WO2022224681A1

WO2022224681A1 - Battery monitoring device and electric vehicle having same installed therein

Info

Publication number: WO2022224681A1
Application number: PCT/JP2022/013586
Authority: WO
Inventors: 正規内山; 大祐倉知; 裕基堀
Original assignee: 株式会社デンソー
Priority date: 2021-04-21
Filing date: 2022-03-23
Publication date: 2022-10-27
Also published as: JP2022166578A

Abstract

A battery monitoring device (96) monitors a battery pack (93) which has a series-connected body comprising a plurality of battery cells (B). An impedance detection unit (31) of the battery monitoring device detects the impedance (Z) of the plurality of battery cells at the pack power storage amount change time at which the power storage amount (Q) in the battery pack changes over time. A cell power storage amount calculation unit (33) of the battery monitoring device calculates the power storage amount (Q) of the battery cells on the basis of a change (Zdd) in the change trend (Zd) of the detected impedance. A pack power storage amount calculation unit (34) of the battery monitoring device calculates the battery pack power storage amount (ΣQ) on the basis of the calculated power storage amount in the battery cells.

Description

Battery monitoring device and electric vehicle equipped with it

Cross-reference to related applications

This application is based on Japanese Application No. 2021-071859 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 charge in the cell battery based on the voltage of the cell battery. As a document showing such a technique, there is the following Patent Document 1.

JP 2013-44734 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 charge in the cell battery 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 more difficult to calculate the amount of charge in the cell based on the voltage of the cell. If it is difficult to calculate the amount of electricity stored in a cell battery, it is of course difficult to calculate the amount of electricity stored in a battery pack having a plurality of such cell batteries.

The present disclosure has been made in view of the above circumstances, and it is an object of the present invention to enable calculation of the amount of charge in a battery pack even under circumstances in which it is difficult to calculate the amount of charge in a cell battery based on the voltage of the cell battery. is the main purpose.

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 cell storage amount calculation section, and a pack storage amount 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 cell storage amount calculation unit calculates the storage amount of the cell battery based on the detected change in the change tendency of the impedance. The pack power storage amount calculation unit calculates the power storage amount of the battery pack based on the calculated power storage amount of the cell battery.

According to the present disclosure, the following effects can be obtained. When the amount of electricity stored in the pack changes, such as when the battery pack is being charged or when electricity is being used, the tendency of the impedance changes in each cell battery according to the amount of electricity stored at that time. Therefore, in the present disclosure, the power storage amount of the battery cell is calculated based on the change in the change tendency. Based on the amount of electricity stored in the cell battery, the amount of electricity stored in the battery pack is calculated. Therefore, even in situations where it is difficult to calculate the amount of power stored in the cell battery based on the voltage of the cell battery, the amount of power stored in the cell battery can be calculated based on the impedance of the cell battery to calculate the amount of power stored in the battery pack. be able to.

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 by the battery monitoring device, FIG. 6 is a graph showing the transition of each value before and after charging, FIG. 7 is a graph showing the transition of each value from the time of charging to the time of starting the vehicle, and before and after that. FIG. 8 is a graph showing the transition of each value with the passage of discharge time in the second embodiment, FIG. 9 is a flow chart showing control by the battery monitoring device.

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 running motor and onboard electrical 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".

Also, hereinafter, the dischargeable charge (Ah) stored in the battery pack 93 is referred to as "pack storage amount ΣQ". The pack charge amount ΣQ corresponds to the minimum cell charge amount Qmin. Further, hereinafter, the pack power storage amount ΣQ at the time of full charge is referred to as “pack power storage capacity ΣQf”.

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 problem to be solved by this embodiment and the outline of the means for solving the problem 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, naturally, it is also difficult to calculate the pack charge amount ΣQ based on these cell charge amounts Q.

Therefore, in the present embodiment, in the plateau region, the cell storage amount Q is calculated based on the cell impedance Z, and the pack storage amount ΣQ is calculated based on the cell storage amount Q. 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 differentiation of the cell voltage V with respect to the cell temperature T will be referred to as "heat generation coefficient dV/dT". It says.

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". The cell charge amount Q at the acceleration timing tP can be identified as 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". The cell charge amount Q at the suppression timing tS can be identified as the interval 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 calculated even in the plateau region or the like. Based on these cell storage amounts Q, the pack storage amount ΣQ can be calculated.

