Battery system

Abstract

To exploit the performance of a battery module having cells connected in parallel.SOLUTION: A control device executes processing including: a step (S100) of acquiring a distribution factor, a request value and a threshold value of a system current; a step (S104) of calculating an upper limit value of the current by multiplying the request value by the distribution factor and dividing the result by the number of cells, if the distribution factor is equal to or greater than the threshold value (YES at S102); a step (S106) of calculating the upper limit value of the current by multiplying the request value by the threshold value and dividing the result by the number of cells, if the distribution factor is smaller than the threshold value (NO at S102); and a step (S110) of calculating an allowable time using the calculated upper limit value of the current.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a battery system. [Background technology]

[0002] In a battery system having a battery module formed by connecting multiple cells in parallel, the resistance difference between the cells may cause variation in the current flowing through each cell. For example, JP 2018-129190 A (Patent Document 1) discloses a technology for estimating the maximum current that may be generated due to the variation and controlling the current so that it does not exceed the upper limit current of the cell. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-129190 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, it is not easy to accurately estimate the maximum current, and it is necessary to set a margin on the safe side for the estimated maximum current. If the margin is not set appropriately, the performance of the battery module may not be fully utilized.

[0005] The present disclosure has been made to solve the above-mentioned problems, and has an object to provide a battery system that brings out the performance of a battery module having cells connected in parallel. [Means for solving the problem]

[0006] A battery system according to an aspect of the present disclosure includes a plurality of battery modules, each of which is configured by connecting a plurality of cells in parallel and which are connected in series, and a control device that controls a current flowing through the plurality of battery modules. The control device obtains a distribution degree indicating a degree of current division among the plurality of cells in any of the battery modules based on a voltage difference between adjacent battery modules and a required value of current, and if the obtained distribution degree is greater than a threshold value, calculates an upper limit value of a current flowing through an individual cell using the distribution degree, the required value, and the number of cells in the battery module, and if the obtained distribution degree is smaller than the threshold value, calculates an upper limit value using the threshold value, the required value, and the number of cells, and sets an allowable time during which current flow at the calculated upper limit value is allowed.

[0007] In this way, by changing the calculation method of the upper limit of the current depending on the degree of distribution, the upper limit of the current and the permissible time can be calculated with high accuracy, thereby making it possible to fully utilize the performance of the battery. Effect of the Invention

[0008] According to the present disclosure, it is possible to provide a battery system that brings out the performance of a battery module having cells connected in parallel. [Brief description of the drawings]

[0009] [Figure 1] 1 is a diagram showing an example of a configuration of a battery system according to an embodiment of the present invention; [Diagram 2] 4 is a flowchart showing an example of a process executed in the control device. [Diagram 3] FIG. 13 is a diagram showing the relationship between current, distribution degree, and the upper limit of current or voltage difference. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference characters and their description will not be repeated.

[0011] FIG. 1 is a diagram showing an example of the configuration of a battery system 1 according to the present embodiment. As shown in FIG. 1, the battery system 1 is composed of a plurality of battery modules connected in series. Each of the plurality of battery modules is composed of a plurality of cells connected in parallel. In the present embodiment, a first battery module 10, a second battery module 20, and a third battery module 30 are representatively shown in FIG. 1. The first battery module 10 includes cells 11 and 12. The second battery module 20 includes cells 21 and 22. The third battery module 30 includes cells 31 and 32.

[0012] The battery system 1 includes a current sensor 102 that detects a current flowing through the battery system 1 (hereinafter referred to as system current Ix), a first voltage sensor 104 that detects a voltage Va of the first battery module 10, a second voltage sensor 106 that detects a voltage Vb of the second battery module 20, a third voltage sensor 108 that detects a voltage Vc of the third battery module 30, and a control device 100 that controls the current flowing through the battery system 1 using the detection results of the various sensors.

[0013] The cells constituting each battery module are formed of secondary batteries such as nickel-metal hydride batteries and lithium-ion batteries containing solid or liquid electrolytes. The battery system 1 is intended to be mounted as a power source in an electrically powered vehicle such as an electric vehicle or a hybrid vehicle.

[0014] As shown in the right diagram of FIG. 1, each cell is a rectangular prismatic cell. Each cell has a positive terminal and a negative terminal on the same surface. Two adjacent cells that constitute the same battery module are provided with terminals of the same pole adjacent to each other. On the other hand, two adjacent cells that constitute different battery modules are provided with terminals of different poles adjacent to each other.

