WO2025211145A1 - Battery management system and battery management method - Google Patents

Abstract

Provided is a battery management system capable of reducing the time required to measure the AC impedance of a vehicle-mounted battery, and capable of reducing the charge/discharge load on the vehicle-mounted battery during AC impedance measurement. This battery management method comprises a voltage data transmission step for measuring the voltage of the vehicle-mounted battery and transmitting voltage data, a current data transmission step for measuring the current charged or discharged to or from the vehicle-mounted battery and transmitting current data, and a battery management step for managing the vehicle-mounted battery on the basis of the voltage data and the current data, wherein, in the battery management step, it is possible to execute a first calculation mode for calculating the AC impedance of a single battery cell on the basis of the voltage data and the current data measured without the application of a specific AC signal to the vehicle-mounted battery, and a second calculation mode for calculating the AC impedance of the single battery cell on the basis of the voltage data and the current data measured with the application of the specific AC signal to the vehicle-mounted battery.

Description

Battery management system and battery management method

The present invention relates to a battery management system and a battery management method for managing an on-board battery.

Batteries (hereinafter referred to as "vehicle batteries") installed in mobile vehicles such as electric vehicles (BEVs) and hybrid electric vehicles (HEVs) have the tendency to deteriorate over time depending on their usage. One known method for testing the degree and cause of battery deterioration is to monitor changes in the battery's AC impedance. Another known method for measuring the battery's AC impedance is the FRA (Frequency Response Analyzer) method.

The FRA method is a highly accurate measurement method that is also used in AC impedance measuring instruments. It involves sequentially applying or sequentially superimposing multiple AC signals (AC current or AC voltage) over a wide frequency range, from below 1 Hz to several kHz, to a battery in a steady state, and then calculating the AC impedance based on the current time series data and voltage time series data measured at that time.

However, the FRA method, which employs the above mechanism, requires a considerable amount of time to complete AC impedance measurement, making it difficult to use the FRA method to measure AC impedance when a mobile vehicle is in motion, where the battery's steady state cannot be maintained for long periods due to the effects of continuous or sporadic charging and discharging.

Furthermore, when measuring AC impedance using the FRA method, it is necessary to apply or superimpose an AC signal that is not actually necessary to the battery, which raises concerns that the unnecessary charge/discharge load generated by the battery could reduce battery capacity or accelerate battery degradation due to heat generation.

Here, with regard to AC impedance measurement methods other than the FRA method, paragraph 0034 of Patent Document 1 states, "The impedance calculation unit (measurement means) 140 samples the fuel cell 40 voltage (FC voltage) Vf detected by the voltage sensor 141 and the fuel cell 40 current (FC current) If detected by the current sensor 142 at a predetermined sampling rate, and performs Fourier transform processing (FFT calculation processing or DFT calculation processing) or the like. The impedance calculation unit 140 determines the impedance of the fuel cell 40 by, for example, dividing the FC voltage signal after Fourier transform processing by the FC current signal after Fourier transform processing," and discloses a method of measuring AC impedance using Fourier transform processing.

JP 2007-12414 A

However, as explained in paragraph 0032 of Patent Document 1, "Figure 4 is a diagram illustrating the signal waveform of the impedance measurement signal generated by the superimposed signal generation unit 125. As shown in Figure 4, the superimposed signal generation unit 125 generates an impedance measurement signal (such as a sine wave of a specific frequency) whose amplitude value changes gradually (gradually)," the impedance measurement signal used in Patent Document 1 is a fixed frequency signal.

As a result, a single measurement alone cannot provide the FC voltage data and FC current data required to calculate AC impedance using Fourier transform processing, and it is necessary to collect data multiple times using impedance measurement signals of different frequencies to obtain sufficient FC voltage data and FC current data. Therefore, when calculating AC impedance using the technology of Patent Document 1, there is the problem that, like the FRA method described above, it takes a long time to measure AC impedance.

The present invention therefore aims to provide a battery management system and battery management method that can shorten the time required to measure the AC impedance of an on-board battery and further reduce the charge/discharge load on the on-board battery during AC impedance measurement.

In order to solve the above-mentioned problems, the battery management system of the present invention is a battery management system that manages the onboard battery of a mobile body, and includes an onboard battery containing multiple single battery cells, a data transmission device that measures the voltage of each single battery cell and transmits the voltage data, a current sensor that measures the current charged and discharged to the onboard battery and transmits the current data, and a battery management device that manages the onboard battery based on the voltage data and the current data, and the battery management device is capable of executing a first calculation mode in which the AC impedance of the single battery cells is calculated based on the voltage data and the current data measured without applying or superimposing a predetermined AC signal to the onboard battery, and a second calculation mode in which the AC impedance of the single battery cells is calculated based on the voltage data and the current data measured after applying or superimposing a predetermined AC signal to the onboard battery.

