Battery system control method and battery system

Abstract

Provided is a battery system control method and a battery system that can use an initial capacity by sufficiently charging and discharging, even when a plurality of battery modules are connected in parallel. The present invention comprises: a module (M) provided with a plurality of stacked battery cells (C), a plurality of modules (M) being connected in parallel; a pressurization mechanism (P) that is provided for each of a plurality of modules (M) and that can change the pressure applied to a module (M); and a control controller (1) that controls the pressurization mechanism (P). The control controller (1) executes current distribution to the modules (M) connected in parallel by controlling pressurization on the plurality of modules (M) through the pressurization mechanism (P).

Description

Battery system control method and battery system

[0001] An embodiment of the present invention relates to a battery system control method and a battery system.

[0002] When multiple batteries are connected in parallel, if a voltage difference occurs among the batteries due to, for example, differences in the environment or performance, a current flows between the batteries, which is called a circulating current. When a circulating current occurs, a battery being charged may be overcharged, while a battery being discharged may be overdischarged. Therefore, the technology disclosed in Patent Document 1 prevents overcharging due to a circulating current, particularly during charging, by stopping charging and discharging early when such a condition occurs.

[0003] JP 2018-050400 A

[0004] However, if the charging / discharging process is stopped early to avoid the adverse effects of circulating current, the charging process may end before a battery is fully charged, while the discharging process may end before a battery is fully discharged. This can result in a situation where the capacity of an individual battery or the entire battery system consisting of multiple batteries cannot be fully utilized.

[0005] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a battery system control method and a battery system that can utilize the initial capacity by sufficiently charging and discharging even when multiple battery modules are connected in parallel.

[0006] A control method for a battery system in an embodiment of the present invention includes a module having a plurality of stacked battery cells, a plurality of which are connected in parallel, a pressure mechanism provided for each of the plurality of modules and capable of changing the pressure applied to the module, and a control controller that controls the pressure mechanism, and the control controller distributes current to the modules connected in parallel by controlling the pressure applied to the plurality of modules by the pressure mechanism.

[0007] Furthermore, a battery system according to an embodiment of the present invention includes a module having a plurality of stacked battery cells connected in parallel, a pressurizing mechanism provided for each of the modules and capable of changing the pressure applied to the module, and a control controller that controls the pressurizing mechanism, and the control controller controls the pressurizing mechanism to change the pressure applied to each of the modules when a difference between estimated values ​​of the progress of open-circuit voltages (hereinafter referred to as "OCV: Open-Circuit Voltage") in each of the modules is greater than a preset threshold value.

[0008] Since the present invention employs such a configuration, even if a plurality of battery modules are connected in parallel, the initial capacity can be utilized by sufficiently charging and discharging the battery modules.

[0009] Fig. 1 is a block diagram showing the overall configuration of a battery system according to an embodiment of the present invention. Fig. 2 is a block diagram showing the internal configuration of a control controller according to an embodiment of the present invention. Fig. 3 is an explanatory diagram showing the intention of control in a control method for a battery system according to an embodiment of the present invention. Fig. 4 is an explanatory diagram explaining the relationship between pressure applied to a battery cell and the internal resistance value of a module in a control method for a battery system according to an embodiment of the present invention. Fig. 5 is a flowchart showing the flow of a control method for a battery system according to an embodiment of the present invention. Fig. 6 is a flowchart showing the flow of another method for calculating a current distribution ratio in a control method for a battery system according to an embodiment of the present invention.

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the drawings are schematic and may differ from the actual product. Furthermore, the embodiments of the present invention shown below are merely examples of devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention does not limit the structure, arrangement, etc. of the components to those described below. The technical concept of the present invention can be modified in various ways within the technical scope defined by the claims.

[0011] 1 is a block diagram showing the overall configuration of a battery system BS according to an embodiment of the present invention. The battery system BS according to the embodiment of the present invention includes at least a module M, a pressurizing mechanism P, and a controller 1. The battery system BS is mounted on a vehicle for use, for example.

[0012] The module M is composed of a plurality of stacked battery cells C. Each battery cell C is, for example, a stacked electrode body in which a predetermined number of flat-shaped unit cells, each of which is made by stacking a positive electrode, an electrolyte, and a negative electrode (not shown), are stacked in the thickness direction, and the stacked electrode body is housed in an exterior material such as a laminate film.

[0013] A battery cell C includes a main body that houses the stacked electrode assembly and electrode tabs that protrude from both sides of the main body in a direction perpendicular to the stacking direction. The electrode tabs are joined to the current collectors of the electrodes (positive or negative electrodes) of the battery cell C. Thus, the positive electrode tabs are connected to the respective positive electrodes in the battery cell C, and the negative electrode tabs are connected to the respective negative electrodes, thereby extracting current from the respective electrodes (moving electrons to the outside of the battery cell C).

[0014] In the embodiment of the present invention, the battery constituting the module M may be any of various secondary batteries, such as a lithium ion battery that uses a solid electrolyte as the electrolyte and lithium metal or a lithium-containing alloy as the negative electrode.

[0015] In the module M according to the embodiment of the present invention, a plurality of these individual battery cells C are stacked and arranged. The module M also includes a pressure mechanism P that applies pressure to the plurality of cells C in the stacking direction.

[0016] The pressure mechanism P includes a pair of pressure plates PP, PP, a motor gear MG, and a driver D. The pair of pressure plates PP, PP are arranged on both ends of the stacking direction of the battery cells C, and sandwich the stacked battery cells C. The battery cells C are pressed by being sandwiched between the pair of pressure plates PP, PP arranged on both ends.

[0017] Furthermore, the outermost battery cell C of the stacked battery cells C is in contact with a pair of pressure plates PP, PP. Therefore, pressure from the pressure plate PP is applied directly to the stacked battery cells C. However, instead of the battery cell C and the pressure plate PP being in direct contact, for example, an elastic body such as a spring may be provided between the pressure plate PP and the battery cell C.

