Battery capacity estimation method and battery SOC estimation method

Abstract

The invention relates to a battery capacity estimation method and a battery SOC estimation method. Provided are a method for accurately estimating the battery capacity and a method for accurately estimating the SOC of a battery on the basis of the estimated battery capacity obtained by the battery capacity estimation method. A method for estimating a battery capacity includes causing a computer to execute the following steps: (a) charging at a predetermined temperature and a predetermined provisional SOC of 80% or more over a predetermined time at a predetermined charging speed to obtain a specific internal resistance; and (b) deriving the estimated battery capacity from the specific internal resistance on the basis of the specific first relationship. The method for estimating the SOC of the battery includes, after the step (b), further causing the computer to execute a step (i) of obtaining an estimated change amount of the SOC associated with deterioration of the battery from the estimated battery capacity on the basis of a predetermined second relationship, or (ii) obtaining an estimated SOC after a change associated with deterioration of the battery from the estimated battery capacity on the basis of a predetermined third relationship.

Description

Technical Field

[0001] The present disclosure relates to a method for estimating battery capacity and a method for estimating the state of charge (SOC) of a battery. Background Art

[0002] Techniques for estimating the state of charge (SOC) based on the open circuit voltage (OCV) of a battery are known.

[0003] For example, Patent Document 1 discloses a SOC estimation device and a SOC estimation method that, for changes in the SOC-OCV characteristics caused by charge and discharge history, estimate a more accurate SOC-OCV characteristic based on the charge and discharge implementation status, and use the estimated SOC-OCV characteristic to estimate the value of SOC, thereby reducing the SOC estimation error.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2014-059206 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] In addition to this, various SOC estimation methods are known, but there is still a desire for a method for accurately estimating SOC.

[0009] In addition, in addition to being able to accurately estimate the SOC of a battery, it is also desired to be able to accurately estimate the battery capacity.

[0010] An object of the present disclosure is to provide a method for accurately estimating battery capacity and a method for accurately estimating the SOC of a battery based on the estimated battery capacity obtained by using such a method for estimating battery capacity.

[0011] Means for Solving the Problems

[0012] The inventors of the present application have found that the above problems can be solved by adopting the following means.

[0013] <Solution 1>

[0014] A method for estimating battery capacity, comprising causing a computer to execute the following steps:

[0015] (a) Charging at a specified charging rate for a specified time at a specified provisional SOC of 80% or more and a specified temperature to obtain a specific internal resistance; and

[0016] (b) Based on a previously determined first relationship between the specific internal resistance and the battery capacity, obtaining an estimated battery capacity from the specific internal resistance.

[0017] <Scheme 2>

[0018] A method for estimating the SOC of a battery, which includes, after the process (b) in the method described in Scheme 1, further causing a computer to execute the following process:

[0019] (i) Based on a previously determined second relationship between the estimated battery capacity and the change amount of the SOC associated with the deterioration of the battery, obtaining the estimated change amount of the SOC associated with the deterioration of the battery from the estimated battery capacity, or

[0020] (ii) Based on a previously determined third relationship between the estimated battery capacity and the changed SOC associated with the deterioration of the battery, obtaining the estimated changed SOC associated with the deterioration of the battery from the estimated battery capacity.

[0021] <Scheme 3>

[0022] According to the method described in Scheme 1 or 2, wherein the first relationship has a linear equation, and the coefficient of determination of the linear equation is 0.8 or more.

[0023] <Scheme 4>

[0024] According to the method described in Scheme 1 or 2, wherein the specified time is 20 seconds or more, and the specified charging rate is 3C or more.

[0025] Effects of the Invention

[0026] According to the present disclosure, it is possible to provide a method for correctly estimating the battery capacity and a method for correctly estimating the SOC of the battery based on the estimated battery capacity obtained by using such a method for estimating the battery capacity. Description of the Drawings

[0027] Figure 1 A flowchart of the method of the present disclosure for estimating the battery capacity and the SOC.

[0028] Figure 2 A conceptual diagram of a map showing the relationship between a specific internal resistance and the battery capacity.

[0029] Figure 3 A conceptual diagram of a map showing the relationship between the estimated battery capacity and the change amount of the SOC associated with the deterioration of the battery.

[0030] Figure 4 An exemplary coordinate diagram of the SOC-OCV curve before and after the durability test.

[0031] Figure 5 A coordinate diagram showing the relationship between the specific internal resistance and the battery capacity at each tentative SOC.

[0032] Figure 6To show the coefficient of determination R of a map showing the relationship between the tentative SOC and a specific internal resistance and battery capacity 2 of the relationship.

