Battery Remaining Amount Estimation Device

Abstract

To provide a remaining battery level estimation device that estimates the remaining level of a secondary battery on the basis of a specific remaining level of the secondary battery when a specific parameter correlated with the remaining level of the secondary battery changes specifically, in which the accuracy of estimating the remaining level of the secondary battery is improved.SOLUTION: A remaining battery level estimation device (50) estimates the remaining level of a secondary battery on the basis of a specific remaining level of the secondary battery when a parameter correlated with the remaining level of a secondary battery (41) changes specifically. The remaining battery level estimation device comprises: a determination unit (52) that determines, when electricity is discharged from a state where the remaining level of the secondary battery is higher than the specific remaining level to a lower state, that a prescribed condition is satisfied that a change amount of the remaining level in a prescribed period till charging to the secondary battery starts is lower than or equal to a prescribed change amount; and an estimation unit (53) that, when, while it is determined by the determination unit that the prescribed condition is satisfied, a prescribed parameter changes specifically during charging of the secondary battery, estimates the remaining level of the secondary battery at the time, on the basis of the specific remaining level.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an apparatus for estimating the remaining amount of a secondary battery.

Background Art

[0002] Conventionally, there has been an apparatus that estimates the remaining capacity of a secondary battery at the time when a singular point at which the change amount of the voltage of the secondary battery detected by a voltage detection unit reaches a maximum value appears, as the remaining capacity corresponding to the singular point (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, when detecting the above-mentioned singular point during charging of the secondary battery, the inventor of the present application has noticed that the remaining capacity (remaining amount) at the time when the singular point appears may deviate from the remaining capacity corresponding to the singular point depending on the discharge state of the secondary battery before charging.

[0005] The present invention has been made to solve the above problems, and its main object is to improve the accuracy of estimating the remaining amount of a secondary battery in a battery remaining amount estimating apparatus that estimates the remaining amount of the secondary battery based on a specific remaining amount of the secondary battery when a predetermined parameter correlated with the remaining amount of the secondary battery changes peculiarly.

Means for Solving the Problems

[0006] A first means for solving the above problems is a battery remaining amount estimating apparatus (50) that estimates the remaining amount of the secondary battery based on a specific remaining amount of the secondary battery when a predetermined parameter correlated with the remaining amount of the secondary battery (41) changes peculiarly, When discharging from a state where the remaining amount of the secondary battery is more than the specific remaining amount to a state where it is less, a determination unit (52) determines that a predetermined condition is satisfied, where the change amount of the remaining amount in a predetermined period until the start of charging of the secondary battery is equal to or less than a predetermined change amount; When it is determined by the determination unit that the predetermined condition is satisfied, an estimation unit (53) estimates the remaining amount of the secondary battery at that time based on the specific remaining amount when the predetermined parameter changes peculiarly during charging of the secondary battery; It is provided with.

[0007] According to the above configuration, the battery remaining amount estimation device estimates the remaining amount of the secondary battery based on the specific remaining amount of the secondary battery when a predetermined parameter correlated with the remaining amount of the secondary battery changes peculiarly.

[0008] Here, the inventor of the present application noted that when the discharge amount increases after the remaining amount becomes less than the specific remaining amount when discharging the secondary battery, the remaining amount when the predetermined parameter changes peculiarly during charging deviates from the specific remaining amount. In this regard, the determination unit determines that a predetermined condition is satisfied, where the change amount of the remaining amount (hereinafter referred to as "remaining amount change amount during discharging before charging") in a predetermined period until the start of charging of the secondary battery is equal to or less than a predetermined change amount when discharging from a state where the remaining amount of the secondary battery is more than the specific remaining amount to a state where it is less. Therefore, the determination unit can determine that the discharge amount does not increase after the remaining amount becomes less than the specific remaining amount when discharging the secondary battery, based on the change amount of the remaining amount during discharging in a predetermined period until the start of charging of the secondary battery.

[0009] And when it is determined by the determination unit that the predetermined condition is satisfied, the estimation unit estimates the remaining amount of the secondary battery at that time based on the specific remaining amount when the predetermined parameter changes peculiarly during charging of the secondary battery. Therefore, it is possible to estimate the remaining amount when the predetermined parameter changes peculiarly during charging based on the specific remaining amount in a state where the discharge amount does not increase after the remaining amount becomes less than the specific remaining amount when discharging the secondary battery. Therefore, the accuracy of estimating the remaining amount of the secondary battery can be improved.

[0010] In the second means, the remaining amount of the secondary battery is the remaining capacity of the secondary battery represented by the product of current and time, or the charge rate representing the ratio of the remaining capacity to the full capacity of the secondary battery.

[0011] According to the above configuration, when discharging the secondary battery, it is possible to determine that the discharge amount after the remaining amount becomes less than the specific remaining amount is not large by using the remaining capacity of the secondary battery represented by the product of current and time, or the charge rate representing the ratio of the remaining capacity to the full capacity of the secondary battery.

[0012] Inside the secondary battery, there are parts with high resistance and low resistance. When charging and discharging are performed, current concentrates in the part with low resistance, and parts with high and low capacity (charge storage amount) are generated (capacity unevenness occurs). Then, the inventor of the present application focused on the fact that in the state where capacity unevenness occurs, the remaining amount when a predetermined parameter changes peculiarly during charging deviates from the specific remaining amount. Capacity unevenness is likely to be eliminated when the change rate of the predetermined parameter with respect to the remaining amount of the secondary battery exceeds a high change rate part where the change rate is higher than the predetermined change rate. On the contrary, it is difficult to eliminate in the low change rate part where the change rate of the predetermined parameter with respect to the remaining amount of the secondary battery is equal to or less than the predetermined change rate. For this reason, the longer the discharge in the low change rate part, the more likely capacity unevenness is to occur, and the more likely the remaining amount when a predetermined parameter changes peculiarly during charging is to deviate from the specific remaining amount.

