs the results to an ECU, such as a battery control ECU (Electronic Control Unit). The current limiting resistor 11, FET 12, shunt resistor 13, and monitoring IC 20 constitute a secondary battery impedance measurement device 10.

[0020] The monitoring IC 20 outputs an AC current using a battery module 41 including a battery cell 42 to be measured as a power source. The monitoring IC 20 alternately switches the FET 12 on and off to output an AC current (which can also be considered an intermittent current) from the battery module 41 (i.e., the battery cell 42) as shown in Fig. 2. When the AC current flows from the battery cell 42, a response signal (voltage fluctuation) that reflects information about the complex impedance (equivalent to impedance) is generated in the terminal voltage of the battery cell 42.

[0021] The voltage response measurement unit 22 measures the terminal voltage of the battery cell 42, measures the response signal (voltage fluctuation) in response to the AC current, converts the analog value of the measured response signal into a digital value, and inputs it to the impedance measurement unit 23.

[0022] The current measuring unit 21 measures the AC current from the voltage across the shunt resistor 13 and the resistance value of the shunt resistor 13 , converts the analog value of the measured AC current into a digital value, and inputs it to the impedance measuring unit 23 .

[0023] The impedance measuring unit 23 analyzes the measured AC current using the frequency (measurement frequency) of each AC signal, and extracts and acquires each AC signal (measurement signal) that actually flowed. Then, the impedance measuring unit 23 analyzes the response signal based on the acquired AC signals, and calculates values ​​proportional to the real part and imaginary part of the response signal (information on complex impedance). Based on these, the impedance measuring unit 23 calculates the absolute value (corresponding to the magnitude of the impedance), phase, etc. of the complex impedance at the measurement frequency of the AC signal. The values ​​proportional to the real part and imaginary part of the response signal are each average values ​​(integral values) from the start of output of each AC signal.

[0024] Incidentally, the measured values ​​of AC current and voltage fluctuation contain random errors, which arise due to the random motion of electrons in semiconductors included in circuits that measure AC current and voltage fluctuations (e.g., FET 12, ADC (Analog Digital Converter) that converts analog values ​​into digital values, etc.).

[0025] Generally, the random error decreases as the measurement time for measuring AC current and voltage fluctuations increases. Therefore, the random error contained in the measured impedance value also decreases as the measurement time for AC current and voltage fluctuations increases. Figure 3 is a graph showing the frequency of impedance measurements when the measurement time is short. Figure 4 is a graph showing the frequency of impedance measurements when the measurement time is long. The random error N in the measured impedance value when the measurement time is long is smaller than the random error N in the measured impedance value when the measurement time is short.

[0026] Here, the inventors focused on the S / N ratio, which is the ratio between the magnitude of impedance (S: Signal) and random error (N: Noise).The inventors believed that even if the measurement time of AC current and voltage fluctuations is shortened, the reliability of the impedance measurement value will not decrease as long as the S / N ratio does not become smaller.

[0027] The impedance measuring device 10 shortens the measurement time for measuring AC current and voltage fluctuations as the impedance increases. That is, the impedance measuring device 10 shortens the measurement time for measuring AC current and voltage fluctuations as the magnitude of a correlation parameter (e.g., the impedance itself) that correlates with the magnitude of the impedance changes in the direction of increasing impedance. For example, as shown in FIG. 5, the measurement time when the impedance is large is made shorter than the measurement time when the impedance is small. This makes it possible to make the S / N ratio when the impedance is large closer to the S / N ratio when the impedance is small. That is, the random error (N) is allowed to increase as the impedance (S) increases.

[0028] 6 is a flowchart showing the impedance measurement procedure. This series of processes is executed by the monitoring IC 20 for each battery cell 42.

[0029] First, the impedance Z is measured under a first condition where the measurement time for the AC current and voltage fluctuation is a first time t1 (S10). The first time t1 is, for example, the shortest measurement time in which the impedance Z of the battery cell 42 can be measured, or a measurement time in which the impedance Z can be measured with low accuracy.

