Battery state estimation device

Abstract

To update an OCV-SOC map in accordance with the degradation of a battery and estimate the SOC with good accuracy.SOLUTION: A battery state estimation device includes a controller (14) for estimating an SOC on the basis of the voltage of a battery (B) and an OCV-SOC map. The controller calculates dV / dSOC on the basis of the voltage and current values of the battery during constant current charging of the battery, identifies the SOCpeak of the battery when the peak of dV / dSOC has appeared, calculates, on the basis of SOC[-]peak and SOCpeak, SOC[-]TOP that represents the remaining capacity of a cathode when the SOC is 100%, and updates the OCV-SOC map where the SOC is of a prescribed range on the basis of the open-circuit potential OCPpos of the cathode from the lower-limit to the upper-limit value of the remaining capacity of the cathode and the open-circuit potential OCPneg of an anode from the lower-limit to the upper-limit values of the remaining capacity of the anode.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a battery state estimation device that estimates the state of a battery mounted on a vehicle. [Background technology]

[0002] Conventionally, vehicles equipped with a motor as a power source, such as electric vehicles and plug-in hybrid vehicles, use secondary batteries such as lithium-ion batteries to supply power to the motor. The batteries installed in electric vehicles and plug-in hybrid vehicles are charged from an external power source, such as a household commercial power source.

[0003] In such electric vehicles, accurately understanding the battery's state of charge (SOC) is extremely important for preventing overcharging and over-discharging of the battery and for accurately informing passengers of the remaining battery capacity while driving. However, it is difficult to determine the SOC by directly detecting the internal state of the battery.

[0004] Therefore, methods for estimating the SOC without directly detecting the internal state of a battery are known, such as a method of estimating the current SOC by adding or subtracting the value obtained by integrating the charge / discharge current of the battery over time to or from the initial SOC value at the start of charge / discharge (hereinafter referred to as the "integration method"), and a method of successively estimating the open circuit voltage (OCV) of the battery by inputting the current value and terminal voltage value of the battery into an equivalent circuit model of the battery, and estimating the SOC of the battery by referring to an OCV-SOC map that shows the correspondence relationship between the OCV and the SOC (hereinafter referred to as the "OCV method") (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-227840 Summary of the Invention [Problem to be solved by the invention]

[0006] However, as the battery continues to be used, the difference in the rate at which the positive and negative electrodes deteriorate causes the capacity balance between the positive and negative electrodes to be disrupted, gradually changing the relationship between OCV and SOC. As a result, the accuracy of estimating SOC from battery voltage using an OCV-SOC map that corresponds to the battery before deterioration deteriorates decreases.

[0007] The present invention has been made to solve the problems of the conventional technology described above, and has an object to provide a battery state estimating device that can update the OCV-SOC map in accordance with battery deterioration and accurately estimate the SOC. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention provides a battery state estimation device for estimating the state of a battery mounted on a vehicle, the device comprising: a current sensor for measuring the charge / discharge current of the battery; a voltage sensor for measuring the voltage of the battery; a memory for storing an OCV-SOC map that defines the relationship between the open circuit voltage OCV of the battery and the SOC of the battery; and a controller configured to estimate the SOC of the battery based on the measured voltage and the OCV-SOC map, wherein the controller calculates dV / dSOC, which represents the rate of change of voltage in response to a change in the SOC of the battery, based on the voltage value and current value of the battery during constant current charging of the battery, and determines the SOC of the battery when a peak of dV / dSOC appears. peak and a predetermined value representing the remaining capacity of the negative electrode of the battery when the peak of dV / dSOC occurs is determined as SOC[-] peak and SOC peak Based on this, SOC[-] represents the remaining capacity of the negative electrode when the battery SOC is 100%. TOP Calculate the SOC[-] from the data of the open circuit potential OCPpos of the positive electrode from the lower limit to the upper limit of the remaining capacity of the battery positive electrode and the lower limit of the remaining capacity of the negative electrode TOPThe OCV-SOC map for a predetermined range of SOC is obtained based on data on the negative electrode open circuit potential OCPneg up to the predetermined range, and the OCV-SOC map stored in the memory is updated. In the present invention configured as described above, the controller calculates dV / dSOC during constant current charging of the battery, and calculates the SOC of the battery when a peak of dV / dSOC appears. peak The SOC [-] represents the remaining capacity of the negative electrode when the peak of dV / dSOC occurs. peak and SOC peak Based on this, SOC[-] represents the remaining capacity of the negative electrode when the battery SOC is 100%. TOP Calculate the open circuit potential OCPpos of the positive electrode from the lower limit to the upper limit of the remaining capacity of the positive electrode and the SOC[-] from the lower limit of the remaining capacity of the negative electrode TOP Based on the data of the negative electrode open circuit potential OCPneg up to dV / dSOC, the OCV-SOC map for the specified range of SOC is obtained and the OCV-SOC map stored in the memory is updated. In other words, the SOC at which the capacity balance between the positive and negative electrodes is disrupted due to the deterioration of the positive electrode more than the negative electrode, and the peak of dV / dSOC occurs peak When the SOC shifts to the high SOC side, peak Based on the shift in SOC[-], the upper limit of SOC[-] of the negative electrode TOP By identifying the OCV-SOC map, it is possible to obtain an OCV-SOC map that reflects the imbalance in capacity between the positive and negative electrodes due to deterioration, and therefore the SOC can be accurately estimated based on the OCV-SOC map updated in accordance with the battery deterioration.

