WO2022224682A1 - Battery monitoring device - Google Patents

Abstract

A battery monitoring device (96) monitors a battery pack (93) that includes a serially connected body of a plurality of cell batteries (B). An impedance detection unit (31) of the battery monitoring device detects the impedance (Z) of the plurality of cell batteries when a pack storage amount changes, i.e., when the storage amount of the battery pack changes over time. A storage amount identification unit (32) of the battery monitoring device identifies that the storage amount (Q) of a cell battery has reached a specific storage amount (QL, QU) on the basis of the change (Zdd) in the change trend (Zd) of the detected impedance. A variation computation unit (33) of the battery monitoring device computes the variation (ΔQ) in the storage amount between cell batteries on the basis of the differences, among the cell batteries, in the identification timings (tP, tS) at which the storage amount was identified to have reached the specific storage amount.

Description

battery monitor Cross-reference to related applications

This application is based on Japanese Application No. 2021-071858 filed on April 21, 2021, and the contents thereof are incorporated herein.

The present disclosure relates to a battery monitoring device that monitors a battery pack having a series connection of multiple cell batteries.

Some battery monitoring devices calculate the amount of stored electricity based on the voltage of the cell battery. As a document showing such a technique, there is the following Patent Document 1.

JP 2018-125977 A

　While charging the battery pack or using power, current flows through the internal resistance of the cell battery, so the true voltage of the cell battery, that is, the OCV (open circuit voltage) cannot be detected. Therefore, when the battery pack is being charged or power is being used, it is difficult to calculate the amount of stored electricity based on the voltage of the cell battery.

Furthermore, some cell batteries include a plateau region where voltage changes are small with respect to changes in the amount of charge. In that plateau region, it is even more difficult to calculate the amount of charge based on the cell battery voltage. If it is difficult to calculate the amount of electricity stored in the cell batteries, naturally it is also difficult to calculate the variation in the amount of electricity stored among the cell batteries.

The present disclosure has been made in view of the above circumstances, and is intended to enable calculation of variations in the amount of charge between cell batteries even in situations where it is difficult to calculate the amount of charge based on the voltage of the cell battery. The main purpose is to

The battery monitoring device of the present disclosure monitors a battery pack having a series connection of multiple cell batteries. The battery monitoring device has an impedance detection section, a charged amount identification section, and a variation calculation section.

The impedance detection unit detects the impedance of the plurality of cell batteries when the amount of electricity stored in the battery pack changes over time. The stored electricity amount specifying unit specifies that the stored electricity amount of the cell battery has reached a specific stored electricity amount based on the detected change in the tendency of impedance change. The variation calculation unit calculates the variation in the charged amount between the cell batteries based on the difference in the specified timing at which the charged amount reaches the specified charged amount between the cell batteries. do.

The present disclosure provides the following effects. When the amount of stored electricity in the pack changes, such as when the battery pack is being charged or when electric power is used, the trend of impedance change changes when the amount of stored electricity in each cell battery reaches a specific amount of stored electricity. Therefore, in the present disclosure, it is specified that the charged amount of the cell battery has reached the specified charged amount based on the change in the change trend. Based on the difference in the specific timing, the variation in the amount of charge between the cell batteries is calculated. Therefore, even in a situation where it is difficult to calculate the amount of stored electricity based on the voltage of the cell batteries, the variation in the amount of stored electricity between the cell batteries can be calculated based on the impedance of the cell batteries.

The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description with reference to the accompanying drawings. The drawing is
FIG. 1 is a circuit diagram showing the battery monitoring device of the first embodiment and its periphery; FIG. 2 is a graph showing the waveform of battery current when AC voltage is applied to the battery pack; FIG. 3 is a graph showing the transition of each value as the amount of electricity stored in the cell battery increases. FIG. 4 is a graph showing the transition of each value with the passage of charging time, FIG. 5 is a flowchart showing control during charging, FIG. 6 is a graph showing the transition of each value during charging, FIG. 7 is a graph showing the transition of each value with the passage of discharge time in the second embodiment, FIG. 8 is a flow chart showing control when power is used, FIG. 9 is a flowchart showing control during charging in the third embodiment, FIG. 10 is a flow chart showing control when power is used.

The embodiments of the present disclosure will be described below with reference to the drawings. However, the present disclosure is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the disclosure.

[First embodiment]
FIG. 1 is a circuit diagram showing a battery monitoring device 96 and its surroundings according to this embodiment. An electric vehicle 90 is equipped with a load 91 such as a driving motor and onboard equipment, a battery pack 93 that supplies power to the load 91 , and a battery monitoring device 96 that monitors the battery pack 93 . The electric vehicle 90 may be one without an engine, or may be a plug-in hybrid vehicle or the like with an engine. Hereinafter, "electrically connected" is simply referred to as "connected".

The battery pack 93 has a series connection of cell batteries B. Each cell battery B is an LFP battery (lithium iron phosphate battery). Battery pack 93 is connected to load 91 . When the battery pack 93 is charged, the external power supply 80 is connected to the battery pack 93 . The external power supply 80 performs CC charging (constant current charging) until just before the battery pack 93 is fully charged, and switches to CV charging (constant voltage charging) just before that.

The current flowing through the battery pack 93 is hereinafter referred to as "battery current I". Therefore, the battery current I is also the current flowing through each cell battery B. As shown in FIG. In the following description, the time-integrated value of the battery current I is referred to as "integrated current value∫Idt". The voltage of the cell battery B is called "cell voltage V", and the electric charge (Ah: ampere hour) stored in the cell battery B is called "cell storage amount Q". The cell storage amount Q of the cell battery B with the smallest cell storage amount Q is referred to as "minimum cell storage amount Qmin". Then, the value obtained by subtracting the minimum cell storage amount Qmin from the cell storage amount Q (Q-Qmin) is called "variation amount ΔQ".

Also, hereinafter, the cell storage amount Q at full charge is referred to as "cell storage capacity Qf", and the ratio (Q/Qf) of the cell storage amount Q to the cell storage capacity Qf is referred to as "cell SOC". Note that SOC is an abbreviation for "State Of Charge". The initial (when new) cell storage capacity Qf is called "initial cell storage capacity Qfo", and the ratio of the current cell storage capacity Qf to the initial cell storage capacity Qfo (Qf/Qfo) is called "cell SOH". Note that SOH is an abbreviation for "State Of Health".