[0013] In this regard, in the third means, the predetermined change amount is set to be equal to or less than the remaining amount of the secondary battery corresponding to the width of the low change rate part where the change rate of the predetermined parameter with respect to the remaining amount of the secondary battery is equal to or less than the predetermined change rate, which exists in the range where the remaining amount of the secondary battery is less than the specific remaining amount. Therefore, when discharging the secondary battery, the remaining amount of the secondary battery can be estimated based on the specific remaining amount in a state where the discharge amount after the remaining amount becomes less than the specific remaining amount is equal to or less than the remaining amount of the secondary battery corresponding to the width of the low change rate part. Therefore, it is possible to suppress the remaining amount when a predetermined parameter changes peculiarly during charging from deviating from the specific remaining amount, and it is possible to suppress a decrease in the accuracy of estimating the remaining amount of the secondary battery.

[0014] The capacity unevenness is more easily eliminated as the temperature of the secondary battery is higher, and is less easily eliminated as the temperature of the secondary battery is lower.

[0015] In this regard, in the fourth means, the predetermined change amount is set to a smaller change amount as the temperature of the secondary battery is lower. According to such a configuration, it can be required as the above-described predetermined condition that the change amount of the remaining amount during pre-charge discharge is smaller as the temperature of the secondary battery is lower. Therefore, even when the temperature of the secondary battery is low, it is possible to suppress a decrease in the accuracy of estimating the remaining amount of the secondary battery.

[0016] The capacity unevenness is more easily eliminated as the time during which the discharge rate is maintained in a state lower than the predetermined discharge rate (including the state in which the secondary battery is not discharged) is longer, and is less easily eliminated as the time during which the discharge rate is maintained in a state lower than the predetermined discharge rate is shorter.

[0017] In this regard, in the fifth means, the predetermined change amount is set to a smaller change amount as the time (hereinafter referred to as "low discharge time") during which the discharge rate is maintained in a state lower than the predetermined discharge rate until the start of charging of the secondary battery is shorter. According to such a configuration, it can be required as the above-described predetermined condition that the change amount of the remaining amount during pre-charge discharge is smaller as the low discharge time until the start of charging of the secondary battery is shorter. Therefore, even when the low discharge time until the start of charging of the secondary battery is short, it is possible to suppress a decrease in the accuracy of estimating the remaining amount of the secondary battery.

[0018] The present inventors have focused on the fact that the open circuit voltage representing the voltage between both terminals in a state where no load is applied to the secondary battery changes greatly when the remaining amount of the secondary battery crosses the specific remaining amount.

[0019] In this regard, in the sixth means, the predetermined parameter is the open-circuit voltage representing the voltage between both terminals in a state where no load is applied to the secondary battery, and the determination unit determines that the remaining amount of the secondary battery is more than the specific remaining amount when the open-circuit voltage is higher than a predetermined voltage, and determines that the remaining amount of the secondary battery is less than the specific remaining amount when the open-circuit voltage is lower than the predetermined voltage. According to such a configuration, it is possible to easily determine whether the remaining amount of the secondary battery is more or less than the specific remaining amount by using the open-circuit voltage.

[0020] The inventor of the present application has paid attention to the fact that there is a low change rate portion where the change rate of the open-circuit voltage with respect to the remaining amount of the secondary battery is equal to or less than a predetermined change rate on the side where the remaining amount of the secondary battery is less and on the side where it is more with the specific remaining amount in between.

[0021] In this regard, in the seventh means, there are two low change rate portions in the secondary battery where the change rate of the open-circuit voltage with respect to the remaining amount of the secondary battery is equal to or less than a predetermined change rate, and the predetermined voltage is set between the open-circuit voltages corresponding to the two low change rate portions respectively. According to such a configuration, it is possible to highly accurately determine whether the remaining amount of the secondary battery is more or less than the specific remaining amount by using the open-circuit voltage.

[0022] In the eighth means, the specific remaining amount is the remaining amount corresponding to between the two low change rate portions.

[0023] According to the above configuration, the specific remaining amount can be defined with high accuracy based on the two low change rate portions.

[0024] When the secondary battery is a lithium-ion battery having a negative electrode containing graphite, lithium ions are occluded between the layers of the layered structure of graphite. The stage of the negative electrode changes according to the number of interlayers in which lithium ions are not occluded, which exists between two interlayers in which lithium ions are occluded, in the secondary battery, and the stage and the open-circuit voltage change according to the remaining amount of the secondary battery. And the inventor of the present application has paid attention to the fact that the specific remaining amount correlates with a specific stage.

[0025] In this regard, in the ninth means, the secondary battery is a lithium-ion battery having a negative electrode containing graphite, and the lithium ions are occluded between the layers of the layered structure of the graphite. There are stage 1 in which the lithium ions are occluded between each layer, stage 2 in which there is one layer without the lithium ions occluded between two layers with the lithium ions occluded, stage 3 in which there are two layers without the lithium ions occluded between two layers with the lithium ions occluded, and stage 4 in which there are three layers without the lithium ions occluded between two layers with the lithium ions occluded. The predetermined voltage is set between the open circuit voltage corresponding to the region where stage 3 and stage 2 coexist and the open circuit voltage corresponding to the region where stage 2 and stage 1 coexist. According to such a configuration, it is possible to accurately determine whether the remaining amount of the secondary battery is more or less than the specific remaining amount by using the relationship between the stage of the negative electrode of the secondary battery, the open circuit voltage, and the specific remaining amount.

[0026] In the tenth means, the specific remaining amount is the remaining amount corresponding to the region where stage 3 and stage 2 coexist and the region where stage 2 and stage 1 coexist.

[0027] According to the above configuration, the specific remaining amount can be accurately defined based on the stage of the negative electrode of the secondary battery.

[0028] Specifically, like in the eleventh means, the predetermined parameter is the open circuit voltage representing the voltage between both terminals in a state where no load is applied to the secondary battery, and the determination unit can adopt a configuration in which it determines that the predetermined parameter has changed peculiarly during charging of the secondary battery based on the open circuit voltage.

[0029] The inventor of the present application has noted that the change rate of impedance with respect to the remaining amount of the secondary battery changes greatly when the remaining amount of the secondary battery crosses the specific remaining amount.

