JP2021048018A - Battery status estimation method and battery system - Google Patents

Abstract

To provide a battery status estimation method for easily estimating a state of charge (SOC) distribution of a plurality of first batteries 10 included in a battery pack 20.SOLUTION: In a battery status estimation method, the reactance of a battery pack 20 in which a plurality of first batteries 10 are connected in series is measured, a state of charge (SOC) distribution of the plurality of first batteries 10 is estimated based on the reactance of the battery pack 20 and the data of the second battery having the same specification as the first batteries 10, the reactance of the second battery at a plurality of SOCs are measured, an SOC change point which is an SOC at which the reactance of the second battery begins to increase, and an impedance bottom value before the reactance of the second battery begins to increase are calculated, and the data of the second battery including the impedance bottom value is stored.SELECTED DRAWING: Figure 2

Description

In the embodiment of the present invention, a battery state estimation method for estimating the distribution of the charging states of a plurality of batteries contained in the assembled battery and the distribution of the charging states of the plurality of batteries contained in the assembled battery are estimated. Regarding the battery system.

Secondary batteries are used in mobile devices, power tools, electric vehicles, and the like. Among secondary batteries, lithium ion batteries have high voltage, high output, and high energy density because they have a high ionization tendency of lithium. Lithium-ion batteries are also expected to be applied to large power sources such as stationary power sources and emergency power sources. The battery is used as an assembled battery in which a plurality of batteries are connected in series so as to have a voltage specified by the load.

An AC impedance measurement method is known as a method for measuring the characteristics of a secondary battery. Japanese Unexamined Patent Publication No. 2009-97878 discloses a measuring method for analyzing a call-call plot of a battery obtained by an AC impedance method using an equivalent circuit model.

According to JP-A-2018-151194, in the region where the impedance does not change significantly with respect to the charge state (SOC: System of Charge) of the assembled battery, the SOC is estimated from the voltage and the impedance changes significantly with respect to the SOC. Discloses a device that estimates SOC using impedance.

A plurality of batteries (cells) included in an assembled battery are manufactured based on the same specifications and used under the same conditions. However, if batteries having different SOCs are included due to manufacturing variations and slight differences in the usage environment, the performance of the assembled battery may deteriorate at an accelerating rate.

It is relatively easy to evaluate the SOC of a single battery (cell). However, in order to evaluate the SOC of each battery included in the assembled battery, it is necessary to connect an electric wire for evaluation to each battery. In addition, depending on the specifications of the assembled batteries, the SOC of each battery could not be evaluated after assembly because the structure could not connect an electric wire to each battery.

Therefore, development of a battery state estimation method for easily estimating the SOC distribution of a plurality of batteries contained in the assembled battery and a battery system capable of easily estimating the SOC distribution of a plurality of batteries contained in the assembled battery. Was desired.

JP-A-2009-97878 JP-A-2018-151194

In the embodiment of the present invention, a battery state estimation method for easily estimating the SOC distribution of a plurality of batteries contained in an assembled battery and an SOC distribution of a plurality of batteries contained in the assembled battery can be easily estimated. The purpose is to provide a battery system.

In the battery state estimation method of the embodiment of the present invention, a step of measuring the impedance characteristic at a predetermined frequency of an assembled battery in which a plurality of first batteries are connected in series, the impedance characteristic of the assembled battery, and the prior. A step of estimating the distribution of the charged state of the plurality of first batteries based on the stored data of the second battery having the same specifications as that of the first battery is provided. The data of the second battery shows that the impedance characteristics of the second battery in a plurality of charged states are increased at the first step in which the impedance characteristics of the second battery are measured at a predetermined frequency, and the impedance characteristics of the second battery are increased. A second step of calculating the SOC change point in the charging state and the impedance bottom value before starting to increase, and a third step of storing the data of the second battery including the impedance bottom value. And, it is acquired and stored in.

In the battery system of another embodiment, the impedance characteristic at a predetermined frequency of the assembled battery in which a plurality of first batteries are connected in series and the second battery having the same specifications as the first battery changes the charging state. A storage means for storing the data of the second battery including the impedance bottom value which is the impedance characteristic before it starts to change accordingly, and a measuring means for measuring the impedance characteristic at the predetermined frequency of the assembled battery. And the distribution of the charged state of the plurality of first batteries included in the assembled battery is estimated from the impedance characteristic of the assembled battery and the data of the second battery stored in the memory. It is provided with a calculation means.

