Battery system

Abstract

The battery system includes a battery and an ECU. The ECU executes polarization elimination control for eliminating polarization of the battery, and calculation processing for calculating an SOC of the battery after the polarization elimination control. When the polarization cancellation control is executed after the battery is discharged, the polarization cancellation control is a charge control for charging the battery. In a case where the polarization cancellation control is executed after the battery is charged, the polarization cancellation control is a discharge control for discharging the battery.

Description

Technical Field

[0001] The present disclosure relates to battery systems. Background Art

[0002] Japanese Patent Application Laid-Open No. 2019-160721 discloses a battery system including a secondary battery. Summary of the invention

[0003] Calculating the SOC (State Of Charge) of a power storage device such as a secondary battery with high accuracy is important for properly protecting the power storage device or fully using the power storage device. Therefore, a technology for improving the calculation accuracy of the SOC is desired.

[0004] The present disclosure has been made to solve the above-mentioned problems, and an object of the present disclosure is to provide a battery system capable of improving the calculation accuracy of SOC.

[0005] The battery system disclosed in the present invention includes a power storage device and a control device. The control device performs polarization elimination control for eliminating polarization of the power storage device, and a calculation process for calculating the SOC of the power storage device after the polarization elimination control. In the case where the polarization elimination control is performed after the power storage device is discharged, the polarization elimination control is a charging control for charging the power storage device. In the case where the polarization elimination control is performed after the power storage device is charged, the polarization elimination control is a discharge control for discharging the power storage device.

[0006] The polarization of the power storage device changes the voltage of the power storage device, and thus may affect the calculation result of the SOC. The polarization of the power storage device is eliminated by applying a voltage having a polarity opposite to the polarity of the power storage device. Specifically, the polarization of the power storage device after discharge is eliminated by charging the power storage device, and the polarization after charging is eliminated by discharging. By setting the above structure, even in the case of polarization, the SOC is calculated after the polarization is eliminated by the polarization elimination control. In this way, it is possible to avoid the situation where the calculation result of the SOC is affected by the polarization. As a result, the SOC can be calculated with high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like reference numerals represent like elements, and in which:

[0008] Figure 1 This is a diagram schematically showing the overall structure of a vehicle equipped with a battery system according to an embodiment.

[0009] Figure 2A It is a diagram schematically showing the structure of each cell of a battery.

[0010] Figure 2BIt is a diagram schematically showing the structure of each cell of a battery.

[0011] Figure 3 This is a diagram showing an example of a curve indicating the SOC-OCV (Open Circuit Voltage) characteristics of a battery.

[0012] Figure 4A This is a diagram for explaining the influence that the polarization of the battery 10 may have on the calculation accuracy of the SOC.

[0013] Figure 4B This is a diagram for explaining the influence that the polarization of the battery 10 may have on the calculation accuracy of the SOC.

[0014] Figure 5 This is a diagram for specifically explaining the calculation process of estimating the SOC at the time of full charge capacity of the battery 10 by the ECU (Electronic Control Unit).

[0015] Figure 6 This is a flowchart illustrating a process executed by the ECU in association with the calculation process of the SOC. DETAILED DESCRIPTION

[0016] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals and their description will not be repeated.

[0017] Figure 1 FIG. 2 is a diagram schematically showing the overall structure of a vehicle equipped with a battery system according to an embodiment. Figure 1 The vehicle 1 is an electric vehicle (BEV: Battery Electric Vehicle) and is configured to be capable of external charging for charging the battery 10 using electric power supplied from an electric power device 90 outside the vehicle 1 .

[0018] The vehicle 1 includes a battery 10, a voltage sensor 21, a current sensor 22, an SMR (System Main Relay) 25, a PCU (Power Control Unit) 30, and a motor 35. The vehicle 1 also includes an inlet 40, an AC / DC converter 50, a DC-DC converter 65, an auxiliary battery 70, a communication device 75, and an ECU 100. The battery 10, the voltage sensor 21, the current sensor 22, the SMR 25, the AC / DC converter 50, the DC-DC converter 65, the auxiliary battery 70, the communication device 75, and the ECU 100 constitute a battery system 2.

