Battery system control method and battery system

Abstract

Provided are a battery system control method and a battery system that, even when a plurality of battery modules are connected in parallel, enable using an initial capacity through sufficient charging and discharging. The present invention comprises: modules (M) which are connected in parallel and each of which is provided with a plurality of layers of battery cells (C); a pressure application mechanism (P) which is provided for the plurality of modules (M) and capable of varying the pressure to be applied to the modules (M); and a load control device (1) which controls the pressure application mechanism (P). The load control device (1) executes current distribution to the parallel-connected modules (M) through load control on the plurality of modules (M) by the pressure application 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] As a charging system for an all-solid-state battery mounted on a vehicle, a charging system for an all-solid-state battery has been proposed that can increase the rapid charging capacity by controlling the restraining pressure on the all-solid-state battery.

[0003] JP 2015-095281 A

[0004] Although it is possible to control the restraint pressure in accordance with the battery characteristics in this way, when multiple batteries are connected in parallel, there may be differences in capacity among the battery cells that make up the multiple batteries. Such differences in capacity among the multiple battery cells occur because, for example, each battery cell is affected differently by the environment.

[0005] When charging a battery that includes such battery cells, for example, a battery consisting of modules connected in parallel, if an equal current is passed through each module, the following situation may occur: A battery that includes battery cells with small battery capacity will reach the upper limit of chargeability sooner than other batteries, and further charging will be impossible, causing charging to be stopped.

[0006] In this way, if the upper limit of charge for one battery is reached earlier than the upper limit of charge for the other battery, charging of the other battery will stop even though there is still chargeable battery capacity remaining.

[0007] In other words, if charging of the other battery, which still has chargeable capacity, is stopped in the same way as for the first battery, the other battery will not be fully charged, which may result in a situation where the capacity of each battery or the entire battery system consisting of multiple batteries cannot be fully used.

[0008] 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.

[0009] A method for controlling 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 load control device that controls the pressure mechanism, and the load control device distributes current to the modules connected in parallel by controlling the load on the plurality of modules using the pressure mechanism.

[0010] Furthermore, a battery system in an embodiment of the present invention includes 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 load control device that controls the pressure mechanism, and when the load control device determines that the closed circuit voltage difference, which is the difference between the maximum and minimum values ​​of the maximum cell closed circuit voltage in each of the modules, is greater than a threshold value, the load control device controls the pressure mechanism so that the load difference between a first load applied by the pressure mechanism to the module including the battery cell with the maximum cell closed circuit voltage indicating the maximum value and a second load applied by the pressure mechanism to the module including the battery cell with the maximum cell closed circuit voltage indicating the minimum value is greater than the load difference in the previous control.

[0011] 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.

[0012] 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 load control device according to an embodiment of the present invention. FIG. 3 is an explanatory diagram showing the relationship between the charge capacity and voltage value of each battery cell when there is a difference in the internal capacity of the battery cells in the battery system according to an embodiment of the present invention. FIG. 4 is an explanatory diagram showing the relationship between the pressure applied to the battery cell and the internal resistance value of the module in a control method for a battery system according to an embodiment of the present invention. FIG. 5 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. 6 is a flowchart showing the flow of a control method for a battery system according to a first embodiment of the present invention. FIG. 7 is a flowchart showing the flow of a control method for a battery system according to a second embodiment of the present invention. FIG. 8 is a flowchart showing the flow of a control method for a battery system according to a third embodiment of the present invention. FIG. 9 is a flowchart showing the flow of a control method for a battery system according to a third embodiment of the present invention.

[0013] (First embodiment) Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Note that each drawing is a schematic view and may differ from the actual product. Furthermore, the embodiment of the present invention shown below exemplifies an apparatus and method 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.

[0014] 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 load control device 1. The battery system BS is mounted on, for example, a vehicle for use.

[0015] 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.

[0016] 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).

[0017] 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.

[0018] 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.

[0019] 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.

[0020] Furthermore, the outermost battery cells C of the stacked battery cells C are in contact with each of the pair of pressure plates PP, PP, so that pressure from the pressure plate PP can be applied directly to the stacked battery cells C.

[0021] However, instead of the battery cells C and the pressure plate PP being in direct contact with each other, for example, a load displacement absorption mechanism (not shown in Fig. 1) may be provided between the pressure plate PP and the battery cells C. The load displacement absorption mechanism is made of an elastic body such as a spring, and is provided to allow the pressure plate PP to follow the movement of the battery cells C.

[0022] That is, the pressure mechanism P changes the load applied to the battery cells C, but in order to do so, it is necessary that the pressure applied to the battery cells C via the pressure plate PP be reliably transmitted to the battery cells C. Meanwhile, in the case of a secondary battery that uses lithium metal for the negative electrode, for example, as described above, the battery cells C expand and contract as they are charged and discharged.

[0023] Therefore, if the pressure plate PP cannot follow the expansion and contraction of the battery cell C when the battery cell C expands or contracts, it may not be possible to apply pressure to the battery cell C.

[0024] To prevent this from happening, a load displacement absorption mechanism is placed between the pressure plate PP and the battery cells C, so that contact between the pressure plate PP and the battery cells C is maintained even if the pressure plate PP moves or if the battery cells C expand or contract. Furthermore, because the load displacement absorption mechanism has this function, it also has the function of properly housing the battery cells C within the module M.

[0025] The motor gear MG is in contact with one of the pressure plates PP and is capable of changing 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 load control device 1.

[0026] That is, a signal from the load control device 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 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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 load control device 1.

[0031] The load control device 1 receives information on the detected values ​​detected by the ammeter A, voltmeter V, and thermometer T. As will be described later, the load control device 1 also uses the input information on these 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.

[0032] The load control device 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 cell C based on a command from the load control device 1. Furthermore, the power control device 2 is, for example, an inverter for a vehicle drive motor, and extracts power from the battery system BS to obtain driving force, and supplies 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 load control device 1.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 1 also shows solid arrows 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 load control device 1 to the driver D or the power control device 2 are indicated by dashed arrows directed from the load control device 1 to the driver D or the power control device 2.

[0037] 2 is a block diagram showing the internal configuration of the load control device 1 according to the embodiment of the present invention. The load control device 1 includes a CPU (Central Processing Unit) 11, a ROM (Read Only Memory) 2, a RAM (Random Access Memory) 13, and an input / output interface 14, all of which are connected via a bus 15. Furthermore, the input / output interface 14 is 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.

[0038] The CPU 11 reads and executes a boot program for starting up the load control device 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.

[0039] 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 load control device 1, calculates current distribution to the modules M connected in parallel, or controls the load on 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.

[0040] Next, before specifically describing the other components that make up the load control device 1, the concept of battery system control in an embodiment of the present invention will be described below with reference to Figures 3 to 5. Figure 3 is an explanatory diagram showing the relationship between the charge capacity [Ah] and voltage value [V] for each battery cell C in a battery system BS in an embodiment of the present invention when there is a difference in the internal capacity of the battery cells C of a module M.

[0041] 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.

[0042] In the explanatory diagram of Fig. 3, the vertical axis represents the voltage [V] of the battery cell C, and the horizontal axis represents the charge capacity [Ah] of the battery cell C. The charge capacity of the battery cell C can also be expressed as the charge time [sec]. That is, in the explanatory diagram of Fig. 3, the charge time becomes longer and the charge capacity becomes larger as one moves to the right from the origin, which indicates the start of charging.