[0018] The motor gear MG is in contact with one of the pressure plates PP, making it possible to change the pressure applied to the battery cell C (module M). A driver D applies a drive signal to the motor gear MG. The driver D applies the drive signal to the motor gear MG based on a signal sent from the controller 1.

[0019] That is, a signal from the controller 1 is input to the driver D, and a drive signal from the driver D is input to the motor gear MG. The motor is then driven, and a force is applied to the pressure plate PP via the gear. This causes the pressure plate PP to move in the stacking direction of the battery cells C in the module M, applying pressure to the battery cells C.

[0020] 1, the pressure mechanism P is depicted as if the motor gear MG is only applied to one of the pair of pressure plates PP, PP, the one to which the motor gear MG is connected. Therefore, no driving force is applied to the other pressure plate PP, so that the other pressure plate PP does not move and instead receives the pressure applied to the battery cells C by the one pressure plate PP.

[0021] However, the present invention is not limited to this mechanism, and for example, not only one pressure plate PP but also the other pressure plate PP may be movable in the stacking direction. In this type of mechanism, pressure is applied to the stacked battery cells C from both of the pair of pressure plates PP, PP located at both ends.

[0022] Furthermore, regarding the motor and gear MG, the example given here is a case where the pressure mechanism P applies pressure to the module M by moving the pressure plate PP using a motor and gear. However, instead of this mechanism, any mechanism other than the above can be used as long as it can change the position of the pressure plate PP by controlling the pressure mechanism P and can arbitrarily change the pressure applied to the battery cells C, without using a combination of motors and gears.

[0023] The module M is provided with an ammeter A that detects the value of the current flowing through the battery cell C, a voltmeter V that detects the value of the voltage, and a thermometer T that detects the value of the temperature. Information regarding the current value, voltage value, and temperature value detected by each detector is sent to the controller 1.

[0024] Information on the detected values ​​detected by the ammeter A, voltmeter V, and thermometer T is input to the control controller 1. Furthermore, as will be described later, the control controller 1 uses the input information on the detected values ​​to calculate the pressure to be applied to the module M (battery cells C), and applies pressure to the battery cells C via the pressure mechanism P based on the calculated pressure value.

[0025] The control controller 1 also transmits a control signal to the power control device 2. The power control device 2 discharges or charges any power from the battery cells C based on commands from the control controller 1. Furthermore, the power control device 2 may be, for example, an inverter for a vehicle drive motor, extracting power from the battery system BS to obtain driving force and supplying regenerated energy to the battery system BS during braking. Alternatively, the power control device 2 may function as a DC-DC converter that charges a low-voltage battery that supplies power to the control controller 1.

[0026] 1, the stacked battery cells C are depicted as a group, and individual battery cells C are not depicted. In addition, the battery system BS according to the embodiment of the present invention is premised on the premise that a plurality of modules M are connected in parallel to the power control device 2.

[0027] 1, two modules M are connected in parallel to the power control device 2, but three or more modules M may be connected in parallel. Furthermore, if multiple modules M are connected in parallel, for example, one of the parallel-connected modules M may further be connected in series. Alternatively, one parallel circuit may be connected in series with multiple modules.

[0028] Although the battery cells C are described here as being included in the module M, other components may also be included. For example, the pressure plates PP, PP arranged at both ends of the battery cells C in the stacking direction can also be understood to be included in the module M.

[0029] 1 also shows solid and dashed arrows. Of these, the solid arrows indicate the actual movement of an object, such as when one of the pressure plates PP is moved by the driving of the motor gear MG. On the other hand, the dashed arrows indicate the flow of information. Therefore, for example, signals transmitted from the control controller 1 to the driver D or the power control device 2 are indicated by dashed arrows directed from the control controller 1 to the driver D or the power control device 2.

[0030] 2 is a block diagram showing the internal configuration of the control controller 1 according to the embodiment of the present invention. The control controller 1 includes a central processing unit (CPU) 11, a read-only memory (ROM) 2, a random access memory (RAM) 13, and an input / output interface 14, all of which are connected via a bus 15. The input / output interface 14 is further connected to an information acquisition unit 16, a storage unit 17, a calculation unit 18, a determination unit 19, and a drive control unit 20.

[0031] The CPU 11 reads and executes a boot program for starting up the controller 1 from the ROM 12 based on an input signal from an input unit (not shown), and reads various operating systems stored in the storage unit 17. The CPU 11 may also control various devices based on input signals from other external devices (not shown in Fig. 2) via the input / output interface 14.

[0032] Furthermore, the CPU 11 reads out programs and data stored in the RAM 13, the storage unit 17, etc., and loads them into the RAM 13. Additionally, based on commands from the programs read out from the RAM 13, the CPU 11 manages the controller 1, calculates current distribution to the modules M connected in parallel, or controls pressure application to the multiple modules M by the pressure mechanism P. Therefore, the CPU 11 is a processing device that realizes a series of processes, such as calculation and processing of data, required for performing these processes.

[0033] The information acquisition unit 16 acquires information on the current value, voltage value, and temperature value detected by the ammeter A, voltmeter V, and thermometer T. The storage unit 17 is composed of a semiconductor or a magnetic disk. The storage unit 17 stores programs and data executed by the CPU 11, for example, for setting the pressure to be applied to the module M using the pressure mechanism P. The storage unit 17 may also store various information acquired by the information acquisition unit 16 as appropriate.

[0034] The calculation unit 18 performs calculations to calculate various values ​​required to determine how much pressure to apply to the modules M. Specifically, the calculation unit 18 first calculates the state of charge (hereinafter referred to as "SOC: State of Charge") of each module M. The method used to calculate the SOC here is a method that uses the integrated value of the current flowing through the module M, but other known methods can also be used.

[0035] Next, the calculation unit 18 calculates the current distribution ratio for each module M. Here, Fig. 1 shows a state in which two modules are connected in parallel to the current control device 2. Therefore, the current distribution ratio for the first module M1 and the second module M2 is calculated.

[0036] In the following, when describing individual modules, module M will be referred to as "first module M1" and "second module M2" as appropriate, and when describing them collectively, they will be referred to as "module M" as before.