Also, hereinafter, the charge stored in the battery pack 93 is referred to as "pack storage amount ΣQ", the pack storage amount ΣQ when fully charged is referred to as "pack storage capacity ΣQf", and the initial (new) pack storage capacity ΣQf is referred to as “initial pack storage capacity ΣQfo”. The ratio of the current pack storage capacity ΣQf to the initial pack storage capacity ΣQfo (ΣQf/ΣQfo) is called “pack SOH”.

Also, hereinafter, the impedance of the cell battery B with respect to alternating current is referred to as "cell impedance Z". The cell impedance Z depends on the resistance, capacitance component, inductor component, etc. existing inside the cell battery B. FIG. A time-differentiated value of the cell impedance Z is called an "impedance change Zd", and a time-differentiated value of the impedance change Zd is called an "impedance twice differentiated Zdd". In other words, the impedance second derivative Zdd indicates a change in the tendency of the cell impedance Z to change.

The battery monitoring device 96 has a current sensor 10, a voltage sensor 20 and a BMU 30. BMU is an abbreviation for "Battery Management Unit". The current sensor 10 measures the battery current I by measuring the current in the wiring to the battery pack 93 . The voltage sensor 20 is connected between both terminals of the battery pack 93 and between each two cell batteries B adjacent in series in the battery pack 93 . That is, the voltage sensor 20 is connected to both terminals of each cell battery B. As shown in FIG. The voltage sensor 20 has a multiplexer and the like, and is configured to be able to measure the voltage of each cell battery B. FIG.

The BMU 30 is an ECU (electronic control unit) having a CPU, a ROM, a RAM, etc. Based on the battery current I measured by the current sensor 10 and the cell voltage V measured by the voltage sensor 20, the battery pack Monitor 93.

Next, with reference to FIGS. 3 and 4, the problems to be solved by this embodiment and the outline of the means for solving them will be described.

FIG. 3(a) is a graph showing the relationship between the cell charge amount Q (horizontal axis) and the cell voltage V (vertical axis). As described above, each cell battery B is an LFP battery. Due to its characteristics, each cell battery B has a plateau region where the change in the cell voltage V (vertical axis) with respect to the change in the cell storage amount Q (horizontal axis) is smaller than a predetermined reference. Hereinafter, the time when the cell charge amount Q is within the plateau region is referred to as the "plateau time", and the time when the cell charge amount Q is outside the plateau range is referred to as the "non-plateau time". During the plateau region, it is difficult to calculate the cell charge amount Q (horizontal axis) based on the cell voltage V (vertical axis). Therefore, it is also difficult to calculate the amount of variation ΔQ.

Therefore, in this embodiment, the amount of variation ΔQ is calculated based on the cell impedance Z during the plateau region. The mechanism will be explained below. Hereinafter, the heat generated in the cell battery B will be referred to as "cell heat generation," the temperature of the cell battery B will be referred to as "cell temperature T," and the cell voltage V differentiated by the cell temperature T will be referred to as "heat generation coefficient dV/dT." .

The cell heat generation is the sum of the Joule heat generated by the battery current I and the reaction heat shown below. The reaction heat is the product (T×I×dV/dT) of the cell temperature T, the battery current I, and the heat generation coefficient dV/dT. Therefore, the greater the heat generation coefficient dV/dT, the greater the cell heat generation.

FIG. 3(b) is a graph showing the relationship between the cell charge amount Q (horizontal axis) and the heat generation coefficient dV/dT (vertical axis). When the cell charge amount Q is within a predetermined high heat generation section (QL to QU), the heat generation coefficient dV/dT increases and the cell heat generation increases. Hereinafter, the storage amount that is the lower limit of the high heat generation section (QL to QU) will be referred to as "section lower limit amount QL", and the storage amount that will be the upper limit of the high heat generation section (QL to QU) will be referred to as "section upper limit amount QU". .

Then, in the cell battery B, which is an LFP battery, the higher the cell temperature T, the smaller the cell impedance Z. Therefore, when the cell charge amount Q is within the high heat generation section (QL to QU), the cell heat generation increases, the cell temperature T increases, and the cell impedance Z decreases significantly.

FIG. 4(a) is a graph showing changes in cell impedance Z during charging of the battery pack 93, and FIG. 4(b) is a graph showing changes in cell storage amount Q during charging. As shown in FIG. 4(b), when charging is started from a state in which the cell battery B is substantially empty, the cell storage amount Q remains in the high heat generation section ( QL to QU), the cell heat generation is small and the cell temperature T rises slowly. Therefore, the decrease in the cell impedance Z shown in FIG. 4(a) is moderate.

After that, as shown in FIG. 4(b), when the cell power storage amount Q reaches the section lower limit amount QL, the cell power storage amount Q enters the high heat generation section (QL to QU), and as shown in FIG. 3(b) The heat generation coefficient dV/dT increases rapidly, and the cell heat generation increases rapidly. As a result, the increase in cell temperature T is rapidly accelerated, and the decrease in cell impedance Z shown in FIG. 4(a) is rapidly accelerated. Hereinafter, the timing at which the decrease in cell impedance Z is rapidly accelerated is referred to as "acceleration timing tP". At the acceleration timing tP, it can be specified that the cell charged amount Q has reached the interval lower limit amount QL shown in FIG. 4(b).

After that, as shown in FIG. 4(b), when the cell storage amount Q reaches the section upper limit amount QU due to charging, the cell storage amount Q escapes from the high heat generation section (QL to QU), ) rapidly decreases. As a result, the cell heat generation is rapidly reduced, and the increase in the cell temperature T is rapidly suppressed, thereby rapidly suppressing the decrease in the cell impedance Z shown in FIG. 4(a). Hereinafter, the timing at which the decrease in cell impedance Z is suddenly suppressed is referred to as "suppression timing tS". At the suppression timing tS, it can be specified that the cell charged amount Q has reached the section upper limit amount QU shown in FIG. 4(b).

Therefore, when the cell storage amount Q is calculated based on, for example, the integrated current value ∫Idt, the error in the cell storage amount Q can be calculated from the timing when the cell storage amount Q reaches the section lower limit amount QL and the section upper limit amount QU. can be reset at any time. That is, the cell charge amount Q can be specified even in the plateau region or the like. Then, the variation amount ΔQ can be calculated based on the specific timing difference between the cell batteries B. FIG.