[0030] Next, a measurement time n for the AC current and voltage fluctuations is determined from the impedance Z measured under the first condition (S11). The measurement time n (corresponding to the second time t2) is a measurement time that allows the impedance of the battery cell 42 to be measured with higher accuracy than under the first condition, and is longer than the first time t1 (n>t1). Specifically, as shown in FIG. 7, where n is the measurement time, Z is the impedance measured under the first condition, and a is a predetermined coefficient, the measurement time n for the AC current and voltage fluctuations is determined (set) by the following equation (1). Note that "Z^2" represents the square of Z.

[0031] n=a / Z^2 (1) Generally, the random error N is expressed by the following equation (2).

[0032] N=x / (√n) (2) where x is the measured impedance value and n is the measurement time. The ratio (S / N ratio) of the magnitude (S) of the impedance Z to the random error N can be expressed as the following equation (3) using equation (2).

[0033] S / N=Z / {x / (√n)} (3) By modifying equation (3) and solving for the measurement time n, the above equation (1) can be obtained. a = (Sx / N)^2. Here, to maintain the reliability of the impedance measurement value, the S / N (S / N ratio) is set to a constant value. The magnitude of the S / N can be set based on the accuracy required for the impedance measurement value. The impedance measurement value x can be a measurement value obtained by measuring the impedance of the battery cell 42 in advance under specified conditions, or an approximate value assumed to be the measured impedance of the battery cell 42. For this reason, the specified coefficient a is a constant. The optimal value of the coefficient a can be obtained in advance based on tests, etc.

[0034] Next, the impedance of the battery cell 42 is measured using the determined measurement time n (S12). That is, the impedance of the battery cell 42 is measured under the second condition where the measurement time is measurement time n, and the impedance of the battery cell 42 is determined.

[0035] The series of processes shown in the flowchart of FIG. 6 corresponds to a method for measuring impedance of a secondary battery, and the program that causes the monitoring IC 20 to execute the series of processes shown in the flowchart of FIG. 6 corresponds to a program for measuring impedance of a secondary battery.

[0036] The present embodiment described above in detail has the following advantages.

[0037] The impedance measuring device 10 shortens the measurement time n for measuring AC current and voltage fluctuations as the magnitude of a correlation parameter (impedance in this embodiment) correlated with the magnitude of the impedance changes in the direction of increasing impedance. That is, the impedance measuring device 10 allows the random error N to increase as the impedance (corresponding to S) increases. Therefore, even if the measurement time n for AC current and voltage fluctuations is shortened, it is possible to prevent the S / N ratio from decreasing. Therefore, the impedance measuring device 10 can prevent a decrease in the SOC of the battery cell 42 while suppressing a decrease in the reliability of the impedance measurement value due to the random error N.

[0038] The impedance measuring device 10 shortens the measurement time n as the impedance Z increases. With this configuration, the measurement time n can be shortened as the impedance (corresponding to S) increases, i.e., it is possible to allow the random error N to increase. Therefore, the impedance measuring device 10 can suppress a decrease in the SOC of the battery cell 42 while suppressing a decrease in the reliability of the impedance measurement value due to the random error N.

[0039] The impedance measuring device 10 sets the measurement time n (corresponding to the second time) under the second condition based on the impedance Z measured under the first condition in which the measurement time n is the first time t1. The first time t1 is shorter than the measurement time n. This makes it possible to shorten the discharge time of the battery cell 42 when measuring the impedance Z under the first condition, while appropriately setting the measurement time n when measuring the impedance under the second condition.

[0040] When the measurement time is n, the impedance measured under the first condition is Z, and the predetermined coefficient is a, the relationship n=a / Z^2 is satisfied. With this configuration, the S / N ratio can be kept constant regardless of the magnitude of the impedance. Therefore, the measurement time n can be shortened according to the magnitude of the impedance while maintaining the reliability of the impedance measurement value. Therefore, a decrease in the SOC of the battery cell 42 can be suppressed.

[0041] The first embodiment can be modified as follows: The same parts as those in the first embodiment are denoted by the same reference numerals and the description thereof will be incorporated herein.