[0030] In this regard, in the twelfth means, the predetermined parameter is the impedance of the secondary battery, and the determination unit determines that the predetermined parameter has changed peculiarly during charging of the secondary battery based on the rate of change of the impedance with respect to the remaining amount of the secondary battery. According to such a configuration, it is possible to accurately determine that the predetermined parameter has changed peculiarly during charging of the secondary battery by using the rate of change of the impedance with respect to the remaining amount of the secondary battery.

[0031] Specifically, as in the thirteenth means, in the sixth means, a configuration such that the secondary battery is a lithium-ion battery having a positive electrode containing lithium, iron, and phosphorus can be adopted.

Brief Description of the Drawings

[0032]

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Mode for Carrying Out the Invention

[0033] (First Embodiment) Hereinafter, the first embodiment embodied in a battery control device mounted on an electric vehicle will be described with reference to the drawings.

[0034] As shown in FIG. 1, the battery control device 100 is a device that monitors the capacity and charge / discharge state of the battery 40. The battery 40 is a rechargeable lithium-ion battery, and specifically, it is a battery pack in which a plurality of lithium-ion batteries 41 are connected in series. In this embodiment, as the lithium-ion battery 41 (secondary battery), one using lithium iron phosphate (containing lithium, iron, and phosphorus) as the positive electrode active material and graphite (carbon) as the negative electrode active material is used.

[0035] The battery 40 is connected to the rotating electrical machine 10 via the inverter 20. The rotating electrical machine 10 performs power input and output with the battery 40. During power running, propulsion force is applied to the vehicle by the power supplied from the battery 40. During regeneration, power generation is performed using the deceleration energy of the vehicle, and power is output to the battery 40.

[0036] The battery control device 100 includes a voltage sensor 30, a current sensor 31, first to fourth relay switches 32 to 35, and a BMU (Battery Management Unit) 50 as a battery monitoring device.

[0037] The voltage sensor 30 detects the inter-terminal voltage of each lithium-ion battery 41 constituting the battery 40, and detects the battery voltage VB obtained by summing these inter-terminal voltages. The current sensor 31 is provided on the connection line LC connecting the battery 40 and the inverter 20, and detects the magnitude and direction of the charge and discharge current IS, which is the current flowing into and out of the battery 40. The detection values of each sensor are input to the BMU 50.

[0038] The battery 40 is configured to be connectable to an external charger 200 via first and second external charging terminals TA and TB. The external charger 200 is, for example, a DC rapid charger. When the external charger 200 is connected to the first and second external charging terminals TA and TB of the battery 40, the battery 40 is charged at a constant current or a constant voltage by the high-voltage DC power input from the external charger 200.

[0039] The first and second external charging terminals TA and TB are connected to the connection line LC via first and second charging paths LA and LB. Specifically, the first external charging terminal TA is connected to a first contact point PA between the positive terminal of the battery 40 and the inverter 20 on the connection line LC via the first charging path LA. The second external charging terminal TB is connected to a second contact point PB between the negative terminal of the battery 40 and the inverter 20 on the connection line LC via the second charging path LB.

[0040] The first release switch 32 is provided between the first contact PA on the connection line LC and the inverter 20, and the second release switch 33 is provided between the second contact PB on the connection line LC and the inverter 20. The first and second release switches 32 and 33 switch the connection state between the battery 40 and the rotating electrical machine 10. Also, the third release switch 34 is provided in the first charging path LA, and the fourth release switch 35 is provided in the second charging path LB. The third and fourth release switches 34 and 35 switch the connection state between the battery 40 and the off-vehicle charger 200.

[0041] The BMU 50 is a control device composed of a CPU, a ROM, a RAM, an input / output interface, etc. The BMU 50 calculates the capacity of the lithium-ion battery 41 (battery 40) based on the detection values input from each sensor. The BMU 50 calculates the SOH (State Of Health) indicating the degradation state of the lithium-ion battery 41 based on the calculated capacity of the lithium-ion battery 41. SOH [%] is represented by (current full capacity / new product full capacity) × 100 of the lithium-ion battery 41, and represents the ratio of the current full capacity of the lithium-ion battery 41 to the full capacity of the new lithium-ion battery 41. The BMU 50 includes a determination unit 52 and an estimation unit 53 described later. Note that the determination unit 52 and the estimation unit 53 constitute a remaining battery amount estimation device.

[0042] Also, the BMU 50 is connected to the first to fourth release switches 32 to 35, and switches the connection states of the first to fourth release switches 32 to 35 based on the capacity of the battery 40. Further, the BMU 50 is communicably connected to the travel control ECU 70 via the in-vehicle network interface 51, and outputs a command to control the rotating electrical machine 10 to the travel control ECU 70 based on the capacity of the battery 40. The travel control ECU 70 controls the inverter 20 to control the control amount of the rotating electrical machine 10 according to the command from the BMU 50. The control amount is, for example, torque.

[0043] By the way, as a method for calculating the capacity of the lithium-ion battery 41 (battery 40), a method using an SOC-OCV characteristic showing the correlation between the state of charge (SOC) indicating the state of charge of the lithium-ion battery 41 and the open circuit voltage (OCV) is known. The open circuit voltage OCV is the voltage between both terminals in a state where no load is applied to the lithium-ion battery 41 (a state where the circuit of the lithium-ion battery 41 is open). Note that the SOC (charge rate) [%] is expressed as (remaining capacity / full capacity) × 100 of the lithium-ion battery 41, and represents the ratio of the remaining capacity to the full capacity of the lithium-ion battery 41.

[0044] In this embodiment, as the lithium-ion battery 41 constituting the battery 40, one using lithium iron phosphate as the positive electrode active material and graphite (graphite) as the negative electrode active material is used. In the lithium-ion battery 41 using these active materials, the open circuit voltage OCV is stable in a wide range of SOC (or battery capacity), and has a region where the change in the open circuit voltage OCV accompanying the change in SOC is small, that is, a plateau region PR. In the plateau region PR (low change rate portion), the change rate of the open circuit voltage OCV (predetermined parameter) with respect to the capacity (remaining amount) of the lithium-ion battery 41 is equal to or less than a predetermined change rate. In the plateau region PR, it is difficult to calculate the SOC of the lithium-ion battery 41 and calculate the capacity using the SOC-OCV characteristic.

