JP7194383B2 - Battery state estimation method and battery system - Google Patents

Description

Embodiments of the present invention provide a battery state estimation method for estimating the distribution of the state of charge of an assembled battery in which a plurality of batteries are connected in series, and a method for estimating the distribution of the state of charge in an assembled battery in which a plurality of batteries are connected in series. Regarding battery systems.

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

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

In Japanese Patent Application Laid-Open No. 2018-151194, in a region where the impedance does not change greatly with respect to the state of charge (SOC) of the assembled battery, the SOC is estimated from the voltage, and the region where the impedance changes greatly with respect to the SOC. discloses an apparatus for estimating SOC using impedance.

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

Evaluating the SOC of a single battery (cell) is relatively easy. However, in order to evaluate the SOC of each battery included in the assembled battery, it is necessary to connect a wire for evaluation to each battery. In addition, depending on the specifications of the assembled battery, it was not possible to evaluate the SOC of each battery after assembly due to a structure in which electric wires could not be connected to each battery.

Development of an evaluation method for easily estimating the SOC distribution of multiple batteries included in an assembled battery and a battery system capable of easily estimating the SOC distribution of multiple batteries included in an assembled battery have been desired. .

JP 2009-97878 A JP 2018-151194 A

Embodiments of the present invention provide a battery state estimation method for easily estimating the SOC distribution of a plurality of batteries included in an assembled battery, and a method for easily estimating the SOC distribution of a plurality of batteries included in the assembled battery. The object is to provide a battery system.

A battery state estimation method according to an embodiment of the present invention comprises a step of measuring impedance characteristics at a predetermined frequency of an assembled battery in which a plurality of first batteries are connected in series at each of a plurality of first temperatures; A distribution of state of charge of the plurality of first batteries is estimated using the impedance characteristics of the assembled battery at the plurality of first temperatures and prestored data of the second batteries. and wherein the data of the second battery is such that the impedance characteristics at the frequency of the second battery having the same specifications as the first battery are at a plurality of states of charge and a plurality of second batteries. A first step measured at two temperatures, and an SOC change point, which is the state of charge at which the impedance characteristic begins to change in response to a change in the state of charge, at each of the plurality of second temperatures, and the change a second step of acquiring an impedance bottom value, which is the impedance characteristic before starting to perform, and a third step of acquiring the data of the second battery including the relationship between the impedance bottom value and temperature and a fourth step of storing said data of said second battery.

A battery system according to another embodiment comprises an assembled battery in which a plurality of first batteries are connected in series; a measuring means for measuring impedance characteristics of the assembled battery at a predetermined frequency at a plurality of first temperatures; The impedance characteristics of a second battery having the same specifications as the first battery at each of a plurality of second temperatures before the impedance characteristics at the predetermined frequency start to change according to changes in the state of charge. storage means for storing data of the second battery including the relationship between the impedance bottom value and the plurality of second temperatures; the impedance characteristics of the assembled battery at the plurality of first temperatures; and the storage. and calculating means for estimating the distribution of the state of charge of the assembled battery from the data of the second battery stored by the means, wherein the data of the second battery is the impedance characteristic of the state of charge. and the plurality of second temperatures .
A battery system according to another embodiment comprises an assembled battery in which a plurality of first batteries are connected in series; a measuring means for measuring impedance characteristics of the assembled battery at a predetermined frequency at a plurality of first temperatures; The impedance characteristics of a second battery having the same specifications as the first battery at each of a plurality of second temperatures before the impedance characteristics at the predetermined frequency start to change according to changes in the state of charge. storage means for storing data of the second battery including the relationship between the impedance bottom value and the plurality of second temperatures; the impedance characteristics of the assembled battery at the plurality of first temperatures; and the storage. and calculating means for estimating the distribution of the state of charge of the assembled battery from the data of the second battery stored by the means, wherein the predetermined frequency is equal to or lower than the first frequency and the second and the first frequency is the lowest frequency in a region where the diffusion resistance component is zero in a Cole-Cole plot, which is the frequency characteristic of the complex impedance of the second battery in a predetermined state of charge, and A second frequency is a frequency at which reactance is the same as the first frequency in a region including the diffusion resistance component in the Cole-Cole plot.

