JP7563286B2 - Battery monitoring device - Google Patents

Description

The present invention relates to a battery monitoring device that monitors a battery pack having multiple cell batteries connected in series.

Some battery monitoring devices calculate the amount of stored electricity based on the voltage of the cell battery. The following Patent Document 1 shows such technology.

JP 2018-125977 A

When the battery pack is charging or power is being used, current flows through the internal resistance of the cell battery, making it impossible to detect the true voltage of the cell battery, i.e., the OCV (open circuit voltage). Therefore, when the battery pack is charging or power is being used, it is difficult to calculate the amount of stored energy based on the cell battery voltage.

Furthermore, some cell batteries contain a plateau region where the change in voltage relative to the change in the amount of stored charge is small. In this plateau region, it is even more difficult to calculate the amount of stored charge based on the voltage of the cell battery. And when it is difficult to calculate the amount of stored charge in a cell battery, it is naturally difficult to calculate the variation in the amount of stored charge between cell batteries.

The present invention was made in consideration of the above circumstances, and its main objective is to make it possible to calculate the variation in the amount of stored energy between cell batteries even in situations where it is difficult to calculate the amount of stored energy based on the voltage of the cell batteries.

The battery monitoring device of the present invention monitors a battery pack having a series connection of multiple cell batteries. The battery monitoring device has an impedance detection unit, a charge amount determination unit, and a variation calculation unit.

The impedance detection unit detects the impedance of the multiple cell batteries when the amount of stored power in the battery pack changes over time. The amount of stored power specification unit specifies that the amount of stored power in the cell battery has reached a specific amount of stored power based on a change in the trend of change in the detected impedance. The variation calculation unit calculates the variation in the amount of stored power between the cell batteries based on the difference between the specific timings at which the amount of stored power reached the specific amount of stored power between the cell batteries.

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

A circuit diagram showing a battery monitoring device and its surroundings according to a first embodiment. Graph showing the waveform of the battery current when an AC voltage is applied to the battery pack A graph showing the change in each value as the amount of stored electricity in the cell battery increases Graph showing the change in each value over charging time Flowchart showing control during charging Graph showing the changes in each value during charging Graph showing the transition of each value with the passage of discharge time in the second embodiment Flowchart showing control when power is used 11 is a flowchart showing control during charging in the third embodiment. Flowchart showing control when power is used

The following describes an embodiment of the present invention with reference to the drawings. However, the present invention is not limited to the following embodiment, and can be modified as appropriate without departing from the spirit of the invention.

[First embodiment]
1 is a circuit diagram showing a battery monitoring device 96 of this embodiment and its periphery. An electric vehicle 90 is equipped with a load 91 such as a driving motor and on-board 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 that does not have an engine, or may be a plug-in hybrid vehicle or the like that has an engine. In the following, being "electrically connected" will simply be referred to as being "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). The battery pack 93 is connected to a load 91. When charging the battery pack 93, an external power source 80 is connected to the battery pack 93. The external power source 80 performs CC charging (constant current charging) until the battery pack 93 is about to be fully charged, and then switches to CV charging (constant voltage charging) immediately before that point.

In the following, the current flowing through the battery pack 93 is referred to as "battery current I." Therefore, the battery current I is also the current flowing through each cell battery B. In the following, the time integral of the battery current I is referred to as "current integration value ∫Idt." The voltage of cell battery B is referred to as "cell voltage V," and the charge (Ah: ampere-hours) stored in cell battery B is referred to as "cell charge Q." The cell charge Q of the cell battery B with the smallest cell charge Q is referred to as "minimum cell charge Qmin." The cell charge Q minus the minimum cell charge Qmin (Q-Qmin) is referred to as "variation ΔQ."

In the following, the cell charge Q when fully charged is referred to as the "cell charge capacity Qf," and the ratio of the cell charge Q to the cell charge capacity Qf (Q/Qf) is referred to as the "cell SOC." SOC stands for "State Of Charge." The initial (new) cell charge capacity Qf is referred to as the "initial cell charge capacity Qfo," and the ratio of the current cell charge capacity Qf to the initial cell charge capacity Qfo (Qf/Qfo) is referred to as the "cell SOH." SOH stands for "State Of Health."

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

In the following, the impedance of cell battery B with respect to AC will be referred to as "cell impedance Z." This cell impedance Z is determined by the resistance, capacitance, inductance, and other components present inside cell battery B. The time derivative of cell impedance Z is referred to as "impedance change Zd," and the further time derivative of this impedance change Zd is referred to as "impedance double derivative Zdd." In other words, impedance double derivative Zdd indicates the change in the trend of change in cell impedance Z.

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 to both terminals of the battery pack 93 and between each two adjacent cell batteries B in series within the battery pack 93. In other words, the voltage sensor 20 is connected to both terminals of each cell battery B. The voltage sensor 20 has a multiplexer or the like, and is configured to be able to measure the voltage of each cell battery B.

