Battery system control method, battery system, and program

Abstract

A contact pressure application unit (67) applies contact pressure to a plurality of cells. A contact pressure information acquisition unit (61) acquires contact pressure information indicating a cell contact pressure that is the contact pressure applied to the plurality of cells. A temperature information acquisition unit (62) acquires temperature information indicating a cell temperature that is the temperature of the plurality of cells. A voltage value information acquisition unit (63) acquires voltage value information indicating a cell voltage value that is a voltage value for the plurality of cells. A contact pressure determination unit (66) determines the cell contact pressure to be applied to the plurality of cells such that the current value of a circulating current determined from the cell contact pressure, the cell temperature, and the cell voltage value is at or below a maximum allowable current value determined from the cell temperature when the charging state of a plurality of modules is adjusted by the circulating current.

Description

Battery system control method, battery system, and program

[0001] The present invention relates to a control method for a battery system, a battery system, and a program.

[0002] Currently, battery systems are known in which multiple series circuits, each including multiple modules connected in series, are connected in parallel. In such battery systems, the state of charge of the multiple modules may be adjusted using a circulating current. However, if the circulating current is too large, excessive dendrites may form on the negative electrodes of the cells in the modules being charged. Excessive dendrite formation may result in short circuits, etc.

[0003] Patent Document 1 describes a technology for suppressing the generation of excessive circulating current and suppressing the generation of dendrites. More specifically, Patent Document 1 describes a technology for determining whether or not to connect two battery packs in parallel in a power supply system equipped with two battery packs based on the voltage values ​​and temperatures of the two battery packs.

[0004] Japanese Patent Application Laid-Open No. 2018-50401

[0005] However, the technology described in Patent Document 1 may not adjust the state of charge of the two battery packs. For example, if the potential difference between the two battery packs is too large, the technology described in Patent Document 1 determines that the two battery packs should not be connected in parallel, and does not adjust the state of charge of the two battery packs. For this reason, there is a need for a technology that adjusts the state of charge of multiple modules while suppressing the generation of dendrites.

[0006] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a battery system control method, a battery system, and a program that adjust the state of charge of multiple modules while suppressing the occurrence of dendrites.

[0007] In order to achieve the above object, the present invention provides a battery system control method for adjusting the state of charge of a plurality of modules each including a plurality of cells that are lithium secondary batteries using a circulating current, and includes the following steps: First, apply a surface pressure to the plurality of cells. Then, obtain surface pressure information indicating the cell surface pressure, which is the surface pressure applied to the plurality of cells. Also, obtain temperature information indicating the cell temperature, which is the temperature of the plurality of cells. Also, obtain voltage value information indicating the cell voltage values, which are the voltage values ​​of the plurality of cells. Here, when adjusting the state of charge of the plurality of modules using a circulating current, determine the cell surface pressure applied to the plurality of cells so that the current value of the circulating current is equal to or less than a maximum allowable current value determined from the cell temperature. Note that the circulating current has a current value determined from the cell surface pressure, cell temperature, and cell voltage value.

[0008] According to the present invention, it is possible to adjust the state of charge of a plurality of modules while suppressing the occurrence of dendrites.

[0009] 1 is a configuration diagram of a battery system according to embodiment 1. FIG. 2 is a diagram showing the connection relationship of modules in the battery system according to embodiment 1. FIG. 3 is a configuration diagram of a pressurizing mechanism according to embodiment 1. FIG. 4 is a diagram showing a circulation circuit according to embodiment 1. FIG. 5 is a graph showing the correspondence relationship between the resistance value of the circulation circuit and the current value of the circulating current. FIG. 6 is a functional configuration diagram of a battery control unit according to embodiment 1. FIG. 7 is a diagram showing the correspondence relationship between the charging rate, cell temperature, cell surface pressure, and DC resistance. FIG. 8 is a flowchart showing a state of charge adjustment process executed by the battery system according to embodiment 1. FIG. 9 is a configuration diagram of a pressurizing mechanism according to embodiment 2. FIG. 10 is a functional configuration diagram of a battery control unit according to embodiment 2. FIG. 11 is a flowchart showing a state of charge adjustment process executed by the battery system according to embodiment 2.

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, in which the same or corresponding parts are designated by the same reference numerals.

[0011] (First Embodiment) Fig. 1 is a configuration diagram of a battery system 100 according to the first embodiment. Fig. 2 is a diagram showing the connection relationship of modules 20 in the battery system 100 according to the first embodiment. The battery system 100 is a battery system that supplies stored power to a load and stores power supplied from a charger, a generator, etc. The battery system 100 is mounted on, for example, an electric device. Possible examples of the electric device include an electric vehicle and a hybrid vehicle.

[0012] The battery system 100 has a function of adjusting the state of charge of the multiple modules 20. The state of charge is also called the state of charge (SOC) and corresponds to, for example, the charging rate. Adjusting the state of charge means balancing the states of charge and making the charging rates uniform. As shown in FIG. 1 , the battery system 100 includes multiple modules 20, a switch 40, a switch 41, a switch 42, a positive terminal 51, a negative terminal 52, and a battery control unit 60.

[0013] The module 20 is a group of multiple cells 10. The module 20 includes multiple cells 10, a module control unit 21, a voltage sensor 22, a current sensor 23, a temperature sensor 24, a pressurizing mechanism 25, and a pressure sensor 26. The cell 10 is the smallest unit for storing power. The cell 10 corresponds to a single battery and is also called a single cell. In this embodiment, the cell 10 is a lithium secondary battery containing a solid electrolyte as an electrolyte. The electrolyte contained in the cell 10 may be composed only of a solid electrolyte, or may be composed of a polymer electrolyte, a liquid electrolyte, or the like in addition to the solid electrolyte.

[0014] In this embodiment, the module 20 includes 30 cells 10 connected in series. Also, in this embodiment, the battery system 100 is configured such that two series circuits 30, each of which has seven modules 20 connected in series, are connected in parallel. One series circuit 30 is referred to as series circuit 30a, and the other series circuit 30 is referred to as series circuit 30b. In this embodiment, the battery system 100 includes 30 x 7 x 2 = 420 cells 10.

[0015] The module control unit 21 communicates with the battery control unit 60 and controls the overall operation of the module 20. For example, the module control unit 21 acquires voltage value information from the voltage sensor 22, current value information from the current sensor 23, temperature information from the temperature sensor 24, and pressure information from the pressure sensor 26. The module control unit 21 transmits the voltage value information, current value information, temperature information, pressure information, etc. to the battery control unit 60. The module control unit 21 also controls the pressure mechanism 25 under control of the battery control unit 60. The module control unit 21 includes, for example, a central processing unit (CPU), read-only memory (ROM), random access memory (RAM), and real-time clock (RTC). The CPU is also called a central processing unit, central arithmetic unit, processor, microprocessor, microcomputer, or digital signal processor (DSP), and functions as a central processing unit that executes processing and calculations related to the control of the module 20.

