SOC estimating device

Abstract

A processor of this SOC estimating device executes processing including: generating plot data in which a correction index corresponding to a trip period to which an end-time SOC belongs and the integrated value of an absolute current amount up to the trip period to which the end-time SOC belongs are associated with one another; determining whether battery polarization has been eliminated at the start of the trip period; if it has been determined that battery polarization has not been eliminated, deriving an estimated value of the correction index corresponding to the trip period immediately preceding the trip period to which the current time point belongs, on the basis of the past plot data; and deriving an initial value of the SOC in the trip period to which the current time point belongs, on the basis of the estimated value of the correction index.

Description

SOC estimation device

[0001] The present invention relates to an SOC (State Of Charge) estimation device for estimating the SOC of a battery.

[0002] For example, Patent Document 1 discloses a technique for estimating the SOC using an open circuit voltage method and a technique for estimating the SOC using a current integration method. In Patent Document 1, a reference time is set using a combined error obtained by combining an error value of the SOC obtained by the open circuit voltage method and an error value of the SOC obtained by the current integration method, and the SOC is estimated using the set reference time.

[0003] JP 2014-202551 A

[0004] In the current integration method, the amount of change in SOC relative to the initial value of SOC is calculated based on the current integration value, and the SOC is estimated by adding the initial value of SOC to the amount of change in SOC. The initial value of SOC is estimated, for example, by the open circuit voltage method. However, for example, if the polarization of the battery is not eliminated, it is difficult to estimate an appropriate initial value of SOC using the open circuit voltage method.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an SOC estimation device that is capable of estimating an appropriate initial value of SOC.

[0006] In order to solve the above problem, an SOC estimation device according to one embodiment of the present invention includes: a battery mounted on a vehicle; and a control device that estimates the SOC of the battery, wherein the control device has one or more processors and one or more memories connected to the processors, wherein a period from when the vehicle is ready on to when it is ready off is a trip period, and the processor: derives a difference between an end SOC that is the SOC estimated using a current integration method at the end of the trip period and a start SOC that is the SOC estimated using an open circuit voltage method at the start of the trip period following the trip period to which the end SOC belongs, as an SOC correction amount that indicates an estimation error of the SOC corresponding to the trip period to which the end SOC belongs; and derives an absolute current amount that is a value obtained by adding together an integrated value of the absolute values ​​of the charging current in the battery and an integrated value of the absolute values ​​of the discharging current in the battery during the trip period; The method executes a process including: dividing the SOC correction amount corresponding to the trip period to which the end SOC belongs by the absolute current amount in the trip period to which the end SOC belongs, to derive a correction index corresponding to the trip period to which the end SOC belongs; deriving an integrated absolute current amount value which is a value obtained by integrating the absolute current amount from a predetermined reference point over a plurality of the trip periods; generating plot data correlating the correction index corresponding to the trip period to which the end SOC belongs with the integrated absolute current amount up to the trip period to which the end SOC belongs; determining whether polarization of the battery has been eliminated at the start of the trip period; and if it is determined that polarization of the battery has not been eliminated, deriving an estimated value of the correction index corresponding to the trip period immediately before the trip period to which the current time belongs based on the past plot data; and deriving an initial value of SOC for the trip period to which the current time belongs based on the estimated value of the correction index.

[0007] According to the present invention, it is possible to estimate an appropriate initial value of SOC.

[0008] FIG. 1 is a schematic block diagram showing the configuration of a vehicle to which the SOC estimation device according to this embodiment is applied. FIG. 2 is a diagram illustrating an example of an SOC estimation method and estimation timing. FIG. 3 is a diagram illustrating another example of an SOC estimation method and estimation timing. FIG. 4 is a diagram illustrating derivation of an initial SOC value based on an estimated value of a correction index. FIG. 5 is a diagram illustrating the relationship between the correction index and permitted power. FIG. 6 is a diagram illustrating an example of multiple plot data when the trend of the correction index according to the trend of the absolute current integrated value is increasing. FIG. 7 is a diagram illustrating an example of multiple plot data when the trend of the correction index according to the trend of the absolute current integrated value is decreasing. FIG. 8 is a diagram illustrating an example of multiple plot data when the trend of the correction index according to the trend of the absolute current integrated value is approximately constant. FIG. 9 is a flowchart illustrating the operation flow of the SOC estimation unit. FIG. 10 is a flowchart illustrating the flow of processing periodically repeated by the SOC estimation unit after the processing of FIG. 9 until the vehicle is ready-off. FIG. 11 is a flowchart illustrating the flow of processing to derive an initial SOC value. Fig. 12 is a flowchart illustrating the flow of the full charge capacity update determination process, and Fig. 13 is a flowchart illustrating the flow of the correction value derivation process.

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Specific dimensions, materials, numerical values, etc. shown in the embodiments are merely examples for facilitating understanding of the invention and do not limit the present invention unless otherwise specified. In this specification and drawings, elements having substantially the same functions and configurations are designated by the same reference numerals to avoid redundant explanation, and elements not directly related to the present invention are not shown.

[0010] 1 is a schematic block diagram showing the configuration of a vehicle 1 to which an SOC estimation device 10 according to this embodiment is applied. The vehicle 1 is, for example, an electric vehicle equipped with a motor generator as a drive source. Note that the vehicle 1 may also be a hybrid electric vehicle equipped with an engine and a motor generator as drive sources.

[0011] The vehicle 1 includes a battery 20 , a voltage sensor 22 , a current sensor 24 , a storage device 26 and a control device 30 .

[0012] The battery 20 is a secondary battery that can be charged and discharged, such as a lithium-ion battery. The battery 20 is not limited to a lithium-ion battery, and may be composed of any known battery composition that can be charged and discharged. The battery 20 is mounted on the vehicle 1. The battery 20 is, for example, a high-voltage battery that supplies power to the motor generator. The battery 20 is charged by power regenerated when the motor generator functions as a generator. The vehicle 1 may also be configured to be able to charge the battery 20 by power supplied from outside the vehicle 1.

[0013] The voltage sensor 22 is configured to be able to detect the voltage of the battery 20. For example, when the battery 20 is electrically disconnected from the electrical system of the vehicle 1, the voltage sensor 22 can detect the open circuit voltage of the battery 20. Hereinafter, the open circuit voltage may be referred to as OCV.

[0014] The current sensor 24 is configured to be able to detect the charging current input to the battery 20 and the discharging current output from the battery 20 .

[0015] The storage device 26 is configured with a nonvolatile storage element. The nonvolatile storage element may include an electrically readable and writable nonvolatile storage element such as a flash memory. The storage device 26 can store, for example, various information and data related to the estimation of the SOC of the battery 20.

