Battery management system and battery management method

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

[0001] The present invention relates to a battery management system and a battery management method for managing an on-board battery.

[0002] Batteries (hereinafter referred to as "vehicle batteries") installed in mobile vehicles such as electric vehicles (BEVs) and hybrid electric vehicles (HEVs) tend to deteriorate over time depending on their usage conditions. One known method for inspecting 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 Frequency Response Analyzer (FRA) method.

[0003] 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 currents or AC voltages) 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.

[0004] However, the FRA method, which employs the above-described mechanism, requires a considerable amount of time to complete the measurement of AC impedance, making it difficult to measure AC impedance using the FRA method when a mobile vehicle is traveling, where the battery cannot maintain a steady state for long periods due to the effects of continuous or sporadic charging and discharging.

[0005] Furthermore, when measuring AC impedance using the FRA method, it is necessary to apply or superimpose an AC signal that is not actually required to the battery. This raises concerns that unnecessary charge and discharge loads generated in the battery may result in a decrease in battery capacity or accelerate battery degradation due to heat generation.

[0006] Regarding AC impedance measurement methods other than the FRA method, paragraph 0034 of Patent Document 1 states that "the impedance calculation unit (measurement means) 140 samples the voltage (FC voltage) Vf of the fuel cell 40 detected by the voltage sensor 141 and the current (FC current) If of the fuel cell 40 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.

[0007] JP 2007-12414 A

[0008] 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 (e.g., 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.

[0009] Therefore, a single measurement alone cannot provide the FC voltage data and FC current data required for AC impedance calculation by Fourier transform processing, and it was 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 was the problem that the time required to measure AC impedance was long, just like the above-mentioned FRA method.

[0010] Therefore, the present invention aims to provide a battery management system and a 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.

[0011] In order to solve the above-mentioned problems, the battery management system of the present invention is a battery management system that manages an on-board battery of a mobile body, and includes an on-board battery having a plurality of built-in 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 on-board battery and transmits the current data, and a battery management device that manages the on-board 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 on-board 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 on-board battery.

[0012] In this way, the first calculation mode does not require a signal for impedance measurement, and therefore does not require time for impedance measurement. Furthermore, if the impedance of a predetermined frequency cannot be measured in the first calculation mode, it is sufficient to measure the impedance only at that predetermined frequency in the second impedance calculation mode, which significantly reduces the measurement time and also reduces the charge / discharge load on the battery for impedance measurement.

[0013] 1. An example of the configuration of a battery management system according to a first embodiment. A configuration diagram of a battery monitoring unit. An example of AC impedance of a lithium ion battery before degradation. An example of AC impedance of a lithium ion battery after degradation. An example of a voltage waveform and a current waveform of an on-board battery when a mobile object is traveling. An example of AC impedance measured in the first calculation mode (FFT method). Another example of AC impedance measured in the first calculation mode (FFT method). A flowchart of AC impedance calculation processing according to the first embodiment. An example of AC impedance measured using a combination of the first calculation mode (FFT method) and the second calculation mode (FRA method). Another example of a configuration diagram of a battery management system according to the first embodiment. A flowchart of AC impedance calculation processing according to a second embodiment. A flowchart of AC impedance calculation processing according to a third embodiment.

[0014] An embodiment of a battery management system 100 of the present invention will be described below with reference to the drawings. The battery management system 100 of the present invention is a system mounted on a mobile object such as an electric vehicle (BEV), a plug-in hybrid electric vehicle (PHEV), a hybrid electric vehicle (HEV), or a railroad car, and is a system for monitoring the state of charge (SOC) of an on-board battery 1 and managing the on-board battery 1 so that the SOC does not become too high (overcharge) or too low (overdischarge).

[0015] First, a battery management system 100 according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 10. FIG.

[0016] 1 shows an example of the configuration of a battery management system 100 according to this embodiment. As shown in the figure, the battery management system 100 includes an on-board battery 1, multiple data transmission devices 2 (2a to 2n), and a battery management unit 3. Each of these will be described in detail below.

[0017] <Vehicle 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. Note that the single battery cells C are, for example, lithium-ion batteries, but may also be other types of secondary battery cells as long as they are devices that can store and discharge electric charge.

[0018] <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 .

[0019] The cell state measurement unit 21 individually measures the state (voltage, temperature, etc.) of each single battery cell C in the module. In addition, the wireless communication unit 22 and the 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.

