JP7636310B2 - How to charge the battery - Google Patents

Description

The present invention relates to a method for charging a battery.

Patent document 1 discloses that the maximum charging current value during charging is calculated based on the battery's condition (usage history, deterioration state).

JP 2017-108604 A

In the configuration described in Patent Document 1, the charging current value is calculated taking into account the deterioration state of the battery, but it is difficult to accurately grasp the deterioration state of the battery. Therefore, if there is a large error in the estimation of the battery capacity and the estimation accuracy of the capacity deterioration state is low, the charging current value may exceed the allowable current value, or the allowable current value may be restricted in advance more than necessary, which may prevent appropriate charging.

The present invention has been made in consideration of the above circumstances, and aims to provide a battery charging method that can perform appropriate charging even when there is a large error in the estimation of the battery capacity.

The present invention is a method for charging a battery, comprising the steps of estimating a capacity degradation coefficient indicating the degree of capacity degradation of the battery, calculating a time degradation coefficient indicating the degree of time degradation of the battery, and calculating a limit current value based on the smaller of the capacity degradation coefficient and the time degradation coefficient, and charging the battery with the calculated limit current value.

In the present invention, the charging current value is set using the smaller of the capacity degradation coefficient and the time degradation coefficient, so that appropriate charging can be performed even if the estimation error of the battery capacity is large. When the estimation error of the battery capacity is large and the capacity degradation coefficient is estimated to be a value larger than the actual degradation state, the limit current value is calculated using the smaller coefficient, the time degradation coefficient, so that appropriate charging according to the degradation state of the battery can be performed.

FIG. 1 is a diagram illustrating a charging system according to an embodiment. FIG. 2 is a map diagram showing an allowable current value map when the battery temperature is 25°C. FIG. 3 is a diagram showing the relationship between the capacity maintenance rate and the capacity deterioration coefficient when there is no estimation error. FIG. 4 is a diagram showing the relationship between the capacity maintenance rate and the capacity deterioration coefficient when the estimation error is X %. FIG. 5 is a diagram showing the relationship between the capacity maintenance rate and the capacity deterioration coefficient when the estimation error is 10%. FIG. 6 is a map showing the relationship between the capacity maintenance rate and the capacity deterioration coefficient, in which the estimation error of the capacity estimation is reflected. FIG. 7 is a map diagram showing a time deterioration coefficient map. FIG. 8 is a flow chart illustrating a method for charging a battery. FIG. 9 is a map diagram showing a case where the capacity deterioration coefficient and the time deterioration coefficient are used in combination.

The battery charging method according to an embodiment of the present invention will be described in detail below with reference to the drawings. Note that the present invention is not limited to the embodiment described below.

Figure 1 is a schematic diagram of a charging system according to an embodiment. When charging a battery 2, the charging system 1 electrically connects the battery 2 to a charger 3. The charging system 1 includes a charging control device 10, which controls the charging current value during charging.

Battery 2 is a secondary battery, and is composed of, for example, a lithium ion battery. This battery 2 is an assembled battery composed of multiple battery cells. When discharging, the power stored in battery 2 is supplied to a motor, etc. When charging, in charging system 1, power supplied from an external power source via charger 3 is stored in battery 2.

The charger 3 is a device that can supply power from an external power source to the battery 2. When charging the battery 2, the charger 3 is attached to the device in which the battery 2 is mounted, and the battery 2 and the external power source are electrically connected via the charger 3. When the battery 2 is not being charged, the charger 3 can be removed from the device in which the battery 2 is mounted.

In the charging system 1, as shown in FIG. 1, a second connection part 31 provided on the charger 3 is connected to a first connection part 21 provided on a device that carries the battery 2. The first connection part 21 is a connection part on the battery 2 side, and includes a positive electrode side connection part 21a connected to the positive electrode of the battery 2 and a negative electrode side connection part 21b connected to the negative electrode of the battery 2. The second connection part 31 is a connection part on the charger 3 side, and includes a positive electrode side connection part 31a connected to the positive electrode side connection part 21a of the first connection part 21 and a negative electrode side connection part 31b connected to the negative electrode side connection part 21b of the first connection part 21. An electric circuit is formed during charging by connecting the positive electrode side connection part 21a on the battery 2 side to the positive electrode side connection part 31a on the charger 3 side, and connecting the negative electrode side connection part 21b on the battery 2 side to the negative electrode side connection part 31b on the charger 3 side.