[0045] FIG. 2 is a graph showing the relationship between the capacity Q and the OCV of the lithium-ion battery 41 before and after deterioration. Between the plateau region PR1 and the plateau regions PR21 and PR22, the rate of change Rv of the open circuit voltage OCV with respect to the capacity of the lithium-ion battery 41 becomes larger than the rate of change Rv in the plateau regions PR1, PR21, and PR22. Specifically, between the plateau region PR1 and the plateau regions PR21 and PR22, the rate of change Rv takes a maximum value at the capacity A (see the broken line in FIG. 3). Further, the capacity A (specific remaining amount) of the lithium-ion battery 41 when the rate of change Rv takes the maximum value is substantially the same for the initial lithium-ion battery 41 and the deteriorated lithium-ion battery 41. For this reason, when the rate of change Rv takes the maximum value, the capacity of the lithium-ion battery 41 at that time can be estimated to be the capacity A. The capacity A is a capacity determined by the structural change of the negative electrode of the lithium-ion battery 41, and the details thereof will be described later.

[0046] Here, the inventor of the present application noticed that when the discharge amount increases after the capacity of the lithium-ion battery 41 becomes less than the capacity A during discharge, the capacity at which the rate of change Rv of the OCV takes the maximum value (shows a specific change) deviates from the capacity A during charging. FIG. 3 is a graph showing a mode in which the maximum value of the rate of change Rv corresponding to the capacity A deviates. The figure shows an example in which the lithium-ion battery 41 is discharged to near the capacity of 0 and then charged, and the capacity at which the rate of change Rv takes the maximum value deviates to the low-capacity side from the capacity A. In this case, if the capacity of the lithium-ion battery 41 when the rate of change Rv takes the maximum value is estimated to be the capacity A, the estimated capacity will deviate from the correct capacity.

[0047] FIG. 4 is a schematic diagram showing the capacity unevenness of the lithium-ion battery 41. As shown on the left side of the figure, when the lithium-ion battery 41 is left for a long time without being charged or discharged (when the charge and discharge rate is lower than a predetermined rate), the internal capacity of the lithium-ion battery 41 becomes uniform.

[0048] Subsequently, when the lithium-ion battery 41 is charged and discharged, as shown in the figure, a portion with a high capacity and a portion with a low capacity occur inside the lithium-ion battery 41 (capacity unevenness occurs). The reason for the occurrence of capacity unevenness is that there are portions with high resistance and low resistance inside the lithium-ion battery 41, and when charging and discharging are performed, the current concentrates in the portion with low resistance.

[0049] After that, when the lithium-ion battery 41 is left without being charged and discharged, as shown on the right side of the figure, the capacity inside the lithium-ion battery 41 becomes uniform as the elapsed time becomes longer.

[0050] FIG. 5 is a graph showing regions where capacity unevenness is likely to occur. During charging and discharging, the higher the change rate Rv of the OCV with respect to the capacity of the lithium-ion battery 41, the easier it is for the capacity unevenness to be eliminated, and the lower the change rate Rv, the more difficult it is for the capacity unevenness to be eliminated. That is, during charging and discharging, when the change rate Rv of the OCV with respect to the capacity of the lithium-ion battery 41 exceeds a high change rate portion higher than a predetermined change rate, the capacity unevenness is easily eliminated. On the contrary, in a low change rate portion where the change rate Rv of the OCV with respect to the capacity of the lithium-ion battery 41 is equal to or lower than the predetermined change rate, it is difficult for the capacity unevenness to be eliminated. For this reason, the longer the discharge in the plateau regions PR1 and PR2 shown by hatching in the figure, the more likely it is for capacity unevenness to occur. And in a state where capacity unevenness has occurred in the lithium-ion battery 41, the present inventors have focused on the fact that the capacity when the change rate Rv reaches a maximum value during charging deviates from capacity A.

[0051] FIG. 6 is a schematic diagram showing the relationship between the state of the lithium-ion battery 41 and the detection accuracy of capacity A. Note that this figure is a schematic representation (image diagram) of the state of the lithium-ion battery 41 and does not necessarily accurately represent the state of the lithium-ion battery 41. If capacity unevenness occurs in the lithium-ion battery 41 at the start of charging, the detection error of capacity A becomes large. Also, the greater the deviation of the capacity at the start of charging from capacity A, the greater the detection error of capacity A. For this reason, when charging is performed from a capacity close to capacity A in a state where no capacity unevenness has occurred in the lithium-ion battery 41, capacity A can be detected with high accuracy.

[0052] FIG. 7 is a schematic diagram showing a discharge state suitable for detecting the capacity A. Note that this figure is a schematic representation (image diagram) of the state of the lithium-ion battery 41, and does not necessarily accurately represent the state of the lithium-ion battery 41. When, during discharge, the change rate Rv of the OCV with respect to the capacity of the lithium-ion battery 41 exceeds a high OCV change portion (high change rate portion), the capacity unevenness is likely to be eliminated. Therefore, when the discharge amount from the capacity A is small, the capacity unevenness is less likely to occur, and a state suitable for detecting the capacity A during charging is obtained.

[0053] FIG. 8 is a diagram showing the detection conditions for the capacity A. Based on the above, the BMU 50 detects (estimates) the capacity A during charging when the following three conditions are satisfied.

[0054] Condition 1. The capacity of the lithium-ion battery 41 at the start of discharge is on the higher capacity side than the capacity A. Condition 2. The discharge amount until the end of discharge is small. Condition 3. The capacity of the lithium-ion battery 41 at the end of discharge is on the lower capacity side than the capacity A.

[0055] FIG. 9 is a flowchart showing the procedure for capacity A detection and SOH update. This series of processes is executed by the BMU 50.

[0056] First, it is determined whether the OCV can be obtained (S10). Specifically, it is determined that the OCV can be obtained when the electric vehicle is in a stationary state at the start of running or charging, and it is determined that the OCV cannot be obtained in other cases. In this determination, when it is determined that the OCV cannot be obtained (S10: NO), the current and time are integrated to calculate the current integrated value (S18).