[0016] The voltage sensor 22 is a sensor that measures the cell voltage value, which is the voltage value between both ends of the cell 10. In this embodiment, the cell voltage values ​​of the cells 10 in one module 20 are assumed to be the same, and the voltage sensor 22 measures the cell voltage value of any one of the 30 cells 10. The voltage sensor 22 supplies voltage value information, which is information indicating the cell voltage value, to the module control unit 21. Note that the module voltage value, which is the voltage value between both ends of the module 20, is the sum of the cell voltage values ​​of all the cells 10 included in the module 20.

[0017] The current sensor 23 is a sensor that measures the current value of the current flowing through the cell 10. The current flowing through the cell 10 is the current flowing through the module 20. The current sensor 23 supplies current value information indicating the current value of the current flowing through the cell 10 to the module control unit 21. The temperature sensor 24 is a sensor that measures the cell temperature, which is the temperature of the cell 10. In this embodiment, it is assumed that the cell temperatures of all the cells 10 included in one module 20 are the same, and the temperature sensor 24 measures the cell temperature of any one of the 30 cells 10. The temperature sensor 24 supplies temperature information indicating the cell temperature to the module control unit 21.

[0018] The pressure mechanism 25 is a mechanism that applies surface pressure to the multiple cells 10 included in the module 20. The surface pressure applied to the cells 10 is called cell surface pressure. The cell surface pressure is pressure applied to the surface of the cell. In this embodiment, the cell surface pressure of the cells 10 in one module 20 is considered to be the same. The pressure mechanism 25 is controlled by the battery control unit 60 via the module control unit 21. As shown in FIG. 3 , the pressure mechanism 25 includes a fixing plate 251A, a fixing plate 251B, a fixing plate 251C, a guide member 252A, a guide member 252B, a pressure plate 253A, a pressure plate 253B, an elastic body 254, and an actuator 255.

[0019] Fixing plates 251A, 251B, and 251C are plate-shaped members for fixing the position of the stack of cells 10. Guide members 252A and 252B are members connected to fixing plates 251A and 251B, and are members that guide pressure plates 253A and 253B. Guide members 252A and 252B extend in the stacking direction of the cells 10.

[0020] The pressure plates 253A and 253B are plates that apply pressure to the cells 10 by pressing the cells 10 in the stacking direction of the cells 10. The pressure plate 253A moves in the direction in which the guide members 252A and 252B extend in accordance with the power from the actuator 255. The elastic body 254 is a member provided between the pressure plates 253A and 253B. The elastic body 254 has the function of transmitting the pressure applied by the pressure plate 253A to the pressure plate 253B. The elastic body 254 is a rubber plate, a spring, or the like.

[0021] The actuator 255 generates power to move the pressure plate 253A under the control of the module control unit 21, and moves the pressure plate 253A. When increasing the surface pressure of the multiple cells 10, the module control unit 21 controls the actuator 255 so that the pressure plate 253A moves away from the fixed plate 251A. In this case, the pressure that the pressure plate 253B receives from the pressure plate 253A via the elastic body 254 increases, and the pressure that the pressure plate 253B applies to the multiple cells 10 increases. Furthermore, when decreasing the surface pressure of the multiple cells 10, the module control unit 21 controls the actuator 255 so that the pressure plate 253A moves closer to the fixed plate 251A. In this case, the pressure that the pressure plate 253B receives from the pressure plate 253A via the elastic body 254 decreases, and the pressure that the pressure plate 253B applies to the multiple cells 10 decreases. The actuator 255 includes, for example, a stepping motor.

[0022] The pressure sensor 26 measures the cell surface pressure, which is the surface pressure applied to the cell 10. The pressure sensor 26 is fixed between the fixing plate 251B and the fixing plate 251C. The pressure sensor 26 measures the pressure applied by the fixing plate 251C, which is pressed by the stack of multiple cells 10, as the cell surface pressure. The pressure sensor 26 supplies surface pressure information indicating the measured cell surface pressure to the module control unit 21. The pressure sensor 26 is, for example, a load cell.

[0023] Switches 40, 41, and 42 are switches for controlling the connection relationship between series circuits 30a, 30b, and positive terminal 51. Switches 40, 41, and 42 are controlled by battery control unit 60. When switches 40 and 41 are turned on, the positive pole of series circuit 30a is connected to positive terminal 51. When switches 40 and 42 are turned on, the positive pole of series circuit 30b is connected to positive terminal 51. In this embodiment, the negative pole of series circuit 30a and the negative pole of series circuit 30b are always connected to negative terminal 52.

[0024] When switch 40 is turned off and switches 41 and 42 are turned on, the positive electrode of series circuit 30a is connected to the positive electrode of series circuit 30b, forming a circulation circuit 70 shown in Fig. 4. In circulation circuit 70, the positive electrode of series circuit 30a is connected to the positive electrode of series circuit 30b, and the negative electrode of series circuit 30a is connected to the negative electrode of series circuit 30b, and a circulating current flows through it. When there is a difference in the series circuit voltage values ​​of two series circuits 30, the circulating current flows from the series circuit 30 with the higher series circuit voltage value to the series circuit 30 with the lower series circuit voltage value.

[0025] The series circuit voltage value is the voltage value across the series circuit 30, and is the sum of the module voltage values ​​of the multiple modules 20 included in the series circuit 30. The series circuit 30 with the higher series circuit voltage value is a discharge circuit that discharges when the circulation circuit 70 is formed. The series circuit 30 with the lower series circuit voltage value is a charge circuit that charges when the circulation circuit 70 is formed. The module 20 included in the discharge circuit has a relatively high module voltage value and is a discharge module that discharges when the circulation circuit 70 is formed. The module 20 included in the charge circuit has a relatively low module voltage value and is a charge module that is charged when the circulation circuit 70 is formed.

[0026] Series circuit 30a can be considered to be a circuit having a voltage source 31a that generates a voltage Ea and a resistor 32a having a resistance value Ra. Series circuit 30b can be considered to be a circuit having a voltage source 31b that generates a voltage Eb and a resistor 32b having a resistance value Rb. Ea is the series circuit voltage value of series circuit 30a. Eb is the series circuit voltage value of series circuit 30b.

[0027] In this embodiment, Ea is higher than Eb, the series circuit 30a is a discharge circuit, and the series circuit 30b is a charge circuit. Ra is the resistance value of the series circuit 30a, which is basically the sum of the resistance values ​​of all the cells 10 included in the series circuit 30a. Rb is the resistance value of the series circuit 30b, which is basically the sum of the resistance values ​​of all the cells 10 included in the series circuit 30b.

[0028] Here, if the current value of the circulating current is Ir, the resistance value of the circulating circuit 70 is Rab, and the potential difference between the series circuits 30a and 30b is ΔE, then Ir = (Ea - Eb) / (Ra + Rb) = ΔE / Rab. FIG. 5 shows the correspondence between Rab, which is the resistance value of the circulating circuit 70, and Ir, which is the current value of the circulating current. As shown in FIG. 5, the smaller Rab and the larger ΔE, the larger Ir. Here, if Ir is too large, excessive dendrites may occur at the negative electrodes of the cells 10 included in the charging circuit, potentially causing short circuits or the like. The dendrites may be lithium dendrites.