[0015] 1, the cells 11, 12 of the first battery module are arranged so that their positive terminals are adjacent to each other and their negative terminals are adjacent to each other. Similarly, the cells 21, 22 of the second battery module 20 and the cells 31, 32 of the third battery module 30 are arranged so that their positive terminals are adjacent to each other and their negative terminals are adjacent to each other.

[0016] The cell 11 of the first battery module 10 and the cell 32 of the adjacent third battery module 30 are arranged so that different terminals are adjacent to each other. The cell 12 of the first battery module 10 and the cell 21 of the adjacent second battery module 20 are arranged so that different terminals are adjacent to each other.

[0017] The negative electrode terminals of the cells 11, 12 of the first battery module 10 are connected to the positive electrode terminals of the cells 21, 22 of the second battery module 20 using a bus bar 50. The positive electrode terminals of the cells 11, 12 of the first battery module 10 are connected to the negative electrode terminals of the cells 31, 32 of the third battery module 30 using a bus bar 40. The positive electrode terminals of the cells 31, 32 of the third battery module 30 are connected to the negative electrode terminals (not shown) of two cells of an adjacent battery module other than the first battery module 10 using a bus bar 60. The negative electrode terminals of the cells 21, 22 of the second battery module 20 are connected to the positive electrode terminals (not shown) of two cells of an adjacent battery module other than the first battery module 10 using a bus bar 70.

[0018] The control device 100 includes, for example, a processor that executes a program such as a CPU (Central Processing Unit), and memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory) (neither of which are shown). The memories include control programs for executing the various control processes described above. For example, the control device 100 may control the current when the battery system 1 is charged or discharged by outputting a control signal to a PCU (Power Control Unit) or the like connected to the battery system 1, or may output a current control request value to a vehicle control device (not shown) that controls the behavior of the electric vehicle.

[0019] In each battery module of the battery system 1 having the above configuration, the resistance difference between the parallel-connected cells may cause variation (shunting) in the current flowing through each cell. Therefore, it is necessary to estimate the maximum current that may occur due to the variation and control the current so that it does not exceed the upper limit current of the cell. However, it is not easy to accurately estimate the maximum current, and a margin is set on the safe side for the estimated maximum current, which may result in the battery module not being able to fully utilize its performance.

[0020] Therefore, in this embodiment, the control device 100 operates as follows. That is, the control device 100 acquires a distribution degree Y indicating the degree of current division between the multiple cells in any one of the battery modules based on the voltage difference ΔV between the adjacent battery modules and the required value Ir of the system current Ix. When the acquired distribution degree Y is greater than a threshold value Z, the control device 100 calculates an upper limit value Imax of the current flowing through each cell from the distribution degree Y, the required value Ir, and the number of cells in the battery module. When the acquired distribution degree Y is smaller than the threshold value Z, the control device 100 calculates the upper limit value Imax from the threshold value Z, the required value Ir, and the number of cells. Furthermore, the control device 100 sets an allowable time Ta during which current flow at the calculated upper limit value Imax is allowed, and controls the current so that it does not exceed the allowable time Ta. The distribution degree Y indicates, for example, the ratio of the current when division occurs to a value obtained by equally dividing the system current Ix in each of the multiple cells. In this embodiment, for example, when the degree of distribution Y is 1.15, this indicates that in the one of the two cells through which a larger current flows, a current that is 1.15 times the equal divided value flows.

[0021] In this way, by changing the calculation method of the upper limit Imax of the current depending on the degree of distribution, the upper limit Imax of the current and the permissible time Ta can be calculated with high accuracy, thereby making it possible to fully utilize the battery performance.

[0022] An example of the process executed in the control device 100 will be described below with reference to Fig. 2. Fig. 2 is a flowchart showing an example of the process executed in the control device 100. A series of processes shown in this flowchart is repeatedly executed at predetermined intervals.

[0023] In step (hereinafter, step will be abbreviated as S) 100, the control device 100 acquires the distribution degree Y, the required value Ir of the system current Ix, and the threshold value Z. Specifically, the control device 100 acquires the required value Ir of the system current Ix based on an acceleration request or the like from a vehicle control device (not shown) that controls the electric vehicle. The control device 100 acquires the distribution degree Y from memory. Furthermore, the control device 100 acquires the threshold value Z using the acquired required value Ir and a map (see the right diagram in FIG. 3 ) that is stored in the memory and indicates the relationship between the required value Ir and the distribution degree Y.

