JP2022047616A - Battery system - Google Patents

Abstract

To provide a battery system that appropriately determines whether or not to execute a voltage equalization process when a plurality of battery modules are connected in parallel.SOLUTION: A battery system 100 with a plurality of battery modules 1 includes: voltage sensors V that each measures a voltage of each of the plurality of battery modules, an electric circuit (switches SW1 to SW3) that connect the plurality of battery modules in series or in parallel, and a control unit 10 that controls the electric circuit. The control unit calculates a permissible recirculation current value, estimates a recirculation current, and control the electric circuit such that remaining ones of the battery modules are connected in parallel when there becomes no battery module whose estimated recirculation current exceeds a corresponding permissible recirculation current value.SELECTED DRAWING: Figure 1

Description

The present invention relates to a battery system including a plurality of battery modules.

Rechargeable secondary batteries have been widely put into practical use in various fields. For example, an electric vehicle such as an electric vehicle or a plug-in hybrid vehicle includes a large capacity secondary battery for supplying power to a traveling motor.

Large capacity secondary batteries often include multiple battery modules connected in parallel. Then, electric power is supplied to a load such as a motor from a plurality of battery modules connected in parallel. The configuration for connecting a plurality of batteries in parallel is described in, for example, Patent Documents 1 to 4.

However, when charging a secondary battery provided with a plurality of battery modules, the charging efficiency may be higher if the plurality of battery modules are connected in series. Therefore, a battery system including a plurality of battery modules has a function of switching between series connection and parallel connection.

By the way, when power is supplied to a load from a plurality of battery modules connected in parallel, it is preferable that the voltages of the plurality of battery modules are the same as each other. Therefore, a method of equalizing the voltages of a plurality of battery modules when switching from the series connection to the parallel connection has been proposed. For example, Patent Document 1 describes, as an example of voltage equalization processing, a procedure for excluding some battery modules among a plurality of battery modules when it is estimated that a reflux current exceeding a threshold value flows. There is.

Japanese Unexamined Patent Publication No. 2019-090909 Japanese Unexamined Patent Publication No. 2016-082667 Japanese Unexamined Patent Publication No. 2014-180080 JP-A-2019-080474

When the voltages of a plurality of battery modules are dispersed and connected in parallel, a reflux current is generated so as to equalize the voltages of the plurality of battery modules. Then, when electric power is supplied to the load from the battery module in this state, a total current in which the return current is added to the drive current for driving the load flows.

Therefore, if it is determined whether or not the voltage equalization processing is necessary based only on the estimated value of the return current, an excessive current exceeding an assumption may flow when the load is connected. At this time, if the total current obtained by adding the return current to the drive current exceeds the allowable value, the battery module and / or the circuit components around the battery module are damaged.

This problem can be solved by limiting the drive current that drives the load. However, if the drive current is limited, the output of the load will decrease. Further, an excessive current can be avoided even by a method of providing a large margin in determining the necessity of the voltage equalization process. However, in this method, the voltage equalization process may be executed even when the return current is sufficiently small, and the start of power supply to the load is delayed. It should be noted that this problem can occur not only when driving a load but also when a regenerative current is generated from the load when the load is a motor or the like.

An object of one aspect of the present invention is to appropriately determine whether or not to execute a voltage equalization process when connecting a plurality of battery modules in parallel.

The battery system of one aspect of the present invention includes a plurality of battery modules, a voltage sensor for measuring the voltage of the plurality of battery modules, an electric circuit connecting the plurality of battery modules in series or in parallel, and the electricity. A control unit for controlling the circuit is provided. The control unit calculates the permissible return current value for each battery module based on the difference between the predetermined permissible current value and the maximum operating current determined depending on the internal resistance, and measures the permissible recirculation current value by the voltage sensor. Based on the voltages of the plurality of battery modules, the recirculation current generated when the plurality of battery modules are connected in parallel is estimated for each battery module, and the estimated value of the recirculation current in one or more battery modules is calculated. When the corresponding allowable recirculation current value is exceeded, at least one of the above-mentioned one or more battery modules is excluded until there is no battery module whose estimated recirculation current exceeds the corresponding permissible recirculation current value. When there are no more battery modules whose estimated value exceeds the corresponding allowable recirculation current value, the connection circuit is controlled so that the remaining battery modules are connected in parallel.