[0009] In the present invention, preferably, the lower limit of the remaining capacity of the negative electrode is set to SOC[-] BOT As SOC[-] TOP is calculated by the following formula: JPEG2025148243000002.jpg16169 In the present invention configured as described above, the SOC of the battery when the peak of dV / dSOC appears is peak and SOC[-], which represents the remaining capacity of the negative electrode when the peak of dV / dSOC occurs, which can be specified in advance. peakand the lower limit of the remaining capacity of the negative electrode is SOC[-] BOT Based on this, SOC[-], which represents the capacity imbalance between the positive and negative electrodes, TOP This makes it possible to obtain an OCV-SOC map that accurately reflects the capacity imbalance between the positive and negative electrodes due to degradation.

[0010] In the present invention, the constant current charging of the battery is preferably carried out from when the SOC of the battery is 30% or less until the peak of dV / dSOC appears. In the present invention configured as described above, the SOC of the battery when the peak of dV / dSOC appears is peak This makes it possible to reliably identify the capacity imbalance between the positive and negative electrodes due to deterioration, and obtain an OCV-SOC map that accurately reflects this imbalance.

[0011] According to another aspect of the present invention, a battery state estimation device is a battery state estimation device that estimates the state of a battery that has a plurality of cells connected in series and is mounted on a vehicle, and includes: a current sensor that measures the charge / discharge current of the battery; a voltage sensor that measures the voltage of each of the plurality of cells; a memory that stores an OCV-SOC map that defines the relationship between the open circuit voltage OCV of the battery and the SOC of the battery; and a controller configured to estimate the SOC of the battery based on the measured voltage and the OCV-SOC map, and the controller is configured to estimate the SOC of the battery based on the maximum value V of the voltages of the plurality of cells during constant current charging of the battery. cell max and minimum value V cell min and the battery current value, V according to the battery SOC cell max and V cell min Calculate the difference between V cell max and V cell min The battery SOC when the peak of the difference between the SOC and the battery SOC appears is the SOC of the battery when the peak of dV / dSOC appears, which represents the rate of change of voltage in response to changes in the battery SOC. peakand a preset SOC [-] which represents the remaining capacity of the negative electrode of the battery when the peak of dV / dSOC occurs. peak and SOC peak Based on this, SOC[-] represents the remaining capacity of the negative electrode when the battery SOC is 100%. TOP Calculate the SOC[-] from the data of the open circuit potential OCPpos of the positive electrode from the lower limit to the upper limit of the remaining capacity of the battery positive electrode and the lower limit of the remaining capacity of the negative electrode TOP The OCV-SOC map for a predetermined range of SOC is obtained based on data on the negative electrode open circuit potential OCPneg up to the predetermined range, and the OCV-SOC map stored in the memory is updated. In the present invention configured in this way, the controller controls V cell max -V cell min Calculate V cell max -V cell min The battery SOC when the peak of dV / dSOC appears is peak The SOC [-] represents the remaining capacity of the negative electrode when the peak of dV / dSOC occurs. peak and SOC peak Based on this, SOC[-] represents the remaining capacity of the negative electrode when the battery SOC is 100%. TOP Calculate the open circuit potential OCPpos of the positive electrode from the lower limit to the upper limit of the remaining capacity of the positive electrode and the SOC[-] from the lower limit of the remaining capacity of the negative electrode TOP Based on the data of the negative electrode open circuit potential OCPneg up to dV / dSOC, the OCV-SOC map for the specified range of SOC is obtained and the OCV-SOC map stored in the memory is updated. In other words, the SOC at which the capacity balance between the positive and negative electrodes is disrupted due to the deterioration of the positive electrode more than the negative electrode, and the peak of dV / dSOC occurs peak When the SOC shifts to the high SOC side, peak Based on the shift in SOC[-], the upper limit of SOC[-] of the negative electrode TOPBy identifying the OCV-SOC map, it is possible to obtain an OCV-SOC map that reflects the imbalance in capacity between the positive and negative electrodes due to deterioration, and therefore it is possible to accurately estimate the SOC based on the OCV-SOC map updated according to the battery's deterioration. cell max -V cell min The SOC at which the peak of dV / dSOC occurs is peak Therefore, the SOC can be calculated without calculating the dV / dSOC of each cell. peak This can reduce the calculation load for estimating the state of the battery. [Effects of the Invention]

