Battery Control Device

Abstract

To provide a battery control device which can properly activate regeneration brake at the time of downhill traveling when a battery is degraded.SOLUTION: A battery control device 10 controlling discharge and charge of a battery 22 mounted on a battery electric vehicle 20 comprises the steps of: predicting vacant capacity of the battery 22 as a pocket capacity CPpt required for activation of regeneration brake at the time of downhill traveling when the battery 22 is charged by an external power source; calculating an upper limit charge rate capable of securing the pocket capacity CPpt as a corrected upper limit charge rate SOCup# based on the pocket capacity CPpt and a degradation rate SOH of the battery 22; and controlling charging from the external power source so that the charge rate SOC of the battery 22 is the corrected upper limit charge rate SOCup# or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This specification discloses a battery control device that controls charging and discharging of a battery mounted on a battery electric vehicle. [Background technology]

[0002] Battery electric vehicles, which use power from a battery installed on the vehicle to drive the traction motor, have been known for some time. When traveling downhill, regenerative braking is used to assist the foot brake. Regenerative braking is a braking force obtained by operating the traction motor as a generator. By using regenerative braking, the use of the foot brake is reduced, which helps prevent deterioration of the foot brake. Furthermore, by activating regenerative braking, a portion of the potential energy can be converted into electricity and stored, improving fuel economy.

[0003] In order to utilize regenerative braking, the battery must have sufficient free capacity (hereinafter referred to as "pocket capacity") to receive the regenerative power. Therefore, techniques have been proposed to adjust the battery's charging rate depending on the possibility of using regenerative braking.

[0004] For example, Patent Document 1 discloses a technology for a hybrid electric vehicle that calculates the difference between an average altitude determined from past altitude records and the current altitude, and changes the target value of the battery charging rate according to this difference. The difference between the current altitude and the average altitude has some correlation with the amount of downhill travel that will occur in the future. Therefore, the technology of Patent Document 1, which changes the target value of the battery charging rate according to this difference, can somewhat increase the possibility of ensuring sufficient free capacity when traveling downhill. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-095105 Summary of the Invention [Problem to be solved by the invention]

[0006] However, Patent Document 1 did not consider what would happen if the battery deteriorated. As a result, with the technology of Patent Document 1, if the battery deteriorates, the pocket capacity cannot be adequately secured, and as a result, there is a risk that regenerative braking may not be fully utilized when traveling downhill. That is, batteries are usually managed based on the ratio of the current charge capacity to the full charge capacity, or the so-called state of charge (SOC). Patent Document 1 also ensures pocket capacity by lowering the target value of the charge rate as the difference between the current altitude and the average altitude increases. However, if the battery deteriorates and the full charge capacity itself decreases, the available free capacity decreases even if the charge rate remains the same.

[0007] For example, consider a case where the full charge capacity drops from 10 kWh to 8 kWh due to battery degradation. In this case, when the battery is charged to a charging rate of 50%, the available capacity that can accept regenerative power drops from 5 kWh before degradation to 4 kWh after degradation. Patent Document 1 does not take battery degradation into consideration, and does not change the target charging rate even if the battery deteriorates. As a result, with the prior art, there is a risk that when the battery deteriorates, the available battery capacity will be insufficient, making it impossible to fully utilize regenerative braking.

[0008] Therefore, this specification discloses a battery control device that can properly operate regenerative braking when traveling downhill even if the battery has deteriorated. [Means for solving the problem]

[0009] The battery control device disclosed in this specification is a battery control device that controls the charging and discharging of a battery mounted on a battery electric vehicle, and is characterized in that when the battery is externally charged, the available capacity of the battery required to activate regenerative braking when driving downhill in the future is predicted as a pocket capacity, and based on the pocket capacity and the deterioration rate of the battery, the upper limit charging rate at which the pocket capacity can be secured is calculated as a modified upper limit charging rate, and the external charging is controlled so that the charging rate of the battery is equal to or less than the modified upper limit charging rate. [Effects of the Invention]

