JP2021128853A - Battery charge state estimation device - Google Patents

Abstract

To provide a battery charge state estimation device capable of estimating the charge state with less error.SOLUTION: The battery charge state estimation device includes a current sensor 35 for detecting a charge/discharge current in a battery in which a plurality of battery cells are stacked and arranged and the plurality of battery cells are electrically connected, a microcomputer 31, and a strain gauge 33 for detecting an expansion/contraction state in a stacking direction in the plurality of battery cells. The microcomputer 31 estimates SOC of the battery by integrating the charge/discharge current detected by the current sensor 35. The microcomputer 31 corrects the SOC of the battery based on the change in the expansion/contraction state by the strain gauge 33.SELECTED DRAWING: Figure 1

Description

The present invention relates to a battery charge state estimation device.

The charging state of a battery is estimated by integrating the charge / discharge current detected by the current sensor (for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2019-144039

However, when time is taken on the horizontal axis and SOC (state of charge) is taken on the vertical axis as shown in FIG. 7, the SOC estimated by integrating the charge / discharge current shown in L10 is, for example, high. When charging is repeated without waiting for operation and full charge (when replenishment charging is repeatedly used), the difference ΔL10 between the true SOC indicated by L11 and the estimated SOC indicated by L10 becomes large. That is, the current measurement error of the current sensor becomes the SOC error ΔL10 as it is, and the SOC error ΔL10 also increases with the passage of time.

An object of the present invention is to provide a battery charge state estimation device capable of estimating a charge state with less error.

The battery charge state estimation device for solving the above problems is a current sensor that detects the charge / discharge current in a battery in which a plurality of secondary batteries are stacked and arranged and the plurality of secondary batteries are electrically connected. A charging state estimating means that estimates the charging state of the battery by integrating the charge / discharge current detected by the current sensor, and an expansion / contraction state that detects the expansion / contraction state of the plurality of secondary batteries in the stacking direction. The gist is that the detection means and the correction means for correcting the charge state of the battery by the charge state estimation means based on the change in the expansion / contraction state by the expansion / contraction state detection means are provided.

According to this, a plurality of secondary batteries are stacked and arranged, and the charge / discharge current in the battery in which the plurality of secondary batteries are electrically connected is calculated by the current sensor, and the current sensor is calculated by the charging state estimation means. The charge state of the battery is estimated by integrating the charge / discharge current detected in. The expansion / contraction state detecting means detects the expansion / contraction state of a plurality of secondary batteries in the stacking direction, and the correction means corrects the charging state of the batteries by the charging state estimating means based on the change in the expansion / contraction state. NS. Therefore, the charging state can be estimated with less error.

Further, in the battery charge state estimation device, the plurality of secondary batteries are sandwiched between a pair of end plates, and the expansion / contraction state detecting means applies strain to a connecting member connecting the pair of end plates. It should be a strain gauge that detects.

According to the present invention, the charging state can be estimated with less error.

The electrical block diagram of the battery system in embodiment. (A) is a plan view of the battery pack, (b) is a front view of the battery pack, and (c) is a right side view of the battery pack. Perspective view of the battery cell. A characteristic diagram showing the relationship between SOC and battery volume. A flowchart for explaining the action. A time chart showing the transition of SOC in the embodiment. A time chart showing the transition of SOC for explaining the problem.

Hereinafter, an embodiment embodying the present invention will be described with reference to the drawings.
The battery system 9 shown in FIG. 1 includes a battery pack 10, a plurality of loads 20, 21 and a microcomputer 31. The battery system 9 is provided in an electric forklift, and a traveling motor or the like can be driven by the battery pack 10.

As shown in FIGS. 2A, 2B, and 2C, the battery pack 10 is configured by stacking and arranging a plurality of battery cells 11 and electrically connecting the plurality of battery cells 11. Has been done. A lithium ion secondary battery can be used as the battery pack 10 (battery cell 11).

Specifically, the battery cell 11, which is a secondary battery, has a main body portion 12 and positive and negative electrodes 13 as shown in FIG.
The main body 12 has a box shape and has a rectangular upper surface and a lower surface in the plan view shown in FIG. 2 (a), and has a rectangular front surface and a back surface in the front view shown in FIG. 2 (b). It has left and right rectangular sides in the side view shown in (c). Positive and negative electrodes 13 are arranged apart from each other on the upper surface of the main body 12. The main body 12 of each battery cell 11 expands and contracts as the battery is charged and discharged.