[0057] Subsequently, it is determined whether the integrated current value is greater than a predetermined value a (S19). As shown in FIG. 14, the predetermined value a is set to be equal to or less than the capacitance corresponding to the width of the plateau region PR1. For example, half or two-thirds of the capacitance corresponding to the width of the plateau region PR1 can be adopted. In this determination, if it is determined that the integrated current value is greater than the predetermined value a (S19: YES), the capacitance A detection permission flag is set to OFF (S20). The capacitance A detection permission flag is a flag that is set to ON when the detection of capacitance A is permitted and set to OFF when it is not permitted. On the other hand, if it is determined in this determination that the integrated current value is not greater than the predetermined value a (S19: NO), the process proceeds to the process of S21.

[0058] Also, in the determination of S10, if it is determined that the OCV can be acquired (S10: YES), the current OCV, i.e., OCV(n), is detected (calculated) by the voltage sensor 30 in a state where no current is flowing through the battery 40. As shown in FIG. 10, during the running of the electric vehicle, the current and voltage can be detected, and the intercept of the voltage at current 0 can be used as the OCV. Also, as shown in FIG. 11, the product of the current and resistance of the lithium-ion battery 41 can be added to the voltage (CCV: Closed Circuit Voltage) detected by the voltage sensor 30 during the running of the electric vehicle to obtain the OCV.

[0059] Subsequently, the current capacitance region (n) is determined from the detected OCV(n) (S12).

[0060] As shown in FIG. 12, in the lithium-ion battery 41, lithium ions are occluded between the layers of the layered structure of graphite (graphite). In the lithium-ion battery 41, the stage of the negative electrode changes according to the number of interlayers in which lithium ions are not occluded, which exists between two interlayers in which lithium ions are occluded. Specifically, in stage 1, lithium ions are occluded in each interlayer of graphite. In stage 2, there is one interlayer in which lithium ions are not occluded between two interlayers in which lithium ions are occluded. In stage 3, there are two interlayers in which lithium ions are not occluded between two interlayers in which lithium ions are occluded. And in stage 4, there are three interlayers in which lithium ions are not occluded between two interlayers in which lithium ions are occluded.

[0061] FIG. 13 is a graph showing the relationship between the stage of the negative electrode, the OCV, and the capacity A. The capacity A at which the OCV changes greatly (the change rate of the OCV takes a maximum value) corresponds to the region where stage 3 and stage 2 coexist and the region where stage 2 and stage 1 coexist. A predetermined voltage Vj is set between the OCV corresponding to the region where stage 3 and stage 2 coexist and the OCV corresponding to the region where stage 2 and stage 1 coexist, as shown by hatching.

[0062] Returning to FIG. 9, in the process of S12, when OCV(n) is higher than the predetermined voltage Vj, it is determined that the current capacity region (n) is larger than the capacity A, and when OCV(n) is lower than the predetermined voltage Vj, it is determined that the current capacity region (n) is smaller than the capacity A.

[0063] Subsequently, it is determined whether the current capacity region (n) is equal to or greater than the capacity A (S13). In this determination, when it is determined that the current capacity region (n) is equal to or greater than the capacity A (S13: YES), the current integration value, which is the integrated value of the current and time, is reset to 0 (S14). On the other hand, in this determination, when it is determined that the current capacity region (n) is less than the capacity A (S13: NO), the process proceeds to the process of S15.

[0064] Next, it is determined whether the current capacity area (n) is less than or equal to the capacity A and whether the current is the charging start timing (S15). Specifically, when charging is started by the off-vehicle charger 200, it is determined that the current is the charging start timing. In this determination, if an affirmative determination is made (S15: YES), it is determined whether the current integrated value is less than or equal to a predetermined value a (S16). The predetermined value a is common to the determination in S19. Note that the period from when the current integrated value is reset in the process of S14 until the start of charging corresponds to a predetermined period.

[0065] In the determination of S16, if it is determined that the current integrated value is less than or equal to the predetermined value a (S16: YES), the capacity A detection permission flag is turned on (S17). As shown in FIG. 15, the current integrated value increases after being reset in the process of S14, and accordingly, the voltage of the lithium-ion battery 41 increases. The voltage of the lithium-ion battery 41 may be the OCV or the CCV. Note that the conditions of S15 and S16 correspond to predetermined conditions.

[0066] On the other hand, in the determination of S15, if a negative determination is made (S15: NO), the process proceeds to the process of S21.

[0067] Next, it is determined whether the capacity A detection permission flag is ON, the battery 40 is being charged, and it is the detectable timing of the capacity A (S21). Specifically, as shown in FIG. 16, when the differential value based on the current integrated value of the voltage (the rate of change of the voltage with respect to the capacity of the lithium-ion battery 41, a predetermined parameter) reaches a maximum value, it is determined that it is the detectable timing of the capacity A.

[0068] In the determination of S21, if an affirmative determination is made (S21: YES), when the differential value of the voltage reaches a maximum value, it is detected (estimated) that the capacity of the lithium-ion battery 41 at that time is capacity A (S22). That is, when the differential value of the voltage changes peculiarly during the charging of the lithium-ion battery 41, the capacity of the lithium-ion battery 41 at that time is estimated based on capacity A. Subsequently, the current capacity of the lithium-ion battery 41 is updated to capacity A (S23). On the other hand, if a negative determination is made in the determination of S21 (S21: NO), the process proceeds to the process of S24.

[0069] Subsequently, it is determined whether the capacity A detection permission flag is ON and whether the charging is completed (S24). If an affirmative determination is made in this determination (S24: YES), the SOH is calculated and the SOH is updated (S25). Specifically, the current capacity of the lithium-ion battery 41 is updated to capacity A, and then the current capacity at the end of charging is calculated by adding the current integration value of the current. The current SOH is calculated by the formula SOH [%] = (current full capacity of the lithium-ion battery 41 / full capacity of a new product) × 100. Then, the SOH on the left side of the source is updated to the calculated SOH. After that, this series of processes is terminated (END). Note that this series of processes is executed for each lithium-ion battery 41. Also, the processes of S12 to S17 correspond to the processes as a determination unit, and the processes of S21 to S23 correspond to the processes as an estimation unit.

[0070] FIG. 17 is a time chart showing the mode of capacity A detection and SOH update.