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

1 is a configuration diagram of a battery system according to an embodiment; FIG. It is a flow chart for explaining the estimation method of the embodiment. 4 is a graph showing the relationship between reactance and SOC at 45° C. of the second battery. 4 is a graph showing the relationship between reactance and SOC at 25° C. of the second battery. 4 is a graph showing the relationship between reactance and SOC at 0° C. of the second battery. 4 is a graph showing the relationship between reactance and SOC of the second battery at −20° C. FIG. 4 is a graph showing the relationship between the temperature of the second battery and the impedance bottom value; 4 is a graph showing the relationship between the temperature of the second battery and the SOC change point; It is a figure created based on FIG.7 and FIG.8 for demonstrating the estimation method of embodiment. 4 is a graph showing the relationship between the resistance Z' and the SOC of the second battery; 10 is a graph showing the relationship between the impedance absolute value |Z| and the SOC of the second battery. 9 is a flowchart for explaining an estimation method according to a modification of the embodiment; It is a figure for demonstrating the estimation method of the modification of embodiment. It is a figure for demonstrating the estimation method of embodiment. It is an example of a Cole-Cole plot of a second battery. FIG. 16 is a partially enlarged view of FIG. 15;

<Configuration of battery system>
As shown in FIG. 1, the battery system 1 of the embodiment includes an assembled battery 20 in which a plurality of first batteries (battery cells) 10 are connected in series, a temperature adjustment device 29, a CPU 30, a power supply 40, Equipped with The assembled battery 20 and the power supply 40 are connected to a load (motor, etc.) not shown.

The first battery 10 is, for example, a lithium ion secondary battery having a unit cell composed of a positive electrode that absorbs/releases lithium ions, an electrolyte, a separator, and a negative electrode that absorbs/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 polyolefin, for example. The electrolyte is, for example, an electrolyte obtained by dissolving LiPF6 in cyclic and chain carbonates. The first battery 10 may have a structure in which an electrolyte is filled inside a separator made of a porous material or the like.

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

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

The controller 32 controls the entire battery system 1 and includes a temperature control section 32A that controls the temperature of the assembled battery 20 using a temperature adjustment device 29 that includes a temperature sensor 29A. The temperature sensor 29A, which is a temperature detecting means, may be separate from the temperature adjusting device 29. FIG. A measurement circuit 33 measures the impedance characteristics of the assembled battery 20 . Arithmetic circuit 34 estimates the SOC distribution of assembled battery 20 .

The memory 31, controller 32, measurement circuit 33, and arithmetic circuit 34 may be independent circuits, or may be functions performed by the CPU 30 based on a program. Also, in the case where the battery system 1 is used as part of another separate system, the CPU of the other system may be used as the CPU 30 . Another system may be a cloud system that is commonly used by a plurality of battery systems 1 .

The inventors have found that the SOC change point (TSOC), which is the SOC at which the impedance characteristic shifts from a region (constant zone) in which the impedance characteristic does not change significantly with respect to SOC to a region (change zone) in which it changes greatly, greatly depends on temperature. Found it.

The second battery data stored in the memory 31 of the battery system 1 includes the measurement conditions, the relationship between the SOC change point (TSOC) of the second battery and the temperature, and the impedance bottom value which is the impedance characteristic in the constant zone. (ZB) versus temperature. The data of the second battery is common data of the plurality of battery systems 1 and is acquired before manufacturing the battery system 1 . The distribution of the states of charge of the plurality of assembled batteries 20 is estimated using the data of the second battery. Each battery system 1 need not have the function of acquiring the data of the second battery.

In the battery system 1, the arithmetic circuit 34 estimates the state-of-charge distribution (SOC distribution) of the assembled battery 20 from the impedance characteristics measured by the measurement circuit 33 and the data of the second battery stored in the memory 31. do. The data of the second battery may not include the relationship between the SOC change point and the temperature.

