WO2023238817A1

WO2023238817A1 - Battery system and charging method for battery

Info

Publication number: WO2023238817A1
Application number: PCT/JP2023/020792
Authority: WO
Inventors: 保大森; 均丸山; 英訓梶山; 卓矢佐藤; 亮輔鯉江; 翠梨青木
Original assignee: 株式会社豊田自動織機
Priority date: 2022-06-09
Filing date: 2023-06-05
Publication date: 2023-12-14
Also published as: JP2023180402A; TW202401886A

Abstract

This battery system (10) comprises: a battery (11), a temperature sensor (T1) that is configured so as to detect the temperature of the battery; a heater (12) that is configured so as to heat the battery; and a battery control unit (13). The battery control unit is configured so as to detect the state of the battery and control an operation for charging the battery and an operation for raising the temperature of the battery by using the heater. The battery control unit is further configured so as to, when the charging rate or voltage of the battery is below a prescribed threshold level during charging of the battery, control the heater in accordance with a comparison between the temperature of the battery and a preset threshold temperature and, when the charging rate or voltage of the battery is above the threshold level, monitor whether the battery has reached a fully charged state in a state in which the heater has been stopped.

Description

Battery system and battery charging method

The present disclosure relates to a battery system equipped with a temperature raising function that increases the temperature of a battery, and a battery charging method.

It is generally preferable for batteries to operate within a predetermined temperature range. For example, charging efficiency of lithium ion batteries decreases in low temperature environments. For this reason, when charging a battery whose charging efficiency decreases in a low-temperature environment, temperature increase control is sometimes performed to increase the temperature of the battery.

For example, a battery system including a charging mechanism, a temperature increasing mechanism, and a control section is described in Patent Document 1. In this battery system, when the state of charge (SOC) of the battery is less than the charging reference value, the control unit prohibits the temperature raising process and executes the charging process, so that the SOC of the battery reaches the charging reference value. When the battery temperature becomes higher than the reference temperature, if the battery temperature is less than the reference temperature, temperature raising processing is executed. Further, when the SOC of the battery falls below the charging reference value during the temperature raising process, the control unit stops the temperature raising process and charges the battery to the charging stop value. According to this method, while increasing the charging efficiency by increasing the temperature of the battery, it is possible to avoid prolonging the time until full charge by executing the temperature increasing process.

Patent No. 6225977

In the battery system described above, battery charging processing and temperature raising processing are controlled based on the SOC. Here, the SOC is estimated from the open circuit voltage (OCV) of the battery in many cases.

However, the SOC-OCV curve of iron phosphate-based lithium ion batteries, which have become popular in recent years, has a flat region (or plateau region). In a flat region, since OCV is almost constant with respect to SOC, it is difficult to accurately estimate SOC from OCV. Therefore, in a battery whose SOC-OCV curve has a flat region, it is difficult to accurately determine whether the battery has reached a fully charged state.

The fully charged state can also be detected based on the terminal voltage and charging current of the battery. However, in the above-mentioned battery system, a current may flow to raise the temperature even when the battery is nearly fully charged. For this reason, it is difficult to manage the charging current, and it is difficult to accurately determine whether a fully charged state has been reached.

An object of one aspect of the present disclosure is to provide a method for accurately determining whether a battery has reached a fully charged state in a battery system having a function of increasing the temperature of the battery.

A battery system according to one aspect of the present disclosure includes a battery, a temperature sensor configured to detect the temperature of the battery, a heater configured to heat the battery, and a state of the battery. and a battery control unit configured to control an operation of charging the battery and an operation of increasing the temperature of the battery using the heater. During charging of the battery, when the charging rate or voltage of the battery is lower than a predetermined threshold level, the battery control unit controls the heater according to a comparison between the temperature of the battery and a preset threshold temperature. and further configured to monitor whether the battery has reached a fully charged state with the heater stopped when the charging rate or voltage of the battery is higher than the threshold level. .

According to another aspect of the present disclosure, a method of charging a battery is provided. The charging method includes determining whether a charging rate or voltage of the battery is lower than a predetermined threshold level; and, during charging of the battery, when the charging rate or voltage of the battery is lower than a predetermined threshold level. The heater is controlled according to a comparison between the temperature of the battery and a preset threshold temperature, and when the charging rate or voltage of the battery is equal to or higher than the threshold level, the heater is stopped. and monitoring whether the battery has reached a fully charged state.