Hereinafter, the acceleration timing tP and the suppression timing tS are collectively referred to as "specific timing (tP, tS), and the section lower limit amount QL and section upper limit amount QU are collectively referred to as "specific storage amount (QL, QU)." It says.

Next, referring to FIG. 1 again, the configuration for calculating the variation amount ΔQ based on the cell impedance Z described above will be described. As the configuration, the battery monitoring device 96 further has an AC application circuit 40 , and has an impedance detection section 31 , a charged amount identification section 32 and a variation calculation section 33 in the BMU 30 . Further, each cell battery B has graphite in the negative electrode and an olivine structure in the positive electrode. The olivine structure is a crystal structure having a hexagonal close-packed oxygen skeleton.

The reason why the cell battery B has graphite in the negative electrode is that the heat generation coefficient dV/dT becomes significantly large when the cell storage amount Q is within the high heat generation section (QL to QU). On the other hand, the reason why the positive electrode has an olivine structure is that the change in the heat generation coefficient dV/dT at the positive electrode is suppressed. In other words, it is possible to suppress superimposition of the change in the heat generation coefficient dV/dT at the positive electrode as noise on the change in the heat generation coefficient dV/dT at the negative electrode.

One terminal of the AC applying circuit 40 is connected to the positive terminal of the battery pack 93 and the other terminal of the AC applying circuit 40 is connected to the negative terminal of the battery pack 93 . The AC application circuit 40 applies an AC voltage to the battery pack 93 during CC charging (constant current charging) of the battery pack 93 .

FIG. 2 is a graph showing the waveform of battery current I during CC charging. When an AC voltage is applied to the battery pack 93 during CC charging, the AC current is superimposed on the CC current (constant current) that is the charging current. The reason why the AC voltage is applied during the CC charging is that the charging current is constant during the CC charging, so that there is no concern that AC noise due to changes in the charging current will be superimposed on the AC current.

The impedance detection unit 31 shown in FIG. 1 detects each cell impedance Z based on each cell voltage V and battery current I when AC voltage is applied by the AC application circuit 40 during CC charging of the battery pack 93. Calculate. Specifically, for example, a value (AC resistance) obtained by dividing the effective value of the AC component in the cell voltage V by the effective value of the AC component in the battery current I is calculated as the cell impedance Z.

The stored electricity amount identifying unit 32 identifies that the cell stored electricity amount Q has reached a specific stored electricity amount (QL, QU) at a specific timing (tP, tS). Note that in the present embodiment, at least the section upper limit amount QU, which is one of the specific storage amounts (QL, QU), is included in the plateau region.

Specifically, the stored electricity amount identification unit 32 identifies the timing at which the decrease in the detected cell impedance Z is accelerated more than a predetermined standard during CC charging, excluding the start and end times, as the acceleration timing tP. do. More specifically, the acceleration timing tP is determined on condition that the impedance second derivative Zdd has fallen below the negative acceleration determination value ZddP during CC charging excluding the start and end times. At the acceleration timing tP, it is specified that the cell charged amount Q has reached the section lower limit amount QL.

In addition, the stored electricity amount specifying unit 32 specifies the timing at which the decrease in the calculated cell impedance Z is rapidly suppressed by a predetermined reference or more during CC charging, excluding the start and end times, as the suppression timing tS. More specifically, it is determined that it is the suppression timing tS on condition that the impedance second derivative Zdd exceeds the positive suppression determination value ZddS during CC charging except at the start and end. At the suppression timing tS, it is specified that the cell charged amount Q has reached the section upper limit amount QU.

The variation calculation unit 33 calculates, for each cell battery B, the integrated current value ∫Idt after the specific timing (tP, tS) as the variation amount ΔQ. Therefore, specifically, after the promotion timing tP, the integrated current value ∫Idt after the promotion timing tP is calculated as the variation amount ΔQ, and after the suppression timing tS, the integrated current value ∫ after the suppression timing tS is calculated. Idt is calculated as the amount of variation ΔQ. As described above, the variation calculation unit 33 calculates the variation amount ΔQ based on the difference in the specific timings (tP, tS) between the cell batteries B. FIG.

Although the calculation of the amount of variation ΔQ based on the cell impedance Z has been described above, in a non-plateau region and under conditions where the OCV can be measured, the BMU 30 calculates the cell storage amount Q based on the cell voltage V. Then, the amount of variation ΔQ is calculated based on the amount of charge Q of those cells. Since the computation method itself may be a known one, detailed description thereof will be omitted.

Note that in this embodiment, when calculating the amount of variation ΔQ based on the cell impedance Z, the calculation of the amount of variation ΔQ based on the cell voltage V is disabled. However, instead of this, both calculation of the amount of variation ΔQ based on the cell impedance Z and calculation of the amount of variation ΔQ based on the cell voltage V may be attempted.

Next, the utilization of the variation amount ΔQ calculated as above will be explained. The BMU 30 further has an equalization necessity determination section 36 , a failure determination section 37 , and an equalization amount calculation section 38 as a configuration for its utilization.

The equalization necessity determination unit 36 performs an equalization necessity determination for each cell battery B as to whether or not equalization is necessary. In the equalization necessity determination, it is determined that equalization is necessary on the condition that the variation amount ΔQ is larger than a predetermined equalization determination variation amount ΔQE.

At this time, the equalization necessity determining unit 36 sets the equalization determination variation amount ΔQE to be larger when the variation in cell SOH between the cell batteries B is larger than when the variation is smaller than a predetermined reference. . Further, at this time, the equalization necessity determination unit 36 sets the equalization determination variation amount ΔQE smaller when the pack SOH is smaller than when the pack SOH is larger than the predetermined reference. These reasons will be described later.

The failure determination unit 37 performs failure determination as to whether or not the battery pack 93 has failed. In the failure determination, failure is determined on the condition that the variation amount ΔQ is larger than a predetermined failure determination variation amount ΔQX.

At this time, the failure determination unit 37 sets the failure determination variation amount ΔQX larger when the variation in cell SOH between the cell batteries B is larger than when the variation is smaller than a predetermined reference. Further, at this time, the failure determination unit 37 sets the failure determination variation amount ΔQX smaller when the pack SOH is smaller than when the pack SOH is larger than the predetermined reference. These reasons are also mentioned later.

The equalization amount calculation unit 38 calculates the equalization amount for each cell battery B based on the variation amount ΔQ. Specifically, for example, the amount of variation ΔQ itself may be set as the equalization amount, or the amount of variation ΔQ multiplied by a predetermined value less than 1 may be used as the equalization amount, or the amount of variation ΔQ may be set to a predetermined value. may be used as the equalization amount.