[0042] Instead of the graph shown in FIG. 7 , a table specifying the relationship between the impedance Z of the battery cell 42 and the measurement time n may be used. The measured impedance Z may then be applied to the table to determine (set) the measurement time n. The number of impedances in the table may be limited to only two: low impedance and high impedance. Even in this case, comparing the low impedance case with the high impedance case, the measurement time for measuring AC current and voltage fluctuations is shortened as the impedance increases. The number of impedances in the table may be limited to only two: impedances lower than a predetermined impedance and impedances higher than a predetermined impedance. Even in this case, comparing the impedances lower than a predetermined impedance with impedances higher than a predetermined impedance, the measurement time for measuring AC current and voltage fluctuations is shortened as the impedance increases.

[0043] (Second embodiment) A second embodiment in which the correlation parameter correlated with the magnitude of the impedance is changed from the impedance to the temperature T of the battery cell 42 will be described below with reference to the drawings. Note that the same parts as those in the first embodiment are denoted by the same reference numerals and the description thereof will be incorporated herein.

[0044] 8, the impedance measuring device 10 of this embodiment includes a temperature sensor 15. The temperature sensor 15 measures the temperature T of one battery cell 42 included in, for example, a battery module 41, and inputs the temperature T to the impedance measuring unit 23. The battery cell 42 has a characteristic that the impedance increases as the temperature (corresponding to the correlation parameter) decreases.

[0045] 9 is a flowchart showing the impedance measurement procedure. This series of processes is executed by the monitoring IC 20 for each battery cell 42.

[0046] First, the temperature sensor 15 measures the temperature T of the battery cell 42 (S20). The measured temperature T is used as a temperature that represents the temperatures of all the battery cells 42 included in the battery module 41.

[0047] Next, the measurement time n is determined from the measured temperature T (S21). Specifically, the measured temperature T is applied to a graph defining the relationship between the temperature T and the measurement time n shown in FIG. 10 to determine (set) the measurement time n. As shown in the graph, the lower the temperature T, the shorter the measurement time n. An optimal graph defining the relationship between the temperature T and the measurement time n can be obtained in advance based on tests or the like.

[0048] Next, the impedance of the battery cell 42 is measured using the determined measurement time n (S22). That is, the impedance of the battery cell 42 is measured under the second condition where the measurement time is measurement time n, and the impedance of the battery cell 42 is determined.

[0049] The series of processes shown in the flowchart of FIG. 9 corresponds to a method for measuring impedance of a secondary battery, and the program that causes the monitoring IC 20 to execute the series of processes shown in the flowchart of FIG. 9 corresponds to a program for measuring impedance of a secondary battery.

[0050] Only advantages different from the first embodiment will be described below. According to the above configuration, the lower the temperature T of the battery cell 42, i.e., the higher the impedance of the battery cell 42, the shorter the measurement time n of the AC current and voltage fluctuations can be. Therefore, it is possible to allow the random error N to increase as the impedance increases. Therefore, the impedance measuring device 10 can suppress a decrease in the SOC of the battery cell 42 while suppressing a decrease in the reliability of the impedance measurement value due to the random error N.

[0051] The second embodiment can be modified as follows: The same parts as those in the second embodiment are denoted by the same reference numerals and the description thereof will be incorporated herein.

[0052] A temperature sensor 15 may be provided in each battery cell 42. The impedance measuring device 10 may then determine the measurement time n from the temperature T measured by the temperature sensor 15 provided in each battery cell 42 that is the measurement target.

[0053] Instead of the graph shown in FIG. 10, a table specifying the relationship between the temperature T of the battery cell 42 and the measurement time n can be used. The measured temperature T can then be applied to the table to determine (set) the measurement time n. The table may contain only two temperatures: a low temperature and a high temperature. Even in this case, comparing the low temperature and the high temperature, the lower the temperature, i.e., the higher the impedance, the shorter the measurement time for measuring the AC current and voltage fluctuations. The table may contain only two temperatures: a temperature lower than a predetermined temperature and a temperature higher than a predetermined temperature. Even in this case, comparing the high temperature and the high temperature, the lower the temperature, i.e., the higher the impedance, the shorter the measurement time for measuring the AC current and voltage fluctuations.

[0054] The first and second embodiments can be modified as follows: The same parts as those in the first and second embodiments are denoted by the same reference numerals and the description thereof will be incorporated herein.