[0071] Before time t11, the electric vehicle is in a stationary state, the capacity region is indefinite, the capacity A detection permission flag is OFF, and the capacity of the lithium-ion battery 41 is more than capacity A.

[0072] At time t11, when the electric vehicle starts running from a stationary state, OCV acquisition is permitted. Then, the OCV of the lithium-ion battery 41 is acquired, and it is determined that the capacity region is equal to or greater than capacity A. Note that the capacity region is the capacity region (n) at this point in time, but when the capacity region is determined next (at time t12), it becomes the previous capacity region (n - 1). Also, the current integration value is reset to 0. Note that the current integration value becomes a positive value during discharge and a negative value during charging.

[0073] Between times t11 and t12, the electric vehicle is in a running state, the current integration value increases, and the capacity of the lithium-ion battery 41 decreases. Note that when regenerative power generation is performed by the rotating electric machine 10, the capacity of the lithium-ion battery 41 increases. Thereafter, the electric vehicle becomes stationary.

[0074] At time t12, when charging of the battery 40 starts from the stationary state of the electric vehicle, OCV acquisition is permitted. Then, the OCV of the lithium-ion battery 41 is acquired, and it is determined that the current capacity region (n) is equal to or less than capacity A. Further, it is determined that the current integration value is equal to or less than a predetermined value a, and the capacity A detection permission flag is turned ON.

[0075] Between times t12 and t13, when the battery 40 is being charged and the differential value of the voltage of the lithium-ion battery 41 reaches a maximum value, it is determined that it is the timing at which capacity A can be detected. Then, capacity A is detected, and the capacity of the lithium-ion battery 41 at that time is updated to capacity A.

[0076] At time t13, charging is completed, and the calculation and update of the SOH are executed.

[0077] The embodiment described in detail above has the following advantages.

[0078] · When the present inventors discharge the lithium ion battery 41, if the discharge amount increases after the capacity becomes less than capacity A, they focused on the fact that the capacity at the time when the change rate Rv (predetermined parameter) of the OCV changes peculiarly during charging deviates from capacity A. In this regard, the determination unit 52 determines that a predetermined condition is satisfied, that is, when discharging the lithium ion battery 41 from a state where the capacity is greater than capacity A to a state where it is less, the change amount of the capacity (hereinafter referred to as "capacity change amount during discharge before charging") in a predetermined period until the start of charging of the lithium ion battery 41 is equal to or less than a predetermined value a. Therefore, the determination unit 52 can determine that the discharge amount does not increase after the capacity of the lithium ion battery 41 becomes less than capacity A based on the change amount of the capacity during discharge in a predetermined period until the start of charging of the lithium ion battery 41.

[0079] · When the estimation unit 53 determines that the predetermined condition is satisfied by the determination unit 52, when the change rate Rv of the OCV changes peculiarly during charging of the lithium ion battery 41, it estimates the capacity of the lithium ion battery 41 at that time based on capacity A. Therefore, it is possible to estimate the capacity at the time when the change rate Rv of the OCV changes peculiarly during charging in a state where the discharge amount does not increase after the capacity of the lithium ion battery 41 becomes less than capacity A, based on capacity A. Thus, the accuracy of estimating the capacity of the lithium ion battery 41 can be improved. Note that it is also possible to estimate the capacity of the lithium ion battery 41 at the time when the change rate Rv of the OCV changes peculiarly during charging as capacity A corrected based on the discharge amount after the capacity of the lithium ion battery 41 becomes less than capacity A when discharging the lithium ion battery 41.

[0080] · It is possible to determine that the discharge amount does not increase after the capacity of the lithium ion battery 41 becomes less than capacity A by using the current integrated value (capacity of the lithium ion battery 41) represented by the product of current and time.

[0081] ·The predetermined value a is set to be equal to or less than the capacity of the lithium-ion battery 41 corresponding to the width of the plateau region PR1 (low change rate portion) where the change rate Rv of the OCV with respect to the capacity of the lithium-ion battery 41 is equal to or less than a predetermined change rate, and the capacity of the lithium-ion battery 41 exists in a range where the capacity of the lithium-ion battery 41 is less than the capacity A. For this reason, when discharging the lithium-ion battery 41, the capacity of the lithium-ion battery 41 can be estimated based on the capacity A in a state where the discharge amount after the capacity becomes less than the capacity A is equal to or less than the capacity of the lithium-ion battery 41 corresponding to the width of the plateau region PR1. Therefore, it is possible to suppress the deviation of the capacity when the change rate Rv of the OCV changes peculiarly during charging from the capacity A, and it is possible to suppress the decrease in the accuracy of estimating (detecting) the capacity of the lithium-ion battery 41.

[0082] ·The predetermined parameter is the open circuit voltage OCV representing the voltage between both terminals in a state where no load is applied to the lithium-ion battery 41. When the open circuit voltage OCV is higher than a predetermined voltage Vj, the determination unit 52 determines that the capacity of the lithium-ion battery 41 is greater than the capacity A, and when the open circuit voltage OCV is lower than the predetermined voltage Vj, the determination unit 52 determines that the capacity of the lithium-ion battery 41 is less than the capacity A. According to such a configuration, it is possible to easily determine whether the capacity of the lithium-ion battery 41 is greater than or less than the capacity A by using the open circuit voltage OCV.

[0083] · The lithium-ion battery 41 is a lithium-ion battery having a negative electrode containing graphite (carbon), and lithium ions are occluded between the layers of the layered structure of graphite. It changes to stage 1 in which lithium ions are occluded between the layers, stage 2 in which there is one layer without lithium ions occluded between two layers with lithium ions occluded, stage 3 in which there are two layers without lithium ions occluded between two layers with lithium ions occluded, and stage 4 in which there are three layers without lithium ions occluded between two layers with lithium ions occluded. The predetermined voltage Vj is set between the open circuit voltage OCV corresponding to the region where stage 3 and stage 2 coexist and the open circuit voltage OCV corresponding to the region where stage 2 and stage 1 coexist. According to such a configuration, it is possible to accurately determine whether the capacity of the lithium-ion battery 41 is larger or smaller than the capacity A by using the relationship between the stage of the negative electrode of the lithium-ion battery 41, the open circuit voltage OCV, and the capacity A.