[0016] The control device 30 has one or more processors 40 and one or more memories 42 connected to the processors 40. The memories 42 include a ROM in which programs and the like are stored, and a RAM as a work area. The processors 40 of the control device 30 cooperate with the programs stored in the memory 42 to control the entire vehicle 1.

[0017] More specifically, the processor 40 works in cooperation with a program to function as an SOC estimation unit 50 that estimates the SOC (State Of Charge) of the battery 20. The SOC indicates the charge rate, which is the current charge capacity of the battery 20 relative to the fully charged capacity, expressed as a percentage.

[0018] The SOC estimation unit 50 can estimate the SOC using the open circuit voltage method and can also estimate the SOC using the current integration method. Hereinafter, the open circuit voltage method may be referred to as the OCV method.

[0019] The open circuit voltage method is an estimation method for estimating the SOC based on the open circuit voltage of the battery 20. For example, an open circuit voltage SOC map, which is a map in which the open circuit voltage and the SOC are associated one-to-one, is stored in advance in the memory 42. In the open circuit voltage method, the SOC estimation unit 50 applies the open circuit voltage of the battery 20 detected by the voltage sensor 22 to the open circuit voltage SOC map to derive the SOC.

[0020] The current integration method is an estimation method that estimates the SOC based on an integrated current value obtained by integrating the charging current and discharging current of the battery 20 over time. In the current integration method, the SOC estimation unit 50 acquires, using the current sensor 24, the charging current and discharging current of the battery 20, which change over time as the vehicle 1 travels. The SOC estimation unit 50 integrates the acquired charging current and discharging current each time to derive an integrated current value. The SOC estimation unit 50 divides the integrated current value by the full charge capacity to derive the amount of change from the initial value of the SOC. The SOC estimation unit 50 adds the initial value to the amount of change from the derived initial value to derive the current SOC.

[0021] As described above, in the current integration method, the accuracy of estimating the SOC depends on three parameters: the current integration value, the full charge capacity, and the initial SOC value. In contrast, in the open circuit voltage method, the open circuit voltage SOC map is determined in advance, so the accuracy of estimating the SOC depends only on the open circuit voltage detected by the voltage sensor 22. Therefore, the open circuit voltage method can estimate the SOC more accurately than the current integration method.

[0022] The open circuit voltage method is subject to limitations on the timing at which the SOC can be estimated, because the open circuit voltage is detected with the battery 20 disconnected from the electrical system of the vehicle 1. In contrast, the current integration method makes it possible to estimate the SOC even while the vehicle 1 is running, and makes it possible to estimate the SOC without interrupting the running of the vehicle 1.

[0023] Since the open circuit voltage method and the current integration method have the above-mentioned characteristics, estimation by the open circuit voltage method and estimation by the current integration method can be used depending on the situation.

[0024] 2 is a diagram illustrating an example of an SOC estimation method and estimation timing. Hereinafter, the period from when the vehicle 1 is ready-on to when it is ready-off may be referred to as the trip period. That is, the start point of the trip period is when the vehicle 1 is ready-on, and the end point of the trip period is when the vehicle 1 is ready-off.

[0025] As shown in FIG. 2, during a trip period, the battery 20 is charged and discharged as the vehicle 1 travels, and therefore the current of the battery 20 changes.

[0026] When the battery 20 is charged, polarization occurs within the battery 20. Polarization is a phenomenon in which an imbalance of electrons occurs between the positive and negative electrodes of the battery 20, resulting in the appearance of a pseudo-potential difference. When such polarization occurs, the voltage of the battery 20 detected by the voltage sensor 22 is detected as a value higher than the actual voltage by the amount of the pseudo-potential difference. This reduces the accuracy of the SOC calculated by the open-circuit voltage method, which uses the detection result of the voltage sensor 22.

[0027] Such polarization can be eliminated by waiting a predetermined time in a state where charging is not performed after charging the battery 20. Based on this, when the vehicle 1 is ready-off and the next ready-on occurs after a predetermined time has elapsed that allows polarization to be eliminated, the polarization of the battery 20 will be eliminated.

[0028] Hereinafter, the time required for the polarization to be eliminated may be referred to as the polarization elimination time. The polarization elimination time may be, for example, 30 minutes, but may be any time required for the polarization to be eliminated, taking into consideration the type and performance of the battery 20.

[0029] When the polarization is eliminated, the pseudo potential difference substantially disappears, and the detection result of the voltage sensor 22 becomes substantially the same as the actual voltage. In other words, by eliminating the polarization, it is possible to suppress a decrease in the accuracy of the SOC derived by the open circuit voltage method using the detection result of the voltage sensor 22.

[0030] In the example of Figure 2, time T1 corresponds to the time when the ready-on state is reached, and is the time when at least the polarization elimination time has elapsed since the ready-off state of the previous trip period. Time T2 corresponds to the ready-off state of the trip period to which time T1 belongs. Time T3 corresponds to the time when the ready-on state is reached next after the trip period to which time T1 belongs, and is the time when at least the polarization elimination time has elapsed since time T2.

[0031] In the example of Fig. 2, time T3 is the current time. Hereinafter, the trip period to which the current time belongs may be referred to as the current trip period. The trip period immediately preceding the trip period to which the current time belongs may be referred to as the previous trip period. In the example of Fig. 2, the trip period to which time T3 belongs is the current trip period, and the trip period to which time T1 and time T2 belong is the previous trip period.

[0032] As described above, if the polarization is eliminated, the deterioration of the accuracy of the SOC calculated by the OCV method can be suppressed, so the SOC estimation unit 50 determines whether the polarization of the battery 20 is eliminated at the time of ready-on. If the polarization of the battery 20 is eliminated, the SOC estimation unit 50 derives the SOC by the OCV method.

[0033] 2, since a time equal to or longer than the polarization elimination time has elapsed before time T1, the SOC estimating unit 50 can derive the SOC using the OCV method at time T1 when the battery is ready to be turned on. Also, since a time equal to or longer than the polarization elimination time has elapsed before time T3, the SOC estimating unit 50 can derive the SOC using the OCV method at time T3 when the battery is ready to be turned on.

[0034] Furthermore, since the current integration value is derived during the trip period, at time T2, the SOC estimation unit 50 can derive the SOC using the current integration method.

[0035] However, repeated charging and discharging of the battery 20 may cause the battery 20 to deteriorate. As the deterioration of the battery 20 progresses, the full charge capacity of the battery 20 may decrease. The full charge capacity can be calculated when the battery 20 is fully charged. When the battery 20 deteriorates, it is desirable to calculate and update the full charge capacity.

[0036] However, if a decrease in full charge capacity occurs during the trip period, it is unlikely that the full charge capacity will be updated during the trip period. Therefore, in the current integration method, the SOC is estimated using the full charge capacity before the decrease. As a result, the SOC calculated by the current integration method at the end of the trip period may differ from the actual SOC due to the decrease in full charge capacity. For example, in the example of FIG. 2, if a decrease in full charge capacity occurred during the previous trip period between time T1 and time T2, the SOC calculated by the current integration method at time T2 may differ from the actual value.

