Charge state estimation method

Abstract

This invention provides a method for estimating the charge state (SOC) of a rechargeable battery that allows for accurate determination of the waiting time (rest time) required to ensure depolarization before estimating the charge state (SOC) of the rechargeable battery, thereby enabling faster estimation of the charge state. [Solution] The charge state estimation method of the embodiment determines whether the polarization of the battery has been resolved based on whether a predetermined time has elapsed since the end of charging and discharging of the battery, and if it is determined that the polarization has been resolved, it estimates the charge state of the battery based on the open circuit voltage of the battery, wherein the predetermined time is the time until the difference between the open circuit voltage and the terminal voltage of the battery after the end of charging and discharging falls below a predetermined threshold, and the predetermined threshold is the minimum value of the change in the open circuit voltage when the charge state of the battery changes by a predetermined percentage.

Description

Technical Field

[0001] Embodiments of the present invention relate to a method for estimating a state of charge.

Background Art

[0002] Conventionally, it has been proposed to determine depolarization over time and estimate the SOC based on the OCV in a region where the change in OCV is large with respect to the change in the SOC (State Of Charge) of the battery.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in the above conventional technology, depolarization is defined as a range in which the voltage error due to polarization can be tolerated, but no specific method for setting the time for determining depolarization has been proposed.

[0005] An object of the present invention is to surely grasp a waiting time (rest time) for surely performing depolarization prior to estimating the state of charge (SOC) of a rechargeable battery, and to provide a state of charge estimation method capable of estimating the state of charge in a shorter time.

Means for Solving the Problems

[0006] To achieve the above objective, the charge state estimation method of the embodiment determines whether the polarization of the battery has been resolved based on whether a predetermined time has elapsed since the end of charging and discharging of the battery, and if it is determined that the polarization has been resolved, it estimates the charge state of the battery based on the open-circuit voltage of the battery, wherein the predetermined time is the time until the difference between the open-circuit voltage and the terminal voltage of the battery after the end of charging and discharging falls below a predetermined threshold, and the predetermined threshold is the minimum value of the change in the open-circuit voltage when the charge state of the battery changes by a predetermined percentage. [Effects of the Invention]

[0007] According to the present invention, the waiting time (rest time) required to ensure depolarization can be reliably determined, and the charging state can be reliably estimated in a shorter time. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram of the charge state estimation system according to an embodiment. [Figure 2] Figure 2 shows an example of a SOC-OCV curve for a ternary (NMC) battery. [Figure 3] Figure 3 is a diagram illustrating the principle of an embodiment. [Figure 4] Figure 4 is an explanatory diagram of the terminal voltage of the vehicle battery during discharge. [Figure 5] Figure 5 is an explanatory diagram of the threshold table group. [Figure 6] Figure 6 is an explanatory diagram of the threshold table. [Figure 7] Figure 7 is a processing flowchart of the SOC estimation process in the embodiment. [Figure 8] Figure 8 illustrates the relationship between the effective depolarization time and the threshold during discharge. [Figure 9] Figure 9 illustrates the relationship between the effective depolarization time and the threshold during charging. [Modes for carrying out the invention]

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Figure 1 is a schematic diagram of the charge state estimation system according to an embodiment. The charge state estimation system 10 of the embodiment is mounted on a vehicle and includes a vehicle state acquisition unit 11, a polarization determination unit 12, a current detection unit 13, a voltage detection unit 14, and a charge capacity estimation unit 15.

[0010] In this case, the vehicle is equipped with an engine EN, a generator GN, an onboard charger CHG, and a battery monitoring IC_BS. When the generator GN is driven by the engine EN, the onboard charger CHG charges the onboard battery BT using the power supplied by the generator GN. At this time, the battery monitoring IC_BS monitors the voltage, current, and temperature of the onboard battery BT. The battery monitoring IC_BS then outputs the obtained temperature as temperature data to the charge capacity estimation unit 15.

[0011] The vehicle status acquisition unit 11 acquires the vehicle status from another ECU 20 via CAN (Controller Area Network) and outputs vehicle status data ST.