[0019] The battery 10 is an example of a power storage device, and stores electric power for driving the vehicle 1. The battery 10 is a battery pack including a plurality of cells. Each cell is a secondary battery, and in this example, an all-solid-state battery. An all-solid-state battery is a battery having a solid electrolyte layer.

[0020] After charging or discharging the battery 10, polarization of the battery 10 may occur. Polarization is a phenomenon in which an electromotive force (polarization voltage) in the opposite direction to the current is temporarily generated when a current flows through the battery 10. In other words, polarization is a phenomenon in which the voltage VB temporarily rises when the battery 10 is charged or temporarily decreases when the voltage VB is discharged. Polarization disappears naturally after a sufficiently long time has passed after charging or discharging, or disappears when a voltage in the opposite direction to the polarization voltage is applied to the battery 10 (the polarization voltage becomes zero and the voltage VB stabilizes).

[0021] The voltage sensor 21 detects the voltage VB of the battery 10. The current sensor 22 detects the current IB flowing through the battery 10. The current IB during charging is positive, and the current IB during discharging is negative.

[0022] The SMR 25 is connected between the battery 10 and the PCU 30. The PCU 30 performs bidirectional power conversion between the battery 10 and the motor 35. The motor 35 is an AC rotary electric machine, and generates a driving force for the vehicle 1 when the motor 35 is powered. The motor 35 can also perform regenerative power generation when the vehicle 1 is braked or when the acceleration is reduced on a downhill slope. When the motor 35 performs regenerative power generation, the generated power is supplied to the battery 10 through the PCU 30, and the battery 10 is charged.

[0023] The inlet 40 is configured to be able to insert a connector 95 of the power device 90, and receives the power supplied from the power device 90. In this example, the power supplied is AC power. The AC / DC converter 50 converts the power received by the inlet 40 into DC power for charging the battery 10. The AC / DC converter 50 can also convert the power of the battery 10 into AC power and supply the power to the power device 90 via the inlet 40. The power supply from the vehicle 1 to the power device 90 is also referred to as "external power supply". During the external power supply process, the battery 10 is discharged.

[0024] The DC-DC converter 65 is connected to the auxiliary battery 70. The auxiliary battery 70 stores power for operating various auxiliary devices (not shown) of the vehicle 1. The communication device 75 exchanges various information with the power device 90 through, for example, CAN (Controller Area Network) communication. The information includes information indicating the amount of power transmitted between the vehicle 1 and the power device 90 during external charging or external power supply, the start / stop of external charging, or the start / stop of external power supply.

[0025] ECU100 includes a CPU (Central Processing Unit) 102, a memory 104, and a storage device 105. CPU102 performs various calculations. Memory 104 includes ROM (Read Only Memory) and RAM (Random Access Memory). ROM stores programs executed by CPU102 and various data. The data contains information showing characteristics representing the relationship between the SOC and OCV of the battery 10. This characteristic is also called the SOC-OCV characteristic. This characteristic is used to calculate the SOC based on the OCV and is affected by the charge and discharge history record (hysteresis phenomenon) of the battery 10. OCV is determined as the voltage VB when the SMR25 is disconnected. The storage device 105 stores a charge and discharge history record 110 representing the history of the voltage VB and the current IB.

[0026] ECU100 controls various devices of vehicle 1 or calculates the SOC of battery 10 based on signals received from various sensors of monitoring unit 20 and programs and maps stored in memory 104. The devices include SMR25, PCU30, AC / DC converter 50, DC / DC converter 65, and communication device 75. When SMR25 is turned on, ECU100 uses PCU30 to control the charge and discharge of battery 10. ECU100 drives motor 35 by controlling PCU30. ECU100 is configured to be able to perform control (extraction charge control) of controlling DC-DC converter 65 to supply power of auxiliary battery 70 to battery 10.