As described above, in the battery system of one aspect of the present invention, it is monitored whether or not the total current obtained by adding the estimated value of the reflux current to the maximum operating current exceeds the permissible value for each battery module. Then, it is determined whether or not to execute the voltage equalization process according to the monitor result. Therefore, when a plurality of battery modules are connected in parallel, it can be appropriately determined whether or not to execute the voltage equalization process. As a result, damage to the battery module and / or circuit components around the battery module can be avoided or suppressed without excessively limiting the operating current (driving current and / or regenerative current) of the load.

When the estimated return current exceeds the corresponding allowable return current value in one or more battery modules, the control unit sequentially excludes the battery module having the largest estimated return current among the one or more battery modules. You may. Alternatively, when the estimated value of the recirculation current exceeds the corresponding permissible recirculation current value in one or more battery modules, the control unit may sequentially exclude the battery module having the highest voltage or the battery module having the lowest voltage. In this case, overcurrent can be avoided while leaving as many battery modules connected in parallel as possible.

In the procedure of excluding the battery modules from one or more battery modules, the number of remaining battery modules when the estimated value of the recirculation current exceeds the corresponding permissible recirculation current value is equal to or more than a predetermined threshold. If so, the control unit controls the connection circuit so that the remaining battery modules are connected in parallel. In this case, the battery system is connected to the load in a state where it can supply the required power.

According to the above aspect, when connecting a plurality of battery modules in parallel, it is possible to appropriately determine whether or not to execute the voltage equalization process.

It is a figure which shows an example of the battery system which concerns on embodiment of this invention. It is a figure which shows an example of the current which flows when a plurality of battery modules are connected in parallel. It is a figure which shows an example of the method of determining the necessity of voltage equalization processing. It is a figure which shows an example of the case which executes the voltage equalization processing. It is a flowchart which shows an example of the process of determining the necessity of the voltage equalization process. It is a flowchart which shows an example of voltage equalization processing. It is a figure which shows the equivalent circuit of a battery system. It is a figure which shows the variation of the method of determining the necessity of voltage equalization processing.

FIG. 1 shows an example of a battery system according to an embodiment of the present invention. The battery system 100 according to the embodiment of the present invention includes a plurality of battery modules 1 (1a to 1n) and a control unit 10. The battery system 100 may include other circuits or devices not shown in FIG. Also, the battery system is sometimes called a "battery pack".

The battery module 1 is a rechargeable secondary battery. In the example shown in FIG. 1, the battery module 1 is charged by the charging device 200. The battery module 1 is not particularly limited, but is composed of, for example, a plurality of battery cells connected in series. Further, the plurality of battery modules 1a to 1n have substantially the same configuration as each other. However, the characteristics of the battery modules 1a to 1n (for example, the resistance value of the internal resistance) have variations due to manufacturing errors and the like.

A voltage sensor V, a current sensor A, and switches SW1 to SW3 are provided for each battery module 1. The voltage sensor V detects the voltage of the battery module 1. The current sensor A detects the current of the battery module 1. The switch SW1 is provided between the positive electrode of the battery module 1 and the positive power supply line. The positive power supply line is connected to the positive electrode of the power supply device 200 and the load 300. The switch SW2 is provided between the negative electrode of the battery module 1 and the negative power supply line. The negative power supply line is connected to the negative electrode of the power supply device 200 and the load 300. Further, the negative power supply line may be connected to the ground. The switch SW3 is provided between the battery modules 1 adjacent to each other. For example, the switch SW3 of the battery module 1a is provided between the negative electrode of the battery module 1a and the positive electrode of the battery module 1b. The switches SW1 to SW3 are examples of electric circuits for connecting a plurality of battery modules 1a to 1n in series or in parallel.

The control unit 10 connects a plurality of battery modules 1a to 1n in series or in parallel by controlling the switches SW1 to SW3. That is, the control unit 10 can control the switching from the series connection to the parallel connection and the switching from the parallel connection to the series connection for the battery modules 1a to 1n. Further, the control unit 10 controls a voltage equalization process for equalizing the voltages of the battery modules 1a to 1n when the battery modules 1a to 1n are connected in parallel.

The control unit 10 is realized by, for example, a processor system including a processor and a memory. In this case, a program describing the above-mentioned switching process and voltage equalization process is stored in the memory. Then, when the processor executes this program, the processing related to the switching process and the voltage equalization is realized. However, some or all of the functions of the control unit 10 may be realized by a hardware circuit.