[0037] First, the current values ​​flowing through the first module M1 and the second module M2 are acquired. The current values ​​are detected by ammeters A provided in the first module M1 and the second module M2, respectively, and acquired by the information acquisition unit 16. The calculation unit 18 grasps the current values ​​in each module M acquired by the information acquisition unit 16.

[0038] Here, the value of the current flowing through the first module M1 is "I1," and the value of the current flowing through the second module M2 is "I2." The value of the current flowing through the battery system BS, which is provided with multiple modules M, is also indicated as "I." Therefore, the relationship I = I1 + I2 holds.

[0039] Furthermore, if the current distribution ratio for the first module M1 is Ratio1 and the current distribution ratio for the second module M2 is Ratio2, the respective current distribution ratios can be calculated as follows: That is, the current distribution ratio Ratio1 for the first module M1 can be obtained from the following equation (1).

[0040] Ratio1=I1 / (I1+I2)...(1)

[0041] Similarly, the current distribution ratio Ratio2 for the second module M2 can be calculated using the following equation (2): In other words, by calculating the current distribution ratio, it is possible to determine how much of the current flowing through the battery system BS flows to each module M.

[0042] Ratio2=I1 / (I1+I2)...(2)

[0043] After calculating the current distribution ratio for each module M, the calculation unit 18 then calculates a transition value of the value of the voltage information for each module. This "transition value of the value of the voltage information for each module" is a transition value when the charging current Iin flows continuously through the module M for a predetermined time T when the battery system BS is charged under the control of the power control device 2. Here, the "transition value" does not refer to the OCV at the time when the calculation unit 18 performs the calculation, but rather to the OCV transition value after the predetermined time T has elapsed, that is, a value in the future. Therefore, hereinafter, this transition value will be referred to as a "transition estimated value" as appropriate.

[0044] The value calculated as the transition estimated value is a value of voltage information, and the "voltage information" may be, for example, an OCV or an SOC. In the following description, the OCV is used as the voltage information. Therefore, the transition estimated value will also be referred to as an "OCV transition estimated value" as appropriate.

[0045] Furthermore, the values ​​of the predetermined time T and the charging current Iin are set to values ​​that have been previously set through experiments, etc. This is because the OCV transition estimated value calculated by the calculation unit 18 is a future value, and the values ​​of the predetermined time T and the charging current Iin must be set in advance for the calculation.

[0046] When calculating the OCV transition estimated value, the calculation unit 18 first calculates the transition value of the SOC when the charging current Iin continues to flow through the module M for a predetermined time T. Here, if the SOC transition value of the first module M1 is "SOC1e", SOC1e is calculated using the following equation (3).

[0047] SOC1e=SOC1+∫(Iin×Ratio1)dt(t=0~T)÷K×100...(3)

[0048] Similarly, if the SOC transition value in the second module M2 is "SOC2e", SOC2e is calculated using the following equation (2).

[0049] SOC2e=SOC2+∫(Iin×Ratio2)dt(t=0~T)÷K×100...(4)

[0050] In the formulas (3) and (4), K is the battery capacity [Ah] of the module M1 and the module M2.

[0051] Here, "SOC1" in equation (3) and "SOC2" in equation (4) are SOC values ​​calculated in advance by the calculation unit 18 for each module M as described above. That is, "SOC1" is the charging rate of the first module M1, and "SOC2" is the charging rate of the second module M2.

[0052] The "SOC1e" and "SOC2e" calculated by the calculation unit 18 using the formulas (3) and (4) are the charging rates of the respective modules after a predetermined time T has elapsed (in the future). Then, based on the "SOC1e" of the first module M1 and the "SOC2e" of the second module M2, the calculation unit 18 calculates an OCV transition estimated value (OCV1e) in the first module M1 and an OCV transition estimated value (OCV1e) in the second module M2 using the "SOC-OCV characteristic data."

[0053] The "SOC-OCV characteristic data" is stored in advance in the storage unit 17. Therefore, when the calculation unit 18 calculates OCV1e and OCV2e, it accesses the storage unit 17 and assigns the values ​​of SOC1e and SOC2e to the "SOC-OCV characteristic data."

[0054] Then, based on the calculated values ​​of OCV1e and OCV2e, the absolute value of the difference between them is calculated, and the calculated absolute value is transmitted to the determination unit 19. The determination unit 19 compares the absolute value of the difference between the OCV1e of the first module M1 and the OCV2e of the second module M2 calculated by the calculation unit 18 with a threshold value.

[0055] If an unacceptable voltage difference occurs between the first module M1 and the second module M2, there is a possibility that a circulating current will occur as described above. If a circulating current occurs, for example, the module M being charged will be overcharged, but if the charging process is stopped early to avoid overcharging, it may actually result in insufficient charging.

[0056] Therefore, in order to avoid the occurrence of circulating current, the judgment unit 19 judges whether the difference in the future OCV trend estimated values ​​of multiple modules M (here, the first module M1 and the second module M2) connected in parallel is within an allowable voltage difference range.

[0057] The absolute value of the difference between the estimated OCV transition values ​​of the first module M1 and the second module M2 is calculated because it is unknown which of the estimated OCV transition values ​​of the first module M1 and the second module M2 has a larger value. The threshold value is a value that is set in advance, for example, through experiments, based on whether the difference between the estimated OCV transition values ​​of the first module M1 and the second module M2 falls within an allowable range. The threshold value is stored in the storage unit 17.

[0058] If the difference between the estimated OCV transition values ​​of the first module M1 and the second module M2 is within the allowable voltage difference range (difference in estimated OCV transition values≦threshold value), the determination unit 19 can determine that the possibility of circulating current generation is low. Therefore, in this case, there is no need to change the current distribution ratio for each module M.

[0059] On the other hand, if the difference between the estimated OCV transition values ​​of the first module M1 and the second module M2 is not within the allowable voltage difference range (the difference between the estimated OCV transition values ​​is greater than the threshold), the voltage difference between the first module M1 and the second module M2 will be large, increasing the possibility of circulating current. In such a case, the imbalance in the voltage difference is eliminated by controlling the pressure mechanism P, as described below, to change the current distribution ratio and control the amount of current flowing through each module.

