JP7499591B2 - BATTERY STATE ESTIMATION DEVICE AND BATTERY STATE ESTIMATION METHOD - Google Patents

Description

The present invention relates to a battery state estimation device and a battery state estimation method.

The full charge capacity of a battery decreases as a result of repeated charging and discharging. It is also known that the full charge capacity decreases even if the battery is not repeatedly charged and discharged, if it is left for a long time. The full charge capacity is the capacity that can be discharged until a fully charged battery is completely discharged. The full charge capacity of a battery decreases as it deteriorates due to the influence of the charge and discharge current value, temperature, state of charge (SOC), etc., which are the usage environment. For this reason, it is important to accurately detect the full charge capacity that decreases over time. In addition, it is common to express the current full charge capacity ( _Qc ) as a ratio to the initial full charge capacity (Qini) (capacity deterioration rate SOH=(Qc/Qini)×100).

The full charge capacity of a battery can be detected by accumulating the charge capacity until a fully discharged battery is fully charged. The full charge capacity can also be detected by accumulating the discharge capacity until a fully charged battery is fully discharged. Although these methods can accurately detect the full charge capacity of a battery, they have the disadvantage of significantly restricting the environment in which the battery can be used. This is because when a battery is fully discharged, not only does it take a long time to discharge, but the battery cannot be used at all in a discharged state. Furthermore, since batteries tend to deteriorate in the range between full charge and over-discharge, the method of fully discharging the battery and then fully charging it to detect the full charge capacity causes the detection of the full charge capacity to deteriorate the battery.

As a method for eliminating this drawback, Patent Document 1 discloses a method for integrating the charge/discharge current (∫Idt) during a period (e.g., t1 to tx) in which the magnitude of the charge/discharge current exceeds a predetermined threshold, and calculating the difference in the state of charge (SOC) during that period (ΔSOC = |SOC_t1-SOC_tx|) to calculate the full charge capacity (Qc) (Qc = ∫Idt/ΔSOC).

JP 2012-58028 A

In the above conventional inventions, in order to reduce the effect of current sensor errors, it is necessary to limit the charge/discharge current to a certain value or more, which reduces the opportunities to estimate the full charge capacity, and in some cases, it may not be possible to estimate the full charge capacity for a long period of time. Furthermore, if a current sensor with less error is used, the opportunities to estimate the full charge capacity increase, but the sensor becomes expensive and peripheral components such as A/D converters also need to be accurate, which makes the battery state estimation device expensive.

The present invention was made in consideration of the above-mentioned conventional problems, and aims to provide a battery state estimation device and a battery state estimation method that can accurately detect the full charge capacity without completely discharging or fully charging the battery, and even if there is a current sensor error.

To achieve the above object, one aspect of the present invention is a battery state estimation device that includes a charging rate/current offset estimation unit that successively estimates the charging rate SOC and current offset Io of a battery from the charging/discharging current I, voltage V, and temperature T of the battery, and a capacity degradation rate estimation unit that estimates the capacity degradation rate SOHQ when the estimated offset Io is a constant value and the difference ΔSOC of the estimated charging rate SOC is equal to or greater than a predetermined value.

Another aspect of the present invention is a method for estimating a battery state, which is characterized by sequentially estimating the battery's charging rate SOC and current offset Io from the battery's charging and discharging current I, voltage V, and temperature T, and estimating the capacity degradation rate SOHQ when the estimated offset Io is a constant value and the difference ΔSOC between the estimated charging rates SOC is equal to or greater than a predetermined value.

More specific configurations of the present invention are described in the claims.

The present invention provides a battery state estimation device and a battery state estimation method that can accurately detect the full charge capacity without fully discharging or fully charging the battery, even if there is a current sensor error.

Problems, configurations, and advantages other than those described above will become clear from the description of the embodiments below.