According to the embodiment of the present invention, a battery state estimation method for easily estimating the SOC distribution of a plurality of batteries contained in an assembled battery, and a simple method for estimating the SOC distribution of a plurality of batteries included in the assembled battery. A battery system that can be estimated can be provided.

It is a block diagram of the battery system of an embodiment. It is a flowchart for demonstrating the estimation method of an embodiment. It is a graph which shows the relationship between reactance of a 2nd battery and SOC. It is a graph which shows the relationship between reactance of an assembled battery and SOC. It is a graph which shows the relationship between the resistance of the 2nd battery and SOC. It is a graph which shows the relationship between the absolute value | Z | of the impedance of the 2nd battery, and SOC. It is an example of the call call plot of the second battery for demonstrating the first modification. It is a partially enlarged view of FIG. It is a block diagram of the battery system of the modification 2. It is a flowchart for demonstrating the estimation method of the modification 2. It is a graph which shows the relationship between ZB of a 2nd battery, and temperature. It is a graph which shows the relationship between TSOC and temperature of a 2nd battery.

<Battery system configuration>
As shown in FIG. 1, the battery system 1 of the embodiment includes an assembled battery 20 in which a plurality of first batteries 10 are connected in series, a CPU 30, a power supply 40, a temperature sensor 29A which is a temperature detecting means, and the like. Equipped with. The assembled battery 20 and the power supply 40 are connected to a load (motor or the like) (not shown).

The first battery 10 is, for example, a lithium ion secondary battery having a unit cell including a positive electrode that occludes / releases lithium ions, an electrolyte, a separator, and a negative electrode that occludes / releases lithium ions. The positive electrode contains, for example, lithium cobalt oxide. The negative electrode contains, for example, a carbon material. The separator is made of, for example, polyolefin. The electrolyte is, for example, an electrolyte in which LiPF6 is dissolved in cyclic and chain carbonate. The first battery 10 may have a structure in which an electrolyte is filled inside a separator made of porous material or the like.

FIG. 1 illustrates an assembled battery 20 in which four first batteries 10 are connected in series, but as will be described later, the number of the first batteries 10 included in the assembled battery 20 is not particularly limited. ..

The power supply 40 applies a measurement signal to the assembled battery 20. The CPU 30 includes a memory 31 which is a storage means, a controller 32, a measurement circuit 33 which is a measurement means, and a calculation circuit 34 which is a calculation means. The memory 31 stores the control data of the battery system 1. The control data includes data of a second battery (not shown) described later. The second battery and the first battery 10 have the same specifications.

The controller 32, which is a control means, controls the entire battery system 1. The measuring circuit 33 measures the impedance characteristic of the assembled battery 20 at a predetermined temperature at a predetermined frequency. The arithmetic circuit 34 estimates the distribution of the state of charge (SOC) of the first battery 10 included in the assembled battery 20.

The memory 31, the controller 32, the measurement circuit 33, and the arithmetic circuit 34 may be independent circuits, or these may be functions performed by the CPU 30 based on the program. When the battery system 1 is used as a part of another separate system, the CPU of the other system may be used as the CPU 30. The other system may be a cloud system commonly used by a plurality of battery systems 1. The temperature adjusting device 29, the temperature control unit 32A, and the sensor 29A may also be common to the plurality of assembled batteries 20. For example, a plurality of assembled batteries 20 are arranged in a constant temperature bath adjusted to a predetermined temperature.

As will be described later, the data of the second battery stored in the memory 31 of the battery system 1 includes the measurement conditions including the measurement frequency and the temperature, the SOC change point TSOC of the second battery, and the impedance in the constant zone. It includes the characteristic impedance bottom value ZB (see FIG. 3). The data of the second battery is common data of the plurality of battery systems 1, and is acquired before manufacturing each battery system 1. Using the data of the second battery, the SOC distributions of the plurality of assembled batteries 20 are estimated.

Each battery system 1 does not need to have a function of acquiring data of the second battery.

In the battery system 1, the arithmetic circuit 34 estimates the distribution of the charged state of the assembled battery 20 from the impedance characteristics measured by the measuring circuit 33 and the data of the second battery stored in the memory 31.

The battery system 1 can easily estimate the SOC distribution of the assembled battery 20 by using the data of the second battery.

As will be described later, the data of the second battery stored in the memory 31 does not have to include the SOC change point TSOC.