The battery system 1 simply estimates the SOC distribution of the assembled battery 20 using the temperature dependence of the SOC change point.

<Battery system operation>
A battery state estimation method by the battery system 1 will be described along the flowchart of FIG. 2 . In addition, below, the battery system 1 including the assembled battery 20 in which the four 1st batteries 10 are connected in series is demonstrated to an example.

<Steps S10 to S30> First step (second battery measurement step)
In step S10, impedance characteristics at predetermined frequencies at a plurality of second temperatures of a second battery (not shown) having the same specifications as the first battery 10 are measured at a plurality of states of charge (SOC). .

For example, the impedance characteristics of the second battery are measured at 45° C., one of the plurality of second temperatures, while varying the SOC from 0% to 100%. For example, a sinusoidal alternating signal with an amplitude of 5 mV and a frequency of 100 mHz is applied to the second battery during charging or discharging and the voltage is measured.

The relationship between the SOC and voltage of the second battery is obtained in advance. For example, the voltage of the second battery is 4.20 V at 100% SOC and 3.00 V at 0% SOC.

The number of SOCs (voltage) to be measured is preferably 101 when measuring every 1%, ie, 0% to 100%, but may be every 5%, ie, about 21. Also, the SOC range to be measured may be limited according to the estimated SOC range, as will be described later.

A measurement frequency of 100 mHz is a frequency at which the impedance characteristics change greatly with respect to the SOC. 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 with 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: impedance, f: frequency) is the measurement frequency.

The impedance characteristic is at least one of a real component (resistance) Z′, an imaginary component (reactance) Z′′, a phase angle θ, and an absolute value |Z|. A constant temperature bath, for example, is used to maintain the second battery at a predetermined temperature.

FIG. 3 shows the relationship between the reactance and SOC of the second battery at 45°C. In the SOC range of 30% or more and 90% or less (constant zone), the reactance is substantially constant. In the range where the SOC is 30% or less (change zone), the reactance increases greatly. The reactance increases even in the range where the SOC is 90% or more (change zone). That is, the relationship between the reactance and the SOC is a so-called bathtub type in which the reactance reaches the impedance bottom value ZB, which is a constant minimum value, in the vicinity of the SOC median value (50%).

In step S20, if the measurements at the plurality of preset states of charge (SOC) and the plurality of second temperatures are all completed (Yes), the process proceeds to step S40. If the measurement has not ended (No), the SOC or the second temperature is changed in step S30.

FIG. 4 shows the relationship between reactance and SOC of the second battery at 25°C. FIG. 5 shows the relationship between reactance and SOC of the second battery at 0°C. FIG. 6 shows the relationship between reactance and SOC of the second battery at -20.degree. At any temperature, the relationship between reactance and SOC is a bathtub type.

The number of second temperatures is at least two, but preferably three or more, particularly preferably four or more, in order to cover a wide SOC range when estimating the SOC of the assembled battery 20 . Although there is no particular upper limit to the number of second temperatures, it is, for example, 200 or less. Steps S10 to S30 are steps for acquiring basic data for estimating the SOC of the first battery 10. Therefore, even if measurements are performed at many temperatures, the distribution of the state of charge of the assembled battery 20 cannot be estimated in time. no effect.

The second temperature preferably includes temperatures below and above room temperature (25° C.) in order to cover a wide SOC range. In this embodiment, as shown in FIGS. 3 to 6, there are four second temperatures: 45° C., 25° C., 0° C., and −20° C. FIG.

<Step S40> Second step (ZB and TSOC acquisition)
An impedance bottom value ZB is obtained, which is the reactance before the reactance at each second temperature starts to change with changes in the state of charge. The impedance bottom value ZB may be the minimum value of the reactance, or may be obtained from a straight line approximating the value of the SOC 30% or more and 50% or less region (constant zone) in FIG. 3, for example.

Next, an SOC change point (TSOC) at each second temperature is obtained. The boundary between the constant zone and the change zone is the SOC change point. In the present embodiment, the SOC change point is the SOC on the low SOC side (SOC≦50%) of the two change zones in which the impedance characteristics change according to the change in SOC.