[0043] 3 shows the relationship between voltage and charge capacity for two battery cells C, where the solid line indicates the first battery cell C1 in the first module M1, while the dashed line indicates the second battery cell C2 in the second module M2. Here, it is assumed that the first battery cell C1 has a smaller battery capacity than the second battery cell C2.

[0044] Furthermore, the first module M1 including the first battery cell C1 and the second module M2 including the second battery cell C2 are connected in parallel, and when a charging process is performed on the first module M1 and the second module M2, for example, a charging current flows equally through the first module M1 and the second module M2.

[0045] Since the first battery cell C1 has a smaller battery capacity than the second battery cell C2, the time from the start of charging to full charging is shorter. When the charging process is executed, the point at which full charging is determined is determined, for example, by whether the charging voltage of each battery cell has reached a predetermined voltage value. Here, the voltage value at which full charging is determined is referred to as the "upper limit voltage."

[0046] Since the battery capacity of the first battery cell C1 is smaller than that of the second battery cell C2, the first battery cell C1 reaches the upper limit voltage in a shorter time, and therefore the charging process for the first battery cell C1 is stopped when the upper limit voltage is reached.

[0047] In Figure 3, the dotted line representing the upper limit voltage is drawn parallel to the horizontal axis, and charging is stopped where the dotted line intersects with the solid line representing the relationship between the charge capacity and voltage of the first battery cell C1. Therefore, in Figure 3, a dotted line drawn parallel to the vertical axis from the point where the dotted line representing the upper limit voltage and the solid line for the first battery cell C1 intersects with the horizontal axis, and the line indicates "charging stopped."

[0048] On the other hand, the second battery cell C2 (second module M2) connected in parallel to the first battery cell C1 (first module M1) has a larger charge capacity than the first battery cell C1. Therefore, until the second battery cell C2 is fully charged, i.e., until the second battery cell C2 reaches the upper limit voltage through the charging process, the charging time required is longer than that required for the first battery cell C to be fully charged, as indicated by the large open double-headed arrow A, as shown by the dashed line in Figure 3.

[0049] However, as described above, when the first battery cell C1 is fully charged by the charging process, the charging process for the battery system BS is stopped at the point where charging is stopped as shown in Fig. 3. Therefore, the second battery cell C2 is not charged after charging is stopped.

[0050] In other words, from the perspective of the second battery cell C2, the charging time is insufficient by the time indicated by the large open double-headed arrow A. Therefore, the charging is not sufficient to fill the charge capacity of the entire battery system BS. Therefore, the initial capacity of the battery system BS cannot be used.

[0051] Therefore, as will be described later, the load control device 1 in the embodiment of the present invention employs the following control method to prevent such problems from occurring: That is, when a charging process is executed for a battery system BS in which each of the battery cells C constituting a plurality of modules M includes a battery cell C with a low battery capacity, the pressure mechanism P is controlled so that the battery cell C with the low battery capacity does not prematurely stop charging of the entire battery system BS.

[0052] In other words, by controlling the pressure applied to the module M via the pressure mechanism P, the internal resistance value of each battery cell C is changed, thereby equalizing the charge amount for each battery cell C, and making it possible to use the initial capacity of the battery system BS.

[0053] Next, we will explain why the load control device 1 controls the pressure mechanism P in this way to prevent charging of a battery cell C with low battery capacity from being stopped early during charging, with the aid of Figure 4. Figure 4 is an explanatory diagram illustrating the relationship between the pressure applied to the battery cell C and the internal resistance value of the module M in the control method for the battery system BS according to an embodiment of the present invention.

[0054] As described above, the pressure applied to the modules M (battery cells C) is changed by the control of the load control device 1. As shown in FIG. 1 , each of the two modules M in this embodiment of the present invention is provided with a pressure mechanism P. Therefore, pressure can be applied to either the first module M1 or the second module M2. Alternatively, pressure can be applied to both of them simultaneously.

[0055] In this way, any pressure mechanism P can be selected and controlled when controlling the pressure mechanism P. However, in the following description, it is assumed that the pressure mechanism P controlled by the load control device 1 is a module M equipped with a battery cell C having a small battery capacity. That is, as shown in the explanatory diagram of FIG. 3 , the first module M1 equipped with the first cell C1 has a small battery capacity and reaches the upper limit voltage first after charging starts. Therefore, it is assumed that the pressure mechanism P (module M) to be controlled is that of the first module M1.

[0056] 4, the pressure applied from the pressure mechanism P to the module M (battery cells C) before the pressure mechanism P is controlled will be referred to as the "initial surface pressure." The pressure applied to the module M (battery cells C) after the pressure mechanism P is controlled will be referred to as the "surface pressure after load control."

[0057] In the explanatory diagram of Figure 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, with the internal resistance value increasing from bottom to top on the vertical axis.

[0058] When the surface pressure applied to the battery cell C by the pressure mechanism P is the initial surface pressure, the internal resistance value indicates the value 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 load 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.

[0059] 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, the load control device 1, for example, controls the pressure mechanism P connected to the first module M1 to reduce the surface pressure so that charging of the battery system BS is not stopped early by the first battery cell C1 with a low battery capacity when performing the charging process.

[0060] That is, as shown in Fig. 4, the pressure applied to the first battery cell C1 in the first module M1 is reduced so that the surface pressure after load control decreases from the initial surface pressure. As the pressure applied to the first battery cell C1 decreases, the internal resistance of the first battery cell C1 increases from internal resistance M to internal resistance N, as shown in the explanatory diagram of Fig. 4, for example. Because the internal resistance of the first module M1 increases in this way, it becomes more difficult for current to flow through the first module M1.

[0061] Fig. 5 is an explanatory diagram showing the control intent of the control method for the battery system BS according to the embodiment of the present invention. In the explanatory diagram shown in Fig. 5, the vertical axis represents the voltage [V] of the battery cell C, and the horizontal axis represents the charge capacity [Ah] of the battery cell C, as in Fig. 3. Also, Fig. 5 shows thick solid lines, thin solid lines, and thick dashed lines, thin dashed lines.

[0062] Of these, the thin solid line and thin dashed line show the relationship between the charge capacity and voltage of the first battery cell C1 and the second battery cell C2 shown in Fig. 3, and are shown with the same slope as Fig. 3. The thick solid line C11 and thick dashed line C21 are shown in the directions of the arrows from these thin solid line and thin dashed line, respectively. The thick solid line C11 and thick dashed line C21 show the results of pressure being applied to the first module M1 and the second module M2 by the load control device 1 via the pressure mechanism P.

[0063] That is, the thin solid line and thin dashed line show the relationship between the charge capacity and voltage of each battery cell C when pressure is not applied to the battery cell C by the pressure mechanism P during charging. The thick solid line C11 and thick dashed line C21 show the relationship between the charge capacity and voltage of each battery cell C when pressure is applied to the battery cell C by the pressure mechanism P during charging.