<Operation of battery system 1>
The estimation method by the battery system 1 will be described with reference to the flowchart of FIG.

<Steps S10 to S30> First step (second battery measurement step)
In step S10, the impedance characteristics of the second battery (not shown) having the same specifications as the first battery 10 at a predetermined measurement frequency and a predetermined temperature are measured in a plurality of charging states (SOCs).

The measurement frequency is a frequency at which the impedance characteristics change significantly with respect to the SOC, for example, 100 MHz. The measurement frequency is set in advance based on the frequency dependence of the impedance characteristics of the second batteries of the plurality of SOCs.

Specifically, the frequency characteristics of the impedance characteristics of the second batteries having different SOCs are measured, the frequency dependence of the rate of change of the impedance characteristics with respect to the SOC is calculated, and the largest rate of change (ΔZ / Δf; Z: The frequency of impedance (f: frequency) is taken as the measurement frequency.

For example, an AC sine wave signal having an amplitude of 5 mV and a frequency of 100 MHz is applied to a second battery being charged or discharged while changing the SOC from 0% to 100%. The number of SOCs to be measured is preferably 101 every 1%, that is, when measuring 0% to 100%, but may be every 5%, that is, about 21. The SOC range to be measured may be limited according to the estimated SOC range.

If the relationship between the SOC and the voltage of the second battery has been acquired in advance, the voltage may be used instead of the SOC. For example, a second battery may be connected to the load and the impedance characteristics may be measured while discharging. Of course, the impedance characteristics may be measured while charging. For example, the voltage of the second battery is 4.20V at 100% SOC and 3.00V at 0% SOC.

The temperature is a temperature range in which the battery does not deteriorate, for example, an arbitrary temperature of −20 ° C. or higher and 60 ° C. or lower. As will be described later, the reference value for SOC distribution estimation changes depending on the temperature. In this embodiment, the temperature is 0 ° C.

The impedance characteristic is at least one of a real number component (resistance) Z`, an imaginary number component (reactance) −Z`, a phase angle θ, and an absolute value | Z |. In this embodiment, the impedance characteristic is reactance.

FIG. 3 shows an example (temperature 0 ° C.) of the relationship between the reactance (-Z`) of the second battery and the SOC. In the range where the SOC is 45% or more and 80% or less (constant zone), the reactance is almost constant. On the other hand, in the range where the SOC is 45% or less (change zone), the reactance increases significantly. The reactance is increasing even when the SOC is in the range of 80% or more (change zone). That is, the relationship between the reactance and the SOC is a so-called bathtub type in which the reactance becomes the impedance bottom value ZB, which is a constant minimum value, in the vicinity of the median SOC (50%).

<Step S40> Second step (TSOC, bottom price ZB acquisition)
The impedance bottom value ZB and the SOC change point TSOC are acquired. In the present embodiment, the SOC change point is the SOC on the low SOC side (SOC ≦ 50%) in which the impedance characteristic changes according to the change in SOC.

Before the reactance begins to change in response to the change in SOC, that is, the SOC in the constant zone is the impedance bottom value ZB. The impedance bottom value ZB may be the minimum value of reactance, or may be obtained from a straight y-intercept that approximates the value of a region (constant zone) where SOC is more than 45% and less than 80% in FIG. 3, for example.

SOC change point TSOC is the SOC of the boundary between the constant zone and the change zone. Various methods can be used to obtain the SOC change point (TSOC). In the example shown in FIG. 3, the TSOC is 37%, which is the SOC whose reactance is 105% of the impedance bottom value ZB.

The SOC change point TSOC is an SOC whose reactance is larger than the impedance bottom value ZB by ΔZ, and ΔZ is, for example, 1% or more and 100% or less of the impedance bottom value ZB. ΔZ may be set by a reactance value. Further, the SOC change point TSOC may be obtained from the intersection of a straight line that approximates the change zone and a straight line that approximates the constant zone.

<Step S50> Third step (memory step)
The data of the second battery including the measurement conditions, the SOC change point TSOC, and the impedance bottom value ZB are stored in the memory 31 of the battery system 1.

Even if the processes of steps S10 to S40 are performed on the plurality of second batteries, the data of the plurality of second batteries are averaged, and the averaged data is used in each battery system 1. good.