For example, in FIG. 3 (45° C.), the SOC change point (TSOC) is the SOC at which the slope of the reactance reaches or exceeds the predetermined value of 0.001 (Ω/%), and the value is 9%. As a method of obtaining the SOC change point, the SOC at the intersection of a straight line approximating the value of the SOC 5% or less region (change zone) and the approximation of the value of the SOC 30% or more and 50% or less region (constant zone). 5.5% may be used.

Various methods can be used to acquire the SOC change point (TSOC). For example, the SOC change point TSOC may be an SOC where the reactance is larger than the impedance bottom value ZB by ΔZ. ΔZ is, for example, 1% or more and 100% or less of the impedance bottom value ZB. ΔZ may be set by the absolute value of reactance.

The reactances shown in FIGS. 3-6 show an increase in reactance in the transition zone. However, depending on the type of impedance characteristic, the impedance characteristic may decrease in the change zone.

<Step S50> Third step (acquisition of relationship between temperature and impedance bottom value ZB)
The relationship between impedance bottom value ZB and temperature shown in FIG. 7 is obtained from FIGS. Also, the relationship between the SOC change point (TSOC) and the temperature as shown in FIG. 8 is acquired.

These relationships may be obtained as mathematical expressions or as tables. As will be described later, it is preferable to obtain these relationships as mathematical formulas, since the relationship between measurement points can be approximated and used. That is, these relationships do not consist only of data at actually measured temperatures.

<Step S60> Fourth step (data storage of second battery)
As already described, the second battery data (the relationship between the SOC change point and the temperature and the relationship between the impedance bottom value and the temperature) obtained in steps S10 to S50 are common data for the plurality of battery systems 1. is. That is, in producing a plurality of battery systems 1, data of the second battery is acquired and stored in each memory 31. FIG.

The processing of steps S10 to S50 may be performed on a plurality of second batteries, and the acquired data of the plurality of second batteries may be averaged and stored in the memory 31 .

<Steps S70 to S90> Assembled Battery Measurement Process Each of the plurality of first batteries 10 included in the assembled battery 20 has the same specifications as the second battery, but the SOC of each is unknown. For example, the battery system 1 inspects the assembled battery 20 before shipment.

In order to estimate the SOC distribution of the plurality of first batteries 10 included in the assembled battery 20, reactances of the assembled battery 20 are measured at a plurality of first temperatures. The power supply 40 applies to the assembled battery 20 an AC signal of the same frequency as when the data of the second battery was measured.

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

The temperature control unit 32A controls the temperature adjustment device 29 so that the temperature of the assembled battery 20 detected by the sensor 29A becomes a predetermined first temperature. The temperature adjustment device 29 has, for example, a heater and a Peltier element. The temperature controller 32A controls the temperature controller 29 so that the temperature of the assembled battery 20 is one of the plurality of first temperatures, for example, 45°C. The temperature adjusting device 29, the temperature control section 32A and the sensor 29A may be common to the plurality of assembled batteries 20. FIG. For example, a plurality of assembled batteries 20 are arranged in a constant temperature bath adjusted to a predetermined temperature.

In step S70, measurements are made at a first temperature. In step S80, when all the measurements at a plurality of preset first temperatures are completed (Yes), the process proceeds to step S100. If the measurement has not finished (No), the temperature is changed to another first temperature in step S90. Then, in step S70 again, the reactance of the assembled battery 20 is measured.

The temperature of the assembled battery 20 is raised by leaving the assembled battery 20 cooled to −20° C. or lower, which is the lowest temperature among the plurality of first temperatures, in an environment of 45° C. or higher, which is the highest temperature. may be used to measure the reactance at a plurality of first temperatures. The assembled battery 20 heated to 45° C. or higher may be left in an environment of −20° C. or lower for measurement. The temperature control section 32A and the temperature adjustment device 29 are not essential components of the present invention.

The number of first temperatures may be the same as the number of second temperatures. However, in order to shorten the processing time, it is preferable that the number of first temperatures is less than the number of second temperatures. For example, even if the number of second temperatures is 101, it is preferable that the number of first temperatures is 10 or less.