[0060] The pressure mechanism P is controlled by the drive control unit 20 in the controller 1 by transmitting a control signal to the driver D of the pressure mechanism P provided in the module M to be controlled. In other words, the drive control unit 20 controls the pressure mechanism P based on the determination result of the determination unit 19.

[0061] 3 is an explanatory diagram showing the intent of control in the control method for the battery system BS according to the embodiment of the present invention. In the explanatory diagram shown in FIG. 3, the horizontal axis represents time, and a predetermined time T is indicated at a certain point on the horizontal axis. The vertical axis represents the OCV transition estimated value of the module M, and the OCV transition estimated value OCV1e of the first module M1 and the OCV transition estimated value OCV2e of the second module M2 at the predetermined time T are shown.

[0062] The diagram also shows transitions X and Y, which are indicated by solid lines. The transition X represents a change in the estimated OCV transition value over time in the first module M1. The transition Y represents a change in the estimated OCV transition value over time in the second module M2. Although the transitions X and Y coincide at the origin of the diagram, a difference occurs in the estimated OCV transition value as time passes.

[0063] On the other hand, the transition Z indicated by the dashed line in the explanatory diagram of FIG. 3 indicates the change in the OCV transition estimated value when there is no difference R (zero) between the OCV transition estimated values ​​in the first module M1 and the second module M2 at a predetermined time T.

[0064] That is, transition Z indicates a state in which there is no voltage difference between the OCV transition estimated value of the first module M1 and the OCV transition estimated value of the second module M2 from time zero (origin) to a predetermined time T.

[0065] 3, the transitions X, Y, and Z are all shown rising to the right. That is, this diagram shows the change in the estimated OCV transition value when charging the module M. On the other hand, although not shown, when the change in the estimated OCV transition value when discharging is performed is shown using the transitions X, Y, and Z in the same way as in FIG. 3, all of them are shown falling to the right.

[0066] When viewing the transitions X and Y in this diagram, the difference between the estimated OCV transitions of the first module M1 and the second module M2 at a predetermined time T is indicated by the symbol R in FIG. 3. If the absolute value of the difference R is equal to or less than a threshold, it can be determined that the possibility of circulating current occurring is low. Therefore, in such a case, the current current distribution ratio between the first module M1 and the second module M2 may be maintained.

[0067] On the other hand, if the absolute value of the difference R in the estimated OCV transition values ​​between the first module M1 and the second module M2 at the predetermined time T is greater than the threshold value, it can be determined that there is a high possibility of a circulating current occurring. In such a case, the controller 1 changes the current distribution ratio between the first module M1 and the second module M2 and controls the pressurizing mechanism P so that the difference R in the estimated OCV transition values ​​between the first module M1 and the second module M2 at the predetermined time T becomes smaller.

[0068] For example, the controller 1 controls the pressure mechanism P provided in the first module M1 to make the change in the estimated OCV1e gradual. When such control is performed, the estimated OCV1e changes in the direction indicated by the downward arrow in the explanatory diagram of Figure 3, while the estimated OCV1e for the second module M2 changes in the direction indicated by the upward arrow. That is, the absolute value of the difference R between the estimated OCVs for the first module M1 and the second module M2 at the predetermined time T becomes smaller.

[0069] Alternatively, the controller 1 controls the pressure mechanism P provided in the second module M2 to make the change in the estimated OCV2e steeper. By performing such control, the second module M2 changes in the direction indicated by the upward arrow, while the first module M1 changes in the direction indicated by the downward arrow in the explanatory diagram of FIG. 3. That is, the absolute value of the difference R between the estimated OCVs of the second module M2 and the first module M1 at the predetermined time T becomes smaller.

[0070] Instead of controlling the pressure mechanism P of either the first module M1 or the second module M2, the controller 1 may control each of the pressure mechanisms P of both modules so that the transitions X and Y approach each other, resulting in a change in the estimated OCV transition value as shown by the transition Z, for example.

[0071] Next, the reason why the controller 1 controls the pressurizing mechanism P in this manner to cause a change in the estimated OCV transition value will be described with reference to Fig. 4. As a premise for the description, it is assumed that the pressurizing mechanism P controlled by the controller 1 is the module M having a large estimated OCV transition value.

[0072] 3, for example, the first module M1, indicated by the transition X, shows a large transition estimated value at a predetermined time T. Therefore, the pressure mechanism P (module M) to be controlled is assumed to be the first module M1.

[0073] As described above, when the determination unit 19 determines that the absolute value of the difference between the OCV transition estimated values ​​is greater than the threshold value, it controls the pressurizing mechanism P. Note that, hereinafter, the pressure applied from the pressurizing mechanism P to the first module M1 (battery cell C) before the pressurizing mechanism P is controlled via the drive control unit 20 will be referred to as the "initial surface pressure" as appropriate.

[0074] Furthermore, the pressure applied to the first module M1 (battery cell C) by controlling the pressure mechanism P based on the determination result by the determination unit 19 will be referred to as the "surface pressure after pressure control" below.

[0075] 4 is an explanatory diagram illustrating the relationship between the pressure applied to the battery cells C and the internal resistance value of the module M in the control method for the battery system BS according to the embodiment of the present invention. In the explanatory diagram of FIG. 4, the horizontal axis represents the pressure (surface pressure) (MPa) applied to the module M (battery cells C) by the pressure mechanism P. The surface pressure increases from left to right on the horizontal axis. Meanwhile, the vertical axis represents the internal resistance value (Ω) of the module M.

[0076] The internal resistance value when the surface pressure applied to the battery cell C by the pressure mechanism P is the initial surface pressure is indicated by the symbol M. However, as indicated by the left-pointing arrow in the explanatory diagram of Figure 4, when the pressure applied to the battery cell C is reduced by controlling the pressure mechanism P so that the initial surface pressure becomes the surface pressure after pressure control, the internal resistance value changes from the value indicated by the symbol M to the value indicated by the symbol N. In other words, the relationship between the surface pressure applied to the battery cell C and the internal resistance value of the battery cell C is such that the lower the surface pressure, the higher the internal resistance value, and the higher the surface pressure, the lower the internal resistance value.