<Step S60> Battery Assembly Measurement Step A measurement signal under the condition that the power supply 40 is stored in the memory 31 under the control of the controller 32 in order to estimate the SOC distribution of the plurality of first batteries 10 included in the assembly battery 20. Is applied to the assembled battery 20 at a predetermined temperature, and the reactor of the assembled battery 20 is measured by the measuring circuit 33. The power supply 40 applies a measurement signal having the same frequency as when the data of the second battery is measured to the assembled battery 20 having substantially the same temperature as when the data of the second battery is measured.

The amplitude of the measurement signal applied to the assembled battery 20 is set according to the number of the first batteries 10 included in the assembled battery 20 in order to match the measured value with the second battery. For example, when the assembled battery 20 includes 20 first batteries 10, the amplitude of the measured signal of the assembled battery 20 is 20 times the measurement signal of the second battery.

The impedance characteristics of a battery are affected by temperature. Therefore, the battery system 1 estimates the distribution of the charged state when the temperature measured by the temperature sensor 29A, which is the temperature detecting means, is, for example, the temperature of the second battery ± 5 ° C. The temperature sensor 29A may be a shared sensor with another system.

<Step S70> Step of estimating the SOC distribution of the assembled battery 20 The reactance of the assembled battery 20 and the data (TSOC, ZB) of the second battery stored in the memory 31 are used to calculate the SOC distribution of the assembled battery 20. Estimated by 34.

Here, the reactance of the assembled battery 20 is the sum of the reactances of the k first batteries 10 (k is an integer) connected in series. Therefore, the impedance bottom value of the assembled battery 20 including the k first batteries 10 shown in FIG. 4 is kZB with respect to the impedance bottom value ZB of the second battery shown in FIG.

Then, as shown in the region A of FIG. 4, if the reactance of the assembled battery 20 is approximately k times (kZB) the impedance bottom value ZB, the SOC of the assembled battery 20 is the estimated reference value (TSOC) 37. It is estimated that the first battery 10 of% or less is not included. On the other hand, if the reactance of the assembled battery 20 is more than k times the impedance bottom value ZB as in the B region, the assembled battery 20 is a first battery having an SOC of 37% or less, which is an estimated reference value. It is estimated that 10 is included.

In addition, in order to estimate that the assembled battery 20 does not include the first battery 10 which is different from the other first battery 10 based on a certain estimation reference value, the memory 31 The SOC change point (TSOC) does not have to be stored in. However, in the battery system 1 including the memory 31 in which the TSOC is also stored, it is clear that the SOC of the estimated reference value is the TSOC.

The number of the first batteries 10 included in the assembled battery 20 is not particularly limited, but if the number is 10 or more, a desired voltage can be obtained, and if the number is 100 or less, the SOC distribution can be easily estimated.

In the above description, it is an estimation method when the SOC is 50% or less, that is, when the range of the SOC change point is 60% or less. However, it is also possible to estimate an SOC with an SOC of more than 50%. To estimate the high SOC range, the boundary between the constant zone and the change zone on the right side (high SOC range) of the bathtub-shaped curve shown in FIG. 5 and the like is used as the SOC change point. The data of the second battery in the low SOC range and the data of the second battery in the high SOC range may be stored in the memory 31.

As described above, steps S10 to S50 are common steps of the plurality of battery systems 1 performed in the manufacturing process of the battery system 1. Further, in the case of the inspection process in which steps S60 and S70 are performed in the factory of the assembled battery 20, the CPU 30 and the power supply 40 also have a common configuration of the plurality of assembled batteries 20, and the assembled batteries estimated to be good products after the inspection. 20 will be shipped.

The first battery 10 is not limited to the lithium ion battery, and may be, for example, a lithium polymer battery or a lithium sulfur battery. Further, the first battery 10 may be an all-solid-state battery in which the electrolyte is a solid electrolyte. Further, the first battery 10 may be a bipolar battery in which adjacent batteries (cells) have a common current collector for the positive electrode and the negative electrode. Further, the first battery 10 may be a bipolar all-solid-state battery in which the electrolyte is a solid electrolyte.

Further, in the present embodiment, the impedance characteristic is reactance, and the measurement frequency is 100 MHz. However, the measurement conditions such as the type of impedance characteristic, the measurement frequency, and the applied voltage can be appropriately selected depending on the specifications of the battery.

As described above, as the impedance characteristic, instead of the reactance, the relationship with the SOC is a bathtub type, the resistance Z` (Fig. 5), the absolute value of the impedance | Z | (Fig. 6), or the phase angle θ. (Not shown) can also be used. However, since the change in SOC with respect to the impedance characteristic is the most remarkable, it is preferable to use reactance as the impedance characteristic.