According to each of the above configurations, when the charging rate or voltage of the battery is lower than the threshold level, the heater is controlled according to the comparison between the battery temperature and the threshold temperature. Therefore, the battery is charged in a temperature range with good charging efficiency. In addition, since the heater is stopped when monitoring whether the battery has reached a fully charged state, the effect of the current consumed by the heater on a method that determines full charge based on the current supplied to the battery system Therefore, the accuracy of full charge determination is good.

In the above battery system, when the battery temperature falls below the threshold temperature while the charging rate or voltage of the battery is higher than the threshold level, the battery control unit stops the charging operation of the battery and further controls the heater to generate heat. may be configured. According to this configuration, the battery can always be charged in a temperature range with good charging efficiency.

A battery system according to another aspect of the present disclosure includes a battery, a temperature sensor configured to detect the temperature of the battery, a heater configured to heat the battery, and a state of the battery. and a battery control unit configured to control the operation of charging the battery and the operation of increasing the temperature of the battery using the heater, as well as detecting the outside temperature of the device in which the battery is mounted. It may further include a second temperature sensor. In this case, the battery control unit obtains a charge start target temperature corresponding to the outside temperature and the battery charging rate when starting battery charging, and when the battery temperature is lower than the charge start target temperature, , further configured to raise the temperature of the battery to a charging start target temperature using a heater, and to monitor whether the battery has reached a fully charged state with the heater stopped while the battery is being charged. may be done.

According to further aspects of the present disclosure, a method of charging a battery is provided. The charging method includes obtaining, when starting charging the battery, a charging start target temperature corresponding to an outside temperature of a device in which the battery is mounted and a charging rate of the battery, and a temperature of the battery that corresponds to the charging start target. determining whether or not the battery temperature is lower than the charging start target temperature; and if the battery temperature is lower than the charging start target temperature, the battery temperature is raised to the charging start target temperature using a heater before charging the battery starts. and monitoring whether or not the battery has reached a fully charged state while the heater is stopped while the battery is being charged.

According to each of the above configurations, since the temperature of the battery at the time of starting charging is equal to or higher than the charging start target temperature, the battery is charged in a temperature range with good charging efficiency. In addition, since the heater is stopped during charging, the accuracy of full charge determination is good.

According to the above aspect, in a battery system having a function of increasing the temperature of the battery, it is possible to accurately determine whether the battery has reached a fully charged state.

1 is a diagram illustrating an example of a battery system according to an embodiment of the present disclosure. 2 is a diagram illustrating an example of a method for charging a battery using the battery system of FIG. 1. FIG. FIG. 3 is a diagram showing an example of CV charging in FIG. 2; 2 is a flowchart showing an example of charging control and temperature control by the battery system of FIG. 1. FIG. 2 is a flowchart showing a method of charging while giving priority to battery temperature control by the battery system of FIG. 1. FIG. FIG. 6 is a diagram (depending on outside temperature) for explaining temperature control by the battery system according to a variation of the embodiment of the present disclosure. FIG. 6 is a diagram (depending on outside temperature) for explaining temperature control by the battery system according to a variation of the embodiment of the present disclosure. FIG. 6 is a diagram (SOC dependent) for explaining temperature control by the battery system according to a variation of the embodiment of the present disclosure. FIG. 6 is a diagram (SOC dependent) for explaining temperature control by the battery system according to a variation of the embodiment of the present disclosure. FIG. 7 is a diagram illustrating an example of a charging start target temperature table included in a battery system according to a variation of the embodiment of the present disclosure. 12 is a flowchart illustrating an example of charging control and temperature control by the battery system according to a variation of the embodiment of the present disclosure.

FIG. 1 shows an example of a battery system 10 according to an embodiment of the present disclosure. The battery system 10 includes a battery 11, a heater 12, a voltage sensor V, a current sensor I, a temperature sensor T1, a temperature sensor T2, a relay RL, and a battery control section 13. Note that the battery system 10 may include other circuits or devices not shown in FIG.

Although the battery 11 is not particularly limited, in this embodiment, it is a lithium ion battery. Moreover, the battery 11 is composed of a plurality of battery packs connected in series and/or in parallel, although the battery 11 is not particularly limited. In this case, each battery pack may be composed of a plurality of battery cells connected in series.

The heater 12 is provided near the battery 11 and generates heat in response to instructions from the battery control unit 13. That is, the heater 12 can raise the temperature of the battery 11 according to instructions from the battery control section 13. The heater 12 is realized, for example, by a resistance wire. In this case, the heater 12 generates heat by passing a current through this resistance wire. Furthermore, the battery control unit 13 switches the heater 12 between the on state and the off state by controlling the current flowing through the resistance wire.

