Battery management device

Abstract

To provide a battery management device that can appropriately prompt a user to charge a battery.SOLUTION: A battery management device includes a calculation unit that calculates the SOC and a coefficient from measured values of the battery's current and voltage on the basis of an estimation model that estimates the polarization voltage according to the SOC of the battery and the coefficient related to the increase in voltage corresponding to the SOC among the polarization voltages due to discharging the battery, and a notification unit that notifies the user to charge the battery when the SOC is below a threshold, and the notification unit lowers the threshold as the coefficient becomes smaller.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a battery management device. [Background technology]

[0002] For example, Patent Document 1 discloses a technology for estimating the state of charge (SOC) of a battery using an equivalent circuit model of a vehicle battery and using the SOC to manage the battery. The SOC serves as a guideline for encouraging the user to charge the battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-77199 Summary of the Invention [Problem to be solved by the invention]

[0004] For example, in lithium-ion batteries, when discharging, the diffusion resistance due to polarization increases in the low SOC range (for example, below 20%). As the diffusion resistance increases, the available power of the battery decreases. Therefore, even if the user is prompted to charge the battery in response to a drop in SOC, there may actually be an excess of power in the battery, or conversely, there may be an excessive power shortage, causing problems with the operation of the load.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to provide a battery management device that can appropriately prompt a user to charge the battery. [Means for solving the problem]

[0006] The battery management device of the present invention includes a calculation unit that calculates the SOC and the coefficient from measured values ​​of the current and voltage of the battery based on an estimation model that estimates the polarization voltage according to the SOC of the battery and a coefficient related to the increase in voltage corresponding to the SOC among the polarization voltages due to discharge of the battery, and a notification unit that notifies the user to charge the battery if the SOC is below a threshold, and the notification unit lowers the threshold as the coefficient becomes smaller.

[0007] In the battery management device, the notification unit may change the threshold value so that a linear relationship is established between the threshold value and the coefficient.

[0008] In the above-mentioned battery management device, the calculation unit may periodically calculate the voltage of the battery using the estimation model, and calculate the SOC and the coefficient so that the difference between the calculated value of the voltage of the battery and the measured value of the voltage of the battery converges.

[0009] In the battery management device, the battery may be a lithium ion battery.

[0010] In the above battery management device, the battery may supply power to an electric motor that drives a vehicle. [Effects of the Invention]

[0011] According to the present invention, it is possible to appropriately prompt the user to charge the battery. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of a battery system for a vehicle V. As shown in FIG. [Figure 2] FIG. 2 is a graph showing an example of the change in diffusion resistance of a lithium ion battery during charging and discharging relative to the SOC. [Figure 3] Fig. 3(a) is a functional block diagram showing an example of a state calculation unit, and Fig. 3(b) is a diagram showing an example of time variation of SOC when a battery cell is being discharged. [Figure 4]FIG. 4 is a graph showing an example of a change in discharge polarization voltage with respect to SOC. [Figure 5] FIG. 5 is a diagram illustrating an example of the threshold map. [Figure 6] FIG. 6 is a flowchart showing an example of the operation of the control device. DETAILED DESCRIPTION OF THE INVENTION

[0013] (Battery system configuration) 1 is a schematic diagram showing an example of a battery system for a vehicle V. The vehicle V has a control device 1 including one or more ECUs (Electronic Control Units), a battery pack 2 serving as a power source, an in-vehicle display 3 that displays various information to be communicated to a passenger (user), an inlet 6 for charging and discharging the battery pack 2, an inverter 4 that converts direct current to alternating current, and an electric motor (MG) 5 that serves as the power source for the vehicle V.

[0014] The battery pack 2 has battery cells 20, which are an example of batteries, a current sensor 21 that detects the current flowing through the battery cells 20, a voltage sensor 22 that detects the voltage of the battery cells 20, and a temperature sensor 23 that detects the temperature T of the battery cells 20. The detected values ​​of the current sensor 21, the voltage sensor 22, and the temperature sensor 23 are output to the control device 1. The battery cells 20 may be, for example, lithium ion batteries, but are not limited to this.

[0015] The control device 1 is an example of a battery management device. The control device 1 is a computer including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc. The ECU 1 operates the CPU according to a program stored in the ROM.