[0010] According to the technology disclosed in this specification, the upper limit charging rate is corrected taking into account battery degradation, so that regenerative braking can be appropriately activated when traveling downhill even if the battery is degraded. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram of a battery electric vehicle equipped with a battery control device. [Figure 2] FIG. 10 is a block diagram showing a process for calculating a corrected upper limit charging rate. [Figure 3] FIG. 10 is a diagram illustrating a change in the pocket charging rate due to deterioration of the battery. [Figure 4] 10 is a graph showing changes in the battery charging rate over time. DETAILED DESCRIPTION OF THE INVENTION

[0012] The battery control device 10 will be described below with reference to the drawings. FIG. 1 is a schematic diagram of a battery electric vehicle (hereinafter referred to as "vehicle 20") equipped with the battery control device 10. The vehicle 20 runs using power stored in a battery 22 as an energy source. The battery 22 is electrically connected to a traction motor 32 via an inverter 30. The traction motor 32 is driven by power supplied from the battery 22 and rotates drive wheels 38. The traction motor 32 also functions as a generator. For example, when the vehicle 20 runs downhill, if the traction motor 32 is operated in regenerative mode, the traction motor 32 generates power using power transmitted from the drive wheels 38. At this time, the regenerative torque generated by the traction motor 32 functions as a regenerative brake that brakes the rotational drive of the drive wheels 38. The regenerative power generated by the traction motor 32 is stored in the battery 22 via the inverter 30.

[0013] The battery 22 is a secondary battery that can be charged and discharged. The battery 22 can be charged using the regenerated power described above and power supplied from the external power source 50. For external charging, the vehicle 20 is provided with a charging port 36 and a charger 34. The battery 22 is electrically connected to the external power source 50 via the charging port 36. The charger 34 converts AC power supplied from the external power source 50 into DC power and supplies it to the battery 22.

[0014] The battery 22 is provided with a voltage sensor 24, a current sensor 26, and a temperature sensor 28 to detect the state of the battery 22. The detected values ​​of these sensors 24, 26, and 28 are sent to the battery control device 10 as needed.

[0015] The battery control device 10 controls the charging and discharging of the battery 22. The battery control device 10 is physically a computer having a processor 12 and a memory 14. This "computer" also includes a microcontroller in which a computer system is incorporated into a single integrated circuit. Furthermore, the number of processors 12 and memories 14 is not limited to one, and multiple processors and memories 12 and 14 may be provided. Therefore, the battery control device 10 may be configured by combining two or more physically separated computers.

[0016] The battery control device 10 controls the charging and discharging of the battery 22 so that the state of charge (SOC) of the battery 22 falls within a predetermined allowable range. Here, the state of charge (SOC) is the ratio of the current charge capacity to the full charge capacity CPmx of the battery 22, and is usually expressed as a percentage. The state of charge (SOC) is calculated, for example, based on the voltage of the battery 22 detected by the voltage sensor 24 and the temperature of the battery 22 detected by the temperature sensor 28. Alternatively, the state of charge (SOC) may be calculated from an integrated value of the input / output current of the battery 22 detected by the current sensor 26.

[0017] If the charging rate SOC of the battery 22 is excessively high or low, the battery 22 may be deteriorated. Therefore, the battery control device 10 pre-stores an upper limit value and a lower limit value of the charging rate SOC of the battery 22 as a standard upper limit charging rate SOCup and a standard lower limit charging rate SOClw, respectively. The battery control device 10 then controls the charging and discharging of the battery 22 so that the charging rate SOC of the battery 22 does not exceed the standard upper limit charging rate SOCup or fall below the standard lower limit charging rate SOClw. Note that the standard upper limit charging rate SOCup and the standard lower limit charging rate SOClw are not particularly limited as long as they can appropriately protect the battery 22. For example, the standard upper limit charging rate SOCup is set to a predetermined value between 70% and 99%. For example, the standard lower limit charging rate SOClw is set to a predetermined value between 1% and 30%.

[0018] Furthermore, when externally charging the battery 22, the battery control device 10 calculates a corrected upper limit charging rate SOCup# and controls the charger 34 so that the battery 22 is externally charged up to this corrected upper limit charging rate SOCup#. Fig. 2 is a block diagram showing the calculation process of the corrected upper limit charging rate SOCup#. Before explaining Fig. 2, the reason for calculating the corrected upper limit charging rate SOCup# will be explained with reference to Figs. 3 and 4.