Then, the battery monitoring device 96 equalizes the cell power storage amount Q based on the calculated equalization amount. That is, each cell battery B is discharged by the calculated equalization amount. Since the discharge method itself may be a known method, detailed description thereof is omitted.

FIG. 5 is a flowchart showing control by the battery monitoring device 96 during CC charging of the battery pack 93 . This flow is performed for each cell battery B, and is repeatedly performed at predetermined intervals.

First, in S101, the impedance detection unit 31 detects the cell impedance Z. Next, in S102, the stored electricity amount specifying unit 32 determines whether or not the decrease in the cell impedance Z is rapidly accelerated beyond a predetermined standard. If it is determined that the acceleration is rapid (S102: YES), the process proceeds to S103, specifies that the cell charged amount Q has reached the section lower limit amount QL, and then proceeds to S106. At this time, it is preferable to update the calculated value of the cell power storage amount Q itself to the interval lower limit amount QL, but it does not have to be updated. On the other hand, if it is not determined in S102 that the speed is rapidly accelerated (S102: NO), the process proceeds to S104.

In S104, the stored electricity amount specifying unit 32 determines whether or not the decrease in the cell impedance Z is rapidly suppressed by a predetermined standard or more. If it is determined that it is rapidly suppressed (S104: YES), the process proceeds to S105, specifies that the cell charged amount Q has reached the section upper limit amount QU, and then proceeds to S106. At this time, it is preferable to update the calculated value of the cell power storage amount Q itself to the interval upper limit amount QU, but it does not have to be updated. On the other hand, if it is not determined in S104 that it is being suppressed rapidly (S104: NO), the process proceeds to S106.

In S106, the variation calculation unit 33 determines whether or not it has been specified that the cell storage amount Q of each cell battery B has reached the specific storage amount (QL, QU). That is, either specifying that the cell storage amount Q of each cell battery B has reached the section lower limit amount QL or specifying that the cell storage amount Q of each cell battery B has reached the section upper limit amount QU is performed. Determine whether or not it has been achieved. If it is determined that the cell storage amount Q of any of the cell batteries B has not reached the specified storage amount (QL, QU) (S106: NO), the flow ends. On the other hand, if it is determined that the cell storage amount Q has reached the specific storage amount (QL, QU) for each cell battery B (S106: YES), the process proceeds to S107.

In S107, the integrated current value ∫Idt after the specific timing (tP, tS) is calculated as the amount of variation ΔQ.

In the following S108, the equalization necessity determining unit 36 determines whether the variation amount ΔQ is larger than the equalization determination variation amount ΔQE. If it is determined that it is smaller than the equalization determination variation amount ΔQE (S108: NO), the flow proceeds to S109, determines that equalization is unnecessary, and then terminates the flow. On the other hand, when it is determined in S108 that the variation amount ΔQ is larger than the equalization determination variation amount ΔQE (S108: YES), the process proceeds to S110.

At S110, the failure determination unit 37 determines whether or not the variation amount ΔQ is smaller than the failure determination variation amount ΔQX. If it is determined to be larger than the failure determination variation amount ΔQX (S110: NO), the process proceeds to S112, determines that there is a failure, and then terminates the flow. On the other hand, when it is determined in S110 that the variation amount ΔQ is smaller than the failure determination variation amount ΔQX (S110: YES), the process proceeds to S111.

In S111, the equalization amount calculation unit 38 calculates the equalization amount based on the variation amount ΔQ, and the BMU 30 performs equalization based on the equalization amount, and then the flow ends.

FIG. 6 is a graph showing transition of each value during CC charging of the battery pack 93 . Hereinafter, the predetermined timings (t1 to t4) are referred to as "first timing t1", "second timing t2", "third timing t3", and "fourth timing t4" in chronological order.

Here, as shown in FIG. 6(a), it is assumed that CC charging is performed from the first timing t1 to the third timing t3. Then, due to the CC charging, the charge amount Q of each cell changes from outside the plateau region to within the plateau region shown in FIG. It is assumed that the battery pack 93 is charged until it is out of the high heat generation section (QL to QU).

At this time, as shown in FIG. 6B, after the first timing t1 at the start of charging, the cell storage amount Q is outside the plateau region for a while, so the cell voltage V decreases with the passage of time t. growing. However, when the cell charged amount Q approaches the plateau region at the second timing t2, the cell voltage V becomes substantially flat thereafter.

Further, as shown in FIG. 6(c), after the first timing t1 at the start of charging, for a while, the cell charge amount Q is within the high heat generation section (QL to QU), so the cell heat generation becomes noticeable. As a result, the cell impedance Z decreases significantly. However, when the cell storage amount Q reaches the section upper limit amount QU at a predetermined timing (tS(B)), the cell storage amount Q leaves the high heat generation section (QL to QU), and the cell heat generation rapidly decreases. Decrease in cell impedance Z is abruptly suppressed. At this time, as shown in FIG. 6(d), the impedance second derivative Zdd increases momentarily and exceeds the suppression determination value ZddS, so that it is determined to be the suppression timing tS(B).

From this suppression timing tS(B), the calculated variation amount ΔQ increases as shown in FIG. 6(e). This is because the integrated current value ∫Idt after the suppression timing tS(B) increases from the suppression timing tS(B). Then, the increase in the variation amount ΔQ stops when the suppression timing tS(Bmin) of the minimum voltage cell battery Bmin is specified. Thereby, the amount of variation ΔQ is specified.

At this time, as shown in FIG. 6(e), if the variation amount ΔQ is larger than the equalization determination variation amount ΔQE and smaller than the failure determination variation amount ΔQX, at the subsequent fourth timing t4, FIG. Equalization is initiated, as shown in a). As a result, as shown in FIG. 6(e), the amount of variation ΔQ decreases.

The effects of this embodiment are summarized below.

When the battery pack 93 is charged, the impedance change tendency changes when the cell storage amount Q reaches the specific storage amount (QL, QU). Therefore, the impedance detector 31 calculates each cell impedance Z when the battery pack 93 is charged. The stored electricity amount identifying unit 32 identifies that the cell stored electricity amount Q has reached the specific stored electricity amount (QL, QU) based on the second impedance differential Zdd, which is the change in the tendency of change in the cell impedance Z. FIG. Variation calculator 33 calculates variation amount ΔQ based on the difference in specific timing (tP, tS) between cell batteries B. FIG. Therefore, even in a situation where it is difficult to calculate the cell charge amount Q based on the cell voltage V, such as in the plateau region, the variation amount ΔQ can be calculated based on the difference between the specific timings (tP, tS).