[0016] The control device 1 controls the inverter 4. The inverter 4 is connected between the battery pack 2 and the electric motor 5, and converts direct current into alternating current by the switching operation of multiple switch elements such as MOS-FETs (Metal-Oxide-Semiconductor Field Effect Transistors). The control device 1 outputs a PWM (Pulse Width Modulation) signal with a duty ratio according to the driving state of the vehicle V to the inverter 4.

[0017] The control device 1 also controls the charging of the battery cells 20. The battery cells 20 have a configuration in which, for example, multiple lithium-ion batteries are connected in series. The battery cells 20 supply DC power to an inverter 4, which drives an electric motor 5. The battery cells 20 are charged from an external charging stand 9 via an inlet 6. The control device 1 instructs, for example, the charging stand 9, on a target value of the current to be output during charging.

[0018] The control device 1 has, as software functions formed by program operation, an operation control unit 10, a capacity estimation unit 11, a state calculation unit 12, and a charge notification unit 13. Note that the operation control unit 10, the capacity estimation unit 11, the state calculation unit 12, and the charge notification unit 13 may be realized by hardware such as an integrated circuit.

[0019] The control device 1 also includes a nonvolatile memory 14 such as an EEPROM (Electrically Erasable Programmable ROM). The memory 14 stores OCV (Open Circuit Voltage) map data (OCV map) 140 and threshold map data (threshold map) 141.

[0020] The OCV map 140 and the threshold map 141 are generated based on experimental results and simulation results of the characteristics of the battery cell 20 and are written in advance to the memory 14. The OCV map 140 shows the correlation between the OCV and SOC of the battery cell 20. The threshold map 141 shows the correlation between the SOC threshold for promoting charging of the battery cell 20 and the discharge polarization coefficient, which will be described later.

[0021] The operation control unit 10 instructs the capacity estimation unit 11, the state calculation unit 12, and the charge notification unit 13 to operate in a predetermined sequence. The operation control unit 10 also controls the charging stand 9 and the inverter 4 during charging and discharging.

[0022] Cap=100÷(SOCe-SOCs)×Is (1)

[0023] The capacity estimation unit 11 estimates the full charge capacity Cap of the battery cell 20, for example, during charging at the charging stand 9. The capacity estimation unit 11 calculates the full charge capacity Cap, for example, according to the above formula (1). In formula (1), Is is an integrated value obtained by integrating the current value of the battery cell 20 for a predetermined period of time, SOCs is the SOC of the battery cell 20 when integration of the current of the battery cell 20 starts, and SOCe is the SOC of the battery cell 20 when integration of the current ends. The capacity estimation unit 11 calculates the integrated value Is from the detection value of the current sensor, for example, and obtains the detection value of the voltage sensor 22 during charging, i.e., the SOCe and SOCs according to the OCV, from the OCV map 140.

[0024] The state calculation unit 12 is an example of a calculation unit. The state calculation unit 12 calculates the SOC and the discharge polarization coefficient from the measured values ​​of the current and voltage of the battery cell 20 based on an estimation model that estimates the discharge polarization voltage according to the SOC of the battery cell 20 and the discharge polarization coefficient related to the increase in voltage according to the SOC among the polarization voltages (discharge polarization voltages) due to discharge of the battery cell 20. The measured values ​​of the current and voltage are obtained as the detected values ​​of the current sensor 21 and the voltage sensor 22, for example. The estimation model is constructed based on a circuit equation for the closed circuit voltage (CCV) of the battery cell 20, as will be described later.

[0025] The charge notification unit 13 is an example of a notification unit. When the SOC of the battery cell 20 is equal to or lower than a threshold, the charge notification unit 13 notifies the user of the vehicle V to prompt the user to charge the battery cell 20. The charge notification unit 13 acquires the SOC and discharge polarization coefficient calculated by the state calculation unit 12 via the operation control unit 10, and acquires a threshold value corresponding to the discharge polarization coefficient from the threshold map 141. The charge notification unit 13 determines whether charging is necessary using the threshold value corresponding to the discharge polarization coefficient, and therefore can appropriately prompt the user to charge according to the usage state of the battery cell 20, as will be described later.