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

Next, with reference to Figures 3 and 4, we will explain the problem to be solved in this embodiment and an overview of the means for solving it.

Figure 3(a) is a graph showing the relationship between cell charge Q (horizontal axis) and cell voltage V (vertical axis). As mentioned above, each cell battery B is an LFP battery. Due to its characteristics, each cell battery B has a plateau region in which the change in cell voltage V (vertical axis) relative to the change in cell charge Q (horizontal axis) is smaller than a predetermined standard. In the following, the time when the cell charge Q is within the plateau region is referred to as the "plateau region", and the time when the cell charge Q is outside the plateau region is referred to as the "non-plateau region". In the plateau region, it is difficult to calculate the cell charge Q (horizontal axis) based on the cell voltage V (vertical axis). Therefore, it is also difficult to calculate the variation ΔQ.

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

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

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

And in 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 Q is within the high heat generation range (QL to QU), the cell heat generation increases, the cell temperature T increases significantly, and the cell impedance Z decreases significantly.

Figure 4(a) is a graph showing the change in cell impedance Z when the battery pack 93 is being charged, and Figure 4(b) is a graph showing the change in cell charge Q when the battery pack 93 is being charged. As shown in Figure 4(b), when charging is started from a nearly empty state, the cell charge Q is outside the high heat generation section (QL-QU) until the cell charge Q reaches the section lower limit QL, so the cell heat generation is small and the cell temperature T rises slowly. Therefore, the decrease in cell impedance Z shown in Figure 4(a) is slow.

After that, as shown in FIG. 4(b), when the cell charge Q reaches the section lower limit QL, the cell charge Q enters the high heat generation section (QL to QU), causing the heat generation coefficient dV/dT shown in FIG. 3(b) to increase rapidly, resulting in a sudden increase in cell heat. This causes a sudden increase in the cell temperature T, and a sudden increase in the decrease in cell impedance Z shown in FIG. 4(a). In the following, the timing at which the decrease in cell impedance Z is suddenly accelerated in this way is referred to as the "acceleration timing tP." At this acceleration timing tP, it can be determined that the cell charge Q has reached the section lower limit 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 leaves the high heat generation section (QL-QU), and the heat generation coefficient dV/dT shown in FIG. 3(b) suddenly decreases. This causes a sudden decrease in cell heat generation, and the increase in cell temperature T is suddenly suppressed, so that the decrease in cell impedance Z shown in FIG. 4(a) is suddenly suppressed. In the following, the timing at which the decrease in cell impedance Z is suddenly suppressed in this way is referred to as "suppression timing tS." At that suppression timing tS, it can be determined that the cell storage amount Q has reached the section upper limit amount QU shown in FIG. 4(b).

Therefore, when the cell charge amount Q is calculated based on, for example, the current integrated value ∫Idt, the error in the cell charge amount Q can be reset at the timing when the cell charge amount Q reaches the section lower limit amount QL and the timing when the cell charge amount Q reaches the section upper limit amount QU. In other words, the cell charge amount Q can be determined even in the plateau region, etc. Then, the variation amount ΔQ can be calculated based on the difference in the timing of determination between the cell batteries B.

In the following, the promotion timing tP and the suppression timing tS are collectively referred to as the "specific timing (tP, tS)," and the section lower limit amount QL and the section upper limit amount QU are collectively referred to as the "specific storage amount (QL, QU)."

Next, referring again to FIG. 1, the configuration for calculating the variation ΔQ based on the cell impedance Z shown above will be described. As this configuration, the battery monitoring device 96 further has an AC application circuit 40, and has an impedance detection unit 31, a storage amount determination unit 32, and a variation calculation unit 33 within the BMU 30. Furthermore, 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 with a hexagonal close-packed oxygen skeleton.

Cell battery B has graphite in the negative electrode because the heat generation coefficient dV/dT becomes significantly large when the cell charge Q is within the high heat generation range (QL to QU). On the other hand, the positive electrode has an olivine structure because it suppresses changes in the heat generation coefficient dV/dT at the positive electrode. In other words, it is possible to suppress changes in the heat generation coefficient dV/dT at the positive electrode from being superimposed as noise on changes in the heat generation coefficient dV/dT at the negative electrode.

One terminal of the AC application circuit 40 is connected to the positive terminal of the battery pack 93, and the other terminal of the AC application 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.

Figure 2 is a graph showing the waveform of battery current I during CC charging. When an AC voltage is applied to battery pack 93 during CC charging, the AC current is superimposed on the CC current (constant current), which is the charging current. Note that an AC voltage is applied during CC charging in this manner because, since the charging current is constant during CC charging, there is no need to worry about AC noise caused by changes in the charging current being superimposed on the AC current.

The impedance detection unit 31 shown in FIG. 1 calculates 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. Specifically, for example, the cell impedance Z is calculated as the 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.

The power storage amount determination unit 32 determines that the cell power storage amount Q has reached a specific power storage amount (QL, QU) at a specific timing (tP, tS). In this embodiment, at least one of the specific power storage amounts (QL, QU), the section upper limit amount QU, is included in the plateau region.