FIG. 1 is a block diagram of a battery state estimation device according to a first embodiment of the present invention; FIG. 2 is a block diagram of a state of charge (SOC) and current offset (Io) estimation unit 210 of FIG. Battery equivalent circuit model used in the state of charge (SOC) and current offset (Io) estimation unit 210 in the battery state estimation device of the first embodiment 1 is a graph showing an example of time-series data of battery current and battery voltage input to a battery state estimation device according to a first embodiment; Graph showing an example of a state of charge (SOC) and a current offset (Io) estimated by the battery state estimation device of the first embodiment. FIG. 1 is a block diagram of a battery state estimation device according to a second embodiment of the present invention; FIG. 13 is a block diagram of a battery state estimation device according to a third embodiment of the present invention. FIG. 4 is a block diagram of a state of charge (SOC), current offset (Io), and full charge capacity (Qc) estimation unit 410 in a battery state estimation device according to a third embodiment. Graph showing an example of a current offset (Io) and a full charge capacity (Qc) estimated by a battery state estimation device according to a third embodiment. FIG. 13 is a block diagram of a battery state estimation device according to a fourth embodiment of the present invention.

The following describes an embodiment of the present invention with reference to the drawings. FIG. 1 is a configuration diagram of a battery state estimation device according to a first embodiment. As shown in FIG. 1, the battery state estimation device 200 is composed of a state of charge (SOC), current offset (Io) estimation unit 210 that estimates the state of charge (SOC) and current offset (Io), and a capacity degradation rate (SOHQ) estimation unit 220 that estimates the full charge capacity (Qc) and capacity degradation rate (SOHQ).

Figure 2 is a block diagram of the state of charge (SOC) and current offset (Io) estimation unit 210 in Figure 1. The SOC estimation unit 211 and Io estimation unit 210 are calculated using a Kalman filter, and the SOC is calculated sequentially according to the following formula (1), and Io is calculated sequentially according to the following formula (2).

Here, Gsoc and Gio indicate the Kalman gains that are sequentially calculated by the Kalman filter. Also, t is the sensing period of the voltage, current, and temperature, or the calculation period of the state of charge (SOC) and current offset (Io) estimation unit 210, and for example, t=1 for every second.

Figure 3 shows a battery equivalent circuit model used in the state of charge (SOC) and current offset (Io) estimation unit 210 in the battery state estimation device of Example 1. The CCV (battery terminal voltage) estimation unit 213 in Figure 2 calculates the CCV from the battery equivalent circuit model in Figure 3. The CCV (battery terminal voltage) estimation unit 213 has battery equivalent circuit parameters (OCV (open circuit voltage), R1, R2, τ2 (time constant), R3, τ3 (time constant)) set in advance as a map for each SOC and temperature. Then, the battery parameters are determined from the SOC and temperature (T) input to the CCV (battery terminal voltage) estimation unit 213, and the CCV is calculated from the input current (I) and current offset (Io). The difference ΔCCV between this CCV and the battery terminal voltage (V) measured by the voltage sensor is calculated, and the difference is multiplied by the Kalman gain (Gsoc, Gio), and the result is added to the SOC and Io, respectively, to update the SOC and Io (see equations (1) and (2)).

Figure 4 is a graph showing an example of time series data of the battery current and battery voltage input to the battery state estimation device of Example 1, and Figure 5 is a graph showing an example of the state of charge (SOC) and current offset (Io) estimated by the battery state estimation device of Example 1. An offset current of -4.0A was input in advance to the cell current. Io starts from an initial value of 0 and is estimated in the negative direction as time passes. After that, from about 16,000 seconds, Io becomes a constant value of about -4.0A. In other words, it converges toward the true value of Io, which is -4.0A. Also, looking at the progress of the SOC estimation, it can be seen that the estimated SOC until Io becomes a constant value contains an error compared to the true SOC value, but the estimated SOC when Io is a constant value has a small error. In other words, in the present invention, by calculating the full charge capacity (Qc) when Io is a constant value, Qc can be calculated with high accuracy.

Next, the capacity deterioration rate (SOHQ) estimation unit 220 will be described. The capacity deterioration rate (SOHQ) estimation unit 220 receives the SOC and Io estimated by the state of charge (SOC) and current offset (Io) estimation unit 210, and calculates the full charge capacity (Qc) using the calculation formula (3) for a period in which the Io estimate is constant. When the capacity deterioration rate (SOHQ) estimation unit 220 recognizes that Io is constant, it stores the SOC (to) at that time and starts current integration. After that, it monitors the SOC input during the constant Io period, and when the SOC becomes equal to or greater than a predetermined SOC difference (ΔSOC) from the SOC (to), it ends the current integration and calculates the full charge capacity (Qc) based on the calculation formula (3). In addition, it outputs the calculated Qc to the state of charge (SOC) and current offset (Io) estimation unit 210. The state of charge (SOC) and current offset (Io) estimation unit 210 uses this Qc to calculate the SOC.