[0026] When the SOC is equal to or lower than the threshold value, the charge notification unit 13 displays a charge notification, for example, using letters or symbols, on the in-vehicle display 3. This allows the user to recognize that the battery cell 20 needs to be charged at the appropriate time, and allows the user to charge the battery cell 20 at the appropriate time when the battery cell 20 is not in a state of excess power and before the power runs short. Note that, although the in-vehicle display 3 is used in this example as a means for notifying the user of the need for charging, this is not limiting, and other means such as audio notification using a speaker or light emission by an LED (Light Emitting Diode) may also be used.

[0027] (Processing of the state calculation unit)

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[0028] The state calculation unit 12 uses, for example, the above formula (2) as an estimation model. In formula (2), OCV is the open circuit voltage of the battery cell 20, and SOC is the charging rate of the battery cell 20. I is the detection value of the current sensor 21, and R is the internal resistance value of the battery cell 20. Cap is the full charge capacity of the battery cell 20 (see formula (1) above). Δt is the execution period of the calculation according to formula (2).

[0029] Vc is the portion of the polarization voltages (charge polarization voltage and discharge polarization voltage) that are generated by charging and discharging the battery cell 20 that does not depend on the SOC (charge polarization voltage), p is the discharge polarization coefficient, and a to d are constants that are set in advance based on previous experimental results and simulations.

[0030] In equation (2), the term (discharge polarization estimation term) including the discharge polarization coefficient p, constants a to d, detected value I, full charge capacity Cap, and execution period Δt is the discharge polarization voltage of the battery cell 20 that depends on the amount of change in SOC within the execution period Δt. The discharge polarization estimation term calculates the amount of change in SOC within the execution period Δt from the ratio of the integrated value of the current detected value I to the full charge capacity Cap, and estimates the increase in discharge polarization voltage associated with an increase in diffusion resistance in the low SOC region from the value multiplied by the discharge polarization coefficient p, which is a weighting coefficient. The constants a to d are determined, for example, from the characteristics of the diffusion resistance during discharge of the battery cell 20, which will be described below.

[0031] FIG. 2 shows an example of the change in diffusion resistance (mΩ) of a lithium-ion battery during charging (see "△") and discharging (see "●") versus SOC (%). The diffusion resistance during charging is substantially constant regardless of the SOC. On the other hand, the diffusion resistance during discharging is substantially constant when the SOC is 20 to 100%, but increases as the SOC decreases when the SOC is 0 to 20%.

[0032] When the diffusion resistance increases, the polarization voltage of the battery cell 20 increases. The discharge polarization coefficient p is a parameter that indicates the degree (weight) of the increase in the discharge polarization voltage that depends on the SOC, and indicates a larger value in the low SOC range (0 to 20% in the above example) than in other ranges. By using an estimation model that includes the discharge polarization coefficient p, the state calculation unit 12 can perform highly accurate calculations that take into account the increase in the discharge polarization voltage in the low SOC range. Note that the discharge polarization coefficient p is an example of a coefficient.

[0033] The state calculation unit 12 acquires the detected values ​​I and V from the current sensor 21 and the voltage sensor 22, respectively, every execution period Δt, and calculates the CCV using equation (2). At this time, the state calculation unit 12 acquires the latest full charge capacity Cap from the capacity estimation unit 11. The state calculation unit 12 updates the internal resistance value R, the charge / discharge polarization voltage Vc, and the discharge polarization coefficient p every execution period Δt according to the difference between the detected value V of the voltage sensor 22 and the CCV. The state calculation unit 12 calculates the SOC and the discharge polarization coefficient p according to, for example, a prediction error method, so as to minimize the difference between the CCV and the detected value V of the voltage sensor.

[0034] 3(a) is a functional block diagram showing an example of the state calculation unit 12. The state calculation unit 12 has an estimation model 120 expressed by equation (2), a parameter update unit 121, and an adder 122. The estimation model 120 calculates the CCV from equation (2) according to the detection value I of the current sensor 21 for each execution period Δt, and outputs the CCV to the adder 122.