Specifically, the storage amount determination unit 32 determines the timing at which the decrease in the detected cell impedance Z is rapidly accelerated by more than a predetermined standard during CC charging, excluding the start and end, as the promotion timing tP. More specifically, during CC charging, excluding the start and end, the promotion timing tP is determined to be the condition that the impedance second derivative Zdd falls below a negative promotion determination value ZddP. At that promotion timing tP, it is determined that the cell storage amount Q has reached the section lower limit amount QL.

The charge amount determination unit 32 also determines the suppression timing tS as the timing at which the decrease in the calculated cell impedance Z is suppressed more rapidly than a predetermined standard during CC charging, excluding the start and end. More specifically, the suppression timing tS is determined to be the condition that the impedance second derivative Zdd exceeds a positive suppression determination value ZddS during CC charging, excluding the start and end. At that suppression timing tS, the cell charge amount Q is determined to have reached the section upper limit amount QU.

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

The calculation of the variation amount ΔQ based on the cell impedance Z has been described above, but in a non-plateau region and in a situation where the OCV can be measured, the BMU 30 calculates the cell charge amount Q based on the cell voltage V, and calculates the variation amount ΔQ based on the cell charge amount Q. The calculation method itself may be a publicly known method, so a detailed description will be omitted.

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

Next, we will explain how to utilize the amount of variation ΔQ calculated as above. As a configuration for utilizing the amount of variation ΔQ, the BMU 30 further includes an equalization necessity determination unit 36, a failure determination unit 37, and an equalization amount calculation unit 38.

The equalization necessity determination unit 36 performs an equalization necessity determination for each cell battery B to determine whether equalization is necessary. In this equalization necessity determination, it is determined that equalization is necessary if the variation amount ΔQ is greater than a predetermined equalization determination variation amount ΔQE.

At this time, the equalization necessity determination unit 36 sets the equalization judgment variation amount ΔQE to be larger when the variation in cell SOH between the cell batteries B is larger than a predetermined standard compared to when it is smaller than the predetermined standard. Furthermore, at this time, the equalization necessity determination unit 36 sets the equalization judgment variation amount ΔQE to be smaller when the pack SOH is smaller than the predetermined standard compared to when it is larger than the predetermined standard. The reasons for this will be described later.

The failure determination unit 37 performs a failure determination as to whether or not the battery pack 93 is faulty. In the failure determination, a failure is determined if the variation amount ΔQ is greater than a predetermined failure determination variation amount ΔQX.

At this time, the failure determination unit 37 sets the failure determination variation amount ΔQX to be larger when the variation in cell SOH between cell batteries B is larger than a predetermined standard compared to when it is smaller than the predetermined standard. Furthermore, at this time, the failure determination unit 37 sets the failure determination variation amount ΔQX to be smaller when the pack SOH is smaller than the predetermined standard compared to when it is larger than the predetermined standard. The reasons for this will be described 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 variation amount ΔQ itself may be set as the equalization amount, the variation amount ΔQ may be multiplied by a predetermined value less than 1, or the equalization amount may be the variation amount ΔQ minus a predetermined value.

The battery monitoring device 96 then equalizes the cell storage amounts Q based on the calculated equalization amount. In other words, each cell battery B is discharged by the calculated equalization amount. The discharge method itself may be a publicly known method, so a detailed description is omitted.

Figure 5 is a flowchart showing the 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 repeated at predetermined intervals.

First, in S101, the impedance detection unit 31 detects the cell impedance Z. Next, in S102, the charge amount determination unit 32 determines whether the decrease in the cell impedance Z has been accelerated rapidly by a predetermined standard or more. If it is determined that the decrease has been accelerated rapidly (S102: YES), the process proceeds to S103, where it is determined that the cell charge amount Q has reached the section lower limit amount QL, and then the process proceeds to S106. At this time, it is preferable to update the calculated value of the cell charge amount Q itself to the section lower limit amount QL, but this is not necessary. On the other hand, if it is not determined that the decrease has been accelerated rapidly in S102 (S102: NO), the process proceeds to S104.

In S104, the charge amount determination unit 32 determines whether the decrease in cell impedance Z has been abruptly suppressed by a predetermined standard or more. If it is determined that the decrease has been abruptly suppressed (S104: YES), the process proceeds to S105, where it is determined that the cell charge amount Q has reached the section upper limit amount QU, and then the process proceeds to S106. At this time, it is preferable to update the calculated value of the cell charge amount Q itself to the section upper limit amount QU, but this is not necessary. On the other hand, if it is not determined in S104 that the decrease has been abruptly suppressed (S104: NO), the process proceeds directly to S106.