In the battery system 100 having the above configuration, when charging the battery modules 1a to 1n, the control unit 10 connects the battery modules 1a to 1n in series. In this case, the control unit 10 is the switch SW1 of the battery module 1 (battery module 1a in FIG. 1) arranged on the positive electrode side most among the battery modules 1a to 1n, and the most among the battery modules 1a to 1n. The switch SW2 of the battery module 1 (battery module 1n in FIG. 1) arranged on the negative electrode side is controlled to be in the on state, and the other switches SW1 and SW2 are controlled to be in the off state. In addition, the control unit 10 controls each switch SW3 to be in the ON state. As a result, the battery modules 1a to 1n are connected in series.

When power is supplied from the battery modules 1a to 1n to the load 300, the control unit 10 connects the battery modules 1a to 1n in parallel. In this case, the control unit 10 controls all the switches SW1 and SW2 to the on state and controls all the switches SW3 to the off state. As a result, the battery modules 1a to 1n are connected in parallel.

However, as described above, the characteristics of the battery modules 1a to 1n (for example, the resistance value of the internal resistance) have variations due to manufacturing errors and the like. Therefore, when the battery modules 1a to 1n are switched from the series connection to the parallel connection after the charging operation is completed, the voltages of the battery modules 1a to 1n may not be equalized. Then, when the battery modules 1a to 1n are connected in parallel in a state where the voltages of the battery modules 1a to 1n are not equalized, a reflux current is generated.

FIG. 2 shows an example of the current flowing when a plurality of battery modules are connected in parallel. In this example, it is assumed that the voltage of the battery module 1b is the highest when the battery modules 1a to 1n are switched from the series connection to the parallel connection. Further, the voltages of the battery modules 1a and 1n are assumed to be lower than the average of the voltages of the battery modules 1a to 1n, respectively. In FIG. 2, the switches SW1 to SW3, the voltage sensor V, and the current sensor A are omitted in order to make the drawings easier to see.

When the battery modules 1a to 1n are connected in parallel, a reflux current is generated so that the voltages of the battery modules 1a to 1n are equalized. That is, when the voltage of the battery module 1b is high and the voltage of the battery modules 1a and 1n is low, the reflux current shown in FIG. 2A is generated. At this time, a discharge current flows through the battery module 1b, and a charging current flows through the battery modules 1a and 1n. That is, a reflux current that is output from the battery module 1b, passes through the battery modules 1a and 1n, and returns to the battery module 1b is generated.

Here, it is assumed that the battery modules 1a to 1n are connected in parallel, and at the same time, power is supplied from the battery modules 1a to 1n to the load 300. In this case, the drive current shown in FIG. 2B flows. The drive current is an example of the operating current that flows when the load 300 is in operation.

Therefore, in the case where the battery modules 1a to 1n are connected in parallel and the power is supplied from the battery modules 1a to 1n to the load 300, the reflux current shown in FIG. 2A and the drive current shown in FIG. 2B are generated. It flows. That is, a total current obtained by adding a return current to the drive current flows through each of the battery modules 1a to 1n. Here, in the battery module having a high voltage (battery module 1b in FIG. 2), the direction in which the drive current flows and the direction in which the return current flows are the same. Therefore, in the battery module having a high voltage, a total current larger than the current assumed when the load 300 is operated may be generated. When this total current exceeds the permissible value, the battery module and / or the circuit components around the battery module (for example, switches SW1 and SW2) are damaged.

When the load 300 is a motor, a regenerative current is generated as shown in FIG. 2 (c). In this case, a total current obtained by adding a reflux current to the regenerative current flows through each of the battery modules 1a to 1n. Here, in the battery module having a low voltage (battery module 1a or 1n in FIG. 2), the direction in which the regenerative current flows and the direction in which the recirculation current flows are the same. Therefore, in a battery module having a low voltage, a total current larger than the current assumed at the time of regeneration by the load 300 may be generated. The regenerative current is also an example of the operating current that flows when the load 300 is operating.

Therefore, the battery system 100 executes the voltage equalization process in consideration of the recirculation current that may occur when the battery modules 1a to 1n are connected in parallel and the operating current (driving current and / or regenerative current) of the load 300. Determine whether or not to do so. Then, when it is determined that the voltage equalization process is to be executed, the battery system 100 executes the voltage equalization process before connecting the battery modules 1a to 1n in parallel. In this case, after the voltage equalization process is executed, the return current does not occur, or even if it does occur, it becomes a very small value. Therefore, it is less likely that an excessive current will be generated when the battery modules 1a to 1n are connected in parallel. On the other hand, when it is determined that the voltage equalization process is not executed, the battery system 100 immediately connects the battery modules 1a to 1n in parallel without executing the voltage equalization process. In this case, the battery system 100 can start supplying power to the load 300 without delay.