[0029] In this embodiment, the current value of the circulating current is adjusted to minimize the occurrence of dendrites. That is, if ΔE is too large, Rab is adjusted to be larger. If Ir is too small, the time required to adjust the state of charge becomes longer. Therefore, if ΔE is too small, Rab is adjusted to be smaller.

[0030] Here, if the current Rab is R1, a decrease in the cell surface pressure causes Rab to become larger than R1, and an increase in the cell surface pressure causes Rab to become smaller than R1. Therefore, when ΔE is too large, the battery system 100 decreases the cell surface pressure to reduce the current value of the circulating current so that an excessively large circulating current does not flow. On the other hand, when ΔE is too small, the battery system 100 increases the cell surface pressure to increase the current value of the circulating current so that a certain amount of circulating current flows.

[0031] The positive terminal 51 and the negative terminal 52 are terminals connected to a load, a charger, a generator, or the like. For example, the positive terminal 51 and the negative terminal 52 are connected to a motor that not only converts electrical energy into kinetic energy but also converts kinetic energy into electrical energy. The potential of the positive terminal 51 is basically equal to or higher than the potential of the negative terminal 52. When the positive terminal 51 and the negative terminal 52 are connected to a load and the switches 40, 41, and 42 are turned on, power released from the series circuits 30a and 30b is supplied to the load. When the positive terminal 51 and the negative terminal 52 are connected to a charger, a generator, or the like and the switches 40, 41, and 42 are turned on, the series circuits 30a and 30b are charged with power supplied from the charger, the generator, or the like.

[0032] The battery control unit 60 communicates with the module control unit 21 and controls the operation of the entire battery system 100. For example, the battery control unit 60 acquires voltage value information, current value information, temperature information, and pressure information via the module control unit 21. The battery control unit 60 also applies surface pressure to the cells 10 via the module control unit 21. The battery control unit 60 also controls the states of the switches 40, 41, and 42. The battery control unit 60 includes, for example, a CPU, ROM, RAM, RTC, etc. The CPU is also called a central processing unit, central arithmetic unit, processor, microprocessor, microcomputer, DSP, etc., and functions as a central arithmetic processing unit that executes processing and calculations related to the control of the battery system 100. The battery control unit 60 is an example of a control unit.

[0033] Next, the functions of the battery control unit 60 will be described with reference to FIG. 6 . The battery control unit 60 functionally includes a surface pressure information acquisition unit 61, a temperature information acquisition unit 62, a voltage value information acquisition unit 63, a tolerance value determination unit 64, a target resistance value determination unit 65, a surface pressure determination unit 66, a surface pressure application unit 67, and a switch control unit 68. Each of these functions is realized by software, firmware, or a combination of software and firmware. The software and firmware are written as programs and stored in ROM, RAM, etc. The CPU then executes the programs stored in ROM, RAM, etc. to realize each of these functions. The surface pressure information acquisition unit 61 is an example of a surface pressure information acquisition means. The temperature information acquisition unit 62 is an example of a temperature information acquisition means. The voltage value information acquisition unit 63 is an example of a voltage value information acquisition means. The surface pressure determination unit 66 is an example of a surface pressure determination means. The surface pressure application unit 67 is an example of a surface pressure application means.

[0034] The surface pressure information acquisition unit 61 acquires surface pressure information from the pressure sensor 26 via the module control unit 21. The surface pressure information acquisition unit 61 acquires measured surface pressure information from each module 20. The temperature information acquisition unit 62 acquires temperature information from the temperature sensor 24 via the module control unit 21. The temperature information acquisition unit 62 acquires temperature information from each module 20. The voltage value information acquisition unit 63 acquires voltage value information from the voltage sensor 22 via the module control unit 21. The voltage value information acquisition unit 63 acquires voltage value information from each module 20.

[0035] The tolerance value determination unit 64 determines a maximum allowable current value, which is the maximum current value allowed for the circulating current. If the circulating current value is too large, dendrites may form in the negative electrodes of the cells 10 included in the charging module. Therefore, the battery system 100 controls the resistance value Rab of the circulating circuit 70 so that the circulating current value does not exceed the maximum allowable current value. In other words, the maximum allowable current value is the upper limit current value at which dendrites do not form.

[0036] The maximum allowable current value increases as the cell temperature of the cells 10 in the charging circuit increases. Therefore, the tolerance value determiner 64 determines a larger maximum allowable current value as the cell temperature increases. For example, the tolerance value determiner 64 may determine the maximum allowable current value from the cell temperature of the cells 10 in the charging circuit by referencing a table showing the correspondence between cell temperature and maximum allowable current value. Such a table may be stored in, for example, a ROM included in the battery control unit 60. The cell temperature of the cells 10 in the charging circuit can be adjusted as appropriate. For example, a representative value based on the cell temperatures of multiple charging modules in the charging circuit can be considered as the cell temperature of the cells 10 in the charging circuit. Possible representative values ​​include the average, median, maximum, and minimum values ​​of the cell temperatures of each charging module. The tolerance value determiner 64 supplies tolerance value information indicating the determined maximum allowable current value to the target resistance value determiner 65.

[0037] The target resistance value determination unit 65 determines a target resistance value of the circulating circuit 70. The target resistance value is a resistance value targeted as the resistance value of the circulating circuit 70. The target resistance value is a resistance value that adjusts the circulating current to an appropriate current value equal to or less than the maximum allowable current value. If the resistance value that adjusts the circulating current to the maximum allowable current value is defined as a lower limit resistance value, the target resistance value is a resistance value equal to or greater than the lower limit resistance value. In other words, the target resistance value is a resistance value that does not generate dendrites. Note that if the circulating current value is too small compared to the maximum allowable current value, it takes a long time to adjust the state of charge. Therefore, it is preferable that the target resistance value be the lower limit resistance value or a resistance value slightly greater than the lower limit resistance value. The target resistance value determination unit 65 determines the target resistance value based on the maximum allowable current value indicated by the allowable value information supplied from the allowable value determination unit 64 and the cell voltage value indicated by the voltage value information acquired by the voltage value information acquisition unit 63.

[0038] As described above, Ir, which is the current value of the circulation circuit 70, is the value obtained by dividing ΔE, which is the difference between the voltage values ​​of the two series circuits 30, by Rab, which is the resistance value of the circulation circuit 70. Therefore, the target resistance value determination unit 65 calculates, for example, a value obtained by dividing ΔE by the maximum allowable current value as the target resistance value. When the series circuit 30a is a discharge circuit and the series circuit 30b is a charge circuit, ΔE can be calculated by subtracting Eb from Ea.