In this way, the first calculation mode does not require a signal for impedance measurement, so no time is required for impedance measurement. Furthermore, if the impedance of a specified frequency cannot be measured in the first calculation mode, it is sufficient to measure the impedance at only that specified frequency in the second impedance calculation mode, which significantly reduces measurement time and also reduces the charge/discharge load on the battery for impedance measurement.

1 is an example of the configuration of a battery management system according to a first embodiment. FIG. 3 is a diagram illustrating the configuration of a battery monitoring unit. An example of the AC impedance of a lithium-ion battery before degradation. An example of the AC impedance of a degraded lithium-ion battery. An example of the voltage and current waveforms of an onboard battery when a vehicle is moving. 10 is an example of AC impedance measured in the first calculation mode (FFT method). 10 is another example of AC impedance measured in the first calculation mode (FFT method). 4 is a flowchart of an AC impedance calculation process according to the first embodiment. 10 is an example of AC impedance measured using both the first calculation mode (FFT method) and the second calculation mode (FRA method). FIG. 4 is another example of a configuration diagram of the battery management system according to the first embodiment. 10 is a flowchart of an AC impedance calculation process according to a second embodiment. 10 is a flowchart of an AC impedance calculation process according to a third embodiment.

The following describes an embodiment of the battery management system 100 of the present invention, using the drawings. The battery management system 100 of the present invention is a system mounted on mobile objects such as electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), hybrid electric vehicles (HEVs), and railroad cars, and is a system for monitoring the state of charge (SOC) of the on-board battery 1 and managing the on-board battery 1 to prevent the SOC from becoming too high (overcharging) or too low (over-discharging).

First, a battery management system 100 according to a first embodiment of the present invention will be described using Figures 1 to 10.

Figure 1 shows an example of the configuration of a battery management system 100 in this embodiment. As shown here, the battery management system 100 comprises an on-board battery 1, multiple data transmission devices 2 (2a-2n), and a battery management unit 3. Each of these will be explained in detail below.

<Automotive Battery 1>
First, the vehicle battery 1 to be managed will be described. In this embodiment, the vehicle battery 1 is a battery configured by connecting multiple battery modules 1a to 1n in series. Each battery module is a module configured by connecting multiple single battery cells C in series or series-parallel. Here, the single battery cells C are charge/discharge devices that are the smallest units of control, and have an operating voltage in the range of approximately 2.5 to 4.5 V. The single battery cells C are, for example, lithium-ion batteries, but other types of secondary battery cells may also be used as long as they are devices that can store and discharge electric charge.

<Data transmission device 2>
The data transmission device 2 (2a to 2n) is a slave device installed in each of the battery modules 1a to 1n, and includes a cell state measurement unit 21, a wireless communication unit 22, and an antenna .

The cell state measurement unit 21 individually measures the state (voltage, temperature, etc.) of each single battery cell C within the module. Furthermore, the wireless communication unit 22 and antenna 23 wirelessly transmit the state data (voltage data, temperature data, etc.) of each cell measured by the cell state measurement unit 21 to the battery management unit 3.

Note that while Figure 1 illustrates a configuration in which wireless communication is used to send and receive information such as voltage information and temperature information about the battery cells C, wired communication may also be used instead of wireless communication.

<Battery management device 3>
The battery management device 3 is a master device that communicates wirelessly with each data transmission device 2 , and includes a battery monitoring unit 31 , a wireless communication unit 32 , and an antenna 33 .

The wireless communication unit 32 and antenna 33 wirelessly receive the status data of each cell measured by the cell status measurement unit 21 from the data transmission device 2.

The battery monitoring unit 31 also monitors the single battery cells C based on the status data received by the wireless communication unit 32. Furthermore, the battery monitoring unit 31 monitors the current of the vehicle battery 1 based on the current data measured by the current sensor 4, and controls the charging and discharging of the single battery cells C and battery modules 1a-1n as necessary.

Here, the monitoring of the single battery cell C performed by the battery monitoring unit 31 specifically refers to monitoring the AC impedance of the single battery cell C. Therefore, the battery monitoring unit 31 calculates the AC impedance of the single battery cell C based on the voltage time series data of the single battery cell C acquired from the data transmission device 2 and the current time series data acquired from the current sensor 4.