In S106, the variation calculation unit 33 determines whether or not it has been possible to identify the cell storage amount Q of each cell battery B as being the specific storage amount (QL, QU). In other words, it determines whether or not it has been possible to identify the cell storage amount Q of each cell battery B as being the section lower limit amount QL, or to identify the cell storage amount Q of each cell battery B as being the section upper limit amount QU. If it is determined that the cell storage amount Q of any cell battery B has not been identified as being the specific storage amount (QL, QU) (S106: NO), the flow ends. On the other hand, if it is determined that the cell storage amount Q of each cell battery B has been identified as being the specific storage amount (QL, QU) (S106: YES), the flow proceeds to S107.

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

In the next S108, the equalization necessity determination unit 36 determines whether the variation amount ΔQ is greater than the equalization judgment variation amount ΔQE. If it is determined that the variation amount ΔQ is less than the equalization judgment variation amount ΔQE (S108: NO), the flow proceeds to S109, where it is determined that equalization is not necessary, and the flow ends. On the other hand, if it is determined in S108 that the variation amount ΔQ is greater than the equalization judgment variation amount ΔQE (S108: YES), the flow proceeds to S110.

In S110, the failure determination unit 37 determines whether the variation amount ΔQ is smaller than the failure determination variation amount ΔQX. If it is determined that the variation amount ΔQ is larger than the failure determination variation amount ΔQX (S110: NO), the flow proceeds to S112, a failure is determined, and the flow ends. On the other hand, if it is determined in S110 that the variation amount ΔQ is smaller than the failure determination variation amount ΔQX (S110: YES), the flow proceeds to S111.

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

Figure 6 is a graph showing the progression of each value during CC charging of the battery pack 93. In what follows, the specified timings (t1 to t4) are referred to in chronological order as the "first timing t1," "second timing t2," "third timing t3," and "fourth timing t4."

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

At this time, as shown in FIG. 6(b), after the first timing t1 when charging starts, the cell charge Q is outside the plateau region for a while, so the cell voltage V increases as time t passes. However, when the cell charge Q enters the plateau region at the second timing t2, the cell voltage V remains roughly constant thereafter.

As shown in FIG. 6(c), after the first timing t1 at which charging starts, the cell charge Q is in the high heat generation section (QL-QU) for a while, and as a result the cell heats up significantly, causing a noticeable decrease in the cell impedance Z. However, when the cell charge Q reaches the section upper limit QU at a predetermined timing (tS(B)), the cell charge Q leaves the high heat generation section (QL-QU), causing a sudden decrease in cell heat and a sudden suppression of the decrease in cell impedance Z. At this time, as shown in FIG. 6(d), the impedance second derivative Zdd momentarily increases and exceeds the suppression judgment value ZddS, and it is determined that it is 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 current integrated value ∫Idt after the suppression timing tS(B) increases from this suppression timing tS(B). The increase in this variation amount ΔQ stops when the suppression timing tS(Bmin) of the minimum voltage cell battery Bmin is identified. This allows the variation amount ΔQ to be identified.

At this time, as shown in FIG. 6(e), if the variation amount ΔQ is greater than the equalization judgment variation amount ΔQE and smaller than the failure judgment variation amount ΔQX, equalization is started at the fourth timing t4 thereafter as shown in FIG. 6(a). This causes the variation amount ΔQ to decrease as shown in FIG. 6(e).

The effects of this embodiment are summarized below.

When the battery pack 93 is charged, the impedance change tendency changes when the cell charge Q reaches a specific charge (QL, QU). Therefore, the impedance detection unit 31 calculates each cell impedance Z when the battery pack 93 is charged. The charge amount determination unit 32 determines that the cell charge Q reaches a specific charge (QL, QU) based on the impedance second derivative Zdd, which is a change in the change tendency of the cell impedance Z. The variation calculation unit 33 calculates the variation ΔQ based on the difference in the specific timing (tP, tS) between the cell batteries B. Therefore, even in a situation where it is difficult to calculate the cell charge Q based on the cell voltage V, such as in a plateau region, the variation ΔQ can be calculated based on the difference in the specific timing (tP, tS).

Based on the calculated amount of variation ΔQ, the equalization necessity determination unit 36 performs an equalization necessity determination, the failure determination unit 37 performs a failure determination, and the equalization amount calculation unit 38 calculates the equalization amount. Therefore, even during a plateau region, etc., the equalization necessity determination, failure determination, and equalization amount calculation can be performed without any problems.

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

The AC application circuit 40 also applies an AC voltage to the battery pack 93. Therefore, the AC resistance of the cell battery B can be measured as the cell impedance Z. The AC application circuit 40 also applies an AC voltage to the battery pack 93 during CC charging. Therefore, there is no need to worry about AC noise due to changes in the charging current being superimposed on the AC current due to the AC voltage. Therefore, the impedance detection unit 31 can accurately detect the cell impedance Z. Therefore, the promotion timing tP and the suppression timing tS can be accurately identified, and the variation amount ΔQ can be accurately calculated.