Next, referring to FIG. 1 again, the configuration for calculating the pack charge amount ΣQ based on the cell impedance Z described above will be described. As the configuration, the battery monitoring device 96 further includes an AC application circuit 40, and an impedance detection unit 31, a base charge amount specifying unit 32, a cell charge amount calculation unit 33, and a pack charge amount calculation unit 34 in the BMU 30. have. 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.

During CC charging, the base storage amount specifying unit 32 specifies (updates) the base storage amount Qb, which is the basis for calculating the cell storage amount Q, to the section lower limit amount QL at the promotion timing tP, and also specifies (updates) the interval lower limit amount QL at the suppression timing tS. to identify (update) the interval upper limit quantity QU. The interval lower limit amount QL and the interval upper limit amount QU are preferably obtained in advance by experiments, simulations, or the like. In this embodiment, at least the interval upper limit QU is included in the plateau region.

Specifically, the base charged amount specifying unit 32 designates the timing at which the decrease in the calculated cell impedance Z is rapidly accelerated by a predetermined reference or more during CC charging excluding the start and end times as the acceleration timing tP. Identify. 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, as described above, the base charge amount Qb is updated to the interval lower limit amount QL.

In addition, the base storage 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 of charging, 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, as described above, the base storage amount Qb is updated to the section upper limit amount QU.

In addition, the BMU 30 calculates the cell storage amount Q based on the cell voltage V in a non-plateau region and under conditions where the OCV (open circuit voltage) can be measured. Note that the method itself for calculating the cell charge amount Q based on such cell voltage V may be a known method, and therefore detailed description thereof will be omitted.

Then, when the cell power storage amount Q is calculated based on the cell voltage V in this way, the base power storage amount specifying unit 32 updates the base power storage amount Qb to the calculated cell power storage amount Q. Hereinafter, the timing at which the cell voltage V is measured in this way will be referred to as "voltage measurement timing tV", and the cell storage amount Q calculated based on the cell voltage V will be referred to as "the storage amount Qv based on the cell voltage V". . Therefore, the base storage amount specifying unit 32 updates the base storage amount Qb to the storage amount Qv based on the cell voltage V at the voltage measurement timing tV.

The cell storage amount calculation unit 33 calculates the sum (Qb+∫Idt) of the base storage amount Qb and the current integrated value ∫Idt as the current cell storage amount Q. Here, the cell storage amount calculator 33 resets the integrated current value ∫Idt to zero when the base storage amount Qb is updated. Therefore, the cell storage amount calculator 33 calculates the current cell storage amount Q by adding the current integrated value ∫Idt after the timing at which the base storage amount Qb is updated to the base storage amount Qb.

Specifically, after the acceleration timing tP during CC charging, the cell storage amount calculation unit 33 adds the current integrated value ∫Idt after the acceleration timing tP to the interval lower limit amount QL, thereby Compute the quantity Q. Then, after the suppression timing tS during CC charging, the current cell storage amount Q is calculated by adding the current integrated value ∫Idt after the suppression timing tS to the section upper limit amount QU. After the voltage measurement timing tV, the current cell storage amount Q is calculated by adding the current integrated value ∫Idt after the voltage measurement timing tV to the storage amount Qv based on the cell voltage V.

The pack power storage amount calculation unit 34 calculates the minimum cell power storage amount Qmin, which is the minimum value of the calculated cell power storage amounts Q, as the pack power storage amount ΣQ.

Next, utilization of the pack power storage amount ΣQ calculated as described above will be described. BMU 30 further has a remaining charge time calculation unit 36 , a power failure determination unit 37 , and a battery failure determination unit 38 , and electric vehicle 90 further has a cruising range calculation unit 97 as a configuration for utilization thereof.

Using the calculated pack storage amount ΣQ, the remaining charge time calculation unit 36 calculates the remaining charge time, which is the time required to charge the battery pack 93 until the pack storage amount ΣQ reaches the pack storage capacity ΣQf. . Therefore, the larger the difference (ΣQf−ΣQ) between the pack power storage capacity ΣQf and the pack power storage amount ΣQ, the larger the remaining charging time is estimated.

The electricity shortage determination unit 37 determines whether or not there is a shortage of electric power using the calculated pack power storage amount ΣQ. Specifically, it is determined that the electric power is insufficient, for example, on the condition that the pack charged amount ΣQ is smaller than a predetermined value.