[0084] · The capacity A is the capacity corresponding to the region where stage 3 and stage 2 coexist and the region where stage 2 and stage 1 coexist. According to the above configuration, the capacity A can be accurately defined based on the stage of the negative electrode of the lithium-ion battery 41.

[0085] (Second Embodiment) Hereinafter, the second embodiment will be described centering on the differences from the first embodiment. For the parts identical to those of the first embodiment, the description will be omitted by attaching the same reference numerals.

[0086] As shown in FIG. 18, the inventors of the present application have noticed that there are plateau regions PR1 and PR2 (low change rate portions) in which the change rate Rv of the open circuit voltage OCV with respect to the capacity of the lithium-ion battery 41 is equal to or less than a predetermined change rate on the side where the capacity of the lithium-ion battery 41 is less and on the side where it is more, sandwiching the capacity A.

[0087] Therefore, a predetermined voltage Vj is set between the open circuit voltages OCV corresponding to the plateau regions PR1 and PR2, respectively. Then, using this predetermined voltage Vj, the determination in S12 of FIG. 9 is executed. According to such a configuration, it is possible to accurately determine whether the capacity of the lithium-ion battery 41 is more or less than the capacity A using the open circuit voltage OCV.

[0088] And the capacity A is set as the capacity corresponding to between the plateau regions PR1 and PR2. According to the above configuration, the capacity A can be accurately defined based on the plateau regions PR1 and PR2. Incidentally, by discharging the lithium-ion battery 41 to a capacity of 0 from when the voltage change rate Rv reaches a maximum value, the capacity A (specific remaining amount) corresponding to when the voltage change rate Rv reaches a maximum value can also be defined.

[0089] (Third Embodiment) Hereinafter, the third embodiment will be described centering on the differences from the first embodiment. For the parts identical to those of the first embodiment, the description will be omitted by attaching the same reference numerals.

[0090] As shown in FIG. 19, the present inventors have noted that the change rate (slope) of the real part Zre (impedance) of the impedance of the lithium-ion battery 41 with respect to the capacity of the lithium-ion battery 41 changes greatly when the capacity of the lithium-ion battery 41 crosses the capacity A. Incidentally, the impedance can be calculated based on the amplitude of the alternating voltage and the amplitude of the alternating current.

[0091] Therefore, as a predetermined parameter correlated with the capacity (remaining amount) of the lithium-ion battery 41, the real part Zre of the impedance of the lithium-ion battery 41 is adopted. And the determination unit 52 determines that a specific change has occurred in the predetermined parameter during the charging of the lithium-ion battery 41 based on the change rate of the real part Zre of the impedance with respect to the capacity of the lithium-ion battery 41. Specifically, as shown in FIG. 20, when the change amount of the differential value of the current integration value of the real part Zre of the impedance is equal to or greater than a predetermined value x, it is determined that a specific change has occurred in the predetermined parameter. And in the process of S22 in FIG. 9, when the change amount of the differential value of the real part Zre of the impedance becomes equal to or greater than the predetermined value x, it is detected (estimated) that the capacity of the lithium-ion battery 41 at that time is the capacity A. According to such a configuration, it is possible to accurately determine that a specific change has occurred in the predetermined parameter during the charging of the lithium-ion battery 41 by using the change rate of the real part Zre of the impedance with respect to the capacity of the lithium-ion battery 41.

[0092] Note that instead of the real part Zre of the impedance of the lithium-ion battery 41, the imaginary part Zim of the impedance, the absolute value of the impedance, or the phase of the impedance can also be used.

[0093] Note that the first to third embodiments can also be implemented by making the following changes. For parts identical to those in the first to third embodiments, the description will be omitted by attaching the same reference numerals.

[0094] · The unevenness in capacity is more easily eliminated as the temperature of the lithium-ion battery 41 is higher, and is more difficult to eliminate as the temperature of the lithium-ion battery 41 is lower. Therefore, in the processes of S16 and S19 in FIG. 9, the predetermined value a for determining the magnitude of the current integration value may be set to a smaller value (less change amount) as the temperature of the lithium-ion battery 41 is lower. Specifically, as shown in FIG. 21, between the process of S15 and the process of S16, a process of S15A for acquiring the temperature of the lithium-ion battery 41 and a process of S15B for setting the predetermined value a based on the acquired temperature are inserted. The predetermined value a is set based on the table shown in FIG. 22. According to such a configuration, it can be required that the smaller the temperature of the lithium-ion battery 41 is, the smaller the current integration value in the pre-charge discharge is (the smaller the capacity change amount is). Therefore, even when the temperature of the lithium-ion battery 41 is low, it is possible to suppress a decrease in the accuracy of detecting (estimating) the capacity of the lithium-ion battery 41. Note that the temperature of the lithium-ion battery 41 may be measured by a temperature sensor or the like attached to the lithium-ion battery 41, or the ambient temperature measured by an ambient temperature sensor may be used as the temperature of the lithium-ion battery 41. Also, the capacity of the lithium-ion battery 41 when the change rate of the voltage or the change rate of the impedance (predetermined parameter) has a specific change can be estimated as the corrected capacity A based on the temperature of the lithium-ion battery 41.

[0095] · The longer the time the lithium-ion battery 41 is maintained in a state where the discharge rate is lower than the predetermined discharge rate (including the state where the lithium-ion battery 41 is not discharged), the easier it is to eliminate the capacity unevenness, and the shorter the time it is maintained in a state where the discharge rate is lower than the predetermined discharge rate, the more difficult it is to eliminate. Therefore, the predetermined value a may be set to a smaller value (a smaller change amount) as the time (hereinafter referred to as "low discharge time") that the discharge rate is maintained lower than the predetermined discharge rate until the charging of the lithium-ion battery 41 starts is shorter. According to such a configuration, it can be required that the smaller the low discharge time until the charging of the lithium-ion battery 41 starts, the smaller the current integrated value (the smaller the capacity change amount) in the pre-charge discharge. Therefore, even when the low discharge time until the charging of the lithium-ion battery 41 starts is short, it is possible to suppress a decrease in the accuracy of detecting (estimating) the capacity of the lithium-ion battery 41. Also, the capacity of the lithium-ion battery 41 when the change rate of the voltage or the change rate of the impedance (predetermined parameter) makes a specific change can be estimated as the corrected capacity A based on the low discharge time.