[0012] The polarization determination unit 12 counts the duration of the rest state based on the vehicle state data ST, and determines whether the rest state has continued for a predetermined time or longer, that is, whether the polarization state of the onboard battery BT has been effectively resolved, and outputs polarization determination data PO to the charge capacity estimation unit 15.

[0013] The current detection unit 13 outputs current detection data DI to the charging capacity estimation unit 15 based on the output of the current sensor SC, which detects the current (charging / discharging current) I flowing through the vehicle battery BT. The voltage detection unit 14 outputs voltage detection data DV to the charging capacity estimation unit 15 based on the output of the voltage sensor SV which detects the voltage V of the vehicle battery BT.

[0014] The charge capacity estimation unit 15 estimates the state of charge (SOC) of the in-vehicle battery BT and outputs the estimated SOC to the ECU that manages the in-vehicle battery BT. The charge capacity estimation unit 15 includes a first estimation unit 15-1 and a second estimation unit 15-2. The first estimation unit 15-1 estimates the SOC of the in-vehicle battery BT by SOC-OCV estimation. SOC-OCV estimation utilizes the fact that the relationship between SOC and OCV (Open Circuit Voltage) is hardly affected by the state of the rechargeable battery, more specifically, the deterioration state, the temperature state, and the C-rate (charge / discharge rate). Here, OCV is the battery voltage when left unloaded for a long time, and the time to reach OCV is affected by the usage history of the battery.

[0015] FIG. 2 is a diagram showing an example of the SOC-OCV curve of a ternary (NMC-based) battery. The SOC-OCV curve of a battery always draws a similar curve if the battery configuration is the same. Therefore, if OCV can be measured, the SOC can be accurately estimated.

[0016] The second estimation unit 15-2 estimates the SOC of the in-vehicle battery BT by Coulomb count estimation. Coulomb count estimation estimates the SOC of the in-vehicle battery BT by counting the current flowing into the in-vehicle battery BT and the current flowing out of the in-vehicle battery BT. However, in Coulomb count estimation, the initial value of the SOC cannot be estimated. Therefore, the SOC of the in-vehicle battery BT estimated by SOC-OCV estimation is used as the SOC reference value, and based on this reference value, the current flowing into the in-vehicle battery BT and the current flowing out of the in-vehicle battery BT are counted to estimate the SOC of the in-vehicle battery BT.

[0017] Here, the outline operation of the charge state estimation system 10 of the embodiment will be described. The vehicle status acquisition unit 11 acquires the vehicle status from another ECU 20 and outputs the vehicle status data ST to the polarization determination unit 12.

[0018] The polarization determination unit 12 determines, based on the vehicle state data ST, whether the vehicle's rest state has continued for a predetermined time or longer, that is, whether the polarization state of the on-board battery BT has been effectively resolved, and outputs the polarization determination data PO to the charge capacity estimation unit 15.

[0019] Based on the polarization determination data PO, the charging capacity estimation unit 15 assumes that the voltage detection data DV output by the voltage detection unit 14 is the OCV if the polarization state of the vehicle battery BT has been effectively resolved, and performs SOC-OCV estimation by the first estimation unit 15-1 to estimate the SOC of the vehicle battery BT.

[0020] Furthermore, if the polarization state of the vehicle battery BT has not been resolved based on the polarization determination data PO, the second estimation unit 15-2 uses the SOC previously estimated by the first estimation unit 15-1 as a reference value and performs a Coulomb count estimation based on the current detection data DIOCV output by the current detection unit 13 to count the current flowing into the vehicle battery BT and the current flowing out of the vehicle battery BT, thereby estimating the SOC of the vehicle battery BT.

[0021] Here, we will explain in detail how to set a predetermined time as a threshold for the duration of the rest state (polarization depolarization time threshold) for determining whether or not the polarization state of the vehicle battery BT has been effectively resolved.