[0020] Although FIG. 1 illustrates a configuration in which wireless communication is used to transmit and receive voltage information and temperature information of the single battery cells C, a configuration in which wired communication is used instead of wireless communication may also be used.

[0021] <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 .

[0022] The wireless communication unit 32 and the antenna 33 wirelessly receive the state data of each cell measured by the cell state measurement unit 21 from the data transmission device 2 .

[0023] 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 the battery modules 1a to 1n as necessary.

[0024] Here, the monitoring of the single battery cell C performed by the battery monitoring unit 31 specifically means 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.

[0025] 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 of the built-in timers of the data transmission device 2 and the battery management device 3 are synchronized before measuring the AC impedance.

[0026] 2 is a diagram showing the impedance calculation configuration within the battery monitoring unit 31. As shown here, the battery monitoring unit 31 processes voltage time series data and current time series data for each battery cell in a first calculation mode M1 (FFT) or a second calculation mode M2 ​​(FRA) to output the AC impedance for each battery cell. When using the first calculation mode M1 (FFT), the switches 31a and 31b are simultaneously switched to the first calculation mode M1 (FFT) side, and when using the second calculation mode M2 ​​(FRA), the switches 31a and 31b are simultaneously switched to the second calculation mode M2 ​​(FRA) side.

[0027] Figure 3 shows the AC impedance of a typical lithium-ion battery. This diagram plots the impedance at each frequency on a complex plane, and is called a Nyquist plot or Cole-Cole plot. In this diagram, the horizontal axis represents the real component Z of the complex impedance. Ｒｅ The vertical axis represents the imaginary component of the complex impedance -Z Ｉｍ This shows:

[0028] The impedance of a lithium-ion battery is determined by the DC resistance R ＤＣ and reaction resistance R ＣＴ and the diffusion resistance R ＤＩ It can be roughly divided into three components: DC resistance R ＤＣ The reaction resistance R includes the conduction resistance of lithium ions in the electrolyte and the electrical resistance at the electrodes (positive and negative electrodes). ＣＴ includes the charge transfer resistance at the electrode / electrolyte interface (resistance when lithium ions move in and out of the active material) and the film resistance. ＤＩ includes the resistance associated with the diffusion of lithium into the active material.

[0029] 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 conduction 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.

[0030] As shown by the solid line in FIG. 4, when the lithium ion battery deteriorates, the DC resistance R ＤＣ and reaction resistance R ＣＴ and the diffusion resistance R ＤＩ Since the resistance of one of the resistances increases or multiple resistances increase, the battery monitoring unit 31 can grasp the degree of deterioration of the vehicle battery 1 and the cause of the deterioration by analyzing the Nyquist plot.

[0031] Here, when the vehicle is traveling, the charging and discharging of the vehicle battery 1 enters an unsteady state in which signals of various frequencies are included. Therefore, the battery management device 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 FIG. 5 , and executes FFT processing in the first calculation mode M1 in the battery monitoring unit 31, thereby making it possible to determine the impedances of multiple frequencies and create a Nyquist plot.

[0032] Figure 6 shows an example of a Nyquist plot of impedance measurement results based on current and voltage waveforms measured in a certain driving pattern. In this figure, the x points indicate plotted impedance measurement results. In this example, measurement results are obtained from high to low frequencies, and the DC resistance R of the monitored single battery cell C is ＤＣ , reaction resistance R ＣＴ , diffusion resistance R ＤＩ Therefore, based on this Nyquist plot, it is possible to easily determine whether the vehicle battery 1 has deteriorated, and if so, what the deterioration state is.

[0033] Next, Fig. 7 shows another example of a Nyquist plot of the impedance measurement results based on the current waveform and voltage waveform measured in a different driving pattern. In this example, the impedance cannot be measured on the low frequency side, so the reaction resistance R of the monitored single battery cell C is ＣＴ and diffusion resistance R ＤＩ As a result, it is not possible to confirm the components of the single battery cell C, and it is not possible to determine the deterioration of the single battery cell C based on these components. As in this example, depending on the driving pattern, it may not be possible to measure the impedance from high frequency to low frequency from the current and voltage waveforms of the single battery cell C.

[0034] 7, when it is not possible to measure the impedance of the single battery cell C from high frequency to low frequency while the vehicle is traveling, 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 the vehicle is not traveling, (2) when the vehicle battery 1 is being continuously charged or discharged at a constant value, or (3) when the vehicle battery is being charged or discharged at a constant frequency.

[0035] <<Impedance Calculation Processing>> FIG. 8 shows a flowchart of the impedance calculation processing in this embodiment.