[0024] Fig. 3 is a diagram showing an example of the relationship between the current, the distribution degree, and the upper limit of the current or the voltage difference. The right diagram in Fig. 3 shows the relationship between the required value Ir of the system current Ix, the distribution degree Y, and the voltage difference ΔV.

[0025] The horizontal axis in the right diagram of FIG. 3 indicates the current (required value Ir). The vertical axis in the right diagram of FIG. 3 indicates the distribution degree Y. Furthermore, in the right diagram of FIG. 3, the distribution of the voltage difference ΔV corresponding to the required value Ir and the distribution degree Y is shown by a plurality of isopotential lines set at predetermined intervals. LN2 in the right diagram of FIG. 3 is the isopotential line of the voltage difference ΔV corresponding to the threshold value Z. The voltage difference ΔV corresponding to the threshold value Z is a predetermined value, which is the lower limit of the voltage difference ΔV at which the distribution degree can be detected. When the required value Ir is I(0), the control device 100 acquires the value Z(0) specified using LN2 in the right diagram of FIG. 3 as the threshold value Z.

[0026] In S102, the control device 100 determines whether the acquired distribution degree Y is equal to or greater than the threshold value Z. If it is determined that the calculated distribution degree Y is equal to or greater than the threshold value Z (YES in S102), the process proceeds to S104.

[0027] In S104, the control device 100 calculates the upper limit value Imax of the current of a single cell (whichever of the cells 11, 12 of the first battery module 10 has the higher distribution degree) by multiplying the required value Ir by the distribution degree Y and dividing the result by the number of cells in the battery module, 2. The control device 100 may calculate the upper limit value Imax using the required value Ir of the current, the distribution degree Y, and a map showing the relationship between the required value Ir, the distribution degree Y, and the upper limit value Imax.

[0028] The left diagram in Fig. 3 is a diagram showing the relationship between the required value Ir, the distribution degree Y, and the upper limit value Imax. The horizontal axis in the left diagram in Fig. 3 indicates the required current value Ir. The vertical axis in the left diagram in Fig. 3 indicates the distribution degree Y. In the left diagram in Fig. 3, the distribution of the upper limit value Imax of the current of an individual cell corresponding to the required value Ir and the distribution degree Y is shown by isocurrent lines. The control device 100 may obtain the upper limit value Imax from the obtained required value Ir and distribution degree Y and the map shown in the left diagram in Fig. 3.

[0029] Thereafter, the process proceeds to S108. If it is determined that the calculated distribution degree Y is less than the threshold value Z (NO in S102), the process proceeds to S106.

[0030] In S106, the control device 100 calculates the upper limit value Imax of the current of a single cell by multiplying the required value Ir by the threshold value Z and dividing the result by the number of cells in the battery module, 2. After that, the process proceeds to S108.

[0031] In S108, the control device 100 calculates the permissible time Ta using the calculated upper limit value Imax of the current. Specifically, the control device 100 calculates the permissible time Ta using a map (see LN1 in FIG. 2) showing the relationship between the current and the permissible time. For example, when the upper limit value of the current is Imax(0), the control device 100 calculates the permissible time Ta(0) from the map as the permissible time Ta. Then, the process proceeds to S110.

[0032] In S110, the control device 100 sets Wout (discharge power limit value) that does not exceed the permissible time Ta. For example, when the calculated permissible time Ta is shorter than the time required to discharge the requested amount of power, the control device 100 sets Wout to a value lower than the value calculated from the upper limit value Imax of the current and the output voltage of the battery system 1. Note that the control device 100 may transmit information about the set Wout or information about the upper limit value Imax and the permissible time Ta to the vehicle control device. After that, the process proceeds to S112.

[0033] In S112, the control device 100 determines whether the distribution degree Ya calculated from the voltage difference ΔV exceeds the threshold value Z. The control device 100 calculates, for example, the voltage difference ΔV between the voltage Va detected by the first voltage sensor 104 and the voltage Vb detected by the second voltage sensor 106. The control device 100 calculates the distribution degree Ya using the calculated voltage difference ΔV and a map (see the right diagram in FIG. 3). If it is determined that the distribution degree Ya exceeds the threshold value Z (YES in S112), the process proceeds to S114.