[0022] First, we will explain the principle of the method for setting the predetermined time in the embodiment. Figure 3 is a diagram illustrating the principle of an embodiment. Figure 3(A) shows the SOC-OCV curve in the initial state of the vehicle battery. Furthermore, Figure 3(B) shows the change in OCV (ΔOCV) when the SOC changes by 1% in the state shown in Figure 3(A). Figure 4 is an explanatory diagram of the terminal voltage of the vehicle battery during discharge. In Figure 4, the vertical axis represents the terminal voltage (V) of the vehicle battery BT, and the horizontal axis represents the elapsed time (s) since the end of discharge. Once the discharge is complete (time = 0) and the polarization of the vehicle battery BT settles down, reaching an equilibrium state, the terminal voltage should become OCV. However, as shown in Figure 4, although the terminal voltage of the vehicle battery BT continues to gradually decrease, the terminal voltage does not reach the OCV. Basically, a very long rest time is required for the voltage of the vehicle's battery BT to reach the OCV (Overcurrent Voltage) in a strict sense.

[0023] However, in practice, since the rate of change in terminal voltage gradually decreases, it is acceptable to consider the vehicle battery BT to have reached its OCV when the rate of change in SOC over time in the SOC-OCV curve becomes n% or less (for example, n=1).

[0024] In other words, when the change in OCV ΔV is less than or equal to the design allowable value (for example, the minimum value ΔVmin) when the change in SOC = n%, the change in OCV ΔV is used as a threshold, and the time when the voltage difference between the terminal voltage and OCV when the change in SOC = n% is less than or equal to the change in OCV ΔV is determined as the polarization depolarization time. The time until the polarization depolarization time, i.e., the predetermined rest time (threshold), is then set and processed accordingly. In this case, the value of n is set as the tolerance range for the estimated SOC. That is, if the tolerance for the estimated SOC is 1%, then n is set to 1.

[0025] Incidentally, it is known that the depolarization time depends on many parameters such as the temperature of the automotive battery BT, SOC, C-rate (charge / discharge rate), charge / discharge time, and SOH (State of Health: SOC in the initial state of the battery / SOC in the degraded state of the battery). Therefore, it is difficult to directly determine the time until polarization is resolved, and consequently, the rest time.

[0026] Therefore, in this embodiment, the slope of the temporal change in the terminal voltage, that is, the change in terminal voltage per unit time, is monitored, and when this voltage change approaches zero and becomes smaller than a predetermined threshold, it is considered that polarization has been eliminated and the terminal voltage has reached OCV, and processing is performed accordingly.

[0027] As mentioned above, the depolarization time depends on many parameters, but among these, temperature T, SOC, and C rate are considered to have a particularly significant impact on the depolarization time. Therefore, in this embodiment, a threshold table is prepared in advance, with temperature T, SOC, and C rate as parameters, and the threshold value TH being the voltage difference per unit time of the terminal voltage of the onboard battery BT at the point in time when polarization is considered to have been resolved. Based on this, it is determined whether or not polarization has been resolved.

[0028] Now, let's discuss how to create a threshold table. Specifically, for example, an evaluation test is performed by discharging or charging while keeping the temperature T, SOC, and C rate constant. As shown in Figure 3(B), the change in OCV ΔV when the SOC changes by a predetermined n% (1% in the example in Figure 3(B)) is determined in the range of SOC=0% to SOC=100%, and the threshold TH is defined as the OCV change ΔV at which the obtained OCV change ΔV is smallest (= minimum value of OCV change ΔV). Then, for example, while keeping the C rate fixed, a threshold TH is calculated using temperature T and SOC as parameters, and this becomes a threshold table for that C rate. Then, multiple threshold tables are created for each C rate, forming a group of threshold tables.

[0029] Mathematically, the threshold TH is set as the OCV change ΔV that corresponds to the point when the slope of the OCV-SOC curve obtained by differentiating the OCV-SOC curve becomes smaller. In this case, the change in OCV ΔV corresponds to the error originating from polarization in the SOC estimation. Therefore, the error due to polarization can be reduced to n% or less (1% in the example above).

[0030] Here, we will explain the threshold table group and the threshold table itself. Figure 5 is an explanatory diagram of the threshold table group. The threshold table group TBG consists of two sets: a threshold table group for discharge and a threshold table group for charge. Figure 5 shows the threshold table group for discharge.