[0077] Since there is such a relationship between the surface pressure applied to the battery cell C and the internal resistance value of the battery cell C, when the absolute value of the difference between the OCV transition estimated values ​​of the first module M1 and the second module M2 indicates a value greater than a threshold value, the control controller 1 drives the pressure mechanism P connected to the first module M1 to reduce the surface pressure.

[0078] That is, as shown in Fig. 4, the pressure applied to the battery cells C in the first module M1 is reduced so that the surface pressure after pressure control decreases from the initial surface pressure. As the pressure applied to the battery cells C decreases, the internal resistance of the battery cells C increases from internal resistance M to internal resistance N, for example, as shown in the explanatory diagram of Fig. 4.

[0079] Because the internal resistance value of the first module M1 increases in this way, it becomes more difficult for current to flow through the first module M1. This reduces the growth (increase) of the estimated OCV transition value of the first module M1. As a result, the slope of the transition X becomes gentler, as shown by the downward arrow in FIG. 3 , which indicates the change in the estimated OCV transition value over time in the first module M1.

[0080] On the other hand, the fact that the current flowing through the first module M1 becomes difficult means that the amount of current flowing through the second module M2 connected in parallel increases, which means that the current distribution ratio between the first module M1 and the second module M2 is changed.

[0081] Therefore, when the amount of current flowing through the second module M2, which has a relatively lower estimated OCV transition value than the first module M1, increases, the estimated OCV transition value of the second module M2 increases. In other words, the slope of the transition Y, which indicates the change in the estimated OCV transition value of the second module M2 over time in FIG. 3, becomes steeper than the previous slope, as indicated by the upward arrow.

[0082] As described above, by controlling the pressure mechanism P connected to the first module M1 to reduce the surface pressure, the difference between the estimated OCV transition value OCV1e in the first module M1 and the estimated OCV transition value OCV2e in the second module M2 becomes smaller. If the difference between the two values ​​becomes smaller in this way, it is possible to reduce the possibility of a circulating current occurring in the battery system BS.

[0083] The above description has been given taking as an example a case where the module M of the battery system BS is charged. In contrast, a case where discharging is performed will be described below. Note that the module M controlled by the controller 1 in this case is the first module M1, which is the "module with the high OCV transition estimated value."

[0084] As described above, the relationship between the surface pressure applied to the battery cell C and the internal resistance value of the battery cell C is such that the lower the surface pressure, the higher the internal resistance value, and vice versa. Therefore, the controller 1 controls the pressure mechanism P connected to the first module M1 to drive and increase the surface pressure.

[0085] That is, the pressure applied to the battery cells C in the first module M1 is increased so that the surface pressure after pressure control increases from the initial surface pressure. As the pressure applied to the battery cells C increases, the internal resistance value of the battery cells C decreases.

[0086] Since the internal resistance value of the first module M1 is reduced in this manner, it becomes easier for the first module M1 to discharge. This increases the growth (increase) of the estimated OCV transition value of the first module M1. As a result, the slope of the change in the estimated OCV transition value over time in the first module M1 increases.

[0087] On the other hand, the fact that the first module M1 is more easily discharged means that the second module M2 connected in parallel is less able to discharge, and the amount of discharged current decreases. In other words, the current distribution ratio between the first module M1 and the second module M2 is changed.

[0088] Therefore, when the amount of current discharged from the second module M2, which has a relatively higher estimated OCV transition value than the first module M1, decreases, the estimated OCV transition value of the second module M2 decreases, i.e., the slope of the transition indicating the change in the estimated OCV transition value of the second module M2 over time decreases.

[0089] As described above, by controlling the pressure mechanism P connected to the first module M1 to increase the surface pressure, it is possible to reduce the difference between the OCV transition estimated value OCV1e in the first module M1 and the OCV transition estimated value OCV2e in the second module M2. If the difference between the two is reduced in this way, it is possible to reduce the possibility of circulating current occurring in the battery system BS.

[0090] As described above, the calculation of the current distribution ratio explained so far is performed based on the current value detected by the ammeter A. However, the current distribution ratio may also be calculated based on, for example, the internal resistance value of the battery cell C instead of the current value.

[0091] The method for calculating the current distribution ratio based on the internal resistance values ​​is as follows. First, the calculation unit 18 determines the current value in each module M acquired by the information acquisition unit 16. In the battery system BS according to the embodiment of the present invention, two modules, a first module M1 and a second module M2, are connected in parallel as shown in Fig. 1. Therefore, the current value I1 in the first module M1 and the current value I2 in the second module M2 are determined.

[0092] Additionally, the calculation unit 18 also acquires the temperature values ​​of the respective modules M detected by the thermometers T provided in the respective modules M from the information acquisition unit 16. Here, the temperature value of the first module M1 is defined as "T1," and the temperature value of the second module M2 is defined as "T2."

[0093] Next, the calculation unit 18 calculates the SOC of each module M. As described above, the SOC can be calculated using a known method, such as using an integrated value of the current flowing through the module M. The SOC of the first module M1 is defined as "SOC1," and the SOC of the second module M2 is defined as "SOC2."

[0094] As described above, the current value I, temperature value T, and SOC of each module M are grasped. These values ​​are then used to calculate the internal resistance value of each module M. As before, the internal resistance value of the first module M1 is designated as "DCR1," and the internal resistance value of the second module M2 is designated as "DCR2."

[0095] Regarding internal resistance, the following relationship is observed between temperature and SOC. That is, first, looking at the relationship between temperature and internal resistance, as the temperature decreases, the internal resistance increases. Conversely, as the temperature increases, the internal resistance decreases. Next, regarding the relationship between SOC and internal resistance, assuming that the temperature remains the same, as the SOC decreases, the internal resistance increases, and conversely, as the SOC increases, the internal resistance decreases.