[0012] According to the battery state estimating device of the present invention, the OCV-SOC map can be updated in accordance with the deterioration of the battery, and the SOC can be estimated with high accuracy. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a plan view showing a schematic configuration of a vehicle to which a battery state estimating device according to an embodiment of the present invention is applied; [Figure 2] 1 is a block diagram showing a functional configuration of a battery state estimating device according to an embodiment of the present invention. [Figure 3] 1 is a diagram showing a simplified structure of a lithium-ion battery according to an embodiment of the present invention; [Figure 4] FIG. 2 is a diagram showing an example of an OCV-SOC map according to an embodiment of the present invention. [Figure 5] FIG. 2 is a diagram illustrating the relationship between SOC and dV / dSOC of a lithium ion battery according to an embodiment of the present invention. [Figure 6] 4 is a flowchart illustrating a battery state estimation process according to an embodiment of the present invention. [Figure 7] FIG. 10 is a diagram illustrating the relationship between SOC and Vcell max-Vcell min of a lithium ion battery according to another embodiment of the present invention. [Figure 8]10 is a flowchart illustrating a battery state estimation process according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, a battery state estimating device according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0015] <System configuration> First, the configuration of a battery state estimating device according to this embodiment will be described with reference to Figures 1 and 2. Figure 1 is a plan view showing a schematic configuration of a vehicle to which the battery state estimating device according to this embodiment is applied, and Figure 2 is a block diagram showing the functional configuration of the battery state estimating device according to this embodiment.

[0016] As shown in FIG. 1, the vehicle 1 of this embodiment is a plug-in hybrid vehicle equipped with an internal combustion engine 2 and a motor 4 as power sources. The internal combustion engine 2 and the motor 4 are mounted, for example, in the front of the vehicle body of the vehicle 1. The internal combustion engine 2 is, for example, a gasoline engine or a diesel engine. Torque output from the internal combustion engine 2 and the motor 4 is transmitted to a transmission 6 via a clutch (not shown). The transmission 6 outputs the input torque to a pair of drive shafts 8 at a predetermined reduction ratio. This drives a pair of drive wheels 10 (left and right front wheels in the example of FIG. 1) attached to the outer ends of each drive shaft 8 in the vehicle width direction. In addition, the motor 4 functions as a generator that outputs regenerative power when the vehicle 1 decelerates.

[0017] Battery B, which supplies power to motor 4, is a lithium-ion battery and is mounted, for example, at the rear of the vehicle body 1. Battery B has, for example, an output voltage of 48 V, a maximum discharge current value of 80 A, and a capacity of 20 kWh. Furthermore, an inverter 12 is disposed near motor 4. Inverter 12 converts DC power supplied from battery B into AC power and supplies it to motor 4, and converts regenerative power generated by motor 4 into DC power and supplies it to battery B, thereby charging battery B. In addition, inverter 12 is electrically connected to controller 14, and is capable of inputting and outputting control signals to and from controller 14.

[0018] The vehicle 1 also has a temperature sensor SN1 that detects the temperature of battery B, a voltage sensor SN2 that detects the voltage of battery B, and a current sensor SN3 that detects the charge / discharge current value of battery B. Each of these sensors is electrically connected directly or indirectly to the controller 14, and outputs a detection signal corresponding to each detection value to the controller 14.

[0019] In the vehicle 1, a controller 14 performs various controls. As shown in Fig. 2, the controller 14 has a processor 16 and a memory 18 (ROM, RAM, etc.) for storing various programs (including basic control programs such as an OS and application programs that are run on the OS to achieve specific functions) that are interpreted and executed by the processor 16, and various data. The memory 18 stores an OCV-SOC map 18a, data on the open circuit potential OCPpos of the positive electrode of the battery B before deterioration, from the lower limit to the upper limit of the remaining capacity, and data on the open circuit potential OCPneg of the negative electrode of the battery B before deterioration, from the lower limit to the upper limit of the remaining capacity.

[0020] The controller 14 functions as a controller of the powertrain system of the vehicle 1. That is, the controller 14 controls the internal combustion engine 2 and the inverter 12 in response to the driver's operation of the accelerator pedal, and supplies electric power from the battery B to the motor 4 via the inverter 12, or supplies regenerative electric power from the motor 4 to the battery B, thereby realizing a desired output torque or regenerative torque in response to the accelerator operation. Furthermore, the controller 14 is configured to control the charging and discharging of the battery B based on signals input from the various sensors SN1 to SN3 described above.

[0021] Next, the structure of battery B of this embodiment will be described with reference to Figures 3 to 5. Figure 3 is a simplified diagram showing the structure of a lithium ion battery, Figure 4 is a diagram showing an example of an OCV-SOC map, and Figure 5 is a diagram illustrating the relationship between SOC and dV / dSOC of the lithium ion battery.

[0022] Battery B of this embodiment is a lithium-ion battery, and as shown in FIG. 3, includes a positive electrode, a negative electrode, and a separator that insulates the positive electrode from the negative electrode, and uses a nonaqueous electrolyte solution as a supporting electrolyte, in which a main electrolyte and a secondary electrolyte are dissolved in a nonaqueous solvent.