[0031] The threshold table group TBG is configured to include, for example, six threshold tables TB1 to TB6 with discharge C rates of 0.5C, 1.0C, 1.5C, ..., 3.0C.

[0032] Figure 6 is an explanatory diagram of the threshold table. In Figure 6, the threshold table TB1 for the case where the C rate = 0.5C is used as an example to illustrate the threshold table.

[0033] The threshold table TB1 stores the values ​​at which the OCV change per unit time ΔV of a battery with the same specifications as the onboard battery BT becomes smallest when discharge is performed at a discharge rate of 0.5C, changing the temperature T from -30 to 120°C in 10°C increments. For each temperature, with a SOC of 0, 10, ..., 90, 100, the thresholds TH11 to TH111 (temperature -30°C), TH21 to TH211 (temperature -20°C), ..., TH161 to TH1611 (temperature 120°C) are associated with temperature T and SOC.

[0034] Therefore, once the temperature, state of charge (SOC), and discharge rate (C rate) of the vehicle battery BT are determined, the threshold TH can be uniquely determined.

[0035] Next, the operation of the embodiment will be described. Figure 7 is a processing flowchart of the SOC estimation process in the embodiment. The processing flowchart in Figure 7 represents what is known as interrupt processing, and it is a process that is repeated at predetermined intervals. In the following explanation, we will first use the discharge of the vehicle battery BT as an example.

[0036] The vehicle status acquisition unit 11 of the charging status estimation system 10 acquires the vehicle status from another ECU 20 and determines whether the vehicle status is in a rest state or not (step S11).

[0037] In this case, the vehicle being in a rest state means that the vehicle's engine EN, generator GN, and onboard charger CHG are not charging the onboard battery BT, and the onboard battery BT is not discharging high power (such as starting the engine).

[0038] In the determination in step S11, if the vehicle state is in a rest state (step S11; Yes), the polarization determination unit 12 counts the duration of the rest time (step S17). Then the process ends.

[0039] In the determination in step S11, if the vehicle state is not in the rest state (step S11; No), it is determined whether the previous value of the vehicle state (the determination value at the time of the previous interrupt processing) was in the rest state (step S12). In other words, the system determines whether this is the first time that the system has transitioned from a rest state to an active state.

[0040] In the determination in step S12, if the previous value of the vehicle state (the determination value at the time of the previous interrupt processing) is not the rest state (step S12; No), the process proceeds to step S13.

[0041] In the determination in step S12, if the previous value of the vehicle state (the determination value at the time of the previous interrupt processing) was in the rest state (step S12; Yes), the polarization determination unit 12 reads the threshold TH by referring to the threshold tables TB1 to TB6 which constitute the threshold table group TBG using the temperature corresponding to the temperature detection data TM output by the battery monitoring IC_BS, the previous SOC, and the C rate of the current discharge as parameters, and determines whether the counted rest time is equal to or greater than the polarization depolarization time corresponding to the threshold TH (step S15).

[0042] In this case, as mentioned above, it is difficult to determine the actual depolarization time in the vehicle battery BT. Therefore, in practice, attention is paid to the change in the differential voltage between the terminal voltage of the vehicle battery BT and the OCV. The terminal voltage of the vehicle battery BT is detected every unit of time (e.g., 1 second), and it is determined whether the differential voltage with the OCV has fallen below the threshold voltage TH (ΔV).

[0043] Next, the rest time is initialized (step S13), the Coulomb count is estimated (step S14), and the process is terminated.

[0044] Figure 8 illustrates the relationship between the effective depolarization time and the threshold during discharge. Figure 8(A) shows the change in terminal voltage after discharge at a state of charge (SOC) of 10%, a temperature of -10°C, and a C rate of 1C.

[0045] In Figure 8(A), the vertical axis represents the terminal voltage [V] of the vehicle battery BT, and the horizontal axis represents the elapsed time [s] after the end of discharge. Figure 8(B) shows the change in the differential voltage between the terminal voltage and the OCV immediately after discharge in Figure 8(A). In Figure 8(B), the vertical axis represents the differential voltage [V], and the horizontal axis represents the rest time after discharge [s].