[0036] First, in step S1, the battery monitoring unit 31 acquires the voltage waveform and current waveform of the vehicle battery 1 while the vehicle is running, and calculates the battery impedance in the first calculation mode M1 (FFT method).

[0037] 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, the DC resistance R ＤＣ , reaction resistance R ＣＴ , diffusion resistance R ＤＩ The frequency range is from a high frequency of about 1 kHz to a low frequency of about 1 Hz, including the frequencies corresponding to each of the above. If the impedance can be calculated at the predetermined frequency, the impedance measurement is terminated. On the other hand, if the impedance cannot be calculated at the predetermined frequency, the process proceeds to step S3.

[0038] 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.

[0039] The second calculation mode M2 ​​(FRA method) is a mode in which an AC current or AC voltage of a 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, a low frequency that could not be measured while driving is superimposed on the charging current or the charging current is turned on and off to obtain the current waveform and voltage waveform of the single battery cell C at that time, and the battery monitoring unit 31 performs processing in the second calculation mode M2 ​​(FRA method) to calculate the low frequency impedance.

[0040] 9 shows the results of measuring the impedance at frequencies f1, f2, and f3 in the second calculation mode M2 ​​(FRA method). In this way, by combining the impedance (x points) obtained in the first calculation mode M1 (FFT method) and the impedance (△ points) obtained in the second calculation mode M2 ​​(FRA method), it is possible to measure the impedance characteristics of the single battery cell C from high frequencies to low frequencies.

[0041] 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. When equalizing the SOCs of the single battery cells C (during cell balancing), the cell state measurement unit 21 of each data transmission device 2 may superimpose the measurement frequency current on the balancing current, or may turn the balancing current on and off at the measurement frequency.

[0042] <Effects of this Example> As described above, the battery management system of this example is provided with a first calculation mode M1 (FFT method) for measuring AC impedance without applying or superimposing an AC signal for impedance measurement, and a second calculation mode M2 ​​(FRA method) for measuring AC impedance by applying or superimposing an AC signal for impedance measurement.

[0043] As a result, in situations where AC impedance can be measured using only the first calculation mode M1 (FFT method), the measurement of AC impedance can be completed in a short time, and the generation of a charge / discharge load due to the AC signal 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 in the second calculation mode M2 ​​(FRA method).

[0044] Next, a battery management system 100 according to a second embodiment will be described with reference to Fig. 11. Note that, in the following, overlapping descriptions of points common to the first embodiment will be omitted.

[0045] As the vehicle battery 1 deteriorates, its 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 its battery capacity is 80% of its initial capacity.

[0046] 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 is expressed as a direct current resistance R ＤＣ , reaction resistance R ＣＴ , diffusion resistance R ＤＩ 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.

[0047] For example, DC resistance R ＤＣ and diffusion resistance R ＤＩ If the resistance rises, it can be judged that the electrolyte or electrodes have deteriorated over time. ＣＴ The increase in resistance is due to 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 solid electrolyte, so it is possible to suppress the increase in resistance by tightening the electrode and solid electrolyte.

[0048] Therefore, the battery management system 100 of this embodiment calculates the impedance according to the flowchart of FIG.

[0049] First, in step S21, the battery monitoring unit 31 determines whether the SOH of the vehicle battery 1 is equal to or lower than a predetermined value (e.g., 80%). If the requirement is met, the process proceeds to step S22, and if the requirement is not met, the process in FIG. 11 ends.

[0050] Next, in step S22, the battery monitoring unit 31 measures impedance in a predetermined 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 predetermined frequency range may be a wide range of frequencies from low frequencies of 1 Hz or less to high frequencies of several kHz, or it may be a specific number of frequencies.

[0051] The predetermined SOH value used as the reference in step S21 may be variable. For example, by setting SOH=80% as the initial value and measuring the impedance based on that reference, and then setting SOH=75% as the next predetermined value, it becomes possible to change the starting condition for impedance measurement in the second calculation mode M2 ​​(FRA method) according to the progress of the SOH.

[0052] Next, a battery management system 100 according to a third embodiment will be described with reference to Fig. 12. Note that, in the following, overlapping descriptions of points common to the above-described embodiments will be omitted.

[0053] To efficiently use the automotive battery 1 in which the 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 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 that has 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 to an SOC of 85% or higher.