FIG. 3 shows an example of a method for determining the necessity of voltage equalization processing. In this example, the battery system 100 includes four battery modules M1 to M4. Then, when the battery modules M1 to M4 are connected in parallel, the voltage of the battery modules M1 and M4 is assumed to be higher than the voltage of the battery modules M2 and M3.

The permissible current value represents the upper limit of the current that can be passed without damaging the battery module. That is, if a current larger than the allowable current value flows through the battery module, the battery module may be damaged. The allowable current value depends on the structure and characteristics of the battery module, and in this example, it is assumed to be the same for the battery modules M1 to M4. Further, the permissible current value when the battery module is discharged and the permissible current value when the battery module is charged may be the same as each other or may be different from each other.

C1 to C4 represent the reflux current flowing through the battery modules M1 to M4 when the battery modules M1 to M4 are connected in parallel. In this example, the voltage of the battery modules M1 and M4 is higher than the voltage of the battery modules M2 and M3. Therefore, a discharge current flows through the battery modules M1 and M4, and a charge current flows through the battery modules M2 and M3. Here, the reflux current of each battery module is estimated by the control unit 10. At this time, the control unit 10 estimates the recirculation current generated when a plurality of battery modules are connected in parallel for each battery module based on the voltage measured by the voltage sensor V. The method of estimating or calculating the return current will be described later.

D1 to D4 represent the maximum drive current of the battery modules M1 to M4. The maximum drive current of each battery module M1 to M4 is determined based on the maximum drive current of the load 300. The maximum drive current of the load 300 is the maximum value of the current that flows to drive the load 300, and is preset by specifications or the like. Therefore, the maximum drive current of each battery module is calculated by dividing the maximum drive current of the load 300 by the number of battery modules included in the battery system 100. In this example, the maximum drive currents D1 to D4 of the battery modules M1 to M4 are calculated by dividing the maximum drive current of the load 300 by "4".

However, the characteristics of the battery modules M1 to M4 (for example, the resistance value of the internal resistance) have variations due to manufacturing errors and the like. Therefore, it is preferable to calculate the maximum drive currents D1 to D4 of the battery modules M1 to M4 in consideration of the resistance values of the internal resistances of the battery modules M1 to M4.

E1 to E4 represent the maximum regenerative current of the battery modules M1 to M4. The maximum regenerative current of each battery module M1 to M4 is determined based on the maximum regenerative current of the load 300. The maximum regenerative current of the load 300 is the maximum value of the current regenerated from the load 300, and is preset by specifications or the like. Therefore, the maximum regenerative current of each battery module is calculated by dividing the maximum regenerative current of the load 300 by the number of battery modules included in the battery system 100. In this example, the maximum regenerative currents E1 to E4 of each battery module M1 to M4 are calculated by dividing the maximum regenerative current of the load 300 by "4". The maximum regenerative currents E1 to E4 of the battery modules M1 to M4 are also preferably calculated in consideration of the resistance values of the internal resistances of the battery modules M1 to M4.

The control unit 10 compares the recirculation currents C1 to C4 with the permissible recirculation current values TH1 to TH4 corresponding to each of the battery modules M1 to M4. In this embodiment, the permissible return current value represents the difference between the permissible current value and the maximum drive currents D1 to D4 or the maximum regenerative currents E1 to E4. Specifically, in the battery modules (M1, M4) in which the discharge current is generated as the return current, the difference between the allowable current value THD during operation of the load 300 and the corresponding maximum drive current (D1, D4) is calculated, respectively. Will be done. In the battery modules (M2, M3) in which the charging current is generated as the return current, the difference between the allowable current value THE at the time of regeneration of the load 300 and the corresponding maximum regeneration current (E1, E4) is calculated, respectively. That is, the following allowable return current values TH1 to TH4 are calculated for the battery modules M1 to M4.

