Battery level 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 change rate of voltage of the secondary battery, in which a decrease in the accuracy of estimating the remaining level of the secondary battery is suppressed.SOLUTION: A remaining battery level estimation device (50) estimates the remaining level of a secondary battery on the basis of a charge parameter correlated to the charge time of a secondary battery (41) and a change rate of voltage of the secondary battery to the charge parameter. The remaining battery level estimation device comprises: a determination unit (52) that determines that a prescribed condition is satisfied that a change amount of the charge parameter from charging of the secondary battery starts to when a voltage change rate reaches a maximum value is smaller than or equal to a prescribed change amount; and an estimation unit (53) that, when it is determined by the determination unit that the prescribed condition is satisfied, estimates the remaining level corresponding to between two maximum values that the voltage change rate has taken during charging of the secondary battery, as the remaining level of the secondary battery.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a device for estimating the remaining capacity of a secondary battery. [Background technology]

[0002] Conventionally, there is a device that, when a singular point appears where the amount of change (rate of change) in the voltage of a secondary battery detected by a voltage detection unit becomes a maximum value, estimates the remaining capacity of the secondary battery at that time as the remaining capacity corresponding to the singular point (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-167457 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, the inventors of the present application have noticed that when detecting the above-mentioned singularity during charging of a secondary battery, depending on the charging state of the secondary battery until the singularity is detected, the remaining capacity (remaining amount) at the time the singularity appears may deviate from the remaining capacity corresponding to the singularity.

[0005] The present invention has been made to solve the above-mentioned problems, and its main objective is to prevent a decrease in the accuracy of estimating the remaining charge of a secondary battery in a battery remaining charge estimation device that estimates the remaining charge of a secondary battery based on the rate of change of the voltage of the secondary battery. [Means for solving the problem]

[0006] The first means for solving the above problem is A battery remaining capacity estimation device (50) that estimates a remaining capacity of a secondary battery (41) based on a charging parameter that correlates with a charging time of the secondary battery (41) and a rate of change of a voltage of the secondary battery with respect to the charging parameter, a determination unit (52) that determines whether a predetermined condition is satisfied, that is, an amount of change in the charging parameter from when charging of the secondary battery is started until the rate of change in the voltage reaches a maximum value is equal to or smaller than a predetermined amount of change; an estimation unit (53) that estimates a remaining capacity of the secondary battery that corresponds to a value between two minimum values ​​of the rate of change of the voltage during charging of the secondary battery when the determination unit determines that the predetermined condition is satisfied; and Equipped with.

[0007] According to the above configuration, the battery remaining capacity estimation device estimates the remaining capacity of the secondary battery based on a charging parameter that correlates with a charging time of the secondary battery and a rate of change of the voltage of the secondary battery with respect to the charging parameter. In detail, as described in Patent Document 1, the remaining capacity of the secondary battery can be estimated based on a specific remaining capacity, which is the remaining capacity of the secondary battery when the rate of change of the voltage of the secondary battery with respect to the charging parameter takes a maximum value.

[0008] Here, the inventors of the present application have noticed that when the amount of change in the charging parameter from the start of charging until the rate of change in voltage reaches its maximum value (hereinafter referred to as "amount of change in the charging parameter from the start of charging") increases, the remaining charge at which the rate of change in voltage reaches its maximum value during charging deviates from a specific remaining charge. In this regard, the determination unit determines whether a predetermined condition is satisfied, that is, the amount of change in the charging parameter from the start of charging of the secondary battery until the rate of change in the voltage reaches its maximum value is equal to or less than a predetermined amount of change. Therefore, the determination unit can determine that the amount of change in the charging parameter from the start of charging is not large, based on the amount of change in the charging parameter from the start of charging until the rate of change in voltage reaches its maximum value.

[0009] When the determination unit determines that the predetermined condition is satisfied, the estimation unit estimates the remaining capacity of the secondary battery to be the remaining capacity between two minimum values ​​of the rate of change of the voltage during charging. A maximum value exists between the two minimum values ​​of the rate of change of the voltage during charging, and the remaining capacity between the two minimum values ​​is close to a specific remaining capacity corresponding to the maximum value. Therefore, when the amount of change in the charging parameters since the start of charging is not large, a remaining capacity close to the specific remaining capacity can be estimated as the remaining capacity of the secondary battery. This makes it possible to suppress a decrease in accuracy in estimating the remaining capacity of the secondary battery.

[0010] Specifically, as in the second aspect, the charging parameter may be an integrated current value obtained by integrating the current and time. With this configuration, the charging parameter may be calculated using general-purpose elements such as a current sensor for detecting the current and a CPU clock.

[0011] Inside a secondary battery, there are parts with high resistance and parts with low resistance, and when charging and discharging, current concentrates in the parts with low resistance, resulting in parts with high and low capacity (amount of stored electricity) (capacity unevenness occurs). The inventors of the present application have noticed that when capacity unevenness occurs, the remaining capacity when the rate of change of voltage during charging reaches a maximum value deviates from the specified remaining capacity. Capacity unevenness is easily eliminated when the rate of change of voltage with respect to the charging parameters exceeds a high rate of change portion where the rate of change of voltage is higher than a predetermined rate of change, but is difficult to eliminate in a low rate of change portion where the rate of change of voltage with respect to the charging parameters is equal to or lower than the predetermined rate of change. For this reason, the longer charging is performed in the low rate of change portion, the more likely capacity unevenness occurs, and the more likely the remaining capacity when the rate of change of voltage during charging reaches a maximum value deviates from the specified remaining capacity.