[0019] As shown in the upper part of FIG. 3, consider a case where the vehicle 20 travels downhill after external charging at a charging station. In this case, the driver uses the foot brake as needed to prevent the vehicle from increasing in speed. However, frequent use of the foot brake can lead to deterioration of the foot brake. Therefore, when traveling downhill, the vehicle 20 operates the traction motor 32 in regenerative mode as much as possible to activate the regenerative brake. This reduces the need to use the foot brake. Such use of regenerative braking is particularly important for vehicles 20 with a large vehicle weight, such as commercial vehicles such as trucks.

[0020] Here, when traveling downhill, if the battery 22 does not have sufficient free capacity to accept regenerated power, the battery 22 cannot be operated in a regenerative manner. Therefore, a technique for adjusting the external charge amount so that sufficient free capacity (hereinafter referred to as "pocket capacity CPpt") to accept regenerated power generated during downhill traveling is secured when the battery 22 is externally charged has been proposed. Specifically, a conventional battery control device 10 predicts the required free capacity, i.e., pocket capacity CPpt, based on the altitude AL and other factors when performing external charging, and further calculates the ratio of this pocket capacity CPpt to the full charge capacity CPmx as the pocket charging rate SOCpt. Next, the battery control device 10 calculates a value obtained by subtracting the pocket charging rate SOCpt from the standard upper limit charging rate SOCup as the corrected upper limit charging rate SOCup#. The battery control device 10 then controls the external charging so that the charging rate SOC of the battery 22 is equal to or less than this corrected upper limit charging rate SOCup#. This configuration enables appropriate regenerative braking during downhill traveling.

[0021] However, in the past, the calculation of the corrected upper limit state of charge SOCup# did not take into account the deterioration of the battery 22. As a result, there were cases where a sufficient pocket capacity CPpt could not be secured, and the regenerative brake could not be operated appropriately when traveling downhill.

[0022] For example, consider the situation shown in Figure 3. In Figure 3, the fully charged capacity CPmx of the battery 22in in the initial state is 50 kWh. To prevent overcharging, the standard upper limit charging rate SOCup of the initial battery 22in is 90%. Furthermore, in Figure 3, after external charging, the vehicle 20 runs downhill while operating the regenerative brakes, generating 15 kWh of regenerative power.

[0023] In Figure 3 <b1>In the case of the initial battery 22in titled "initial battery 22in," the pocket capacity CPpt is 15 kWh, and the pocket charging rate SOCpt is 15 / 50×100=30%. Therefore, the corrected upper limit charging rate SOCup# is the value obtained by subtracting the pocket charging rate SOCpt from the standard upper limit charging rate SOCup, i.e., 90−30=60%. During external charging, the battery control device 10 controls the charging rate SOC of the initial battery 22in to be 60%. With this configuration, available capacity for receiving regenerative power can be secured, making it possible to activate regenerative braking when traveling downhill.

[0024] However, the battery 22 gradually deteriorates due to aging and the like, and the full charge capacity CPmx decreases. For example, in FIG. <b2>Consider a degraded battery 22dg entitled "Degraded Battery 22dg." The degradation rate SOH of the degraded battery 22dg is 80%. The degradation rate SOH is the ratio of the full charge capacity CPmx# after degradation to the full charge capacity CPmx in the initial state, expressed as a percentage, and is a parameter generally referred to as SOH (State of Health).

[0025] In this case, the full charge capacity of the degraded battery 22dg (hereinafter referred to as "degraded full charge capacity CPmx#") is 50 x 80% = 40 kWh. Conventionally, the corrected upper limit charging rate SOCup# was calculated in the same way as for the initial battery 22in, without taking into account this capacity decrease of the degraded battery 22dg. In other words, the degraded battery 22dg in Figure 3 was also externally charged up to 60%, just like the initial battery 22in.