[0027] ECU100 is configured to be able to execute external charging control for controlling external charging and external power supply control for controlling external power supply. These controls are executed using AC / DC converter 50 and communication device 75. ECU100 is configured to be able to estimate the full charge capacity of battery 10 by dividing the charge amount of battery 10 by the increment (ΔSOC) of SOC during charging of battery 10. The charge amount of battery 10 is determined based on the integrated value of current IB.

[0028] Figure 2A , Figure 2B 1 is a diagram schematically showing the structure of each unit of the battery 10. Figure 2A , Figure 2B The battery cell 15 includes a positive electrode layer 15a, a negative electrode layer 15b and a solid electrolyte layer 15c.

[0029] The positive electrode layer 15a includes a positive electrode active material layer 15d and a positive electrode current collector 15e. The positive electrode active material layer 15d includes lithium cobalt oxide, lithium nickel oxide, or lithium iron phosphate. The positive electrode active material layer 15d is bonded to the solid electrolyte layer 15c. Figure 2AIn this example, the layers are in close contact. Region 16 is the junction region of these layers. The negative electrode layer 15b includes a negative electrode active material layer 15f and a negative electrode current collector 15g. The negative electrode active material layer 15f includes a metal active material or a carbon active material. The negative electrode active material layer 15f is joined to the solid electrolyte layer 15c, and in this example, they are in close contact. The solid electrolyte layer 15c is between the positive electrode layer 15a and the negative electrode layer 15b. The positive electrode layer 15a, the solid electrolyte layer 15c, and the negative electrode layer 15b are stacked in the direction (Y direction) in which the plurality of units 15 are stacked.

[0030] When the all-solid-state battery is repeatedly charged and discharged, a portion of the bond between the electrode layer such as the positive electrode layer 15a and the solid electrolyte layer 15c may be peeled off ( Figure 2B ). Such a phenomenon is also called interlayer peeling. Region 17 and region 18 are the non-bonding region and bonding region of the electrode layer (in this case, the positive electrode layer 15a) and the solid electrolyte layer during interlayer peeling, respectively. During interlayer peeling, the resistance of region 17 is high and the resistance of region 18 is low. Such non-uniformity of resistance affects the diffusion of charge carriers and easily leads to non-uniformity of electron density. As a result, in all-solid-state batteries, lithium salts and the like are easy to diffuse and polarization is easy to occur. Furthermore, during interlayer peeling, due to the low resistance of region 18, a large current is easy to flow through the all-solid-state battery. When the all-solid-state battery is discharged immediately after being charged (overcharged) with a large current, a large amount of discharge current flows into region 18. As a result, the all-solid-state battery is discharged with a large current, and the polarization after charging is immediately eliminated.

[0031] Figure 3 It is a diagram showing an example of a curve indicating the SOC-OCV characteristics of the battery 10 . Figure 4A , Figure 4B This is a diagram for explaining the influence that the polarization of the battery 10 may have on the calculation accuracy of the SOC.

[0032] Reference Figure 3 , line 200 illustrates the SOC-OCV characteristics when the battery 10 is charged. In this example, this characteristic is equivalent to the SOC-OCV characteristics when the battery 10 is charged from a fully discharged state to a fully charged state. Line 200 is also represented as a "charging curve". Line 220 illustrates the SOC-OCV characteristics when the battery 10 is discharged. In this example, this characteristic is equivalent to the SOC-OCV characteristics when the battery 10 is discharged from a fully charged state to a fully discharged state. Line 220 is also represented as a "discharging curve". In this way, the SOC-OCV characteristics vary depending on the charge and discharge history (hysteresis phenomenon). Lines 200 and 220 respectively represent the SOC-OCV characteristics when polarization of the battery 10 does not occur (or is eliminated).

[0033] Line 240 illustrates the SOC-OCV characteristics when the battery 10 is charged from a fully discharged state to a fully charged state, but is different from line 200 in that the characteristics are obtained under a polarization condition. Line 260 illustrates the SOC-OCV characteristics when the battery 10 is discharged from a fully charged state to a fully discharged state, but is different from line 220 in that the characteristics are obtained under a polarization condition. In this way, the SOC-OCV characteristics change due to the influence of polarization in addition to the influence of the hysteresis phenomenon. In this example, lines 200 and 220 are respectively stored in the memory 104, but each of lines 240 and 260 is not stored in the memory 104.