[0023] The positive electrode is formed by mixing a positive electrode active material and additives (binder and conductive additive) and applying the mixture to a current collector. A preferred current collector is, for example, aluminum foil.

[0024] Preferable positive electrode active materials include composite metal oxides containing one or more elements selected from the group consisting of cobalt, manganese, and nickel and lithium, lithium phosphate compounds, and lithium silicate compounds. Lithium phosphate compounds are particularly preferred. These positive electrode active materials may be used alone or in combination of two or more.

[0025] The negative electrode is formed by mixing a negative electrode active material and additives (binder and conductive additive) and applying the mixture to a current collector. A preferred current collector is, for example, copper foil.

[0026] As the negative electrode active material, it is preferable to use a graphite-based carbon material, i.e., artificial graphite or natural graphite. From the viewpoint of improving the ability to absorb and release Li ions, graphite-based carbon materials with a low degree of graphitization are preferred. Artificial graphite with a low degree of graphitization and hard carbon are preferred as negative electrode active materials. Highly crystalline natural graphite deteriorates quickly when used alone, so it is preferable to use it in combination with surface-treated natural graphite or artificial graphite.

[0027] The separator is not particularly limited, but may be a single-layer or multi-layer microporous film, woven fabric, nonwoven fabric, or the like, made of polyolefin such as polypropylene or polyethylene.

[0028] The non-aqueous electrolyte solution is a solution in which a lithium salt (supporting electrolyte) is dissolved in a non-aqueous solvent, and additives may be added as needed.

[0029] Battery B is provided with a heater for heating battery B and a heat exchanger for cooling battery B. The heater raises the temperature of battery B when the temperature is low, for example, at room temperature, to a temperature of, for example, about 45°C. This temperature increase makes it possible to increase the limit integrated current amount, as will be described later. The heater may be, for example, an electric heater, but is not limited to this. For example, when the temperature of the coolant for the internal combustion engine 2 is high, equal to or higher than a predetermined temperature, the coolant can be used to raise the temperature.

[0030] The heat exchanger is activated when the temperature of battery B reaches a predetermined temperature (for example, 50°C) and prevents the temperature of battery B from rising above an allowable upper limit temperature (for example, 60°C). Any suitable heat exchanger can be used, such as an air-cooled or water-cooled type.

[0031] Figure 4 shows an example of an OCV-SOC map that shows the relationship between the open-circuit voltage (OCV) and the battery's state of charge (SOC). In the OCV-SOC map in Figure 4, the dotted line represents the map for the battery immediately after manufacture, when no degradation has occurred, and the solid line represents the map for the battery after its full charge capacity has degraded to 60% of its value immediately after manufacture. Each map can be determined by measuring the open-circuit potential (OCPpos) of the positive electrode and the open-circuit potential (OCPneg) of the negative electrode over the entire SOC range and calculating the potential difference between them. However, since such measurements cannot be performed after the battery is installed in a vehicle, the SOC has traditionally been estimated using an OCV-SOC map based on the battery's state immediately after manufacture.

[0032] As a battery continues to be used, the capacity balance between the positive and negative electrodes is disrupted due to the difference in the rate of degradation of the positive and negative electrodes, gradually changing the relationship between OCV and SOC. In lithium-ion batteries, the positive electrode typically deteriorates faster than the negative electrode, resulting in a smaller positive electrode capacity than the negative electrode. As a result of this disruption in the capacity balance between the positive and negative electrodes, the OCV changes significantly in response to changes in the SOC of the lithium-ion battery. That is, as shown in Figure 4, as the battery deteriorates, the OCV-SOC map shifts toward a lower open-circuit voltage corresponding to the same SOC (or toward a higher SOC corresponding to the same open-circuit voltage / OCV). Therefore, using an OCV-SOC map corresponding to a battery immediately after manufacture, as in the past, will result in an underestimated SOC of a deteriorated battery. Therefore, the inventors considered that if it were possible to identify the extent to which the capacity balance between the positive electrode and the negative electrode has shifted due to degradation, it would be possible to update the OCV-SOC map to one that accurately represents the relationship between OCV and SOC after degradation by calculating the OCV based on data for the portion of the pre-specified open circuit potential OCPpos of the positive electrode and the open circuit potential OCPneg of the negative electrode that corresponds to the capacity balance after degradation.

[0033] Figure 5 shows the relationship between dV / dSOC [mV / %], which is the differentiation of the OCV-SOC map shown in Figure 4 with respect to SOC, and SOC [%]. In Figure 5, the dotted line illustrates the dV / dSOC immediately after battery manufacture when no degradation has occurred, and the solid line illustrates the dV / dSOC after degradation. As shown in Figure 5, the dV / dSOC curve has a peak between 40% and 80% SOC. This peak occurs due to a change in the crystalline structure of the negative electrode, and therefore occurs at a specific remaining capacity of the negative electrode, regardless of the degradation state of the positive electrode.