[0012] In this regard, in the third aspect, the predetermined change amount is set to be smaller than the charging parameter corresponding to the width of the low rate of change portion with the lower voltage of the secondary battery, of two low rate of change portions where the rate of change of the voltage is equal to or smaller than the predetermined rate of change. Therefore, the remaining capacity of the secondary battery can be estimated in a state where the amount of change in the charging parameter from the start of charging is smaller than the charging parameter corresponding to the width of the low rate of change portion with the lower voltage. Therefore, it is possible to prevent the remaining capacity when the rate of change of the voltage takes a maximum value during charging from deviating from the specific remaining capacity, and to prevent a decrease in the accuracy of estimating the remaining capacity of the secondary battery.

[0013] The higher the temperature of the secondary battery, the easier it is to eliminate capacity unevenness, and the lower the temperature of the secondary battery, the harder it is to eliminate capacity unevenness.

[0014] In this regard, in the fourth aspect, the lower the temperature of the secondary battery, the smaller the predetermined change amount is set. With this configuration, it is possible to require, as the predetermined condition, that the lower the temperature of the secondary battery, the smaller the amount of change in the charging parameters from the start of charging. Therefore, even if the temperature of the secondary battery is low, it is possible to prevent a decrease in the accuracy of estimating the remaining capacity of the secondary battery.

[0015] Capacity unevenness is more likely to occur when the current used to charge the secondary battery is larger, and is less likely to occur when the current used to charge the secondary battery is smaller.

[0016] In this regard, in the fifth aspect, the predetermined change amount is set to a smaller amount as the current for charging the secondary battery is larger. With this configuration, it is possible to require, as the predetermined condition, that the amount of change in the charging parameters from the start of charging is smaller as the current for charging the secondary battery is larger. Therefore, even if the current for charging the secondary battery is large, it is possible to prevent a decrease in the accuracy of estimating the remaining capacity of the secondary battery.

[0017] In a sixth means, the judgment unit judges that the voltage change rate has reached a maximum value when, after charging of the secondary battery begins, the voltage change rate goes from less than a first predetermined value (K) to exceed a second predetermined value (B) that is greater than the first predetermined value, and then goes below a third predetermined value (C) that is smaller than the second predetermined value.

[0018] According to the above configuration, it is possible to easily determine whether the rate of change in voltage has reached a maximum value, based on a magnitude comparison between the rate of change in voltage and three predetermined values.

[0019] As described above, when the amount of change in the charging parameters from the start of charging increases, the remaining capacity when the rate of change in the voltage during charging reaches a maximum value deviates from the specific remaining capacity. However, even in such a case, it is preferable to make it possible to estimate the remaining capacity of the secondary battery while preventing problems from occurring, rather than making it impossible to estimate the remaining capacity of the secondary battery.

[0020] In this regard, in the seventh means, when the determination unit determines that the predetermined condition is not satisfied, the estimation unit estimates the remaining capacity of the secondary battery by subtracting the remaining capacity corresponding to the interval between two minimum values ​​of the rate of change of the voltage during charging of the secondary battery. With this configuration, when the predetermined condition is not satisfied, the remaining capacity of the secondary battery is estimated to be smaller than when the predetermined condition is satisfied. Therefore, even if there is a risk of a decrease in the accuracy of estimating the remaining capacity of the secondary battery, it is possible to estimate the remaining capacity of the secondary battery while preventing the remaining capacity of the battery from running out faster than expected.

[0021] When determining that the rate of change of the voltage of the secondary battery with respect to the charging parameters has reached a maximum value, if the current for charging the secondary battery is greater than a predetermined current, it becomes difficult to determine the maximum value. In response to this, the inventors of the present application have noticed that, during charging of the secondary battery, the rate of change of the temperature of the secondary battery with respect to the charging parameters and the rate of change of the impedance of the secondary battery with respect to the charging parameters change significantly at the charging parameters at which the rate of change of the voltage reaches a maximum value.

[0022] In this regard, in the eighth means, the determination unit determines that the rate of change of the voltage has reached a maximum value when the rate of change of the temperature of the secondary battery relative to the charging parameter or the rate of change of the impedance of the secondary battery relative to the charging parameter has changed beyond a predetermined degree. With this configuration, it is possible to determine that the rate of change of the voltage of the secondary battery relative to the charging parameter has reached a maximum value even if the current charging the secondary battery is greater than a predetermined current.

[0023] The rate of change of the voltage of the secondary battery with respect to the charging parameters due to the structural change of the negative electrode of the secondary battery reaches a maximum value between two low change rate portions where the rate of change of the voltage is equal to or lower than a predetermined change rate. Therefore, when the voltage of the secondary battery is lower than the low change rate portion with the lower voltage of the secondary battery, the rate of change of the voltage due to the structural change of the negative electrode of the secondary battery does not reach a maximum value.

[0024] In this regard, in a ninth aspect, the predetermined condition includes that the voltage of the secondary battery is higher than the minimum voltage of the secondary battery in the lower low change rate portion of two low change rate portions in which the voltage change rate is equal to or lower than a predetermined change rate. With this configuration, it is possible to prevent the maximum value of the voltage change rate caused by a structural change in the positive electrode of the secondary battery from being erroneously determined to be the maximum value of the voltage change rate caused by a structural change in the negative electrode.