[0034] Points P1 and P2 are points on lines 240 and 260 corresponding to V1, respectively. Points P1 and P2 correspond to operating points when OCV is V1 and polarization occurs, respectively.

[0035] Reference Figure 4A , Figure 4B , the polarization of the battery 10 may affect the calculation accuracy of the SOC of the battery 10. For example, when the OCV is V1 during charging, polarization may actually occur, so sometimes the actual operating point is point P1 and the actual SOC is X1 ( Figure 4A ). However, since the charging curve stored in the memory 104 is not the line 240 but the line 200, there is a possibility that the operating point is erroneously determined to be the point P1f based on the line 200 and the SOC is calculated as X1f. As a result, the calculation result of the SOC includes an error of ΔE1. ​​Similarly, in the case where polarization occurs during discharge, although the actual operating point is the point P2 (SOC is X2), there is a possibility that the operating point is erroneously determined to be the point P2f based on the line 220 and the SOC is calculated as X2f ( Figure 4B As a result, the SOC calculation result may contain an error of ΔE2. In this way, polarization can easily lead to a decrease in the calculation accuracy of SOC. In particular, in all-solid-state batteries, due to interlayer peeling ( Figure 2A , Figure 2B ) is prone to polarization, so a technology is desired to avoid the reduction in SOC calculation accuracy caused by polarization.

[0036] The inventors have focused on improving the calculation accuracy of SOC by eliminating polarization and calculating SOC after polarization elimination. Polarization is eliminated by applying a voltage with a polarity opposite to its polarity. Specifically, polarization after discharge is eliminated by charging, and polarization after charging is eliminated by discharging.

[0037] In the embodiment, the ECU 100 performs a polarization elimination control for eliminating polarization of the battery 10, and a calculation process for calculating the SOC of the battery 10 after the polarization elimination control. In the case where the polarization elimination control is performed after the battery 10 is charged, the polarization elimination control is a discharge control for discharging the battery 10. This control may be a control performed using the PCU 30 while the vehicle 1 is running, or it may be an external power supply control. In the case where the polarization elimination control is performed after the battery 10 is discharged, the polarization elimination control is a charging control for charging the battery 10. This control may be a control performed using the PCU 30 while the vehicle 1 is running, or it may be an external charging control.

[0038] According to the above calculation process, even when polarization occurs, polarization is eliminated by polarization elimination control, and then SOC is calculated. Thus, it is possible to avoid the situation where the calculation result of SOC is affected by polarization. Furthermore, polarization is eliminated by polarization elimination control before a sufficiently long time has passed for polarization to be eliminated naturally, so SOC can be calculated earlier.

[0039] ECU100 uses the SOC-OCV characteristics (lines 200, 220) stored in memory 104 to perform SOC calculation processing according to the OCV of battery 10. For example, when discharge control is performed as polarization elimination control after battery 10 is charged, the above calculation processing is equivalent to the processing of calculating SOC using line 220 (discharge curve). For example, when the OCV at the start of the discharge control is V1, the operating point of battery 10 changes from point P1 to point P1a via line 250 due to the discharge control (OCV drops from V1 to V1a), and then changes on line 220 ( Figure 4A ). Line 250 is not stored in the memory 104. After the discharge control, the ECU 100 calculates the SOC from the OCV using line 220. For example, when the OCV after the discharge control is V1a, the calculation result of the SOC is Xa. Xa is lower than X1 by ΔXa.

[0040] When charging control is performed as polarization elimination control after the battery 10 is discharged, the above calculation process corresponds to the process of calculating the SOC using the line 200 (charging curve). For example, when the OCV at the start of the charging control is V1, the operating point changes from point P2 to point P2a via line 270 due to the charging control (OCV rises from V1 to V1b), and then changes on line 200 ( Figure 4B ). Line 270 is not stored in the memory 104. After the charge control, the ECU 100 calculates the SOC from the OCV using line 200. For example, when the OCV after the charge control is V1b, the calculation result of the SOC is Xb. Xb is higher than X2 by ΔXb.