[0037] In contrast, the SOC estimated by the OCV at time T3, which is the start of the current trip period, is estimated without using the full charge capacity, and therefore, even if a decrease in the full charge capacity occurred during the previous trip period, the SOC will be an actual value that reflects the decrease in the full charge capacity.

[0038] 2, the current of the battery 20 does not change between time T2 and time T3. Ideally, the actual SOC at time T2 and the actual SOC at time T3 are the same value. In this case, the SOC calculated by the OCV method at time T3 can be considered to be the SOC at time T2.

[0039] In light of this, in this embodiment, the concept of an SOC correction amount corresponding to the deviation of the SOC between the end of a trip period and the start of the next trip period is introduced. Here, for convenience of explanation, the SOC estimated using the current integration method at the end of a trip period may be referred to as the end SOC. The SOC estimated using the open circuit voltage method at the start of the trip period following the trip period to which the end SOC belongs may be referred to as the start SOC.

[0040] The SOC correction amount is calculated from the difference between the end SOC and the start SOC (SOC correction amount = end SOC - start SOC). In the example of FIG. 2, the SOC correction amount is the difference between the SOC calculated by the current integration method at time T2 and the SOC calculated by the OCV method at time T3. The SOC correction amount indicates the estimation error of the SOC corresponding to the trip period to which the end SOC belongs.

[0041] As described above, assume that a decrease in full charge capacity occurs during the trip period between time points T1 and T2. Also, as described above, the SOC calculated by the OCV system at time point T3 can be considered the SOC at time point T2. In this case, the SOC correction amount corresponds to the error between the SOC calculated by the current integration system, which does not reflect the decrease in full charge capacity, and the actual SOC calculated by the OCV system, which reflects the decrease in full charge capacity. In other words, the SOC correction amount corresponds to the error in estimating the SOC from the actual SOC due to the decrease in full charge capacity during the trip period.

[0042] The SOC correction amount at the time when the SOC correction amount is derived corresponds to the trip period immediately preceding the trip period to which the SOC correction amount is derived.

[0043] In this embodiment, the concept of absolute current amount is further introduced. The absolute current amount is the sum of the integrated value of the absolute values ​​of the charging current in the battery 20 and the integrated value of the absolute values ​​of the discharging current in the battery 20. The absolute current amount is calculated during a trip period, and is calculated for each trip period. The absolute current amount indicates how much the battery 20 has been charged and discharged in one trip period.

[0044] In the current integration method, the current integration value is calculated by taking the discharging current as a positive value and the charging current as a negative value, whereas the absolute current amount uses absolute values ​​for both the charging current and the discharging current, so both the charging current and the discharging current are integrated as positive values.

[0045] In this embodiment, the concept of a correction index based on the SOC correction amount and the absolute current amount is further introduced. The correction index is derived by dividing the SOC correction amount corresponding to the trip period to which the end SOC belongs by the absolute current amount in the trip period to which the end SOC belongs (correction index = SOC correction amount / absolute current amount). The correction index corresponds to the trip period to which the end SOC belongs.

[0046] In the example of Figure 2, the correction index is derived by dividing the SOC correction amount corresponding to the previous trip period derived at the current time point T3 by the absolute current amount at time point T2, which is the end point of the previous trip period.

[0047] The correction index is obtained by removing the influence of charging and discharging during the trip period immediately preceding the time point at which the correction index is derived from the SOC estimation error during that trip period.

[0048] In this embodiment, the concept of an absolute current integrated value based on the absolute current amount is further introduced. The absolute current integrated value is a value obtained by integrating the absolute current amounts over multiple trip periods from a predetermined reference point in time. For example, if three trip periods have elapsed since the predetermined reference point in time, the absolute current integrated value is the sum of the absolute current amounts for the first trip period, the second trip period, and the third trip period.

[0049] As described above, the SOC correction amount indicates an error in the SOC estimation due to a decrease in the full charge capacity, and therefore is a value related to the decrease in the full charge capacity. In light of this, the predetermined reference point in the above-mentioned absolute current amount integrated value is set to the point in time when the full charge capacity of the battery 20 was last updated.

[0050] In this embodiment, the concept of plot data based on a correction index and an integrated absolute current amount is further introduced. The plot data is data that associates a correction index corresponding to a trip period to which the end SOC belongs with an integrated absolute current amount up to the trip period to which the end SOC belongs. Like the associated correction index, the plot data corresponds to the trip period to which the end SOC belongs.

[0051] The plot data at the time when the plot data is generated corresponds to the trip period immediately preceding the trip period to which the plot data is generated.

[0052] In the example of Figure 2, the plot data corresponding to the previous trip period is generated by associating the correction index corresponding to the previous trip period derived at the current time point T3 with the integrated value of the absolute current amount up to the previous trip period.

[0053] In the present embodiment, when it is determined that the polarization of the battery 20 has been eliminated, the SOC estimating unit 50 derives an SOC correction amount, a correction index, and generates plot data. The derived SOC correction amount, correction index, and plot data are stored and accumulated in the storage device 26.

[0054] Since the SOC derived by the OCV method is used to derive the SOC correction amount, the SOC correction amount is derived only when the polarization of the battery 20 is eliminated. Furthermore, since the SOC correction amount is used to derive the correction index and the correction index is used for the plot data, the correction index and the plot data are derived only when the polarization of the battery 20 is eliminated, similar to the SOC correction amount. In other words, if the polarization of the battery 20 is not eliminated, the plot data is not generated.

[0055] More specifically, the SOC estimation unit 50 may derive the SOC correction amount, correction index, and plot data when the polarization of the battery 20 is eliminated and both specific first and second conditions are satisfied.

[0056] The first specific condition is that the SOC is estimated using the open circuit voltage method at the start of the trip period immediately preceding the trip period to which the current time belongs. In the example of Figure 2, the SOC is estimated using the OCV method at time T1, which corresponds to the start of the trip period immediately preceding the current time, and therefore the first specific condition is met.

[0057] If the SOC is estimated using the OCV method at the start of a trip period, the estimated SOC can be used as the initial value to accurately obtain the initial value of the SOC for that trip period. Therefore, it is assumed that the SOC estimated using the current integration method during that trip period is estimated with relatively high accuracy. In this case, the SOC estimated with relatively high accuracy using the current integration method is used as the SOC at the end of the trip period, thereby improving the accuracy of the SOC correction amount.

[0058] The second specific condition is that the period from the end of the trip period immediately preceding the trip period to which the current time belongs to until the trip period to which the current time belongs to is within a predetermined period. Hereinafter, for convenience of explanation, the period from the end of the trip period immediately preceding the trip period to which the current time belongs to until the trip period to which the current time belongs to may be referred to as the immediately preceding stop period.