[0025] The tenth means calculates the deterioration state of the secondary battery based on the remaining charge of the secondary battery estimated by the estimation unit, an integrated current value obtained by integrating the current and time from when the remaining charge of the secondary battery is estimated until the secondary battery satisfies a full charge condition, and the full capacity of a new secondary battery.

[0026] According to the above configuration, the current full capacity of the secondary battery can be calculated by adding an integrated current value, which is obtained by integrating the current and the time from when the remaining capacity of the secondary battery is estimated until the secondary battery satisfies a full charge condition, to the remaining capacity of the secondary battery estimated by the estimation unit. Then, the degradation state of the secondary battery can be calculated by calculating the ratio of the current full capacity of the secondary battery to the full capacity of a new secondary battery.

[0027] Specifically, as in an eleventh aspect, a configuration can be adopted in which the secondary battery is a lithium ion battery having a negative electrode containing graphite.

[0028] Specifically, as in a twelfth aspect, a configuration can be adopted in which the secondary battery is a lithium ion battery having a positive electrode containing lithium, iron, and phosphorus. [Brief description of the drawings]

[0029] [Figure 1] FIG. 2 is a circuit diagram showing the configuration of a battery control device. [Diagram 2] 1 is a graph showing the relationship between the initial and deteriorated battery capacity and the OCV. [Diagram 3] 13 is a graph showing a state in which the maximum value of the voltage change rate corresponding to the capacitance A shifts. [Figure 4] FIG. 1 is a schematic diagram showing capacity unevenness of a lithium-ion battery. [Diagram 5] Graph showing a charging state suitable for detecting capacity A. [Figure 6] 4 is a flowchart showing a procedure for detecting a capacitance A and calculating an SOH. [Figure 7] 1 is a graph showing voltage thresholds. [Figure 8] Schematic diagram showing each stage of a negative electrode. [Figure 9] Graph showing the relationship between negative electrode stage, OCV, and capacity A. [Figure 10] 1 is a graph showing the relationship between the capacity, OCV, and voltage threshold of a lithium-ion battery. [Figure 11]6 is a graph showing a manner in which a capacitance A is detected based on a maximum value of a differential value of a voltage. [Figure 12] 11 is a graph showing a predetermined value a for determining the magnitude of a current integrated value. [Figure 13] 6 is a graph showing a modified example of detection of the capacity of a lithium-ion battery; [Figure 14] 13 is a graph showing the relationship between the integrated current value and the real part of the impedance. [Figure 15] 13 is a flowchart showing a modified example of the procedure for detecting the capacitance A and calculating the SOH. [Figure 16] 6 is a graph showing a manner in which a capacitance A is detected based on a differential value of a real part of an impedance. [Figure 17] 4 is a table showing the relationship between battery temperature and predetermined value a. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] (First embodiment) Hereinafter, a first embodiment embodied in a battery control device mounted on an electric vehicle will be described with reference to the drawings.

[0031] 1, the battery control device 100 is a device that monitors the capacity and charge / discharge state of a battery 40. The battery 40 is a rechargeable lithium ion battery, and more specifically, is an assembled battery in which a plurality of lithium ion batteries 41 are connected in series. In this embodiment, the lithium ion battery 41 (secondary battery) uses lithium iron phosphate (containing lithium, iron, and phosphorus) as the positive electrode active material and graphite as the negative electrode active material.

[0032] The battery 40 is connected to the rotating electric machine 10 via the inverter 20. The rotating electric machine 10 inputs and outputs electric power to and from the battery 40, and during power running, it provides a propulsive force to the vehicle using electric power supplied from the battery 40, and during regeneration, it generates electric power using the deceleration energy of the vehicle and outputs the electric power to the battery 40.

[0033] 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.

[0034] The voltage sensor 30 detects the terminal voltage of each of the lithium ion batteries 41 constituting the battery 40, and detects the battery voltage VB which is the sum of these terminal voltages. The current sensor 31 is provided on the connection line LC which connects the battery 40 and the inverter 20, and detects the magnitude and direction of the charge / discharge current IS which flows in and out of the battery 40. The detection values ​​of each sensor are input to the BMU 50.

[0035] The battery 40 is configured to be connectable to an off-vehicle charger 200 via first and second external charging terminals TA, TB. The off-vehicle charger 200 is, for example, a DC quick charger. When the off-vehicle charger 200 is connected to the first and second external charging terminals TA, TB, the battery 40 is constant-current charged or constant-voltage charged by high-voltage DC power input from the off-vehicle charger 200.

[0036] The first and second external charging terminals TA, TB are connected to the connection line LC via first and second charging paths LA, LB. Specifically, the first external charging terminal TA is connected to a first contact PA on the connection line LC between the positive terminal of the battery 40 and the inverter 20 via the first charging path LA. The second external charging terminal TB is connected to a second contact PB on the connection line LC between the negative terminal of the battery 40 and the inverter 20 via the second charging path LB.

[0037] The first relay switch 32 is provided between a first contact PA on the connection line LC and the inverter 20, and the second relay switch 33 is provided between a second contact PB on the connection line LC and the inverter 20. The first and second relay switches 32, 33 switch the connection state between the battery 40 and the rotating electric machine 10. The third relay switch 34 is provided on the first charging path LA, and the fourth relay switch 35 is provided on the second charging path LB. The third and fourth relay switches 34, 35 switch the connection state between the battery 40 and the off-vehicle charger 200.