[0046] In Figure 8(B), the dashed line represents the threshold TH[V] read from the threshold table group TBG for the case where the temperature is -10°C, SOC is 10%, and the C rate during discharge is 1C.

[0047] As shown in Figure 8(A), when the terminal voltage of the vehicle battery BT changes in a way that it gradually decreases, the difference voltage of the terminal voltage per unit time (= previous voltage value - current voltage value) changes as shown in Figure 8(B), and the rest time when the difference voltage value equals the threshold TH corresponds to the depolarization time Tdpd. In the case of Figure 8(B), the depolarization time Tdpd is approximately 2300 [s].

[0048] In the determination in step S15, if the counted rest time is greater than or equal to the polarization depolarization time Tdpd corresponding to the threshold TH (step S15; Yes), that is, if the differential voltage is less than or equal to the threshold TH, then the polarization depolarization time Tdpd has elapsed, and the terminal voltage of the onboard battery BT is considered to be OCV, and the polarization determination unit 12 outputs polarization determination data PO indicating that the polarization inheritance time has elapsed to the charging capacity estimation unit 15. As a result, the charging capacity estimation unit 15 determines that SOC-OCV estimation is possible, assumes that the terminal voltage of the vehicle battery BT is the OCV, and performs SOC-OCV estimation using the first estimation unit 15-1 to estimate the SOC of the vehicle battery BT (step S16), and then terminates the process.

[0049] On the other hand, in the determination in step S15, if the counted rest time is less than the depolarization time Tdpd corresponding to the threshold TH (step S15; No), and in the determination in step S12, if the previous value of the vehicle state is not the rest state (step S12; No), the polarization determination unit 12 initializes the rest time (step S13), and since the depolarization time Tdpd has not elapsed, the terminal voltage of the onboard battery BT cannot be considered to be OCV, the polarization determination unit 12 outputs polarization determination data PO to the charging capacity estimation unit 15 indicating that the depolarization time Tdpd has not elapsed. As a result, the charge capacity estimation unit 15 estimates the state of charge (SOC) of the vehicle battery BT by performing Coulomb count estimation using the second estimation unit 15-2 (step S14), and then terminates the process.

[0050] Next, I will explain the operation during charging. Figure 9 illustrates the relationship between the effective depolarization time and the threshold during charging. Figure 9(A) shows the change in terminal voltage after charging at a state of charge (SOC) of 10%, a temperature of -10°C, and a C-rate of 1C.

[0051] In Figure 9(A), the vertical axis represents the terminal voltage [V] of the vehicle battery BT, and the horizontal axis represents the elapsed time [s] after the end of discharge. Figure 9(B) shows the change in the differential voltage between the terminal voltage and the OCV immediately after charging, as shown in Figure 9(A). In Figure 9(B), the vertical axis represents the differential voltage [V], and the horizontal axis represents the rest time [s] after charging is complete.

[0052] In Figure 9(B), the dashed line represents the threshold TH[V] read from the threshold table group TBG for the case where the temperature is -10°C, SOC is 10%, and the C rate during charging is 1C.

[0053] As shown in Figure 9(A), when the terminal voltage of the vehicle battery BT changes to gradually increase, the differential voltage of the terminal voltage per unit time (= previous voltage value - current voltage value) changes as shown in Figure 9(B), and the rest time when the value of the differential voltage equals the threshold TH corresponds to the depolarization time Tdpc. In the case of Figure 9(B), the depolarization time Tdpc is approximately 3400 [s].

[0054] The vehicle status acquisition unit 11 of the charging status estimation system 10 acquires the vehicle status from another ECU 20 and determines whether the vehicle status is in a rest state or not (step S11).

[0055] In the determination in step S11, if the vehicle state is in a rest state (step S11; Yes), the polarization determination unit 12 counts the duration of the rest time (step S17) and terminates the process.