Based on the calculated variation amount ΔQ, the equalization necessity determination unit 36 performs equalization necessity determination, the failure determination unit 37 performs failure determination, and the equalization amount calculation unit 38 determines the equalization amount. Calculate. Therefore, even in the plateau region or the like, it is possible to perform equalization necessity determination, failure determination, and equalization amount calculation without any problem.

Further, the variation calculation unit 33 calculates the variation amount ΔQ based on the integrated current value ∫Idt after the specific timing (tP, tS). Therefore, the variation amount ΔQ can be calculated with higher accuracy than when the variation amount ΔQ is calculated simply based on the elapsed time after the specific timing.

Also, the AC application circuit 40 applies AC voltage to the battery pack 93 . Therefore, the AC resistance of the cell battery B can be measured as the cell impedance Z. Furthermore, the AC application circuit 40 applies an AC voltage to the battery pack 93 during CC charging. Therefore, there is no concern that AC noise due to changes in the charging current will be superimposed on the AC current due to the AC voltage. Therefore, the impedance detector 31 can detect the cell impedance Z with high accuracy. Therefore, the acceleration timing tP and the suppression timing tS can be specified with high accuracy, and the variation amount ΔQ can be calculated with high accuracy.

Further, the variation calculation unit 33 not only calculates the variation amount ΔQ based on the cell impedance Z in the plateau region during CC charging, but also in the non-plateau region and when the OCV can be measured. The amount of variation ΔQ is calculated based on. Therefore, the amount of variation ΔQ can be calculated not only during CC charging, but also in the non-plateau region and when the OCV can be measured.

In addition, cell battery B has graphite in the negative electrode. The graphite remarkably increases the heat generation coefficient dV/dT when the cell charge amount Q is within the high heat generation section (QL to QU). Therefore, when the cell storage amount Q enters the high heat generation section (QL to QU), the decrease in the cell impedance Z is accelerated, and when the cell storage amount Q exits the high heat generation section (QL to QU), the cell impedance Z suppression of the decrease in Therefore, in this respect as well, the promotion timing tP and the suppression timing tS can be specified with high accuracy, and the variation amount ΔQ can be calculated with high accuracy.

Moreover, cell battery B has an olivine structure in the positive electrode. The olivine structure suppresses the change in the heat generation coefficient dV/dT at the positive electrode. As a result, it is possible to suppress superimposition of the change in the heat generation coefficient dV/dT at the positive electrode as noise on the change in the heat generation coefficient dV/dT at the negative electrode. Therefore, in this respect as well, the promotion timing tP and the suppression timing tS can be specified with high accuracy, and the variation amount ΔQ can be calculated with high accuracy.

In addition, the equalization necessity determination unit 36 sets the equalization determination variation amount ΔQE larger when the cell SOH variation is larger than when the variation is smaller than the predetermined reference. This is because, if the variation in the cell SOH is large, even if the variation in the cell SOC is not so large, the variation in the cell charged amount Q, that is, the variation amount ΔQ becomes large. In such a situation, if equalization is performed simply based on the fact that the variation amount ΔQ is greater than the equalization determination variation amount ΔQE, even if the variation in the cell power storage amount Q is reduced, the variation in the cell SOC will conversely increase. There may be adverse effects such as increasing the size. In this respect, the equalization necessity determination unit 36 sets the equalization determination variation amount ΔQE larger when the variation in the cell SOH is large, so that it is difficult to determine that equalization is necessary. , can suppress such adverse effects.

In addition, the failure determination unit 37 sets the failure determination variation amount ΔQX larger when the variation in the cell SOH is larger than when the variation is smaller than the predetermined reference. This is because, as described above, if the variation in the cell SOH is large, the variation amount ΔQ, which is the variation in the storage amount Q of the cell, becomes large even if the variation in the cell SOC is not so large. In such a situation, if a failure is determined simply based on the fact that the amount of variation ΔQ is larger than the amount of variation ΔQX in failure determination, there is a problem that a failure is determined even if the variation in the cell SOC is not so large. It can happen. In this respect, the failure determination unit 37 sets the failure determination variation amount ΔQX larger when the variation in the cell SOH is large, so that it is difficult to determine that there is a failure. can be suppressed.

In addition, the equalization necessity determination unit 36 sets the equalization determination variation amount ΔQE to be smaller when the pack SOH is smaller than when the pack SOH is larger than the predetermined reference. This is because when the battery pack 93 deteriorates and the pack SOH (ΣQf/ΣQfo) becomes smaller, the pack power storage capacity ΣQf becomes smaller, and the variation amount ΔQ, which is the variation in the cell power storage amount Q, tends to become smaller. As a result, the amount of variation ΔQ becomes less likely to exceed the amount of variation ΔQE for determination of equalization, which may cause a problem such as making it difficult to determine that equalization is necessary. In this respect, the equalization necessity determination unit 36 sets the equalization determination variation amount ΔQE smaller when the pack SOH is small in this way, so that it is easier to determine that equalization is necessary. It is possible to prevent such adverse effects.

Furthermore, the failure determination unit 37 sets the failure determination variation amount ΔQX smaller when the pack SOH is smaller than when the pack SOH is larger than the predetermined reference. This is because, as described above, when the battery pack 93 deteriorates and the pack SOH (ΣQf/ΣQfo) becomes smaller, the pack storage capacity ΣQf becomes smaller, and thus the variation amount ΔQ, which is the variation in the cell storage amount Q, tends to become smaller. Become. As a result, the amount of variation ΔQ is less likely to exceed the amount of variation ΔQX for failure determination, and a problem may occur such that it is difficult to determine that there is a failure. In this respect, the failure determination unit 37 sets the failure determination variation amount ΔQX smaller when the pack SOH is small as described above. .

[Second embodiment]
Next, a second embodiment will be described. In the following embodiments, the same reference numerals are given to members that are the same as or correspond to those of the previous embodiments. The present embodiment will be described based on the first embodiment, focusing on the differences, and the description of the same or similar parts as those of the first embodiment will be omitted as appropriate.

In this embodiment, the amount of variation ΔQ is calculated based on the cell impedance Z not only during CC charging but also during power use (discharging). The mechanism will be explained below.