[0034] In S114, the control device 100 calculates the distribution degree Ytmp using the maximum value |ΔVmax| among the magnitudes of the voltage differences ΔV between adjacent battery modules, the required value Ir, and a map (see the right diagram in FIG. 3). After that, the process proceeds to S116.

[0035] In S116, the control device 100 determines whether the calculated distribution degree Ytmp is equal to or greater than the distribution degree Y acquired in S100. If it is determined that the distribution degree Ytmp is equal to or greater than the distribution degree Y (YES in S116), the process proceeds to S118.

[0036] In S118, the control device 100 sets the distribution degree Ytmp as a new distribution degree Y, and updates the information stored in the memory. The process then ends. Note that if it is determined that the distribution degree Ya is equal to or less than the threshold value Z (NO in S112) or if the calculated distribution degree Ytmp is smaller than the distribution degree Y (NO in S116), this process ends.

[0037] The operation of the battery system 1 according to the present embodiment based on the above configuration and flowchart will be described.

[0038] For example, assume that the battery system 1 is required to discharge when accelerating an electric vehicle. At this time, the control device 100 acquires a required value Ir of the system current Ix, a distribution degree Y, and a threshold value Z corresponding to the required value Ir (S100).

[0039] If it is determined that the distribution degree Y is equal to or greater than the threshold value Z (YES in S102), the upper limit Imax of the current of a single cell is calculated by multiplying the required value Ir by the distribution degree Y and dividing the result by the number of cells, 2 (S104). For example, if the required value Ir is 1500 A and the distribution degree Y is 1.26, Imax is calculated as 945 A (=1500×1.26 / 2).

[0040] On the other hand, if it is determined that the distribution degree Y is less than the threshold value Z (NO in S102), the upper limit value Imax of the current of a single cell is calculated by multiplying the required value Ir by the threshold value Z and dividing the result by the number of cells, 2 (S104).

[0041] The allowable time Ta is calculated using the calculated upper limit value Imax of the current (S108), and a discharge power limit value Wout that does not exceed the allowable time Ta is set (S110). Then, when the distribution degree Ya calculated from the voltage difference ΔV between the voltage Va of the first battery module 10 and the voltage Vb of the second battery module 20 exceeds the threshold value Z (YES in S112), the distribution degree Ytmp is calculated from the maximum value |ΔVmax| of the voltage differences ΔV between the cells, the required value Ir, and a map (see the right diagram in FIG. 3) (S114). Then, when the calculated distribution degree Ytmp is equal to or greater than the distribution degree Y (YES in S116), the calculated distribution degree Ytmp is set as a new distribution degree Y (S118).

[0042] As described above, according to the battery system 1 of the present embodiment, the method of calculating the upper limit of the current is changed depending on the degree of distribution, so that the upper limit of the current Imax and the permissible time Ta can be calculated with high accuracy. This allows the battery performance to be fully utilized. Therefore, it is possible to provide a battery system that brings out the performance of a battery module having cells connected in parallel.

[0043] Modifications will be described below.

[0044] In the above-described embodiment, an example has been described in which the discharge power limit value Wout is set based on the distribution degree Y in the first battery module 10. However, the discharge power limit value Wout may also be set based on the distribution degree in the second battery module 20 or the third battery module 30, or the discharge power limit value Wout may be set based on the maximum distribution degree among the multiple battery modules.

[0045] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0046] 1 battery system, 10 first battery module, 11, 12, 21, 22, 31, 32 cells, 20 second battery module, 30 third battery module, 40, 50, 60, 70 busbars, 100 control device, 102 current sensor, 104 first voltage sensor, 106 second voltage sensor, 108 third voltage sensor.

Claims

[Claim 1] A plurality of battery modules each including a plurality of cells connected in parallel and connected in series; a control device for controlling a current flowing through the plurality of battery modules; The control device includes: obtaining a distribution degree indicating a degree of current division among the plurality of cells in any one of the battery modules based on a voltage difference between the adjacent battery modules and the required current value; When the acquired distribution degree is greater than a threshold value, an upper limit value of a current flowing through a single cell is calculated using the distribution degree, the required value, and the number of cells of the battery module; If the acquired distribution degree is smaller than the threshold value, the upper limit value is calculated using the threshold value, the required value, and the number of cells; The battery system sets an allowable time during which current flow at the calculated upper limit value is allowed.

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