[0034] In the example of Figure 5, if there is no degradation immediately after battery manufacture, the peak of dV / dSOC occurs when the SOC is approximately 52%. If there is no degradation of the battery, the capacity balance between the positive and negative electrodes is not off and the battery SOC and the remaining capacity of the negative electrode match, so it can be assumed that the peak of dV / dSOC occurs when the remaining capacity of the negative electrode is 52%.

[0035] On the other hand, when a battery deteriorates, the positive electrode deteriorates more rapidly than the negative electrode, and the full charge capacity of the battery decreases accordingly. In other words, the capacity balance between the positive and negative electrodes is disrupted, and when the battery's SOC is 100%, the remaining capacity of the negative electrode becomes lower than 100%. As a result, the SOC corresponding to the remaining capacity of the negative electrode, where the dV / dSOC peak occurs, shifts to a higher SOC. In the example of Figure 5, the dV / dSOC peak shifts to a position where the SOC is approximately 60%.

[0036] Therefore, when the battery deteriorates, by identifying the SOC at which the peak of dV / dSOC occurs, the remaining capacity of the negative electrode at 100% SOC [-] can be calculated. TOP This allows you to identify the data of the open circuit potential OCPpos of the positive electrode when the remaining capacity is 100% from the lower limit and the data of the data of the open circuit potential OCPpos of the positive electrode when the remaining capacity is 100% from the lower limit TOP Based on the data on the negative electrode open circuit potential OCPneg up to 100%, an OCV-SOC map with a predetermined SOC range (for example, from 0% to 100%), i.e., an OCV-SOC map that reflects battery degradation, can be obtained.

[0037] <Battery state estimation> Next, the battery state estimation process according to this embodiment will be described with reference to Fig. 6. Fig. 6 is a flowchart showing the battery state estimation process according to this embodiment. The battery state estimation process shown in Fig. 5 is repeatedly executed by the controller 14 at a predetermined interval when the power supply of the vehicle 1 is ON.

[0038] When the battery state estimation process is started, the controller 14 acquires signals from the sensors SN1 to SN3 (step S1). Acquisition of signals from the sensors SN1 to SN3 is constantly performed in the background even during the processes from step S1 onwards.

[0039] Next, the controller 14 estimates the SOC of battery B based on the information acquired in step S1, and determines whether it is equal to or lower than a predetermined state estimation start threshold (step S2). At this time, the controller 14 calculates the SOC based on the voltage, current, and temperature of battery B, using the current OCV-SOC map 18a and an equivalent circuit model of battery B previously stored in memory 18. The state estimation start threshold is a threshold for starting constant current charging of battery B in order to identify the peak of dV / dSOC, and is the SOC at which the peak of dV / dSOC occurs. peak The initial value of the SOC of battery B immediately after manufacture peak ) In this embodiment, the state estimation start threshold is set to, for example, 50%.

[0040] If the result of step S2 shows that the SOC of battery B is not below the state estimation start threshold, or in this embodiment, is higher than 50% (step S2: NO), the conditions for starting constant current charging of battery B are not met, so the controller 14 terminates the battery state estimation process.

[0041] On the other hand, if the SOC of battery B is equal to or lower than the state estimation start threshold (step S2: YES), the controller 14 determines whether constant current charging (CC charging) is being performed based on the current value of battery B (step S3).

[0042] As a result, if constant current charging of battery B is not being performed (step S3: NO), for example, when vehicle 1 is disconnected from the charger and starts running, the peak of dV / dSOC cannot be identified and the state of battery B cannot be estimated, so controller 14 terminates the battery state estimation process.

[0043] On the other hand, if constant current charging of battery B is being performed (step S3: YES), the controller 14 acquires the current full charge capacity Cap [Ah] of battery B (step S4). The full charge capacity Cap is calculated as needed using a known method based on the voltage, current, temperature, etc. of battery B in a process separate from the battery state estimation process.

[0044] Next, the controller 14 calculates dV / dSOC based on the voltage and current values ​​of battery B and the full charge capacity Cap acquired in step S4 (step S5). For example, the controller 14 calculates the SOC increment dSOC per unit time by dividing the current value of constant current charging by the full charge capacity Cap, and then calculates dV / dSOC by dividing the voltage increase dV of battery B per unit time by dSOC. That is, dV / dSOC represents the rate of change of voltage V in response to changes in SOC. The controller 14 also calculates the SOC at the time of calculating dV / dSOC and stores this data in memory 18 as data specifying the relationship between SOC and dV / dSOC, as shown in FIG. 5. The SOC at this time can be calculated by obtaining the initial value of SOC at the start of constant current charging from the current OCV-SOC map 18a and adding the integrated value of dSOC after the start of constant current charging to the initial value (the so-called current integration method). Thereafter, calculation of dV / dSOC and SOC and data storage are continued until a peak of dV / dSOC is detected in the next step S6.

