Battery management system

Abstract

To reduce a voltage difference between cells.SOLUTION: A battery management system is a system for managing a battery pack made by laminating cells, each of which includes a positive electrode and a negative electrode, and comprises a CPU of a battery management ECU and a voltage sensor for identifying a voltage difference between the cells. The CPU calculates a SOC with respect to residual electric energy of the battery pack (step S114) and executes processing for controlling the battery pack using a correction value lowered as compared with the calculated SOC (step S112 to step S114) when the identified voltage difference is equal to or larger than a specified value. Thereby, processing for controlling the battery pack using the correction value lowered as compared with the calculated SOC of the battery pack, is executed, when the voltage difference between the cells is equal to or larger than the specified value. By controlling the battery pack using the correction value lowered as compared with the calculated SOC, the battery pack is used in a range of high residual electric energy. Discharge is easy at the high residual electric energy. The voltage difference is gradually mitigated.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a battery management system, and more particularly to a battery management system that manages a battery pack in which cells including a positive electrode and a negative electrode are stacked. [Background technology]

[0002] Conventionally, there has been a battery pack in which multiple nickel-metal hydride cells are connected in series. In this battery pack, the voltage of each block consisting of a predetermined number of cells is detected. Then, when the voltage difference between the blocks reaches a predetermined value or more, the SOC (State Of Charge) of the battery pack is set to the lower control limit even if the SOC is equal to or higher than the lower control limit, and charging is started assuming that the SOC has reached the lower control limit (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2000-14029 A Summary of the Invention [Problem to be solved by the invention]

[0004] In a battery cell in which positive and negative electrodes are stacked and immersed in an electrolyte, minute foreign matter may be mixed into the cell due to manufacturing reasons. In this case, there is no problem with the charge / discharge performance, but the capacity may decrease. In such a case, in Patent Document 1, the voltage difference between the blocks becomes equal to or exceeds a predetermined value, and charging is started. If such charging is performed frequently, there is a risk of misunderstanding that the battery should be replaced, even though the battery performance is good.

[0005] This disclosure has been made to solve the above-mentioned problems, and has an object to provide a battery management system capable of reducing the voltage difference between cells. [Means for solving the problem]

[0006] The battery management system according to the present disclosure is a system for managing an assembled battery in which cells including positive and negative electrodes are stacked, and includes a processor and a determination unit for determining a voltage difference between the cells. The processor calculates an index value related to the remaining power of the assembled battery, and when the voltage difference determined by the determination unit is equal to or greater than a predetermined value, executes a process for controlling the assembled battery using a correction value that is smaller than the index value.

[0007] According to this configuration, when the voltage difference between the cells becomes equal to or greater than a predetermined value, a process is executed to control the battery pack using a correction value that is smaller than the calculated index value related to the remaining power of the battery pack. By controlling the battery pack using a correction value that is smaller than the index value related to the remaining power, the battery pack is used in a range where the remaining power is high. When the remaining power is high, the battery pack is easily discharged. Therefore, the voltage difference is gradually alleviated. As a result, a battery management system capable of reducing the voltage difference between the cells can be provided.

[0008] The processor may execute a process for controlling the battery pack by using a value obtained by subtracting a fixed value from the index value as a correction value. With this configuration, the correction value can be easily calculated.

[0009] The voltage difference may be a difference in voltage between adjacent cells, or a difference between an average cell voltage and the cell voltage. With this configuration, the voltage difference can be appropriately determined.

[0010] The processor may execute a process for controlling the battery pack using the index value after a period of time has elapsed since the processor started outputting the correction value, during which the variation in the voltage difference is eliminated. With this configuration, the period during which the correction value is used can be minimized.