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

Cell battery B also has graphite in the negative electrode. This graphite significantly increases the heat generation coefficient dV/dT when the cell charge Q falls within the high heat generation range (QL-QU). This significantly accelerates the decrease in cell impedance Z when the cell charge Q enters the high heat generation range (QL-QU), and significantly suppresses the decrease in cell impedance Z when the cell charge Q leaves the high heat generation range (QL-QU). Therefore, in this respect as well, the promotion timing tP and suppression timing tS can be accurately identified, and the variation amount ΔQ can be accurately calculated.

Moreover, cell battery B has an olivine structure in the positive electrode. This olivine structure suppresses changes in the heat generation coefficient dV/dT at the positive electrode. This suppresses the change in the heat generation coefficient dV/dT at the positive electrode from being superimposed 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 accurately identified, and the variation amount ΔQ can be accurately calculated.

The equalization necessity determination unit 36 also sets the equalization determination variation amount ΔQE larger when the variation in cell SOH is larger than the predetermined standard compared to when it is smaller. This is because if the variation in cell SOH is large, the variation in cell charge amount Q, i.e., the variation amount ΔQ, will be large even if the variation in cell SOC is not so large. In such a situation, if equalization is performed simply based on the variation amount ΔQ being larger than the equalization determination variation amount ΔQE, the variation in cell charge amount Q may be reduced, but the variation in cell SOC may increase. In this regard, the equalization necessity determination unit 36 sets the equalization determination variation amount ΔQE larger when the variation in cell SOH is large in this way, making it more difficult to determine that equalization is necessary, thereby suppressing such adverse effects.

Failure determination unit 37 also sets the failure determination variation ΔQX to a larger value when the variation in cell SOH is larger than the predetermined standard compared to when it is smaller. This is because, as described above, if the variation in cell SOH is large, the variation ΔQ, which is the variation in cell charge Q, becomes large even if the variation in cell SOC is not so large. In such a situation, if a failure is determined simply based on the variation ΔQ being larger than the failure determination variation ΔQX, a problem may occur in which a failure is determined even if the variation in cell SOC is not so large. In this regard, since failure determination unit 37 sets the failure determination variation ΔQX to a larger value when the variation in cell SOH is large, it is difficult to determine a failure, and such a problem can be suppressed.

In addition, the equalization necessity determination unit 36 sets the equalization judgment variation amount ΔQE smaller when the pack SOH is smaller than the predetermined standard compared to when it is larger. This is because, if the battery pack 93 deteriorates and the pack SOH (ΣQf/ΣQfo) becomes smaller, the pack storage capacity ΣQf becomes smaller, and the variation amount ΔQ, which is the variation in the cell storage amount Q, tends to become smaller. Therefore, the variation amount ΔQ is less likely to exceed the equalization judgment variation amount ΔQE, and it may become difficult to determine that equalization is necessary. In this regard, the equalization necessity determination unit 36 sets the equalization judgment variation amount ΔQE smaller when the pack SOH is small in this way, making it easier to determine that equalization is necessary, and suppressing such adverse effects.

Furthermore, the failure determination unit 37 sets the failure determination variation ΔQX smaller when the pack SOH is smaller than the predetermined standard compared to when it is larger. This is because, as described above, if the battery pack 93 deteriorates and the pack SOH (ΣQf/ΣQfo) becomes smaller, the pack storage capacity ΣQf becomes smaller, and the variation ΔQ, which is the variation in the cell storage amount Q, tends to become smaller. Therefore, the variation ΔQ is less likely to exceed the failure determination variation ΔQX, which may cause problems such as making it difficult to determine a failure. In this regard, the failure determination unit 37 sets the failure determination variation ΔQX smaller when the pack SOH is small in this way, making it easier to determine a failure and suppressing such problems.

[Second embodiment]
Next, a second embodiment will be described. In the following embodiments, the same reference numerals will be used for the same or corresponding members as those in the previous embodiments. This embodiment will be described based on the first embodiment, focusing on the differences, and descriptions of the same or similar parts as the first embodiment will be omitted as appropriate.

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

Figure 7(a) is a graph showing the change in cell impedance Z when the battery pack 93 is using power, and Figure 7(b) is a graph showing the change in cell charge Q when power is being used. As shown in Figure 7(b), when cell battery B starts using power from a nearly fully charged state, until the cell charge Q decreases to the upper limit QU, the cell charge Q is outside the high heat generation section (QL to QU), so cell heat generation is small. Therefore, the decrease in cell impedance Z shown in Figure 7(a) is gradual.

After that, as shown in FIG. 7(b), when the cell charge Q decreases to the section upper limit QU due to power usage, the cell charge Q enters the high heat generation section (QL-QU), causing the heat generation coefficient dV/dT to increase rapidly and cell heat generation to increase rapidly. This rapidly accelerates the rise in cell temperature T, and rapidly accelerates the decrease in cell impedance Z shown in FIG. 7(a). At this promotion timing tP, it can be determined that the cell charge Q has reached the section upper limit QU shown in FIG. 7(b). Thus, the difference is that, while the cell charge Q can be determined to have reached the section lower limit QL at the promotion timing tP during charging as described above, the cell charge Q can be determined to have reached the section upper limit QU at the promotion timing tP during power usage.

