Battery charging method

Abstract

A battery charging method includes the following steps: estimating a capacity degradation coefficient indicating the degree of capacity degradation of the battery; calculating a time degradation coefficient indicating the degree of degradation of the battery over time; and calculating a limiting current value based on the smaller of the capacity degradation coefficient and the time degradation coefficient, and charging the battery with the calculated limiting current value.

Description

Technical Field

[0001] The present invention relates to a battery charging method. Background Art

[0002] Japanese Patent Application Laid-Open No. 2017-108604 discloses calculating a maximum charging current value during charging based on the state of the battery (usage history, degradation state). Summary of the Invention

[0003] While the configuration described in Japanese Patent Application Laid-Open No. 2017-108604 calculates the charging current value based on the battery's degradation state, it is difficult to accurately determine the battery's degradation state. Consequently, if the battery capacity estimation error is large and the estimation accuracy of the capacity degradation state is low, the charging current value may exceed the allowable current value, or the allowable current value may be unnecessarily limited, potentially preventing proper charging.

[0004] The present invention provides a battery charging method capable of performing appropriate charging even when an estimation error of the battery capacity is large.

[0005] The present invention is a battery charging method, which includes the following steps: estimating a capacity degradation coefficient indicating the degree of capacity degradation of the battery; calculating a time degradation coefficient indicating the degree of degradation of the battery over time; and calculating a limiting current value based on the smaller coefficient between the capacity degradation coefficient and the time degradation coefficient, and charging the battery with the calculated limiting current value.

[0006] In the present invention, the smaller of the capacity degradation coefficient and the time-dependent degradation coefficient is used to set the charging current value. This allows for appropriate charging even when the battery capacity estimation error is large. Even if the battery capacity estimation error is large and the capacity degradation coefficient is estimated to be greater than the actual degradation state, the smaller coefficient, the time-dependent degradation coefficient, is used to calculate the limit current value. This allows for appropriate charging appropriate to the battery's degradation state.

[0007] In the battery charging method disclosed above, in the step of estimating the capacity degradation coefficient, the capacity degradation coefficient can be estimated based on a capacity maintenance rate and a capacity degradation coefficient map, wherein the capacity maintenance rate is obtained based on a value reflecting an estimation error in an estimated value of the battery capacity of the battery.

[0008] The capacity degradation coefficient map may be a map indicating a relationship between the capacity maintenance rate and the capacity degradation coefficient.

[0009] In the battery charging method disclosed above, when an estimated error in the estimated value of the battery capacity is X%, the limiting current value can be calculated based on the time-dependent degradation coefficient in the step of charging the battery at the limiting current value until the capacity maintenance rate calculated in the step of estimating the capacity degradation coefficient becomes the capacity maintenance rate when the estimated value of the battery capacity is 100-X%. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like numerals represent like elements, and in which:

[0011] Figure 1 It is a diagram schematically showing a charging system in an embodiment.

[0012] Figure 2 This is a map showing an allowable current value map when the battery temperature is 25°C.

[0013] Figure 3 This is a graph showing the relationship between the capacity retention rate and the capacity degradation coefficient when there is no estimation error.

[0014] Figure 4 This is a graph showing the relationship between the capacity retention rate and the capacity degradation coefficient when the estimation error is X%.

[0015] Figure 5 This is a graph showing the relationship between the capacity maintenance rate and the capacity degradation coefficient when the estimation error is 10%.

[0016] Figure 6 It is a map showing the relationship between the capacity maintenance rate and the capacity degradation coefficient, which reflects the estimation error in capacity estimation.

[0017] Figure 7 : is a map showing a degradation coefficient map over time.

[0018] Figure 8 is a flowchart illustrating a battery charging method.

[0019] Figure 9 This is a map showing the case where the capacity degradation coefficient and the time degradation coefficient are used together. DETAILED DESCRIPTION

[0020] Hereinafter, a battery charging method in an embodiment of the present invention will be specifically described with reference to the accompanying drawings. It should be noted that the present invention is not limited to the embodiment described below.

[0021] Figure 1Schematic diagram of a charging system in an embodiment. When charging a battery 2, the charging system 1 is electrically connected to the battery 2 and the charger 3. The charging system 1 includes a charging control device 10 that controls the charging current during charging.

[0022] Battery 2 is a secondary battery, such as a lithium-ion battery. It is a battery pack composed of multiple battery cells. During discharge, the power stored in battery 2 is supplied to an electric motor, etc. During charging, power supplied from an external power source via charger 3 in charging system 1 is stored in battery 2.