[0039] Ea corresponds to the sum of the cell voltage values ​​of all the cells 10 included in the series circuit 30a. Eb corresponds to the sum of the cell voltage values ​​of all the cells 10 included in the series circuit 30b. Each series circuit 30 includes 210 cells 10. Therefore, for example, if the average difference between the cell voltage values ​​of the cells 10 included in the series circuit 30a and the cell voltage values ​​of the cells 10 included in the series circuit 30b is 0.2 V, ΔE is 0.2 × 210 = 42 V. The target resistance value determination unit 65 supplies resistance value information indicating the determined target resistance value to the surface pressure determination unit 66.

[0040] The surface pressure determination unit 66 determines the cell surface pressure of each cell 10 so that the resistance value of the circulation circuit 70 becomes the target resistance value. In this embodiment, the surface pressure determination unit 66 determines the cell surface pressure of the cells 10 included in the discharge circuit, and then determines the cell surface pressure of the cells 10 included in the charge circuit. Note that the surface pressure determination unit 66 may set the same cell surface pressure for all discharge modules included in the discharge circuit, assuming that all discharge modules included in the discharge circuit have the same cell temperature and cell voltage. Alternatively, the surface pressure determination unit 66 may set the same cell surface pressure for all charge modules included in the charge circuit, assuming that all charge modules included in the charge circuit have the same cell temperature and cell voltage. Below, with reference to FIG. 7 , the correspondence between the charging rate, cell temperature, cell surface pressure, and DC resistance in one module 20 will be described.

[0041] The charging rate is the charging rate of the module 20, and is the charging ratio when a fully charged state is 100% and a fully discharged state is 0%. The charging rate corresponds to the charging state. The charging rate can be calculated from the module voltage value. The higher the module voltage value, the higher the charging rate. The cell temperature is the cell temperature of the cells 10 included in the module 20, and is also the temperature of the module 20. The cell surface pressure is the cell surface pressure of the cells 10 included in the module 20, and is also the surface pressure of the module 20. The series resistance, also known as DCR (Direct Current Resistance), is the series resistance between both ends of the module 20, and is the total resistance value of all the cells 10 included in the module 20. Hereinafter, the resistance value of the cell 10 will be referred to as the cell resistance value as appropriate.

[0042] As shown in Figure 7, the series resistance depends on the charge / discharge state, charge rate, cell temperature, cell surface pressure, etc. For example, the series resistance during charging is different from the series resistance during discharging, and the series resistance of the charge module is different from the series resistance of the discharge module. For example, if other conditions are the same, the series resistance of the charge module is higher than the series resistance of the discharge module. Also, for example, the series resistance is smallest when the charge rate is about 50%. Also, for example, the series resistance decreases as the cell temperature increases. Also, for example, the series resistance decreases as the cell surface pressure increases. Here, if the charge / discharge state, charge rate, cell temperature, etc. are predetermined, the series resistance can be adjusted by adjusting the surface pressure.

[0043] As the discharge of the cell 10 progresses, lithium dissolves from the negative electrode of the cell 10, causing the thickness of the cell 10 to decrease. As a result, the cell surface pressure of the cell 10 decreases, the contact resistance between the electrodes increases, and the cell resistance value increases. Therefore, as the discharge of the discharge module progresses, the module resistance value of the discharge module increases. As the module resistance value of the discharge module increases, the resistance value of the discharge circuit increases. The resistance value of the circulation circuit 70 is the sum of the resistance value of the discharge circuit and the resistance value of the charge circuit.

[0044] Therefore, when the resistance value of the discharge circuit increases, the resistance value of the circulation circuit 70 also increases. An increase in the resistance value of the circulation circuit 70 is undesirable because it reduces the current value of the circulating current. Here, if the cell surface pressure at the start of discharge is low, the increase in cell resistance due to the decrease in cell surface pressure is large, and the increase in the resistance value of the discharge circuit is also large. Furthermore, if the cell surface pressure at the start of discharge is low, there is a high possibility that lithium will dissolve unevenly. For this reason, the discharge circuit is restricted to requiring a high cell surface pressure at the start of discharge. On the other hand, the charge circuit basically does not have such restrictions. Therefore, the surface pressure determination unit 66 determines the cell surface pressure of the cells 10 included in the discharge module, and then determines the cell surface pressure of the cells 10 included in the charge module.

[0045] As charging of the cell 10 progresses, lithium accumulates on the negative electrode of the cell 10, increasing the thickness of the cell 10. As a result, the cell surface pressure of the cell 10 increases, the contact resistance between the electrodes decreases, and the cell resistance value decreases. Therefore, as charging of the charging module progresses, the module resistance value of the charging module decreases. When the module resistance value of the charging module decreases, the resistance value of the charging circuit decreases. However, the increase in the resistance value of the discharge circuit often cannot be offset by the decrease in the resistance value of the charging circuit. Therefore, as described above, priority is given to increasing the cell surface pressure at the start of discharge in the discharge circuit.

[0046] The surface pressure determination unit 66 determines the cell surface pressure for the discharge module based on the state of charge (SOC) based on the cell voltage value and the cell temperature. As described above, the cell surface pressure for the discharge module is desirably high enough to prevent a significant increase in cell resistance during discharge. Furthermore, the cell surface pressure for the discharge module is desirably high enough to prevent uneven dissolution of lithium. Furthermore, if the cell surface pressure for the discharge module is too low, the resistance of the discharge circuit may become too high, and the resistance of the circulation circuit 70 may exceed the target resistance value regardless of how the resistance of the charging circuit is adjusted. Therefore, the cell surface pressure for the discharge module is desirably high enough to prevent the resistance of the discharge module from becoming too high.

[0047] On the other hand, if the cell surface pressure is too high, the cells 10, module 20, etc., are more likely to be damaged or dendrites to form. Therefore, the cell surface pressure needs to be equal to or lower than a predetermined upper limit surface pressure. Furthermore, taking into consideration the above-mentioned damage, dendrite formation, etc., it is desirable that the cell surface pressure be as low as possible. Therefore, the surface pressure determination unit 66 determines the cell surface pressure of the discharge module to be a surface pressure that is high enough to suppress a significant increase in the cell resistance value during discharge, suppress uneven dissolution of lithium, and achieve the target resistance value, but is as low as possible below the upper limit surface pressure.

[0048] Specifically, the surface pressure determination unit 66 determines the cell surface pressure of the discharge module to be the minimum surface pressure within the surface pressure range where the slope of the dashed line indicating the series resistance of the discharge module is nearly flat in the graph shown in Fig. 7. For example, as shown in Fig. 7, in the graph showing the relationship between cell surface pressure and series resistance when the cell temperature is 25°C and the SOC is 50%, if the slope of the dashed line is nearly flat in the surface pressure range of 2 MPa or more, the surface pressure determination unit 66 determines the cell surface pressure of the discharge module to be 2 MPa.