FIG. 7(a) is a graph showing the transition of the cell impedance Z when the battery pack 93 is using electric power, and FIG. 7(b) is a graph showing the transition of the cell storage amount Q when the electric power is being used. As shown in FIG. 7(b), when the use of electric power is started from the state where the cell battery B is substantially fully charged, the cell storage amount Q remains high until the cell storage amount Q decreases to the section upper limit amount QU. Since it is outside the heat generation section (QL-QU), the cell heat generation is small. Therefore, the decrease in the cell impedance Z shown in FIG. 7(a) is moderate.

After that, as shown in FIG. 7B, when the cell storage amount Q decreases to the section upper limit amount QU due to the use of electric power, the cell storage amount Q enters the high heat generation section (QL to QU), and the heat generation coefficient dV /dT increases rapidly, and the cell heat generation increases rapidly. As a result, the increase in cell temperature T is rapidly accelerated, and the decrease in cell impedance Z shown in FIG. 7(a) is rapidly accelerated. At the acceleration timing tP, it can be specified that the cell charged amount Q has reached the section upper limit amount QU shown in FIG. 7(b). Therefore, during the above-described charging, it can be determined that the cell storage amount Q has reached the section lower limit amount QL at the acceleration timing tP, whereas during power use, the cell storage amount Q has reached the section upper limit amount QU at the acceleration timing tP. It is different in that it can be specified that it has become.

After that, as shown in FIG. 7(b), when the cell storage amount Q decreases to the section lower limit amount QL due to the use of electric power, the cell storage amount Q exits the high heat generation section (QL to QU), and the heat generation coefficient dV/dT drops sharply and cell heat generation drops sharply. As a result, the increase in cell temperature T is abruptly suppressed, and the decrease in cell impedance Z shown in FIG. 7(a) is abruptly suppressed. At the suppression timing tS, it can be specified that the cell charged amount Q has reached the interval lower limit amount QL shown in FIG. 7(b). Therefore, during the above-described charging, it can be specified that the cell storage amount Q reaches the section upper limit amount QU at the suppression timing tS, whereas during power use, the cell storage amount Q reaches the section lower limit amount QL at the suppression timing tS. It is different in that it can be identified as

Therefore, the error in the cell storage amount Q can be reset at the timing when the cell storage amount Q decreases to the section upper limit amount QU and the timing when it decreases to the section lower limit amount QL. That is, the cell charge amount Q can be specified even in the plateau region or the like. Then, the variation amount ΔQ can be calculated based on the specific timing difference between the cell batteries B. FIG.

Next, referring to FIG. 1, which is the same as in the first embodiment, the configuration for calculating the amount of variation ΔQ when using electric power will be described.

The AC application circuit 40 applies AC voltage to the battery pack 93 not only during CC charging but also during power usage. The impedance detector 31 calculates the cell impedance Z for each cell battery B based on the cell voltage V and the battery current I when an AC voltage is applied while power is being used.

The stored electricity amount specifying unit 32 specifies the timing at which the decrease in the detected cell impedance Z is accelerated abruptly by a predetermined standard or more in a state where the power usage is stable by a predetermined standard or more as the promotion timing tP. More specifically, it is determined that it is the promotion timing tP on the condition that the impedance second derivative Zdd has fallen below the negative acceleration determination value ZddP in a state where the power consumption is stable at a predetermined reference or more. At the acceleration timing tP, it is specified that the cell charged amount Q has reached the section upper limit amount QU.

In addition, the stored electricity amount specifying unit 32 specifies the timing at which the decrease in the detected cell impedance Z is rapidly suppressed by a predetermined standard or more in a state where the power usage is stable by a predetermined standard or more as the suppression timing tS. . More specifically, it is determined that it is the suppression timing tS on the condition that the impedance second derivative Zdd exceeds the positive suppression determination value ZddS in a state where the power consumption is stable at a predetermined reference or more. At the suppression timing tS, it is specified that the cell charged amount Q has reached the section lower limit amount QL.

FIG. 8 is a flowchart showing control by the battery monitoring device 96 when the power of the battery pack 93 is used. This flow is performed for each cell battery B, and is repeatedly performed at predetermined intervals. In this flow, compared with the flow for CC charging shown in FIG. However, it is different in that it specifies that the interval lower limit amount QL has been reached instead of the interval upper limit amount QU.

Specifically, first, in S201, the cell impedance Z is calculated. Next, in S202, if it is determined that the decrease in cell impedance Z has been accelerated more rapidly than a predetermined standard (S202: YES), proceed to S203 to specify that the cell charged amount Q has reached the section upper limit amount QU. , the process proceeds to S206. On the other hand, if it is not determined in S202 that the speed is rapidly accelerated (S202: NO), the process proceeds to S204.

If it is determined in S204 that the decrease in the cell impedance Z is rapidly suppressed by a predetermined criterion or more (S204: YES), the process proceeds to S205, where it is specified that the cell charged amount Q has reached the section lower limit amount QL. , S206. On the other hand, if it is determined not to be abruptly suppressed in S204 (S204: NO), the process proceeds to S206. S206 to S212 are the same as S106 to S112 in the CC charging flow shown in FIG.

According to this embodiment, the amount of variation ΔQ can be calculated based on the cell impedance Z not only during charging but also during power usage.

[Third embodiment]
Next, a third embodiment will be described. This embodiment will be described based on the second embodiment, focusing on the points that differ from it, and the description of the same or similar parts as those of the second embodiment will be omitted as appropriate.

FIG. 9 is a flowchart showing control of the battery monitoring device 96 during CC charging of the battery pack 93 . The flowchart of FIG. 9 differs from the flowchart of FIG. 5 only in S106. That is, in S106 of the first and second embodiments, the process proceeds to S107 on the condition that the cell storage amount Q of each cell battery B has reached the specific storage amount (QL, QU). On the other hand, in S106 of the present embodiment, even if there is a cell battery B that cannot be specified that the cell storage amount Q has reached the specific storage amount (QL, QU), if the predetermined time has passed, the process proceeds to the next step S107. .

Hereinafter, a cell battery B that can be specified that the cell storage amount Q has reached the specified storage amount (QL, QU) will be referred to as an "identifiable cell battery B", and the cell storage amount Q will be the specified storage amount (QL, QU ), the cell battery B that cannot be specified is referred to as an “unspecified cell battery B”. Among the identifiable cell batteries B, the amount of variation ΔQ of the one with the largest amount of variation ΔQ is referred to as the “maximum identifiable amount of variation ΔQ”.