[0023] Charger 3 is a device that can supply power from an external power source to battery 2. When charging battery 2, charger 3 is attached to a device equipped with battery 2, electrically connecting battery 2 and the external power source via charger 3. When not charging battery 2, charger 3 can be removed from the device equipped with battery 2.

[0024] In the charging system 1, as Figure 1 As shown, the first connection portion 21 provided on the device carrying the battery 2 is connected to the second connection portion 31 provided on the charger 3. The first connection portion 21 is a connection portion on the battery 2 side, and includes a positive-side connection portion 21a connected to the positive pole of the battery 2 and a negative-side connection portion 21b connected to the negative pole of the battery 2. The second connection portion 31 is a connection portion on the charger 3 side, and includes a positive-side connection portion 31a connected to the positive-side connection portion 21a of the first connection portion 21 and a negative-side connection portion 31b connected to the negative-side connection portion 21b of the first connection portion 21. The connection between the positive-side connection portion 21a on the battery 2 side and the positive-side connection portion 31a on the charger 3 side, and the connection between the negative-side connection portion 21b on the battery 2 side and the negative-side connection portion 31b on the charger 3 side, forms a circuit for charging.

[0025] For example, if the device equipped with battery 2 is a vehicle, battery 2 is an onboard battery, and charger 3 is a charging station or other charging facility. In this case, during discharge, the power stored in battery 2 can be supplied to the electric motor for driving. During charging, the charging cable provided in charger 3 is connected to the charging port provided in the vehicle, electrically connecting battery 2 to an external power source and enabling charging. This allows battery 2 to be charged with power supplied from the external power source.

[0026] The charge control device 10 is an electronic control device that controls the charging current value based on the state of the battery 2. This electronic control device comprises a microcomputer equipped with a CPU, RAM, ROM, and input / output interfaces. Therefore, the charge control device 10 performs signal processing according to a program pre-stored in the ROM. For example, the charge control device 10 is installed in a device equipped with the battery 2.

[0027] In addition, signals from various sensors are input to the charging control device 10. For example, signals from the voltage / temperature detection device 4 that detects the voltage and temperature of the battery 2 and the current detection device 5 that detects the current value during charging are input to the charging control device 10. When the battery 2 is composed of multiple cells, the voltage / temperature detection device 4 detects the voltage and temperature of each cell respectively. The current detection device 5 detects the value of the current flowing in the circuit after the battery 2 and the charger 3 are electrically connected. Figure 1 As shown, the current detection device 5 is disposed on the negative electrode side of the battery 2 and detects the value of the current flowing from the charger 3 side to the battery 2 .

[0028] Furthermore, the charging control device 10 performs charging control based on the signals input from the voltage / temperature detection device 4 and the current detection device 5. Specifically, the charging control device 10 performs charging control appropriate to the current state of the battery 2. This charging control ensures that the charging current does not exceed the allowable current value Idc of the battery 2. During charging, the charging control device 10 controls the charging current value to a desired current value appropriate to the current state of the battery 2. In this process, the charging control device 10 outputs a control signal to the charger 3 to control the charging current value.

[0029] like Figure 1 As shown, the charging control device 10 includes a computing unit 11 .

[0030] The calculation unit 11 calculates the state of charge (SOC) of the battery 2 based on the voltage and temperature of the battery 2 detected by the voltage / temperature detection device 4. Since the voltage and temperature of the battery 2 during charging can be detected by the voltage / temperature detection device 4, the calculation unit 11 can calculate the current SOC based on the voltage and temperature of the battery 2 during charging.

[0031] The calculation unit 11 also estimates the degradation amount (deterioration state) of the battery 2 based on the usage history of the battery 2, such as the capacity retention rate. Specifically, the calculation unit 11 estimates a capacity degradation coefficient Dcap, which is a coefficient indicating the degree of capacity degradation of the battery 2.

[0032] The calculation unit 11 also calculates a degradation coefficient based on the elapsed time since the start of use of the battery 2. That is, the calculation unit 11 calculates a coefficient indicating the degree of degradation of the battery 2 over time, namely, a coefficient indicating the degree of degradation over time.

[0033] When the charge control device 10 executes charge control, the calculation unit 11 calculates the allowable current value Idc based on the current battery state (temperature, SOC). Furthermore, the calculation unit 11 calculates the limit current value Ilim by multiplying the allowable current value Idc by the smaller of the capacity degradation coefficient Dcap corresponding to the current estimated capacity value and the time degradation coefficient Dtime corresponding to the time elapsed since the battery 2 began to be used. The charge control device 10 then charges the battery 2 at the limit current value Ilim. That is, during charging, the charge control device 10 controls the charging current value to the limit current value Ilim.