[0096] · When determining whether the current integrated value (the change amount of the capacity) in the predetermined period until the charging of the lithium-ion battery 41 starts is equal to or less than the predetermined value a (predetermined change amount), the predetermined period can also be changed as follows. As shown in FIG. 23, from an arbitrary point in time from the time t31 immediately before the capacity of the lithium-ion battery 41 falls below the capacity A to the time t32 immediately after it has fallen below the capacity A, the period until the start of charging can be set as the predetermined period. Even with such a configuration, it is possible to determine with a certain degree of accuracy that the discharge amount after the capacity of the lithium-ion battery 41 becomes less than the capacity A when discharging the lithium-ion battery 41 is not large.

[0097] · As the remaining amount of the lithium-ion battery 41, SOC can also be used instead of the current integrated value. Then, it is possible to determine that the change amount of the remaining amount within a predetermined period until the charging of the lithium-ion battery 41 starts is equal to or less than a predetermined change amount using the SOC. Further, when the change rate Rv (predetermined parameter) of the voltage with respect to the SOC reaches a maximum value (shows a specific change), the remaining amount of the lithium-ion battery 41 at that time can be estimated as a specific SOC (specific remaining amount). The specific SOC is the SOC corresponding to the capacity A.

[0098] · As the lithium-ion battery 41, a ternary lithium-ion battery using a lithium-containing metal oxide containing elements of Co, Mn, and Ni as the positive electrode active material can also be adopted.

Explanation of Signs

[0099] 40… Battery, 41… Lithium-ion battery, 50… BMU, 52… Determination unit, 53… Estimation unit.

Claims

1. A battery remaining capacity estimating device (50) for estimating the remaining capacity of a secondary battery (41) based on a specific remaining capacity of the secondary battery when a differential value obtained by integrating the current of the open circuit voltage of the secondary battery as a predetermined parameter correlated with the remaining capacity of the secondary battery reaches a maximum value, or when a change amount of a differential value obtained by integrating the current of the real part (Zre) of the impedance of the secondary battery as the predetermined parameter is equal to or greater than a predetermined value, a determination unit (52) that determines that a predetermined condition is satisfied, the predetermined condition being that when the remaining capacity of the secondary battery discharges from a state where the remaining capacity is greater than the specific remaining capacity to a state where the remaining capacity is less than the specific remaining capacity, a change amount of the remaining capacity in a predetermined period until the start of charging of the secondary battery is equal to or less than a predetermined change amount; and an estimation unit (53) that, when it is determined by the determination unit that the predetermined condition is satisfied, estimates the remaining capacity of the secondary battery at that time based on the specific remaining capacity when the differential value obtained by integrating the current of the open circuit voltage reaches a maximum value during charging of the secondary battery, or when the change amount of the differential value obtained by integrating the current of the real part of the impedance of the secondary battery is equal to or greater than a predetermined value. A battery remaining capacity estimating device comprising the above.

2. The battery remaining capacity estimating device according to claim 1, wherein the remaining capacity of the secondary battery is a remaining capacity of the secondary battery represented by a product of current and time, or a charging rate representing a ratio of the remaining capacity to the full capacity of the secondary battery.

3. The battery remaining capacity estimating device according to claim 1 or 2, wherein the predetermined change amount is set to be equal to or less than the remaining capacity of the secondary battery corresponding to a width of a low change rate portion (PR1) where a change rate of the open circuit voltage with respect to the remaining capacity of the secondary battery is equal to or less than a predetermined change rate, and the remaining capacity of the secondary battery exists in a range where the remaining capacity of the secondary battery is less than the specific remaining capacity.

4. The battery remaining capacity estimating device according to claim 1 or 2, wherein the predetermined change amount is set to be smaller as the temperature of the secondary battery is lower.

5. The battery remaining capacity estimating device according to claim 1 or 2, wherein the predetermined change amount is set to be smaller as a time during which a discharge rate is maintained lower than a predetermined discharge rate until the start of charging of the secondary battery is shorter.

6. The predetermined parameter is an open circuit voltage representing a voltage between both terminals in a state where no load is applied to the secondary battery. The determination unit determines that the remaining amount of the secondary battery is greater than the specific remaining amount when the open-circuit voltage is higher than a predetermined voltage, and determines that the remaining amount of the secondary battery is less than the specific remaining amount when the open-circuit voltage is lower than the predetermined voltage. The battery remaining amount estimation device according to claim 1 or 2.

7. In the secondary battery, there are two low change rate portions (PR1, PR2) where the change rate of the open-circuit voltage with respect to the remaining amount of the secondary battery is equal to or less than a predetermined change rate. The predetermined voltage is set between the open-circuit voltages respectively corresponding to the two low change rate portions. The battery remaining amount estimation device according to claim 6.

8. The specific remaining amount is the remaining amount corresponding to between the two low change rate portions. The battery remaining amount estimation device according to claim 7.

9. The secondary battery is a lithium-ion battery having a negative electrode containing graphite, and the lithium ions are occluded between the layers of the layered structure of the graphite. The lithium ions are occluded in stage 1 where the lithium ions are occluded in each layer, stage 2 where there is one layer without lithium ions occluded between two layers with lithium ions occluded, stage 3 where there are two layers without lithium ions occluded between two layers with lithium ions occluded, and stage 4 where there are three layers without lithium ions occluded between two layers with lithium ions occluded. The predetermined voltage is set between the open-circuit voltage corresponding to the region where stage 3 and stage 2 coexist and the open-circuit voltage corresponding to the region where stage 2 and stage 1 coexist. The battery remaining amount estimation device according to claim 6.

10. The specific remaining amount is the remaining amount corresponding to between the region where stage 3 and stage 2 coexist and the region where stage 2 and stage 1 coexist. The battery remaining amount estimation device according to claim 9.

11. The secondary battery is a lithium-ion battery having a positive electrode containing lithium, iron, and phosphorus. The battery remaining amount estimation device according to claim 6.

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