[0041] According to the above-mentioned polarization elimination control, the battery 10 is discharged after being charged, or the battery 10 is charged after being discharged, thereby eliminating polarization. As a result, the SOC is calculated in a state where polarization is eliminated (a state where the operating point is on the line 200 or 220), thereby avoiding a decrease in the calculation accuracy of the SOC due to polarization.

[0042] Furthermore, it is preferable that the period during which the polarization elimination control is performed (hereinafter also referred to as “polarization elimination period”) is appropriately short. This is to avoid the situation in which a polarization voltage in the opposite direction to the original polarization voltage is newly generated due to the control.

[0043] When the battery 10 is discharged immediately before the depolarization period (specifically, the start time thereof), the period during which the battery 10 is discharged in this way is also indicated as the "immediately before discharge period". When the battery 10 is charged immediately before the depolarization period, the period during which the battery 10 is charged in this way is also indicated as the "immediately before charge period". "Immediately before the depolarization period" basically means (when shorter than a prescribed upper limit described later) the period closest to the current time among the charging period (the period during which the battery 10 is charged) and the discharging period (the period during which the battery 10 is discharged) before the start of the control. This period corresponds to the period from the time when the charge / discharge of the battery 10 was last switched (the time when the positive and negative of the current IB were last switched) to the current time. When the length of this period is longer than a prescribed upper limit (for example, 3 minutes), "immediately before the depolarization period" (immediately before the charge period or the discharge period) is determined as a period having the length of the prescribed upper limit. Information on the charging period and the discharging period is generated based on the current IB and stored in the memory 104.

[0044] The polarization elimination period after charging is shorter than the immediately preceding charging period. Similarly, the polarization elimination period after discharging is shorter than the immediately preceding discharging period. Assuming that the polarization elimination period is too long, it is conceivable that a polarization voltage in the opposite direction to the original polarization voltage is newly generated, but in the embodiment, the polarization elimination period is short, so the above situation can be avoided.

[0045] In addition, since the calculation process of SOC is performed after the polarization elimination control, the shorter the polarization elimination period is, the earlier the calculation process starts. In the embodiment, the polarization elimination period is short, so the polarization elimination control in this period is completed in a short time. As a result, the SOC can be calculated quickly.

[0046] The polarization elimination period is not preferably too short. In this case, the polarization may not be fully eliminated. In addition, there is a period of time when the operating point is from point P1 ( Figure 4A , Figure 4B) changes to a point on line 220 (e.g., point P1a), or changes from point P2 to a point on line 200 (e.g., point P2a) (i.e., halfway when the action point moves on line 250 or 270). The memory 104 stores lines 200 and 220, but since lines 250 and 270 are not stored, the SOC calculated at the above timing may be inaccurate.

[0047] The inventors have obtained the following insights through experiments: if the length of the polarization elimination period is greater than 1 / 11 and less than 1 / 9 of the length of the immediately preceding discharge period or the immediately preceding charge period (hereinafter also expressed as "about 1 / 10"), polarization is easily eliminated fully, and it is difficult to generate a polarization voltage in the opposite direction to the original polarization voltage. Specifically, by setting the length of the polarization elimination period in this way, the operating point can be changed from points P1 and P2 to points on lines 220 and 200, respectively (in detail, points P1a, P2a or points near them). Therefore, in the embodiment, when polarization elimination control (charging control) is performed after the battery 10 is discharged, the length of the polarization elimination period is set to about 1 / 10 of the length of the immediately preceding discharge period. Similarly, when polarization elimination control (discharging control) is performed after the battery 10 is charged, the length of the polarization elimination period is set to about 1 / 10 of the length of the immediately preceding charge period. In this way, the length of the polarization elimination period is basically longer as the length of the immediately preceding charge period or the immediately preceding discharge period is longer.