The voltage sensor V detects the voltage of the battery 11. Note that the voltage sensor V may detect the voltage between the positive terminal and the negative terminal of the battery 11, may detect the voltage of each battery pack, or may detect the voltage of each battery cell. Good too. Current sensor I detects the current flowing through battery 11. However, when using the heater 12, the current sensor I detects the sum of the current flowing through the battery 11 and the current flowing through the heater 12. That is, current sensor I detects the current supplied from charger 20 to battery system 10 . Note that in a configuration in which the current flowing through the battery 11 and the current flowing through the heater 12 are individually detected, the number of current sensors increases and the cost of parts increases. Therefore, in the embodiment of the present disclosure, the sum of the current flowing through the battery 11 and the current flowing through the heater 12 is detected.

The temperature sensor T1 is provided near the battery 11 and detects the temperature of the battery 11. Temperature sensor T2 detects outside temperature. For example, in a case where the battery system 10 is mounted on a vehicle, the temperature sensor T2 is configured to detect the temperature around the vehicle. Relay RL can conduct or disconnect the power line connected to battery 11 according to instructions from battery control unit 13 .

The battery control unit 13, which is a processing circuit, includes (1) one or more processors that operate according to a computer program (software), and (2) an application-specific integrated circuit (ASIC) that executes at least some of various processes. or (3) a combination thereof. A processor includes a CPU and memory, such as RAM and ROM, where the memory stores program codes or instructions configured to cause the CPU to perform processing. Memory or non-transitory computer-readable media includes any available media that can be accessed by a general purpose or special purpose computer. Various controls by the battery control unit 13 are executed by the CPU executing programs stored in the memory at predetermined calculation cycles.

The battery control unit 13 controls the charging operation of the battery 11. At this time, the battery control unit 13 may control the charging current and charging voltage of the battery 11 while exchanging control signals with the charger 20. For example, the battery control unit 13 may transmit a current command value representing the current required by the battery system 10 to the charger 20. Further, the battery control unit 13 detects the state of charge of the battery 11. As the state of charge, for example, the SOC of the battery 11 is calculated. SOC is an index representing the charging rate, and 100 percent and 0 percent represent a fully charged state and a completely discharged state, respectively.

SOC can be calculated or estimated using known techniques. For example, the battery control unit 13 can calculate the SOC based on the integrated value of the current detected by the current sensor I. However, this method may accumulate errors. Therefore, when calculating the SOC based on the integrated value of current, it is preferable to reset the SOC according to a predetermined trigger. For example, the SOC may be reset to "100 percent" when the battery 11 is considered to be in a fully charged state, or the SOC may be reset to "0 percent" when the battery 11 is considered to be in a fully discharged state. . Note that the SOC value is preferably recorded in a memory that can be accessed by the battery control unit 13. Furthermore, the battery control unit 13 may estimate the SOC using other methods. For example, the battery control unit 13 may estimate the SOC based on the OCV of the battery 11.

The charger 20 includes a power circuit 21 and a charger control section 22. The power circuit 21 converts power supplied from a system power supply (not shown) into DC power in response to instructions from the charger control unit 22. The hardware configuration of the charger control section 22 may be the same as that of the battery control section 13, for example. Charger control section 22 controls power circuit 21 while exchanging control signals with battery control section 13 of battery system 10 . For example, the charger control unit 22 controls the power circuit 21 to generate the current specified by the current command value received from the battery control unit 13.

FIG. 2 shows an example of a method for charging the battery 11. The battery control unit 13 and the charger 20 charge the battery 11 of the battery system 10 using, for example, a CCCV (Constant-Current Constant-Voltage) method.

In CCCV charging, the battery 11 is charged with a predetermined constant target current until the voltage of the battery 11 reaches a predetermined target voltage. In the following description, the operation of charging the battery 11 with a constant current may be referred to as "CC charging." Note that the current command value representing the target current is notified from the battery control section 13 to the charger control section 22. Then, the charger control unit 22 controls the power circuit 21 so that the current supplied from the charger 20 to the battery system 10 approaches the target current. Note that in this embodiment, the battery control section 13 and the charger control section 22 increase the charging current in stages from zero to the target current. Further, the target current may be, for example, the maximum current of the charger 20.