After that, as shown in FIG. 7(b), when the cell charge Q decreases to the section lower limit QL due to power usage, the cell charge Q leaves the high heat generation section (QL-QU), causing a sudden decrease in the heat generation coefficient dV/dT and a sudden decrease in cell heat generation. This causes a sudden suppression of the increase in cell temperature T, and a sudden suppression of the decrease in cell impedance Z shown in FIG. 7(a). At the suppression timing tS, it can be determined that the cell charge Q has reached the section lower limit QL shown in FIG. 7(b). Thus, the difference is that, while the cell charge Q can be determined to have reached the section upper limit QU at the suppression timing tS during charging as described above, the cell charge Q can be determined to have reached the section lower limit QL at the suppression timing tS during power usage.

Therefore, the error in the cell charge amount Q can be reset at the timing when the cell charge amount Q decreases to the section upper limit amount QU and the timing when the cell charge amount Q decreases to the section lower limit amount QL. In other words, the cell charge amount Q can be determined even during a plateau region, etc. Then, the variation amount ΔQ can be calculated based on the difference in the timing of determination between the cell batteries B.

Next, referring to FIG. 1, which is the same as in the first embodiment, we will explain the configuration for calculating the amount of variation ΔQ when electricity is used.

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

The power storage amount determination unit 32 determines the timing at which the decrease in the detected cell impedance Z is rapidly accelerated by more than a predetermined standard when the power usage is stable above a predetermined standard as the promotion timing tP. More specifically, when the power usage is stable above a predetermined standard, the promotion timing tP is determined to be the case when the impedance second derivative Zdd falls below a negative promotion determination value ZddP. At that promotion timing tP, the cell power storage amount Q is determined to have reached the section upper limit amount QU.

The power storage amount determination unit 32 also determines the suppression timing tS as the timing at which the decrease in the detected cell impedance Z is suddenly suppressed by a predetermined standard or more when the power usage is stable above a predetermined standard. More specifically, when the power usage is stable above a predetermined standard, it determines that the suppression timing tS has occurred on the condition that the impedance second derivative Zdd exceeds a positive suppression determination value ZddS. It determines that the cell power storage amount Q has reached the section lower limit amount QL at that suppression timing tS.

Figure 8 is a flowchart showing the control by the battery monitoring device 96 when the power of the battery pack 93 is being used. This flow is performed for each cell battery B, and is repeatedly performed at a predetermined cycle. This flow differs from the flow during CC charging shown in Figure 5 in that in S203, it is determined that the cell storage amount Q has reached the section upper limit amount QU rather than the section lower limit amount QL, and in S205, it is determined that the cell storage amount Q has reached the section lower limit amount QL rather than the section 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 the cell impedance Z has accelerated more rapidly than a predetermined standard (S202: YES), the process proceeds to S203, where it is determined that the cell storage amount Q has reached the upper limit amount QU of the section, and then the process proceeds to S206. On the other hand, if it is not determined in S202 that the decrease has accelerated rapidly (S202: NO), the process proceeds to S204.

If it is determined in S204 that the decrease in cell impedance Z has been rapidly suppressed to a level equal to or greater than the predetermined standard (S204: YES), the process proceeds to S205, where it is determined that the cell charge amount Q has reached the section lower limit amount QL, and then the process proceeds to S206. On the other hand, if it is not determined in S204 that the decrease has been rapidly suppressed (S204: NO), the process proceeds directly to S206. S206 to S212 are the same as S106 to S112 in the flow for CC charging shown in FIG. 5.

According to this embodiment, the variation amount 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. The third embodiment will be described based on the second embodiment, focusing on the differences from the second embodiment, and descriptions of parts that are the same as or similar to the second embodiment will be omitted as appropriate.

Figure 9 is a flowchart showing the control of the battery monitoring device 96 during CC charging of the battery pack 93. The flowchart in Figure 9 differs from the flowchart in Figure 5 only in S106. That is, in S106 in the first and second embodiments, the process proceeds to the next step S107 on the condition that it has been determined that the cell charge amount Q for each cell battery B has reached the specific charge amount (QL, QU). In contrast, in S106 in this embodiment, even if there is a cell battery B whose cell charge amount Q cannot be determined to have reached the specific charge amount (QL, QU), the process proceeds to the next step S107 if a predetermined time has elapsed.

In the following, a cell battery B whose cell storage amount Q can be identified as having reached a specific storage amount (QL, QU) is referred to as an "identifiable cell battery B," and a cell battery B whose cell storage amount Q cannot be identified as having reached a specific storage amount (QL, QU) is referred to as an "unidentifiable cell battery B." The amount of variation ΔQ of the identifiable cell battery B 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 maximum identifiable 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 specified 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 the same as the maximum identifiable variation amount ΔQ. Accordingly, in the equalization in S111, the equalization amount of the unidentifiable cell battery B is set to the same as the equalization amount of the cell battery B related to the maximum identifiable variation amount ΔQ.