[0048] When the length of the polarization elimination period is shorter than one-eleventh of the length of the immediately preceding charging period or the immediately preceding discharging period, there is a possibility that polarization is not sufficiently eliminated, or the SOC is calculated in the middle of the movement of the operating point on the line 250 or 270, and the calculation accuracy of the SOC may be reduced. When the length of the polarization elimination period is longer than one-ninth of the length of the immediately preceding charging period or the immediately preceding discharging period, a polarization voltage in the opposite direction to the original polarization voltage is newly generated, and the calculation accuracy of the SOC may be reduced. In contrast, in the embodiment, such a problem can be avoided.

[0049] In the case where the immediately preceding charging period or the immediately preceding discharging period is determined to be a period having the above-mentioned upper limit, the length of the polarization elimination period is set (limited) to about 1 / 10 of the upper limit. Otherwise, the length of the polarization elimination period is set to about 1 / 10 of the length of the immediately preceding charging period or the immediately preceding discharging period. Thus, even in the case where the battery 10 is charged or discharged for a long time before the polarization elimination control, it is possible to avoid a situation where the polarization elimination period is too long and the calculation of the SOC is delayed.

[0050] Figure 51 is a diagram for specifically explaining the calculation process of the SOC when the ECU 100 estimates the full charge capacity of the battery 10. Figure 5 , line 300 shows an example of the transition of SOC.

[0051] During the period from time t0 to time t1 (period P01), the vehicle 1 is traveling and the battery 10 is charged or discharged. At time t1, the vehicle 1 is connected (plugged in) to the power equipment 90 via the inlet 40. The period from time t01 to time t1 (period P01a) is the immediately preceding discharge period. It is assumed that polarization occurs at time t1.

[0052] At time t1, ECU100 determines that the battery 10 is discharged during period P01a based on the charge and discharge history record 110. Based on the determination result, ECU100 performs charging control as polarization elimination control during the period from time t1 to time t2 (period P12). This control is external charging control. Period P12 is a polarization elimination period when polarization elimination control is performed after the battery 10 is discharged. During period P12, ECU100 performs external charging control so that the charging power of the battery 10 becomes a small power. In this example, the length of period P12 is one tenth of period P01a (immediately preceding discharge period).

[0053] At time t2, ECU100 stops external charging control with low charging power and calculates SOC. Thereafter, during the period from time t2 to time t3 (period P23), external charging control is performed so that the charging power is larger than that during period P12.

[0054] At time t3, ECU100 stops external charging control. The period from time t23 to time t3 (period P23a) is the immediately preceding charging period. In this example, the length of the period from the time when the charge / discharge of the battery 10 was last switched to the current time is longer than the upper limit, so the period P23a (immediately preceding charging period) is a period having the length of the upper limit. It is assumed that polarization occurs at time t3.

[0055] ECU100 determines that the battery 10 is charged during period P23a based on the charge and discharge history record 110. Based on the determination result, ECU100 performs discharge control as polarization elimination control during the period from time t3 to time t4 (period P34). This control is external power supply control. Period P34 is a polarization elimination period when polarization elimination control is performed after the battery 10 is charged. In this example, the length of period P34 is one tenth of the length of period P23a. At time t4, ECU100 stops external power supply control and calculates SOC.

[0056] The ECU 100 calculates the absolute value of the difference between the SOC calculated at time t2 and the SOC calculated at time t4 as ΔSOC, thereby estimating the full charge capacity.

[0057] Figure 6 This is a flowchart illustrating a process related to the calculation process of the SOC and executed by the ECU 100. This flowchart starts when the vehicle 1 is plugged in.

[0058] Reference Figure 6 ECU 100 reads the charge and discharge history record 110 ( S105 ), and determines whether the battery 10 was charged or discharged immediately before the current time ( S107 ).