The battery failure determination unit 38 determines whether or not the battery pack 93 has failed using the calculated pack charge amount ΣQ. Specifically, for example, on the condition that the pack charged amount ΣQ is smaller than a predetermined lower limit threshold, an overdischarge failure is determined, and on the condition that the pack charged amount ΣQ is larger than a predetermined upper threshold, an overcharge failure is determined. I judge.

The cruising range calculation unit 97 calculates the cruising range as the distance that the electric vehicle 90 can travel, using the calculated pack power storage amount ΣQ. Therefore, the larger the pack power storage amount ΣQ, the larger the estimated cruising range. Specifically, the cruising range may be calculated from the pack power storage amount ΣQ and the power consumption at that time, or may be calculated using the power consumption as a predetermined value.

FIG. 5 is a flowchart showing control by the battery monitoring device 96. FIG. This flow is repeated, for example, at predetermined intervals.

First, in S101, it is determined whether or not it is in the non-plateau region and the OCV can be measured. Whether or not it is in the non-plateau region may be determined, for example, based on whether the cell voltage V or the cell storage amount Q (calculated value) is within a predetermined range, or the most recent cell storage amount Q ( The determination may be made based on whether the time change of the cell voltage V with respect to the time change of the calculated value) is smaller than a predetermined value. Whether or not the OCV can be measured can be determined, for example, based on whether or not a predetermined time or more has elapsed since the end of charging or the end of discharging.

If it is determined in S101 that the vehicle is in the plateau region or that the OCV cannot be measured (S101: NO), proceed to S102 to determine whether CC charging is in progress. Whether or not CC charging is being performed can be determined, for example, based on whether or not the remaining charging time is equal to or longer than a predetermined value. When it is determined in S102 that CC charging is in progress (S102: YES), the process proceeds to S201. The flow from S201 to S403 described later is performed for each cell battery B.

In S201, the cell impedance Z is detected by the impedance detection unit 31. Next, in S202, the base charged 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 rapidly accelerated (S202: YES), the process proceeds to S203, updates the base charge amount Qb to the interval lower limit amount QL, and then proceeds to S401.

On the other hand, in retroactive S203, if it is not determined that the decrease in cell impedance Z has rapidly accelerated beyond the predetermined standard (S202: NO), proceed to S204. In S204, similarly, the base charged 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 (S204: YES), the process proceeds to S205, updates the base charged amount Qb to the section upper limit amount QU, and then proceeds to S401.

On the other hand, if it is not determined in S204 that the decrease in cell impedance Z has been suppressed abruptly by the predetermined criterion or more (S204: NO), the process proceeds to S402, and the cell storage amount calculation unit 33 updates the integrated current value ∫Idt. do. Specifically, by adding the time integrated value of the battery current I from S401 in the previous flow to S401 in the current flow to the previous integrated current value ∫Idt, the current integrated value ∫ Update Idt. Then, the process proceeds to S403.

On the other hand, in retroactive S101, if it is determined that it is in the non-plateau region and the OCV can be measured, the process proceeds to S301. The flow from S301 to S403 described later is performed for each cell battery B. In S<b>301 , the cell voltage V is measured by the voltage sensor 20 . In subsequent S302, the BMU 30 calculates the amount of stored electricity Qv based on the cell voltage V. FIG. In subsequent S303, the base charged amount specifying unit 32 updates the base charged amount Qb to the charged amount Qv based on the cell voltage V, and the process proceeds to S401.

In S401, the cell power storage amount calculator 33 resets the integrated current value ∫Idt to zero, and then proceeds to S403. In S403, the cell storage amount calculator 33 calculates the sum of the base storage amount Qb and the integrated current value ∫Idt (Qb+∫Idt) as the cell storage amount Q.

In subsequent S404, the pack power storage amount calculation unit 34 calculates the minimum cell power storage amount Qmin, which is the minimum value of the cell power storage amounts Q calculated in S403, as the pack power storage amount ΣQ. proceed to

In S501, the remaining charging time calculation unit 36 calculates the remaining charging time. In S502, the power failure determination unit 37 determines whether or not the power is insufficient. In S503, the battery failure determination unit 38 determines whether or not there is a battery failure. In S504, the cruising distance calculation unit 97 calculates the cruising distance. The flow ends when these S501 to S504 are completed.