[0034] Here, refer to Figures 2 to 7 The allowable current value map, the capacity degradation coefficient Dcap, and the time degradation coefficient Dtime are described in more detail.

[0035] First, refer to Figure 2 The allowable current value map will be described.

[0036] The allowable current value map is a map pre-set for each temperature and SOC of battery 2. In the charging method of the embodiment, the pre-set allowable current value map is referenced when calculating the allowable current value Idc corresponding to the current state (temperature, SOC) of battery 2. In other words, the charging control device 10 uses the allowable current value map when calculating the allowable current value Idc.

[0037] For example, when the temperature of the battery 2 is 25°C, a charging rate is set for each SOC. The charging rate indicates the speed of charging and relatively expresses the magnitude of the current value. In the case of constant current charge and discharge measurement, the magnitude of the current value that fully charges the theoretical capacity of the battery 2 within the maintenance time is defined as 1C. 1C during charging is the current value that takes 1 hour from a fully discharged state to a fully charged state. Figure 2 As shown, when the battery temperature is 25°C, the charging rate is 1C when the SOC is less than approximately 30%, and the charging rate is less than 1C when the SOC is greater than approximately 30%. In this example, the charging rate is divided into cases where the SOC is approximately 30% and cases where the SOC is less than 1C. In the range above approximately 30%, the charging rate gradually decreases as the SOC increases.

[0038] To explain the method for creating the allowable current value map, in a non-degraded battery 2, the allowable current value Idc at which lithium deposition does not occur is determined experimentally for each temperature and SOC of the battery 2. The experimentally determined allowable current value Idc is then mapped for each temperature and SOC of the battery 2. This allows the charge control device 10 to pre-set the allowable current value map for each temperature and SOC of the battery 2.

[0039] Next, refer to Figures 3 to 6 The capacity degradation coefficient Dcap will be described below. Figure 3 This is a graph showing the relationship between the capacity retention rate and the capacity degradation coefficient when there is no estimation error. Figure 4 This is a graph showing the relationship between the capacity retention rate and the capacity degradation coefficient when the estimation error is X%. Figure 5 This is a graph showing the relationship between the capacity maintenance rate and the capacity degradation coefficient when the estimation error is 10%. Figure 6 It is a map showing the relationship between the capacity maintenance rate and the capacity degradation coefficient, which reflects the estimation error in capacity estimation.

[0040] The capacity degradation coefficient map shows the relationship between the capacity retention rate, calculated based on an estimated value of the battery capacity calculated based on usage history, and its degradation coefficient, namely, the capacity degradation coefficient Dcap. The capacity retention rate of Battery 2 is set to a value that reflects the estimation error in the capacity estimation.

[0041] For example, in the case where there is no estimation error in capacity estimation, Figure 3 As shown, the capacity degradation coefficient Dcap is set to "1.00" when the capacity maintenance rate is "100"%, and the capacity degradation coefficient Dcap is set to "0.5" when the capacity maintenance rate is "50"%.

[0042] When the estimated error of the capacity estimation is "X%", Figure 4 As shown in Figure 1, the capacity retention rate can be expressed as a value that includes an estimated error, such as "50 + X"% or "60 + X"%. Furthermore, when the capacity retention rate is "50 + X," the capacity degradation coefficient Dcap is set to "0.50," and when the capacity retention rate is "60 + X," the capacity degradation coefficient Dcap is set to "0.60."

[0043] Therefore, if the estimation error of the capacity estimation is "10%", Figure 5 As shown, when the capacity retention rate is "60%" (which reflects an estimated error of 10%), the capacity degradation coefficient Dcap is set to "0.50." When the capacity retention rate is "70%" (which reflects an estimated error of 10%), the capacity degradation coefficient Dcap is set to "0.60." However, in this state, the maximum capacity degradation coefficient Dcap will be "0.9" from the initial state.

[0044] And, as Figure 6 As shown, the map of the capacity degradation coefficient Dcap is a map that can determine the capacity degradation coefficient Dcap based on the capacity retention rate that reflects the estimation error of the battery capacity.

[0045] Next, refer to Figure 7 The time degradation coefficient Dtime will be described. Figure 7 : is a map showing a degradation coefficient map over time.