[0064] 5 shows the change in the relationship between charge capacity and voltage when pressure is applied to each battery cell C by the pressure mechanism P from when it is not applied to the other battery cells C. This is indicated by the arrows pointing from the thin solid line to the thick solid line C11 and the arrows pointing from the thin dashed line to the thick dashed line C21.

[0065] Specifically, when control is performed to reduce the pressure applied to the first battery cell C1 in the first module M1 so that the surface pressure after load control decreases from the initial surface pressure, the internal resistance value in the first module M1 increases, making it difficult for current to flow through the first module M1.

[0066] Therefore, the growth (increase) in the charge capacity of the first module M1 can be reduced, and as indicated by the downward arrow in Figure 5, the slope of the thick solid line C11, which shows the change in charge capacity over time in the first module M1, becomes gentler than the thin solid line.

[0067] 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.

[0068] Therefore, when the amount of current flowing through the second module M2, which has a relatively larger charge capacity than the first module M1, increases, the charge capacity of the second module M2 is filled up more quickly than before. In other words, the slope of the thick dashed line C21 in Figure 5, which shows the change in charge capacity of the second module M2 over time, becomes steeper than the slope of the thin dashed line, as indicated by the upward arrow.

[0069] As described above, for example, by controlling the pressure mechanism P connected to the first module M1 to reduce the surface pressure, the difference between the charge capacity of the first module M1 and the charge capacity of the second module M2 can be reduced. In other words, the insufficient charge time of the second battery cell C2, indicated by the large white arrow A' in Figure 3, can be increased by the time indicated by the thick black double-headed arrow B in Figure 5.

[0070] Therefore, although the charge capacity for the first battery cell C1 does not change, the charge capacity for the second battery cell C2 can be increased, and as a result, the charge capacity of the entire battery system BS can be increased.

[0071] In this example, the current flowing through the second module M2 is increased relatively by reducing the pressure applied to the first cell C1 of the first module M1. However, it is also possible to more actively control the load control device 1 to drive the pressure mechanism P connected to the second module M2 to increase the surface pressure.

[0072] In other words, the pressure applied to the second battery cell C2 in the second module M2 is increased by controlling the pressure after the load control from the initial pressure, as shown by the arrow in Fig. 4 in the opposite direction. This control reduces the internal resistance of the second battery cell C2, making it easier for current to flow through the second module M2.

[0073] Therefore, it is possible to control the pressure applied to the first module M1 to be decreased while simultaneously increasing the pressure applied to the second module M2. Alternatively, it is possible to control only the pressure applying mechanism P provided in the second module M2, rather than controlling the pressure applying mechanism P provided in the first module M1.

[0074] Returning to Fig. 2, the information acquisition unit 16 acquires information on the current, voltage, and temperature values ​​detected by the ammeter A, voltmeter V, and thermometer T. It also acquires the closed-circuit voltage (hereinafter referred to as "CCV" as appropriate) of each battery cell C that constitutes each module M.

[0075] As explained using Figures 3 and 5, in this embodiment of the present invention, when charging a module M, an upper limit voltage is used as a parameter for terminating charging. That is, charging is stopped when the upper limit voltage is reached according to the charge capacity of the battery cells C. Here, the upper limit voltage also changes depending on the deterioration state of the battery cells C, so the deterioration state of the battery cells C must take into account the state of the current flowing through the battery cells C. Therefore, the CCV value is used to execute load control using the pressure mechanism P for each module M.

[0076] Furthermore, the maximum CCV value (hereinafter referred to as "maximum cell CCV") for each battery cell C is acquired as the CCV value for each battery cell C. As described above, the charging process for each module M constituting the battery system BS depends on the battery cell C with the lowest charge capacity among the charge capacities of the battery cells C included in each module M. Therefore, the maximum cell CCV, which is the CCV for each battery cell C, is acquired in advance.

[0077] By acquiring the maximum cell CCV value for each battery cell C, if there is no large difference in the maximum cell CCV value for each battery cell C, it is thought that the charge capacities of the other battery cells C will be less affected by the battery cell C with the lowest charge capacity when charging the module M. In other words, in such a case, even if charging of a battery cell C with a small maximum cell CCV value, i.e., the battery cell C with the lowest charge capacity, is stopped because it is fully charged, it is still possible to charge battery cells C with larger charge capacities to a certain extent.

[0078] On the other hand, if there is a predetermined difference in the maximum cell CCV value for each battery cell C, and charging is stopped because the battery cell C with the lowest charge capacity is fully charged, the charge capacity for the battery cell C with the larger charge capacity will not be satisfied. This state, as shown by the large open double-headed arrow A in the explanatory diagram of Figure 3, results in the charging process being interrupted midway by the battery cell C with the lowest charge capacity, even though more time is actually required to fully charge.

[0079] Therefore, in order to determine under what circumstances the pressure mechanism P should be used to control the application of pressure to the battery cells C, the information acquisition unit 16 acquires the value of the maximum cell CCV for each of the multiple battery cells C that make up each module M.

[0080] The storage unit 17 is composed of a semiconductor or a magnetic disk, and 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 pieces of information acquired by the information acquisition unit 16 as appropriate.

[0081] As described above, if there is a difference in the maximum cell CCV values ​​for each battery cell C acquired by the information acquisition unit 16, there is a possibility that the battery cell C with the largest maximum cell CCV value will not be sufficiently charged when a charging process is performed. Therefore, the calculation unit 18 calculates the difference based on the maximum cell CCV values ​​for each battery cell C acquired by the information acquisition unit 16. Specifically, the calculation unit 18 calculates the difference between the maximum cell CCV value showing the largest value and the maximum cell CCV value showing the smallest value (hereinafter referred to as the "CCV difference" where appropriate).

[0082] The determination unit 19 then compares the CCV difference calculated by the calculation unit 18 with a predetermined threshold value. Here, the "threshold value" is a fixed value set, for example, through experiments, etc. This value is used to determine whether or not there is a possibility that a battery cell C with a large maximum cell CCV value will not be sufficiently charged when a charging process is performed.

[0083] That is, for example, in a state where the maximum cell CCV showing the largest value and the maximum cell CCV showing the smallest value in the battery cell C frequently switch, the power consumption executed for the battery cell C (module M) increases. Therefore, more specifically, for example, a value of about 1 to 10 mV may be set as the threshold value.

[0084] If the determination unit 19 compares the CCV difference with the threshold value and determines that the CCV difference is greater than the threshold value, there is a possibility that the charge capacity of the battery cell C with the greater charge capacity will not be met if charging of the battery cell C with the lowest charge capacity is stopped because the battery cell C with the lowest charge capacity is fully charged. Therefore, the determination unit 19 instructs the drive control unit 20 to apply pressure to the battery cells C of the module M. Therefore, the drive control unit 20 controls the pressure mechanism P.

[0085] Specifically, load control is performed on the battery cells C of the module M to be controlled so that the load difference between the load applied to the module M having the largest cell CCV with the largest value and the load applied to the module M having the largest cell CCV with the smallest value becomes large.

[0086] The reason for controlling the load difference to be large is that the internal resistance value changes depending on the pressure (surface pressure) applied to the battery cell C. That is, as explained using FIG. 4 , for example, if the surface pressure on the battery cell C with the smallest maximum cell CCV value is reduced without changing the surface pressure on the other battery cells C, the load difference will increase. When such control is performed, the internal resistance value for that battery cell C increases. This makes it more difficult to charge that battery cell C, and the charge capacity (charging time) until full charge can be extended. Furthermore, extending the charging time increases the charge capacity of the other battery cells C.