<Step S100> Step of estimating SOC distribution of assembled battery 20 From the reactance of the assembled battery 20 at a plurality of first temperatures and the second battery data (FIGS. 7 and 8) stored in the memory 31, , the arithmetic circuit 34 estimates the SOC distribution of the assembled battery 20 .

The dotted line at the bottom of FIG. 9 is a graph showing the relationship between the temperature shown in FIG. 7 and the impedance bottom value ZB of the second battery. The impedance bottom value ZB of the four second batteries connected in series is 4ZB as indicated by the solid line. The upper part of FIG. 9 is a graph showing the relationship between the temperature shown in FIG. 8 and the SOC change point TSOC.

A black circle in the graph at the bottom of FIG. 9 indicates an example of the reactance (−Z′′) of the assembled battery 20 . The reactance of the assembled battery 20 is greater than the impedance bottom value ZB20 at -20°C and 0°C, and is substantially equal to the impedance bottom value ZB20 at 25°C and 45°C.

From the upper graph of FIG. 9, the TSOC at a temperature of 0° C. is 38% and the TSOC at a temperature of 25° C. is 20%. Therefore, it is estimated that the assembled battery 20 includes not only first batteries with an SOC of less than 20%, but also first batteries with an SOC of less than 38% and 20% or more.

On the other hand, for example, if the reactance of the assembled battery 20 is greater than the impedance bottom value ZB20 at 25° C. or lower and is substantially the same as the impedance bottom value ZB20 at 45° C., the assembled battery 20 has an SOC of 10. %, as well as first batteries with an SOC of less than 20% and 10% or more are included.

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. The assembled battery 20 including many first batteries 10 has a large impedance bottom value ZB20. Then, the SOC distribution is estimated based on the temperature at which the reactance becomes even larger than the impedance bottom value ZB20.

If it is only assumed that the assembled battery 20 includes the first battery 10 with an SOC outside the reference value, the memory 31 stores the relationship between the SOC change point and the temperature of the second battery. No need. However, in the battery system 1 including the memory 31 in which the relationship between the SOC change point and the temperature is stored, it is clear that the reference value is the TSOC.

In the above description, the estimation method is used when the SOC is 50% or less, that is, when the SOC change point range is 60% or less. However, it is also possible to estimate SOC above 50% in the same way. 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 curve shown in FIG. 5 etc. is used as the SOC change point. Data of the second battery in the low SOC range and data of the second battery in the high SOC range may be stored in the memory 31 .

The first battery 10 is not limited to a lithium ion battery, and may be, for example, a lithium polymer battery or a lithium sulfur battery. The first battery 10 may be an all-solid battery in which the electrolyte is a solid electrolyte. 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. The first battery 10 may be a bipolar all-solid battery in which the electrolyte is a solid electrolyte. A plurality of assembled batteries 20 may be connected in parallel.

In this embodiment, the impedance characteristic was reactance, and the measurement frequency was 100 mHz. However, the measurement conditions such as the type of impedance characteristic, frequency, and applied voltage can be appropriately selected depending on the specifications of the battery.

As already explained, instead of the reactance, the impedance characteristic may be the resistance Z′ (FIG. 10), the impedance absolute value |Z| (FIG. 11), or the phase angle θ ( (not shown) can also be used. However, it is preferable to use reactance as the impedance characteristic because the change in TSOC with respect to temperature is the most significant.

The higher the impedance characteristic measurement frequency is, the shorter the measurement time is. Therefore, the frequency is preferably 10 mHz or more and 500 mHz or less.

By using multiple frequencies, more accurate measurements are possible than measurements using a single frequency. For example, each step is performed at frequencies of 50 mHz, 100 mHz, and 150 mHz, and the measurement accuracy is improved by combining the measurement results at frequencies at which TSOC changes significantly with respect to temperature.

<Modification>
The battery state estimation method and battery system 1A of the modified example are similar to the battery state estimation method and battery system 1 of the embodiment, and have the same effects, so the same reference numerals are given to components having the same functions. Description is omitted.