[0011] The processor may execute a process for controlling the battery pack using the correction value when the index value is between the upper limit and lower limit of the charge / discharge control of the battery pack, and execute a process for controlling the battery pack using the index value when the index value is not between the upper limit and lower limit. With this configuration, when the index value is not between the upper limit and lower limit of the charge / discharge control, the index value is used instead of the correction value, so that it is possible to prevent a burden from being placed on the cells. Effect of the Invention

[0012] According to this disclosure, it is possible to provide a battery management system capable of reducing the voltage difference between cells. [Brief description of the drawings]

[0013] [Figure 1] 1 is a diagram showing an outline of the configuration of a battery management system according to an embodiment of the present invention; [Diagram 2] 4 is a flowchart showing the flow of a battery management process in this embodiment. [Diagram 3] 10 is a diagram for explaining raising of the control center of SOC of the battery pack 10 according to this embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference characters and their description will not be repeated.

[0015] Fig. 1 is a diagram showing an outline of the configuration of a battery management system 1 in this embodiment. With reference to Fig. 1, in this embodiment, the battery management system 1 is mounted on a vehicle. The battery management system 1 includes a battery pack 10, a battery management ECU (Electronic Control Unit) 100, and a load 900.

[0016] The battery pack 10 is a chargeable and dischargeable secondary battery, and includes a plurality of cells 20 each having an electrode plate 11, a negative electrode 12, a separator 14, a positive electrode 13, and another electrode plate 11 stacked in this order. A plurality of spaces surrounded by the electrode plates 11 and a case 31 are filled with an electrolyte 21 such as an electrolytic solution or a gel electrolyte. In this embodiment, the cells 20 are nickel-metal hydride batteries.

[0017] The electrode plate 11 is made of, for example, nickel or nickel steel plate. The positive electrode 13 includes a positive electrode active material layer. For example, nickel hydride is used as the positive electrode active material. In addition to the positive electrode active material, a conductive material and a binder may be contained. The negative electrode 12 includes a negative electrode active material. For example, a hydrogen storage alloy is used as the negative electrode active material. The separator 14 is made of a porous film made of a polyolefin resin such as polyethylene (PE) or polypropylene (PP), or a woven or nonwoven fabric made of polypropylene, polyethylene terephthalate (PET), methylcellulose, or the like, and is formed, for example, in a sheet shape. The separator 14 may be reinforced with a vinylidene fluoride resin compound.

[0018] An electrode plate 11 coated with a negative electrode 12 on one side and a positive electrode 13 on the other side is called a bipolar electrode. A battery having such a structure in which the electrode plate 11, in which the positive electrodes 13 and negative electrodes 12 of adjacent cells 20 are stacked, is shared between adjacent cells 20, is called a bipolar battery.

[0019] The battery management ECU 100 includes a CPU 110 which is a processor for executing predetermined processes, and a memory 120 which serves as a storage unit for storing predetermined information. The battery management ECU 100 is capable of communicating with another ECU 200.

[0020] The load 900 is a device that consumes power (for example, a drive device, a lighting device, a control device), but here it also includes a device that supplies power (for example, a power generation device, a power system). A current sensor 132 that measures the current flowing between the battery pack 10 and the load 900, and a switch 133 that opens and closes the current flowing between the battery pack 10 and the load 900 are provided between the battery pack 10 and the load 900. Voltage sensors 131A to 131N are provided as measurement units for measuring the potential difference between adjacent electrode plates 11 of the battery pack 10. Signals indicating the current and voltage measured by the current sensor 132 and the voltage sensors 131A to 131N, respectively, are transmitted to the battery management ECU 100. The opening and closing of the switch 133 is controlled by the battery management ECU 100.

[0021] In such a battery management system 1, minute foreign matter may be mixed into the cells 20 of the assembled battery 10 due to manufacturing reasons. For example, minute foreign matter may adhere to the surface of the negative electrode 12. In this case, there is no problem with the charge / discharge performance, but the capacity may decrease. In such a case, it is possible to control the charging to start when the voltage difference between the cells 20 becomes a predetermined value or more. If such charging is performed frequently, there is a risk of misunderstanding that it is better to replace the assembled battery 10 even though the battery performance is good.

[0022] Therefore, the CPU 110 of the battery management ECU 100 of the battery management system 1 calculates the SOC, which is an index value related to the remaining power amount of the battery pack 10, and when the voltage difference identified by the voltage sensors 131A to 131N that measure the voltage difference between the cells 20 becomes equal to or greater than a predetermined value, executes processing to control the battery pack 10 using a correction value that is smaller than the calculated SOC.