[0087] Conversely, increasing the surface pressure on a battery cell C that exhibits a large maximum cell CCV value reduces the internal resistance of that battery cell C. This makes it easier to charge that battery cell C, shortening the charge capacity (charging time) required to reach full charge. This control also makes it possible to increase the load difference.

[0088] Alternatively, control may be performed to reduce the surface pressure on the battery cell C with the smallest maximum cell CCV value, and simultaneously increase the surface pressure on the other battery cells C with larger maximum cell CCV values. Even with such control, the load difference between modules M when load control is executed can be made larger than the load difference before load control was executed.

[0089] 1, when two modules M (a first module M1 and a second module M2) are connected in parallel, pressure is applied to the battery cells C of each module M. Alternatively, it is also possible that no pressure is applied to any of the modules M.

[0090] Regardless of whether pressure is being applied to each module M, there is pressure being applied to each module M prior to the load control based on the judgment of the judgment unit 19, and it is possible to grasp the load difference between the two. The load difference is calculated using the load applied to the module M with the largest maximum cell CCV and the load applied to the module M with the smallest maximum cell CCV.

[0091] Incidentally, the load difference may be calculated, for example, by the determination unit 19 instructing the calculation unit 18 to calculate the load difference, or may be calculated together with the calculation unit 18 calculating the CCV difference as described above.

[0092] Alternatively, the pressures applied to the first module M1 and the second module M2 in the load control performed before the current load control may be stored, for example, in the memory unit 17. In this case, for example, the determination unit 19 may transmit the current load difference from the memory unit 17 to the drive control unit 20 together with the determination result.

[0093] Furthermore, if the same amount of pressure is applied to both the first module M1 and the second module M2, the load difference is zero. On the other hand, if a greater pressure is applied to one of the first module M1 and the second module M2 than to the other, a load difference exists. Therefore, the "load difference" here is a concept that includes both cases where there is a load difference and cases where there is not.

[0094] [Operation] Next, a flow of control for preventing the stopping of charging of modules M that still have charge capacity due to an early stopping of charging in a battery system BS in which multiple modules M are connected in parallel will be described with reference to Fig. 6. Fig. 6 is a flowchart showing the flow of a control method for the battery system BS in the first embodiment of the present invention.

[0095] First, the charging process for the battery system BS is started (ST1), and the information acquisition unit 16 acquires the maximum cell CCV value for each of the plurality of battery cells C that make up each module M (ST2).

[0096] The calculation unit 18 then calculates the difference (CCV difference) between the largest and smallest maximum cell CCV values ​​for each battery cell C acquired by the information acquisition unit 16 (ST3). The calculated CCV difference information is sent from the calculation unit 18 to the determination unit 19.

[0097] The calculation unit 18 also determines the pressure (load) currently being applied to each module M (ST4). Methods for determining the load include, for example, obtaining information from a pressure gauge (not shown) via the information obtaining unit 16, or, if the currently applied pressure is stored in the storage unit 17, accessing the storage unit 17 to obtain the information.

[0098] The determination unit 19 acquires threshold information stored in advance in the storage unit 17 and compares the CCV difference with the threshold (ST5). If it determines that the CCV difference is greater than the threshold (YES in ST5), it instructs the drive control unit 20 to execute load control on the module M (ST6).

[0099] Specifically, load control is performed on the battery cells C of the module M to be controlled so that the load difference between the load applied to the module M having the largest cell CCV that has been identified to date and the load applied to the module M having the largest cell CCV that has the smallest value becomes larger.

[0100] On the other hand, if the determination unit 19 determines that the CCV difference is equal to or less than the threshold value (NO in ST5), the load difference applied to each module M is maintained (ST7). In other words, there is no change in the pressure currently applied to each module M, and therefore the determination unit 19 does not issue any instruction to the drive control unit 20.

[0101] The determination unit 19 then determines whether or not the charging process for the battery system BS has ended (ST8). A specific method of determination is, for example, whether or not any of the battery cells C included in the multiple modules M that make up the battery system BS has reached an upper limit voltage.

[0102] If the determination unit 19 determines that the upper limit voltage has not been reached in any of the battery cells C (NO in ST8), the charging process continues. Then, the process returns to step ST2, where the information acquisition unit 16 acquires the maximum cell CCV value in each battery cell C, and the above-mentioned process is executed. On the other hand, if the determination unit 19 determines that the upper limit voltage has been reached in any of the battery cells C (YES in ST8), the charging process for the battery system BS ends.

[0103] By employing the control method for the battery system BS as described above, even if a plurality of battery modules are connected in parallel, sufficient charging and discharging can be performed, allowing the initial capacity to be used.

[0104] Second Embodiment Next, a second embodiment of the present invention will be described. In the second embodiment, the same components as those described in the first embodiment are denoted by the same reference numerals, and redundant descriptions of the same components will be omitted.

[0105] The control method of the battery system BS in the second embodiment is based on the control method of the battery system BS in the first embodiment described above, and further performs load control when performing the charging process by referring to the internal resistance value of the battery cell C.

[0106] Specifically, the information acquisition unit 16 not only acquires the maximum cell CCV value for each battery cell C as described above, but also acquires information on the current value and temperature in each module M. The current value is acquired from the ammeter A shown in FIG. 1, and the temperature value is acquired from the thermometer T shown in FIG. 1.

[0107] Furthermore, the calculation unit 18 uses the current values ​​and temperature values ​​acquired by the information acquisition unit 16 to calculate the open-circuit voltage (hereinafter referred to as "OCV: Open-Circuit Voltage" as appropriate) for each module M, or the charge rate (hereinafter referred to as "SOC: State of Charge" as appropriate) of each module M, and estimated values ​​of the internal resistance value.

[0108] When calculating the SOC, the calculation unit 18 may employ, for example, a method that uses an integrated value of the current flowing through the module M, or may employ another known method. When calculating the OCV value, the calculation unit 18 may use, for example, "SOC-OCV characteristic data" based on the calculated SOC.

[0109] The "SOC-OCV characteristic data" is stored in advance in the storage unit 17. Therefore, when the calculation unit 18 calculates the OCV value, it accesses the storage unit 17 and assigns a separately calculated SOC value to the "SOC-OCV characteristic data."

[0110] On the other hand, the following relationship is observed between temperature and SOC for internal resistance. 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.

[0111] The relationship between the internal resistance value, temperature, and SOC is as described above, but it can also change depending on the surface pressure (pressure applied to the battery cell C), as explained using FIG. 4 , for example. The relationship between these four factors is determined in advance by experiment and stored in the storage unit 17. The calculation unit 18 then calculates the internal resistance value based on the obtained temperature value, 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.

[0112] Furthermore, the calculation unit 18 calculates an estimated value (first estimated value) of the total internal resistance in each module M when the load difference applied to each module M is maintained. The calculation unit 18 also calculates an estimated value (second estimated value) of the total internal resistance in each module M when the load difference applied to each module M is changed.