Here, Io is defined as a constant value by finding the slope of Io (mIo = |(I(t-1)-I(t))|/Δt) for each time step, and if it is below a predetermined value, it is considered to be a constant value. For example, from the results in Figure 5, when ΔIo = 0.1A from 0 to 3000 seconds, mIo = 3.331e-5, but this is not considered to be a constant value. Between 16000 and 26000 seconds, ΔIo ≦ 0.01A, and mIo = 1e-6. Since Io is considered to be a constant value at this time, the predetermined value of mIo can be set to 2e-5 or less.

The capacity degradation rate (SOHQ) estimation unit 220 also calculates the capacity degradation rate (SOHQ) based on equation (4) using the estimated Qc and the set initial full charge capacity (Qini).

In the first embodiment, the condition for calculating the SOHQ in the capacity deterioration rate (SOHQ) estimation unit 220 was that the input Io was constant and exceeded a predetermined SOC difference during a certain period of time, but in the second embodiment, a temperature condition was added in addition to the condition in the first embodiment. The reason is that when the cell is generating heat due to charging and discharging current, the cell surface temperature sensed by the temperature sensor deviates from the cell internal temperature. Generally, a temperature sensor senses the cell surface temperature. Using the temperature data and SOC, the parameters (OCV, R1, R2, R3, τ2, τ3) of the battery equivalent circuit model are obtained from the map to calculate the CCV. At this time, if the cell surface temperature and the cell internal temperature deviate, the cell internal temperature is close to the true temperature of the cell, so the CCV is calculated using the deviated parameters. As a result, the ΔCCV also becomes a deviated value, and the SOC and Io are also estimated to be deviated values. Therefore, if Qmax and SOHQ are estimated when the difference between the cell surface temperature and the cell internal temperature is thought to be small, high accuracy can be achieved.

Usually, the greater the difference between the cell's ambient temperature and cell surface temperature, the greater the difference between the cell's internal temperature and surface temperature due to the heat generated by the cell. Therefore, the cell's ambient temperature and cell surface temperature are sensed by a temperature sensor, and Qmax and SOHQ are estimated when the temperature difference (ΔT) is equal to or less than a predetermined value. FIG. 6 is a configuration diagram of a battery state estimation device of Example 2. As a difference from Example 1, a temperature sensor 300 is installed around the cell, and temperature data Ten from the temperature sensor 300 is input to the capacity deterioration rate (SOHQ) estimation unit 220. The cell surface temperature T is also input to the capacity deterioration rate (SOHQ) estimation unit 220. The capacity deterioration rate (SOHQ) estimation unit 220 calculates Qmax and SOHQ when the following three conditions are satisfied.
Three conditions: (Io constant value) and (ΔSOC is a predetermined value or more) and (ΔT is a predetermined value or less)

Figure 7 is a configuration diagram of a battery state estimation device of Example 3. As shown in Figure 7, the battery state estimation device 400 is composed of a state of charge (SOC), current offset (Io), and full charge capacity (Qc) estimation unit 410 that estimates the state of charge (SOC), current offset (Io), and full charge capacity (Qc), and a capacity deterioration rate (SOHQ) estimation unit 420 that estimates the capacity deterioration rate (SOHQ). Figure 8 is a configuration diagram of the state of charge (SOC), current offset (Io), and full charge capacity (Qc) estimation unit 410 in the battery state estimation device of Example 3. The SOC estimation unit 411, Io estimation unit 212, and Qc estimation unit 412 are obtained by a Kalman filter, and SOC is calculated sequentially according to the above-mentioned formula (1), Io is calculated according to the above-mentioned formula (2), and Qc is calculated according to the following formula (5).

Here, Gqc represents the Kalman gain that is calculated sequentially using the Kalman filter.

Figure 9 is a graph showing an example of the current offset (Io) and full charge capacity (Qc) estimated by the battery state estimation device of Example 3. The input data to the estimation unit 410 is the same as that shown in Figure 4. As with Figure 5, Io approaches the true value (-4.0 A) over time and becomes a constant value. As for Qc, there is no significant variation over the entire range. The capacity degradation rate (SOHQ) estimation unit 420 receives the SOC, Io, and full charge capacity (Qc) estimated by the estimation unit 410,

The estimated Qc is the Qc at a certain time in the section where Io is a constant value. Alternatively, the estimated Qc may be the average Qc in the section where Io is constant and the SOC range is, for example, from 40% to 70%.