A plurality of battery cells 11 are arranged so as to be superposed, and the plurality of battery cells 11 are connected in series with electrodes 13 of adjacent battery cells 11 in an electrically connected state by a conductor.
A plurality of battery cells 11 arranged in a stacked manner are sandwiched between the end plates 14 and 15 in the stacking direction. As shown in FIG. 2B, the end plates 14 and 15 have a rectangular shape when viewed from the front, and have a larger dimension than the main body 12 of the battery cell 11. Through bolts 16 are provided at the four corners of the rectangular end plates 14 and 15, respectively. The through bolt 16 is used together with the nut 17. The through bolt 16 penetrates the end plates 14 and 15. The head portion 16a of the through bolt 16 is located on the outer surface of the end plate 15, and the nut 17 is screwed into the threaded portion 16b of the through bolt 16 on the outer surface of the end plate 14.

A state in which a plurality of stacked battery cells 11 are compressed and fixed between the end plate 14 and the end plate 15 while the distance between the end plate 14 and the end plate 15 is kept constant by the through bolt 16. It is sandwiched between.

As shown in FIG. 1, the negative electrode of the battery pack 10 is grounded, and the load 20, the load 21, and the like are connected in parallel to the positive electrode. Then, electric power is supplied from the battery pack 10 to the load 20, the load 21, and the like.

As shown in FIG. 1, the charger 25 can be connected to the positive electrode of the battery pack 10 at the charging station. Then, the forklift can travel to the charging station, and the battery pack 10 mounted on the forklift can be charged using the charger 25.

As shown in FIG. 1, the forklift is equipped with a microcomputer 31, a memory 32, a strain gauge 33, an SOC display 34, and a current sensor 35. A memory 32, a strain gauge 33, an SOC display 34, and a current sensor 35 are connected to the microcomputer 31.

In the present embodiment, the battery charge state estimation device 30 is configured by the microcomputer 31, the strain gauge 33, and the current sensor 35, and the microcomputer 31 uses the current sensor 35 and the strain gauge 33 to determine the SOC as the battery charge state. It is estimated and stored in the memory 32 and displayed on the SOC display 34.

The current sensor 35 can detect the charge / discharge current in a battery in which a plurality of battery cells 11 are stacked and arranged and the plurality of battery cells 11 are electrically connected.
The SOC of the battery can be estimated by integrating the charge / discharge current detected by the current sensor 35 with the microcomputer 31.

As shown in FIGS. 2 (a) and 2 (c), the strain gauge 33 is attached to the through bolt 16, and the strain applied to the through bolt 16 that holds a constant distance between the pair of end plates 14 and 15. Is detected. This makes it possible to detect the expansion / contraction state of the plurality of battery cells 11 in the stacking direction, that is, the expansion / contraction amount. Specifically, the microcomputer 31 detects the amount of expansion and contraction of the through bolt 16 due to the volume expansion of the battery cell from the strain gauge 33. Specifically, the stress corresponding to the amount of strain applied to the through bolt 16 detected by the strain gauge 33 can be taken in.

The microcomputer 31 can correct the SOC, which is the charged state of the battery, based on the change in the expansion / contraction state.
FIG. 4 shows the characteristics of the battery cell with respect to the battery volume, with SOC on the horizontal axis and battery volume on the vertical axis. In FIG. 4, as the characteristic line L20, when the SOC is smaller than 55%, the battery volume is constant, and when the SOC is larger than 55%, the battery volume gradually increases. That is, the battery cell expands and contracts as the battery cell 11 is charged and discharged, and the battery volume, which is the degree of expansion and contraction, corresponds to the SOC, and the inclination of the battery volume suddenly changes when the SOC is around 55%.

Next, the action will be described.
The microcomputer 31 estimates the state of charge of the battery by integrating the charge / discharge current detected by the current sensor 35. Specifically, the SOC is estimated by the following equation (1). X is the SOC (remaining amount SOC) at startup by key-on of the battery system 9, Y is the total capacity of the battery, I is the detected charge / discharge current, and t is the time.

・・・（１）
マイコン３１は、図５に示すＳＯＣリセット処理ルーチンを実行する。この処理ルーチンは一定時間ごとに起動される。

... (1)
The microcomputer 31 executes the SOC reset processing routine shown in FIG. This processing routine is started at regular intervals.

FIG. 6 shows the transition of SOC. In FIG. 6, the horizontal axis represents time and the vertical axis represents SOC. In FIG. 6, L1 shows the estimated SOC in this embodiment. Also, in FIG. 6, L11 shows the true SOC. Further, in FIG. 6, the SOC estimated in the conventional method (same as L10 in FIG. 7) is shown in L10.