For example, if the device equipped with the battery 2 is a vehicle, the battery 2 is an on-board battery and the charger 3 is a charging station or other such charging equipment. In this case, the power stored in the battery 2 can be supplied to the driving motor during discharging. During charging, the charging cable provided on the charger 3 is connected to a charging port provided on the vehicle, electrically connecting the battery 2 to an external power source and enabling charging. This allows the power supplied from the external power source to be charged into the battery 2.

The charging 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 is configured to include a microcomputer equipped with a CPU, RAM, ROM, and an input/output interface. Therefore, the charging control device 10 performs signal processing according to a program pre-stored in the ROM. For example, the charging control device 10 is provided in a device equipped with the battery 2.

In addition, signals from various sensors are input to the charging control device 10. For example, signals from a voltage/temperature detection device 4 that detects the voltage and temperature of the battery 2, and a 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. The current detection device 5 detects the value of the current flowing through the electric circuit that electrically connects the battery 2 and the charger 3. As shown in FIG. 1, this current detection device 5 is placed on the negative electrode side of the battery 2, and detects the value of the current flowing from the charger 3 to the battery 2.

Then, the charge control device 10 executes charge control based on the signals input from the voltage/temperature detection device 4 and the current detection device 5. That is, the charge control device 10 executes charge control according to the current state of the battery 2. The charge control is a control for charging within a range in which the charging current value does not exceed the allowable current value Idc of the battery 2. During charging, the charge control device 10 controls the charging current value to a desired current value according to the current state of the battery 2. At that time, the charge control device 10 outputs a control signal to the charger 3 to control the charging current value.

As shown in FIG. 1, the charging control device 10 includes a calculation unit 11.

The calculation unit 11 calculates the SOC (State of charge) of the battery 2 based on the voltage and temperature of the battery 2 detected by the voltage and temperature detection device 4. Because the voltage and temperature detection device 4 can detect the voltage and temperature of the battery 2 during charging, the calculation unit 11 can calculate the current SOC based on the voltage and temperature of the battery 2 during charging.

The calculation unit 11 also estimates the amount of deterioration (deterioration state) of the battery 2 based on the usage history such as the capacity maintenance rate of the battery 2. In other words, the calculation unit 11 estimates the capacity deterioration coefficient Dcap, which is a coefficient indicating the degree of capacity deterioration of the battery 2.

The calculation unit 11 also calculates a deterioration coefficient due to the passage of time since the start of use of the battery 2. In other words, the calculation unit 11 calculates a time deterioration coefficient Dtime, which is a coefficient indicating the degree of deterioration of the battery 2 over time.

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 limited current value Ilim by multiplying the allowable current value Idc by the smaller of the capacity degradation coefficient Dcap according to the current capacity estimate value and the time degradation coefficient Dtime according to the elapsed time since the start of use of the battery 2. The charge control device 10 then charges the battery 2 at the limited current value Ilim. In other words, during charging, the charge current value is controlled to the limited current value Ilim by the charge control device 10.

Now, with reference to Figures 2 to 7, we will explain in more detail the allowable current value map, the capacity degradation coefficient Dcap, and the time degradation coefficient Dtime.

First, let us explain the allowable current value map with reference to Figure 2.

The allowable current value map is a map that is preset for each temperature and SOC of the battery 2. In the charging method of the embodiment, the preset allowable current value map is referenced when calculating the allowable current value Idc according to the current state (temperature, SOC) of the battery 2. That is, the charging control device 10 uses the allowable current value map when calculating the allowable current value Idc.

For example, when the temperature of the battery 2 is 25°C, the charge rate is set for each SOC. The charge rate indicates the speed of charging and is a relative expression of the magnitude of the current value. In the case of constant current charge/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 when the battery goes from a fully discharged state to a fully charged state in one hour. As shown in Figure 2, when the battery temperature is 25, the charge rate is 1C when the SOC is less than about 30%, and the charge rate is less than 1C when the SOC is greater than about 30%. In this example, the charge rate is either 1C or less than 1C at the border of about 30% SOC. In the range of SOC greater than about 30%, the charge rate gradually decreases as the SOC increases.