[0049] Furthermore, for example, in the graph shown in Fig. 7, if there is no range of surface pressure where the slope of the dashed line indicating the series resistance of the discharge module is nearly flat, the surface pressure determination unit 66 determines the upper limit surface pressure as the cell surface pressure of the discharge module. For example, as shown in Fig. 7, if there is no range of surface pressure where the slope of the dashed line is nearly flat in the graph showing the relationship between cell surface pressure and series resistance when the cell temperature is 25°C and the SOC is 25%, the surface pressure determination unit 66 determines the cell surface pressure of the discharge module to be 6 MPa, which is the upper limit surface pressure. Note that the shaded area in Fig. 7 is the area where the cell surface pressure is equal to or greater than the upper limit surface pressure.

[0050] The surface pressure determination unit 66 calculates the resistance value of the discharge circuit based on the cell surface pressure determined for the discharge module. For example, the surface pressure determination unit 66 identifies the series resistance corresponding to the determined cell surface pressure based on the correspondence relationship between cell surface pressure and series resistance shown in the graph of Figure 7, and specifies the identified series resistance as the resistance value of the discharge module. The surface pressure determination unit 66 calculates the total value of the resistance values ​​of all discharge modules included in the discharge circuit as the resistance value of the discharge circuit.

[0051] For the charging module, the surface pressure determination unit 66 determines the cell surface pressure based on the state of charge, which is based on the cell voltage value, and the cell temperature, so that the resistance value of the charging circuit is the target resistance value minus the resistance value of the discharge circuit. In other words, the surface pressure determination unit 66 determines the resistance value of the charging circuit to be the value obtained by subtracting the resistance value of the discharge circuit from the target resistance value determined by the target resistance value determination unit 65. The surface pressure determination unit 66 calculates the resistance value of the charging module by dividing the determined resistance value of the charging circuit by the number of charging modules included in the charging circuit.

[0052] The surface pressure determination unit 66 determines the state of charge of the charging module from the cell voltage values ​​of the cells 10 included in the charging module included in the charging circuit. The surface pressure determination unit 66 also determines the cell temperatures of the cells 10 included in the charging module. Of the six graphs shown in FIG. 7 , the surface pressure determination unit 66 determines a graph that corresponds to the determined state of charge and the determined cell temperature. The surface pressure determination unit 66 determines a cell surface pressure that corresponds to the calculated resistance value of the charging module based on the correspondence relationship between cell surface pressure and series resistance shown in the determined graph, and sets the determined cell surface pressure as the cell surface pressure of the charging module. The surface pressure determination unit 66 supplies determined surface pressure information indicating the determined cell surface pressure to the surface pressure application unit 67.

[0053] The surface pressure application unit 67 applies the cell surface pressure determined by the surface pressure determination unit 66 to the cells 10 included in each module 20. In the present embodiment, the surface pressure application unit 67 applies the same cell surface pressure to all of the cells 10 included in the series circuit 30a, and applies the same cell surface pressure to all of the cells 10 included in the series circuit 30b. The surface pressure application unit 67 applies the cell surface pressure to the cells 10 by transmitting a pressurization instruction signal to the pressurization mechanism 25 via the module control unit 21, instructing the pressurization mechanism 25 to pressurize the cells 10 to the specified cell surface pressure.

[0054] For example, when the cell surface pressure indicated by the surface pressure information acquired by the surface pressure information acquisition unit 61 is less than the cell surface pressure determined by the surface pressure determination unit 66, the surface pressure application unit 67 moves the pressure plate 253A in a direction away from the fixed plate 251A to increase the cell surface pressure applied to the cell 10. When the cell surface pressure indicated by the surface pressure information acquisition unit 61 exceeds the cell surface pressure determined by the surface pressure determination unit 66, the surface pressure application unit 67 moves the pressure plate 253A in a direction closer to the fixed plate 251A to decrease the cell surface pressure applied to the cell 10. The surface pressure application unit 67 compares the cell surface pressure indicated by the surface pressure information acquired by the surface pressure information acquisition unit 61 with the cell surface pressure determined by the surface pressure determination unit 66, and increases or decreases the cell surface pressure.

[0055] The switch control unit 68 controls the switches 40, 41, and 42. The switch control unit 68 controls the state of each switch by sending an open / close instruction signal to each switch instructing it to transition to either an open state or a closed state. The switch control unit 68 forms a circulation circuit 70 by controlling each switch, and adjusts the state of charge of the multiple modules 20. Specifically, when starting adjustment of the state of charge of the multiple modules 20, the switch control unit 68 sends an open / close instruction signal to the switch 40 instructing it to transition to the closed state, and sends open / close instruction signals to the switches 41 and 42 instructing them to transition to the open state. Once the circulation circuit 70 is formed, adjustment of the state of charge of the multiple modules 20 starts.

[0056] Next, a description will be given of a state-of-charge adjustment process executed by the battery system 100 with reference to the flowchart in Fig. 8. The state-of-charge adjustment process is a process for adjusting the states of charge of the multiple modules 20. The state-of-charge adjustment process is executed, for example, in response to the difference in voltage values ​​between the two series circuits 30 exceeding a threshold, in response to a user instruction, or periodically.

[0057] First, the battery control unit 60 included in the battery system 100 acquires temperature information (step S101). The battery control unit 60 acquires temperature information indicating cell temperatures measured by the temperature sensors 24 from all modules 20. After completing the process of step S101, the battery control unit 60 acquires voltage value information (step S102). The battery control unit 60 acquires voltage value information indicating cell voltage values ​​measured by the voltage sensors 22 from all modules 20.

[0058] Upon completing the process of step S102, the battery control unit 60 estimates the state of charge (step S103). The battery control unit 60 estimates the state of charge for all modules 20. For example, the battery control unit 60 calculates the sum of the cell voltage values ​​of all cells 10 included in the module 20 as the module voltage value, and estimates the state of charge from the calculated module voltage value. Upon completing the process of step S103, the battery control unit 60 identifies the maximum allowable current value (step S104). For example, the battery control unit 60 identifies the maximum allowable current value based on the cell temperature indicated by the temperature information collected from each module 20.

[0059] After completing the process of step S104, the battery control unit 60 determines a target resistance value of the circulation circuit 70 (step S105). For example, the battery control unit 60 calculates a lower limit resistance value by dividing the difference between the voltage value of the series circuit 30a and the voltage value of the series circuit 30b by the maximum allowable current value, and determines a resistance value equal to or greater than the lower limit resistance value as the target resistance value.

[0060] After completing the process of step S105, the battery control unit 60 determines the cell surface pressure of the discharge module (step S106). For example, the battery control unit 60 determines the cell surface pressure of the discharge module based on the charge rate of the discharge module calculated from the cell voltage of the discharge module, the cell temperature of the discharge module, and the correspondence relationship between the charge rate, cell temperature, cell surface pressure, and DC resistance.