FIG. 6 is a time chart showing changes in values before and after CC charging. Here, as shown in FIG. 6A, a case is shown in which the battery pack 93 is CC-charged between a predetermined first timing t1 and a second timing t2. This CC charging is performed until the cell storage amount Q is greater than or equal to the section lower limit amount QL and less than or equal to the section upper limit amount QU, that is, from the state of the high heat generation section (QL to QU) to the cell storage amount Q becoming larger than the section upper limit amount QU. shall be implemented.

At this time, as shown in FIG. 6B, for a while from the first timing t1 when CC charging is started, the cell charge amount Q is within the high heat generation section (QL to QU) and the heat generation coefficient dV/ Due to the large dT, the cell impedance Z is significantly reduced.

After that, when the cell charge amount Q reaches the section upper limit amount QU at a predetermined timing (tS(B)), the cell charge amount Q exits the high heat generation section (QL to QU), and the heat generation coefficient dV/dT changes. Then, as shown in FIG. 6(b), the decrease in cell impedance Z is rapidly suppressed. At this time, as shown in FIG. 6(c), the impedance second derivative Zdd suddenly increases for a moment and exceeds the positive suppression determination value ZddS. As a result, it is determined that it is the suppression timing tS(B), the base storage amount Qb is updated to the interval upper limit amount QU, and the integrated current value ∫Idt is reset as shown in FIG. 6(d).

When the minimum cell charge amount Qmin (calculated value) changes due to the update and reset at the suppression timing tS(B), the pack charge amount ΣQ=Qmin (calculated value) also changes as shown in FIG. 6(e). change to After that, when the cell storage amount Q of another cell battery B reaches the section upper limit QU, the base storage amount Qb of that cell battery B is updated to the section upper limit QU, and the integrated current value ∫Idt is reset. . Also at this timing, when the minimum cell charged amount Qmin (calculated value) changes, the pack charged amount ΣQ=Qmin (calculated value) similarly changes. As described above, each time any cell storage amount Q reaches the section upper limit QU and the base storage amount Qb is updated and the current integrated value ∫Idt is reset, the calculated value of the pack storage amount ΣQ becomes the true value ( Qmin).

FIG. 7 is a time chart showing transition of each value during CC charging, subsequent running of the electric vehicle 90, subsequent activation of the electric vehicle 90, and before and after these times. As shown in 7th (a), it is assumed that CC charging is performed between the first timing t1 and the second timing t2 as described above. Then, it is assumed that the electric vehicle 90 travels from the second timing t2 to the subsequent third timing t3, and the electric vehicle 90 stops from the third timing t3 to the subsequent fourth timing t4. Then, it is assumed that the electric vehicle 90 starts up between the fourth timing t4 and the subsequent fifth timing t5, and the electric vehicle 90 runs again between the fifth timing t5 and the subsequent sixth timing t6. do.

As shown in FIG. 7(a), the battery current I flows in the discharge direction (negative direction in the graph) while the vehicle is running (t2 to t3). Due to the discharge, the cell storage amount Q decreases as shown from the second timing t2 to the third timing t3 in FIG. 7(d). Along with the decrease, the divergence between the calculated value (solid line) and the true value (broken line) of the cell storage amount Q gradually increases.

As shown in FIG. 7(c), the reliability of the cell voltage V is low for a while even after the third timing t3 when the vehicle ends running. This is because polarization occurs in the cell battery B due to the use (discharge) of electric power, but the polarization does not subside until some time has passed from the third timing t3 at which the vehicle ends running. Here, as shown in FIG. 7(c), it is assumed that the polarization subsides and the reliability of the cell voltage V recovers by the fourth timing t4 at which the electric vehicle 90 starts to start.

In this case, the BMU 30 calculates the storage amount Qv based on the cell voltage V, which is the OCV, at the fourth timing t4 at startup. Then, the base storage amount specifying unit 32 updates the base storage amount Qb to the storage amount Qv based on the cell voltage V. FIG. Then, the cell storage amount calculator 33 resets the integrated current value ∫Idt to zero.

When the minimum cell storage amount Qmin (calculated value) changes due to the update of the base storage amount Qb and the reset of the current integrated value ∫Idt at the fourth timing t4, the pack storage amount ΣQ=Qmin (calculated value) is also changed accordingly. , changes as shown in FIG. As a result, the calculated value of the pack charged amount ΣQ approaches the true value.