[0055] The battery cell 42 has a characteristic that the impedance increases as the degree of degradation (corresponding to the correlation parameter) increases. Therefore, the impedance measuring device 10 may shorten the measurement time n for measuring AC current and voltage fluctuations as the magnitude of the correlation parameter (degradation degree) correlated with the magnitude of the impedance changes in the direction of increasing impedance (in the direction of increasing degradation). Even with this configuration, the impedance measuring device 10 can suppress a decrease in the SOC of the battery cell 42 while suppressing a decrease in the reliability of the impedance measurement value due to random error N.

[0056] The SOC (corresponding to a correlation parameter) of the battery cell 42 correlates with the magnitude of the impedance of the battery cell 42. Therefore, the impedance measuring device 10 may shorten the measurement time n for measuring AC current and voltage fluctuations as the magnitude of the correlation parameter (SOC) correlated with the magnitude of the impedance changes in the direction of increasing impedance. Even with this configuration, the impedance measuring device 10 can suppress a decrease in the SOC of the battery cell 42 while suppressing a decrease in the reliability of the impedance measurement value due to random error N. Note that the relationship between the SOC and the magnitude of the impedance of the battery cell 42 varies depending on the type of battery cell 42, but can be obtained in advance based on tests, etc.

[0057] The monitoring IC 20 may execute the process of S10 in Fig. 6 and the process of S20 in Fig. 9, and may use a map that defines the relationship between the impedance measured under the first condition, the measured temperature of the battery cell 42, and the measurement time n. The impedance measured under the first condition and the measured temperature may then be applied to the map to determine (set) the measurement time n.

[0058] Instead of the FET 12, a switching element such as an IGBT (Insulated-Gate Bipolar Transistor) can be used.

[0059] 11, the monitoring IC 20 may include an AC current generating unit 51 connected to each battery cell 42 via a first electrical path 81, a voltage response measuring unit 52 connected to each battery cell 42 via a second electrical path 82, a modulation signal generator 53 connected to the AC current generating unit 51, and an arithmetic processing unit 54 connected to the voltage response measuring unit 52 and the modulation signal generator 53. In this case, the current limiting resistor 11, the FET 12, and the shunt resistor 13 can be omitted.

[0060] The AC current generation unit 51 (current generation unit) outputs an AC current using the battery cell 42, which is the measurement target, as a power source. Specifically, the AC current generation unit 51 causes the battery cell 42 to output an AC current based on an instruction signal input from the modulation signal generator 53. The voltage response measurement unit 52 (voltage measurement unit) measures a response signal (voltage fluctuation) between the terminals of the battery cell 42 that reflects information about the complex impedance of the battery cell 42. The modulation signal generator 53 includes an oscillator that generates an AC signal of an arbitrary waveform. The modulation signal generator 53 causes the oscillator to generate the AC signal in accordance with a command from the calculation processing unit 54. The modulation signal generator 53 converts the AC signal into a digital signal to generate an instruction signal, and instructs (outputs) the AC current generation unit 51 to generate an AC current based on the instruction signal.

[0061] The arithmetic processing unit 54 has a function of calculating the complex impedance of the battery cell 42. Here, an overview of a method for calculating the complex impedance will be described. The arithmetic processing unit 54 instructs the modulation signal generator 53 on the measurement frequency of the complex impedance. The modulation signal generator 53 generates an AC current from the battery cell 42 via the AC current generation unit 51 based on the instruction of the arithmetic processing unit 54. The voltage response measurement unit 52 measures the voltage between the terminals of the battery cell 42, measures a response signal (voltage fluctuation) responding to the AC current, and inputs the measured response signal to the arithmetic processing unit 54. The arithmetic processing unit 54 calculates information related to the complex impedance of the battery cell 42 based on the response signal. With the above configuration, it is possible to achieve the same effects as in the first and second embodiments.

[0062] The impedance measuring device 10 is not limited to a configuration that measures the impedance of all battery cells 42 included in the battery module 41, but may be a configuration that measures the impedance of some or just one battery cell 42.