[0038] The BMU 50 is a control device that includes a CPU, a ROM, a RAM, and an input / output interface. 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 a SOH (State Of Health) indicating the deterioration state of the lithium ion battery 41 based on the calculated capacity of the lithium ion battery 41. The SOH [%] is expressed as (current full capacity / new full capacity)×100 of the lithium ion battery 41, and indicates the ratio of the current full capacity of the lithium ion battery 41 to the full capacity of a new lithium ion battery 41. The BMU 50 includes a determination unit 52 and an estimation unit 53, which will be described later. The determination unit 52 and the estimation unit 53 constitute a battery remaining capacity estimation device.

[0039] The BMU 50 is also connected to the first to fourth relay switches 32 to 35, and switches the connection states of the first to fourth relay switches 32 to 35 based on the capacity of the battery 40. The BMU 50 is also communicatively connected to the cruise control ECU 70 via an in-vehicle network interface 51, and outputs a command to the cruise control ECU 70 to control the rotating electric machine 10 based on the capacity of the battery 40. Based on the command from the BMU 50, the cruise control ECU 70 controls the inverter 20 so as to control the control amount of the rotating electric machine 10 in accordance with the command. The control amount is, for example, torque.

[0040] Incidentally, a method of calculating the capacity of the lithium ion battery 41 (battery 40) is known that uses the SOC-OCV characteristic, which indicates the correlation between the SOC (State Of Charge) and the open circuit voltage OCV (Open Circuit Voltage) of the lithium ion battery 41. The open circuit voltage OCV is the voltage between both terminals when no load is applied to the lithium ion battery 41 (when the circuit of the lithium ion battery 41 is open). The SOC (charging rate) [%] is expressed as (remaining capacity / full capacity)×100 of the lithium ion battery 41, and indicates the ratio of the remaining capacity to the full capacity of the lithium ion battery 41.

[0041] In this embodiment, the lithium ion battery 41 constituting the battery 40 uses lithium iron phosphate as the positive electrode active material and graphite as the negative electrode active material. In the lithium ion battery 41 using these active materials, the open circuit voltage OCV is stable over a wide range of SOC (or battery capacity), and has a region where the change in the open circuit voltage OCV with the change in SOC is small, that is, a plateau region PR. In the plateau region PR (low change rate portion), the rate of change 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 lower than a predetermined change rate. In the plateau region PR, it is difficult to calculate the SOC of the lithium ion battery 41 using the SOC-OCV characteristics and calculate the capacity.

[0042] FIG. 2 is a graph showing the relationship between the capacity Q and the OCV of the initial and deteriorated lithium ion battery 41. Between the plateau region PR1 and the plateau regions PR21 and PR22, the rate of change Rv of the open circuit voltage OCV (CCV: Closed Circuit Voltage) with respect to the capacity of the lithium ion battery 41 is larger than the rate of change Rv in the plateau regions PR1, PR21, and PR22. In detail, between the plateau region PR1 and the plateau regions PR21 and PR22, the rate of change Rv reaches a maximum value at the capacity A (see the broken line in FIG. 3). Furthermore, the capacity A (specific remaining capacity) of the lithium ion battery 41 when the rate of change Rv reaches a maximum value is almost the same for the initial lithium ion battery 41 and the deteriorated lithium ion battery 41. Therefore, when the rate of change Rv reaches a 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 a structural change in the negative electrode of the lithium ion battery 41, and the details of this will be described later.

[0043] Here, the inventor of the present application noticed that when the amount of change in capacity (charging parameter) from when the charging of the lithium ion battery 41 is started until the rate of change Rv of the OCV (CCV) reaches a maximum value increases, the capacity at which the rate of change Rv of the OCV reaches a maximum value (performs an unusual change) during charging deviates from the capacity A. FIG. 3 is a graph showing a manner in which the maximum value of the rate of change Rv corresponding to the capacity A shifts. The figure shows an example in which charging is started from a state in which the capacity of the lithium ion battery 41 is close to 0, and the capacity at which the rate of change Rv reaches a maximum value shifts from the capacity A to the low capacity side. In this case, if the capacity of the lithium ion battery 41 at which the rate of change Rv reaches a maximum value is estimated to be capacity A, the estimated capacity will deviate from the correct capacity.

[0044] 4 is a schematic diagram showing uneven capacity of lithium ion battery 41. As shown on the left side of the figure, when lithium ion battery 41 is left for a long time without being charged or discharged (a state in which the charge / discharge rate is lower than a predetermined rate), the internal capacity of lithium ion battery 41 becomes uniform.

[0045] Next, when lithium ion battery 41 is charged and discharged, as shown in the figure, high and low capacity areas are created inside lithium ion battery 41 (capacity unevenness occurs). The reason for the capacity unevenness is that lithium ion battery 41 has high and low resistance areas inside, and when it is charged and discharged, current is concentrated in the low resistance areas.

[0046] If the lithium ion battery 41 is subsequently left without being charged or discharged, the internal capacity of the lithium ion battery 41 becomes uniform as the time of leaving it is increased, as shown on the right side of the figure.

[0047] 5 is a graph showing a charging state suitable for detecting capacity A. When the amount of increase ΔQ (amount of change) in the capacity of the lithium ion battery 41 from the start of charging to capacity A is small, capacity unevenness is unlikely to occur, and the state is suitable for detecting capacity A during charging. The amount of increase ΔQ in the capacity of the lithium ion battery 41 can be calculated, for example, from a current integrated value (charging parameter) obtained by integrating current and time.