[0056] In the determination in step S11, if the vehicle state is not in the rest state (step S11; No), it is determined whether the previous value of the vehicle state (the determination value at the time of the previous interrupt processing) was in the rest state (step S12). In other words, the system determines whether this is the first time that the system has transitioned from a rest state to an active state.

[0057] In the determination in step S12, if the previous value of the vehicle state (the determination value at the time of the previous interrupt processing) is not the rest state (step S12; No), the process proceeds to step S13.

[0058] In the determination in step S12, if the previous value of the vehicle state (the determination value at the time of the previous interrupt processing) was in the rest state (step S12; Yes), the polarization determination unit 12 reads the threshold TH by referring to the threshold tables TB1 to TB6 which constitute the threshold table group TBG using the temperature corresponding to the temperature detection data TM output by the battery monitoring ICBS, the previous SOC, and the C rate of the current discharge as parameters, and determines whether the counted rest time is equal to or greater than the polarization depolarization time Tdpc corresponding to the threshold TH (step S15).

[0059] In the determination in step S15, if the counted rest time is greater than or equal to the polarization depolarization time Tdpc corresponding to the threshold TH (step S15; Yes), that is, if the differential voltage is less than or equal to the threshold TH, then the polarization depolarization time Tdpc has elapsed, and the terminal voltage of the onboard battery BT is considered to be OCV, and the polarization determination unit 12 outputs polarization determination data PO to the charging capacity estimation unit 15 indicating that the polarization inheritance time has elapsed.

[0060] As a result, the charging capacity estimation unit 15 determines that SOC-OCV estimation is possible, assumes that the terminal voltage of the vehicle battery BT is the OCV, performs SOC-OCV estimation using the first estimation unit 15-1 to estimate the SOC of the vehicle battery BT, and then terminates the process.

[0061] On the other hand, in the determination in step S15, if the counted rest time is less than the polarization depolarization time Tdpc corresponding to the threshold TH (step S15; No), and in the determination in step S12, if the previous value of the vehicle state is not the rest state (step S12; No), the polarization determination unit 12 initializes the rest time and determines that the terminal voltage of the onboard battery BT cannot be considered OCV because the polarization depolarization time Tdpc has not elapsed, and outputs polarization determination data PO to the charging capacity estimation unit 15 indicating that the polarization inheritance time has not elapsed. As a result, the charging capacity estimation unit 15 performs coulomb count estimation using the second estimation unit 15-2 to estimate the state of charge (SOC) of the vehicle battery, and then terminates the process.

[0062] As described above, according to this embodiment, the SOC can be reliably estimated with an estimation error of n% (1% in the above example) or less. Furthermore, it is possible to easily and quickly determine whether or not the depolarization time has elapsed.

[0063] Although embodiments of the present invention have been described above, these embodiments are presented as examples only and are not intended to limit the scope of the invention. This novel embodiment can be implemented in various other forms. Furthermore, various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. Moreover, this embodiment is included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents.

[0064] In the above explanation, the threshold table used temperature, SOC, and C-rate as parameters, but these are not the only parameters that can be used. For example, in a system where the C-rate is constant, it is possible to use only temperature and SOC as parameters. Also, if the change in OCV is similar within the actual usable SOC range, it is possible to configure the system to exclude SOC from the parameters. Furthermore, while the threshold TH was previously defined as the minimum value of the OCV change ΔV when the battery charge state changed by a predetermined amount, it is also possible to set it to a value greater than the minimum OCV change ΔV, although this will reduce measurement accuracy, or to a value smaller than the minimum OCV change ΔV, although this will lengthen the depolarization time Tdpd.

[0065] Furthermore, if you want to suppress the depolarization time Tdpd, it is possible to use the value of ΔV, which is used as the threshold TH, as a function of SOC. In this case, the SOC used is a value that includes the error before estimation, so it is preferable to give the value of SOC a range that includes the error, and use the OCV change amount ΔV that is smaller within that range of SOC.