The effects of this embodiment are summarized below.

When the battery pack 93 is charged, the change tendency of the cell impedance Z changes according to the cell charge amount Q at that time. Therefore, the impedance detector 31 detects the cell impedance Z when the battery pack 93 is charged. The cell storage amount calculation unit 33 calculates the cell storage amount Q based on the second impedance differential Zdd, which is the change in the change tendency of the cell impedance Z. FIG. Based on the cell storage amounts Q, the pack storage amount calculation unit 34 calculates the pack storage amount ΣQ. Therefore, even in situations where it is difficult to calculate the cell storage amount Q based on the cell voltage V, such as when the plateau region or when the OCV cannot be measured, the cell storage amount Q can be calculated based on the cell impedance Z, The pack storage amount ΣQ can be calculated based on the cell storage amount Q of .

In addition, the cell storage amount calculation unit 33 calculates the cell storage amount Q based on the base storage amount Qb and the integrated current value ∫Idt after the timing at which the base storage amount Qb is specified. Therefore, the cell storage amount Q can be calculated with higher accuracy than when the cell storage amount Q is calculated simply based on the base storage amount Qb and the elapsed time from the timing at which the base storage amount Qb is specified. Therefore, the pack charged amount ΣQ can be calculated with high accuracy.

Also, the charge stored in the battery pack 93 can be discharged only until the minimum cell storage amount Qmin reaches the dischargeable lower limit storage amount near zero. In this regard, the pack power storage amount calculator 34 calculates the minimum cell power storage amount Qmin as the pack power storage amount ΣQ. Therefore, the charge (Ah) that can be discharged by the battery pack 93 can be calculated as the pack storage amount ΣQ.

Also, the AC application circuit 40 applies AC voltage to the battery pack 93 . Then, the impedance detection unit 31 detects the impedance of the cell battery B when the AC voltage is applied 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 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. Therefore, in this respect as well, the cell storage amount Q can be calculated with high accuracy, and the pack storage amount ΣQ can be calculated with high accuracy.

In addition, the cell storage amount calculation unit 33 not only calculates the cell storage amount Q 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. A charged amount Qv based on the cell voltage V is calculated. Therefore, the pack charge amount ΣQ 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 acceleration timing tP and the suppression timing tS can be specified with high accuracy, and the pack charged amount ΣQ 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 acceleration timing tP and the suppression timing tS can be specified with high accuracy, and the pack charged amount ΣQ can be calculated with high accuracy.

Further, using the pack power storage amount ΣQ calculated as described above, the remaining charge time calculation unit 36 calculates the remaining charge time, and the power shortage determination unit 37 determines whether or not the power is insufficient. A failure determination unit 38 determines whether or not the battery pack 93 has failed, and a cruising distance calculation unit 97 calculates a cruising distance. Therefore, even in the plateau region or the like, it is possible to calculate the remaining charging time, determine the lack of electricity, determine the failure of the battery pack 93, and calculate the cruising range without any problem.

[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, not only during CC charging but also during power use (discharging), the cell storage amount Q is calculated based on the cell impedance Z, and the pack storage amount ΣQ is calculated based on the cell storage amount Q. Calculate. The mechanism will be explained below.

FIG. 8(a) is a graph showing changes in the cell impedance Z when the battery pack 93 is using power, and FIG. 8(b) is a graph showing changes in the cell storage amount Q when using power. As shown in FIG. 8(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. 8(a) is moderate.

After that, as shown in FIG. 8(b), 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. 8(a) is rapidly accelerated. The cell charged amount Q at the promotion timing tP can be identified as the section upper limit amount QU shown in FIG. 8(b). Therefore, during the aforementioned charging, the cell storage amount Q at the promotion timing tP can be specified as the interval lower limit amount QL, whereas during power use, the cell storage amount Q at the acceleration timing tP can be specified as the interval upper limit amount QU. They are different in an identifiable way.

After that, as shown in FIG. 8(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. 8(a) is abruptly suppressed. The cell charge amount Q at the suppression timing tS can be identified as the interval lower limit amount QL shown in FIG. 8(b). Therefore, during the aforementioned charging, the cell storage amount Q at the suppression timing tS can be specified as the section upper limit amount QU, whereas during power use, the cell storage amount Q at the suppression timing tS can be specified as the section lower limit amount QL. They are different in an identifiable way.