[0048] 6 is a flowchart showing a procedure for detecting the capacitance A and calculating the SOH. This series of processes is executed by the BMU 50.

[0049] First, it is determined whether charging of the lithium ion battery 41 (battery 40) has started (S10). If it is determined that charging of the lithium ion battery 41 has not started (S10: NO), the process of S10 is executed again.

[0050] On the other hand, when it is determined in the determination of S10 that charging of the lithium ion battery 41 has started (S10: YES), it is determined whether or not the voltage of the lithium ion battery 41 is higher than the voltage threshold V1 (S11). As shown in Fig. 7, when charging starts, the current integrated value increases, and the voltage of the lithium ion battery 41 rises accordingly. Here, the condition is that the voltage of the lithium ion battery 41 at the start of charging is higher than the voltage threshold V1.

[0051] As shown in FIG. 8, in the lithium ion battery 41, lithium ions are absorbed between layers of a layered structure of graphite. In the lithium ion battery 41, the stage of the negative electrode changes depending on the number of interlayers in which lithium ions are not absorbed that exist between two interlayers in which lithium ions are absorbed. Specifically, in stage 1, lithium ions are absorbed between each interlayer of graphite. In stage 2, there is one interlayer in which lithium ions are not absorbed between two interlayers in which lithium ions are absorbed. In stage 3, there are two interlayers in which lithium ions are not absorbed between two interlayers in which lithium ions are absorbed. And, in stage 4, there are three interlayers in which lithium ions are not absorbed between two interlayers in which lithium ions are absorbed.

[0052] 9 is a graph showing the relationship between the negative electrode stage, OCV, and capacity A. Capacity A at which the OCV changes significantly (the rate of change of the OCV reaches a maximum value) corresponds to a region between the region where stage 3 and stage 2 coexist and the region where stage 2 and stage 1 coexist.

[0053] 10, the rate of change Rv of the OCV of the lithium ion battery 41 with respect to the capacity due to the structural change of the negative electrode of the lithium ion battery 41 reaches a maximum value between two plateau regions PR1, PR2 (low change rate portions) where the rate of change Rv of the OCV is equal to or lower than a predetermined rate of change. Therefore, when the voltage of the lithium ion battery 41 is lower than the plateau region PR1 where the OCV is lower, the rate of change Rv of the OCV due to the structural change of the negative electrode of the lithium ion battery 41 does not reach a maximum value. Therefore, the voltage threshold V1 is set to the minimum voltage of the lithium ion battery 41 in the plateau region PR1 of the two plateau regions PR1, PR2.

[0054] Returning to FIG. 6, if it is determined in step S11 that the voltage of the lithium ion battery 41 is not higher than the voltage threshold V1 (S11: NO), this series of processes is ended (END).

[0055] On the other hand, when it is determined in step S11 that the voltage of the lithium ion battery 41 is higher than the voltage threshold V1 (S11: YES), calculation of the rate of change of the voltage of the lithium ion battery 41 is started (S12). Specifically, a differential value of the voltage with respect to the current integrated value (rate of change of the voltage with respect to the capacity of the lithium ion battery 41) is calculated (see FIG. 11).

[0056] Next, the current and time since the start of charging are integrated to calculate an integrated current value (S13).

[0057] Next, it is determined whether or not the rate of change of the voltage has a maximum value (S14). Specifically, as shown in Fig. 11, it is determined whether or not the differential value of the voltage with respect to the current integrated value has a maximum value. In this determination, if it is determined that the rate of change of the voltage has no maximum value (S14: NO), the process of S14 is executed again. Note that if charging of the lithium ion battery 41 (battery 40) is completed during the execution of the process of S14, this series of processes is terminated.

[0058] On the other hand, if it is determined in step S14 that the rate of change of the voltage has a maximum value (S14: YES), it is determined whether the current integrated value is equal to or less than a predetermined value a (S15). As shown in Fig. 12, the predetermined value a is set to be equal to or less than the capacity corresponding to the width of the plateau region PR1, and may be, for example, half or 2 / 3 of the capacity corresponding to the width of the plateau region PR1. If it is determined in this determination that the current integrated value is not equal to or less than the predetermined value a (S15: NO), this series of processes is terminated (END).

[0059] On the other hand, when it is determined in the judgment of S15 that the current integrated value is equal to or less than the predetermined value a (S15: YES), the detection of the capacity A is confirmed (S16). Specifically, as shown in Fig. 11, when the voltage differential value takes a maximum value, the capacity of the lithium ion battery 41 at that time is detected (estimated) to be capacity A (the remaining amount corresponding to the amount between two minimum values).

[0060] Next, the current and time from when the differential value of the voltage reaches its maximum value are integrated to calculate an integrated current value (S17).

[0061] Next, it is determined whether or not full charge of the lithium ion battery 41 has been detected (S18). In this determination, if it is determined that full charge of the lithium ion battery 41 has not been detected (S18: NO), the process of S18 is executed again.

[0062] On the other hand, when it is determined in S18 that the lithium ion battery 41 is fully charged (S18: YES), the SOH is calculated (S19). Specifically, the current integrated value calculated in the process of S17 is added to the capacity A, and the capacity at the time of full charge detection is calculated as the current full capacity. The current SOH is calculated by the formula: SOH [%] = (current full capacity of the lithium ion battery 41 / full capacity of a new battery) x 100. Then, this series of processes ends (END).