[0023] As a result, when the voltage difference between the cells 20 becomes equal to or greater than a predetermined value, a process is executed to control the battery pack 10 using a correction value that is smaller than the calculated SOC of the battery pack 10. By controlling the battery pack 10 using a correction value that is smaller than the calculated SOC, the battery pack 10 is used in a range where the remaining power is high. When the remaining power is high, the cells 20 are likely to be discharged. Therefore, the voltage difference between the cells 20 is gradually alleviated. As a result, the voltage difference between the cells 20 can be reduced.

[0024] Fig. 2 is a flowchart showing the flow of the battery management processing in this embodiment. Referring to Fig. 2, the program for this battery management processing is stored in the memory 120 of the battery management ECU 100, and is called from a higher-level process and executed by the CPU 110 of the battery management ECU 100 at predetermined intervals.

[0025] In this embodiment, the battery management system 1 is started when the vehicle is Ready-ON. The CPU 110 of the battery management ECU 100 determines whether or not this is the first execution cycle of the battery management process when the vehicle is Ready-ON (step S111). If it is determined that this is not the first execution cycle when the vehicle is Ready-ON (NO in step S111), the CPU 110 advances the process to be executed to step S121.

[0026] On the other hand, if it is determined that it is the first execution cycle when ReadyON is active (YES in step S111), CPU 110 identifies the voltage differences between the cells 20 from the voltage values ​​indicated by the signals from voltage sensors 131A-131N (step S112). Then, CPU 110 determines whether any of the identified voltage differences exceeds a predetermined value (step S113). If minute foreign matter is mixed into the cells 20 for manufacturing reasons, the voltage differences between the cells 20 may exceed the predetermined value.

[0027] If CPU 110 determines that none of the voltage differences exceeds the predetermined value (NO in step S113), CPU 110 proceeds to step S121. On the other hand, if CPU 110 determines that any of the voltage differences exceeds the predetermined value (YES in step S113), CPU 110 increases the control center of SOC by a predetermined amount (step S114).

[0028] 3 is a diagram for explaining the raising of the control center of SOC of the battery pack 10 according to this embodiment. Referring to FIG. 3, the base line is the line before the control center of SOC is raised. On this base line, the calculated SOC and the corrected SOC value are the same value.

[0029] When the calculated SOC is between a% (lower control limit) and f% (upper control limit), the line where the control center is raised (the line corresponding to a micro-short circuit in the figure) shows that the SOC correction value for the calculated SOC is smaller than the base line.

[0030] Specifically, when the calculated SOC is between b% and e%, the line corresponding to the small short circuit is smaller than the base line by k%. By following this line corresponding to the small short circuit, for example, when the calculated SOC is c%, the corrected SOC value is ck%, so that when the actual SOC is c%, the charge / discharge control for the SOC being ck% is executed.

[0031] That is, the control center may be used such that when the SOC is higher than the control center, control is given priority to discharging from the battery, whereas when the SOC is lower than the control center, control is given priority to charging to the battery. In this case, if the control center is g (= dk)%, when the SOC correction value is not used, control is performed such that the charge / discharge priority control is switched when the actual SOC is g%. On the other hand, when the SOC correction value is used, control is performed such that the charge / discharge priority control is switched when the actual SOC is d%. In this way, the control center is raised by using the correction value.

[0032] When the calculated SOC is between b% and e%, the line corresponding to the micro short circuit has the same slope as the base line. As a result, for example, when the SOC is displayed on a meter panel, the battery management ECU 100 transmits a correction value of the SOC to an ECU that controls the display of the meter panel, which is one of the other ECUs 200, so that when the actual SOC is between b% and e%, the displayed SOC changes between bk% and ek%, and the relationship between the increase and decrease between the two is not lost. Also, in a hybrid vehicle, the relationship between the SOC value that switches between engine running and motor running before and after the SOC correction can be maintained.

[0033] Between b% and a%, and between e% and f%, the difference in SOC between the micro-short circuit compatible wire and the base wire gradually decreases from k% to 0%. At the lower limit, over-discharge can be suppressed and the cell 20 can be protected. At the upper limit, an increase in internal pressure can be suppressed and the cell 20 can be protected.