As described above, 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 calculated even in the plateau region or the like. Based on these cell storage amounts Q, the pack storage amount ΣQ can be calculated.

Next, referring to FIG. 1, which is the same as the first embodiment, the configuration for calculating the pack charge amount ΣQ based on the cell impedance Z when electric power is used 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 detection unit 31 calculates each cell impedance Z based on each cell voltage V and battery current I when the AC voltage is applied while the power is being used.

The base power storage 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 acceleration 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 promotion timing tP, the base storage amount Qb is updated to the section upper limit amount QU.

In addition, the base storage 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. do. 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, the base storage amount Qb is updated to the section lower limit amount QL.

FIG. 9 is a flowchart showing control by the battery monitoring device 96. FIG. This flow is repeated, for example, at predetermined intervals. This flow differs from the float in FIG. 5 of the first embodiment in that it has S103, S211, S212, and S214.

Specifically, when it is determined in S101 that it is in the plateau region or when it is determined that the OCV cannot be measured (S101: NO), if it is determined in S102 that CC charging is not being performed (S102: NO), S103 proceed to At S103, it is determined whether power is being used. Specifically, for example, it is determined that power is being used on condition that the battery current I is equal to or greater than a predetermined value in the discharging direction. If it is determined in S103 that power is not being used (S103: NO), the process proceeds to S402 to update the integrated current value ∫Idt. On the other hand, if it is determined in S103 that power is being used, the process proceeds to S211.

In S211, the impedance detection unit 31 calculates the cell impedance Z. In subsequent S212, the base charged 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 rapidly accelerated (S212: YES), the process proceeds to S205, updates the base charge amount Qb to the section upper limit amount QU, and then proceeds to S401.

On the other hand, in retroactive S212, if it is not determined that the decrease in cell impedance Z has rapidly accelerated beyond the predetermined standard (S212: NO), proceed to S214. In S214, the base charged 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 (S214: YES), the process proceeds to S203, updates the base charge amount Qb to the section lower limit amount QL, and then proceeds to S401. On the other hand, if it is determined in S214 that the decrease in the cell impedance Z is not rapidly suppressed by the predetermined criterion or more (S214: NO), the process proceeds to S402 to reset the integrated current value ∫Idt to zero. Subsequent steps are the same as in the case of the first embodiment.

According to this embodiment, not only during charging but also during power use, the cell storage amount Q is calculated based on the cell impedance Z, and the pack storage amount ΣQ is calculated based on the cell storage amount Q. be able to.

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

In the first and second 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, it is possible to calculate the pack charge amount ΣQ based on the cell impedance Z when it is difficult to calculate the cell charge amount Q based on the cell voltage V. It works.

In the first and second 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 and second embodiments, "impedance change Zd" is obtained by differentiating the cell impedance Z with time, and "impedance second differentiation 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, it is possible to specify the promotion timing tP and the suppression timing tS with high accuracy even in a situation where the current is not constant.

In the first and second 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 cell storage amount calculation unit 33 calculates the base storage amount in terms of energy (Wh) and the integrated power (Wh) may be used to calculate the cell storage amount (Wh) in terms of energy. The integrated power value is the time integral value (∫VIdt) of the product of the cell voltage V and the battery current I. In this case, the value obtained by multiplying the minimum cell storage amount (Wh) in terms of energy by the number of cells, which is the number of cell batteries B included in the battery pack 93, is the "pack storage amount (Wh)" in terms of energy. can be calculated as

In addition, when the stored energy is used as the stored amount in this way, the cell impedance Z differentiated by the integrated power value is defined as "impedance change Zd", and the impedance change Zd further differentiated by the power integrated value is defined as "impedance change Zd". 2nd derivative 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 and second embodiments, the cell storage amount Q is calculated based on the base storage amount Qb and the current integrated value ∫Idt. Alternatively, the cell storage amount Q may be calculated simply based on the base storage amount Qb and the elapsed time from the timing at which the base storage amount Qb was updated.

In the first and second embodiments, the cell storage amount Q is calculated as the sum of the base storage amount Qb and the integrated current value ∫Idt. Alternatively, the cell storage amount Q may be calculated by performing a predetermined correction on the sum of the base storage amount Qb and the integrated current value ∫Idt.