[0061] Upon completing the process of step S106, the battery control unit 60 determines the cell surface pressure of the charging module (step S107). For example, the battery control unit 60 determines the resistance value of the charging circuit by subtracting the resistance value of the discharging circuit calculated from the cell surface pressure of the discharging module from the target resistance value. The battery control unit 60 determines the cell surface pressure of the charging module based on the charging rate of the charging module calculated from the cell voltage of the charging module, the cell temperature of the charging module, the resistance value of the charging module calculated from the determined resistance value of the charging circuit, and the correspondence relationships between the charging rate, cell temperature, cell surface pressure, and DC resistance.

[0062] Upon completing the process of step S107, the battery control unit 60 applies the determined cell surface pressure to each cell 10 (step S108). For example, the battery control unit 60 applies the cell surface pressure determined for the charge module to the cells 10 included in the charge module, and applies the cell surface pressure determined for the discharge module to the cells 10 included in the discharge module. Upon completing the process of step S108, the battery control unit 60 turns on the circulation circuit 70 (step S109). That is, the battery control unit 60 turns off the switch 40 and turns on the switches 41 and 42.

[0063] After completing the process of step S109, the battery control unit 60 determines whether the difference in the voltage values ​​of the two series circuits 30 is equal to or less than the threshold value (step S110). If the battery control unit 60 determines that the difference in the voltage values ​​of the two series circuits 30 is not equal to or less than the threshold value (step S110: NO), the battery control unit 60 returns to the process of step S110.

[0064] On the other hand, if the battery control unit 60 determines that the difference in voltage values ​​between the two series circuits 30 is equal to or less than the threshold value (step S110: YES), it turns off the circulation circuit 70 (step S111). That is, the battery control unit 60 turns on the switch 40 and turns off the switches 41 and 42. After completing the process of step S111, the battery control unit 60 restores the cell surface pressure to its original state (step S112). For example, the battery control unit 60 applies a predetermined cell surface pressure to all of the cells 10. After completing the process of step S112, the battery control unit 60 completes the state-of-charge adjustment process.

[0065] In this embodiment, when adjusting the state of charge of the plurality of modules 20, the cell surface pressure applied to the plurality of cells 10 is determined so that the current value of the circulating current is equal to or less than the maximum allowable current value determined from the cell temperature. Therefore, according to this embodiment, it is possible to adjust the state of charge of the plurality of modules 20 while suppressing the generation of dendrites.

[0066] Furthermore, in this embodiment, the cell surface pressure of the discharge module is determined first, and then the cell surface pressure of the charge module is determined. According to this embodiment, the cell surface pressure of the discharge module, which has many restrictions on cell surface pressure, is determined first, thereby preventing various problems caused by the application of inappropriate cell surface pressure to the cells 10 of the discharge module. For example, a significant increase in cell resistance value as the discharge of the discharge module progresses is prevented. Furthermore, uneven dissolution of lithium in the discharge module is prevented.

[0067] (Embodiment 2) In Embodiment 1, an example was described in which the cell surface pressure is measured using the pressure sensor 26. Also, in Embodiment 1, an example was described in which the cell surface pressure is not changed after adjustment of the state of charge is started. In Embodiment 2, an example is described in which the cell surface pressure is estimated without using the pressure sensor 26. Also, in this embodiment, an example is described in which the cell surface pressure is changed according to the current value of the circulating current after adjustment of the state of charge is started. Hereinafter, a battery system 100A according to this embodiment will be described with reference to Figures 9, 10, and 11. Note that descriptions of configurations and functions similar to those in Embodiment 1 will be omitted or simplified as appropriate.

[0068] Battery system 100A has the same configuration as battery system 100, except that it includes a plurality of modules 20A instead of the plurality of modules 20, and a battery control unit 60A instead of battery control unit 60. Module 20A has the same configuration as module 20, except that it includes a pressurizing mechanism 25A instead of pressurizing mechanism 25, and a distance measuring sensor 27 instead of pressure sensor 26. As shown in Fig. 9 , pressurizing mechanism 25A has the same configuration as pressurizing mechanism 25, except that it does not include fixing plate 251C that sandwiches pressure sensor 26 between fixing plate 251B.

[0069] The current sensor 23 measures the current value of the circulating current while adjusting the state of charge of the multiple modules 20A, and supplies current value information indicating the measured current value of the circulating current to the current value information acquisition unit 69. Note that the current flowing through the module 20A while adjusting the state of charge is the circulating current.

[0070] The distance measurement sensor 27 measures L1, which is the distance from the fixed plate 251A to the pressure plate 253A. In this embodiment, the distance measurement sensor 27 is installed on the fixed plate 251A and measures the distance to the pressure plate 253A. The distance measurement sensor 27 supplies distance information indicating the measured distance to the module control unit 21. The distance information is information for estimating the cell surface pressure. The longer the distance indicated by the distance information, the higher the cell surface pressure.

[0071] 10 , the functions of a battery control unit 60A included in a battery system 100A according to the present embodiment will be described. Functionally, the battery control unit 60A includes a distance information acquisition unit 61A, a surface pressure estimation unit 61B, a temperature information acquisition unit 62, a voltage value information acquisition unit 63, an allowable value determination unit 64, a target resistance value determination unit 65, a surface pressure determination unit 66, a surface pressure application unit 67, a switch control unit 68, and a current value information acquisition unit 69. The battery control unit 60A has the same functions as the battery control unit 60, except that it includes the distance information acquisition unit 61A and the surface pressure estimation unit 61B instead of the surface pressure information acquisition unit 61, and further includes the current value information acquisition unit 69. The surface pressure estimation unit 61B is an example of a surface pressure information acquisition means.

[0072] The distance information acquisition unit 61A acquires distance information from the distance measurement sensor 27 via the module control unit 21. The distance information acquisition unit 61A acquires distance information from each module 20A. The distance information acquisition unit 61A supplies the acquired distance information to the surface pressure estimation unit 61B.

[0073] The surface pressure estimation unit 61B estimates the cell surface pressure based on the distance information acquired by the distance information acquisition unit 61A. The method by which the surface pressure estimation unit 61B estimates the cell surface pressure can be adjusted as appropriate. For example, the surface pressure estimation unit 61B may estimate the cell surface pressure from L1 by referencing a table showing the correspondence between L1 and cell surface pressure. Such a table may be stored, for example, in a ROM included in the battery control unit 60A. Basically, the longer L1, the higher the cell surface pressure. Furthermore, if the cells 10 expand and contract depending on the charge rate of the module 20A, a table that takes the charge rate into consideration may be used. In this case, a table showing the correspondence between L1, the charge rate, and the cell surface pressure is used. The surface pressure estimation unit 61B estimates the cell surface pressure for each module 20A. The surface pressure estimation unit 61B supplies estimated surface pressure information indicating the estimated surface pressure to the surface pressure application unit 67. The estimated surface pressure information is an example of surface pressure information.

[0074] While adjusting the charge states of the multiple modules 20A, the current value information acquisition unit 69 acquires current value information from the current sensor 23 via the module control unit 21. The current value information acquisition unit 69 acquires current value information from at least one module 20A. The current value information acquisition unit 69 supplies the acquired current value information to the surface pressure determination unit 66.