[0063] This series of processes is executed for each lithium ion battery 41. The processes of S10 to S15 correspond to the processes performed by a determination section, the conditions of S13 to S15 correspond to predetermined conditions, and the process of S16 corresponds to the processes performed by an estimation section.

[0064] The present embodiment described above in detail has the following advantages.

[0065] The inventors of the present application have noticed that when the amount of change in capacity (integrated current value) from the start of charging until the rate of change in voltage of lithium ion battery 41 reaches a maximum value (hereinafter referred to as "amount of capacity change from the start of charging") increases, the capacity at which the rate of change in voltage reaches a maximum value during charging deviates from capacity A. In this regard, judgment unit 52 judges that a predetermined condition is satisfied, that the amount of change in capacity from the start of charging of lithium ion battery 41 until the rate of change in voltage reaches a maximum value is equal to or less than predetermined value a. For this reason, judgment unit 52 can judge that the amount of change in capacity from the start of charging until the rate of change in voltage reaches a maximum value is not large, based on the amount of change in capacity from the start of charging until the rate of change in voltage reaches a maximum value.

[0066] When the determination unit 52 determines that the predetermined condition is satisfied, the estimation unit 53 estimates the capacity corresponding to between two minimum values ​​of the rate of change of the voltage during charging of the lithium ion battery 41 as the capacity of the lithium ion battery 41. Then, a maximum value exists between the two minimum values ​​of the rate of change of the voltage during charging, and the capacity corresponding between the two minimum values ​​is close to the capacity A corresponding to the maximum value. Therefore, when the amount of change in capacity since the start of charging is not large, a capacity close to the capacity A can be estimated as the capacity of the lithium ion battery 41. Therefore, it is possible to suppress a decrease in the accuracy of estimating the capacity of the lithium ion battery 41.

[0067] The capacity of the lithium ion battery 41 can be expressed as an integrated current value obtained by integrating the current and time. With this configuration, the capacity can be calculated using general-purpose elements such as the current sensor 31 that detects the current and the CPU clock.

[0068] The predetermined value a is set to be smaller than the capacity corresponding to the width of the plateau region PR1 having the lower voltage of the lithium ion battery 41 out of two plateau regions PR1, PR2 in which the rate of change of the voltage is equal to or smaller than the predetermined rate of change. Therefore, the capacity of the lithium ion battery 41 can be estimated in a state in which the amount of change in capacity from the start of charging is smaller than the capacity corresponding to the width of the plateau region PR1 having the lower voltage. Therefore, it is possible to prevent the capacity when the rate of change of the voltage is at a maximum value during charging from deviating from the capacity A, and to prevent a decrease in the accuracy of estimating the capacity of the lithium ion battery 41.

[0069] The predetermined condition includes that the voltage of the lithium ion battery 41 is higher than the minimum voltage (voltage threshold V1) of the lithium ion battery 41 in the lower plateau region PR1 of the two plateau regions PR1, PR2 in which the voltage change rate is equal to or lower than a predetermined change rate. With this configuration, it is possible to suppress erroneous determination that the maximum value of the voltage change rate due to a structural change in the positive electrode of the lithium ion battery 41 is the maximum value of the voltage change rate due to a structural change in the negative electrode.

[0070] The current full capacity of the lithium-ion battery 41 can be calculated by adding an integrated current value obtained by integrating the current and time from when the capacity A of the lithium-ion battery 41 is estimated until the lithium-ion battery 41 satisfies the full charge condition to the capacity A of the lithium-ion battery 41 estimated by the estimation unit 53. Then, the SOH (state of health) of the lithium-ion battery 41 can be calculated by calculating the ratio of the full capacity of the current lithium-ion battery 41 to the full capacity of a new lithium-ion battery 41.

[0071] Capacity A is a capacity corresponding to a region between the region where the negative electrode stages 3 and 2 coexist and the region where the negative electrode stages 2 and 1 coexist. According to the above configuration, capacity A can be determined with high accuracy based on the stage of the negative electrode of lithium ion battery 41.

[0072] The first embodiment can be modified as follows: The same parts as those in the first embodiment are denoted by the same reference numerals and the description thereof will be omitted.

[0073] The capacitance A may be set to a capacitance corresponding to the gap between the plateau regions PR1 and PR2. With this configuration, the capacitance A can be determined with high accuracy based on the plateau regions PR1 and PR2.

[0074] By discharging the lithium ion battery 41 to a capacity of 0 from the time when the rate of change of the voltage Rv reaches its maximum value, it is also possible to determine the capacity A (specific remaining capacity) corresponding to the time when the rate of change of the voltage reaches its maximum value.

[0075] As shown in FIG. 13, the determination unit 52 can determine that the voltage change rate has reached a maximum value when, after the start of charging the lithium ion battery 41, the voltage change rate exceeds a second predetermined value B that is greater than the first predetermined value K from a state where the voltage change rate is less than a third predetermined value C that is less than the second predetermined value B. The charging parameters are parameters that correlate with the charging time, and may include time, the capacity of the lithium ion battery 41, the current integrated value, the SOC of the lithium ion battery 41, the temperature of the lithium ion battery 41, the temperature rise of the lithium ion battery 41, and the impedance of the lithium ion battery 41. The predetermined values ​​K, B, and C are set corresponding to the period from when the voltage change rate changes from a downward trend to an upward trend to the right until when the voltage change rate changes from a downward trend to the right. With this configuration, it is possible to easily determine that the voltage change rate has reached a maximum value based on a comparison of the magnitude between the voltage change rate and the three predetermined values ​​K, B, and C. In the first embodiment, the charging parameters may be adopted in addition to the current integrated value.