[0035] The adder 122 receives the detection value V of the voltage sensor 22 and the CCV calculated by the estimation model 120. The detection value V of the voltage sensor 22 is a closed circuit voltage corresponding to the value of the current flowing through the battery cell 20 (detection value I of the current sensor 21). The adder 122 outputs the difference ΔV (=V−CCV) between the detection value V and the CCV to the parameter update unit 121.

[0036] SOC[t+Δt]=SOC[t]-I×Δt / 3600 / Cap×100 +Ga×ΔV (3) R[t+Δt]=R[t]+Gb×ΔV (4) Vc[t+Δt]=Vc[t]+Gc×ΔV (5) p[t+Δt]=p[t]+Gd×ΔV (6)

[0037] The parameter update unit 121 updates the SOC, internal resistance value R, charge / discharge polarization voltage Vc, and discharge polarization coefficient p of the battery cell 20 according to the above equations (3) to (6) in accordance with the difference ΔV between the detected value V and the CCV. The SOC, internal resistance value R, charge / discharge polarization voltage Vc, and discharge polarization coefficient p are stored in the memory 14 each time they are calculated.

[0038] In equations (3) to (6), Ga, Gb, Gc, and Gd are the gains of the difference ΔV related to the SOC, internal resistance R, charge / discharge polarization voltage Vc, and discharge polarization coefficient p, respectively. The gains Ga to Gd are set so that the difference ΔV converges based on prior experimental results, simulation results, etc. Note that the internal resistance R may be calculated by referring to map data from the SOC and the detection value of the temperature sensor 23, instead of equation (4). Furthermore, at the start of calculation, the parameter update unit 121 calculates the SOC[t+Δt] using equation (3) with the difference ΔV=0 from the last stored SOC[t]. Note that the latest values ​​of the SOC, internal resistance R, charge / discharge polarization voltage Vc, and discharge polarization coefficient p are stored in the memory 14 as needed, and their initial values ​​are set based on the actual measured values ​​of the battery cell 20.

[0039] The parameter update unit 121 calculates each value at time (t+Δt) (see [t+Δt]) by adding the product of each of the difference ΔV and the gains Ga to Gd to each value of the SOC, internal resistance value R, charge / discharge polarization voltage Vc, and discharge polarization coefficient p at time t (see [t]). The parameter update unit 121 outputs the SOC, internal resistance value R, charge / discharge polarization voltage Vc, and discharge polarization coefficient p at time (t+Δt) to the estimation model 120.

[0040] The estimation model 120 calculates the CCV from the internal resistance value R, charge / discharge polarization voltage Vc, and discharge polarization coefficient p input from the parameter update unit 121, and the detection value I of the current sensor 21. At this time, the state calculation unit 12 calculates the OCV according to the SOC based on the OCV map 140. The estimation model 120 outputs the discharge polarization coefficient p and the SOC to the charge notification unit 13 via the operation control unit 10.

[0041] In this way, the state calculation unit 12 periodically calculates the CCV of the battery cell 20 using the estimation model 120, and calculates the SOC and the discharge polarization factor p according to the prediction error method so that the difference ΔV between the calculated CCV value and the detected value V of the voltage sensor 22 converges. This allows the state calculation unit 12 to calculate the SOC and the discharge polarization factor p with high accuracy. Note that the state calculation unit 12 may also calculate the SOC and the discharge polarization factor p according to a method other than the prediction error method.

[0042] 3(b) is a diagram showing an example of the change over time in SOC (%) during discharge of the battery cell 20. The solid line indicates the SOC calculated by the estimation model 120 using the above formula (2) (Example), the dashed-dotted line indicates the SOC calculated by the estimation model 120 using a formula obtained by removing the discharge polarization estimation term from formula (2) (Comparative Example), and the dotted line indicates the actually measured value of SOC.

[0043] In the comparative example, the error from the actual measurement value increases when the SOC becomes about 15% or less because the increase in discharge polarization voltage due to the increase in diffusion resistance in the low SOC region as shown in Fig. 2 is not calculated. In contrast, in the example, the increase in discharge polarization voltage is calculated using the discharge polarization estimation term, so the error from the actual measurement value is smaller than in the comparative example even when the SOC becomes about 15% or less.

[0044] In this way, the state calculation unit 12 can calculate the SOC with high accuracy by reflecting the increase in diffusion resistance during discharge using the discharge polarization estimation term including the discharge polarization coefficient p.