During the charging operation, the battery control unit 13 monitors the voltage of the battery 11 using the output signal of the voltage sensor V. After the voltage of the battery 11 reaches the target voltage, the battery control unit 13 generates a current command value and transmits it to the charger 20 so as to maintain the target voltage. Then, since the charger control unit 22 controls the power circuit 21 according to the current command value, the battery 11 is charged with a predetermined constant voltage. In the following description, the operation of charging the battery 11 with a constant voltage may be referred to as "CV charging." Here, if charging of the battery 11 is continued while the voltage of the battery 11 is held at a constant value, the charging current will inevitably decrease. Then, when the charging current decreases to a predetermined charging end current, the battery control section 13 and the charger control section 22 end the charging operation.

Figure 3 shows an example of CV charging. In this embodiment, the voltage of the battery 11 increases due to the CC charging described with reference to FIG. 2, and the voltage of the battery 11 reaches the target voltage at time T0. That is, at time T0, CC charging is switched to CV charging. Therefore, after time T0, the battery control section 13 generates a current command value for maintaining the voltage of the battery 11 at the target voltage and sends it to the charger control section 22. Charger 20 then controls the current supplied to battery 11 according to the current command value.

The battery control unit 13 and charger control unit 22 reduce the charging current by ΔI at time T0. Then, the voltage of the battery 11 temporarily decreases. After this, the charging operation continues at "target current - ΔI". Therefore, the voltage of the battery 11 increases and reaches the target voltage again at time T1. Subsequently, the battery control unit 13 and charger control unit 22 further reduce the charging current by ΔI at time T1. Then, the voltage of the battery 11 temporarily decreases. After this, the charging operation continues at "target current -2ΔI". Then, the voltage of the battery 11 reaches the target voltage again at time T2.

By reducing the charging current in stages as described above, the voltage of the battery 11 is substantially maintained at the target voltage. Then, when the charging current decreases to the charging end current shown in FIG. 2, the battery control unit 13 determines that the battery 11 has reached a fully charged state, and notifies the charger 20 of an instruction to end the charging operation. . At this time, the battery control unit 13 may determine whether the battery 11 is fully charged based on the current command value calculated by itself, or may determine whether the battery 11 is fully charged based on the current value detected using the current sensor I. It may also be determined whether the battery 11 is fully charged.

In this way, the battery control unit 13 controls the charging operation. At this time, the battery control unit 13 executes temperature control to adjust the temperature of the battery 11 using the heater 12 in parallel with the charging control. For example, when the temperature of the battery 11 is lower than a predetermined threshold temperature, charging efficiency deteriorates. Therefore, when the temperature of the battery 11 is lower than the threshold temperature, the battery control unit 13 uses the heater 12 to raise the temperature of the battery 11.

When increasing the temperature of the battery 11, a portion of the current supplied from the charger 20 is consumed by the heater 12. That is, when the charger 20 generates a current according to the current command value, if the heater 12 is used, the current that actually flows through the battery 11 becomes smaller than the current represented by the current command value. For this reason, when a full charge determination is made based on the charging current, the determination accuracy may deteriorate. Therefore, the battery system 10 according to the embodiment of the present disclosure has a function of stopping the heater 12 and determining full charge as necessary even when the temperature of the battery 11 is low.

FIG. 4 is a flowchart showing an example of charging control and temperature control. In this example, when the user gives an instruction to start charging, the battery control unit 13 starts charging control and temperature control.

In S1, the battery control unit 13 detects the temperature of the battery 11 using the output signal of the temperature sensor T1. Thereafter, the battery control unit 13 monitors the temperature of the battery 11 until charging is completed. In S2, the battery control unit 13 calculates the SOC of the battery 11. Note that the current SOC value is recorded, for example, in a memory (not shown). Further, the battery control unit 13 estimates the SOC of the battery 11 by constantly integrating the charging current and the discharging current measured using the current sensor I.

In S3, the battery control unit 13 generates a current command value. For example, in the CCCV charging shown in FIG. 2, the current command value represents a predetermined target current during the period in which CC charging is performed. This target current may be, for example, the maximum current of charger 20. Further, during the period when CV charging is performed, for example, a current command value that realizes the current control described with reference to FIG. 3 is generated. The current command value generated by the battery control unit 13 is notified to the charger 20. Charger 20 then generates a charging current according to the current command value.

In S4, the battery control unit 13 compares the temperature of the battery 11 with a predetermined threshold temperature X1. The threshold temperature X1 is set, for example, based on the temperature at which the charging efficiency of the battery 11 begins to decrease. Although it depends on the characteristics of the battery 11, the threshold temperature X1 is, for example, about 5°C.