[0034] Furthermore, the amount by which the line corresponding to a minute short circuit is made smaller than the base line (here, k%) can be determined, for example, so that the deterioration in fuel economy is less than a predetermined rate (for example, 0.5%).

[0035] Returning to FIG. 2, next, the CPU 110 of the battery management ECU 100 calculates the elimination time for the variation in the voltage difference (step S115). In the battery pack 10 (particularly nickel-metal hydride batteries) of this embodiment, the cells 20 have a characteristic that they are easily discharged at a high SOC, so by raising the control center, the SOC difference (voltage difference) is gradually alleviated as the battery pack 10 is charged and discharged. This reduces the variation in the voltage difference. For example, the elimination time is calculated as the time when all the voltage differences between the cells 20 become equal to or less than a predetermined percentage (e.g., 50%) of the predetermined value used in step S113.

[0036] For example, during soaking from ReadyOFF to ReadyON and during driving from ReadyON to ReadyOFF, the self-discharge current of the cell 20 increases in a predetermined relationship with an increase in SOC and an increase in the temperature of the battery pack 10. Using this relationship, an acceleration coefficient map is created in advance to specify an acceleration coefficient for the self-discharge current during soaking and driving. Then, the acceleration coefficient for the self-discharge current is multiplied by the actual time of the soaking time or driving time to calculate the dissolution time.

[0037] After step S115, or if the answer is NO in step S111 or step S113, CPU 110 determines whether the resolution time calculated in step S115 has elapsed since the control center of SOC was raised in step S114 (step S121). If the resolution time has elapsed (YES in step S121), CPU 110 cancels the raising of the control center of SOC (step S122).

[0038] If it is determined that the resolution time has not elapsed (NO in step S121), or after step S122, CPU 110 returns the process to be executed to the upper process that called this battery management process.

[0039] [Variations] (1) In the above-described embodiment, the battery pack 10 is of a bipolar type. However, this is not limited thereto, and the battery pack 10 may be configured by connecting terminals of a plurality of independently formed cells in series with a bus bar.

[0040] (2) In the above-described embodiment, one pair of a positive electrode and a negative electrode is provided in one cell 20. However, this is not limited thereto, and multiple pairs of a positive electrode and a negative electrode may be provided in one cell.

[0041] (3) In the above-described embodiment, the battery management system 1 is mounted on a vehicle. The vehicle may be a battery-equipped vehicle such as a BEV (Battery Electric Vehicle), a HEV (Hybrid Electric Vehicle), a PHEV (Plug-in Hybrid Electric Vehicle), a FCEV (Fuel Cell Electric Vehicle), or an engine vehicle that uses gasoline, diesel, hydrogen, or the like as fuel. The battery management system 1 may also be mounted on another machine or a stationary power storage device.

[0042] (4) In the above-described embodiment, the calculated SOC or correction value is used for charge / discharge control of the battery pack 10 by the battery management ECU 100. However, the present invention is not limited to this, and the calculated SOC or correction value may be used for charge / discharge control of the battery pack 10 by the other ECU 200, or for other control of the battery pack 10 by the battery management ECU 100 or the other ECU 200, such as displaying the SOC of the battery pack 10 on a meter panel.

[0043] (5) In the above-described embodiment, the index value related to the remaining power of the battery pack 10 is the SOC. However, the index value is not limited to this and may be another index value, for example, the remaining power (kWh) itself.

[0044] (6) In the above-described embodiment, this disclosure is applicable to the battery pack 10 that is a nickel-metal hydride battery. However, this is not limited thereto, and this disclosure is applicable to other battery packs as long as the battery has the characteristic that the self-discharge amount increases as the battery approaches a high SOC region.

[0045] (7) The above-described embodiment can be understood as a disclosure of the battery management system 1, and can be understood as a disclosure of a charge management method in the battery management system 1, or a program for charge management processing executed by the battery management ECU 100, or a recording medium having a program recorded thereon.