[0075] The surface pressure determination unit 66 changes the cell surface pressure according to the current value of the circulating current while adjusting the state of charge of the multiple modules 20A. For example, when increasing the cell surface pressure according to a decrease in the current value of the circulating current, the surface pressure determination unit 66 increases the cell surface pressure within a range that does not exceed a predetermined upper limit of the surface pressure. During adjustment of the state of charge, the voltage value of the discharge circuit gradually decreases and the voltage value of the charge circuit gradually increases. Therefore, during adjustment of the state of charge, the difference between the voltage value of the discharge circuit and the voltage value of the charge circuit gradually decreases, and the current value of the circulating current gradually decreases.

[0076] However, a decrease in the circulating current value means that it takes longer to adjust the state of charge. In other words, to quickly complete the adjustment of the state of charge, it is preferable to maintain the circulating current value as large as possible. Therefore, the surface pressure determination unit 66 increases the cell surface pressure to suppress a decrease in the circulating current value.

[0077] Specifically, while adjusting the state of charge, the surface pressure determination unit 66 monitors the current value of the circulating current indicated by the current value information acquired by the current value information acquisition unit 69, and if the current value of the circulating current decreases, determines the cell surface pressure for increasing the current value of the circulating current. For example, while adjusting the state of charge, the surface pressure determination unit 66 changes the cell surface pressure applied to each cell 10 so that the current value of the circulating current does not fall below a reference current value. The reference current value may be an initial current value, which is the current value of the circulating current at the start of adjusting the state of charge, or a current value smaller than the initial current value.

[0078] The method by which the surface pressure determination unit 66 determines the cell surface pressure can be adjusted as appropriate. For example, the surface pressure determination unit 66 may increase the cell surface pressure by a specified value while the current value of the circulating current is below a reference current value. The surface pressure determination unit 66 may increase both the cell surface pressure of the discharge module and the cell surface pressure of the charge module, or may increase only the cell surface pressure of the discharge module, or may increase only the cell surface pressure of the charge module. The surface pressure determination unit 66 also increases the cell surface pressure within a range that does not exceed a predetermined upper limit of the surface pressure. This is because if the cell surface pressure exceeds the upper limit of the surface pressure, the cells 10, the module 20A, etc., are more likely to be damaged or dendrites may precipitate.

[0079] The surface pressure applying unit 67 applies the cell surface pressure determined by the surface pressure determining unit 66 to each cell 10. For example, when the surface pressure determining unit 66 determines to increase the cell surface pressure, the surface pressure applying unit 67 moves the pressure plate 253A in a direction away from the fixed plate 251A to increase the cell surface pressure applied to the cell 10. The surface pressure applying unit 67 compares the cell surface pressure estimated by the surface pressure estimating unit 61B with the cell surface pressure determined by the surface pressure determining unit 66, and increases or decreases the cell surface pressure.

[0080] Next, the state-of-charge adjustment process executed by the battery system 100A will be described with reference to the flowchart of FIG.

[0081] First, the processes from step S101 to step S109 are the same as those described in the first embodiment, and therefore will not be described again. When the battery control unit 60A provided in the battery system 100A determines that the difference in the voltage values ​​of the two series circuits 30 is not equal to or less than the threshold value (step S110: NO), the battery control unit 60A acquires current value information indicating the current value of the circulating current (step S113). For example, the battery control unit 60A acquires current value information indicating the current value of the circulating current from at least one module 20A.

[0082] After completing the process of step S113, the battery control unit 60A determines whether the current value of the circulating current is less than the reference current value (step S114). If the battery control unit 60A determines that the current value of the circulating current is less than the reference current value (step S114: YES), the battery control unit 60A determines whether the cell surface pressure has reached the upper limit surface pressure (step S115). If the battery control unit 60A determines that the cell surface pressure has not reached the upper limit surface pressure (step S115: NO), the battery control unit 60A increases the cell surface pressure (step S116). For example, the battery control unit 60A increases at least one of the cell surface pressure of the discharge module and the cell surface pressure of the charge module by a predetermined value.

[0083] If the battery control unit 60A determines that the current value of the circulating current is not less than the reference current value (step S114: NO), if the battery control unit 60A determines that the cell surface pressure has reached the upper limit surface pressure (step S115: YES), or if the process of step S116 is completed, the process returns to step S110. If the battery control unit 60A determines that the difference in the voltage values ​​of the two series circuits 30 is equal to or less than the threshold value (step S110: YES), the battery control unit 60A turns off the circulating circuit 70 (step S111). After completing the process of step S111, the battery control unit 60 restores the cell surface pressure to its original value (step S112). After completing the process of step S112, the battery control unit 60 completes the state of charge adjustment process.

[0084] In this embodiment, the cell surface pressure is changed according to the current value of the circulating current while adjusting the state of charge of the multiple modules 20A. Therefore, according to this embodiment, the current value of the circulating current can be adjusted. For example, if the current value of the circulating current decreases as charging and discharging progresses, the resistance value of the circulation circuit 70 can be reduced by increasing the cell surface pressure. Therefore, according to this embodiment, the decrease in the current value of the circulating current is suppressed, and adjustment of the state of charge is completed quickly.

[0085] In this embodiment, when the cell surface pressure is increased, the cell surface pressure is increased within a range that does not exceed a predetermined upper limit of the surface pressure, thereby suppressing damage to the cells 10, modules 20, etc. due to the application of excessive surface pressure, and suppressing the generation of dendrites due to the application of excessive surface pressure.

[0086] (Modifications) Although the embodiments have been described above, modifications and applications in various forms are possible. It is up to the discretion of which parts of the configurations, functions, and operations described in the above embodiments to adopt. Furthermore, in addition to the above-described configurations, functions, and operations, further configurations, functions, and operations may be adopted. Furthermore, the configurations, functions, and operations described in the above embodiments can be freely combined.

[0087] In the first embodiment, an example has been described in which, in the battery system 100, two series circuits 30 are connected in parallel, each of which is made up of seven modules 20, each of which is made up of 30 cells 10 connected in series. The numbers, connections, and the like of the cells 10, modules 20, and series circuits 30 are not limited to this example. For example, the number of cells 10 included in a module 20 may be 29 or less, or 31 or more. The number of modules 20 included in a series circuit 30 may be six or less, or eight or more. The number of series circuits 30 may be three or more. In this case, each of the three or more series circuits 30 is classified as either a discharge circuit or a charge circuit, and when adjusting the state of charge, power is supplied from a discharge module included in at least one discharge circuit to a charge module included in at least one charge circuit.

[0088] Furthermore, all of the cells 10 included in the module 20 do not have to be connected in series. For example, multiple cell strings, each of which has multiple cells 10 connected in series, may be connected in parallel within the module 20. Even in this case, the multiple cells 10 included in one module 20 can be considered to have approximately the same cell voltage value, cell temperature, cell surface pressure, etc.