As shown by L1 and L10 in FIG. 6, charging is repeated without waiting for high operation and full charge (SOC = 100%). That is, replenishment charging is repeatedly used. As a result, charging and discharging are repeated in the range where the SOC is less than 100% and, for example, 10% or more. As a result, the current measurement error of the current sensor 35 is directly reflected in the SOC error ΔL10 (see FIG. 7). That is, in FIG. 7, the difference ΔL10 between the true SOC shown by L11 and the conventional SOC shown by L10 increases with the passage of time.

The microcomputer 31 takes in the stress corresponding to the amount of strain applied to the through bolt 16 from the strain gauge 33 in step S100 of FIG. Then, in step S101, the microcomputer 31 determines whether or not the inclination of the stress corresponding to the amount of strain applied to the through bolt 16 has suddenly changed.

In FIG. 4, there is no change in the battery volume (distortion) from 0 to 55% in the direction in which the SOC increases during charging. That is, the inclination is almost zero, and the inclination does not change suddenly. Similarly, in FIG. 4, the amount of change in the battery volume (strain) is almost constant until the SOC is around 100 to 55% in the direction in which the SOC decreases during discharge. That is, when the SOC is 55% or more, the increase is monotonous, the slope remains almost the same, and the slope does not change suddenly. In FIG. 4, the inclination, which is a change in the battery volume (strain), suddenly changes when the SOC is around 55%. Therefore, in step S101 of FIG. 5, it is determined whether or not the slope of the stress corresponding to the amount of strain suddenly changes.

In FIG. 5, when the microcomputer 31 detects a sudden change in the slope of the stress corresponding to the amount of strain, it corrects it by overwriting the SOC to 55% in step S102.
Explaining with reference to FIG. 6, when the SOC changes in the downward direction during discharging, the SOC is forcibly overwritten to 55% at the timing of t1 in FIG. Similarly, the SOC is forcibly overwritten to 55% at the timing of t3 in FIG.

If the SOC changes in the increasing direction during charging, the SOC is forcibly overwritten to 55% at the timing of t2 in FIG. Similarly, the SOC is forcibly overwritten to 55% at the timing of t4 in FIG.

In addition, when shifting from step S101 to step S102 in FIG. 5, if the sudden change in the stress gradient corresponding to the strain amount occurs a plurality of times in step S101, the process shifts to step S102 and the SOC is overwritten with 55%. It may be.

As described above, in the present embodiment, the battery pack is a battery that expands and contracts with charging and discharging. In addition, as shown in FIG. 4, the battery has one or more points where the slope of volume expansion / contraction suddenly changes when graphed with SOC on the horizontal axis and battery volume on the vertical axis.

Then, at the time of control, the SOC in which the volume of the battery suddenly changes is obtained in advance, and when the sudden change in volume is detected, the SOC reset is executed. Specifically, in the battery having the characteristics of FIG. 4, the SOC is overwritten with 55% when a sudden change in volume is detected.

As described above, a plurality of battery cells 11 are superposed, sandwiched between the end plates 14 and 15, and compressed and fixed by the through bolts 16. A strain gauge 33 is attached to the through bolt 16 to detect the amount of expansion and contraction of the through bolt 16 due to the volume expansion of the battery cell 11. From the relationship between the battery volume and the SOC, the relationship between the stress applied to the through bolt 16 detected by the strain gauge 33 and the SOC is obtained in advance.

Conventionally, the current value detected by the current sensor is integrated (integrated) with time to calculate the SOC fluctuation, but if the SOC is calculated only by this method, the detection error of the current sensor becomes the SOC error as it is. In addition, the SOC error increases as time passes. Therefore, the SOC due to the current sensor error is used by using a method of overwriting the SOC to 100% when a predetermined charging sequence is completed or a method of overwriting the SOC from the SOC-OCV curve at the timing when the polarization is settled without charging / discharging for a while. The method of resetting the error is taken.

In the present embodiment, the SOC is reset to overwrite the SOC when a predetermined condition is satisfied.
When a user (for example, a forklift occupant) operates at high speed and repeatedly uses recharge without waiting for full charge, the SOC is not reset, current sensor error is accumulated, and the SOC error continues to increase. Further, in the case of the method of overwriting the SOC from the SOC-OCV curve, for example, when the vehicle is always running, the battery is continuously used, the battery cannot be polarized, the SOC cannot be overwritten, and the current sensor error is accumulated. And the SOC error continues to increase.

In the present embodiment, by increasing the chances of resetting the SOC, it is possible to facilitate the reset of the SOC even in a usage such as high operation and recharge, and it is possible to suppress the continuous accumulation of the current sensor error.