[0059] The predetermined period under the specific second condition is set to a period longer than the polarization elimination time. The predetermined period is set to, for example, 7 days, but can be set to an appropriate period taking into account the self-discharge of the battery 20.

[0060] If the immediately preceding stop period is excessively long, self-discharge of the battery 20 will progress. If self-discharge progresses, for example, the actual SOC at time T3 may substantially change from the actual SOC at time T2. As a result, the OCV SOC at time T3 may deviate from the actual SOC at time T2. As a result, the accuracy of the SOC correction amount may decrease.

[0061] In light of this, by deriving the SOC correction amount only when the immediately preceding stop period is not excessively long under the specific second condition, it is possible to prevent a decrease in the accuracy of the SOC correction amount, and as a result, it is also possible to prevent a decrease in the accuracy of the correction index and the plot data.

[0062] Note that, here, an example has been described in which the SOC correction amount, the correction index, and the plot data are derived when three conditions are met: the polarization of battery 20 is eliminated, the specific first condition is satisfied, and the specific second condition is satisfied. However, if a decrease in accuracy of the SOC correction amount or the like is tolerable, SOC estimator 50 may omit the specific first condition and second condition, and derive the SOC correction amount, the correction index, and the plot data when at least the polarization of battery 20 is eliminated.

[0063] FIG. 3 is a diagram illustrating another example of the SOC estimation method and estimation timing. In FIG. 3, the period from time T1 to time T2 is the same as in FIG. 2. FIG. 3 shows a case where the ready-on signal is generated at time T4 after time T2 but before the polarization elimination time has elapsed, and the next trip period begins. In FIG. 3, time T4 is assumed to be the current time.

[0064] If the battery is ready-on before the polarization elimination time has elapsed, it is possible that the polarization of the battery 20 has not been eliminated. In such a case, it is not appropriate to estimate the SOC using the OCV method at the current time point T4, as shown in FIG.

[0065] Therefore, in this embodiment, when the SOC estimating unit 50 determines that the polarization of the battery 20 has not been eliminated, it derives an estimated value of the correction index corresponding to the trip period immediately before the trip period to which the current time belongs, based on past plot data. The SOC estimating unit 50 derives an initial value of the SOC for the trip period to which the current time belongs, based on the derived estimated value of the correction index. Hereinafter, the initial value of the SOC may be referred to as an initial SOC value.

[0066] More specifically, since the polarization of the battery 20 has not been eliminated at the start of the current trip period, the SOC cannot be properly derived using the OCV method, and the correction index corresponding to the previous trip period cannot be derived from the definition equation. Therefore, the SOC estimation unit 50 estimates the correction index corresponding to the previous trip period based on past plot data.

[0067] By estimating the correction index corresponding to the previous trip period, the extent of the SOC estimation error during the previous trip period can be determined. Then, by taking into account the absolute current amount during the previous trip period, the SOC at the end of the previous trip period, which reflects the SOC estimation error during the previous trip period, can be determined.

[0068] Ideally, the SOC at the end of the previous trip period can be considered to be substantially the same as the SOC at the start of the current trip period. Therefore, by deriving the SOC at the end of the previous trip period based on the estimated value of the correction index corresponding to the previous trip period, the SOC at the start of the current trip period can be substantially derived. The SOC at the start of the current trip period derived in this manner can be used as the initial value of the SOC for the current trip period.

[0069] 4 is a diagram illustrating the derivation of the initial SOC value based on the estimated value of the correction index. In FIG. 4, the horizontal axis represents the absolute current amount integrated value from a predetermined reference point in time, specifically, the point in time when the full charge capacity was updated. The vertical axis represents the correction index.

[0070] The black circles in Figure 4 indicate past plot data generated after a predetermined reference point in time. Plot data Pm is the past plot data that is closest to the current point in time among the past plot data. Plot data Pn indicated by white circles indicates estimated values ​​of plot data corresponding to the previous trip period. Note that from the perspective of the correction index and the estimation timing of the plot data, the white circles correspond to the current point in time.

[0071] In the example of Fig. 4, the absolute current integrated value xn is the absolute current integrated value for the trip period immediately preceding the trip period to which the current time belongs, i.e., the previous trip period. The absolute current integrated value xm is the absolute current integrated value corresponding to the plot data closest to the current time among the past plot data. The trip period corresponding to the plot data closest to the current time among the past plot data is, for example, the trip period before the previous one, which is one period immediately preceding the previous trip period.

[0072] 4, the absolute current difference integrated value α is the difference between the absolute current difference integrated value xn and the absolute current difference integrated value xm (α=xn-xm). In other words, the absolute current difference integrated value xn is the sum of the absolute current difference integrated value α and the absolute current difference integrated value xm (xn=xm+α).

[0073] For example, if the absolute current integrated value xm is the absolute current integrated value for the trip period two trips ago, the differential absolute current integrated value α corresponds to the absolute current amount for the previous trip period. Therefore, the differential absolute current integrated value α is known at the time of estimating the correction index. The absolute current integrated value xm is also known at the time of estimating the correction index.

[0074] In the example of FIG. 4, the correction index yn is an estimated value of the correction index corresponding to the previous trip period.

[0075] The SOC estimation unit 50 uses a plurality of past plot data to derive an approximation formula for the plurality of past plot data. The approximation formula is, for example, a linear function (y = ax + b). Line L1 in FIG. 4 is an example of the approximation formula.

[0076] The SOC estimating unit 50 derives the correction index yn, which is an estimated value, by substituting the value "xm+α" obtained by adding the differential absolute current integrated value α to the absolute current integrated value xm into the approximation formula.

[0077] The SOC estimator 50 multiplies the derived estimated value of the correction index, i.e., the correction index yn, by the differential absolute current integrated value α to derive a correction value (correction value = yn × α). The correction index includes information on the SOC correction amount, and therefore includes information on the SOC estimation error due to a decrease in full charge capacity. Therefore, the correction value is a value that includes the influence of the decrease in full charge capacity during the previous trip period.

[0078] For ease of explanation, the trip period corresponding to the plot data closest to the present time among the past plot data may be referred to as the trip period of the previous plot data. Also, the SOC calculated by the open circuit voltage method during the trip period of the previous plot data may be referred to as the SOC by the previous OCV.

[0079] The SOC estimation unit 50 adds the derived correction value to the end SOC derived at the end of the previous trip period to derive the initial SOC value (initial SOC value = previous end SOC + correction value). As described above, the correction value includes the influence of the decrease in full charge capacity during the previous trip period, and therefore the initial SOC value reflects the influence of the decrease in full charge capacity.

[0080] In this way, when it is determined that polarization has not been eliminated, the initial value of the SOC can be derived based on the estimated value of the correction index, so that the initial value of the SOC can be derived with high accuracy even if polarization has not been eliminated.