[0046] The time-dependent degradation coefficient map is a map showing the relationship between the time elapsed since the start of use of the battery 2 and its degradation coefficient, that is, the time-dependent degradation coefficient Dtime. The elapsed time can be obtained using the time information.

[0047] As the elapsed time information, the number of days that have passed since the start of use of the battery 2 can be used. The number of days that have passed can be obtained by the charge control device 10 calculating the time that has passed since the start of use of the battery 2.

[0048] For example, during the operation of the device equipped with the battery 2, the number of days when the device is operated under the most stringent conditions and the degradation coefficient calculated based on the life of the battery 2 are used, as shown in FIG. Figure 7 As shown in , a time-dependent degradation coefficient map corresponding to the number of days has been created. The time-dependent degradation coefficient map is not affected by the capacity estimation error. Figure 7 As shown, when the number of elapsed days is “0”, the time-dependent degradation coefficient Dtime is set to “1.00.” Then, as the number of elapsed days increases, the time-dependent degradation coefficient Dtime continues to decrease.

[0049] The charge control device 10 configured in this manner calculates the limit current value Ilim during charging using a preset allowable current value map and the capacity degradation coefficient Dcap and the time degradation coefficient Dtime set according to the current state of the battery 2. An example of a charging method for charging the battery 2 based on the limit current value Ilim is shown in FIG. Figure 8 .

[0050] Figure 8 is a flowchart illustrating a battery charging method. Figure 8 The control shown is performed by the charging control device 10 .

[0051] The charging control device 10 calculates the allowable current value Idc corresponding to the temperature and SOC of the battery 2 (step S1). In step S1, the SOC is calculated based on the voltage and temperature detected by the voltage / temperature detection device 4. The allowable current value Idc is then calculated based on the SOC and battery temperature by referring to an allowable current value map. This allowable current value map is a preset map.

[0052] The charging control device 10 determines whether the capacity degradation coefficient Dcap is greater than the time degradation coefficient Dtime (step S2). In step S2, the capacity degradation coefficient Dcap is determined by referring to the capacity degradation coefficient map based on the capacity maintenance rate that reflects the estimation error in the capacity estimation. Furthermore, in step S2, the time degradation coefficient Dtime corresponding to the number of days elapsed is determined by referring to the time degradation coefficient map. Thus, the capacity degradation coefficient Dcap and the time degradation coefficient Dtime corresponding to the current state of the battery 2 are determined, and the degradation coefficients are compared.

[0053] If the capacity degradation coefficient Dcap is determined to be greater than the time degradation coefficient Dtime (step S2: YES), the charge control device 10 uses the smaller time degradation coefficient Dtime to calculate a limit current value Ilim by multiplying the time degradation coefficient Dtime by the allowable current value Idc (step S3). In step S3, the time degradation coefficient Dtime, which indicates the current degree of time degradation in the battery 2, is multiplied by the allowable current value Idc calculated in step S1.

[0054] If it is determined that the capacity degradation coefficient Dcap is less than the time degradation coefficient Dtime (step S2: No), the charge control device 10 uses the relatively smaller capacity degradation coefficient Dcap to calculate a limit current value Ilim by multiplying the capacity degradation coefficient Dcap by the allowable current value Idc (step S4). In step S4, the capacity degradation coefficient Dcap, which indicates the current degree of capacity degradation in the battery 2, is multiplied by the allowable current value Idc calculated in step S1.

[0055] After either step S3 or S4 is executed, the charge control device 10 performs charging at the limit current value Ilim (step S5). In step S5, the charging current value of the battery 2 is controlled to the limit current value Ilim, and charging is performed within a range that does not exceed the allowable current value Idc.

[0056] The charging control device 10 then determines whether the charge capacity of the battery 2 is greater than or equal to a specified value (step S6). In step S6, the current charge capacity of the battery 2 is calculated, and a determination is made as to whether the charge capacity is greater than or equal to a predetermined value. For example, the charging control device 10 can calculate the charge capacity of the battery 2 based on the current SOC. Alternatively, the charging control device 10 can calculate the charge capacity of the battery 2 using the detected value of the charging current input from the current detection device 5 and the detected values ​​of the voltage and temperature input from the voltage / temperature detection device 4.

[0057] If it is determined that the charge level of the battery 2 is equal to or greater than the predetermined value (step S6 : Yes), the control routine ends. In this case, the charge control device 10 ends the charging of the battery 2 .