[0063] An AC current may be passed through each battery cell 42 to measure the voltage fluctuation (and hence the impedance) of each battery cell 42. Alternatively, an AC current may be passed through the entire battery module 41 to measure the voltage fluctuation (and hence the impedance) of each battery cell 42, or the voltage fluctuation (impedance) of the entire battery module 41 (corresponding to a secondary battery) may be measured. Alternatively, an AC current may be passed through the entire battery pack to measure the voltage fluctuation (impedance) of each battery cell 42, or the voltage fluctuation (impedance) of the entire battery pack (corresponding to a secondary battery) may be measured.

[0064] The impedance measuring device 10 (impedance measuring method, impedance measuring program) of the first embodiment, the second embodiment, and their modified examples can be applied not only to the power supply system of a vehicle, but also to diagnostic systems, maintenance systems, etc. owned by vehicle dealers, repair shops, etc.

[0065] The impedance measuring device 10 can be mounted not only on vehicles but also on electric aircraft, electric ships, and the like.

[0066] The above-described embodiment and modifications may be combined within the scope of possible combinations.

[0067] The impedance measuring device 10 and the method described herein may be implemented by a special-purpose computer configured with a processor and memory programmed to execute one or more functions (instructions) embodied in a computer program. Alternatively, the impedance measuring device 10 and the method described herein may be implemented by a special-purpose computer configured with a processor configured with one or more dedicated hardware logic circuits. Alternatively, the impedance measuring device 10 and the method described herein may be implemented by one or more special-purpose computers configured with a processor and memory programmed to execute one or more functions and a processor configured with one or more hardware logic circuits. Furthermore, the computer program may be stored in a computer-readable non-transitory tangible storage medium as instructions executed by the computer. [Explanation of symbols]

[0068] 10...impedance measuring device, 11...current limiting resistor, 12...FET, 13...shunt resistor, 20...monitoring IC, 41...battery module, 42...battery cell

Claims

1. An impedance measuring device (10) for measuring the impedance of a secondary battery (41, 42) based on a measured value of an AC current flowing from the secondary battery and a measured value of a voltage fluctuation between terminals of the secondary battery in response to the AC current, The impedance measuring device for a secondary battery shortens the measurement time for measuring the AC current and the voltage fluctuations as the magnitude of a correlation parameter correlated with the magnitude of the impedance changes in the direction in which the impedance increases.

2. the correlation parameter is the impedance of the secondary battery; 2. The impedance measuring device for a secondary battery according to claim 1, wherein the measurement time is shortened as the impedance increases.

3. The secondary battery has a characteristic that the impedance increases as the temperature decreases, the correlation parameter is the temperature of the secondary battery; 2. The impedance measuring device for a secondary battery according to claim 1, wherein the lower the temperature, the shorter the measurement time.

4. the correlation parameter is the impedance of the secondary battery; measuring the impedance under a first condition in which the measurement time is a first time; setting a second time period longer than the first time period based on the impedance measured under the first condition, and measuring the impedance under the second condition in which the measurement time period is the second time period to determine the impedance; 2. The impedance measuring device for a secondary battery according to claim 1, wherein the second time period is set to be shorter as the impedance measured under the first condition is larger.

5. 5. The impedance measuring device for a secondary battery according to claim 4, wherein the relationship n=a / Z^2 is satisfied, where n is the second time period, Z is the impedance measured under the first condition, and a is a predetermined coefficient.

6. An impedance measurement method for measuring impedance of a secondary battery (41, 42) based on a measurement value of an AC current flowing from the secondary battery and a measurement value of a voltage fluctuation between terminals of the secondary battery in response to the AC current, comprising: The method for measuring impedance of a secondary battery further comprises shortening the measurement time for measuring the AC current and the voltage fluctuations as the magnitude of a correlation parameter correlated with the magnitude of the impedance changes in a direction in which the impedance increases.

7. An impedance measurement program that causes a computer (20) to execute a process of measuring the impedance of a secondary battery (41, 42) based on a measurement value of an AC current flowing from the secondary battery (41, 42) and a measurement value of a voltage fluctuation between terminals of the secondary battery in response to the AC current, A secondary battery impedance measurement program that causes the computer to execute a process of shortening the measurement time for measuring the AC current and the voltage fluctuations as the magnitude of a correlation parameter correlated with the magnitude of the impedance changes in the direction in which the impedance increases.

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