[0081] 4 illustrates an example in which the trip period of the previous plot data is the trip period before the previous one. However, the trip period of the previous plot data may be a trip period even earlier than the trip period before the previous one. In other words, there may be one or more trip periods in which polarization was not resolved and plot data could not be generated between the trip period of the previous plot data and the current trip period.

[0082] If there are many trip periods during which plot data could not be generated between the trip period of the previous plot data and the current trip period, the accuracy of the approximation formula may decrease.

[0083] Therefore, SOC estimation unit 50 may determine whether the number of trip periods from the trip period of the previous plot data to the trip period immediately preceding the trip period to which the current time belongs is less than a predetermined number. Hereinafter, for ease of explanation, the period from the trip period of the previous plot data to the trip period immediately preceding the trip period to which the current time belongs may be referred to as the period from the trip period of the previous plot data to the previous trip period.

[0084] If the number of trip periods between the trip period of the previous plot data and the previous trip period is less than a predetermined number, the SOC estimator 50 may derive an estimated value of the correction index and derive an initial value of the SOC based on the estimated value of the correction index. The predetermined number here is set to, for example, three times, but can be set to any number taking into account the tolerance for accuracy of the approximation formula.

[0085] In this way, by using the number of trip periods between the trip period of the previous plot data as a judgment condition, it is possible to suppress a decrease in the accuracy of the approximation formula, and as a result, it is possible to suppress a decrease in the accuracy of the estimated value and the correction value of the correction index.

[0086] The determination condition regarding the number of trip periods between the trip period of the previous plot data and the previous trip period may be omitted.

[0087] The upper limit of the absolute value of power permitted to be input to the battery 20 may be referred to as permitted input power. The upper limit of the absolute value of power permitted to be output from the battery 20 may be referred to as permitted output power. The permitted input power and permitted output power may be collectively referred to as permitted power. In other words, permitted power refers to at least either the permitted input power or the permitted output power.

[0088] Such an allowed power is set for the battery 20. Here, the estimated SOC value may be higher than the actual SOC by an amount corresponding to an error. In this case, the allowed power is set to a relatively low value that includes a margin corresponding to the error of the SOC from the actual SOC.

[0089] In this embodiment, the SOC estimating unit 50 changes the value of the permitted power of the battery 20 based on the correction index.

[0090] Fig. 5 is a diagram illustrating the relationship between the correction index and the allowed power. For example, an allowed power map in which the correction index and the allowed power are correlated one-to-one, as illustrated in Fig. 5, is stored in advance in the memory 42. Note that the values ​​illustrated in Fig. 5 are merely examples, and each value in the allowed power map may be set to an arbitrary value taking into consideration the type and specifications of the battery 20, etc.

[0091] The permission level indicates the level of permitted power. Permission level "0" corresponds to the initial setting value of permitted power. As shown in Fig. 5, the permission level and permitted power are associated with each other so that the permitted power increases as the permission level increases.

[0092] As described above, the smaller the correction index, the smaller the SOC estimation error. Based on this, the allowed power map associates the correction index with the allowed power so that the smaller the correction index, the larger the allowed power.

[0093] The SOC estimator 50 derives the allowed power by applying the derived correction index to the allowed power map. When the allowed power map is used to derive the allowed power in this manner, the allowed power can be increased above the initial setting value of the allowed power as the correction index decreases. In other words, the allowed power can be increased below the initial setting value of the allowed power.

[0094] That is, in this embodiment, the degree of the estimation error of the SOC can be grasped by the correction index, and therefore the margin in the permitted power can be set to an appropriate value in accordance with the degree of the estimation error of the SOC.

[0095] Therefore, when an estimated SOC value is derived that reduces the SOC estimation error, excessive restriction of the permitted power can be suppressed. As a result, the permitted power is increased, thereby improving the driving performance of the vehicle 1.

[0096] In the present embodiment, the SOC estimating unit 50 may determine whether or not the full charge capacity needs to be updated based on a plurality of plot data from a predetermined reference point in time.

[0097] In addition, in this embodiment, the SOC estimation unit 50 may determine whether or not an abnormality has occurred in the derivation of the SOC based on a plurality of plot data from a predetermined reference point in time.

[0098] FIG. 6 is a diagram showing an example of a plurality of plot data when the correction index changes in accordance with the change in the integrated value of the absolute current amount in an increasing trend.

[0099] For example, an approximation formula for a plurality of plot data may be derived, and if the slope of the approximation formula is a positive value equal to or greater than a predetermined value, it may be determined that the trend of the correction index according to the trend of the integrated value of the absolute current amount is increasing. Note that the method of determining the trend is not limited to the method using the approximation formula, and any known method may be used, such as determining the trend based on a moving average of a plurality of plot data.

[0100] If the trend of the correction index according to the trend of the integrated value of the absolute current amount is on the rise, it means that there is a gradual decrease in the full charge capacity of the battery 20. Note that the gradual decrease in the full charge capacity of the battery 20 is a normal deterioration pattern and is not abnormal.

[0101] Therefore, when the trend of the correction index according to the trend of the integrated value of the absolute current amount is increasing and the latest correction index exceeds a predetermined upper limit threshold, the SOC estimating unit 50 determines that the full charge capacity needs to be updated. The predetermined upper limit threshold may be set to an appropriate value taking into consideration the frequency of updating the full charge capacity, etc.

[0102] This allows a decrease in the full charge capacity to be properly detected, and an update of the full charge capacity can be requested at an appropriate timing and at an appropriate frequency when the full charge capacity decreases.

[0103] Furthermore, by including the condition that the trend of the correction index according to the trend of the absolute current integrated value is an increasing trend, it is possible to avoid a situation where an outlier, such as when the correction index accidentally exceeds the upper threshold, results in an unnecessary request to update the full charge capacity.

[0104] In addition, the condition for the correction index to exceed the upper limit threshold is not limited to the latest correction index, but may be satisfied when the correction index exceeds the upper limit threshold in at least one of multiple plot data from a specified reference point in time.

[0105] When it is determined that the full charge capacity needs to be updated, the SOC estimating unit 50 turns on an update request flag indicating that the full charge capacity needs to be updated. Then, when a condition for deriving the full charge capacity is satisfied, such as when the battery 20 is fully charged, if the update request flag is on, the SOC estimating unit 50 derives and updates the full charge capacity.

[0106] Furthermore, when the battery is ready-on after the full charge capacity is updated, the SOC estimation unit 50 resets the absolute current amount integrated value to the initial value.

[0107] Furthermore, if the trend of the correction index in accordance with the trend of the absolute current integrated value is on the rise, it is assumed that the SOC has been estimated appropriately, and the SOC estimation unit 50 determines that there is no abnormality in the derivation of the SOC.