[0033] Figure 7 A coordinate diagram showing the relationship between the battery voltage and the voltage differential (dQ / dV) of the capacity during charging under specified conditions for two batteries with different battery capacities due to deterioration. Detailed Description of the Invention

[0034] The embodiments of the present disclosure will be described in detail below. It should be noted that the present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the disclosed gist.

[0035] "Method for Estimating Battery Capacity"

[0036] The method of the present disclosure for estimating the battery capacity includes causing a computer to execute the following steps: (a) charging at a specified charging rate for a specified time at a specified tentative SOC of 80% or more and a specified temperature to obtain a specific internal resistance; and (b) obtaining an estimated battery capacity from the specific internal resistance based on a previously determined first relationship between the specific internal resistance and the battery capacity.

[0037] As Figure 5 and 6 shown, according to the research of the inventors of the present application, the coefficient of determination of the linear equation representing the relationship between the internal resistance (specific internal resistance) of the battery measured by charging under specified conditions where the tentative SOC is 80% or more and the battery capacity is 0.8 or more. That is, the specific internal resistance and the battery capacity in this case show a high correlation. Thus, the inventors of the present application found that the battery capacity can be correctly estimated from the specific internal resistance. That is, in the method of the present disclosure, although the measurement conditions are restricted, the battery capacity can be correctly estimated.

[0038] And similarly as Figure 5 and 6 shown, the coefficient of determination of the linear equation representing the relationship between the specific internal resistance of the battery measured by charging under specified conditions where the tentative SOC is less than 80% and the battery capacity is less than 0.8. That is, the correlation between the specific internal resistance and the battery capacity in this case is low.

[0039] Furthermore, Figure 5 in, the values of the specific internal resistance and the battery capacity are shown as relative values when the maximum value of each measured value is set to 1.0.

[0040] Figure 7For two batteries with different battery capacities due to deterioration, the relationship between the battery voltage (V) and the voltage differential of the capacity (dQ / dV) when charging at 1C for 5 seconds is shown. As shown in this Figure 7 When charging at a battery voltage corresponding to a tentative SOC of 80% or more, for two batteries with different battery capacities due to deterioration, the difference in the voltage differential of the capacity (dQ / dV) can be correctly distinguished (refer to the right side of the straight line indicating "SOC 80%" in Figure 7 ).

[0041] That is, as shown in Figure 7 , when charging at a battery voltage corresponding to a tentative SOC of 80% or more, the dQ / dV curve of the battery with a smaller battery capacity due to deterioration ("battery with small capacity") can be separated from the dQ / dV curve of the battery with a larger battery capacity that has not deteriorated and remains large ("battery with large capacity"). Here, the voltage differential of the capacity (dQ / dV) means the battery capacity at each voltage. Therefore, as shown in Figure 7 , when charging at a battery voltage corresponding to a tentative SOC of 80% or more, the difference in battery capacity between the battery with a smaller battery capacity due to deterioration ("battery with small capacity") and the battery with a larger battery capacity that has not deteriorated and remains large ("battery with large capacity") is clear. That is, Figure 7 implies that there is also a correlation between the battery voltage and the battery capacity.

[0042] Similarly, as shown in Figure 7 , when charging at a battery voltage corresponding to a tentative SOC of less than 80%, the difference in battery capacity between the battery with a smaller battery capacity due to deterioration ("battery with small capacity") and the battery with a larger battery capacity that has not deteriorated and remains large ("battery with large capacity") cannot be distinguished (refer to the left side of the straight line indicating "SOC 80%" in Figure 7 ).

[0043] Furthermore, in Figure 7 , the value of dQ / dV is shown as a relative value with the maximum measured value set to 1.0, and the value of the battery voltage is shown as a relative value with the case of SOC 80% set to 1.0.

[0044] Furthermore, regarding the present disclosure, the so-called "tentative SOC" means the SOC measured or estimated before step (a).

[0045] The specified provisional SOC may be 80% or more, 85% or more, 90% or more, or 95% or more, and may be less than 100%, 95% or less, 90% or less, 85% or less, or 80% or less.

[0046] Regarding the present disclosure, the so-called "specific internal resistance" means the internal resistance of a battery measured by charging at a specified charging rate for a specified time at a specified temperature with a specified provisional SOC of 80% or more.

[0047] Regarding the method of the present disclosure, the first relationship may have a linear equation (linear function), and the coefficient of determination R of the linear equation 2 is 0.8 or more. Further, the coefficient of determination R 2 is the value obtained by squaring the correlation coefficient R. The closer the coefficient of determination R 2 is to 1.0, the higher the correlation between the specific internal resistance and the battery capacity and the higher the fitness of the regression equation. Here, as the first relationship having a linear equation, for example, it may be a mapping representing the relationship between the specific internal resistance and the battery capacity.