Battery module M1: TH1 = THD-D1
Battery module M2: TH2 = THE-E2
Battery module M3: TH3 = THE-E3
Battery module M4: TH4 = THD-D4

Then, when there is a battery module whose recirculation currents C1 to C4 are larger than the corresponding permissible recirculation current values TH1 to TH4, the control unit 10 executes the voltage equalization process. However, in the example shown in FIG. 3, the reflux current is smaller than the corresponding allowable reflux current value. That is, the recirculation current C1 is smaller than the permissible recirculation current value TH1, the recirculation current C2 is smaller than the permissible recirculation current value TH2, the recirculation current C3 is smaller than the permissible recirculation current value TH3, and the recirculation current C4 is smaller than the permissible recirculation current value TH4. Therefore, in this case, the control unit 10 connects the battery modules M1 to M4 in parallel without executing the voltage equalization process. Then, the battery system 100 supplies electric power to the load 300 by using the battery modules M1 to M4.

FIG. 4 shows an example of a case where the voltage equalization process is executed. In this example, as shown in FIG. 4A, the recirculation current C1 of the battery module M1 is larger than the corresponding permissible recirculation current value TH1. In this case, the control unit 10 executes the voltage equalization process before connecting the battery modules M1 to M4 in parallel. At this time, the control unit 10 excludes the battery module (that is, the battery module M1) whose return current is larger than the corresponding allowable return current value as the voltage equalization process. As a result, as shown in FIG. 4B, the battery modules M2 to M4 remain as the battery modules to be connected. Then, the control unit 10 recalculates the return current for the remaining battery modules. That is, the recirculation currents C2 to C4 of the battery modules M2 to M4 are calculated. The return current of each battery module is determined based on the voltage balance of those battery modules. Therefore, the recirculation currents C2 to C4 estimated before the battery module M1 is excluded and the recirculation currents C2 to C4 estimated after the battery module M1 is excluded are basically different values.

After that, the control unit 10 compares the recirculation current with the corresponding permissible recirculation current value for each battery module (that is, the battery modules M2 to M4) that remains without being excluded. Each permissible return current value TH2 to TH4 does not change from the previously calculated value. Then, when all the recirculation currents C2 to C4 become smaller than the corresponding permissible recirculation current values TH2 to TH4, the control unit 10 ends the voltage equalization process and connects the battery modules M2 to M4 in parallel.

When a battery module having a recirculation current larger than the corresponding permissible recirculation current value is found among the battery modules M2 to M4, the above process is repeatedly executed. That is, the battery modules to be connected are excluded one by one until all the reflux currents are smaller than the corresponding allowable reflux current values.

As described above, in the battery system 100 according to the embodiment of the present invention, the permissible return current value of each battery module is calculated based on the maximum operating current of the load 300 and the resistance value of the internal resistance of each battery module. Further, the reflux current flowing through each battery module is estimated based on the voltage of each battery module. Then, when the recirculation current exceeds the corresponding permissible recirculation current value in one or more battery modules, the voltage equalization process is executed. On the other hand, when the recirculation current is equal to or less than the corresponding permissible recirculation current value in all the battery modules, the battery modules M1 to M4 are immediately connected in parallel without executing the voltage equalization process. That is, the estimated value of the recirculation current and the permissible recirculation current value are compared for each battery module in consideration of the variation caused by the manufacturing error and the like, and the necessity of the voltage equalization processing is determined based on the comparison. Therefore, the necessary voltage equalization process is surely executed, and the overcurrent caused by the reflux current is suppressed. In addition, since unnecessary voltage equalization processing is suppressed, the start of power supply to the load 300 is accelerated.

In the examples shown in FIGS. 3 to 4, both the current (discharge current) when driving the load 300 and the current (charging current) when the load 300 regenerates the current are monitored for voltage equalization processing. Although the necessity is determined, the present invention is not limited to this procedure. For example, when the load supplied with power by the battery system 100 does not generate a regenerative current, it may be determined whether or not the voltage equalization process is necessary only for the current (discharge current) when driving the load 300. ..

FIG. 5 is a flowchart showing an example of a process for determining the necessity of the voltage equalization process. The processing of this flowchart is executed by the control unit 10 before connecting a plurality of battery modules in parallel.

In S1, the control unit 10 calculates the maximum operating current of each battery module based on the maximum operating current of the load 300 and the resistance value of the internal resistance of each battery module. The maximum operating current of the load 300 is known and is stored in advance in, for example, a memory (not shown). Further, the resistance value of the internal resistance of each battery module is measured in advance and stored in advance in a memory (not shown). In the description of this flowchart, the maximum operating current includes the maximum drive current and the maximum regenerative current.

In S2, the control unit 10 calculates the permissible return current value from the permissible current value and the maximum operating current for each battery module. As an example, the allowable return current value can be obtained by subtracting the maximum operating current from the allowable current value. The permissible current value is the same for all battery modules and is pre-stored in a memory (not shown).