[0108] FIG. 7 is a diagram showing an example of a plurality of plot data when the correction index changes in accordance with the change in the integrated value of the absolute current amount in a decreasing trend.

[0109] For example, an approximate equation for multiple plot data may be derived, and if the slope of the approximate equation is a negative value less than a predetermined value, it may be determined that the trend of the correction index according to the trend of the absolute current integrated value is decreasing.

[0110] If the trend of the correction index according to the trend of the absolute current integrated value is decreasing, it means that the full charge capacity is increasing from the viewpoint of the full charge capacity. An increase in the full charge capacity rarely occurs under normal circumstances. Therefore, if the trend is decreasing, it is assumed that some abnormality has occurred in the process of estimating the SOC.

[0111] Therefore, the SOC estimating unit 50 may determine that an abnormality has occurred in the derivation of the SOC when the trend of the correction index according to the trend of the integrated value of the absolute current amount is decreasing and the latest correction index is below a predetermined lower threshold. The lower threshold may be set to an arbitrary value taking into account, for example, a normal fluctuation range of the correction index.

[0112] If it is determined that an abnormality has occurred, the occurrence of the abnormality may be notified, for example, by displaying an error, etc. Furthermore, if it is determined that an abnormality has occurred, a predetermined restriction may be imposed on the control of the vehicle 1, for example, by reducing the permitted power below an initial setting value.

[0113] This makes it possible to properly detect when the SOC is not being estimated properly, and as a result, it becomes possible to properly take measures to deal with the abnormality in the derivation of the SOC.

[0114] Furthermore, by including the condition that the trend of the correction index in accordance with the trend of the absolute current integrated value is a downward trend, it is possible to avoid a situation in which an abnormality is mistakenly determined to have occurred due to an outlier, for example, when the correction index accidentally exceeds the lower threshold value.

[0115] In addition, the condition for the correction index to fall below the lower limit threshold is not limited to the latest correction index, but may be satisfied when the correction index falls below the lower limit threshold in at least one of multiple plot data from a specified reference point in time.

[0116] Furthermore, if the trend of the correction index according to the trend of the absolute current integrated value is downward, it is assumed that an abnormality has occurred in the derivation of the SOC, and therefore the SOC estimation unit 50 does not request an update of the full charge capacity.

[0117] FIG. 8 is a diagram showing an example of a plurality of plot data when the tendency of the change in the correction index according to the change in the integrated value of the absolute current amount is approximately constant.

[0118] For example, an approximate equation for multiple plot data may be derived, and if the slope of the approximate equation is a positive value less than a predetermined value and a negative value less than a predetermined value, it may be determined that the tendency of the correction index to change according to the change in the absolute current integrated value is roughly constant.

[0119] If the tendency of the change in the correction index according to the change in the integrated value of the absolute current amount is roughly constant, it is assumed that there is almost no decrease in the full charge capacity.

[0120] Therefore, if the tendency of the change in the correction index according to the change in the integrated value of the absolute current amount is approximately constant, the SOC estimating unit 50 does not request an update of the full charge capacity. For example, the SOC estimating unit 50 turns off the update request flag. This makes it possible to prevent unnecessary updates of the full charge capacity.

[0121] Furthermore, if the tendency of the correction index according to the change in the absolute current integrated value is roughly constant, it is assumed that the SOC is appropriately estimated, and the SOC estimation unit 50 determines that there is no abnormality in the derivation of the SOC.

[0122] 9 is a flowchart illustrating the flow of operations of the SOC estimation unit 50. The SOC estimation unit 50 starts the series of processes shown in FIG. 9 in response to the vehicle 1 being ready-on.

[0123] When the vehicle 1 is ready-on, the SOC estimation unit 50 reads various data necessary for estimating the SOC from the storage device 26 or the memory 42 (S10). The data to be read includes, for example, the absolute current amount during the previous trip period and the integrated value of the absolute current amount up to the previous trip period.

[0124] Next, the SOC estimating unit 50 executes an initial SOC value deriving process (S11) to derive an initial SOC value for the current trip period. The initial SOC value deriving process (S11) will be described in detail later.

[0125] Next, the SOC estimating unit 50 determines whether the full charge capacity has been updated since the previous execution of the series of processes in FIG. 9 until the present time (S12).

[0126] If it is determined that the full charge capacity has been updated (YES in S12), the SOC estimating unit 50 resets the absolute current integrated value to an initial value (S13) and ends the series of processes in Fig. 9. The initial value is, for example, zero. As a result, a new absolute current integrated value is calculated from the current trip period.

[0127] If it is determined that the full charge capacity has not been updated (NO in S12), the SOC estimating unit 50 ends the series of processes in FIG.

[0128] FIG. 10 is a flowchart illustrating the flow of processing that is periodically and repeatedly executed by the SOC estimation unit 50 after the processing of FIG. 9 until the vehicle 1 is ready-off.

[0129] When a predetermined execution timing arrives, the SOC estimation unit 50 derives an integrated current value for the current trip period based on the current detected by the current sensor 24 (S20). Next, the SOC estimation unit 50 derives an absolute current amount for the current trip period based on the current detected by the current sensor 24 (S21). The SOC estimation unit 50 stores the derived integrated current value and absolute current amount in the storage device 26 (S22). Note that the process of FIG. 10 is periodically and repeatedly executed, and therefore the integrated current value and absolute current amount are updated to the latest values ​​each time the process of FIG. 10 is executed.

[0130] Next, the SOC estimation unit 50 determines whether the vehicle 1 has been ready-off (S23). If it is determined that the vehicle 1 has been ready-off (YES in S23), the SOC estimation unit 50 derives the end SOC for the current trip period using the current integration method based on the current integration value derived in step S20 (S24).

[0131] Next, the SOC estimating unit 50 derives an absolute current amount integrated value based on the absolute current amount derived in step S21 (S25). For example, the SOC estimating unit 50 derives an absolute current amount integrated value up to the current trip period by adding the absolute current amount in the current trip period to the absolute charge amount integrated value up to the previous trip period. The SOC estimating unit 50 stores the end SOC and the absolute current amount integrated value in the storage device 26 (S26), and ends the series of processes in FIG. 10.

[0132] On the other hand, if it is determined that the ready-off has not been performed (NO in S23), the SOC estimation unit 50 ends the series of processes in FIG.

[0133] 11 is a flowchart illustrating the flow of the SOC initial value derivation process (S11). When the SOC initial value derivation process (S11) starts, the SOC estimation unit 50 determines whether polarization of the battery 20 has been eliminated (S30). For example, the SOC estimation unit 50 may determine that polarization has been eliminated if the time elapsed since the ready-off point in the previous trip period is equal to or longer than the polarization elimination time.