[0096] The relationship between the internal resistance value, temperature, and SOC is as described above, but it can also change depending on the surface pressure (the pressure applied to the battery cell C). The relationship between these four factors is determined in advance by experiment and stored in the memory unit 17. The calculation unit 18 then calculates the internal resistance value based on the obtained temperature value T, SOC, and pressure applied to the battery cell C. The relationship between these four factors is determined according to the characteristics of each battery cell C included in each module M.

[0097] Furthermore, the calculated internal resistance value also takes into account the degree of deterioration of the battery cell C (module M) (hereinafter referred to as "SOH: State of Health"). The SOH value is calculated, for example, by a known method. The influence of the SOH on the internal resistance value is determined in advance by experiment or the like, and the relationship is stored in the storage unit 17.

[0098] The calculation unit 18 corrects the calculated internal resistance value using the SOH. By performing this process, it is possible to calculate an internal resistance value that takes into account the SOH of the module M and is more in line with the current state of each module M. Note that in the embodiment of the present invention, the SOH is used as a correction coefficient, but it may also be used as a parameter other than the temperature value T when calculating the internal resistance value.

[0099] Then, the calculation unit 18 calculates, based on the internal resistance value, the current distribution ratio for each module M. Specifically, if the current distribution ratio for the first module M1 is Ratio1 and the current distribution ratio for the second module M2 is Ratio2, the respective current distribution ratios can be calculated as follows:

[0100] That is, the current distribution ratio Ratio1 for the first module M1 is calculated using the formula Ratio1 = DCR2 / (DCR1 + DCR2). Similarly, the current distribution ratio Ratio2 for the second module M2 is calculated using the formula Ratio2 = DCR1 / (DCR1 + DCR2). By calculating the current distribution ratios in this way, it is possible to determine how much of the current flowing through the battery system BS flows to each module M.

[0101] After the calculation of the current distribution ratio is completed, as described above, the controller 1 calculates the estimated OCV transition value for each module M. If the absolute value of the difference between the estimated OCV transition values ​​is greater than the threshold value, the controller 1 controls the pressure mechanism P to change the pressure applied to the module M.

[0102] The control by the controller 1 described above is based on the premise that the battery system BS in the embodiment of the present invention shown in Fig. 1 is made up of two modules M. Therefore, the absolute value of the difference between the estimated OCV transition values ​​in the two modules M is calculated and then compared with a threshold value.

[0103] However, if the battery system BS includes three or more modules M, it is also possible to, for example, calculate the average of each OCV transition estimated value and compare the average value of the OCV transition estimated values ​​of the multiple modules M with a threshold value.

[0104] Furthermore, the control by the controller 1 is periodically executed at a preset cycle (for example, every 10 seconds). The control by the controller 1 causes the OCV transition estimated values ​​in the multiple modules M to gradually approach each other. That is, the absolute value of the difference between the multiple OCV transition estimated values ​​does not become equal to or less than the threshold value in a single control, but gradually becomes equal to or less than the threshold value through multiple control operations by the controller 1 described above.

[0105] However, such control is not necessarily required, and it is also possible to control the difference between multiple OCV transition estimated values ​​so that the absolute value of the difference is equal to or less than a threshold value at one time. When performing such control, for example, the relationship between the internal resistance value and the surface pressure is obtained in advance by an experiment or the like. Then, the surface pressure for the modules M is controlled based on the current distribution ratio that makes the OCV transition estimated values ​​the same among the multiple modules M.

[0106] By performing such control, the control controller 1 can complete the control in fewer iterations, rather than gradually reducing the difference in the OCV transition estimated values ​​between multiple modules M by controlling the pressure mechanism P multiple times.

[0107] Furthermore, the above-described control by the controller 1 is based on the premise that the control target is a "module with a high estimated OCV transition value," but the control target is not limited to such a module. For example, the control target may be a "module with a low estimated OCV transition value," or both a "module with a high estimated OCV transition value" and a "module with a low estimated OCV transition value" may be controlled.

[0108] As explained above, when the absolute value of the difference in the estimated OCV transition values ​​between multiple modules M is greater than the threshold value, the pressure applied to the battery cells C is controlled using the pressure mechanism P of the module M in order to reduce the difference in the estimated OCV transition values ​​between the modules M. However, when the difference in the estimated OCV transition values ​​is greater than the threshold value, there are cases where the difference in the estimated OCV transition values ​​is significantly different from the threshold value (the difference is large), and cases where the difference is greater than the threshold value but is small.

[0109] In such a case, for example, control can be performed such that the pressure applied to the module M when the difference is large is greater than the pressure applied to the module M when the difference is small. By performing such control, the difference in the OCV transition estimated values ​​between the multiple modules M can be reduced in approximately the same amount of time, regardless of how far the difference in the OCV transition estimated values ​​is from the threshold value.

[0110] On the other hand, it is also possible to execute control in which approximately the same pressure is applied to the module M each time, regardless of how far the difference in the OCV transition estimated value is from the threshold value. However, when such control is executed, the greater the difference in the OCV transition estimated value is from the threshold value, the longer it takes to reduce the difference in the OCV transition estimated value between the multiple modules M.

[0111] [Operation] Next, a flow of control to prevent circulating current from occurring in a battery system BS in which multiple modules M are connected in parallel will be described with reference to Fig. 5. Fig. 5 is a flowchart showing the flow of a control method for the battery system BS in an embodiment of the present invention.

[0112] First, the current value of each module M is detected (ST1). Specifically, the current value I1 detected by the ammeter A provided in the first module M1 is acquired by the information acquisition unit 16 of the controller 1. Similarly, the current value I2 detected by the ammeter A provided in the second module M2 is acquired by the information acquisition unit 16.

[0113] Next, the calculation unit 18 calculates the current SOC of the first module M1 and the current SOC of the second module M2 using the acquired current values ​​I1 and I2 (ST2). Note that, when calculating the SOC, it is also possible to adopt a method other than the method using current values.

[0114] The calculation unit 18 then further uses the current values ​​to calculate the ratio (current distribution ratio) of the currents flowing through the first module M1 and the second module M2 using the above-mentioned equations (1) and (2) (ST3).