In S5, the battery control unit 13 compares the SOC of the battery 11 with a predetermined threshold SOC. The threshold SOC is set to a value lower than a region where full charge determination may be affected. For example, in the charging methods shown in FIGS. 2 and 3, it is determined that the battery 11 has reached a fully charged state when the charging current decreases to a predetermined charging end current. Furthermore, after transitioning from CC charging to CV charging, the charging current begins to decrease. Therefore, when monitoring whether a fully charged state has been reached based on the charging current, transition from CC charging to CV charging may affect the full charging determination. That is, the period during which CV charging is performed corresponds to a region where full charge determination may be affected. Therefore, the threshold SOC may be set to a value slightly smaller than the SOC value at which CC charging shifts to CV charging. Alternatively, the threshold SOC may be about 60%, although it is not particularly limited.

When the SOC of the battery 11 is lower than the threshold SOC and the temperature of the battery 11 is lower than the threshold temperature X1, the battery control unit 13 operates the temperature raising function. That is, the battery control unit 13 causes current to flow through the heater 12 to generate heat. On the other hand, when the SOC of the battery 11 is equal to or higher than the threshold SOC and/or when the temperature of the battery 11 is equal to or higher than the threshold temperature X1, the battery control unit 13 stops the temperature increasing function. That is, the battery control unit 13 stops supplying current to the heater 12.

In S8 to S9, the battery control unit 13 determines whether the battery 11 has been charged to a fully charged state. At this time, the battery control unit 13 determines, for example, whether the current represented by the current command value has decreased to the above-mentioned charge end current. Then, if the current represented by the current command value has not decreased to the charge end current, the battery control unit 13 determines that the battery 11 has not yet been charged to a fully charged state. In this case, the battery control unit 13 returns to S3 and updates the current command value. That is, the processes of S3 to S9 are repeatedly executed until the battery 11 is fully charged. Then, when the battery 11 becomes fully charged, the charging process ends.

As described above, in the embodiment of the present disclosure, even if the temperature of the battery 11 is lower than the threshold temperature X1, the temperature increase function is stopped when the SOC of the battery 11 is equal to or higher than the threshold SOC. Here, if the temperature raising function is stopped, the current flowing through the battery 11 substantially matches the current represented by the current command value. Therefore, the battery control unit 13 can realize accurate full charge determination using the current command value.

Note that in the above embodiment, it is determined whether or not to use the temperature increase function based on the SOC of the battery 11, but the embodiments of the present disclosure are not limited to this method. For example, the voltage of battery 11 has a correlation with the SOC of battery 11. Therefore, the battery control unit 13 may determine whether to use the temperature increase function based on the voltage of the battery 11. That is, when the SOC or voltage of the battery 11 is lower than a predetermined threshold level, the battery control unit 13 controls the heater 12 according to the comparison between the temperature of the battery 11 and the threshold temperature X1.

Furthermore, the battery control unit 13 may preferentially increase the temperature of the battery 11 over charging the battery 11 when the SOC of the battery 11 is equal to or higher than the threshold SOC. For example, in the embodiment shown in FIG. 5, when the temperature of the battery 11 falls below the threshold temperature X1 when the SOC of the battery 11 is equal to or higher than the threshold SOC, the battery control unit 13 executes S11 to S13. That is, the battery control unit 13 causes the heater 12 to generate heat while the charging operation is stopped. Then, when the temperature of the battery 11 becomes equal to or higher than the threshold temperature X1, the battery control unit 13 restarts the charging operation in S14, and stops the heater 12 in S7. Thereafter, an operation of stopping the heater 12 to charge the battery 11 or an operation of stopping charging of the battery 11 and causing the heater 12 to generate heat is performed until the battery 11 is fully charged. Note that when the SOC of the battery 11 is smaller than the threshold SOC, it is determined whether or not to cause the heater 12 to generate heat based on the temperature of the battery 11, similarly to the procedure shown in FIG.

According to the procedure of the flowchart shown in FIG. 5, charging will not be performed when the temperature of the battery 11 is lower than the threshold temperature X1. Therefore, the battery 11 is always charged in an efficient manner. Note that when the temperature of the battery 11 decreases after the battery 11 reaches a fully charged state and the SOC decreases by using the heater 12, recharging is performed. In this case, the battery control unit 13 may charge the battery 11 while controlling the temperature according to the procedure shown in FIG.

<Variations>
In the procedure shown in FIG. 4, when the SOC of the battery 11 is equal to or higher than the threshold SOC at the start of charging, the heater 12 remains stopped even if the temperature of the battery 11 is low. In this case, charging is performed while the temperature of the battery 11 is low. However, for example, iron phosphate-based lithium ion batteries deteriorate in charging performance in a low temperature region, so charging time may become longer or charging may become difficult.