To explain how to create the allowable current value map, the allowable current value Idc at which lithium deposition does not occur for each temperature and SOC of the battery 2 is experimentally determined for an undegraded battery 2. The allowable current value Idc experimentally determined is then mapped for each temperature and SOC of the battery 2. This allows the charging control device 10 to preset the allowable current value map for each temperature and SOC of the battery 2.

Next, the capacity degradation coefficient Dcap will be described with reference to Figures 3 to 6. Figure 3 is a diagram showing the relationship between the capacity retention rate and the capacity degradation coefficient when there is no estimation error. Figure 4 is a diagram showing the relationship between the capacity retention rate and the capacity degradation coefficient when the estimation error is X%. Figure 5 is a diagram showing the relationship between the capacity retention rate and the capacity degradation coefficient when the estimation error is 10%. Figure 6 is a map diagram showing the relationship between the capacity retention rate and the capacity degradation coefficient, reflecting the estimation error of the capacity estimation.

The capacity degradation coefficient map is a map showing the relationship between the capacity retention rate calculated based on an estimated value of the battery capacity calculated from the usage history, etc., and the capacity degradation coefficient Dcap, which is the degradation coefficient. The capacity retention rate of battery 2 is set to a value that reflects the estimation error of the capacity estimation.

For example, if there is no estimation error in the capacity estimation, as shown in Figure 3, 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".

When the estimated error in the capacity estimation is "X%," as shown in Figure 4, the capacity maintenance rate can be expressed by a value that includes the estimated error, such as "50+X"% or "60+X"% that reflects the estimated error of X%. When the capacity maintenance rate is "50+X", the capacity degradation coefficient Dcap is set to "0.50", and when the capacity maintenance rate is "60+X", the capacity degradation coefficient Dcap is set to "0.60".

Therefore, when the estimated error of the capacity estimation is "10%," as shown in FIG. 5, when the capacity maintenance rate is "60"% reflecting the estimated error of 10%, the capacity degradation coefficient Dcap is set to "0.50", and when the capacity maintenance rate is "70"% reflecting the estimated error of 10%, the capacity degradation coefficient Dcap is set to "0.60". However, in this state, from the initial state, the maximum capacity degradation coefficient Dcap becomes "0.9".

The map of the capacity degradation coefficient Dcap, as shown in Figure 6, is a map that can determine the capacity degradation coefficient Dcap based on the capacity maintenance rate that reflects the estimated error of the battery capacity.

Next, the time-related deterioration coefficient Dtime will be explained with reference to Figure 7. Figure 7 is a map diagram showing the time-related deterioration coefficient map.

The time deterioration coefficient map is a map showing the relationship between the time elapsed since the start of use of the battery 2 and the time deterioration coefficient Dtime, which is the deterioration coefficient of the battery 2. The elapsed time can be calculated using the time information.

The number of days that have passed since the battery 2 began to be used can be used as the time-elapsed information. The number of days that have passed can be obtained by the charging control device 10 calculating the time that has passed since the battery 2 began to be used.

For example, a time deterioration coefficient map according to the number of days elapsed is created as shown in FIG. 7 using the number of days elapsed when the device equipped with the battery 2 was operated under the harshest conditions and the deterioration coefficient calculated from the lifespan of the battery 2. The time deterioration coefficient map is not affected by capacity estimation errors. Therefore, as shown in FIG. 7, when the number of days elapsed is "0", the time deterioration coefficient Dtime is set to "1.00". Then, as the number of days elapsed increases, the time deterioration coefficient Dtime continues to decrease.

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 a capacity degradation coefficient Dcap and a time degradation coefficient Dtime that are set according to the current state of the battery 2. Figure 8 shows an example of a charging method for charging the battery 2 based on this limit current value Ilim.

Figure 8 is a flow chart showing a method for charging a battery. The control shown in Figure 8 is performed by the charging control device 10.

The charging control device 10 calculates the allowable current value Idc according 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, and the allowable current value Idc is calculated by referring to the allowable current value map based on the SOC and the battery temperature. This allowable current value map is a preset map.