Figure 10 is a flowchart showing the control of the battery monitoring device 96 when the power of the battery pack 93 is used. The flowchart in Figure 10 differs from the flowchart in Figure 8 only in S206. That is, in S206 of the second embodiment, the process proceeds to the next step S207 on the condition that it has been determined that the cell storage amount Q for each cell battery B has reached the specific storage amount (QL, QU). In contrast, in S206 of the present embodiment, even if there is a cell battery B whose cell storage amount Q cannot be determined to have reached the specific storage amount (QL, QU), the process proceeds to the next step S207 if a predetermined time has elapsed.

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 considered that the cell storage amount Q had already fallen below the specified storage amount (QL, QU) at the start of power use. Therefore, for the unidentifiable cell battery B, the cell storage amount Q is considered to be 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. As a result, in the determination of whether equalization is necessary in S209, the unidentifiable cell battery B is determined to not require equalization (S210).

As described above, according to this embodiment, even if there is a cell battery B whose cell charge amount Q cannot be determined to be the specific charge amount (QL, QU), the variation amount ΔQ can be calculated.

[Other embodiments]
The embodiment described above can be modified as follows, for example.

In the first to third embodiments, the cell battery B is an LFP battery, but instead of this, other batteries having a plateau region or not having a plateau region may be used. In other words, even if the cell battery B does not have a plateau region, the OCV cannot be obtained during charging or power usage, so it is difficult to calculate the cell charge Q based on the cell voltage V, although not as difficult as when in the plateau region. Therefore, even if the cell battery B does not have a plateau region, the effect of being able to calculate the variation amount ΔQ based on the cell impedance Z when it is difficult to calculate the cell charge Q based on the cell voltage V is achieved.

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

In the first to third embodiments, the time differentiation of the cell impedance Z is defined as the "impedance change Zd", and the time differentiation of the impedance change Zd is defined as the "impedance double differentiation Zdd". Alternatively, the cell impedance Z may be differentiated with the current integration value ∫Idt to define the "impedance change Zd", and the impedance change Zd may be further differentiated with the current integration value ∫Idt to define the "impedance double differentiation Zdd". According to this aspect, even in a situation where the current is not constant, the promotion timing tP and the suppression timing tS can be determined with high accuracy.

In the first to third embodiments, the charge (Ah: ampere-hours) stored in the cell battery B is defined as the "cell charge amount Q". Alternatively, the stored energy (Wh: watt-hours) stored in the cell battery B may be defined as the "cell charge amount". In that case, the variation calculation unit 33 may calculate the variation amount (Wh) in energy conversion using the power integration value (Wh) instead of calculating the variation amount ΔQ (Ah) in charge conversion using the current integration value ∫Idt. The power integration value is the time integral 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 power integration value to obtain the "impedance change Zd", and the impedance change Zd may be further differentiated by the power integration value to obtain the "impedance double differentiation Zdd". According to this aspect, even in a situation where the power is not constant, the promotion timing tP and the suppression timing tS can be accurately determined.

In the first to third embodiments, the battery monitoring device 96 has an equalization necessity determination unit 36, a failure determination unit 37, and an equalization amount calculation unit 38. Alternatively, the battery monitoring device 96 may have only two of these three units, only one of them, or none of them.

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

In the first to third embodiments, the variation calculation unit 33 calculates the variation amount ΔQ based on the current integrated 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 an AC application circuit 40. Alternatively, for example, a discharge switch for each cell battery B may be turned ON and OFF to generate a specific current change for each cell battery B. The impedance (AC resistance) of the cell battery B at that time may then be detected as the cell impedance Z.

In the first to third embodiments, the impedance of cell battery B with respect to AC is referred to as "cell impedance Z." Alternatively, the impedance of cell battery B with respect to DC may be referred to as "cell impedance Z."

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

In the first to third embodiments, in addition to calculating the variation amount ΔQ based on the cell impedance Z, when in a non-plateau region and the OCV can be measured, the variation amount ΔQ is also calculated based on the cell voltage V. Alternatively, the variation amount ΔQ may be calculated based only on the cell impedance Z.

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

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

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

31... impedance detection unit, 32... storage amount determination unit, 33... variation calculation unit, 93... battery pack, 96... battery monitoring device, B... cell battery, tP... promotion timing (specific timing), tS... suppression timing (specific timing), Q... cell storage amount, QL... interval lower limit amount (specific storage amount), QU... interval upper limit amount (specific storage amount), Z... cell impedance, Zd... impedance change, Zdd... impedance second derivative, ΔQ... variation amount.