[0059] If the battery 10 is charged immediately before (Yes in S107), the ECU 100 sets the length of the polarization elimination period to, for example, 1 / 10 of the length of the charging period immediately before (S110). The ECU 100 performs discharge control as polarization elimination control during the set period (S115). This discharge control is equivalent to, for example, external power supply control in period P34. After S115, the ECU 100 determines the OCV of the battery 10 (for example, Figure 4A , Figure 4B V1a), the SOC is calculated from the OCV using line 220 (discharge curve) (S117). In this example, the SOC is calculated as Xa ( Figure 4A , Figure 4B ).

[0060] When the battery 10 is discharged immediately before (No in S107), the ECU 100 sets the length of the polarization elimination period to, for example, 1 / 10 of the length of the immediately preceding discharge period (S120). The ECU 100 performs charging control as polarization elimination control during the set period (S125). This charging control is, for example, equivalent to the external charging control in the period P12. After S125, the ECU 100 determines the OCV of the battery 10 (for example, Figure 4A , Figure 4B V1b), SOC is calculated from OCV using line 200 (charging curve) (S127). In this example, SOC is calculated as Xb ( Figure 4A , Figure 4B ).

[0061] The ECU 100 may execute S105 to S127 while the vehicle 1 is traveling (while the electric motor 35 is being driven). In this case, the charging control and the discharging control are executed using the PCU 30. Alternatively, the charging control may be the above-mentioned extraction charging control.

[0062] As described above, according to the embodiment, it is possible to avoid the situation where the calculation result of SOC is affected by polarization. As a result, SOC can be calculated with high accuracy.

[0063] <Modification of Implementation>

[0064] In this modification, it is assumed that the ECU 100 executes charging control or discharging control using the PCU 30 after the motor 35 performs power running or regeneration for a relatively long time while the vehicle 1 is traveling (when the immediately preceding discharging period or the immediately preceding charging period is long).

[0065] When 1 / 11 of the length of the immediately preceding discharge period is less than 0.1 seconds and 1 / 9 of the length of the immediately preceding discharge period is greater than 0.1 seconds, the length of the polarization elimination period (charging control period) may be less than 0.1 seconds when it is set to be greater than 1 / 11 and less than 1 / 9 of the length of the immediately preceding discharge period. The inventors have obtained the following insight: when the length of the polarization elimination period is less than 0.1 seconds, polarization may not always be fully eliminated by polarization elimination control (charging control). On the other hand, the inventors have obtained the following insight: when the length of the polarization elimination period is greater than 0.1 seconds, polarization is particularly easy to be fully eliminated. Therefore, ECU100 may also set the length of the polarization elimination period to be greater than 0.1 seconds and less than 1 / 9 of the length of the immediately preceding discharge period when 1 / 11 of the length of the immediately preceding discharge period is less than 0.1 seconds and 1 / 9 of the length of the immediately preceding discharge period is greater than 0.1 seconds.

[0066] When 1 / 11 of the length of the immediately preceding charging period is less than 0.1 seconds and 1 / 9 of the length of the immediately preceding charging period is greater than 0.1 seconds, the length of the polarization elimination period (period of discharge control) may be less than 0.1 seconds when it is set to be greater than 1 / 11 and less than 1 / 9 of the length of the immediately preceding charging period. The inventors have obtained the following insight: when the length of the polarization elimination period is less than 0.1 seconds, polarization may not always be fully eliminated by polarization elimination control (discharge control). On the other hand, the inventors have obtained the following insight: when the length of the polarization elimination period is greater than 0.1 seconds, polarization is particularly easy to be fully eliminated. Therefore, ECU100 may also set the length of the polarization elimination period to be greater than 0.1 seconds and less than 1 / 9 of the length of the immediately preceding charging period when 1 / 11 of the length of the immediately preceding charging period is less than 0.1 seconds and 1 / 9 of the length of the immediately preceding charging period is greater than 0.1 seconds.