[0026] Here, the battery 22 cannot be charged above the standard upper limit charging rate SOCup=90%. Therefore, if the degraded battery 22dg is charged to 60%, the available capacity that can accept regenerative power is 40×(90%−60%)=12 kWh. This is smaller than the pocket capacity CPpt=15 kWh required to activate the regenerative brake when traveling downhill. Therefore, if the degraded battery 22dg is externally charged to 60%, like the initial battery 22in, the regenerative brake cannot be fully activated when traveling downhill.

[0027] In this example, to avoid such problems, the corrected upper limit charging rate SOCup# is calculated taking into consideration the deterioration rate SOH of the battery 22. That is, the battery control device 10 calculates the post-deterioration full charge capacity CPmx#, and obtains the ratio of the pocket capacity CPpt to the post-deterioration full charge capacity CPmx# as the corrected pocket charging rate SOCpt#. Furthermore, the battery control device 10 calculates the corrected upper limit charging rate SOCup# by subtracting the corrected pocket charging rate SOCpt# from the standard upper limit charging rate SOCup.

[0028] In Figure 3, <b3>The deteriorated battery 22dg has the corrected upper limit charging rate SOCup# calculated taking into account the deterioration rate SOH. <b3>In this example, the post-degradation full charge capacity CPmx# is 50×80%=40 kWh, and the corrected pocket charging rate SOCpt# is 15 / 40×100=37.5%. Furthermore, since the standard upper limit charging rate SOCup is 90%, the corrected upper limit charging rate SOCup# is 90−37.5=52.5%. Therefore, when the degradation rate SOH of the battery 22 is 20%, the battery control device 10 controls external charging so that the charging rate SOC does not exceed 52.5%. As a result, the battery 22 can secure a margin for accepting 15 kWh of regenerative power, allowing the regenerative brake to be appropriately operated when traveling downhill.

[0029] Figure 4 is a graph showing the change over time in the state of charge (SOC) of battery 22. In Figure 4, the horizontal axis represents time, the right vertical axis represents the state of charge (SOC) of initial battery 22in, and the left vertical axis represents the state of charge (SOC) of deteriorated battery 22dg. In Figure 4, the thin curve L1 represents the change in the state of charge (SOC) of initial battery 22in.

[0030] As shown in Figure 4, the initial battery 22in is externally charged to a charging rate SOC of 60% to ensure a pocket capacity CPpt. Thereafter, from time t2 to time t4, the vehicle 20 travels downhill while operating the regenerative brakes. Operation of the regenerative brakes generates regenerative power, but the initial battery 22in has sufficient free capacity to accept this regenerative power. Therefore, the downhill travel can be completed without the charging rate SOC of the initial battery 22in exceeding the standard upper limit charging rate SOCup of 90%.

[0031] The dashed-dotted curve L2 in Figure 4 shows the change in the state of charge (SOC) in the prior art, in which the battery 22 is externally charged to 60% after degradation, just as it was in the initial state. In this case, the state of charge (SOC) of the degraded battery 22dg reaches the standard upper limit state of charge (SOCup) at time t3, before time t4, when downhill driving ends. In this case, the battery control device 10 stops the regenerative operation of the traction motor 32 because there is no more capacity to accept regenerative power. As a result, regenerative braking cannot be used from time t3 to time t4. Therefore, the foot brake is used more frequently to compensate for the lack of regenerative braking, which leads to foot brake degradation.

[0032] The thick curve L3 in FIG. 4 shows the change in the state of charge (SOC) when the degraded battery 22dg is externally charged using the technology disclosed in this specification. In this case, the degraded battery 22dg is externally charged to 52.5% instead of 60%. This ensures sufficient free capacity to accept regenerative power. As a result, even if the regenerative brake is activated from time t2 to time t4, when downhill driving ends, the regenerative power can be accepted by the battery 22. As a result, use of the foot brake can be reduced, and foot brake degradation can be prevented.

[0033] Next, the flow of calculation of the corrected upper limit charging rate SOCup# will be described in detail with reference to Fig. 2. When external charging is performed, the battery control device 10 calculates the corrected upper limit charging rate SOCup# according to the block diagram of Fig. 2.