The pack power storage amount calculation unit 34 calculates the minimum cell power storage amount Qmin as the pack power storage amount ΣQ. Alternatively, for example, the average value of the cell charged amounts Q may be calculated as the pack charged amount ΣQ. Further, for example, when the stored energy is the stored amount as described above, instead of the value obtained by multiplying the minimum cell stored amount (Wh) by the number of cells, the value obtained by adding each cell stored amount (Wh) is used as the pack stored amount. It may be calculated as an amount (Wh).

In the first and second 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 and second embodiments, the impedance of the cell battery B with respect to alternating current is "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 and second embodiments, in addition to calculating the pack charge amount ΣQ based on the cell impedance Z, when the OCV is measurable in the non-plateau region, the pack charge amount is also calculated based on the cell voltage V. ΣQ is calculated. Alternatively, the pack charge amount ΣQ may be calculated based on the cell impedance Z only.

In the first and second embodiments, the pack storage amount ΣQ based on the cell impedance Z is calculated both during CC charging and during power use. Alternatively, it may be performed only during CC charging or during power use.

The electric vehicle 90 referred to in the first and second embodiments may be a hybrid vehicle having an engine, as described above. In this case, the electric vehicle 90 determines the necessity of engine combustion based on the pack power storage amount ΣQ, such as determining that engine combustion is necessary, on the condition that the calculated pack power storage amount ΣQ is smaller than a predetermined threshold value. You may have the engine combustion necessity determination part which determines.

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

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;
a cell storage amount calculation unit (33) for calculating the storage amount (Q) of the cell battery based on the detected change (Zdd) of the impedance change tendency (Zd);
a pack power storage amount calculator (34) for calculating the power storage amount (ΣQ) of the battery pack based on the calculated power storage amount of the cell battery;
a battery monitor.
a base storage amount specifying unit (32) for specifying a base storage amount (Qb) as a specific storage amount (QL, QU) based on the detected change in the tendency of impedance change;
The cell storage amount calculator calculates the base storage amount and an integrated value (∫Idt ), the battery monitoring device according to claim 1, wherein the amount of charge of the cell battery is calculated based on the above.
The storage amount indicates the amount of stored electric charge, and the pack storage amount calculation unit calculates the storage amount (Qmin) of the cell battery with the smallest calculated storage amount, Calculate as the amount of electricity stored, or
The storage amount indicates the amount of stored energy, and the pack storage amount calculation unit adds the storage amount of the cell battery with the smallest calculated storage amount to the cell included in the battery pack. calculating the value obtained by multiplying the number of batteries as the amount of electricity stored in the battery pack;
The battery monitoring device according to claim 1 or 2.
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 3, wherein said impedance detector detects the impedance of said cell battery when said AC voltage is applied to said battery pack.
The AC application circuit applies the AC voltage during constant current charging of the battery pack, and the impedance detection unit detects the impedance when the AC voltage is applied during the constant current charging. The battery monitoring device according to claim 4.
The cell storage amount calculator calculates the storage amount of the cell battery based on the change in the impedance change trend when the change in the storage amount of the cell battery with respect to the voltage change of the cell battery is in a plateau region smaller than a predetermined reference. 6. The battery monitoring device according to any one of claims 1 to 5, which calculates the amount of charge of the cell battery based on the voltage of the cell battery at a time other than the plateau region.
The battery monitoring device according to any one of claims 1 to 6, wherein the cell battery has graphite in the negative electrode.
The battery monitoring device according to any one of claims 1 to 7, wherein the cell battery has an olivine structure on the positive electrode.
a remaining charge time calculation unit (36) for calculating a remaining charge time, which is the time required to charge the battery pack to its charge capacity, using the calculated pack power storage amount;
a power shortage determination unit (37) that determines whether or not there is a shortage of electric power using the calculated amount of power stored in the pack;
a battery failure determination unit (38) that determines whether or not the battery pack has failed using the calculated pack power storage amount;
The battery monitoring device according to any one of claims 1 to 8, comprising at least one of
An electric vehicle (90) equipped with the battery monitoring device according to any one of claims 1 to 9,
An electric vehicle having a cruising distance calculation unit (97) that calculates a cruising distance as a distance that the electric vehicle can travel, using the calculated pack power storage amount.