[0048] As Figure 5 and 6 shown, according to the research of the inventors of the present application, if the provisional SOC is 80% or more, the coefficient of determination R 2 is greater than 0.8. If the provisional SOC is less than 80%, the coefficient of determination R 2 is less than 0.8. Specifically, when the provisional SOC is 75%, the coefficient of determination R 2 is 0.6 or less. When the provisional SOC is 70% and 65%, the coefficient of determination R 2 is 0.5 or less. That is, if the provisional SOC is 80% or more, the correlation between the specific internal resistance and the battery capacity becomes higher, and thus the estimated battery capacity can be accurately obtained.

[0049] The specified time may be 20 seconds or more, 25 seconds or more, or 30 seconds or more, and may be 30 seconds or less, 25 seconds or less, or 20 seconds or less.

[0050] The specified charging rate may be 3C or more, 4C or more, or 5C or more, and may be 5C or less, 4C or less, or 3C or less.

[0051] "Method for Estimating SOC of Battery"

[0052] The method of the present disclosure for estimating the SOC of a battery includes further causing a computer to execute the following steps after step (b): (i) calculating an estimated change amount of the SOC associated with the deterioration of the battery from the estimated battery capacity based on a predetermined second relationship between the estimated battery capacity and the change amount of the SOC associated with the deterioration of the battery (the change amount of the SOC as the battery deteriorates), or (ii) calculating the estimated changed SOC associated with the deterioration of the battery from the estimated battery capacity based on a predetermined third relationship between the estimated battery capacity and the changed SOC associated with the deterioration of the battery (the changed SOC as the battery deteriorates).

[0053] As described above, a technique for estimating the SOC based on the OCV of a battery is known. In this regard, the inventors of the present application have found that: due to the deterioration of the battery associated with the deterioration of the positive and negative electrodes caused by charge and discharge, that is, for example, a decrease in the battery capacity, a difference occurs between the SOC estimated based on the relationship with the OCV of the battery and the actual SOC, that is, due to the deterioration of the battery, the SOC sometimes changes.

[0054] In this regard, the inventors of the present application have found that: based on a predetermined relationship between the estimated battery capacity and the change amount of the SOC or the changed SOC as the battery deteriorates, the estimated change amount of the SOC or the estimated changed SOC as the battery deteriorates can be calculated from the estimated battery capacity.

[0055] The method of the present disclosure for estimating the SOC of a battery is particularly effective in a battery in which the SOC mainly changes due to the deterioration of the positive and negative electrodes, such as a solid battery. Further, with respect to the present disclosure, a "solid battery" means a battery that uses at least a solid electrolyte as an electrolyte. Therefore, a solid battery may also use a combination of a solid electrolyte and a liquid electrolyte as an electrolyte. In addition, the solid battery of the present disclosure may be an all-solid battery, that is, a battery that uses only a solid electrolyte as an electrolyte.

[0056] The method of the present disclosure for estimating the battery capacity and the SOC can be executed by a system for estimating the battery capacity and the SOC. The system includes an ECU. In a typical configuration of the ECU, it at least includes a ROM (Read Only Memory) that stores a program for performing this control, a CPU (Central Processing Unit) that can execute the program, a RAM (Random Access Memory) that temporarily stores data, and an input / output port.

[0057] Various signals from a voltage sensor, a current sensor, a temperature sensor, etc. are input into the ECU via the input port. In addition, a drive signal to a load (a power consumption machine and / or a power supply machine) is output from the ECU via the output port.

[0058] The ECU includes: a provisional SOC determination means, a specific internal resistance acquisition means and an estimated battery capacity acquisition means, and a SOC change amount acquisition means or a post-change SOC acquisition means.

[0059] The provisional SOC determination means is configured to determine whether the provisional SOC is 80% or more. As a method for determining whether the provisional SOC is 80% or more, there is no particular limitation. For example, as a method for determining whether a measured value is above a threshold value, a conventionally known method commonly used in general battery systems can be adopted.

[0060] The specific internal resistance acquisition means is configured to acquire (estimate) a specific internal resistance. As a method for acquiring the specific internal resistance, there is no particular limitation, and a conventionally known method commonly used in general battery systems can be adopted. For example, a method of estimating the specific internal resistance based on various data detected by using a voltage sensor and a current sensor, by dividing the voltage change amount during charge and discharge by the current change amount at this time can be exemplified (for example, a method of linearly approximating the parameter of the current change amount and the parameter based on the voltage change amount and the impedance change amount, and calculating the slope of the approximate straight line as the impedance of the battery).