By using a plurality of frequencies, it is possible to measure with higher accuracy than the measurement using a single frequency. For example, the measurement accuracy is improved by performing each step at frequencies of 50 MHz, 100 MHz, and 150 MHz and combining the measurement results.

<Modified example of the embodiment>
The battery systems 1A, 1B of the modified example of the embodiment and the battery state estimation method of the modified example have the same effects as those of the battery system 1 of the embodiment and the battery state estimation method of the embodiment, and thus have the same functions. The same reference numerals are given to the components, and the description thereof will be omitted.

<Modification example 1>
As described above, in order to determine the optimum measurement frequency, it is necessary to measure the frequency dependence of the impedance characteristics of the plurality of second batteries having different SOCs.

However, in the battery system 1A of the first modification, the optimum measurement frequency can be determined only by measuring the frequency dependence of the impedance characteristic of one second battery.

In the battery state estimation method of this modification, the measurement frequency is determined by the analysis step of the call call plot as described below.

<Complex impedance measurement process>
In the estimation method of this modification, the frequency characteristics of the complex impedance (resistance Z` and reactance-Z`) of the second battery of the first SOC are measured in order to determine the measurement frequency.

Here, the first SOC is the SOC having a small reactance out of the two SOCs that are desired to be used as the reference for SOC estimation. For example, when estimating the SOC of a change zone in a low SOC range, 20% of the SOC is the first SOC and 10% of the SOC is the second SOC.

The difference between the first SOC and the second SOC is preferably 5% or more and 20% or less. If it is within the above range, the estimation accuracy is high.

In the measurement of the frequency characteristic of the complex impedance, for example, an AC sinusoidal signal having an amplitude of 5 mV is applied to the second battery while changing the frequency from a high frequency (1 kHz) to a low frequency (10 MHz).

FIG. 7 is a call call plot showing the frequency characteristics of the complex impedance of the second battery. In the call-call plot, the horizontal axis is the real component of impedance (resistance Z`) and the vertical axis is the imaginary component of impedance (reactance-Z`). The call-call plot of a secondary battery having a positive electrode and a negative electrode has a semicircle in the high frequency region corresponding to the negative electrode reaction, a semicircle in the low frequency region corresponding to the positive electrode reaction, and an inclination of 45 degrees corresponding to the diffusion resistance component. It can be decomposed into a straight line.

<Acquisition of first frequency>
FIG. 8 is a partially enlarged view of FIG. 7. As shown in FIG. 8, in the call call plot, the intersection of a straight line having a slope of 45 degrees corresponding to the diffusion resistance component and a straight line having a reactance of zero, that is, a point O at which the diffusion resistance component becomes zero is calculated. Then, the frequency of the measurement point A of the call call plot having the same resistance Z ｀ as the resistance Z ｀ of the point O is acquired as the first frequency f1. The measurement point A is the lowest frequency at which the diffusion resistance component becomes zero.

In the example shown in FIG. 8, the impedance real component Z ｀ of the point O is 45 mΩ, and the first frequency f1 of the point A having the same resistance Z ｀ is 610 mHz.

<Acquisition of second frequency>
In the Cole Cole plot, in the region including the diffusion resistance component, the frequency whose reactance is the same as the first frequency f1 is acquired as the second frequency f2. In other words, the region containing the diffusion resistance component is a region having a frequency lower than that of the first frequency f1.

In the example shown in FIG. 8, the reactance of the point A is 6.8 mΩ, and the second frequency f2 of the point B having the same reactance is 40 mHz.

<Measurement frequency determination>
The frequency F in the range of the first frequency f1 or less and the second frequency f2 or more is determined. For example, the frequency that is the reactance of the midpoint C of the straight line connecting the point of the first frequency f1 and the point of the second frequency f2 of the call call plot is determined as the measurement frequency F. In the call-call plot shown in FIG. 8, 100 MHz is determined as the measurement frequency F.

As is clear from FIG. 7, the range f1-f2 of the measurement frequency F is a semicircular range of the low frequency region corresponding to the positive electrode reaction. That is, in this modification, the SOC is estimated based on the change in reactance in the positive electrode reaction of the secondary battery.