[0076] Second embodiment The second embodiment will be described below, focusing on the differences from the first embodiment. The same parts as those in the first embodiment are denoted by the same reference numerals and description thereof will be omitted.

[0077] When determining that the rate of change of the voltage of the lithium ion battery 41 with respect to the capacity (current integrated value) has reached a maximum value, if the current for charging the lithium ion battery 41 is greater than a predetermined current, it becomes difficult to determine the maximum value. In response to this, the inventors of the present application have noticed that, as shown in Fig. 14, during charging of the lithium ion battery 41, the rate of change of the real part Zre (impedance) of the impedance of the lithium ion battery 41 with respect to the capacity changes significantly at the boundary of capacity A where the rate of change of the voltage reaches a maximum value. The impedance can be calculated based on the amplitude of the AC voltage and the amplitude of the AC current.

[0078] The reason that the rate of change of the real part of the impedance Zre changes is that the change in the stage of the negative electrode reduces the heat of reaction during charging, and the reduced heat of reaction slows down the temperature rise, and the slower temperature rise also slows down the decrease in the real part of the impedance Zre.

[0079] Therefore, when the rate of change of the impedance of the lithium ion battery 41 with respect to the capacity changes beyond a predetermined degree, the determination unit 52 determines that the rate of change of the voltage has reached a maximum value. Specifically, as shown in FIG. 15, instead of the process of S12 in FIG. 6, the calculation of the real part Zre of the impedance of the lithium ion battery 41 is started (S12A). Specifically, a differential value of the real part Zre of the impedance with respect to the current integrated value (the rate of change of the impedance with respect to the capacity of the lithium ion battery 41) is calculated (see FIG. 16). Also, instead of the process of S14 in FIG. 6, it is determined whether or not the rate of change of the real part Zre of the impedance has changed significantly (S14A). Specifically, as shown in FIG. 16, it is determined whether or not the differential value of the real part Zre of the impedance with respect to the current integrated value has changed by a predetermined value x or more. With this configuration, even if the current for charging the lithium ion battery 41 is larger than the predetermined current, it can be determined that the rate of change of the voltage of the lithium ion battery 41 with respect to the capacity has reached a maximum value.

[0080] Note that the imaginary part Zim of the impedance, the absolute value of the impedance, or the phase of the impedance may be used instead of the real part Zre of the impedance of the lithium ion battery 41. Also, the rate of change of the temperature of the lithium ion battery 41 may be used instead of the rate of change of the real part Zre of the impedance.

[0081] Third embodiment The third embodiment will be described below, focusing on the differences from the first embodiment. The same parts as those in the first embodiment are denoted by the same reference numerals and description thereof will be omitted.

[0082] As described above, when the amount of change in capacity from the start of charging becomes large, the capacity at which the rate of change in voltage during charging reaches a maximum value deviates from capacity A. However, even in this case, it is preferable to make it possible to estimate the capacity of lithium-ion battery 41 while suppressing the occurrence of problems, rather than making it impossible to estimate the capacity of lithium-ion battery 41.

[0083] 6 and 15, when it is determined that the current integrated value is not equal to or less than the predetermined value a (predetermined condition is not satisfied) (S15: NO), the BMU 50 may estimate the capacity of the lithium ion battery 41 by subtracting the capacity (for example, capacity A) corresponding to the interval between two minimum values ​​of the rate of change of the voltage during charging of the lithium ion battery 41. According to this configuration, when the current integrated value is not equal to or less than the predetermined value a, the capacity of the lithium ion battery 41 is estimated to be smaller than when the current integrated value is equal to or less than the predetermined value a (predetermined condition is satisfied). Therefore, even if there is a risk of a decrease in the accuracy of estimating the capacity of the lithium ion battery 41, it is possible to estimate the capacity of the lithium ion battery 41 while preventing the battery capacity from running out earlier than expected.

[0084] In addition, if it is determined that the current integrated value is not equal to or less than the predetermined value a (S15: NO), the amount by which the estimated capacity of the lithium ion battery 41 is reduced can be increased the larger the charging current is, or the lower the temperature of the lithium ion battery 41 is.

[0085] Moreover, the first to third embodiments can be modified as follows: The same parts as those in the first to third embodiments are given the same reference numerals and the description thereof will be omitted.

[0086] The process of S19 in Figs. 6 and 15 may be omitted.

[0087] The capacity unevenness is easily eliminated as the temperature of the lithium ion battery 41 is higher, and is difficult to eliminate as the temperature of the lithium ion battery 41 is lower. Therefore, the predetermined value a for determining the magnitude of the current integrated value in the process of S15 in Figs. 6 and 15 may be set to a smaller value (smaller change amount) as the temperature of the lithium ion battery 41 is lower. Specifically, the predetermined value a is set based on the table shown in Fig. 17. With this configuration, it is possible to request that the change amount of the current integrated value from the start of charging (smaller capacity change amount) is smaller as the temperature of the lithium ion battery 41 is lower. Therefore, even if 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. 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 air temperature measured by an air temperature sensor may be used as the temperature of the lithium ion battery 41. The capacity of the lithium ion battery 41 when the rate of change of the voltage or the rate of change of the impedance (predetermined parameter) changes peculiarly may be estimated as a capacity A corrected based on the temperature of the lithium ion battery 41.