[0115] Then, the calculation unit 18 calculates the OCV transition estimated value 1e in the first module M1 and the OCV transition estimated value 2e in the second module M2 when the charging current Iin from the power control device 2 continues for a predetermined time T (ST4).

[0116] Specifically, in calculating these OCV transition estimated values, SOC transition values ​​(SOC1e and SOC2e) are calculated, and then, OCV transition estimated value 1e and OCV transition estimated value 2e are calculated using the SOC-OCV characteristic data stored in the storage unit 17.

[0117] Then, the absolute value of the difference between the OCV transition estimated value 1e in the first module M1 and the OCV transition estimated value 2e in the second module M2 is calculated, and the determination unit 19 compares the absolute value calculated by the calculation unit 18 with a preset threshold value (ST5).

[0118] As a result, if the determination unit 19 determines that the absolute value of the difference is greater than the threshold value (YES in ST5), the controller 1 executes pressure control using the pressure mechanism P on the battery cells C of the module M to be controlled (ST6). As described above, the module M to be controlled is set in advance, and can be, for example, the module M with a large OCV transition estimated value.

[0119] On the other hand, if the judgment unit 19 determines that the absolute value of the difference between the OCV transition estimated value 1e in the first module M1 and the OCV transition estimated value 2e in the second module M2 is less than or equal to the threshold value (NO in ST5), it is considered that there is a low possibility of a circulating current occurring at this time, and therefore pressurization control using the pressurizing mechanism P for the module M is not performed.

[0120] As described above, in the control flow described using the flowchart in Fig. 5, when the calculation unit 18 calculates the current distribution ratio, it uses the current value in each module M. However, it is also possible to calculate the current distribution ratio using, for example, the internal resistance value in each module M.

[0121] 6 is a flowchart showing the flow of another method for calculating the current distribution ratio in the control method of the battery system BS according to the embodiment of the present invention. Note that the processes in the flowchart of FIG. 6 that have the same step numbers as those in the flowchart of FIG. 5 are the same as those described above.

[0122] First, the current value of each module M is detected (ST1). At the same time, the temperature value of each module M is detected (ST21). Specifically, the current value T1 detected by the thermometer T provided in the first module M1 is acquired by the information acquisition unit 16 of the controller 1. Similarly, the current value T2 detected by the thermometer T provided in the second module M2 is acquired by the information acquisition unit 16.

[0123] Next, the calculation unit 18 calculates the SOC of the first module M1 and the SOC of the second module M2 using the acquired current values ​​I1 and I2 (ST2).The calculation unit 18 then calculates the ratio of the currents flowing through the first module M1 and the second module M2 (current distribution ratio) (ST22).Specifically, as described above, the calculation unit 18 calculates the internal resistance value based on the temperature value T, the SOC, and the pressure applied to the battery cell C.

[0124] Then, the internal resistance value is corrected for each module M using the SOH (ST23). The calculation unit 18 calculates the current distribution ratio for each module M using the above-mentioned formula based on the corrected internal resistance value (ST24). Thereafter, the OCV transition estimated value for each module M is calculated (ST4).

[0125] In FIG. 6, the process of step ST4 is indicated by a broken line because the subsequent process is the same as the process from step ST4 onwards described with reference to FIG.

[0126] [Effects of the Example] (1) A control method for a battery system in an embodiment of the present invention includes a module having a plurality of stacked battery cells, a plurality of which are connected in parallel, a pressure mechanism provided for each of the plurality of modules and capable of changing the pressure applied to the module, and a control controller that controls the pressure mechanism, and the control controller distributes current to the modules connected in parallel by controlling the pressure applied to the plurality of modules by the pressure mechanism.

[0127] Since the battery system is controlled using such a control method, even if a plurality of battery modules are connected in parallel, the initial capacity can be utilized by sufficiently charging and discharging the battery modules.

[0128] (2) A control method for a battery system described in (1) above, wherein the pressure control by the control controller includes a step of calculating the state of charge (SOC) for each module having multiple stacked battery cells and multiple modules connected in parallel, a step of calculating a current distribution ratio for each of the multiple modules, a step of calculating a trend estimate value, which is a value of future voltage information for each of the multiple modules, a step of comparing the difference between the trend estimate values ​​for each of the modules with a predetermined threshold value, and a step of controlling the pressure mechanism to change the pressure applied to each of the modules when it is determined that the trend estimate value is greater than the threshold value.

[0129] In this way, when the control controller performs pressure control, by using a trend estimate value, which is the value of future voltage information, it is possible to grasp the likelihood of circulating current occurring in the battery system in the future, and to perform appropriate pressure control for module M.

[0130] (3) In the method for controlling a battery system according to (1), the voltage information is an open circuit voltage (OCV). By using an estimated value of the OCV transition as the voltage information, it is possible to more accurately control the voltage application to the module M.

[0131] (4) A control method for a battery system described in (1) or (2) above, wherein when the control controller controls the pressure mechanism, the degree of pressure applied to the module by the pressure mechanism is varied depending on the difference between the transition estimated value and a threshold value.

[0132] In this way, when the absolute value of the difference in the OCV transition estimated values ​​is greater than the threshold value, the greater the absolute value of the difference in the OCV transition estimated values ​​is from the threshold value, the greater the pressure applied to the module by the pressure mechanism, thereby making it possible to reduce the difference in the OCV transition estimated values ​​between multiple modules M in approximately the same amount of time, regardless of how far the difference in the OCV transition estimated values ​​is from the threshold value.

[0133] (5) A control method for a battery system described in any one of (1) to (4) above, wherein the target of the pressure control performed by the controller using the pressure mechanism is a module whose calculated transition estimated value shows a larger value.

[0134] For example, by selecting the module that shows the larger transition estimated value when multiple modules are connected in parallel as the target of pressure control, pressure control can be performed more effectively to prevent circulating current from occurring.

[0135] (6) In the method for controlling a battery system according to (5), when the controller performs pressure control, for a module having a larger estimated transition value, the controller decreases the pressure applied when charging the module and increases the pressure applied when discharging the module. By performing appropriate control during charging or discharging in the pressure control for the module, it is possible to prevent the generation of circulating current.