When the measurement frequency F is in the above range, the rate of change in reactance is large. For example, the rate of change of reactance ((Z10-Z20) / Z20) was 620% at the first frequency f1, 680% at the second frequency f2, and 1100% at 100 MHz. ..

In the conventional method, the frequency characteristics of the reactance of the battery with 10% SOC and the battery with 20% SOC are measured respectively, and the frequency dependence of the reactance change rate with respect to the SOC is acquired, and the change rate becomes the maximum value. The frequency is calculated. In the conventional method, the rate of change was a maximum value of 1150% at a frequency of 125 MHz.

In this modification, an impedance change rate comparable to that of the conventional method can be obtained only by measuring the frequency characteristic of the reactance of the battery having an SOC of 20%.

In this modification, the SOC of the first battery 10 can be estimated accurately and easily by using the data of the second battery including the appropriate measurement frequency.

<Modification 2>
FIG. 9 shows the configuration of the battery system 1B of the second modification of the embodiment. Since the battery state estimation method by the battery system 1B and the battery system 1B has the same effect as the battery state estimation method by the battery system 1 and the battery system 1, the components having the same function are designated by the same reference numerals. The description is omitted.

The battery system 1B includes a temperature control unit 32A which is a temperature control means. The temperature control unit 32A controls the temperature of the assembled battery 20 by using the temperature control device 29 which is a temperature control means including the temperature sensor 29A. The sensor 29A may be separate from the temperature control device 29.

Since the impedance characteristics of a battery are affected by temperature, the SOC change point (TSOC) also changes with temperature.

The battery system 1B can estimate the SOC distribution of the plurality of first batteries included in the assembled battery 20 with a desired SOC as an estimation reference value.

<Operation of battery system 1B>
A method of estimating the battery state by the battery system 1B will be described with reference to the flowchart of FIG.

<Steps S110 to S130> First step (measurement of the second battery)
In step S110, the impedance characteristics of the second battery (not shown) having the same specifications as the first battery 10 at a plurality of first temperatures are measured in each of the plurality of charging states (SOCs).

For example, the impedance characteristics of the second battery are measured at 45 ° C., which is one of a plurality of first temperatures, changing the SOC to a predetermined range, for example, 0% to 100%. In order to maintain the second battery at a predetermined temperature, for example, a constant temperature bath is used.

In step S120, when all the measurements at the plurality of preset first temperatures have been completed (Yes), the process proceeds to step S130. If the measurement is not completed (No), the first temperature is changed to, for example, 25 ° C. in step S30.

The number of first temperatures is at least two, but to cover a wider SOC range, three or more are preferred, and four or more are particularly preferred.

<Step S140> Second step (TSOC, ZB acquisition)
The relationship between the impedance bottom value ZB and the SOC change point (TSOC) shown in FIGS. 11 and 12 and the temperature (first temperature) is acquired.

<Step S150> Third step (data storage of the second battery)
The data of the second battery including the relationship between ZB and TSOC and the temperature is stored in the memory 31. Based on these relationships and the graphs of FIGS. 11 and 12, it may be stored as an approximate expression or as a table.

<Step S160> Temperature setting In the present embodiment, the temperature is set according to the estimation reference value that is the reference for estimating the SOC distribution. For example, when estimating whether or not the first battery 10 having an SOC of less than 10% is included, the temperature is set to 42 ° C. using the relationship between the TSOC and the temperature shown in FIG. Similarly, when SOC 30% is used as the reference SOC, the temperature is set to 10 ° C.

Then, the temperature control unit 32A controls the temperature adjusting device 29 so that the temperature of the assembled battery 20 detected by the sensor 29A becomes a predetermined temperature. In other words, the temperature of the assembled battery 20 is controlled by the temperature control unit 32A in the temperature adjusting device 29. The temperature control device 29 has, for example, a heater and a Peltier element. When estimating the SOC of a plurality of assembled batteries 20, the plurality of assembled batteries 20 may be arranged in one constant temperature bath or constant temperature room at a predetermined temperature.

<Step S170> Measurement of the assembled battery The reactance of the assembled battery 20 is measured in order to estimate the SOC distribution of the plurality of first batteries 10 included in the assembled battery 20.