[0045] Next, the controller 14 determines the peak of dV / dSOC (step S6). For example, the controller 14 determines that a peak of dV / dSOC has appeared when dV / dSOC changes from increasing to decreasing (i.e., when the slope of dV / dSOC changes from positive to negative), and defines the SOC at that time as the SOC at which the peak of dV / dSOC occurs in the battery B in its current deteriorated state. peak and stores it in the memory 18.

[0046] Next, the controller 14 calculates the SOC at which the peak of dV / dSOC identified in step S6 occurs. peak Based on this, the remaining capacity of the negative electrode when the SOC is 100%, that is, the upper limit of the negative electrode SOC[-], is SOC[-] TOP is calculated (step S7).

[0047] The remaining capacity of the negative electrode when the peak of dV / dSOC occurs is defined as negative electrode SOC[-] peak , the negative electrode remaining capacity when the SOC of battery B is 0% is the lower limit SOC[-] BOT Then, the relationship between the SOC of battery B and the negative electrode SOC[-] can be expressed as the following formula (1). JPEG2025148243000003.jpg21143

[0048] Therefore, SOC[-] TOP is calculated using the following formula (2). JPEG2025148243000004.jpg16169where SOC[-] peak is a fixed value that can be obtained theoretically or experimentally in advance, and in the example shown in FIG. 5 in this embodiment, it is 52%. BOT is also a fixed value calculated in advance, for example 10%. peak and SOC[-] BOT is stored in advance in the memory 18.

[0049] Next, the controller 14 calculates the SOC[-] TOPSpecifically, the controller 14 updates the OCV-SOC map 18a based on the data of the open circuit potential OCPpos of the positive electrode when the remaining capacity is from the lower limit value to 100% stored in the memory 18 and the data of the open circuit potential OCPpos of the positive electrode when the remaining capacity is from the lower limit value SOC[-] BOT to SOC[-] TOP Based on the data of the negative electrode open circuit potential OCPneg up to step S8, an OCV-SOC map for a predetermined SOC range (for example, from 0% to 100%), i.e., an OCV-SOC map reflecting the deterioration of battery B, is obtained and stored in memory 18. After step S8, the controller 14 ends the battery state estimation process.

[0050] Second Embodiment Next, a battery state estimating device according to a second embodiment of the present invention will be described with reference to Fig. 7 and Fig. 8. Fig. 7 shows a battery state estimating device according to the second embodiment, which estimates the SOC and V cell max -V cell min 8 is a diagram illustrating an example of the relationship between the vehicle 1 and the battery B, and FIG. 8 is a flowchart showing the battery state estimation process according to the second embodiment. The configuration of the vehicle 1 and the structure of the battery B are the same as those of the above-described embodiments unless otherwise specified.

[0051] Generally, a battery that supplies power to a motor in an electric vehicle such as an electric car or a plug-in hybrid vehicle is configured to output a required voltage (for example, 400V to 800V) by connecting multiple cells in series, each having a cell voltage of, for example, about 2 to 4V. Therefore, in order to obtain an OCV-SOC map according to the deterioration of battery B in the battery state estimation process according to the above-described embodiment, for example, dV / dSOC is calculated for each of all cells, and the SOC at which the dV / dSOC peak occurs is calculated. peak It is possible to ask for the following.

[0052] However, since it is common for the number of cells in a battery used in an electric vehicle to exceed 100, calculating dV / dSOC for each cell would result in an excessively large calculation load. Therefore, the inventors have developed a method for calculating the SOC at which the peak of dV / dSOC occurs, without calculating dV / dSOC for each cell. peak We have devised a method that can calculate the

[0053] Specifically, the degree of deterioration varies among the battery cells, and the terminal voltage of each cell also varies depending on the degree of deterioration. In particular, the SOC at which the peak of dV / dSOC occurs peak In the vicinity of , the voltage change according to the change in SOC is large, so the variation in the terminal voltage of each cell also becomes large. In other words, the maximum value V cell max and the minimum voltage value V cell min The difference is SOC peak It is thought that the maximum value is reached in the vicinity of V cell max -V cell min By calculating the SOC at which the peak of dV / dSOC occurs, the SOC at which the peak of dV / dSOC occurs can be calculated. peak can be approximately calculated.

[0054] FIG. 7 shows the relationship between SOC and V immediately after manufacturing and after degradation of the same battery as in the embodiment described above. cell max -V cell min In Figure 7, the dotted line indicates the relationship between V and the battery immediately after manufacture when no deterioration has occurred. cell max -V cell min The solid line shows the V cell max -V cell min 7, the degradation states shown by the dotted line and the solid line respectively represent the same degradation states as those shown by the dotted line and the solid line in FIG. 5. According to this FIG. 7, V cell max -Vcell min The curve of V has a peak at the same position as the dV / dSOC curve shown in Figure 5, i.e., when the SOC is about 52% immediately after the battery is manufactured and there is no degradation, and when the SOC is about 60% after the battery has degraded. cell max -V cell min From the SOC at which the peak of dV / dSOC occurs, peak can be obtained.