[0134] If it is determined that the polarization has been eliminated (YES in S30), the SOC estimation unit 50 acquires the OCV detected by the voltage sensor 22, derives the SOC using the OCV method, and sets the derived SOC as the initial SOC value for the current trip period (S31). The initial SOC value derived in step S31 corresponds to the start SOC estimated using the OCV method at the start of the current trip period.

[0135] Next, the SOC estimation unit 50 determines whether or not the initial SOC value was derived from the OCV at the start of the previous trip period, that is, in the initial SOC value derivation process (S11) at the previous ready-on time (S32).

[0136] If it is determined that the initial SOC value was derived from the OCV at the start of the previous trip period (YES in S32), the SOC estimating unit 50 determines whether the immediately preceding stop period is within a predetermined period (S33).

[0137] If it is determined that the immediately preceding stop period is within the predetermined period (YES in S33), the SOC estimating unit 50 derives an SOC correction amount corresponding to the previous trip period (S34). For example, the SOC estimating unit 50 derives the SOC correction amount by subtracting the current SOC initial value derived in step S31 from the end SOC estimated by the current integration method at the end of the previous trip period.

[0138] Next, the SOC estimating unit 50 divides the SOC correction amount derived in step S34 by the absolute current amount for the previous trip period to derive a correction index corresponding to the previous trip period (S35).

[0139] Next, the SOC estimating unit 50 associates the correction index derived in step S35 with the integrated value of the absolute current amount up to the previous trip period, and generates plot data corresponding to the previous trip period (S36).

[0140] Next, the SOC estimating unit 50 stores the derived SOC correction amount, correction index, and plot data in the storage device 26 (S37).

[0141] Next, the SOC estimating unit 50 sets the permitted power of the battery 20 based on the correction index derived in step S34 and the permitted power map stored in the memory 42 (S38). The smaller the correction index derived in step S34, the larger the permitted power set by the SOC estimating unit 50.

[0142] Next, the SOC estimation unit 50 performs a full charge capacity update determination process (S39) including a process of determining whether or not the full charge capacity needs to be updated, and ends the SOC initial value derivation process (S11). The full charge capacity update determination process (S39) will be described in detail later.

[0143] In step S32, if it is determined that the initial SOC value was not derived from the OCV at the start of the previous trip period (NO in S32), the SOC estimating unit 50 ends the initial SOC value derivation process (S11).

[0144] In step S33, when it is determined that the immediately preceding stop period exceeds the predetermined period (NO in S33), SOC estimating unit 50 ends the SOC initial value derivation process (S11).

[0145] If it is determined in step S30 that the polarization has not been eliminated (NO in S30), the SOC estimation unit 50 determines whether the number of trip periods between the trip period of the previous plot data and the previous trip period is equal to or greater than a predetermined number (S40).

[0146] If it is determined that the number of trip periods between the trip period of the previous plot data and the previous trip period is equal to or greater than the predetermined number (YES in S40), the SOC estimation unit 50 sets the end SOC calculated at the end of the previous trip period as the initial SOC value for the current trip period (S41).Then, the SOC estimation unit 50 ends the initial SOC value derivation process (S11).

[0147] If it is determined that the number of trip periods between the trip period of the previous plot data and the previous trip period is less than the predetermined number (NO in S40), SOC estimating unit 50 performs a correction value derivation process (S42) to derive a correction value. The correction value derivation process (S42) will be described in detail later.

[0148] Next, the SOC estimating unit 50 adds the correction value derived in the correction value derivation process (S42) to the end SOC derived at the end of the previous trip period, and sets the result as the initial SOC value for the current trip period (S43).Then, the SOC estimating unit 50 ends the initial SOC value derivation process (S11).

[0149] 12 is a flowchart illustrating the flow of the full charge capacity update determination process (S39). When the full charge capacity update determination process (S39) is started, the SOC estimating unit 50 reads out past plot data after the full charge capacity was updated from the storage device 26 (S50).

[0150] Next, the SOC estimating unit 50 determines whether the trend of the correction index according to the trend of the integrated value of the absolute current amount is increasing in the past plot data (S51).

[0151] If it is determined that the trend of the correction index according to the trend of the absolute current amount integrated value is increasing (YES in S51), the SOC estimating unit 50 determines whether the latest correction index exceeds the upper limit threshold (S52).

[0152] If it is determined that the latest correction index exceeds the upper limit threshold (YES in S51), the SOC estimating unit 50 turns on an update request flag that requests an update of the full charge capacity (S53). As a result, when the condition for deriving the full charge capacity is met later, such as when the battery 20 is fully charged, the update request flag will be on, and the full charge capacity will be updated. Note that when the full charge capacity is updated, the update request flag is turned off.

[0153] After step S53, the SOC estimation unit 50 determines that there is no abnormality in the derivation of the SOC (S54), and ends the full charge capacity update determination process (S39).

[0154] If it is determined in step S52 that the latest correction index does not exceed the upper limit threshold (NO in S51), the SOC estimating unit 50 turns off the update request flag (S55), and the full charge capacity is not updated.

[0155] After step S55, the SOC estimation unit 50 determines that there is no abnormality in the derivation of the SOC (S54), and ends the full charge capacity update determination process (S39).

[0156] If it is determined in step S51 that the trend is not increasing (NO in S51), the SOC estimation unit 50 determines whether the trend of the correction index according to the trend of the absolute current amount integrated value is decreasing (S57).

[0157] If it is determined that the trend of the correction index according to the trend of the absolute current integrated value is decreasing (YES in S57), the SOC estimating unit 50 determines whether the latest correction index has fallen below the lower limit threshold (S58).

[0158] When it is determined that the latest correction index is below the lower limit threshold (YES in S58), the SOC estimating unit 50 sets the update request flag to the OFF state (S59).

[0159] After step S59, the SOC estimating unit 50 determines that there is an abnormality in the derivation of the SOC (S60), notifies the user of the abnormality (S61), and ends the full charge capacity update determination process (S39). Note that if it is determined that there is an abnormality in the derivation of the SOC, the SOC estimating unit 50 may impose a predetermined restriction on the control of the vehicle 1.

[0160] If it is determined in step S57 that the SOC is not decreasing (NO in S57), the SOC estimating unit 50 turns off the update instruction flag (S55). The SOC estimating unit 50 determines that there is no abnormality in the derivation of the SOC (S54), and ends the full charge capacity update determination process (S39).

[0161] If it is determined in step S58 that the latest correction index is not below the lower limit threshold (NO in S58), the SOC estimating unit 50 turns off the update instruction flag (S55). The SOC estimating unit 50 determines that there is no abnormality in the derivation of the SOC (S54), and ends the full charge capacity update determination process (S39).

[0162] 13 is a flowchart illustrating the flow of the correction value derivation process (S42). When the correction value derivation process (S42) is started, the SOC estimation unit 50 reads past plot data from the storage device 26 after the full charge capacity was updated (S70). The SOC estimation unit 50 derives an approximation formula for the past plot data (S71).