Therefore, in a variation of the embodiment of the present disclosure, if the temperature of the battery 11 is low at the start of charging, the heater 12 is used to warm the battery 11 before actually charging. After that, the heater 12 is stopped and charging is performed. At this time, it is preferable that the temperature of the battery 11 is maintained at the threshold temperature X1 or higher until the battery is fully charged with the heater 12 stopped. However, if the outside temperature is high, the temperature of the battery 11 is less likely to drop during charging, but when the outside temperature is low, the temperature of the battery 11 is more likely to drop during charging. Therefore, the battery control unit 13 takes the outside temperature into consideration and determines to what extent the battery 11 should be warmed before starting charging.

FIGS. 6A to 7B are diagrams illustrating temperature control according to variations of the embodiment of the present disclosure. In this example, it is assumed that an instruction to start charging is given to the battery control unit 13 at time T11. X1 corresponds to the threshold temperature of the embodiment shown in FIGS. 4-5. That is, when the temperature of the battery 11 is lower than X1, charging efficiency is poor. Further, it is assumed that the temperature of the battery 11 is lower than X1 when the instruction to start charging is given (ie, time T11). In this case, the battery control unit 13 warms the battery 11 using the heater 12 before starting charging. As a result, the temperature of the battery 11 rises to X2 as shown in FIG. 6A or FIG. 7A. Thereafter, the battery control unit 13 stops the heater 12 and starts charging the battery 11.

In this example, since the heater 12 is stopped during charging, the temperature of the battery 11 gradually decreases. Here, the rate at which the temperature of the battery 11 decreases depends on the outside temperature. Specifically, as shown in FIG. 6A, when the outside temperature is high, the temperature of the battery 11 decreases slowly, but when the outside temperature is low, the temperature of the battery 11 decreases quickly. Furthermore, in the case shown in FIG. 6A, it is assumed that the battery 11 becomes fully charged at time T12. The time it takes for the battery 11 to reach a fully charged state depends on the SOC of the battery 11 at the time of starting charging.

When the outside temperature is high, the temperature of the battery 11 remains at or above X1 at time T12 (that is, when the battery 11 is fully charged). That is, the temperature of the battery 11 is equal to or higher than X1 throughout the charging period. In this case, charging efficiency is good. On the other hand, when the outside temperature is low, the temperature of the battery 11 is lower than X1 at time T12. That is, the temperature of the battery 11 is lower than X1 during part of the charging period. In this case, charging efficiency deteriorates.

This problem can be solved by setting the temperature of the battery 11 at the start of charging according to the outside temperature. Specifically, when the outside temperature is high, there is no need to increase the temperature of the battery 11 so much at the start of charging. On the other hand, when the outside temperature is low, it is necessary to sufficiently raise the temperature of the battery 11 when starting charging.

For example, when charging the battery 11 with the heater 12 stopped, the temperature of the battery 11 at the start of charging may be set so that the temperature of the battery 11 does not become lower than X1 at the time when the battery 11 is expected to reach a fully charged state. Set the temperature of 11. In the example shown in FIG. 6B, when the outside temperature is high, if the temperature of the battery 11 is set to X21 or higher at the start of charging, the temperature of the battery 11 will be higher than X1 throughout the charging period. When the outside temperature is low, if the temperature of the battery 11 is set to X22 or higher at the start of charging, the temperature of the battery 11 will be higher than X1 throughout the charging period. In addition, in the following description, when the battery 11 is charged with the heater 12 stopped, charging is started so that the temperature of the battery 11 does not become lower than X1 at the time when the battery 11 is expected to reach a fully charged state. The temperature of the battery 11 that should be set at times is sometimes referred to as a "charging start target temperature."

On the other hand, the charging time required to bring the battery 11 to a fully charged state depends on the SOC at the time of starting charging. Specifically, the larger the SOC at the start of charging, the shorter the charging time, and the smaller the SOC at the start of charging, the longer the charging time. In the example shown in FIG. 7A, the charging end time in the case where the SOC at the start of charging is large is T13, and the charging end time in the case where the SOC at the start of charging is small is T14.