[0066] [Note] Preferred embodiments of the present invention are described below. [First aspect] A charge state estimation method that determines whether the polarization of a battery has been resolved based on whether a predetermined time has elapsed since the end of charging and discharging of the battery, and if it is determined that the polarization has been resolved, estimates the charge state of the battery based on the open-circuit voltage of the battery, wherein the predetermined time is the time until the difference between the open-circuit voltage and the terminal voltage of the battery after the end of charging and discharging falls below a predetermined threshold, The predetermined threshold is the minimum value of the change in the open-circuit voltage when the charge state of the battery changes by a predetermined percentage. This is a method for estimating the charge state. According to this embodiment, the waiting time (rest time) required to ensure depolarization can be reliably determined, and the charging state can be estimated in a shorter time. [Second aspect] A method for estimating the charge state according to the first embodiment, The predetermined percentage is set to an acceptable error range for the estimated value of the charge state. According to this embodiment, the error in the resulting charge state can be kept within a desired tolerance range. [Third aspect] A method for estimating the charge state according to the first or second embodiment, If the predetermined time has elapsed, the charge state is estimated by SOC-OCV estimation. Except when the aforementioned predetermined time has elapsed, the charge state is estimated by Coulomb count estimation. This is a method for estimating charging. According to this embodiment, when polarization is reliably eliminated, the charge state is estimated by SOC-OCV estimation, and in other cases, the charge state is estimated by Coulomb count estimation, thereby improving estimation accuracy. [Fourth aspect] A method for estimating the charge state according to the first embodiment, The threshold is made variable according to a predetermined charge state, The error range for the charging state is set, and the smallest value among the thresholds corresponding to the error range is used. This is a method for estimating the charge state. According to this embodiment, when determining whether or not the battery polarization has been resolved according to the charging state, the polarization resolution time can be set to be shorter, and the charging state can be estimated in a shorter time. [Fifth aspect] A method for estimating the charge state according to the first embodiment, Based on the results of evaluation tests conducted by changing parameters that affect the charging state of the battery, such as temperature, charge state, and C rate, a table containing candidate values ​​for the predetermined threshold is created in advance, and the threshold is determined by referring to the parameters. A method for estimating the charge state. According to this embodiment, the threshold can be easily set by referring to a table, so the charging state can be estimated simply and quickly. [Sixth aspect] A method for estimating the charge state according to the first embodiment, The aforementioned battery is an on-board battery installed in a vehicle. The charge state of the battery is estimated when the state of the vehicle transitions from a rest state to a non-rest state. This is a method for estimating the charge state. According to this embodiment, the charging state can be reliably estimated at the timing when estimation of the charging state is required. [Explanation of Symbols]

[0067] 10. Charging State Estimation System 11. Vehicle status acquisition unit 12 Polarization determination unit 13 Current detection unit 14 Voltage detection unit 15 Charge capacity estimation section 15-1 1st estimation part 15-2 Second estimation part BT Car Battery CHG on-board charger DI current detection data DV Voltage Detection Data EN engine GN Generator TBG threshold tables BS Battery Monitoring IC PO polarization determination data SC Current Sensor ST Vehicle Status Data SV voltage sensor TB1~TB6 Threshold Table TM Temperature Detection Data Tdpc depolarization time Tdpd depolarization time V Voltage ΔV OCV change

Claims

1. A charge state estimation method that determines whether the polarization of the battery has been resolved based on whether a predetermined time has elapsed since the end of charging and discharging of the battery, and if it is determined that the polarization has been resolved, estimates the charge state of the battery based on the open-circuit voltage of the battery, The predetermined time is the time until the difference between the open-circuit voltage and the terminal voltage of the battery after charging and discharging is below a predetermined threshold. The predetermined threshold is the minimum value of the change in the open-circuit voltage when the charge state of the battery changes by a predetermined percentage. A method for estimating the charge state.

2. The threshold is made variable according to a predetermined charge state, The error range for the charging state is set, and the smallest value among the thresholds corresponding to the error range is used. The method for estimating the charge state according to claim 1.

3. Based on the results of evaluation tests conducted by varying parameters that affect the charging state of the battery, such as temperature, charge state, and C rate, a table containing candidate values ​​for the predetermined threshold is created in advance, and the threshold is determined by referring to the parameters. The method for estimating the charge state according to claim 1.

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