[0113] As described above, the calculation unit 18 calculates an estimated value of the internal resistance value of each module M. As explained above, in the case where two modules M, a first module M1 and a second module M2, are provided in the battery system BS, for example, the internal resistance value of the first module M1 calculated by the calculation unit 18 is assumed to be, for example, an internal resistance value M1R, and the internal resistance value of the second module M2 is assumed to be, for example, an internal resistance value M2R.

[0114] In this case, the estimated value (first estimated value) of the total internal resistance in each module M when the load difference applied to each module M is maintained is the same as the load difference between the internal resistance value M1R and the internal resistance value M2R, since the load difference is maintained. Therefore, for example, the estimated value can be understood as the sum of the internal resistance value M1R and the internal resistance value M2R.

[0115] In contrast, the estimated value (second estimated value) of the total internal resistance in each module M when the load difference applied to each module M is changed is a case in which the internal resistance value M1R and the internal resistance value M2R each can change within the load operating range. In this case, since the internal resistance value M1R and the internal resistance value M2R change within the load operating range, multiple patterns are expected. Therefore, estimated values ​​of the total internal resistance for these multiple patterns are calculated in advance and stored in, for example, the memory unit 17.

[0116] As described above, the calculation unit 18 calculates an estimated value (first estimated value) of the total internal resistance by adding up the calculated internal resistance values ​​for each module M. In addition, based on the calculated internal resistance values ​​for each module M, the calculation unit 18 obtains from the storage unit 17 an estimated value (second estimated value) of the total internal resistance when the internal resistance value is changed within the load operating range.

[0117] The reason for calculating the first estimated value and the second estimated value is to perform the charging process in a state where heat loss in the battery cell C is minimized as much as possible when the charging process is performed.

[0118] That is, when a charging process is performed on a battery cell C, heat is generated in the battery cell C. The amount of heat generated is determined by the magnitude of the internal resistance inside the battery cell C. As explained above with reference to Figures 3 to 5, the control method for the battery system BS in the embodiments of the present invention, including the first embodiment, distributes current to the multiple modules M by increasing or decreasing the pressure applied to the battery cell C, that is, by increasing or decreasing the internal resistance value of the battery cell C.

[0119] Therefore, depending on the control method, for example, if the pressure applied to the battery cell C is significantly reduced during charging, the internal resistance value may increase (see FIG. 4). In this case, it is conceivable that the heat loss in the battery cell C during charging may increase.

[0120] If the heat loss increases, it may lead to a decrease in the charging efficiency of the entire battery system BS. Therefore, in the second embodiment of the present invention, a control method for the battery system BS is adopted that takes into consideration the possibility of a decrease in charging efficiency.

[0121] As described above, the calculation unit 18 calculates the first estimated value and the second estimated value. Then, the two are compared based on these calculated estimated values. If the second estimated value is smaller than the first estimated value, it means that there is a low possibility of heat loss occurring. Alternatively, it means that there is merit in executing the charging process even if heat loss occurs. In such a case, load control is executed on the condition that the comparison result also satisfies the condition that the CCV difference is greater than the threshold value.

[0122] On the other hand, if the second estimated value is equal to or greater than the first estimated value, there is a possibility that heat loss will occur, and therefore, in such a case, load control is not executed.

[0123] [Operation] Next, a flow of control for preventing the stopping of charging of modules M that still have charge capacity due to an early stopping of charging in a battery system BS in which multiple modules M are connected in parallel according to the second embodiment of the present invention will be described with reference to Figures 7 and 8. Figures 7 and 8 are flowcharts showing the flow of a control method for the battery system BS in the second embodiment of the present invention.

[0124] First, the charging process for the battery system BS is started (ST11). At the same time, the information acquisition unit 16 acquires the maximum cell CCV value for each of the plurality of battery cells C that make up each module M (ST12).

[0125] The information acquiring unit 16 also acquires the current value and temperature value from the ammeter A and thermometer T provided in each module M, respectively (ST13). Furthermore, the information acquiring unit 16 also ascertains the load (pressure) applied to each module M at the time of acquiring the information (ST14). Note that, as described above, the information on the load on each module M is acquired based on the pressure gauge or the information stored in the memory unit 17.

[0126] The calculation unit 18 calculates the OCV or SOC and the estimated internal resistance value for each module M based on the information acquired by the information acquisition unit 16 (ST15). Furthermore, the calculation unit 18 also calculates, using the method described above, an estimated value (first estimated value) of the total internal resistance in each module M when the load applied to each module M is maintained, and an estimated value (second estimated value) of the total internal resistance in each module M when the load applied to each module M is changed (ST16, ST17).

[0127] The calculation unit 18 then calculates the difference (CCV difference) between the largest and smallest maximum cell CCV values ​​for each battery cell C acquired by the information acquisition unit 16 (ST18). The calculated CCV difference information is sent from the calculation unit 18 to the determination unit 19.

[0128] The determination unit 19 acquires threshold information stored in advance in the storage unit 17 and compares it with the CCV difference (ST19). As a result, if it is determined that the CCV difference value is greater than the threshold value (YES in ST19), the determination unit 19 further compares the first estimated value and the second estimated value calculated by the calculation unit 18 (ST20).

[0129] If the comparison result of the judgment unit 19 indicates that the second estimated value is smaller than the first estimated value (YES in ST20), the judgment unit 19 instructs the drive control unit 20 to execute load control on the module M (ST21).

[0130] Specifically, load control is performed on the battery cells C of the module M to be controlled so that the load difference between the load applied to the module M having the largest cell CCV that has been identified to date and the load applied to the module M having the largest cell CCV that has the smallest value becomes larger.

[0131] On the other hand, if the determination unit 19 determines that the CCV difference is equal to or less than the threshold value (NO in ST19), or if the second estimated value is equal to or greater than the first estimated value (NO in ST20), the load difference applied to each module M is maintained (ST22). In other words, there is no change in the pressure currently applied to each module M, and therefore the determination unit 19 does not issue any instruction to the drive control unit 20.

[0132] The determination unit 19 then determines whether the charging process for the battery system BS has ended (ST23). A specific method of determination is, for example, whether any of the battery cells C included in the multiple modules M that make up the battery system BS has reached an upper limit voltage.

[0133] If the determination unit 19 determines that the upper limit voltage has not been reached in any of the battery cells C (NO in ST23), the charging process continues. Then, the process returns to step ST12, where the information acquisition unit 16 acquires the maximum cell CCV value in each battery cell C, and the above-mentioned processes are executed. On the other hand, if the determination unit 19 determines that the upper limit voltage has been reached in any of the battery cells C (YES in ST23), the charging process for the battery system BS ends.

[0134] By employing the control method for the battery system BS as described above, even if a plurality of battery modules are connected in parallel, sufficient charging and discharging can be performed, allowing the initial capacity to be used.

[0135] (Third embodiment) Next, a third embodiment of the present invention will be described. In the third embodiment, the same components as those described in the first or second embodiment are denoted by the same reference numerals, and redundant descriptions of the same components will be omitted.

[0136] The battery system control method in the first or second embodiment described so far is a control that is repeatedly performed, for example, at certain time intervals, while charging of the battery system BS is being performed. In contrast, the battery system control method in the third embodiment is a control that performs load control on the module M based on various parameters before charging of the battery system BS starts, and does not perform load control during charging.