That is, even in a situation where the conventional SOC reset (when fully charged, when the polarization is settled) is not possible, the SOC can be reset without complicated control. In addition, the charge state of the battery can be estimated closer to the true SOC by adding only one strain gauge 33 for each battery pack.

According to the above embodiment, the following effects can be obtained.
(1) As a configuration of the battery charge state estimation device 30, the charge / discharge current in a battery in which a plurality of battery cells 11 as secondary batteries are stacked and arranged and the plurality of battery cells 11 are electrically connected is detected. The current sensor 35, the microcomputer 31, and the strain gauge 33 as the expansion / contraction state detecting means for detecting the expansion / contraction state in the stacking direction of the plurality of battery cells 11 are provided. The microcomputer 31 as the charging state estimating means estimates the SOC as the charging state of the battery by integrating the charge / discharge current detected by the current sensor 35. The microcomputer 31 as the correction means corrects the SOC of the battery based on the change in the expansion / contraction state by the strain gauge 33. Therefore, the SOC of the battery is corrected based on the change in the expansion / contraction state, and the SOC can be estimated with less error.

(2) A plurality of battery cells 11 are sandwiched between a pair of end plates 14 and 15, and an expansion / contraction state detecting means is added to a through bolt 16 as a connecting member connecting the pair of end plates 14 and 15. The strain gauge 33 for detecting distortion. Therefore, it is possible to easily detect the expansion / contraction state of the plurality of battery cells 11 arranged in a stacked manner in the stacking direction.

In particular, by adopting a method of overwriting the SOC when the inclination of the battery volume suddenly changes, the SOC can be accurately overwritten (corrected) even when the characteristic line of FIG. 4 shifts due to deterioration of the battery. Therefore, it is possible to make it less susceptible to the deterioration of the battery.

The embodiment is not limited to the above, and may be embodied as follows, for example.
〇 In Fig. 4, there was only one place where the battery volume suddenly changed in response to the change in SOC, but not limited to this, there may be multiple places where the battery volume suddenly changes, and the SOC is changed at each place where the inclination changes suddenly. You may want to reset it.

○ The battery system is provided in an electric forklift and is applied when the traveling motor or the like is driven by the battery pack 10, but it is also applied when it is provided in an electric passenger car and the traveling motor or the like is driven by the battery pack. You may. In particular, a battery in a hybrid vehicle is repeatedly charged and discharged in a range where the SOC is less than 100% and a predetermined SOC or more, and has the same problem as the above-mentioned high operation and repeated recharging without waiting for full charge. However, in this case, by correcting the charging state of the battery based on the change in the expansion / contraction state of the battery, the charging state can be estimated with less error.

〇 Battery systems are not limited to electric vehicles.
○ The secondary battery may be other than a lithium ion secondary battery, and the type of secondary battery does not matter.
〇 The SOC may be overwritten by a method other than the processing shown in FIG. 5, and the SOC may be overwritten (corrected) at the point where the inclination of the battery volume suddenly changes when the relationship shown in FIG. 4 is known in advance.

〇 As the state of charge of the battery, in the above-described embodiment, SOC (state of charge), which is a state variable representing the ratio of the remaining amount of the battery based on the fully charged state, is used. , The depth of discharge (1-SOC) may be used as the charging state of the battery.

10 ... Battery pack, 11 ... Battery cell (secondary battery), 14 ... End plate, 15 ... End plate, 16 ... Through bolt (connecting member), 30 ... Battery charge state estimation device, 31 ... Microcomputer (charge state estimation) Means, correction means), 33 ... strain gauge (expansion / contraction state detecting means), 35 ... current sensor.

Claims (2)

A current sensor that detects the charge / discharge current in a battery in which a plurality of secondary batteries are stacked and arranged and the plurality of secondary batteries are electrically connected.
A charging state estimating means for estimating the charging state of the battery by integrating the charge / discharge current detected by the current sensor, and
An expansion / contraction state detecting means for detecting an expansion / contraction state in the stacking direction of the plurality of secondary batteries, and an expansion / contraction state detecting means.
A correction means for correcting the charging state of the battery by the charging state estimating means based on the change in the expansion / contraction state by the expansion / contraction state detecting means.
A battery charge state estimation device. The plurality of secondary batteries are sandwiched between a pair of end plates, and the plurality of secondary batteries are sandwiched between a pair of end plates.
The battery charge state estimation device according to claim 1, wherein the expansion / contraction state detecting means is a strain gauge that detects a strain applied to a connecting member connecting the pair of end plates.

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