[0088] The larger the current used to charge the lithium ion battery 41, the more likely the capacity unevenness is to occur, and the smaller the current used to charge the lithium ion battery 41, the less likely the capacity unevenness is to occur. Therefore, the predetermined value a may be set to a smaller amount of change as the current used to charge the lithium ion battery 41 is larger. With this configuration, it is possible to require that the amount of capacity change from the start of charging be smaller as the current used to charge the lithium ion battery 41 is larger. Therefore, even when the current used to charge the lithium ion battery 41 is large, it is possible to prevent a decrease in the accuracy of estimating the capacity of the lithium ion battery 41.

[0089] The SOC can be used instead of the current integrated value as the remaining capacity of the lithium ion battery 41. Using the SOC (charging parameter), it can be determined whether the amount of change in SOC from the start of charging the lithium ion battery 41 until the rate of change in voltage reaches a maximum value is equal to or less than a predetermined amount of change. When the rate of change Rv (predetermined parameter) of voltage relative to the SOC reaches a maximum value (subjects to an unusual change), the remaining capacity of the lithium ion battery 41 at that time can be estimated as a specific SOC (specific remaining capacity). The specific SOC is the SOC corresponding to the capacity A.

[0090] The lithium ion battery 41 may be a ternary lithium ion battery that uses a lithium-containing metal oxide containing the elements Co, Mn, and Ni as the positive electrode active material. [Explanation of symbols]

[0091] 40: battery, 41: lithium ion battery, 50: BMU, 52: determination unit, 53: estimation unit.

Claims

1. A battery remaining capacity estimation device (50) for estimating a remaining capacity of a secondary battery (41) based on a charging parameter correlated with a charging time of the secondary battery and a rate of change of a voltage of the secondary battery with respect to the charging parameter, comprising: a determination unit (52) for determining whether a predetermined condition is satisfied, that is, an amount of change in the charging parameter from when charging of the secondary battery is started until the rate of change in the voltage reaches a maximum value is equal to or less than a predetermined amount of change; an estimation unit (53) that estimates a remaining capacity of the secondary battery that corresponds to a value between two minimum values ​​of the rate of change of the voltage during charging of the secondary battery when the determination unit determines that the predetermined condition is satisfied; and A battery remaining capacity estimation device comprising:

2. 2. The battery remaining capacity estimating device according to claim 1, wherein the charging parameter is an integrated current value obtained by integrating a current and a time.

3. 3. The battery remaining capacity estimation device according to claim 1, wherein the predetermined change amount is set to be smaller than the charging parameter corresponding to a width of the low change rate portion (PR1) having a lower voltage of the secondary battery, of two low change rate portions (PR1, PR2) in which the change rate of the voltage is equal to or lower than a predetermined change rate.

4. 3. The battery remaining capacity estimating device according to claim 1, wherein the predetermined change amount is set to a smaller amount as the temperature of the secondary battery decreases.

5. 3. The battery remaining capacity estimating device according to claim 1, wherein the predetermined change amount is set to a smaller amount as the current for charging the secondary battery increases.

6. 3. The battery remaining capacity estimation device according to claim 1, wherein the determination unit determines that the rate of change of the voltage has reached a maximum value when, after charging of the secondary battery begins, the rate of change of the voltage goes from less than a first predetermined value (K) to exceed a second predetermined value (B) greater than the first predetermined value, and then goes to less than a third predetermined value (C) smaller than the second predetermined value.

7. 3. The battery remaining capacity estimation device according to claim 1, wherein when the determination unit determines that the specified condition is not satisfied, the estimation unit estimates the remaining capacity of the secondary battery as a remaining capacity obtained by subtracting a remaining capacity corresponding to a value between two minimum values ​​taken by the rate of change of the voltage during charging of the secondary battery.

8. 3. The battery remaining capacity estimation device according to claim 1, wherein the determination unit determines that the rate of change of the voltage has reached a maximum value when a rate of change of the temperature of the secondary battery with respect to the charging parameter or a rate of change of the impedance of the secondary battery with respect to the charging parameter changes beyond a predetermined degree.

9. 3. The battery remaining capacity estimation device according to claim 1, wherein the predetermined condition includes that the voltage of the secondary battery is higher than a minimum voltage (V1) of the secondary battery in the lower low change rate portion of two low change rate portions in which the change rate of the voltage is equal to or lower than a predetermined change rate.

10. 3. A battery remaining capacity estimation device as described in claim 1 or 2, wherein the deterioration state of the secondary battery is calculated based on the remaining capacity of the secondary battery estimated by the estimation unit, an integrated current value obtained by integrating the current and time from when the remaining capacity of the secondary battery is estimated until the secondary battery satisfies a full charge condition, and a full capacity of a new secondary battery.

11. 3. The battery remaining capacity estimating device according to claim 1, wherein the secondary battery is a lithium ion battery having a negative electrode containing graphite.

12. 12. The battery remaining capacity estimating device according to claim 11, wherein the secondary battery is a lithium ion battery having a positive electrode containing lithium, iron, and phosphorus.

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