Here, it is assumed that the temperature of the battery 11 is raised to X2 at the start of charging. In this case, if the SOC at the start of charging is large, the temperature of the battery 11 remains equal to or higher than X1 when the battery 11 becomes fully charged at time T13. That is, since the temperature of the battery 11 is equal to or higher than X1 throughout the charging period, charging efficiency is good. On the other hand, when the SOC at the start of charging is small, the temperature of the battery 11 is lower than X1 when the battery 11 becomes fully charged at time T14. That is, the temperature of the battery 11 becomes lower than X1 during a part of the charging period, resulting in poor charging efficiency.

This problem can be solved by setting the above-mentioned charging start target temperature according to the SOC at the time of charging start. Specifically, when the SOC is large, the charging start target temperature does not need to be very high. On the other hand, when the SOC is small, it is necessary to set a high charging start target temperature.

As an example, when the battery 11 is charged with the heater 12 stopped, the charging start target temperature is set so that the temperature at the end of charging is equal to or higher than X1. In the case shown in FIG. 7B, when the SOC at the start of charging is large, if the temperature of the battery 11 is set at X23 or higher at the start of charging, the temperature of the battery 11 becomes X1 or higher throughout the charging period. When the SOC at the start of charging is small, if the temperature of the battery 11 is set to X24 or higher at the start of charging, the temperature of the battery 11 will be equal to or higher than X1 during the entire charging period.

Therefore, in a variation of the embodiment of the present disclosure, the charging start target temperature is set based on the outside temperature and the SOC of the battery 11 at the time of starting charging. The battery control unit 13 includes a charging start target temperature table shown in FIG.

In the charge start target temperature table, charge start target temperatures are recorded for combinations of "temperature difference between threshold temperature ing. As described with reference to FIGS. 6A to 7B, the charging start target temperature decreases as the outside temperature increases, and also decreases as the SOC increases. It is assumed that the charging start target temperature is determined in advance by measurement or simulation. Note that the threshold temperature X1 is a fixed value for the battery 11, so "outside temperature" may be used instead of "the temperature difference between the threshold temperature X1 at which the charging efficiency of the battery 11 begins to decrease and the outside air temperature." . That is, a charging start target temperature table may be created for a combination of "outside temperature" and "SOC at the time of charging start".

FIG. 9 is a flowchart illustrating an example of charging control and temperature control by the battery system according to a variation of the embodiment of the present disclosure. Similar to the procedure shown in FIG. 4 or 5, when the user gives an instruction to start charging, the battery control unit 13 starts charging control and temperature control.

In S21, the battery control unit 13 detects the temperature of the battery 11 using the output signal of the temperature sensor T1. In S22, the battery control unit 13 detects the outside temperature using the output signal of the temperature sensor T2. In S23, the battery control unit 13 acquires the SOC of the battery 11. Note that the current SOC value is recorded, for example, in a memory (not shown). In this case, the battery control unit 13 acquires the current SOC value from the memory. Alternatively, the battery control unit 13 may estimate the SOC based on the OCV of the battery 11.

In S24, the battery control unit 13 obtains a charging start target temperature corresponding to the outside air temperature detected in S22 and the SOC obtained in S23. The charge start target temperature can be obtained from the charge start target temperature table shown in FIG. However, the battery control unit 13 may calculate the charging start target temperature by applying the outside temperature and SOC to a calculation formula prepared in advance.

In S25, the battery control unit 13 compares the temperature of the battery 11 detected in S21 with the charging start target temperature. Then, when the temperature of the battery 11 is equal to or higher than the charging start target temperature, the process of the battery control unit 13 proceeds to S29. On the other hand, when the temperature of the battery 11 is lower than the charging start target temperature, the battery control unit 13 causes the heater 12 to generate heat in S26. As a result, the temperature of the battery 11 increases. Thereafter, the battery control unit 13 monitors the temperature of the battery 11 in S27. Then, when the temperature of the battery 11 becomes equal to or higher than the charging start target temperature, the battery control unit 13 stops the heater 12 in S28.

Note that the temperature of the battery 11 during charging when the outside temperature is sufficiently high does not decrease or decreases slowly even if the heater 12 is stopped. Therefore, when the outside temperature is sufficiently high, it is not necessarily necessary to use the heater 12 even if the temperature of the battery 11 at the time of starting charging is below the charging start target temperature. That is, the battery control unit 13 may cause the heater 12 to generate heat in S25 to S26 only when the temperature of the battery 11 is lower than the charging start target temperature and the outside temperature is lower than a predetermined threshold value.

In S29 to S30, the battery control unit 13 charges the battery 11. In this embodiment, the charging method is not particularly limited, but may be the CCCV method described with reference to FIGS. 2 and 3. Then, when the current command value (or the current supplied from the charger 20 to the battery system 10) decreases to a predetermined charging end current, the battery control unit 13 determines that the battery 11 is in a fully charged state and starts charging. end.