The SOC range estimated using the battery state estimation method of the embodiment may be a wide range and not highly accurate when the number of first temperatures is small. Increasing the number of first temperatures to increase accuracy increases the estimation time.

On the other hand, in the estimation method of the modification, an increase in estimation time is minimized by measuring in a third temperature range narrower than the temperature range of the first temperature based on the measurement result at the first temperature. Although limited, the accuracy of the estimated SOC range can be improved, in other words, the estimated SOC range can be narrowed down.

FIG. 12 shows a flowchart of the battery state estimation method of the modification.

<Steps S10-S100> SOC Range Estimation Subroutine The processing of steps S10-S100 already described is performed.

<Step S110> (Is the SOC range the desired accuracy?)
Controller 32 determines whether the SOC range estimated in steps S10-S100 (SOC range estimation subroutine) is of desired accuracy. For example, the estimated SOC distribution that includes not only the first batteries with an SOC of less than 20% but also the first batteries with an SOC of less than 38% and 20% or more does not meet the desired accuracy (No), the process proceeds to step S120.

<Step S120> Setting of Third Temperature A plurality of first temperatures are set between the temperature at which the reactance becomes greater than the impedance bottom value ZB20 and the higher temperature. That is, as shown in FIG. 13, the controller 32 resets a plurality of third temperatures in a temperature range TW2 narrower than the first temperature range TW1.

For example, 5°C, 10°C, 15°C, and 20°C are reset as the plurality of third temperatures between 0°C and 25°C.

<Steps S130 to S150> First Battery Re-Measurement Process Similar to steps S70 to S90, the measurement circuit 33 measures the impedance characteristics (reactance) of the assembled battery 20 at a plurality of third temperatures.

<Step S160> Step of re-estimating the SOC distribution of the assembled battery As in step S100, the SOC of the first battery 10 is obtained from the reactance of the assembled battery 20 at a plurality of third temperatures and the data of the second battery. A range is estimated by arithmetic circuit 34 .

For example, the reactance of the assembled battery 20 indicated by black circles in the lower graph of FIG. 13 is greater than the impedance bottom value ZB20 at 15° C. or lower, and substantially equal to the impedance bottom value ZB20 at 20° C. or higher.

From the upper graph in FIG. 13, it is estimated that the assembled battery 20 includes not only first batteries with an SOC of less than 23%, but also first batteries with an SOC of less than 27% and 23% or more. be.

The SOC threshold range estimated in step S160 is 27% to 23%, which is more accurate than the threshold range of 38% to 20% estimated in step S90 (fifth step).

In step S110, if the SOC range satisfies the desired accuracy (Yes), the process ends. If it is determined that the SOC range still does not meet the desired accuracy (No), the process moves to step S120 again. In this case, the temperature range reset again becomes narrower than the reset third temperature range (TW2).

In the above description, an example of estimating the presence or absence of the first battery 10 deviating from the standard with a predetermined SOC as the standard has been shown. A more detailed distribution can be estimated by more detailed measurements and analysis.

For example, the reactance of the assembled battery 20 indicated by black circles in FIG. 14 is greater than the impedance bottom value ZB20 between temperatures T1 and T2. In other words, there is a change point (inflection point) where the slope changes. Therefore, it is estimated that the first battery 10 having the SOC in the range A is included in the assembled battery 20 . Furthermore, since the impedance bottom value ZB20 is increased by ΔZ1, by comparing ΔZ1 with the impedance increase amount from the impedance bottom value ZB in the case of one second battery, the first battery 10 with the SOC in the range A A number can also be estimated.

The temperature dependence of the reactance has a change point between temperatures T3 and T4 where the reactance rises sharply again. Therefore, it is estimated that the first battery 10 having the SOC in the range B is included in the assembled battery 20 . Furthermore, since there is an increase by ΔZ2 at the inflection point, the number of first batteries 10 with an SOC in range B can also be estimated by comparing ΔZ2 with the amount of impedance increase in the case of one second battery.