[0163] The SOC estimating unit 50 derives an estimated value of the correction index by substituting the sum of the absolute current difference integrated value and the absolute current difference integrated value up to the trip period of the previous plot data into the approximation formula (S72). The SOC estimating unit 50 multiplies the estimated value of the correction index by the absolute current difference integrated value to derive a correction value (S73), and ends the correction value derivation process (S42).

[0164] As described above, the SOC estimation unit 50 of the SOC estimation device 10 of this embodiment generates plot data that associates a correction index corresponding to the trip period to which the end SOC belongs with the absolute current integrated value up to the trip period to which the end SOC belongs. If the SOC estimation unit 50 determines that polarization of the battery 20 has not been eliminated, it derives an estimate of the correction index corresponding to the trip period immediately before the trip period to which the current time belongs, based on the past plot data. The SOC estimation unit 50 derives an initial value of the SOC for the trip period to which the current time belongs, based on the estimate of the correction index.

[0165] The correction index and plot data in this embodiment include information on the estimated error of the SOC from the actual SOC due to a decrease in full charge capacity during the trip period. As a result, in this embodiment, by deriving the initial SOC based on the estimated value of the correction index, it is possible to derive an initial SOC for the current trip period that reflects the influence of the decrease in full charge capacity during the previous trip period.

[0166] Therefore, the SOC estimation device 10 of this embodiment can estimate an appropriate initial value of the SOC even when the polarization of the battery 20 is not eliminated. As a result, the SOC estimation device 10 of this embodiment can improve the accuracy of SOC estimation by the current integration method using the initial value of the SOC.

[0167] While the present invention has been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to such embodiments. It is clear that those skilled in the art can conceive of various modifications and alterations within the scope of the claims, and it is understood that such modifications and alterations also fall within the technical scope of the present invention.

[0168] REFERENCE SIGNS LIST 1 vehicle 10 SOC estimation device 20 battery 30 control device 40 processor 42 memory

Claims

1. A device comprising: a battery mounted on a vehicle; and a control device estimating an SOC of the battery, the control device having one or more processors and one or more memories connected to the processor, a period from when the vehicle is ready on to when it is ready off being a trip period, the processor: deriving a difference between an end SOC, which is an SOC estimated using a current integration method at the end of the trip period, and a start SOC, which is an SOC estimated using an open circuit voltage method at the start of the next trip period to which the end SOC belongs, as an SOC correction amount indicating an estimation error of the SOC corresponding to the trip period to which the end SOC belongs; and deriving an absolute current amount, which is a value obtained by adding an integrated value of the absolute value of the charging current in the battery and an integrated value of the absolute value of the discharging current in the battery during the trip period; dividing the SOC correction amount corresponding to the trip period to which the end SOC belongs by the absolute current amount in the trip period to which the end SOC belongs, to derive a correction index corresponding to the trip period to which the end SOC belongs; deriving an integrated absolute current amount value which is a value obtained by integrating the absolute current amount from a predetermined reference time point over a plurality of the trip periods; generating plot data correlating the correction index corresponding to the trip period to which the end SOC belongs and the integrated absolute current amount value up to the trip period to which the end SOC belongs; determining whether or not polarization of the battery has been eliminated at the start of the trip period; if it is determined that polarization of the battery has not been eliminated, deriving an estimated value of the correction index corresponding to the trip period immediately before the trip period to which the current time belongs based on the past plot data; and deriving an initial value of SOC for the trip period to which the current time belongs based on the estimated value of the correction index. An SOC estimation device that performs a process including the steps of:

2. The SOC estimation device of claim 1, wherein the processor executes processes including: multiplying an absolute current difference integrated value, which is the difference between the absolute current difference integrated value up to the trip period immediately preceding the trip period to which the current time belongs and the absolute current difference integrated value corresponding to the plot data closest to the current time among the past plot data, by the derived estimate of the correction index to derive a correction value; and adding the derived correction value to the end SOC derived at the end of the trip period immediately preceding the trip period to which the current time belongs, to derive an initial SOC value.

3. The SOC estimation device of claim 1, wherein the processor executes processes including: deriving an estimated value of the correction index when the number of trip periods from the trip period corresponding to the plot data that is closest to the current time among the past plot data to the trip period immediately preceding the trip period to which the current time belongs is less than a predetermined number; and deriving an initial value of SOC based on the estimated value of the correction index.

4. The SOC estimation device of claim 1, wherein the processor executes processes including: when it is determined in the determination of whether the polarization of the battery has been eliminated that the polarization of the battery has been eliminated, a process of deriving the SOC correction amount, a process of deriving the correction index, and a process of generating the plot data.

5. The SOC estimation device of claim 1, wherein the processor executes processes including: when it determines that polarization of the battery has been eliminated, and when it estimates the SOC using the open circuit voltage method at the start of the trip period preceding the trip period to which the current time belongs, and when the period from the end of the trip period preceding the trip period to which the current time belongs to the trip period to which the current time belongs is within a predetermined period, it performs processes including: deriving the SOC correction amount, deriving the correction index, and generating the plot data.

6. The SOC estimation device according to claim 1, wherein the processor executes a process including: determining whether or not a full charge capacity of the battery needs to be updated based on a plurality of plot data from the predetermined reference point in time.

7. The SOC estimation device according to claim 6, wherein the processor executes processing including: determining that the full charge capacity of the battery needs to be updated when, in the plurality of plot data from the predetermined reference point in time, the trend of the correction index in accordance with the trend of the integrated value of the absolute current amount is on the rise and the latest correction index exceeds a predetermined upper limit threshold.

8. The SOC estimation device according to claim 1, wherein the processor executes processing including: determining whether or not an abnormality has occurred in the derivation of the SOC based on the plurality of plot data from the predetermined reference point in time.

9. The SOC estimation device according to claim 8, wherein the processor executes processing including: determining that an abnormality has occurred in the derivation of SOC when, in the plurality of plot data from the predetermined reference point in time, the trend of the correction index in accordance with the trend of the integrated value of the absolute current amount is on a downward trend and the latest correction index is below a predetermined lower threshold.

10. The SOC estimation device of claim 1, wherein at least one of an upper limit value of the absolute value of the power permitted to be input to the battery and an upper limit value of the absolute value of the power permitted to be output from the battery is the permitted power, and the processor executes processing including: changing the value of the permitted power based on the derived correction index so that the value of the permitted power increases as the correction index decreases.

11. The SOC estimation device of claim 1, wherein the processor executes a process including: determining whether or not a full charge capacity of the battery has been updated; and resetting the absolute current amount integrated value to an initial value when it is determined that a full charge capacity of the battery has been updated.

12. The SOC estimation device according to claim 1, wherein the predetermined reference point in time is a point in time when the full charge capacity of the battery is updated.

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