In order to synchronize the time series voltage data acquired by the data transmission device 2 with the time series current data acquired by the battery management device 3, the times on the built-in timers of the data transmission device 2 and the battery management device 3 are synchronized before measuring the AC impedance.

Figure 2 is a diagram showing the impedance calculation configuration within the battery monitoring unit 31. As shown here, the battery monitoring unit 31 processes the voltage time series data and current time series data for each battery cell in the first calculation mode M1 (FFT) or the second calculation mode M2 (FRA) to output the AC impedance for each battery cell. When using the first calculation mode M1 (FFT), switches 31a and 31b are simultaneously switched to the first calculation mode M1 (FFT) side, and when using the second calculation mode M2 (FRA), switches 31a and 31b are simultaneously switched to the second calculation mode M2 (FRA) side.

Figure 3 shows the AC impedance of a typical lithium-ion battery. This figure, which plots impedance at each frequency on a complex plane, is called a Nyquist plot or Cole-Cole plot. In this figure, the horizontal axis represents the real component of the complex impedance, _ZRe , and the vertical axis represents the imaginary component of the complex impedance, _-ZIm .

The impedance of a lithium-ion battery can be roughly divided into three components based on the lithium ion transfer reaction process during charge and discharge: DC resistance R _DC , reaction resistance R _CT , and diffusion resistance R _DI . DC resistance R _DC includes the conduction resistance of lithium ions in the electrolyte and the electrical resistance at the electrodes (positive and negative electrodes). Reaction resistance R _CT includes the charge transfer resistance (resistance when lithium ions enter and exit the active material) at the electrode/electrolyte interface and the film resistance. Diffusion resistance R _DI includes the resistance associated with the diffusion of lithium into the active material.

Furthermore, the physical phenomena that govern impedance differ depending on the frequency band. For example, at high frequencies (up to 1 kHz), the main contributors to impedance are conductive resistance due to ion movement in the electrolyte, at low frequencies (<1 Hz), diffusion within the electrode, and at intermediate frequencies (1 Hz to several hundred Hz), charge transfer reactions of ions.

As shown by the solid line in FIG. 4, when the lithium-ion battery deteriorates, depending on the situation, one or more of the resistances of the DC resistance R _DC , the reaction resistance R _CT , and the diffusion resistance R _DI increases. Therefore, by analyzing the Nyquist plot, the battery monitoring unit 31 can grasp the degree of deterioration of the vehicle battery 1 and the cause of the deterioration.

When the vehicle is traveling, the charging and discharging of the vehicle battery 1 enters an unsteady state that includes signals of various frequencies. Therefore, the battery management unit 3 acquires the current waveform (current time series data) and voltage waveform (voltage time series data) of the single battery cell C during traveling, as shown in Figure 5, and performs FFT processing in the first calculation mode M1 in the battery monitoring unit 31, thereby determining the impedance of multiple frequencies and creating a Nyquist plot.

Figure 6 shows an example of a Nyquist plot of impedance measurement results based on current and voltage waveforms measured during a certain driving pattern. In this figure, the x's indicate the plotted impedance measurement results. In this example, measurement results are obtained from high to low frequencies, and all components of the DC resistance R _DC , reaction resistance R _CT , and diffusion resistance R _DI of the monitored single battery cell C can be confirmed. Therefore, based on this Nyquist plot, it is possible to easily determine whether the on-board battery 1 has deteriorated, and if so, what the deterioration state is.

Next, Figure 7 shows another example of a Nyquist plot of impedance measurement results based on current waveforms and voltage waveforms measured with a different driving pattern. In this example, because the impedance cannot be measured on the low-frequency side, the reaction resistance _RCT and diffusion resistance _RDI components of the monitored single battery cell C cannot be confirmed, and deterioration of the single battery cell C cannot be determined based on these components. As in this example, depending on the driving pattern, it may not be possible to measure the impedance from high to low frequencies from the current and voltage waveforms of the single battery cell C.

For this reason, in this embodiment, as in the example of Figure 7, if it is not possible to measure the impedance of the single battery cell C from high to low frequencies while the vehicle is moving, the impedance is measured in the second calculation mode M2 (FRA method) when the vehicle battery 1 is in a steady state. The steady state of the vehicle battery 1 refers to, for example, (1) when the vehicle battery 1 is not being charged or discharged, such as when not moving, (2) when it is being continuously charged or discharged at a constant value, or (3) when it is being charged or discharged at a constant frequency.