Figure 10 is a diagram showing the configuration of a battery state estimation device according to Example 4. In Example 4, the estimated Qc is the Qc when Io, which is a condition for calculating the SOHQ in embodiment 3, becomes constant, and when the temperature difference (ΔT) between the cell's ambient temperature (Ten) and the cell surface temperature (T) is equal to or less than a predetermined value.

As described above, the present invention has been shown to provide a battery state estimation device and a battery state estimation method that can accurately detect the full charge capacity without fully discharging or fully charging the battery, even if there is a current sensor error.

The present invention is not limited to the above-mentioned embodiments, but includes various modified examples. The above-mentioned embodiments are provided to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all of the configurations described. It is also possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

100...battery, 200...battery state estimation device, 210...state of charge (SOC) and current offset (Io) estimation unit, 211...state of charge (SOC) calculation unit, 212...current offset (Io) calculation unit, 213...battery terminal voltage (CCV) estimation unit, 220...capacity degradation rate (SOHQ) estimation unit, 300...temperature sensor, 400...battery state estimation device, 410...state of charge (SOC), current offset (Io), full charge capacity (Qc) estimation unit, 411...state of charge (SOC) calculation unit, 412...full charge capacity (Qc) calculation unit, 420...capacity degradation rate (SOHQ) estimation unit, 500...battery state estimation device, 510...capacity degradation rate (SOHQ) estimation unit.

Claims (10)

a charging rate/current offset estimation unit that successively estimates a charging rate SOC and a current offset Io of the battery from a charging/discharging current I, a voltage V, and a temperature T of the battery;
a capacity degradation rate estimation unit that estimates a capacity degradation rate SOHQ when the estimated current offset Io is a constant value and the estimated difference ΔSOC of the charging rate SOC becomes a predetermined value or more;
A battery state estimating device comprising: a temperature sensor for measuring an ambient temperature of the battery and a surface temperature of the battery;
2. The battery state estimation device according to claim 1, wherein the capacity deterioration rate estimation unit estimates the capacity deterioration rate SOHQ when the estimated current offset Io is a constant value, the difference ΔSOC of the estimated charging rate SOC is equal to or greater than a predetermined value, and the difference between the ambient temperature and the surface temperature is equal to or less than a predetermined value. The charging rate/current offset estimation unit sequentially estimates a full charge capacity Qc,
3. The battery state estimation device according to claim 1, wherein the capacity degradation rate estimation unit estimates the capacity degradation rate SOHQ by using the estimated full charge capacity Qc when the estimated current offset Io is a constant value. 4. The battery state estimating device according to claim 3 , wherein the charging rate SOC, the current offset Io, or the full charge capacity Qc is estimated by a Kalman filter. a battery state estimation device successively estimating a charging rate SOC and a current offset Io of the battery from a charging/discharging current I, a voltage V, and a temperature T of the battery;
a battery state estimation device that estimates a capacity degradation rate SOHQ when the estimated current offset Io is a constant value and a difference ΔSOC of the estimated charging rate SOC becomes a predetermined value or more. a temperature sensor included in the battery state estimation device measures an ambient temperature of the battery and a surface temperature of the battery;
6. The battery state estimation method according to claim 5, wherein the battery state estimation device estimates the capacity degradation rate SOHQ when the estimated current offset Io is a constant value, the difference ΔSOC of the estimated charging rate SOC is equal to or greater than a predetermined value, and the difference between the ambient temperature and the surface temperature is equal to or less than a predetermined value. the battery state estimation device sequentially estimates the charging rate SOC and the current offset Io of the battery, and sequentially estimates a full charge capacity Qc of the battery;
7. The battery state estimation method according to claim 5, wherein the battery state estimation device estimates the capacity degradation rate SOHQ using the estimated full charge capacity Qc when the estimated current offset Io is a constant value. 8. The method of estimating a battery state according to claim 7 , wherein the battery state estimating device estimates the charging rate SOC, the current offset Io, or the full charge capacity Qc using a Kalman filter. 3. The battery state estimating device according to claim 1, wherein the charging rate SOC or the current offset Io is estimated by a Kalman filter. 7. The method for estimating a battery state according to claim 5, wherein the battery state estimating device estimates the charging rate SOC or the current offset Io using a Kalman filter.

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