[0046] [summary] (1) As shown in Fig. 1, the battery management system 1 is a system for managing an assembled battery 10 in which cells 20, each including a positive electrode 13 and a negative electrode 12, are stacked, and includes a CPU 110 of a battery management ECU 100 and voltage sensors 131A-131N for identifying a voltage difference between the cells 20. As shown in Fig. 2 and Fig. 3, the CPU 110 calculates an index value (e.g., SOC) related to the remaining power amount of the assembled battery 10 (e.g., step S114), and when the identified voltage difference becomes equal to or greater than a predetermined value, executes a process for controlling the assembled battery 10 using a correction value that is smaller than the index value (e.g., steps S112-S114).

[0047] As a result, when the voltage difference between the cells 20 becomes equal to or greater than a predetermined value, a process is executed to control the battery pack 10 using a correction value that is smaller than the calculated SOC of the battery pack 10. By controlling the battery pack 10 using a correction value that is smaller than the calculated SOC, the battery pack 10 is used in a range where the remaining power is high. When the remaining power is high, the battery pack 10 is easily discharged. Therefore, the voltage difference is gradually alleviated. As a result, the voltage difference between the cells 20 can be reduced.

[0048] (2) As shown in Fig. 2 and Fig. 3, the CPU 110 may execute a process for controlling the battery pack 10 by using a value obtained by subtracting a fixed value (for example, k%) from the calculated SOC as a correction value. This makes it possible to easily calculate the correction value.

[0049] (3) As shown in Fig. 2, the voltage difference may be the difference in voltage between adjacent cells 20, or may be the difference between the average voltage of all cells 20 included in the battery pack 10 and the voltage of the cell 20. This allows the voltage difference to be appropriately determined.

[0050] (4) As shown in Fig. 2, after the CPU 110 starts outputting the correction value and a period of time for the variation in the voltage difference to be eliminated has elapsed, the CPU 110 may execute a process for controlling the battery pack using the index value (steps S121 and S122). This makes it possible to minimize the period during which the correction value is used.

[0051] 2 and 3, the CPU 110 may execute a process for controlling the battery pack 10 using a correction value when the calculated SOC is between the upper limit and lower limit of the charge / discharge control of the battery pack 10, and may execute a process for controlling the battery pack 10 using the calculated SOC when the calculated SOC is not between the upper limit and lower limit. In this way, when the calculated SOC is not between the upper limit and lower limit of the charge / discharge control, the calculated SOC is used instead of the correction value, so that it is possible to prevent a burden on the cells.

[0052] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the disclosure is defined by the claims, not by the description of the embodiments described above, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0053] 1 battery management system, 10 battery pack, 11 electrode plate, 12 negative electrode, 13 positive electrode, 14 separator, 20 cell, 21 electrolyte, 31 housing, 100 ECU, 110 CPU, 120 memory, 131A to 131N voltage sensors, 132 current sensor, 133 switch, 200 other ECU, 900 load.

Claims

1. A battery management system for managing a battery pack in which cells including a positive electrode and a negative electrode are stacked, A processor; and a determination unit for determining a voltage difference between the cells, The processor, Calculating an index value relating to a remaining power amount of the battery pack; When the voltage difference identified by the identification unit becomes equal to or greater than a predetermined value, a process is executed to control the battery pack using a correction value that is smaller than the index value.

2. The battery management system according to claim 1 , wherein the processor executes a process for controlling the assembled battery by using a value obtained by subtracting a fixed value from the index value as the correction value.

3. The battery management system of claim 1 , wherein the voltage difference is a difference in voltage between adjacent cells or a difference between an average cell voltage and the cell voltage.

4. 2 . The battery management system according to claim 1 , wherein the processor executes a process for controlling the assembled battery using the index value after a period of time has elapsed since the processor started to output the correction value, during which the variation in the voltage difference is eliminated.

5. The processor, When the index value is between an upper limit value and a lower limit value of charge / discharge control of the battery pack, a process is executed to control the battery pack using the correction value, The battery management system according to claim 1 , further comprising: a process for controlling the battery pack using the index value when the index value is not between the upper limit value and the lower limit value.

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