<Frequency determination method>
As already explained, in order to determine the optimum measurement frequency, it was necessary to measure the frequency dependence of the impedance characteristics of a plurality of second batteries with different SOCs.

The optimum measurement frequency can also be determined by simply measuring the frequency dependence of the impedance characteristics of one second battery.

<Complex impedance measurement process>
In this method, the frequency characteristic of the complex impedance (resistance Z′ and reactance Z′′) of the second battery at the first SOC at a given state of charge is measured to determine the measurement frequency.

The first SOC is the SOC with the smaller reactance, of the two SOCs (the first SOC and the second SOC) that serve as the reference for SOC estimation. For example, when estimating the SOC of a change zone in the low SOC range, SOC 20% is the first SOC and SOC 10% 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 complex impedance, for example, an AC signal with 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. 15 is a Cole-Cole plot showing frequency characteristics of the complex impedance of the second battery. In the Cole-Cole plot, the horizontal axis is the real component of impedance (resistance Z') and the vertical axis is the imaginary component of impedance (reactance-Z'). A Cole-Cole 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 a slope of 45 degrees corresponding to the diffusion resistance component. can be decomposed into a straight line and

<Acquisition of first frequency>
16 is a partially enlarged view of FIG. 15. FIG. As shown in FIG. 16, in the Cole-Cole plot, the intersection of the straight line with a slope of 45 degrees corresponding to the diffusion resistance component and the straight line with zero reactance, that is, the point O at which the diffusion resistance component is zero is calculated. Then, the frequency of the measurement point A of the Cole-Cole plot, which has the same resistance Z' as the resistance Z' of the point O, is obtained as the first frequency f1. Note that the measurement point A is the lowest frequency at which the diffusion resistance component becomes zero.

In the example shown in FIG. 16, the impedance real component Z' at point O is 45 mΩ, and the first frequency f1 at point A with the same resistance Z' is 610 mHz.

<Acquisition of the second frequency>
In the Cole-Cole plot, the frequency at which the reactance is the same as the first frequency f1 in the region containing the diffusion resistance component is obtained as the second frequency f2. The region containing the diffusion resistance component is, in other words, a region of frequencies lower than the first frequency f1.

In the example shown in FIG. 16, the reactance at point A is 6.8 mΩ, and the second frequency f2 at point B, which results in the same reactance, is 40 mHz.

<Measurement frequency determination>
A frequency F in the range below the first frequency f1 and above the second frequency f2 is determined. For example, the measurement frequency F is determined as the reactance frequency at the middle point C of the straight line connecting the point of the first frequency f1 and the point of the second frequency f2 on the Cole-Cole plot. 100 mHz is determined as the measurement frequency F in the Cole-Cole plot shown in FIG.

As is clear from FIG. 15, the range f1-f2 of the frequency F is a semicircular range in the low frequency region corresponding to the positive electrode reaction. That is, in this modified example, the SOC is estimated based on the change in reactance in the positive electrode reaction of the secondary battery.

If the frequency F is within the above range, the rate of change in reactance is large. For example, the reactance change rate ((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 reactance frequency characteristics of a battery with an SOC of 10% and a battery with an SOC of 20% are measured, and the frequency dependence of the rate of change of the reactance with respect to the SOC is obtained. Calculated. In the conventional method, the maximum rate of change was 1150% at a frequency of 125 mHz.

In this method, for example, by simply measuring the frequency characteristics of the reactance of a battery with an SOC of 20%, an impedance change rate comparable to that of the conventional method is obtained.

In this method, the SOC of the first battery 10 can be easily estimated with high accuracy by using the data of the second battery including an appropriate measurement frequency.