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 of the capacity estimation. Furthermore, in step S2, the time degradation coefficient Dtime according to the number of days elapsed is determined by referring to the time degradation coefficient map. In this way, the capacity degradation coefficient Dcap and the time degradation coefficient Dtime according to the current state of the battery 2 are determined, and the magnitudes of the degradation coefficients are compared.

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

If it is determined that the capacity degradation coefficient Dcap is equal to or less than the time degradation coefficient Dtime (step S2: No), the charge control device 10 uses the capacity degradation coefficient Dcap, which is the relatively smaller coefficient, to calculate the limit current value Ilim by multiplying the capacity degradation coefficient Dcap and 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.

When either step S3 or S4 is performed, the charging control device 10 charges the battery 2 at the limited current value Ilim (step S5). In step S5, the charging current value of the battery 2 is controlled to the limited current value Ilim, so that charging is performed within a range that does not exceed the allowable current value Idc.

Then, the charge control device 10 determines whether the charge amount of the battery 2 is equal to or greater than a predetermined value (step S6). In step S6, the current charge amount of the battery 2 is calculated, and it is determined whether the charge amount is equal to or greater than a predetermined value set in advance. For example, the charge control device 10 can calculate the charge amount of the battery 2 based on the current SOC. Alternatively, the charge control device 10 may calculate the charge amount 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.

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

If it is determined that the charge level of battery 2 is not equal to or greater than the predetermined value (step S6: No), the control routine returns to step S1.

As described above, according to the embodiment, the charging current value is set using the smaller of the capacity degradation coefficient Dcap and the time degradation coefficient Dtime, so that appropriate charging can be performed even if the estimation error of the battery capacity is large.

In other words, when the estimated error in the battery capacity is large and the capacity degradation coefficient Dcap is estimated to be a value larger than the actual degradation state, the smaller coefficient, the time degradation coefficient Dtime, is used to calculate the limit current value Ilim, so it is possible to charge appropriately according to the degradation state of the battery 2. As a result, even a degraded battery 2 can be charged within a range that does not exceed the allowable current value Idc of the battery 2, and the charging current value of the battery 2 is not restricted more than necessary, so the charging time can be shortened.

As a modified example, it is possible to use a map that uses the capacity degradation coefficient Dcap together with the time degradation coefficient Dtime. 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 an estimation error in the battery capacity. Therefore, the capacity degradation coefficient Dcap is set to a value smaller than "1.00" from the initial state due to the estimation error in the battery capacity. Therefore, as a modified example, this combined map can be created. An example of this combined map is shown in FIG. 9.

Figure 9 is a map diagram showing the case where the capacity degradation coefficient and the time degradation coefficient are used together. If the capacity degradation coefficient map is used as is, when the estimation error is 10%, the capacity maintenance rate is determined to be "100"%, and the capacity degradation coefficient Dcap is set to "0.90", so it may not be possible to fully use the capacity of the battery 2 from the initial state. Therefore, as shown in Figure 9, a degradation coefficient map is created that is used together with the capacity degradation coefficient Dcap and the time degradation coefficient Dtime.

For example, if the estimation error of the capacity estimation is X%, the estimation error of the capacity degradation coefficient map can be ignored until the capacity maintenance rate of the estimated capacity becomes "100-X"% if the time degradation coefficient Dtime is used. In other words, by using the time degradation coefficient Dtime in addition to the capacity degradation coefficient Dcap, it is not necessary to make the initial degradation coefficient smaller than necessary. On the other hand, if only the capacity degradation coefficient Dcap is used, the degradation coefficient is restricted more than necessary from the initial state. On the other hand, if only the time degradation coefficient Dtime is used for control, there is a risk that the allowable current value Idc will be exceeded when degradation progresses more than expected. The map shown in FIG. 9 is created as a degradation coefficient map for the case where the battery 2 is operated under the most severe conditions among the conditions in which the device equipped with the battery 2 is operated.

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.

In addition, the device in which the battery 2 is mounted is not limited to a vehicle, but may be a moving object, a portable electrical device, etc.

REFERENCE SIGNS LIST 1 Charging system 2 Battery 3 Charger 4 Voltage/temperature detection device 5 Current detection device 10 Charging control device 11 Calculation unit 21 First connection part 21a Positive electrode side connection part 21b Negative electrode side connection part 31 Second connection part 31a Positive electrode side connection part 31b Negative electrode side connection part

Claims (1)

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

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