In the above procedure, the process of S29 is executed when it is determined in S25 that the temperature of the battery 11 is equal to or higher than the charging start target temperature. Further, when it is determined in S25 that the temperature of the battery 11 is lower than the charge start target temperature, S29 is executed after the temperature of the battery 11 is warmed to the charge start target temperature or higher in S26 and S27. That is, in either case, the temperature of the battery 11 is equal to or higher than the charging start target temperature at the time when the battery control unit 13 executes charging of the battery 11.

Here, during charging, the heater 12 is stopped. Therefore, the temperature of the battery 11 gradually decreases during charging. However, the temperature of the battery 11 at the time when charging is actually performed is equal to or higher than the charging start target temperature. Further, the charging start target temperature is determined according to the outside temperature and the SOC at the time of charging start so that the temperature of the battery 11 at the end of charging is equal to or higher than a threshold temperature X1 at which charging efficiency starts to decrease. Therefore, the temperature of the battery 11 is maintained in a region with good charging efficiency throughout the charging period. In other words, efficient charging is realized.

Additionally, since the heater 12 is stopped during charging, the charging current flowing through the battery 11 substantially matches the current represented by the current command value. Therefore, when determining full charge using the current command value, the determination accuracy is good.

Claims

battery and
a temperature sensor configured to detect the temperature of the battery;
a heater configured to heat the battery;
a battery control unit configured to detect the state of the battery and control an operation of charging the battery and an operation of increasing the temperature of the battery using the heater,
The battery control unit includes:
during charging of the battery, when the charging rate or voltage of the battery is lower than a predetermined threshold level, controlling the heater in response to a comparison between the temperature of the battery and a preset threshold temperature;
The battery is further configured to monitor whether or not the battery has reached a fully charged state with the heater stopped when the charging rate or voltage of the battery is equal to or higher than the threshold level. system.
When the temperature of the battery falls below the threshold temperature when the charging rate or voltage of the battery is equal to or higher than the threshold level, the battery control unit stops the charging operation of the battery and causes the heater to generate heat. The battery system of claim 1, further configured to: .
battery and
a temperature sensor configured to detect the temperature of the battery;
a heater configured to heat the battery;
a second temperature sensor configured to detect an outside temperature of a device in which the battery is mounted;
a battery control unit configured to detect the state of the battery and control an operation of charging the battery and an operation of increasing the temperature of the battery using the heater,
The battery control unit includes:
At the time of starting charging of the battery, obtaining a charging start target temperature corresponding to the outside temperature and the charging rate of the battery,
When the temperature of the battery is lower than the charge start target temperature, use the heater to raise the temperature of the battery to the charge start target temperature or more before starting charge of the battery,
The battery system is further configured to monitor whether or not the battery has reached a fully charged state with the heater stopped while the battery is being charged.
The charging start target temperature is such that when the battery is charged with the heater stopped, the temperature of the battery at the time when the battery is expected to reach a fully charged state is such that the charging efficiency of the battery decreases. 4. The battery system according to claim 3, wherein the battery system is set so as not to become lower than a threshold temperature at which the temperature starts to decrease.
When the temperature of the battery is lower than the charging start target temperature and the outside air temperature is lower than a second threshold temperature, before starting charging of the battery, the battery control unit is configured to: The battery system according to claim 3, further configured to use the heater to raise the temperature of the battery above the charging start target temperature.
A method for charging a battery, the charging method comprising:
determining whether the charging rate or voltage of the battery is below a predetermined threshold level;
controlling a heater in response to a comparison between a temperature of the battery and a preset threshold temperature when the charging rate or voltage of the battery is lower than a predetermined threshold level while charging the battery;
Charging the battery, including monitoring whether the battery has reached a fully charged state with the heater stopped when the charging rate or voltage of the battery is equal to or higher than the threshold level. Method.
A method for charging a battery, the charging method comprising:
At the time of starting charging of the battery, acquiring a charging start target temperature corresponding to an outside temperature of a device in which the battery is mounted and a charging rate of the battery;
determining whether the temperature of the battery is lower than the charging start target temperature;
When the temperature of the battery is lower than the charge start target temperature, using a heater, raise the temperature of the battery to the charge start target temperature or more before starting charge of the battery;
A method for charging a battery, comprising monitoring whether or not the battery has reached a fully charged state while the heater is stopped while the battery is being charged.