[0136] (7) A control method for a battery system described in (5) or (6) above, in which, when the control controller performs pressure control, for modules other than the module showing the larger transition estimated value, the pressure to be applied is increased when the module is charged, and the pressure to be applied is decreased when the module is discharged.

[0137] When the target of the pressure control is a module other than the module showing the larger transition estimated value, the generation of circulating current can be prevented by performing pressure control to bring the transition estimated value closer to the module showing the larger transition estimated value.

[0138] (8) A control method for a battery system described in any one of (5) to (7) above, wherein the controller performs pressure control on modules other than the module showing the larger transition estimated value, in addition to the module showing the larger transition estimated value.

[0139] When performing pressurization control on a module other than the module with the larger transition estimate value, by performing control opposite to that of the module with the larger transition estimate value, the transition estimate value of the module with the larger transition estimate value can be made closer to the transition estimate values ​​of the modules other than the module with the larger transition estimate value, thereby more quickly preventing the occurrence of circulating current.

[0140] (9) In the battery system control method described in (2), the current distribution ratio is calculated based on the current values ​​flowing through each of the plurality of modules. By calculating the current distribution ratio using the current values, highly accurate voltage control can be performed.

[0141] (10) In the method for controlling a battery system according to (2), the current distribution ratio is calculated based on the internal resistance values ​​of the modules. By calculating the current distribution ratio using the internal resistance values, highly accurate voltage control can be performed.

[0142] (11) In the method for controlling a battery system according to (10), the internal resistance value is calculated based on the SOC, temperature, and pressure applied to the module. By calculating the internal resistance value in consideration of parameters that affect the internal resistance value, more accurate pressure control can be performed.

[0143] (12) In the method for controlling a battery system according to (10) or (11), the internal resistance value is calculated using a state of health (SOH) value of the module. Considering that the internal resistance value varies depending on the SOH, the SOH is used as one of the parameters or a correction coefficient, thereby enabling more accurate pressure control.

[0144] (13) A battery system comprising: a module having a plurality of stacked battery cells, the plurality of cells being connected in parallel; a pressure mechanism provided for each of the plurality of modules and capable of changing the pressure applied to the module; and a control controller that controls the pressure mechanism, wherein the control controller controls the pressure mechanism to change the pressure applied to each of the modules when the difference between the estimated values ​​of the open circuit voltage (OCV) trends in each of the modules is greater than a predetermined threshold value.

[0145] By using such a battery system, even if a plurality of battery modules are connected in parallel, the initial capacity can be utilized by sufficiently charging and discharging the battery modules.

[0146] 1...controller, 11...CPU, 12...ROM, 13...RAM, 14...input / output interface, 15...bus, 16...information acquisition unit, 17...storage unit, 18...calculation unit, 19...determination unit, 20...drive control unit, 2...power control device, A...ammeter, C...battery cell, D...driver, M...module, MG...motor / gear, P...pressure mechanism, PP...pressure plate, T...thermometer, V...voltmeter

Claims

1. A method for controlling a battery system comprising: a module having a plurality of stacked battery cells, the plurality of cells being connected in parallel; a pressure mechanism provided for each of the plurality of modules and capable of changing the pressure applied to the module; and a control controller for controlling the pressure mechanism, wherein the control controller distributes current to the modules connected in parallel by controlling the pressure applied to the plurality of modules by the pressure mechanism.

2. The control method for a battery system described in claim 1, characterized in that the pressure control by the control controller includes the steps of: calculating the state of charge (SOC) for each module having a plurality of stacked battery cells, the plurality of modules being connected in parallel; calculating a current distribution ratio for each of the plurality of modules; calculating a transition estimate value, which is a value of future voltage information, for each of the plurality of modules; comparing the difference between the transition estimate values ​​for each of the modules with a predetermined threshold; and controlling the pressure mechanism to change the pressure applied to each of the modules when it is determined that the transition estimate value is greater than the threshold.

3. The method for controlling a battery system according to claim 2, wherein the voltage information is an open circuit voltage (OCV).

4. A control method for a battery system as described in claim 2, characterized in that when the control controller controls the pressure mechanism, the degree of pressure applied to the module by the pressure mechanism is varied depending on the difference between the transition estimated value and the threshold value.

5. A control method for a battery system as described in claim 1, characterized in that the target of pressure control by the control controller using the pressure mechanism is the module for which the calculated transition estimate value shows a larger value.

6. A control method for a battery system as described in claim 5, characterized in that when the control controller performs pressure control, for a module for which the transition estimation value shows a larger value, the pressure to be applied is lowered when the module is charged, and the pressure to be applied is increased when the module is discharged.

7. A control method for a battery system as described in claim 5, characterized in that when the control controller performs pressure control, for modules other than the module for which the transition estimation value shows a larger value, the pressure to be applied is increased when the module is charged, and the pressure to be applied is decreased when the module is discharged.

8. A control method for a battery system as described in claim 5, characterized in that the control controller performs pressure control on modules other than the module for which the transition estimation value shows a larger value, in addition to the module for which the transition estimation value shows a larger value.

9. The method for controlling a battery system according to claim 2, wherein the current distribution ratio is calculated based on the value of the current flowing through each of the plurality of modules.

10. The method for controlling a battery system according to claim 2, wherein the current distribution ratio is calculated based on the internal resistance value of each of the plurality of modules.

11. The method for controlling a battery system according to claim 10, wherein the internal resistance value is calculated based on the SOC, temperature, and pressure applied to the module.

12. The method for controlling a battery system according to claim 11, wherein the internal resistance value is calculated using a state of health (SOH) value of the module.

13. A battery system comprising: a module having a plurality of stacked battery cells connected in parallel; a pressure mechanism provided for each of the plurality of modules and capable of changing the pressure applied to the module; and a control controller that controls the pressure mechanism, wherein the control controller controls the pressure mechanism to change the pressure applied to each of the modules when the difference between estimated values ​​of the progress of open circuit voltage (OCV) in each of the modules is greater than a predetermined threshold.

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