[0045] (Charging notification processing)

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[0046] 4 is a graph showing an example of the change in discharge polarization voltage (mV) versus SOC (%). This example shows the results of a simulation in which the discharge polarization voltage when a battery cell 20 with an SOC of 30% is discharged while the current is maintained constant is calculated using the left side of the above equation (7) obtained from equation (2). Here, the magnitude of the current (I in equation (7)) was set to three values: "large," "medium," and "small."

[0047] The larger the current of the battery cell 20, the larger the discharge polarization voltage. In the region where the SOC is approximately 15% or less, the discharge polarization voltage increases as the SOC decreases due to an increase in diffusion resistance. At this time, the degree of increase in the discharge polarization voltage increases as the current of the battery cell 20 increases. Therefore, in the region where the SOC is approximately 15% or less, the power of the battery cell 20 is consumed in accordance with the increase in voltage according to the SOC.

[0048] For this reason, when the SOC is low, the effect of discharge polarization varies depending on the usage state of the battery cell 20. If the charge notification unit 13 always prompts the user to charge the battery cell 20 when the SOC becomes 15% or less, regardless of the magnitude of the current, it is conceivable that the battery cell 20 has an excessive amount of power remaining when the current is "small." For example, when the vehicle V is traveling on an ordinary road, the current of the battery cell 20 is small ("small current"), so the charge notification is issued early and it is difficult to use up the power without waste.

[0049] On the other hand, when the current is "large" or "medium," it is possible that the battery cell 20 will have an excessive power shortage. For example, when the vehicle V is traveling on a highway, the current of the battery cell 20 is large (current "large"), so the notification of charging may be delayed, and the lack of power may cause problems in the traveling of the vehicle V.

[0050] Therefore, the smaller the discharge polarization coefficient p, the lower the SOC threshold value (SOC threshold value) used for notifying of charge is, by the charge notification unit 13. For example, the charge notification unit 13 obtains a threshold value according to the discharge polarization coefficient p from the threshold map 141.

[0051] FIG. 5 is a diagram showing an example of the threshold map 141. In FIG. 5, the horizontal axis represents the SOC threshold (%), and the vertical axis represents the discharge polarization coefficient p. Line segment L shows the correlation between the discharge polarization coefficient p and the SOC threshold. In this example, the discharge polarization coefficient p and the SOC threshold have a linear relationship. The charge notification unit 13 acquires the SOC threshold corresponding to the discharge polarization coefficient p based on the line segment L. For example, when the discharge polarization coefficient p is Px, the line segment L determines that SOC_TH is the SOC threshold.

[0052] If the SOC is equal to or lower than the SOC threshold, the charge notification unit 13 displays a notification on the in-vehicle display 3 urging the user to charge the battery cell 20, and if the SOC is higher than the SOC threshold, the charge notification unit 13 does not display a notification on the in-vehicle display 3. In other words, of the two areas Sa, Sb separated by the line segment L, if the SOC and discharge polarization coefficient p calculated by the state calculation unit 12 are in area Sb (the side with the larger SOC threshold), the charge notification unit 13 does not provide a notification, but if the SOC and discharge polarization coefficient p are in area Sa (the side with the smaller SOC threshold), the charge notification unit 13 provides a notification.

[0053] In this way, the larger the discharge polarization coefficient p, the larger the SOC threshold value used by the charge notification unit 13 to determine whether to issue a charge notification. Therefore, in the example of FIG. 4, when the current is "large" or "medium," the determination of whether to issue a charge notification is based on a larger SOC threshold value than when the current is "small." This allows the control device 1 to prompt the user to charge at an appropriate time depending on the usage state of the battery cell 20.

[0054] Furthermore, the charge notification unit 13 changes the SOC threshold so that a linear relationship is established with the discharge polarization coefficient p. Therefore, if the diffusion resistance during discharge of the battery cell 20 increases linearly with the decrease in SOC, the SOC threshold can be set with high accuracy. The maximum and minimum values ​​of the SOC threshold are set appropriately depending on the usage environment of the battery cell 20.

[0055] (Control device operation) 6 is a flowchart showing an example of the operation of the control device 1. This operation is executed, for example, at regular time intervals.