[0137] Specifically, first, the information acquisition unit 16 acquires various pieces of information. Here, the "various pieces of information" are at least information relating to the open circuit voltage (OCV) of the module M, the temperature of the battery cells C, the load applied to the module M, the air temperature in the battery system BS, the maximum charging power for the battery system BS, and the charging current.

[0138] Here, the "air temperature inside the battery system BS" refers to the air temperature near the battery cells C, and is used to more accurately estimate the temperature of the battery cells C during charging. Therefore, it is different from the temperature of the battery cells C. Although a sensor for detecting this air temperature is not depicted in FIG. 1 , it is placed near the battery cells C and detects the air temperature.

[0139] The "maximum charging power" and "charging current" are parameters used to estimate the voltage arrival time, which will be described later. These parameters are set between the load control device 1 and the power control device 2. That is, as described above, the power control device 2 has the role of discharging any power from the battery cell C or charging the battery cell C based on a command from the load control device 1.

[0140] Therefore, more specifically, for example, with regard to the maximum charging power, the maximum charging power value in the power control device 2 is compared with the maximum allowable value of the charging power in the battery system BS, and the smaller value is set as the maximum charging power.

[0141] The calculation unit 18 calculates the internal resistance value of each module M, for example, as described in the second embodiment. It also estimates the CCV and the temperature of the battery cells C during charging under the condition that the load difference between the modules is constant.

[0142] Here, the "constant condition" in the phrase "under a constant condition of the load difference between each module" refers to a condition under which the load difference between each module M does not change during charging. As described above, in the third embodiment of the present invention, the load applied to each module M is not changed after the charging process has started. This is because reducing the frequency of the load change process reduces power consumption during charging in the entire battery system BS and improves charging efficiency. Therefore, the CCV and the temperature of the battery cell C under the above-mentioned constant condition are calculated.

[0143] Furthermore, the calculation unit 18 calculates a "voltage arrival time" and a "temperature arrival time." The "voltage arrival time" is the time from the start of charging until the module M including the battery cell C with the largest maximum cell CCV reaches the upper limit voltage. On the other hand, the "temperature arrival time" is the time from the start of charging until the module M including the battery cell C with the largest maximum cell CCV reaches the upper limit temperature.

[0144] These "voltage arrival time" and "temperature arrival time" are times obtained to set the time for the charging process to be performed on the battery system BS. Then, based on the obtained "voltage arrival time" and "temperature arrival time," the determination unit 19 compares the two. Then, the determination unit 19 sets the time that more quickly reaches the upper limit voltage or the time that more quickly reaches the upper limit temperature, i.e., the time that indicates the shorter time until charging is stopped, as the charging time.

[0145] The charging process may be initiated when the voltage of the battery cell C reaches the upper limit voltage, as described above, or when, for example, the user starts using a vehicle equipped with the battery system BS. Therefore, the charging process must be completed by the time the user starts using the vehicle. Taking this into consideration, it is necessary to maximize the charging capacity as efficiently as possible in a shorter time. Therefore, the charging time is set to the shorter of the "voltage reaching time" and the "temperature reaching time."

[0146] Furthermore, the calculation unit 18 calculates two types of charge capacities for the modules M. One is the charge capacity when the difference (load difference) between the loads applied to the multiple modules M during charging is maintained, calculated based on the loads applied to each of the multiple modules M before charging starts (hereinafter, such a charge capacity will be referred to as the "first charge capacity" as appropriate).

[0147] The other is the charge capacity when the difference in load (load difference) applied to multiple modules M during charging is changed (hereinafter, such a charge capacity will be referred to as the ``second charge capacity'' as appropriate).

[0148] The first charge capacity and the second charge capacity calculated by the calculation unit 18 are sent to the determination unit 10. The determination unit 19 compares the first charge capacity with the second charge capacity. If the determination unit 19 determines that the second charge capacity is greater than the first charge capacity, it instructs the drive control unit 20 to drive the pressure mechanism P.

[0149] Specifically, the drive control unit 20 performs pressure control on the module M to be controlled so as to further increase the load difference between the modules M within the load operating range. The reason for performing such control is to maximize the charging capacity more efficiently within the set charging time.

[0150] On the other hand, if the determination unit 19 determines that the second charge capacity is equal to or less than the first charge capacity, it maintains the load (load difference) applied to each module M. Therefore, in this case, the determination unit 19 instructs the drive control unit 20 to maintain the load difference.

[0151] The processing performed by the load control device 1 up to this point has completed preparations for load control for each module M. While maintaining this control, charging processing for the battery system BS is then initiated. Specifically, the load control device 1 issues an instruction to the power control device 2 to start charging processing.

[0152] Furthermore, the charging process ends when the set charging time has elapsed, or when the battery cell C showing the largest maximum cell CCV value reaches the upper limit voltage or upper limit temperature used when setting the charging time.

[0153] In the above description, the times used to set the charging time are the "voltage arrival time" and the "temperature arrival time." However, in addition to these times, the charging time can also be set taking into account, for example, the time when the user starts using the battery system BS. This case will be described below as a modified example of the third embodiment.

[0154] In this modified example, the time until the user starts using the battery is also taken into consideration as a requirement for setting the charging time. Here, "the time until the user starts using the battery" can be, for example, the time the user uses the vehicle equipped with the battery system BS or the charging start time set by the user. In particular, in the latter case, the start and end of charging can be set using a timer, for example, so the load control device 1 can know the time until the user starts using the battery by detecting the time of the set timer.

[0155] In this way, when setting the charging time, the time until the user starts using the battery is also taken into consideration, thereby maximizing the charge capacity for the module M (battery cells C) even within the charging time specified by the user. In other words, the load control device 1 can estimate the load difference that will allow maximizing the charge capacity within the charging time specified by the user before charging begins, and perform weight control on the module M (battery cells C) so that this load difference is ensured.

[0156] [Operation] Next, a flow of control for preventing early stopping of charging in a battery system BS in which multiple modules M are connected in parallel according to a third embodiment of the present invention from stopping the charging process for modules M that still have charge capacity remaining will be described with reference to Figures 7 and 8. Figures 9 to 11 are flowcharts showing the flow of a control method for the battery system BS according to the third embodiment of the present invention.

[0157] Before starting the charging process in the battery system BS, the information acquisition unit 16 first acquires various information, including at least information relating to the open circuit voltage of the module, the temperature of the battery cells, the load applied to the module, the air temperature inside the battery system, the maximum charging power for the battery system, and the charging current (ST31).

[0158] Using the various pieces of information acquired by the information acquisition unit 16, the calculation unit 18 first calculates an estimated value of the internal resistance value of each module M (ST32).The calculation unit 18 also calculates the CCV during charging and the temperature of the battery cells C under the condition that the load difference between each module M is constant (ST33, ST34).

[0159] The calculation unit 18 also estimates (calculates) the voltage arrival time and temperature arrival time required for the module M including the battery cell C with the largest maximum cell CCV value among the multiple modules M constituting the battery system BS to reach the cell upper limit voltage and upper limit temperature from the start of charging (ST35, ST36). Information on the calculated voltage arrival time and temperature arrival time is sent to the determination unit 19 for comparison (ST37). As a result of comparing the voltage arrival time and temperature arrival time, the determination unit 19 sets the shorter time as the charging time for the battery system BS (ST38).