[0089] In the first embodiment, an example was described in which the module 20 includes one voltage sensor 22 and one temperature sensor 24. The module 20 may also include a voltage sensor 22 and a temperature sensor 24 for each cell 10. In this case, a representative value calculated from the voltage values ​​measured by each voltage sensor 22 may be regarded as the cell voltage value. Similarly, a representative value calculated from the temperatures measured by each temperature sensor 24 may be regarded as the cell temperature. Possible representative values ​​include the average, median, maximum, and minimum values ​​of the measured values. Furthermore, in the first embodiment, an example was described in which the voltage sensor 22 measures the cell voltage value and the module voltage value is calculated from the cell voltage value. The voltage sensor 22 may also measure the module voltage value and the cell voltage value may be calculated from the module voltage value.

[0090] In the above-described embodiments, the CPU in the processor executes a program stored in ROM or RAM to function as each of the components shown in FIGS. 6 and 10 . However, in the present invention, the processor may be dedicated hardware. Dedicated hardware may be, for example, a single circuit, a composite circuit, a programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination thereof. When the processor is dedicated hardware, the functions of each component may be implemented by individual hardware, or the functions of each component may be implemented collectively by a single piece of hardware. Furthermore, some of the functions of each component may be implemented by dedicated hardware, and other components may be implemented by software or firmware. In this way, the processor can implement each of the above-described functions by hardware, software, firmware, or a combination thereof.

[0091] By applying an operating program that defines the operation of the battery control units 60, 60A according to the present invention to a computer such as an existing personal computer or information terminal device, it is possible to cause the computer to function as the battery control units 60, 60A according to the present invention. Furthermore, the method of distribution of such a program is arbitrary, and for example, the program may be stored on a computer-readable recording medium such as a CD-ROM (Compact Disk ROM), a DVD (Digital Versatile Disk), an MO (Magneto Optical Disk), or a memory card, or may be distributed via a communication network such as the Internet.

[0092] The present invention allows various embodiments and modifications without departing from the broad spirit and scope of the present invention. Furthermore, the above-described embodiments are intended to illustrate the present invention and do not limit the scope of the present invention. That is, the scope of the present invention is defined by the claims, not by the embodiments. Various modifications made within the scope of the claims and the meaning of the invention equivalent thereto are considered to be within the scope of the present invention.

[0093] 10 Cell, 20, 20A Module, 21 Module control unit, 22 Voltage sensor, 23 Current sensor, 24 Temperature sensor, 25, 25A Pressurizing mechanism, 26 Pressure sensor, 27 Distance measurement sensor, 30, 30a, 30b Series circuit, 31a, 31b Voltage source, 32a, 32b Resistor, 40, 41, 42 Switch, 51 Positive terminal, 52 Negative terminal, 60, 60A Battery control unit, 61 Surface pressure information acquisition unit, 61A Distance information acquisition unit, 61B Surface pressure estimation unit, 62 Temperature information acquisition unit, 63 Voltage value information acquisition unit, 64 Allowable value determination unit, 65 Target resistance value determination unit, 66 Surface pressure determination unit, 67 Surface pressure application unit, 68 Switch control unit, 70 Circulation circuit, 100, 100A Battery system, 251A, 251B, 251C fixed plates, 252A, 252B guide members, 253A, 253B pressure plates, 254 elastic body, 255 actuator.

Claims

1. A control method for a battery system that adjusts the state of charge of a plurality of modules each having a plurality of cells that are lithium secondary batteries using a circulating current, the control method comprising: applying a surface pressure to the plurality of cells; acquiring surface pressure information indicating the cell surface pressure that is the surface pressure applied to the plurality of cells; acquiring temperature information indicating the cell temperature that is the temperature of the plurality of cells; acquiring voltage value information indicating the cell voltage values ​​that are the voltage values ​​of the plurality of cells; and determining the cell surface pressure to be applied to the plurality of cells when adjusting the state of charge of the plurality of modules using the circulating current having a current value determined from the cell surface pressure, the cell temperature, and the cell voltage value, so that the current value of the circulating current is equal to or less than a maximum allowable current value determined from the cell temperature.

2. A method for controlling a battery system as described in claim 1, wherein current value information indicating a current value of the circulating current is acquired while adjusting the state of charge of the plurality of modules, and the cell surface pressure is changed according to the current value of the circulating current while adjusting the state of charge of the plurality of modules.

3. The method for controlling a battery system according to claim 2, wherein when the cell surface pressure is increased in response to a decrease in the current value of the circulating current, the cell surface pressure is increased within a range not exceeding a predetermined upper limit surface pressure.

4. A method of controlling a battery system according to any one of claims 1 to 3, wherein the circulating current is a current flowing through a circulation circuit connecting a discharge circuit including at least one discharge module that discharges while adjusting the state of charge of the plurality of modules, and a charge circuit including at least one charge module that charges while adjusting the state of charge of the plurality of modules, and the method comprises determining a target resistance value of the circulation circuit so that the current value of the circulating current is equal to or less than the maximum allowable current value, determining the cell surface pressure for the discharge module based on the state of charge based on the cell voltage value and the cell temperature, calculating the resistance value of the discharge circuit based on the cell surface pressure determined for the discharge module, and determining the cell surface pressure for the charge module based on the state of charge based on the cell voltage value and the cell temperature so that the resistance value of the charge circuit is the target resistance value minus the resistance value of the discharge circuit.

5. A battery system comprising: a plurality of modules each having a plurality of cells that are lithium secondary batteries; a pressure mechanism that applies surface pressure to the plurality of cells; a temperature sensor that measures cell temperatures that are temperatures of the plurality of cells; a voltage sensor that measures cell voltage values ​​that are voltage values ​​of the plurality of cells; and a control unit that, when adjusting the state of charge of the plurality of modules by a circulating current having a current value determined from the cell surface pressure that is the surface pressure applied to the plurality of cells, the cell temperature, and the cell voltage value, determines the cell surface pressure to be applied to the plurality of cells so that the current value of the circulating current is equal to or less than a maximum allowable current value determined from the cell temperature, and controls the pressure mechanism in accordance with the determined cell surface pressure.

6. A program that causes a computer included in a battery system that adjusts the state of charge of a plurality of modules each having a plurality of cells that are lithium secondary batteries using a circulating current to function as: a surface pressure application means that applies surface pressure to the plurality of cells; a surface pressure information acquisition means that acquires surface pressure information indicating the cell surface pressure, which is the surface pressure applied to the plurality of cells; a temperature information acquisition means that acquires temperature information that indicates the cell temperature, which is the temperature of the plurality of cells; a voltage value information acquisition means that acquires voltage value information that indicates the cell voltage values, which are voltage values ​​of the plurality of cells; and a surface pressure determination means that determines the cell surface pressure to be applied to the plurality of cells so that the current value of the circulating current, when adjusting the state of charge of the plurality of modules using the circulating current having a current value determined from the cell surface pressure, the cell temperature, and the cell voltage value, is equal to or less than a maximum allowable current value determined from the cell temperature.

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