[0058] When it is determined that the charge amount of the battery 2 is not equal to or greater than the predetermined value (step S6 : NO), the control routine returns to step S1 .

[0059] As described above, according to the embodiment, the smaller of the capacity degradation coefficient Dcap and the time degradation coefficient Dtime is used to set the charging current value. Therefore, even when the estimation error of the battery capacity is large, appropriate charging can be performed.

[0060] Specifically, when the estimated error in battery capacity is large and the capacity degradation coefficient Dcap is estimated to be greater than the actual degradation state, the smaller coefficient, namely the time-dependent degradation coefficient Dtime, is used to calculate the limit current value Ilim. This allows for appropriate charging appropriate to the degradation state of battery 2. Consequently, even a degraded battery 2 can be charged within a range that does not exceed the allowable current value Idc of battery 2. Furthermore, since the charging current value of battery 2 is not unnecessarily restricted, the charging time can be shortened.

[0061] It should be noted that as a modified example, a mapping that uses the time degradation coefficient Dtime in conjunction with the capacity degradation coefficient Dcap can be used. While the time degradation coefficient Dtime is a coefficient that does not include an estimation error, the capacity degradation coefficient Dcap is a coefficient that reflects the estimation error of the battery capacity. Therefore, due to the estimation error of the battery capacity, the capacity degradation coefficient Dcap is set to a value smaller than "1.00" from the initial state. Therefore, this combined mapping can be created as a modified example. An example of this combined mapping is shown in Figure 9 .

[0062] Figure 9 This is a map showing the case where both the capacity degradation coefficient and the time degradation coefficient are used. If the capacity degradation coefficient map is used directly, the capacity retention rate is determined to be "100%" when the estimation error is 10%, and the capacity degradation coefficient Dcap is set to "0.90", so sometimes the capacity of the battery 2 cannot be fully utilized from the initial state. Figure 9 As shown, a degradation coefficient map using the capacity degradation coefficient Dcap and the time degradation coefficient Dtime is created and used.

[0063] For example, when the estimated error of the capacity estimation is X%, if there is a time degradation coefficient Dtime until the capacity maintenance rate of the estimated capacity becomes "100-X"%, the estimated error of the capacity degradation coefficient mapping can be ignored until the capacity maintenance rate of the estimated capacity becomes "100-X"%. That is, by using the time degradation coefficient Dtime for the capacity degradation coefficient Dcap, there is no need to unnecessarily reduce the initial degradation coefficient. On the other hand, in the case of only the capacity degradation coefficient Dcap, the degradation coefficient will be unnecessarily restricted from the initial state. On the contrary, if control is performed only with the time degradation coefficient Dtime, the allowable current value Idc may be exceeded when degradation progresses beyond expectations. It should be noted that Figure 9 The map shown is created as a degradation coefficient map when the battery 2 is operated under the most severe conditions while the device equipped with the battery 2 is in operation.

[0064] Furthermore, although an example in which the battery 2 is mounted on a vehicle has been described, the vehicle may be an electric vehicle or a plug-in hybrid vehicle.

[0065] Furthermore, the device equipped with the battery 2 is not limited to a vehicle, and may be a mobile object, a portable electrical device, or the like.

Claims

1. A battery charging method, characterized in that: The following steps are involved: estimating a capacity degradation coefficient indicating a degree of capacity degradation of the battery based on the capacity maintenance rate and the capacity degradation coefficient map; calculating a time degradation coefficient indicating a degree of time degradation of the battery based on a time degradation coefficient map corresponding to elapsed days created using the number of days elapsed since the start of battery use and a degradation coefficient calculated based on the life of the battery; and A limit current value is calculated based on the smaller of the capacity degradation coefficient corresponding to the current estimated capacity value and the time degradation coefficient corresponding to the number of days since the battery started to be used, and the battery is charged with the calculated limit current value.

2. The battery charging method according to claim 1, wherein: In the step of estimating the capacity degradation coefficient, the capacity retention rate is obtained based on a value obtained by reflecting an estimation error on an estimated value of the battery capacity of the battery. The capacity degradation coefficient map is a map showing the relationship between the capacity maintenance rate and the capacity degradation coefficient.

3. The battery charging method according to claim 2, characterized in that: When the estimation error of the estimated value of the battery capacity is X%, until the capacity retention rate obtained in the step of estimating the capacity degradation coefficient reaches the capacity retention rate when the estimated value of the battery capacity is 100-X%, In the step of charging the battery at the limited current value, the limited current value is calculated based on the time-dependent degradation coefficient.

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