[0160] After transmitting the information on the voltage arrival time and temperature arrival time to the determination unit 19, the calculation unit 18 subsequently estimates (calculates) the first charge capacity when the difference in the loads applied to each module M is maintained (ST39 in FIG. 10 ). The calculation unit 18 also estimates (calculates) the second charge capacity when the load difference is changed (ST40). Information on these two calculated charge capacities is also transmitted to the determination unit 19.

[0161] The determination unit 19 compares the first charge capacity with the second charge capacity and determines whether the second charge capacity is greater than the first charge capacity (ST41). If the result shows that the second charge capacity is greater than the first charge capacity (YES in ST41), the determination unit 19 instructs the drive control unit 20 as follows: That is, based on the instruction from the determination unit 19, the drive control unit 20 executes control to apply pressure to the battery cells CCV of the module M to be controlled so as to increase the difference in loads applied to the multiple modules M within the load operating range (ST42).

[0162] On the other hand, if the determination unit 19 indicates that the first charge capacity is equal to or greater than the second charge capacity (NO in ST41), the determination unit 19 instructs the drive control unit 20 to maintain the load (load difference) applied to each module M (ST43). As described above, the load applied to each module M and the load differences among the multiple modules M are set when performing the charging process on the battery system BS.

[0163] Therefore, the load control device 1 issues an instruction to the power control device 2, and charging processing for the battery system BS is started (ST44). The load control device 1 then determines whether or not a predetermined condition for determining the end of charging has been met (ST45). If the condition is not met (NO in ST45), the charging processing continues. On the other hand, if it is determined that the condition is met (YES in ST45), the charging processing ends.

[0164] Next, the control flow of a modification of the third embodiment will be described with reference to Fig. 11. As described above, the modification differs in that the charging time is set by taking into consideration the time until the user starts using the battery. As shown in the flowchart of Fig. 11, two processes are added.

[0165] That is, after the information acquisition unit 16 acquires various information (ST31), the calculation unit 18 performs various calculations, such as calculating an estimated internal resistance value (ST32). Then, after the calculation unit 18 calculates the voltage arrival time and the temperature arrival time (ST36), the information acquisition unit 16 acquires information about the time when the user will start using the battery (ST51). This information is acquired, for example, from a timer or the like that is set to start charging.

[0166] The determination unit 19 then compares the voltage arrival time, temperature arrival time, and the time from the start of charging until the user starts using the battery, including the time the user started using the battery acquired by the information acquisition unit 16 (ST52). The determination unit 19 then sets the shorter of these times as the charging time (ST38). The subsequent processing flow is as described using FIG. 10.

[0167] As explained above, when a load is applied to the battery cell C (module M), pressure control is performed within the load operating range. This is because, for example, applying too much load to the battery cell C may cause adverse effects such as damage to the components that make up the battery cell C. Therefore, the pressure that does not cause such adverse effects is set as the upper limit.

[0168] On the other hand, as mentioned above, if the pressure applied to the battery cells C is low, the internal resistance value will increase, and there is a possibility that, for example, current will not flow into the battery cells C during charging. Therefore, the lower limit corresponds to the value below which the module M (battery cells C) will not function.

[0169] Furthermore, the above explanation has been given with reference to an example in which a charging process is performed on a battery system, and no mention has been made of a discharging process. This is because, for example, the timing of the discharge end can be considered to be when the use of the vehicle has ended, but this is difficult to define because it depends on how the vehicle is used, and it is therefore considered difficult to apply to the discharging process. However, when the timing of the discharge end is fixed, such as in the case of an output pattern such as constant speed driving or when the battery is fully charged and reaches a lower limit voltage, it is possible to apply the control described above.

[0170] [Effects of the Examples] (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 load control device that controls the pressure mechanism, and the load control device distributes current to the modules connected in parallel by controlling the load on the plurality of modules using the pressure mechanism.

[0171] 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.

[0172] (2) A method for controlling a battery system as described in (1) above, in which the load control device, after starting charging of the battery system, executes control including the steps of: determining the maximum cell closed-circuit voltage for each of a plurality of battery cells included in a module; determining the loads applied to the plurality of modules by the pressurizing mechanisms; calculating a closed-circuit voltage difference, which is the difference between the maximum cell closed-circuit voltage having the largest value and the maximum cell closed-circuit voltage having the smallest value, for each of the determined maximum cell closed-circuit voltages; comparing the calculated closed-circuit voltage difference with a preset threshold; and, when it is determined that the closed-circuit voltage difference is larger than the threshold, controlling the pressurizing mechanism so that the load difference between a first load applied by the pressurizing mechanism to the module including the battery cell with the largest maximum cell closed-circuit voltage and a second load applied by the pressurizing mechanism to the module including the battery cell with the smallest maximum cell closed-circuit voltage is larger than the load difference in previous control.

[0173] In this way, when the load control device performs load control, it controls the pressure using the difference in maximum cell closed circuit voltage (CCV) of each battery cell, which prevents the module with the smallest maximum cell CCV from stopping charging early. This ensures charging time for the other modules, thereby increasing the charging capacity of the entire battery system more than ever before.

[0174] (3) A control method for a battery system described in (2) above, wherein the load control device, between the step of determining the load applied to the module and the step of calculating the closed circuit voltage difference, includes the steps of determining the current value and temperature value for each of the multiple modules, estimating the open circuit voltage or the charging rate and the internal resistance value for each of the multiple modules, and calculating a first estimated value indicating an estimated value of the total internal resistance in each of the modules when the load applied to the multiple modules is maintained, and a second estimated value indicating an estimated value of the total internal resistance in each of the modules when the load applied to the multiple modules is changed. After the step of comparing the calculated closed circuit voltage difference with a predetermined threshold, if it is determined that the closed circuit voltage difference is greater than the threshold, the load control device further performs control including the step of comparing the first estimated value with the second estimated value, and if it is determined that the first estimated value is greater than the second estimated value, controlling the pressurizing mechanism so that the load difference between the first load and the second load is greater than the load difference in the previous control.

[0175] The weighting control device not only uses the CCV difference but also the first and second estimated values ​​to perform control. That is, it performs control to increase the load difference between each module during charging only when it is expected that the charging efficiency will not decrease. This makes it possible to avoid a decrease in charging efficiency due to energy loss (heat loss) caused by heat generation in the battery cells during charging.

[0176] (4) In the battery system control method described in (2) or (3), the pressurizing mechanism is controlled so that the load difference falls within a preset load operating range. By controlling the pressurization within this load operating range, it is possible to avoid problems such as excessive or insufficient load being applied to the battery cells, and to apply the load to the battery cells efficiently.