[0055] In this case, in the battery state estimation process, instead of calculating dV / dSOC (step S5) and determining the peak of dV / dSOC (step S6), V cell max -V cell min Calculation of and V cell max -V cell min Peak determination is performed.

[0056] Here, the battery state estimation process according to the second embodiment will be described with reference to Fig. 8. Fig. 8 is a flowchart showing the battery state estimation process according to the second embodiment. Note that steps S11 to S14 and S17 to S18 are similar to steps S1 to S4 and S7 to S8 in the flowchart shown in Fig. 6.

[0057] In the second embodiment, the battery B has a plurality of cells connected in series. The voltage sensor SN2 detects the voltage of each of the plurality of cells and outputs a detection signal corresponding to the detected value to the controller .

[0058] After step S14, the controller 14 acquires the voltage of each cell of the battery B based on the information acquired in step S1, and calculates the maximum voltage V cell max and the minimum value V cell min Difference V cell max -V cell min(Step S15). cell max -V cell min The SOC at the time of calculation was also calculated, and the relationship between SOC and V as shown in Figure 7 was cell max -V cell min The relationship between V and V is stored in the memory 18 as specified data. The SOC at this time can be calculated by, for example, the current integration method, as in the above-described embodiment. cell max -V cell min until the peak of V is detected. cell max -V cell min And continue to calculate SOC and store data.

[0059] Next, the controller 14 cell max -V cell min The controller 14 determines the peak of, for example, V cell max -V cell min When V cell max -V cell min When the slope of V changes from positive to negative, cell max -V cell min It is determined that a peak has appeared.

[0060] As mentioned above, V cell max -V cell min The controller 14 calculates the SOC at that time as the SOC at which the peak of dV / dSOC occurs in the battery B in its current deteriorated state. peak and stores it in the memory 18.

[0061] The controller 14 then cell max -V cell min The SOC at which the peak of dV / dSOC appears. peak Based on this, similarly to steps S7 and S8 of the flowchart shown in FIG. 6, the upper limit of the negative electrode SOC[-] is set to SOC[-] TOP (Step S17) and SOC[-] TOP Based on this, the OCV-SOC map 18a is updated (step S18).

[0062] <Action and effect> Next, the effects of the battery state estimating device according to the above-described embodiment and modified example will be described.

[0063] First, the controller 14 calculates dV / dSOC during constant current charging of the battery B, and calculates the SOC of the battery B when the peak of dV / dSOC appears. peak The SOC [-] represents the remaining capacity of the negative electrode when the peak of dV / dSOC occurs. peak and SOC peak Based on this, SOC[-] represents the remaining capacity of the negative electrode when the SOC of battery B is 100%. TOP Calculate the open circuit potential OCPpos of the positive electrode from the lower limit to the upper limit of the remaining capacity of the positive electrode and the SOC[-] from the lower limit of the remaining capacity of the negative electrode TOP Based on the data of the negative electrode open circuit potential OCPneg up to dV / dSOC, an OCV-SOC map for a predetermined SOC range is obtained, and the OCV-SOC map 18a stored in the memory 18 is updated. That is, the SOC at which the capacity balance between the positive and negative electrodes is disrupted due to the deterioration of the positive electrode more rapidly than the negative electrode, and a peak in dV / dSOC occurs is calculated. peak When the SOC shifts to the high SOC side, peak Based on the shift in SOC[-], the upper limit of SOC[-] of the negative electrode TOPBy identifying the difference between the positive and negative electrodes, an OCV-SOC map that reflects the imbalance in capacity between the positive and negative electrodes due to deterioration can be obtained, and the SOC can be accurately estimated based on the OCV-SOC map 18a that has been updated in accordance with the deterioration of battery B.

[0064] Also, SOC[-] TOP is calculated using the above formula (2), so the SOC of battery B when the peak of dV / dSOC appears is peak and SOC[-], which represents the remaining capacity of the negative electrode when the peak of dV / dSOC occurs, which can be specified in advance. peak and the lower limit of the remaining capacity of the negative electrode is SOC[-] BOT Based on this, SOC[-], which represents the capacity imbalance between the positive and negative electrodes, TOP This makes it possible to obtain an OCV-SOC map that accurately reflects the capacity imbalance between the positive and negative electrodes due to degradation.

[0065] In addition, the constant current charging of battery B is performed from when the SOC of battery B is 30% or less until the peak of dV / dSOC appears. Therefore, the SOC of battery B when the peak of dV / dSOC appears is peak This makes it possible to reliably identify the capacity imbalance between the positive and negative electrodes due to deterioration, and obtain an OCV-SOC map that accurately reflects this imbalance.