<<Impedance calculation processing>>
FIG. 8 shows a flowchart of the impedance calculation process in this embodiment.

First, in step S1, the battery monitoring unit 31 acquires the voltage waveform and current waveform of the onboard battery 1 while the vehicle is running, and calculates the battery impedance using the first calculation mode M1 (FFT method).

Next, in step S2, the battery monitoring unit 31 checks whether the impedance has been calculated within a predetermined frequency range. In this case, the predetermined frequency range is, for example, a range from a high frequency of about 1 kHz to a low frequency of about 1 Hz, including the frequencies corresponding to the DC resistance R _DC , the reaction resistance R _CT , and the diffusion resistance R _DI . If the impedance has been calculated within the predetermined frequency range, the impedance measurement is terminated. On the other hand, if the impedance has not been calculated within the predetermined frequency range, the process proceeds to step S3.

In step S3, the battery monitoring unit 31 applies an AC signal of a predetermined frequency to the vehicle battery 1 when the battery is steady, such as when not driving, and calculates the charging voltage and current waveforms of the vehicle battery 1 using the second calculation mode M2 (FRA method) to calculate the impedance of the vehicle battery 1 in the range not found in step S1.

The second calculation mode M2 (FRA method) is a mode in which an AC current or AC voltage of the frequency to be measured is applied to the vehicle battery 1, and the impedance is calculated based on the voltage waveform and current waveform of the vehicle battery 1 at that time. For example, by superimposing a low frequency that could not be measured while driving on the charging current or by turning the charging current on and off, the current waveform and voltage waveform of the single battery cell C at that time are obtained, and the battery monitoring unit 31 performs processing in the second calculation mode M2 (FRA method) to calculate the low-frequency impedance.

Figure 9 shows the results of measuring impedance at frequencies f1, f2, and f3 in second calculation mode M2 (FRA method). In this way, by combining the impedance (x points) obtained in first calculation mode M1 (FFT method) with the impedance (△ points) obtained in second calculation mode M2 (FRA method), it is possible to measure the impedance characteristics of single battery cell C from high to low frequencies.

When measuring impedance in the second calculation mode M2 (FRA method), the measurement frequency may be generated by, for example, a command from the battery monitoring unit 31 of the battery management unit 3 to the charging device, which may then turn the charging current on and off at the measurement frequency. Alternatively, the charging device may superimpose the measurement frequency current on the charging current. When the battery is not being charged or discharged, as shown in FIG. 10 , the battery monitoring unit 31 may generate the measurement frequency, input the signal to an FET or transistor 6, and discharge the battery at the measurement frequency via a load 5 such as a resistor.
Furthermore, when equalizing the SOC between the single battery cells C (during cell balancing), the cell state measurement unit 21 of each data transmission device 2 may superimpose a current of the measurement frequency on the balancing current, or may turn the balancing current on and off at the period of the measurement frequency.

<Effects of this embodiment>
As described above, the battery management system of this embodiment is provided with a first calculation mode M1 (FFT method) in which AC impedance is measured without applying or superimposing an AC signal for impedance measurement, and a second calculation mode M2 (FRA method) in which AC impedance is measured by applying or superimposing an AC signal for impedance measurement.

As a result, in situations where AC impedance can be measured using only the first calculation mode M1 (FFT method), AC impedance measurement can be completed in a short time, and the occurrence of charge/discharge loads due to the AC signal used for impedance measurement can be avoided. On the other hand, in situations where AC impedance cannot be measured using only the first calculation mode M1 (FFT method), accurate AC impedance can be measured by taking into account the measurement results from the second calculation mode M2 (FRA method).

Next, the battery management system 100 of Example 2 will be described using Figure 11. Note that, below, overlapping explanations of points common to Example 1 will be omitted.

As the vehicle battery 1 deteriorates, the battery capacity tends to decrease. Therefore, the battery management system 100 of this embodiment measures the battery capacity and then calculates the capacity deterioration (State of Health, SOH) expressed as a percentage of the initial capacity Ah. For example, if SOH = 80%, the vehicle battery 1 is in a deteriorated state where the battery capacity is 80% of its initial capacity.

Furthermore, as the vehicle battery 1 deteriorates, the internal resistance of the battery tends to increase along with a decrease in capacity. The internal resistance of the vehicle battery 1 can be roughly divided into three impedance components, DC resistance R _DC , reaction resistance R _CT , and diffusion resistance R _DI , as shown in Figure 2, but it is also possible to determine whether the deterioration is due to aging or abnormal deterioration depending on the degree to which each resistance has increased according to the SOH.