[0177] (5) A method for controlling a battery system according to (1) above, wherein the load control device includes the steps of: acquiring various information; calculating estimated values ​​of internal resistance values ​​in a plurality of modules; estimating the closed circuit voltages and battery cell temperatures during charging in a plurality of modules under a given condition that a load difference between the plurality of modules is maintained during charging; estimating a voltage arrival time from the start of charging until the module including the battery cell showing the largest value in the maximum cell closed circuit voltage reaches an upper limit voltage; and estimating a temperature arrival time from the start of charging until the module including the battery cell showing the largest value in the maximum cell closed circuit voltage reaches an upper limit temperature. the step of comparing the voltage arrival time with the temperature arrival time; the step of setting the time with the shorter arrival time as the charging time based on the comparison; the step of estimating a first charging capacity when the load difference between the plurality of modules is maintained and a second charging capacity when the load difference between the plurality of modules is changed; the step of comparing the first charging capacity with the second charging capacity; the step of controlling the pressure mechanism so that the load difference becomes large within the load operating range for the module when the second charging capacity is greater than the first charging capacity; the step of maintaining the load difference when the second charging capacity is equal to or less than the first charging capacity; and the step of starting charging of the battery system.

[0178] In this way, by ending the pressurization control for the battery cells (modules) before the charging process for the battery system is started and not performing the pressurization control during charging, it is possible to reduce the power consumption required to control the load change during charging, and to improve the charging efficiency of the entire battery system.

[0179] (6) A method for controlling a battery system as described in (5) above, wherein the load control device includes a step of acquiring information about the time when the user will start using the battery system after the step of acquiring various information, and the charging time is set by comparing the voltage arrival time, the temperature arrival time, and the time from the start of charging until the user starts using the battery system.

[0180] When setting the charging time for the battery system charging process, information about the time when the user will start using the battery system is also taken into consideration. By terminating pressure control for the battery cells (modules) before the charging process begins and not performing pressure control during charging, it is possible to reduce the power consumption required to control changes in load during charging, thereby improving the charging efficiency of the entire battery system.

[0181] (7) In the battery system control method described in (5) or (6), the various information includes at least information on the open circuit voltage of the module, the temperature of the battery cells, the load applied to the module, the air temperature in the battery system, the maximum charging power for the battery system, and the charging current. By using this information, for example, it is possible to estimate the internal resistance value of the battery cells, and to estimate the voltage arrival time and the temperature arrival time. As a result, it is possible to avoid early charging termination and ensure charging time, thereby increasing the charging capacity of the entire battery system more than ever before.

[0182] (8) 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 load control device that controls the pressure mechanism, wherein when the load control device determines that a closed-circuit voltage difference, which is the difference between the maximum and minimum values ​​of the maximum cell closed-circuit voltage in each of the modules, is greater than a threshold value, the load control device controls the pressure mechanism so that the load difference between a first load applied by the pressure mechanism to the module including the battery cell with the maximum cell closed-circuit voltage indicating the maximum value and a second load applied by the pressure mechanism to the module including the battery cell with the maximum cell closed-circuit voltage indicating the minimum value is greater than the load difference in previous control.

[0183] 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.

[0184] 1...Load control device, 11...CPU, 12...ROM, 13...RAM, 14...Input / output interface, 15...Bus, 16...Information acquisition unit, 17...Memory 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 load control device for controlling the pressure mechanism, wherein the load control device distributes current to the modules connected in parallel by controlling the load on the plurality of modules using the pressure mechanism.

2. The control method for a battery system according to claim 1, characterized in that, after starting charging of the battery system, the load control device executes control comprising the steps of: determining a maximum cell closed-circuit voltage for each of the plurality of battery cells included in the module; determining loads applied by the pressurizing mechanism to each of the plurality of modules; calculating a closed-circuit voltage difference which is the difference between the maximum cell closed-circuit voltage which shows the largest value and the maximum cell closed-circuit voltage which shows the smallest value for each of the determined maximum cell closed-circuit voltages; comparing the calculated closed-circuit voltage difference with a predetermined threshold; and, when it is determined that the closed-circuit voltage difference is larger than the threshold, controlling the pressurizing mechanism so that a load difference between a first load applied by the pressurizing mechanism to the module including the battery cell with the maximum maximum cell closed-circuit voltage and a second load applied by the pressurizing mechanism to the module including the battery cell with the minimum maximum cell closed-circuit voltage is larger than the load difference in previous control.

3. The load control device comprises, between the step of grasping the load applied to the module and the step of calculating the closed circuit voltage difference, the steps of grasping a current value and a temperature value for each of the plurality of modules; estimating an open circuit voltage or a charging rate and an internal resistance value for each of the plurality of modules; and calculating a first estimated value indicating an estimated value of the total internal resistance in each of the plurality of modules when the load applied to the plurality of modules is maintained, and a second estimated value indicating an estimated value of the total internal resistance in each of the plurality of modules when the load applied to the plurality of modules is changed; and, after the step of comparing the calculated closed circuit voltage difference with a preset threshold, if it is determined that the closed circuit voltage difference is greater than the threshold, further comprising the steps of comparing the first estimated value with the second estimated value; and, if it is determined that the first estimated value is greater than the second estimated value, controlling the pressurizing mechanism so that the load difference between the first load and the second load is greater than the load difference in previous control.

3. The method for controlling a battery system according to claim 2, wherein the method comprises:

4. A method for controlling a battery system according to claim 2 or 3, characterized in that the pressure mechanism is controlled so that the load difference falls within a preset load operating range.

5. The load control device includes the steps of: acquiring various information; calculating estimated values ​​of internal resistance values ​​in the plurality of modules; estimating the closed circuit voltages and battery cell temperatures during charging in the plurality of modules under a given condition that the load difference between the plurality of modules is maintained during charging; estimating a voltage arrival time from the start of charging until the module including the battery cell with the largest maximum cell closed circuit voltage reaches an upper limit voltage; estimating a temperature arrival time from the start of charging until the module including the battery cell with the largest maximum cell closed circuit voltage reaches an upper limit temperature; comparing the voltage arrival time and the temperature arrival time; setting the shorter arrival time as the charge time based on the comparison; estimating a first charge capacity when the load difference between the plurality of modules is maintained and a second charge capacity when the load difference between the plurality of modules is changed; and comparing the first charge capacity and the second charge capacity.

2. The method for controlling a battery system according to claim 1, further comprising the steps of: controlling the pressurizing mechanism so that the load difference increases within a load operating range for the module when the second charge capacity is greater than the first charge capacity; maintaining the load difference when the second charge capacity is equal to or less than the first charge capacity; and starting charging of the battery system.

6. The method for controlling a battery system described in claim 5, characterized in that the load control device includes a step of acquiring information about the time when the user will start using the battery system after the step of acquiring various information, and the charging time is set by comparing the voltage arrival time, the temperature arrival time, and the time from the start of charging until the user starts using the battery system.

7. A method for controlling a battery system as described in claim 5 or claim 6, characterized in that the various information is at least information regarding the open circuit voltage of the module, the temperature of the battery cells, the load applied to the module, the air temperature within the battery system, the maximum charging power for the battery system, and the charging current.

8. 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 load control device for controlling the pressure mechanism, wherein the load control device, when it is determined that a closed-circuit voltage difference, which is the difference between the maximum and minimum values ​​of maximum cell closed-circuit voltages in each of the modules, is greater than a threshold value, controls the pressure control device so that a load difference between a first load applied by the pressure mechanism to the module including the battery cell with the maximum cell closed-circuit voltage indicating the maximum value and a second load applied by the pressure mechanism to the module including the battery cell with the maximum cell closed-circuit voltage indicating the minimum value is greater than the load difference in previous control.

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