[0067] When 1 / 9 of the length of the immediately preceding discharge period is less than 0.1 seconds, the length of the polarization elimination period is always less than 0.1 seconds when it is set to be greater than 1 / 11 and less than 1 / 9 of the length of the immediately preceding discharge period. In this case, as described above, polarization may not always be fully eliminated by polarization elimination control (charging control). Therefore, ECU 100 may also set the length of the polarization elimination period to be greater than 0.1 seconds (for example, 0.1 seconds) when 1 / 9 of the length of the immediately preceding discharge period is less than 0.1 seconds.

[0068] When 1 / 9 of the length of the immediately preceding charging period is less than 0.1 seconds, the length of the polarization elimination period is always less than 0.1 seconds when it is set to be greater than 1 / 11 and less than 1 / 9 of the length of the immediately preceding charging period. In this case, as described above, polarization may not always be fully eliminated by polarization elimination control (discharge control). Therefore, ECU 100 may also set the length of the polarization elimination period to be greater than 0.1 seconds (for example, 0.1 seconds) when 1 / 9 of the length of the immediately preceding charging period is less than 0.1 seconds.

[0069] <Other Modifications>

[0070] Each unit cell of the battery 10 may be a liquid-type battery such as a liquid-type lithium-ion battery. The above-described polarization elimination control and SOC calculation process can also be applied to a battery system including a liquid-type battery instead of an all-solid-state battery.

[0071] The embodiments disclosed herein are illustrative in all aspects and are not restrictive. The scope of the present invention is indicated by the scope of claims rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

Claims

1. A battery system comprising: an electrical storage device; and a control device for executing polarization elimination control for eliminating polarization of the power storage device and a calculation process for calculating the SOC of the power storage device after the polarization elimination control, When the depolarization control is executed after the power storage device is discharged, the depolarization control is a charge control for charging the power storage device. When the depolarization control is executed after the power storage device is charged, the depolarization control is a discharge control for discharging the power storage device.

2. The battery system according to claim 1, wherein: When the polarization elimination control is performed after the power storage device is discharged, the calculation process is a process of calculating the SOC using the SOC-OCV characteristic of the power storage device when the power storage device is charged, When the polarization elimination control is performed after the power storage device is charged, the calculation process is a process of calculating the SOC using an SOC-OCV characteristic of the power storage device when the power storage device is discharged.

3. The battery system according to claim 1 or 2, wherein: The period during which the polarization elimination control is performed is defined as an elimination period. If the power storage device is charged immediately before the elimination period, the period during which the power storage device is charged is set as the immediately preceding charging period. If the power storage device is discharged immediately before the elimination period, the period during which the power storage device is discharged is set as the immediately preceding discharge period. When the polarization elimination control is executed after the power storage device is discharged, the elimination period is shorter than the immediately preceding discharge period, When the polarization elimination control is executed after the power storage device is charged, the elimination period is shorter than the immediately preceding charging period.

4. The battery system according to claim 3, wherein: When the polarization elimination control is performed after the power storage device is discharged, the length of the elimination period is not less than 1 / 11 and not more than 1 / 9 of the length of the immediately preceding discharge period, When the polarization elimination control is executed after the power storage device is charged, the length of the elimination period is not less than 1 / 11 and not more than 1 / 9 of the length of the immediately preceding charging period.

5. The battery system according to claim 4, wherein: When 1 / 11 of the length of the immediately preceding discharge period is less than 0.1 seconds and 1 / 9 of the length of the immediately preceding discharge period is greater than or equal to 0.1 seconds, the length of the erasing period is greater than or equal to 0.1 seconds and less than or equal to 1 / 9 of the length of the immediately preceding discharge period. When one ninth of the length of the immediately preceding discharge period is less than 0.1 seconds, the length of the elimination period is 0.1 seconds. When 1 / 11 of the length of the immediately preceding charging period is less than 0.1 seconds and 1 / 9 of the length of the immediately preceding charging period is greater than or equal to 0.1 seconds, the length of the elimination period is greater than or equal to 0.1 seconds and less than or equal to 1 / 9 of the length of the immediately preceding charging period. When one ninth of the length of the immediately preceding charging period is less than 0.1 seconds, the length of the erasing period is 0.1 seconds.

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