<Step S180> Estimating the SOC Distribution of the Assembled Battery 20 As described above, for example, the reactance of the assembled battery 20 having a temperature of 42 ° C. is acquired by using the relationship between ZB and the temperature shown in FIG. If the impedance bottom value is k times or less of the bottom value ZB, it is estimated that the assembled battery 20 does not include the first battery 10 having an SOC of 10% or less. On the other hand, if the reactance of the assembled battery 20 is more than k times the impedance bottom value ZB, it is estimated that the assembled battery 20 includes the first battery 10 having an SOC of 10% or less.

According to the battery system 1B and the battery state estimation method of the second modification, the distribution of the charging state based on the desired SOC can be estimated.

Even in a battery system that does not have a temperature control function, the data of the second battery may include data at a plurality of temperatures. When estimating the SOC distribution of the assembled battery 20, the data of the second battery measured at the temperature closest to the temperature detected by the temperature sensor 29A can be used for estimating the assembled battery 20.

The present invention is not limited to the above-described embodiments and the like. The present invention allows various modifications and modifications, for example, combinations of components of the embodiments, without changing the gist of the present invention.

1, 1A, 1B ... Battery system 10 ... First battery 20 ... Assembly battery 31 ... Memory 32 ... Controller 33 ... Measurement circuit 34 ... Calculation circuit 40 ... Power supply

Claims (14)

The process of measuring the impedance characteristics at a predetermined frequency of an assembled battery in which a plurality of first batteries are connected in series, and
The distribution of the charged state of the plurality of first batteries is estimated based on the impedance characteristics of the assembled battery and the data of the second battery having the same specifications as the first battery stored in advance. With the process to be done,
The data of the second battery is
In the first step, in which the impedance characteristics of the second battery in a plurality of charged states are measured at the predetermined frequency,
A second step in which the SOC change point, which is a charged state in which the impedance characteristic of the second battery begins to increase, and the impedance bottom value before the impedance characteristic begins to increase are calculated.
A battery state estimation method, characterized in that the data of the second battery including the impedance bottom value is acquired and stored in the third step of storing the data. The battery state estimation method according to claim 1, wherein the data of the second battery includes the SOC change point. The battery state estimation method according to claim 1 or 2, wherein the impedance characteristic is reactance. The predetermined frequency is equal to or lower than the first frequency and higher than or lower than the second frequency.
The first frequency is the lowest frequency in the region where the diffusion resistance component is zero in the call call plot, which is the frequency characteristic of the complex impedance of the second battery in a predetermined charged state.
The second frequency is any one of claims 1 to 3, wherein the reactance is the same frequency as the first frequency in the region including the diffusion resistance component in the call call plot. The battery state estimation method described in 1. The battery state estimation method according to claim 4, wherein the predetermined frequency is 10 MHz or more and 500 MHz or less. The battery state estimation method according to any one of claims 1 to 5, wherein the data of the second battery includes the data at a plurality of temperatures. The battery state estimation method according to any one of claims 1 to 6, wherein the distribution of a plurality of assembled batteries is estimated using the data of the second battery. An assembled battery in which a plurality of first batteries are connected in series,
Data of the second battery including the impedance bottom value which is the impedance characteristic before the impedance characteristic at a predetermined frequency of the second battery having the same specifications as the first battery begins to change in response to a change in the charging state. And the storage means in which
A measuring means for measuring the impedance characteristic of the assembled battery at the predetermined frequency, and
An calculation for estimating the distribution of the charged state of the plurality of first batteries included in the assembled battery from the impedance characteristics of the assembled battery and the data of the second battery stored by the storage means. A battery system comprising: means. The battery system according to claim 8, wherein the storage means stores an SOC change point, which is a charging state in which the impedance characteristic of the second battery begins to change in response to a change in the charging state. .. The battery system according to claim 8 or 9, wherein the impedance characteristic is reactance. The predetermined frequency is equal to or lower than the first frequency and higher than or lower than the second frequency.
The first frequency is the lowest frequency in the region where the diffusion resistance component is zero in the call call plot, which is the frequency characteristic of the complex impedance of the second battery in a predetermined charged state.
The second frequency is any one of claims 8 to 10, wherein the reactance is the same frequency as the first frequency in the region including the diffusion resistance component in the call call plot. The battery system described in. The battery system according to claim 11, wherein the predetermined frequency is 10 MHz or more and 500 MHz or less. The battery system according to any one of claims 8 to 12, wherein the data of the second battery includes the data at a plurality of temperatures. A temperature adjusting means for adjusting the temperature of the assembled battery and
The battery system according to claim 13, further comprising a temperature control means for controlling the temperature adjusting means.

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