In the calculation of the variation amount ΔQ in S107, the variation amount ΔQ of the unidentifiable cell battery B is determined to be equal to or greater than the identifiable maximum variation amount ΔQ. This is because, for the unidentifiable cell battery B, it is considered that the cell storage amount Q had already exceeded the specific storage amount (QL, QU) at the start of CC charging. Specifically, in this case, for example, the variation amount ΔQ of the unidentifiable cell battery B is set to be the same as the maximum identifiable variation amount ΔQ. According to this, in the equalization in S111, the equalization amount of the unidentifiable cell battery B is set to be the same as the equalization amount of the cell battery B related to the maximum identifiable variation amount ΔQ.

FIG. 10 is a flowchart showing control of the battery monitoring device 96 when the power of the battery pack 93 is used. The flowchart of FIG. 10 differs from the flowchart of FIG. 8 only in S206. That is, in S206 of the second embodiment, the process proceeds to the next S207 on the condition that the cell storage amount Q of each cell battery B has been identified as the specific storage amount (QL, QU). On the other hand, in S206 of the present embodiment, even if there is a cell battery B that cannot be specified that the cell storage amount Q has reached the specific storage amount (QL, QU), if the predetermined time has passed, the process proceeds to the next step S207. .

In the calculation of the variation amount ΔQ in S207, the variation amount ΔQ of the unidentifiable cell battery B is determined to be zero or less. This is because, for the unidentifiable cell battery B, it is conceivable that the cell storage amount Q had already fallen below the specific storage amount (QL, QU) at the start of power use. Therefore, it is considered that the cell storage amount Q of the unidentifiable cell battery B is equal to or less than the calculated minimum cell storage amount Qmin. Specifically, in this case, for example, the variation amount ΔQ of the unidentifiable cell battery B is set to zero. Accordingly, in the equalization necessity determination in S209, it is determined that the unidentifiable cell battery B does not require equalization (S210).

As described above, according to the present embodiment, even when there is a cell battery B for which it cannot be specified that the cell storage amount Q has reached the specific storage amount (QL, QU), the variation amount ΔQ can be calculated.

[Other embodiments]
For example, the embodiment shown above can be modified as follows.

In the first to third embodiments, the cell battery B is an LFP battery, but instead of this, it may be a battery with a plateau region or a battery without a plateau region. That is, even if the cell battery B does not have a plateau region, the OCV cannot be obtained during charging or while power is being used. difficult to calculate. Therefore, even if the cell battery B does not have a plateau region, the variation amount ΔQ can be calculated based on the cell impedance Z when it is difficult to calculate the cell storage amount Q based on the cell voltage V. plays.

In the first to third embodiments, the region in which the change in the cell voltage V with respect to the change in the cell storage amount Q is smaller than a predetermined reference is defined as the "plateau region," and the state in which the cell storage amount Q is within the plateau region is defined as the "plateau region." in the plateau region." Alternatively, the time when the cell voltage V is within a predetermined range or the time when the cell charge amount Q is within a predetermined range may be defined as the "plateau region time".

In the first to third embodiments, "impedance change Zd" is obtained by differentiating the cell impedance Z with time, and "impedance twice differentiated Zdd" is obtained by further differentiating the impedance change Zd with time. Alternatively, the cell impedance Z may be differentiated by the current integrated value ∫Idt to be the “impedance change Zd”, and the impedance change Zd may be further differentiated by the current integrated value ∫Idt to be the “impedance twice differentiated Zdd”. . According to this aspect, the acceleration timing tP and the suppression timing tS can be determined with high accuracy even under a situation where the current is not constant.

In the first to third embodiments, the stored charge (Ah: ampere-hour) stored in the cell battery B is defined as the "cell storage amount Q". Alternatively, the stored energy (Wh: Watt-hour) stored in the cell battery B may be used as the "cell storage amount". In that case, the variation calculation unit 33 uses the integrated power value (Wh) to calculate the variation amount in terms of energy (Wh ) should be calculated. The power integrated value is a time integrated value of the product of the cell voltage V and the battery current I.

In this case, the cell impedance Z may be differentiated by the integrated power value as "impedance change Zd", and the impedance change Zd may be further differentiated by the integrated power value as "impedance twice differential Zdd". According to this aspect, it is possible to specify the promotion timing tP and the suppression timing tS with high accuracy even in a situation where the electric power is not constant.

In the first to third embodiments, the battery monitoring device 96 has the equalization necessity determination unit 36, the failure determination unit 37, and the equalization amount calculation unit . Alternatively, battery monitor 96 may have only any two of these three, only any one, or none. good too.

In the first to third embodiments, equalization is performed by discharging each cell battery B based on the minimum cell storage amount Qmin. Alternatively, the equalization may be performed by charging the cell battery B having a relatively low cell storage amount Q with the electric power of the cell battery B having a relatively high cell storage amount Q. FIG.

In the first to third embodiments, the variation calculator 33 calculates the variation amount ΔQ based on the integrated current value ∫Idt after the specific timing (tP, tS). Alternatively, for example, during CC charging, the variation amount ΔQ may be calculated simply based on the time t after the specific timing (tP, tS).

In the first to third embodiments, the battery monitoring device 96 has the AC application circuit 40. Instead of this, for example, by turning on and off the discharge switch for each cell battery B, a specific current change for each cell battery B may be generated. Then, the impedance (AC resistance) of the cell battery B at that time may be detected as the cell impedance Z.

In the first to third embodiments, the impedance of the cell battery B with respect to alternating current is defined as "cell impedance Z". Alternatively, the impedance of the cell battery B with respect to direct current may be defined as "cell impedance Z".

In the first and second embodiments, the external power supply 80 performs CC charging and CV charging, and the AC applying circuit 40 applies AC voltage to the battery pack 93 during CC charging. Alternatively, for example, the external power supply 80 may be configured to perform CP charging (constant power charging) and CV charging, and the AC application circuit 40 may be configured to apply an AC voltage to the battery pack 93 during CP charging. may

In the first to third embodiments, in addition to calculating the amount of variation ΔQ based on the cell impedance Z, when the OCV is measurable in the non-plateau region, the amount of variation ΔQ is also calculated based on the cell voltage V. calculating. Instead of this, the amount of variation ΔQ may be calculated based only on the cell impedance Z.