[0054] Therefore, the battery management system 100 of this embodiment executes the following balancing process to equalize the SOC of each of the single battery cells C. The balancing process is a process for equalizing the SOC of each of the single battery cells by distributing the capacity of a single battery cell C with a high SOC to other single battery cells C or by discharging the single battery cell C with a high SOC.

[0055] Here, a battery cell C with a higher or lower SOC than the other battery cells C may be deteriorating, for example, with increased internal resistance or reduced capacity. Therefore, in this embodiment, during the balancing process for a battery cell 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 the battery cell C with a high SOC, i.e., its state of deterioration.

[0056] Therefore, the battery management system 100 of this embodiment performs the balancing process according to the flowchart of FIG.

[0057] First, in step S31, the battery monitoring unit 31 checks the SOC of each single battery cell of the in-vehicle battery 1 after charging or discharging, and determines whether balancing processing is necessary, 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, and if the requirements are not met, the flowchart of FIG. 12 ends.

[0058] 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.

[0059] 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 to be subjected to balancing processing in the second calculation mode M2 ​​(FRA method), measures the impedance, and determines the deterioration state of the single battery cell C to be subjected to balancing processing.

[0060] When the SOCs of the individual cells become equal, in step S34, the battery monitoring unit 31 ends the balancing process.

[0061] As described above, according to this embodiment, it is possible to quickly determine the deterioration of a single battery cell C having an abnormality in SOC.

[0062] Next, a battery management system 100 according to a fourth embodiment will be described. Note that, in the following, overlapping descriptions of points common to the above-described embodiments will be omitted.

[0063] For example, when the charging / discharging current and charging voltage of the vehicle battery 1, which contains various frequencies, are calculated using the first calculation mode M1 (FFT method), such as when a BEV is running, errors may occur in the impedance calculation results if sufficient current amplitude and voltage amplitude are not obtained.

[0064] Therefore, in this embodiment, in such cases, the measurement results in the second calculation mode M2 ​​(FRA method) are used to correct the impedance measurement results in the first calculation mode M1 (FFT method). The timing for correction is 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 previously measured value. Correction may also be performed periodically.

[0065] As a correction method, for example, when impedance measurement results are obtained at frequencies of 10 Hz, 50 Hz, 120 Hz, 350 Hz, 630 Hz, and 1 kHz in 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 in the second calculation mode M2 ​​(FRA method), and if the result obtained is an impedance that 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.

[0066] Although a number of other correction methods are possible in addition to this example, the present invention does not define any particular correction method. Furthermore, the impedance at a frequency at which 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 impedance measurement results in the first calculation mode M1 (FFT method) and the second calculation mode M2 ​​(FRA method) may be averaged for correction.

[0067] 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

1. A battery management system for managing an on-board battery of a mobile body, comprising: an on-board battery having a plurality of built-in 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 on-board battery and transmits the current data; and a battery management device that manages the on-board battery based on the voltage data and the current data, wherein 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 on-board 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 on-board battery.

2. The battery management system according to claim 1, wherein in the first calculation mode, AC impedance is calculated using the FFT method, and in the second calculation mode, AC impedance is calculated using the FRA method.

3. The battery management system of claim 1, wherein the first calculation mode is executed when the vehicle battery is in a non-steady state in which the voltage data and the current data include various frequencies, and the second calculation mode is executed when the vehicle battery is in a steady state.

4. The battery management system of claim 1, wherein the second calculation mode is executed when at least one of the following occurs as a result of execution of the first calculation mode: when AC impedance cannot be measured at a predetermined frequency; when the capacity degradation of the vehicle battery falls below a predetermined value; or when balancing of the charging rates of the single battery cells becomes necessary.

5. The battery management system according to claim 1, wherein the AC impedance calculated in the second calculation mode is used to correct the AC impedance calculated in the first calculation mode.

6. A battery management system as described in claim 1, 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.

7. A battery management method for managing an on-board battery having a plurality of built-in single battery cells, comprising: a voltage data transmission step for measuring the voltage of each single battery cell and transmitting voltage data; a current data transmission step for measuring the current charged to and discharged from the on-board battery and transmitting current data; and a battery management step for managing the on-board battery based on the voltage data and the current data, wherein the battery management step is capable of executing: a first calculation mode for calculating the AC impedance of the single battery cells based on the voltage data and the current data measured without applying or superimposing a predetermined AC signal to the on-board battery; and a second calculation mode for calculating the AC impedance of the single battery cells based on the voltage data and the current data measured after applying or superimposing a predetermined AC signal to the on-board battery.

Images