[0061] By using the specific internal resistance acquisition means, it is possible to obtain the specific internal resistance when charging at a specified charging rate for a specified time at a specified provisional SOC of 80% or more and a temperature.

[0062] The estimated battery capacity acquisition means is configured to acquire an estimated battery capacity. The estimated battery capacity can be obtained from the specific internal resistance based on a previously determined first relationship between the specific internal resistance and the battery capacity. Among them, the first relationship can be, for example, a map showing the relationship between the specific internal resistance and the battery capacity.

[0063] Figure 2 FIG. is an example of a map showing the relationship between the specific internal resistance and the battery capacity. This map can be prepared in advance by plotting the specific internal resistance and the battery capacity obtained by using the specific internal resistance acquisition means. This map can be prepared at each temperature during charging.

[0064] The battery capacity can be obtained by any battery capacity acquisition means. As a method for obtaining the battery capacity, there is no particular limitation, and conventionally known methods commonly used in general battery systems can be adopted. For example, a method for obtaining the battery capacity of a secondary battery according to the battery model based on various data detected by using a voltage sensor, a current sensor, a temperature sensor, etc. can be exemplified (for example, storing the open circuit voltage characteristics of the positive and negative electrodes of the secondary battery obtained in advance, referring to the stored data and the data detected by using the voltage sensor, the current sensor, and the temperature sensor, extracting the active material amounts, capacity densities, and resistance values of the positive and negative electrodes, and using the extracted parameters to obtain the battery capacity of the secondary battery).

[0065] The estimated battery capacity acquisition means can derive the estimated battery capacity by causing the ECU to execute a process of substituting the specific internal resistance obtained by using the specific internal resistance acquisition means into the linear equation constituting the created map.

[0066] The SOC change amount acquisition means is configured to acquire the change amount of the SOC accompanying the deterioration of the battery. The change amount of the SOC accompanying the deterioration of the battery can be obtained from the estimated battery capacity based on a predetermined second relationship between the estimated battery capacity and the change amount of the SOC accompanying the deterioration of the battery. Herein, the second relationship can be, for example, a map showing the relationship between the estimated battery capacity and the change amount of the SOC accompanying the deterioration of the battery.

[0067] Figure 3 FIG. is an example of a map showing the relationship between the estimated battery capacity and the change amount of the SOC accompanying the deterioration of the battery. This map can be created in advance by plotting the estimated battery capacity and the change amount of the SOC accompanying the deterioration of the battery. The change amount of the SOC accompanying the deterioration of the battery in this map can be obtained, for example, by performing a general durability test on the battery and creating an SOC-OCV curve before and after the durability test as shown in Figure 4 and obtaining it as the difference in SOC before and after the durability test for the same OCV. Furthermore, during the above-mentioned durability test, the battery capacity is also measured, and by plotting the relationship between the measured battery capacity and the calculated change amount of the SOC, a map can be created. This map can be created at each SOC. Additionally, Figure 4 in, the value of OCV is shown as a relative value with the value before the durability test (initial stage) when the SOC is 0 set to 1.0.

[0068] The SOC change amount acquisition means can derive the change amount of the SOC accompanying the deterioration of the battery by causing the ECU to execute a process of substituting the estimated battery capacity obtained by using the estimated battery capacity acquisition means into the linear equation of the created map.

[0069] The post-change SOC acquisition means is configured to acquire the post-change SOC associated with the deterioration of the battery. The post-change SOC associated with the deterioration of the battery can be obtained from the estimated battery capacity based on a predetermined third relationship between the estimated battery capacity and the post-change SOC associated with the deterioration of the battery. The third relationship can be, for example, a mapping representing the relationship between the estimated battery capacity and the post-change SOC associated with the deterioration of the battery.

[0070] In this method, a mapping representing the relationship with the estimated battery capacity can be created in advance. The post-change SOC associated with the deterioration of the battery in this mapping can be, for example, the SOC after a general durability test of the battery. Further, during the above-mentioned durability test, the battery capacity is also measured, and by plotting the relationship between the measured battery capacity and the post-change SOC associated with the deterioration of the battery, a mapping can be created. This mapping can be created at each SOC.

[0071] The post-change SOC acquisition means can derive the post-change SOC by causing the ECU to execute a process of substituting the estimated battery capacity obtained by using the estimated battery capacity acquisition means into the linear equation constituting the created mapping.