Claims (15)

A battery monitoring device (96) for monitoring a battery pack (93) having a series connection of a plurality of cell batteries (B),
an impedance detection unit (31) for detecting an impedance (Z) of the plurality of cell batteries when the amount of charge stored in the battery pack changes over time;
a storage amount determination unit (32) for determining that the storage amount (Q) of the cell battery has reached a specific storage amount (QL, QU) based on a change (Zdd) in the impedance change tendency (Zd) of the detected cell battery;
a variation calculation unit (33) that calculates a variation (ΔQ) in the amount of stored electricity (Q) between the cell batteries based on a difference between specific times (tP, tS) at which the amount of stored electricity reaches the specific amount of stored electricity between the cell batteries;
A battery monitoring device having The battery monitoring device according to claim 1, further comprising an equalization necessity determination unit (36) that determines whether or not to perform equalization to reduce the variation based on the calculated variation. The battery monitoring device according to claim 1 or 2, further comprising a failure determination unit (37) that determines whether the battery pack is faulty or not based on the calculated variation. The battery monitoring device according to any one of claims 1 to 3, further comprising an equalization amount calculation unit (38) that calculates an equalization amount, which is an amount by which the variation is reduced in equalization for reducing the variation, based on the calculated variation. The battery monitoring device according to any one of claims 1 to 4, wherein the variance calculation unit calculates the variance based on the current (I) or the integrated value (∫Idt) of the cell battery after a specific timing. The impedance includes an AC resistance,
An AC application circuit (40) that applies an AC voltage to the battery pack,
6. The battery monitoring device according to claim 1, wherein the impedance detection unit detects the impedance of the cell battery when the AC voltage is applied to the battery pack. When the change in the voltage of the cell battery relative to the change in the amount of stored electricity of the cell battery is in a plateau region that is smaller than a predetermined standard, the stored electricity amount specifying unit specifies that the amount of stored electricity of the cell battery has reached the specified amount of stored electricity based on a change in the trend of change in the impedance, and the variation calculation unit calculates the variation.
7. A battery monitoring device according to claim 1, wherein the variation is calculated by calculating the amount of charge stored in the cell battery based on the voltage of the cell battery when the cell battery is not in the plateau region. The battery monitoring device according to any one of claims 1 to 7, wherein the cell battery has graphite in the negative electrode. The battery monitoring device according to any one of claims 1 to 8, wherein the cell battery has an olivine structure in the positive electrode. an equalization necessity determination unit (36) that determines to perform equalization to reduce the variation on condition that a variation amount (ΔQ) indicating the magnitude of the variation is greater than an equalization determination variation amount (ΔQE);
The ratio of the current storage capacity to the initial storage capacity is defined as SOH.
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 larger than a predetermined standard compared to when the variation is smaller than the predetermined standard;
The battery monitoring device according to any one of claims 1 to 9. a failure determination unit (37) that determines that the battery pack is malfunctioning on condition that a variation amount (ΔQ) indicating the magnitude of the variation is greater than a malfunction determination variation amount (ΔQX);
The ratio of the current storage capacity to the initial storage capacity is defined as SOH.
the failure determination unit sets the failure determination variation amount to be larger when the variation in SOH between the cell batteries is larger than a predetermined standard compared to when the variation is smaller than the predetermined standard;
The battery monitoring device according to any one of claims 1 to 10. an equalization necessity determination unit (36) that determines to perform equalization to reduce the variation on condition that a variation amount (ΔQ) indicating the magnitude of the variation is greater than an equalization determination variation amount (ΔQE);
The ratio of the current storage capacity to the initial storage capacity is defined as SOH.
the equalization necessity determination unit sets the equalization determination variation amount to be smaller when the SOH of the battery pack is smaller than a predetermined standard compared to when the SOH is larger than the predetermined standard.
The battery monitoring device according to any one of claims 1 to 11. a failure determination unit (37) that determines that the battery pack is malfunctioning on condition that a variation amount (ΔQ) indicating the magnitude of the variation is greater than a malfunction determination variation amount (ΔQX);
The ratio of the current storage capacity to the initial storage capacity is defined as SOH.
the failure determination unit sets the failure determination variation smaller when the SOH of the battery pack is smaller than a predetermined standard than when the SOH is larger than the predetermined standard;
The battery monitoring device according to any one of claims 1 to 12. For each of the cell batteries, the variation (ΔQ) of the cell battery is calculated by subtracting the amount of charge of the cell battery with the smallest amount of charge from the amount of charge of the cell battery.
A battery monitoring device as described in any one of claims 1 to 13, wherein, when there is a cell battery whose stored energy amount is not identified as having reached the specific stored energy amount during charging of the battery pack, the variation calculation unit calculates the amount of variation of the cell battery to be greater than or equal to the amount of variation of the cell battery whose calculated amount of variation is the largest. For each of the cell batteries, the variation (ΔQ) of the cell battery is calculated by subtracting the amount of charge of the cell battery with the smallest amount of charge from the amount of charge of the cell battery.
A battery monitoring device as described in any one of claims 1 to 14, wherein, when the battery pack is discharged, if there is a cell battery whose stored energy amount is not determined to have reached the specified stored energy amount, the variation calculation unit calculates the amount of variation of the cell battery to be zero or less.

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