[0056] First, the operation control unit 10 determines whether the battery cell 20 is being charged (step St1). If the battery cell 20 is being charged (Yes in step St1), the capacity estimation unit 11 estimates the full charge capacity Cap of the battery cell 20 (step St2). If the battery cell 20 is not being charged (No in step St1), the operation of step St2 is not performed.

[0057] Next, the operation control unit 10 determines whether the vehicle V is running (step St3). If the vehicle V is not running (No in step St3), the operation ends. If the vehicle V is running (Yes in step St3), the state calculation unit 12 calculates the SOC and discharge polarization coefficient p of the discharging battery cell 20 using the above method (step St4). Note that while the vehicle V is running, power is supplied from the battery cell 20 to the electric motor 5.

[0058] Next, the charge notification unit 13 calculates the SOC threshold value based on the discharge polarization coefficient p and the threshold value map 141 (step St5). Next, the charge notification unit 13 compares the SOC with the SOC threshold value (step St6). If SOC≦SOC threshold value is satisfied (Yes in step St6), the charge notification unit 13 outputs a charge notification to the in-vehicle display 3 (step St7). On the other hand, if SOC>SOC threshold value is satisfied (No in step St6), the charge notification unit 13 terminates operation without outputting a charge notification. In this manner, the control device 1 operates.

[0059] In this way, the state calculation unit 12 calculates the SOC and the discharge polarization coefficient p from the detected values ​​I and V of the current and voltage of the battery cell 20 based on the estimation model 120 that estimates the discharge polarization voltage according to the SOC of the battery cell 20 and the discharge polarization coefficient p related to the increase in voltage according to the SOC among the discharge polarization voltages of the battery cell 20. When the SOC is equal to or lower than the SOC threshold, the charge notification unit 13 notifies the user to urge them to charge the battery cell 20, and decreases the SOC threshold as the discharge polarization coefficient p becomes smaller.

[0060] Therefore, the state calculation unit 12 can calculate the SOC and discharge polarization coefficient p with high accuracy by reflecting the increase in discharge polarization voltage that accompanies an increase in diffusion resistance in the low SOC region during discharge of the battery cell 20. Furthermore, the charge notification unit 13 can appropriately prompt the user to charge the battery in response to an increase in discharge polarization voltage by lowering the SOC threshold as the discharge polarization coefficient p becomes smaller.

[0061] Furthermore, it is preferable to use lithium-ion batteries as the battery cells 20 because they are highly versatile. Furthermore, since the battery cells 20 supply power to the electric motor 5 that drives the vehicle V, the operation of the control device 1 described above can appropriately prompt the user to charge the battery while the vehicle V is traveling. Note that the control device 1 is not limited to the vehicle V, and may also be used to notify the user to charge the battery cells of electronic devices such as smartphones, for example.

[0062] The above-described embodiment is a preferred example of the present invention, but the present invention is not limited to this and can be modified in various ways without departing from the spirit of the present invention. [Explanation of symbols]

[0063] 1 control device (battery management device), 3 on-board display, 5 electric motor, 12 state calculation unit (calculation unit), 13 charge notification unit (notification unit), 20 battery cell (battery), 120 estimation model, V vehicle

Claims

1. a calculation unit that calculates the SOC and the coefficient from measured values ​​of the current and voltage of the battery based on an estimation model that estimates the polarization voltage according to the SOC of the battery and a coefficient related to an increase in voltage corresponding to the SOC among polarization voltages due to discharge of the battery; a notification unit that notifies a user to charge the battery when the SOC is equal to or lower than a threshold value; The notification unit decreases the threshold value as the coefficient decreases. Battery management device.

2. The notification unit changes the threshold value so that a linear relationship is established between the threshold value and the coefficient. The battery management device according to claim 1 .

3. the calculation unit periodically calculates the voltage of the battery using the estimation model, and calculates the SOC and the coefficient so that a difference between the calculated value of the voltage of the battery and the measured value of the voltage of the battery converges. The battery management device according to claim 1 or 2.

4. The battery is a lithium ion battery. The battery management device according to claim 1 or 2.

5. The battery supplies power to an electric motor that drives the vehicle. The battery management device according to claim 1 or 2.

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