[0072] The following is a description of the method of the present disclosure for the estimated battery capacity and the SOC of the battery, using Figure 1 the flowchart illustrated in

[0073] In S101, the ECU starts charging the battery.

[0074] In S102, the ECU uses the tentative SOC determination means to determine whether the tentative SOC is 80% or more. If the tentative SOC is 80% or more, the ECU executes the process of S103. If the tentative SOC is less than 80%, the ECU executes the process of S101 again.

[0075] In S103, the ECU uses the specific internal resistance acquisition means to acquire the specific internal resistance when charging the battery under specified conditions. The specific internal resistance can be calculated based on the voltage and current of the battery during charging. The ECU can acquire the voltage of the battery based on the output of the voltage sensor. In addition, the ECU can acquire the current of the battery based on the output of the current sensor.

[0076] In S104, the ECU uses the estimated battery capacity acquisition means to obtain the estimated battery capacity from the specific internal resistance obtained in S103, for example, based on a mapping representing the relationship between the specific internal resistance and the battery capacity. The mapping representing the relationship between the specific internal resistance and the battery capacity can be created in advance and stored in the ROM. In this case, the ECU can obtain the estimated battery capacity by executing a process of substituting the specific internal resistance obtained in S103 into the linear equation constituting the above mapping read from the ROM.

[0077] Furthermore, the internal resistance of the battery sometimes varies according to the temperature of the battery. Therefore, if information representing the relationship between the internal resistance of the battery and the temperature is obtained in advance, the internal resistance corresponding to the temperature can be obtained by acquiring the temperature of the battery. The temperature of the battery can be acquired using a temperature sensor. The information representing the relationship between the internal resistance of the battery and the temperature can be stored in the ROM. The information representing the relationship between the internal resistance of the battery and the temperature can be expressed as a map or a function.

[0078] In S105, the ECU can adopt the SOC change amount acquisition means. For example, based on the map representing the relationship between the battery capacity and the change amount of the SOC associated with the deterioration of the battery, the change amount of the SOC associated with the deterioration of the battery can be obtained from the estimated battery capacity obtained in S104. Among them, the map representing the relationship between the battery capacity and the change amount of the SOC associated with the deterioration of the battery can be created in advance and stored in the ROM. In this case, the ECU can obtain the estimated change amount of the SOC associated with the deterioration of the battery by executing the process of substituting the estimated battery capacity obtained in S104 into the linear equation constituting the above map read from the ROM.

[0079] In S106, the ECU can adopt the post-change SOC acquisition means. Based on the map representing the relationship between the battery capacity and the post-change SOC associated with the deterioration of the battery, the post-change estimated SOC associated with the deterioration of the battery can be obtained from the estimated battery capacity obtained in S104. Among them, the map representing the relationship between the battery capacity and the post-change SOC associated with the deterioration of the battery can be created in advance and stored in the ROM. In this case, the ECU can obtain the post-change estimated SOC associated with the deterioration of the battery by executing the process of substituting the estimated battery capacity obtained in S104 into the linear equation constituting the above map read from the ROM.

[0080] By using S105 or S106, the SOC of the battery can be estimated.

[0081] Based on the SOC estimated by using the method of the present disclosure, for example, based on the map created at each temperature representing the relationship between the SOC estimated by using the method of the present disclosure and the output value of the battery, the output of the battery can be controlled with high precision. For example, in the case of not considering the change in the SOC associated with the deterioration of the battery, the output value based on the above map may be different from the actual value. However, based on the SOC estimated by using the method of the present disclosure, the actual value can be output.

Claims

1. Method for estimating battery capacity, comprising causing a computer to execute the following steps: (a) Charging at a specified charging rate for a specified time at a specified provisional SOC of 80% or more and a specified temperature to obtain a specific internal resistance; and (b) Based on a predetermined first relationship between the specific internal resistance and the battery capacity, obtaining an estimated battery capacity from the specific internal resistance.

2. Method for estimating the SOC of a battery, comprising, after step (b) in the method of claim 1, further causing a computer to execute the following steps: (i) Based on a predetermined second relationship between the estimated battery capacity and the change amount of the SOC associated with battery degradation, obtaining an estimated change amount of the SOC associated with battery degradation from the estimated battery capacity, or (ii) Based on a predetermined third relationship between the estimated battery capacity and the changed SOC associated with battery degradation, obtaining the estimated changed SOC associated with battery degradation from the estimated battery capacity.

3. The method according to claim 1 or 2, wherein The first relationship has a linear equation, and the determination coefficient of the linear equation is 0.8 or more.

4. The method according to claim 1 or 2, wherein The specified time is 20 seconds or more, and the specified charging rate is 3C or more.

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