[0066] Also, the controller 14 controls V during constant current charging of battery B. cell max -V cell min Calculate V cell max -V cell min The SOC of battery B when the peak of dV / dSOC appears is the SOC of battery B when the peak of dV / dSOC appears. peak The SOC [-] represents the remaining capacity of the negative electrode when the peak of dV / dSOC occurs. peak and SOC peak Based on this, SOC[-] represents the remaining capacity of the negative electrode when the SOC of battery B is 100%.TOP Calculate the open circuit potential OCPpos of the positive electrode from the lower limit to the upper limit of the remaining capacity of the positive electrode and the SOC[-] from the lower limit of the remaining capacity of the negative electrode TOP Based on the data of the negative electrode open circuit potential OCPneg up to dV / dSOC, an OCV-SOC map for a predetermined SOC range is obtained, and the OCV-SOC map 18a stored in the memory 18 is updated. That is, the SOC at which the capacity balance between the positive and negative electrodes is disrupted due to the deterioration of the positive electrode more rapidly than the negative electrode, and a peak in dV / dSOC occurs is calculated. peak When the SOC shifts to the high SOC side, peak Based on the shift in SOC[-], the upper limit of SOC[-] of the negative electrode TOP By specifying the OCV-SOC map 18a, the SOC of the battery B can be accurately estimated based on the OCV-SOC map 18a updated according to the deterioration of the battery B. cell max -V cell min The SOC at which the peak of dV / dSOC occurs is peak Therefore, the SOC can be calculated without calculating the dV / dSOC of each cell. peak This reduces the calculation load for estimating the state of battery B. [Explanation of symbols]

[0067] 1 vehicle 2. Internal combustion engine 4 motors 6. Transmission 8 Drive shaft 10 drive wheels B Battery 12 inverters 14 Controller 16 processors 18 Memory 18a OCV-SOC map SN1 Temperature Sensor SN2 Voltage Sensor SN3 Current Sensor

Claims

1. A battery state estimation device that estimates the state of a battery mounted on a vehicle, a current sensor for measuring a charge / discharge current of the battery; a voltage sensor for measuring the voltage of the battery; a memory that stores an OCV-SOC map that defines the relationship between an open circuit voltage OCV of the battery and an SOC of the battery; a controller configured to estimate an SOC of the battery based on the measured voltage and the OCV-SOC map; The controller During constant current charging of the battery, a dV / dSOC is calculated based on a voltage value and a current value of the battery, the dV / dSOC representing a rate of change in voltage in response to a change in SOC of the battery; The SOC of the battery when the peak of the dV / dSOC appears peak Identify the A preset SOC [-] that represents the remaining capacity of the negative electrode of the battery when the peak of the dV / dSOC occurs peak and the SOC peak Based on this, SOC [-] representing the remaining capacity of the negative electrode when the SOC of the battery is 100% TOP Calculate Data on the open circuit potential OCPpos of the positive electrode from the lower limit to the upper limit of the remaining capacity of the positive electrode of the battery, and the data on the SOC [-] TOP and an OCV-SOC map for a predetermined range of SOC is acquired based on data of the open circuit potential OCPneg of the negative electrode up to and including the time when the OCV-SOC map is updated. Battery state estimation device.

2. The lower limit of the remaining capacity of the negative electrode is SOC [-] BOT As the SOC [-] TOP is calculated by the following formula: The battery state estimating device according to claim 1 .

3. The constant current charging of the battery is performed from when the SOC of the battery is 30% or less until the peak of the dV / dSOC appears. The battery state estimating device according to claim 1 or 2.

4. A battery state estimation device that estimates the state of a battery mounted on a vehicle and having a plurality of cells connected in series, comprising: a current sensor for measuring a charge / discharge current of the battery; a voltage sensor that measures the voltage of each of the plurality of cells; a memory that stores an OCV-SOC map that defines the relationship between an open circuit voltage OCV of the battery and an SOC of the battery; a controller configured to estimate an SOC of the battery based on the measured voltage and the OCV-SOC map; The controller During constant current charging of the battery, the maximum value V of the voltages of the plurality of cells cell max and the minimum value V cell min and V according to the SOC of the battery based on the current value of the battery. cell max and V cell min Calculate the difference between The V cell max and V cell min The SOC of the battery when a peak of the difference between the SOC and the SOC of the battery appears is expressed as the SOC of the battery when a peak of dV / dSOC occurs, which represents the rate of change of voltage according to the change of the SOC of the battery. peak Identify as A preset SOC [-] that represents the remaining capacity of the negative electrode of the battery when the peak of the dV / dSOC occurs peak and the SOC peak Based on this, SOC [-] representing the remaining capacity of the negative electrode when the SOC of the battery is 100% TOP Calculate Data on the open circuit potential OCPpos of the positive electrode from the lower limit to the upper limit of the remaining capacity of the positive electrode of the battery, and the data on the SOC [-] TOP and an OCV-SOC map for a predetermined range of SOC is acquired based on data of the open circuit potential OCPneg of the negative electrode up to and including the time when the OCV-SOC map is updated. Battery state estimation device.

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