[0034] Specifically, the battery control device 10 calculates the potential energy Epos based on the altitude AL of the current location of the vehicle 20 and the vehicle weight Wv. In theory, the potential energy Epos is converted into regenerative power by activating the regenerative brake. However, in reality, part of the potential energy Epos is converted into heat and becomes a loss LST. Therefore, the pocket capacity CPpt for receiving the regenerative power is calculated by multiplying a value obtained by subtracting the loss LST from the potential energy Epos by a predetermined coefficient K.

[0035] The battery control device 10 also calculates a post-degradation full charge capacity CPmx#. The post-degradation full charge capacity CPmx# is calculated based on the initial full charge capacity CPmx and the degradation rate SOH. Specifically, CPmx#=CPmx×SOH.

[0036] The initial full charge capacity CPmx uses a value that is predetermined for each battery 22. The method for determining the deterioration rate SOH is not particularly limited. Therefore, the battery control device 10 may determine the deterioration rate SOH based on the usage time of the battery 22, the mileage of the vehicle 20, the cumulative charge / discharge amount, etc. This configuration allows the deterioration rate SOH to be determined through a relatively simple calculation. Alternatively, the battery control device 10 may calculate the internal resistance of the battery 22 based on the battery voltage detected by the voltage sensor 24 and the battery current detected by the current sensor 26, and then calculate the deterioration rate SOH based on this internal resistance. Alternatively, the battery control device 10 may store a fluctuation history of the voltage, current, and temperature of the battery 22 detected by the sensors 24, 26, and 28, and calculate the deterioration rate SOH based on this fluctuation history. Considering this fluctuation history allows for a more accurate calculation of the deterioration rate SOH of the battery 22.

[0037] Once the pocket capacity CPpt and post-degradation full charge capacity CPmx# have been calculated, the battery control device 10 calculates the corrected pocket charging rate SOCpt#, which is the ratio of the pocket capacity CPpt to the post-degradation full charge capacity CPmx# expressed as a percentage. That is, the calculation is performed as follows: SOCpt#=CPpt / CPmx#×100.

[0038] Finally, the battery control device 10 calculates the corrected upper limit charging rate SOCup# by subtracting the corrected pocket charging rate SOCpt# from the predetermined standard upper limit charging rate SOCup. When the battery 22 is externally charged, the battery control device 10 controls the charger 34 so that the charging rate SOC of the battery 22 is equal to or lower than this corrected upper limit charging rate SOCup#.

[0039] In this way, by calculating the corrected upper limit charging rate SOCup# taking into account the deterioration rate SOH of the battery 22, it is possible to appropriately use regenerative braking even if the battery 22 has deteriorated. Note that the configuration described above is just an example, and other configurations may be changed as appropriate as long as the corrected upper limit charging rate SOCup# is calculated taking into account the deterioration rate SOH of the battery 22.

[0040] For example, the method of calculating the pocket capacity CPpt may be changed as appropriate. For example, the battery control device 10 may store a history of past altitudes and, from this altitude history, calculate the difference ΔAL=AL-ALave between the average altitude ALave and the current altitude AL. The battery control device 10 may then calculate the potential energy Epos and, ultimately, the pocket capacity CPpt based on this difference ΔAL and the vehicle weight Wv. Furthermore, the battery control device 10 may obtain, from a navigation device (not shown), a travel route from the current position to the point where regenerative braking begins to operate, and add the energy required for traveling this travel route to the loss LST.

[0041] The corrected upper limit charging rate SOCup# calculated according to the block diagram of FIG. 2 may be lower-limit guarded by a predetermined lower limit. That is, if the charging rate SOC immediately after external charging is excessively low, the charging rate SOC may fall below the standard lower limit charging rate SOClw before downhill driving begins, i.e., before regenerative operation of the traction motor 32 begins. Therefore, the battery control device 10 may calculate a value obtained by adding a predetermined margin α to the standard lower limit charging rate SOClw as the lower limit guard charging rate SOCgd. The battery control device 10 may then compare the corrected upper limit charging rate SOCup# calculated according to the block diagram of FIG. 2 with the lower limit guard charging rate SOCgd and set the larger of the two values ​​as the final corrected upper limit charging rate SOCup#. This configuration prevents the charging rate SOC of the battery 22 from decreasing excessively.