For example, if there is an increase in the DC resistance R _DC or the diffusion resistance R _DI , it can be determined that this is due to deterioration of the electrolyte or electrodes over time, but an increase in the reaction resistance R _CT indicates an increase in the resistance at the electrode/electrolyte interface, and in all-solid-state lithium-ion batteries in particular, this is an increase in the physical contact resistance between the electrode and the solid electrolyte, so it is possible to suppress the increase in resistance by tightening the electrodes and the solid electrolyte.

Therefore, the battery management system 100 of this embodiment calculates impedance according to the flowchart in Figure 11.

First, in step S21, the battery monitoring unit 31 determines whether the SOH of the vehicle battery 1 is below a predetermined value (e.g., 80%). If the requirement is met, the process proceeds to step S22; if the requirement is not met, the process in Figure 11 ends.

Next, in step S22, the battery monitoring unit 31 measures impedance in a specified frequency range in the second calculation mode M2 (FRA method) to confirm an increase in the battery's internal resistance. The reason for using the second calculation mode M2 (FRA method) for the impedance measurement here is that it is important to measure the internal resistance of the vehicle battery 1 in detail to identify the cause of deterioration and determine whether countermeasures are possible. The specified frequency range may be a wide range from low frequencies of 1 Hz or less to high frequencies of several kHz, or it may be a specific number of frequencies.

The predetermined SOH value used as the reference in step S21 may be variable. For example, by setting SOH = 80% as the initial predetermined value, measuring impedance based on that reference, and then setting SOH = 75% as the next predetermined value, it becomes possible to change the starting conditions for impedance measurement in the second calculation mode M2 (FRA method) according to the progress of the SOH.

Next, a battery management system 100 according to a third embodiment will be described using Figure 12. Note that, below, overlapping explanations of points common to the above embodiments will be omitted.

To efficiently use an automotive battery 1 in which single battery cells C are connected in series as shown in Figure 1, it is necessary to equalize the SOC of each single battery cell. For example, if the upper charge limit SOC of the single battery cells C is set to 90%, and there is a single battery cell C among the series-connected single battery cells C with an SOC 5% higher than the others, the battery management system 100 will stop charging all cells when that single battery cell C's SOC reaches 90%, and the other single battery cells C will not be able to be charged above an SOC of 85%.

For this reason, the battery management system 100 of this embodiment equalizes the SOC of each battery cell C by performing the following balancing process. Note that the balancing process is a process that equalizes the SOC of each battery cell by distributing capacity from a battery cell C with a high SOC to other battery cells C, or by discharging the battery cell C with a high SOC.

Here, battery cells C with a higher or lower SOC than the other battery cells C may be deteriorating, such as having increased internal resistance or reduced capacity. Therefore, in this embodiment, during the balancing process for battery cells C with a high SOC, a predetermined frequency is applied to the distribution current or discharge current (balancing current) in the second calculation mode M2 (FRA method) to measure the impedance. This makes it possible to check the increase in internal resistance of battery cells C with a high SOC, i.e., their state of degradation.

Therefore, the battery management system 100 of this embodiment performs balancing processing in accordance with the flowchart in Figure 12.

First, in step S31, the battery monitoring unit 31 checks the SOC of each single battery cell of the vehicle battery 1 after charging or discharging, and determines whether balancing processing is required, in other words, whether there is a single battery cell C whose SOC is significantly higher or lower than the other cells. If the requirements are met, the process proceeds to step S32; if the requirements are not met, the flowchart in Figure 12 ends.

Next, in step S32, the battery monitoring unit 31 performs the balancing process described above on the single battery cell C whose SOC is significantly higher or lower than the other cells.

In step S33, the battery monitoring unit 31 applies a predetermined frequency to the distribution current or discharge current (balancing current) of the single battery cell C that is the target of balancing processing in the second calculation mode M2 (FRA method), measures the impedance, and determines the deterioration state of the single battery cell C that is the target of balancing processing.

When the SOCs of the individual battery cells become equal, in step S34, the battery monitoring unit 31 ends the balancing process.

As described above, according to this embodiment, it is possible to quickly determine the deterioration of a single battery cell C with an abnormal SOC.

Next, we will explain the battery management system 100 of Example 4. Note that, below, we will omit redundant explanations of points common to the above examples.

For example, when calculating the charge/discharge current and charge voltage of the vehicle battery 1, which contains a variety of frequencies, using the first calculation mode M1 (FFT method), errors may occur in the impedance calculation results if sufficient current amplitude or voltage amplitude is not obtained, such as when a BEV is running.