The present invention is not limited to the above-described embodiments and the like. Various changes, alterations, combinations of components, etc. are possible for the present invention without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1, 1A...Battery system 10...First battery 20...Battery pack 29...Temperature adjustment device 29A...Temperature sensor 31...Memory 32...Controller 32A...Temperature control part 33...Measurement circuit 34...Arithmetic circuit 40...Power supply

Claims (10)

a step of measuring, at each of a plurality of first temperatures, impedance characteristics at a predetermined frequency of an assembled battery in which a plurality of first batteries are connected in series;
A distribution of state of charge of the plurality of first batteries is estimated using the impedance characteristics of the assembled battery at the plurality of first temperatures and prestored data of the second batteries. and
The data of the second battery is
a first step wherein the impedance characteristic at the frequency of the second battery of the same specification as the first battery is measured at a plurality of states of charge and at a plurality of second temperatures;
At each of the plurality of second temperatures, an SOC change point, which is the state of charge at which the impedance characteristic begins to change in response to a change in the state of charge, and an impedance bottom value, which is the impedance characteristic before the change begins. a second step obtained;
a third step in which the data of the second battery including the relationship between the impedance floor and temperature is obtained;
and a fourth step of storing the data of the second battery. 2. The battery state estimation method according to claim 1, wherein said data of said second battery includes a relationship between said SOC change point and said temperature. 3. The battery state estimation method according to claim 1, wherein the impedance characteristic is reactance. the predetermined frequency is equal to or lower than the first frequency and equal to or higher than the second frequency;
The first frequency is the lowest frequency in a region where the diffusion resistance component is zero in a Cole-Cole plot, which is the frequency characteristic of the complex impedance of the second battery in a predetermined state of charge,
4. The second frequency is a frequency having the same reactance as the first frequency in a region including the diffusion resistance component in the Cole-Cole plot. 2. The battery state estimation method according to item 1. The battery state estimation method according to any one of claims 1 to 4, wherein the predetermined frequency is 10 mHz or more and 500 mHz or less. a step of measuring the impedance characteristics of the assembled battery at a plurality of third temperatures within a narrower range than the plurality of first temperature ranges based on the estimated distribution of the state of charge of the assembled battery; When,
estimating again the distribution of the state of charge of the assembled battery using the impedance characteristics of the assembled battery at the plurality of third temperatures and the data of the second battery. The battery state estimation method according to any one of claims 1 to 5, characterized in that: The battery state estimation method according to any one of claims 1 to 6, wherein 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;
measuring means for measuring impedance characteristics of the assembled battery at a predetermined frequency at a plurality of first temperatures;
The impedance characteristics of a second battery having the same specifications as the first battery, at each of a plurality of second temperatures, before the impedance characteristics at the predetermined frequency start to change according to changes in the state of charge. storage means storing data of the second battery including a relationship between a certain impedance bottom value and the plurality of second temperatures;
computing means for estimating the distribution of the state of charge of the assembled battery from the impedance characteristics of the assembled battery at the plurality of first temperatures and the data of the second battery stored in the storage means; ,
The battery system , wherein the data of the second battery includes a relationship between an SOC change point, which is a state of charge at which the impedance characteristic starts to change according to a change in the state of charge, and the plurality of second temperatures. . an assembled battery in which a plurality of first batteries are connected in series;
measuring means for measuring impedance characteristics of the assembled battery at a predetermined frequency at a plurality of first temperatures;
The impedance characteristics of a second battery having the same specifications as the first battery, at each of a plurality of second temperatures, before the impedance characteristics at the predetermined frequency start to change according to changes in the state of charge. storage means storing data of the second battery including a relationship between a certain impedance bottom value and the plurality of second temperatures;
computing means for estimating the distribution of the state of charge of the assembled battery from the impedance characteristics of the assembled battery at the plurality of first temperatures and the data of the second battery stored in the storage means; ,
the predetermined frequency is equal to or lower than the first frequency and equal to or higher than the second frequency;
The first frequency is the lowest frequency in a region where the diffusion resistance component is zero in a Cole-Cole plot, which is the frequency characteristic of the complex impedance of the second battery in a predetermined state of charge,
The battery system, wherein the second frequency is a frequency having the same reactance as the first frequency in a region including the diffusion resistance component in the Cole-Cole plot. a temperature adjustment device that increases or decreases the temperature of the first battery;
10. The battery system according to claim 8, further comprising a temperature control section that controls the temperature adjustment device.

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