[0042] The surplus amount α is not particularly limited. Therefore, for example, the surplus amount α may be a fixed value between 0 and 20%. Furthermore, for example, the surplus amount α may be a variable value that varies depending on the amount of preliminary power consumption that is expected to be consumed after external charging ends and before regenerative braking starts to operate. To calculate the amount of preliminary power consumption, for example, a travel route from the current position to the point where regenerative braking starts to operate may be obtained from a navigation device (not shown). Then, the amount of preliminary power consumption may be estimated based on the distance and gradient of the obtained travel route.

[0043] Furthermore, the battery control device 10 cannot accurately determine the route the vehicle 20 will travel after external charging. Therefore, depending on the vehicle 20, there may be cases where the vehicle 20 does not travel downhill for a considerable period of time after external charging. In such a case, if external charging is terminated after securing free capacity equivalent to the pocket capacity CPpt, the amount of power available for vehicle travel will be reduced accordingly, and the cruising range of the vehicle 20 will be shortened. Therefore, when performing external charging, the battery control device 10 may inquire of the user whether or not it is necessary to secure the pocket capacity CPpt. If the result of the inquiry indicates that it is not necessary to secure the pocket capacity CPpt, the battery control device 10 may externally charge the battery 22 up to the standard upper limit charging rate SOCup. [Explanation of symbols]

[0044] 10 Battery control unit, 12 Processor, 14 Memory, 20 Vehicle, 22 Battery, 24 Voltage sensor, 26 Current sensor, 28 Temperature sensor, 30 Inverter, 32 Traction motor, 34 Charger, 36 Charging port, 38 Drive wheels, 50 External power supply, AL Altitude, CPmx Initial full charge capacity, CPmx# Full charge capacity after degradation, CPpt Pocket capacity, Epos Potential energy, K coefficient, LST Loss, SOCgd Lower limit guard charging rate, SOClw Standard lower limit charging rate, SOCpt Pocket charging rate, SOCpt# Corrected pocket charging rate, SOCup Standard upper limit charging rate, SOCup# Corrected upper limit charging rate, SOH Degradation rate, Wv Vehicle weight.

Claims

1. A battery control device that controls charging and discharging of a battery mounted on a battery electric vehicle, When the battery is externally charged, the remaining capacity of the battery required for activating regenerative braking during future downhill driving is predicted as a pocket capacity; calculating an upper limit charging rate at which the pocket capacity can be ensured as a corrected upper limit charging rate based on the pocket capacity and the deterioration rate of the battery; controlling the external charging so that the charging rate of the battery is equal to or less than the corrected upper limit charging rate; determining a current full charge capacity of the battery as a post-deterioration full charge capacity based on the full charge capacity of the battery in an initial state and the deterioration rate; A ratio of the pocket capacity to the post-degradation full charge capacity is calculated as a corrected pocket charge rate; A value obtained by subtracting the corrected pocket charging rate from a predetermined standard upper limit charging rate is calculated as the corrected upper limit charging rate. A battery control device characterized by:

2. 2. The battery control device according to claim 1, A battery control device that predicts the pocket capacity based on the altitude of a charging point where the external charging is performed and the weight of the battery electric vehicle.

3. 2. The battery control device according to claim 1, If the corrected upper limit charging rate obtained by subtracting the corrected pocket charging rate from the standard upper limit charging rate is smaller than a predetermined lower limit guard charging rate, the lower limit guard charging rate is set as a new corrected upper limit charging rate; The lower limit guard charging rate is a value obtained by adding a predetermined margin to a standard lower limit charging rate, which is a lower limit of the charging rate of the battery. A battery control device characterized by:

4. 4. The battery control device according to claim 3, a battery control device configured to control the amount of power consumed by the external charging device after the external charging is completed and before the regenerative braking is started;

5. 2. The battery control device according to claim 1, When the battery is externally charged, the user is inquired as to whether or not a limit on the charging rate is required; When it is instructed that the limitation of the charging rate is not necessary, the external charging is controlled so that the charging rate of the battery is equal to or lower than the standard upper limit charging rate without calculating the corrected upper limit charging rate. A battery control device characterized by:

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