In this embodiment, in such cases, the measurement results from the second calculation mode M2 (FRA method) are used to correct the impedance measurement results from the first calculation mode M1 (FFT method). Correction can be performed when the current amplitude or voltage amplitude is small, when the S/N ratio is small, or when the impedance value is significantly different from the previous measurement. Correction can also be performed periodically.

As a correction method, for example, if impedance measurement results are obtained for frequencies of 10 Hz, 50 Hz, 120 Hz, 350 Hz, 630 Hz, and 1 kHz using the first calculation mode M1 (FFT method), the impedance at several of the obtained frequencies (for example, 10 Hz, 120 Hz, and 1 kHz) is measured using the second calculation mode M2 (FRA method), and if the impedance obtained is on average +10% higher than the result of the first calculation mode M1 (FFT method), the impedance at the other frequencies is also corrected to be +10% higher.

There are several other possible correction methods in addition to this example, but no particular correction method is defined in the present invention. Furthermore, the impedance at a frequency where the impedance value is significantly different from the previous value measured in the first calculation mode M1 (FFT method) may be measured in the second calculation mode M2 (FRA method), and the impedance at that frequency may be replaced with the result measured in the second calculation mode M2 (FRA method), or the correction may be performed by averaging the impedance measurement results in the first calculation mode M1 (FFT method) and the second calculation mode M2 (FRA method).

REFERENCE SIGNS LIST 100 Battery management system 1 On-vehicle battery 1a to 1n Battery module C Single battery cell 2 Data transmission device 21 Cell state measurement unit 22 Wireless communication unit 23 Antenna 3 Battery management device 31 Battery monitoring unit 31a, 31b Switch 32 Wireless communication unit 33 Antenna 4 Current sensor 5 Load 6 FET or transistor

Claims (7)

A battery management system that manages an on-board battery of a mobile body,
an on-board battery incorporating a plurality of single battery cells;
a data transmission device that measures the voltage of each battery cell and transmits voltage data;
a current sensor that measures a current charged and discharged from the vehicle battery and transmits the current data;
a battery management device that manages the on-board battery based on the voltage data and the current data,
The battery management device
a first calculation mode in which an AC impedance of the single battery cell is calculated based on the voltage data and the current data measured without applying or superimposing a predetermined AC signal to the vehicle-mounted battery;
a second calculation mode in which an AC impedance of the single battery cell is calculated based on the voltage data and the current data measured by applying or superimposing a predetermined AC signal to the vehicle-mounted battery;
A battery management system capable of executing the above. In the first calculation mode, AC impedance is calculated by the FFT method,
2. The battery management system according to claim 1, wherein in the second calculation mode, the AC impedance is calculated by the FRA method. Executing the first operation mode when the vehicle battery is in an unsteady state in which the voltage data and the current data include various frequencies;
The battery management system according to claim 1 , wherein the second operation mode is executed when the vehicle battery is in a steady state. The second operation mode is a result of the execution of the first operation mode.
If AC impedance cannot be measured at the specified frequency,
When the capacity deterioration of the vehicle battery falls below a predetermined value,
Or, when balancing of the charge rates of the single battery cells becomes necessary,
The battery management system according to claim 1, wherein the battery management system is executed when at least one of the following conditions is met. The battery management system described in claim 1, characterized in that the AC impedance calculated in the first calculation mode is corrected using the AC impedance calculated in the second calculation mode. 2. The battery management system according to claim 1,
A battery management system characterized in that, if there is a time difference between the times at which the voltage data and the current data are acquired, the AC impedance of the single battery cell is calculated based on the voltage data and the current data with the time difference corrected. A battery management method for managing an in-vehicle battery having a plurality of built-in single battery cells, comprising:
a voltage data transmission step of measuring the voltage of each single battery cell and transmitting the voltage data;
a current data transmission step of measuring a current charged/discharged to the vehicle battery and transmitting the current data;
a battery management step of managing the on-board battery based on the voltage data and the current data,
In the battery management step,
a first calculation mode in which an AC impedance of the single battery cell is calculated based on the voltage data and the current data measured without applying or superimposing a predetermined AC signal to the vehicle-mounted battery;
a second calculation mode in which an AC impedance of the single battery cell is calculated based on the voltage data and the current data measured by applying or superimposing a predetermined AC signal to the vehicle-mounted battery;
A battery management method characterized by being capable of executing the above.