In the first embodiment, the calculation of the variation amount ΔQ based on the cell impedance Z is performed only during CC charging, and in the second embodiment, it is performed both during CC charging and during power use. Instead of these, the calculation of the amount of variation ΔQ based on the cell impedance Z may be performed only while power is being used. Further, in the third embodiment, the calculation of the amount of variation ΔQ based on the cell impedance Z is performed both during CC charging and during power use. Alternatively, it may be performed only during CC charging or during power use.

In the first to third embodiments, the equalization determination variation amount ΔQE and the failure determination variation amount ΔQX are set larger when the cell SOH variation is large. Alternatively, even if the cells SOH have different variations, the equalization determination variation amount ΔQE and the failure determination variation amount ΔQX may be set to be the same.

In the first to third embodiments, when the pack SOH is small, the equalization determination variation amount ΔQE and the failure determination variation amount ΔQX are set smaller. Alternatively, even if the pack SOH is different, the equalization determination variation amount ΔQE and the failure determination variation amount ΔQX may be set to be the same.

Although the present disclosure has been described with reference to examples, it is understood that the present disclosure is not limited to those examples or structures. The present disclosure also includes various modifications and modifications within the equivalent range. In addition, various combinations and configurations, as well as other combinations and configurations, including single elements, more, or less, are within the scope and spirit of this disclosure.

Claims (15)

1. In a battery monitoring device (96) that monitors a battery pack (93) having a series connection of a plurality of cell batteries (B),
   an impedance detection unit (31) for detecting the impedance (Z) of the plurality of cell batteries when the amount of stored electricity in the battery pack changes with the passage of time;
   Based on the detected change (Zdd) of the change tendency (Zd) of the impedance of the cell battery, a storage amount specifying that the storage amount (Q) of the cell battery has reached a specific storage amount (QL, QU) a part (32);
   Variation in the charged amount (Q) between the cell batteries based on the difference in specific timing (tP, tS) at which the charged amount reaches the specified charged amount between the cell batteries. a variation calculator (33) for calculating (ΔQ);
   a battery monitor.
2. The battery monitoring device according to claim 1, comprising an equalization necessity determination unit (36) that determines whether or not to perform equalization for reducing the variation based on the calculated variation.
3. The battery monitoring device according to claim 1 or 2, comprising a failure determination unit (37) that determines whether or not the battery pack has failed based on the calculated variation.
4. Claims 1 to 3, comprising an equalization amount calculation unit (38) for calculating an equalization amount, which is an amount by which the variation is reduced in the equalization for reducing the variation, based on the calculated variation. The battery monitoring device according to any one of 1.
5. The variation calculation unit according to any one of claims 1 to 4, wherein the variation calculation unit calculates the variation based on an integrated value (∫Idt) of current (I) or power of the cell battery after a specific timing. Battery monitor.
6. The impedance includes AC resistance,
   Having an AC application circuit (40) for applying an AC voltage to the battery pack,
   The battery monitoring device according to any one of claims 1 to 5, wherein said impedance detector detects the impedance of said cell battery when said AC voltage is applied to said battery pack.
7. When the change in the voltage of the cell battery with respect to the change in the charge amount of the cell battery is in a plateau region smaller than a predetermined reference, the charge amount specifying unit determines the charge amount of the cell battery based on the change in the impedance change tendency. Identifying that the specific storage amount has been reached, calculating the variation by the variation calculation unit,
   The battery monitoring device according to any one of claims 1 to 6, wherein the variation is calculated by calculating the charge amount of the cell battery based on the voltage of the cell battery at a time other than the plateau region.
8. The battery monitoring device according to any one of claims 1 to 7, wherein the cell battery has graphite in the negative electrode.
9. The battery monitoring device according to any one of claims 1 to 8, wherein the cell battery has an olivine structure on the positive electrode.
10. Equalization necessity determination unit ( 36),
    Let SOH be the ratio of the current storage capacity to the initial storage capacity,
    The equalization necessity determination unit sets the equalization determination variation amount to be larger when the variation in the SOH of the cell batteries among the cell batteries is greater than when the variation is smaller than a predetermined reference. ,
    The battery monitoring device according to any one of claims 1-9.
11. a failure judgment unit (37) for judging that the battery pack is out of order on condition that a variation amount (ΔQ) indicating the magnitude of the variation is larger than a failure determination variation amount (ΔQX);
    Let SOH be the ratio of the current storage capacity to the initial storage capacity,
    The failure determination unit sets the failure determination variation amount to be larger when the variation in the SOH of the cell batteries among the cell batteries is larger than when the variation is smaller than a predetermined standard.
    The battery monitoring device according to any one of claims 1-10.
12. Equalization necessity determination unit ( 36),
    Let SOH be the ratio of the current storage capacity to the initial storage capacity,
    The equalization necessity determination unit sets the equalization determination variation amount to be smaller when the SOH of the battery pack is smaller than when the SOH is greater than a predetermined reference,
    The battery monitoring device according to any one of claims 1-11.
13. a failure judgment unit (37) for judging that the battery pack is out of order on condition that a variation amount (ΔQ) indicating the magnitude of the variation is larger than a failure determination variation amount (ΔQX);
    Let SOH be the ratio of the current storage capacity to the initial storage capacity,
    The failure determination unit sets the failure determination variation amount to be smaller when the SOH of the battery pack is smaller than when the SOH is greater than a predetermined reference.
    The battery monitoring device according to any one of claims 1-12.
14. For each cell battery, the amount of charge of the cell battery with the smallest amount of charge is subtracted from the amount of charge of the cell battery, and the amount of variation (ΔQ) of the cell battery is
    When the battery pack is charged and there is a cell battery that is not identified as having a storage amount equal to the specific storage amount, the variation calculation unit calculates the variation amount of the cell battery according to the calculated variation amount. 14. The battery monitoring device according to any one of claims 1 to 13, wherein the calculation is performed to be equal to or greater than the maximum variation of the cell battery.
15. For each cell battery, the amount of charge of the cell battery with the smallest amount of charge is subtracted from the amount of charge of the cell battery, and the amount of variation (ΔQ) of the cell battery is
    The variation calculation unit calculates the variation amount of the cell battery to be zero or less if there is a cell battery that is not identified as having a storage amount of the specific storage amount when the battery pack is discharged. 15. The battery monitoring device according to any one of 1 to 14.

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