In S3, the control unit 10 estimates the reflux current of each battery module. The method of estimating the reflux current of each battery module will be described later.

In S4 to S5, the control unit 10 executes the parallelization determination process. That is, the control unit 10 compares the permissible recirculation current value and the estimated recirculation current for each battery module. When the estimated return current value of one or more battery modules is larger than the corresponding allowable return current value, the control unit 10 determines that voltage equalization processing is required before connecting the plurality of battery modules in parallel. do. In this case, the control unit 10 executes the voltage equalization process in S6. On the other hand, if the estimated return current value of all the battery modules is equal to or less than the corresponding allowable return current value, the voltage equalization process of S6 is skipped.

In S7, the control unit 10 connects a plurality of battery modules in parallel. At this time, the control unit 10 controls the switches SW1 and SW2 of each battery module to be in the ON state, and controls each switch SW3 to the OFF state.

FIG. 6 is a flowchart showing an example of the voltage equalization process. The voltage equalization shown in FIG. 6 corresponds to S6 shown in FIG. That is, the process of the flowchart shown in FIG. 6 is executed when the estimated value of the recirculation current is larger than the corresponding permissible recirculation current value in one or more battery modules.

In S11, the control unit 10 selects one battery module from one or more battery modules whose estimated return current value is larger than the corresponding allowable return current value. At this time, the control unit 10 selects, for example, the battery module having the largest estimated return current from one or more battery modules whose estimated return current is larger than the corresponding allowable return current value.

In S12, the control unit 10 estimates (recalculates) the reflux currents of the remaining battery modules excluding the battery modules selected in S11. The method of estimating the reflux current of each battery module is substantially the same in S3 and S12.

In S13, the control unit 10 determines whether or not the estimated value of the recirculation current in one or more battery modules is larger than the corresponding permissible recirculation current value among the remaining battery modules that are not excluded. This determination is substantially the same in S5 and S13. Then, when the estimated value of the recirculation current is larger than the corresponding permissible recirculation current value in one or more battery modules, the processing of the control unit 10 returns to S11. That is, the processes S11 to S13 are repeatedly executed until the estimated value of the recirculation current of all the remaining battery modules that are not excluded becomes equal to or less than the corresponding permissible recirculation current value. At this time, the number of remaining battery modules is reduced by one. Then, when the estimated value of the recirculation current of all the remaining battery modules that are not excluded becomes equal to or less than the corresponding permissible recirculation current value, the processing of the control unit 10 proceeds to S14.

In S14, the control unit 10 determines whether or not the number of battery modules remaining without being excluded is equal to or greater than a predetermined threshold value. This threshold represents the minimum number of battery modules required for the load 300 to operate normally. For example, it is assumed that the load 300 consumes electric power "75" in normal operation. Further, it is assumed that each battery module can supply electric power "10" to the load 300. In this case, the battery system 100 needs to use at least eight battery modules in order to supply the power required by the load 300. Therefore, in this case, the threshold is 8.

When the number of battery modules remaining without being excluded is equal to or greater than the threshold value, the control unit 10 determines in S15 that the battery modules can be connected in parallel. In this case, in S7 shown in FIG. 5, the control unit 10 connects the remaining battery modules that are not excluded in parallel to supply electric power to the load 300.

When the number of battery modules remaining without being excluded is less than the threshold value, the control unit 10 determines in S16 that the battery modules cannot be connected in parallel. In this case, the control unit 10 does not execute the parallelization of S7 shown in FIG. That is, the battery system 100 does not supply power to the load 300. Further, the control unit 10 may output an alert indicating that power cannot be supplied to the load 300.

In the procedure shown in FIG. 6, the control unit 10 excludes the battery modules one by one from the battery modules whose estimated return current exceeds the corresponding allowable return current value. For example, the battery modules having the largest estimated return current are excluded in order. However, the magnitude of the return current depends on the voltage difference between the plurality of battery modules to be connected in parallel. That is, among the plurality of battery modules, the estimated value of the recirculation current of the battery module having the highest voltage or the battery module having the lowest voltage is considered to be large. Therefore, the control unit 10 may exclude the battery module having the highest voltage or the battery module having the lowest voltage in S11 to S12.

Further, in the embodiment shown in FIG. 5, the battery modules are excluded one by one in S11 to S12, but the present invention is not limited to this procedure. For example, in S11 to S12, two or more battery modules may be collectively excluded. That is, in S11 to S12, at least one battery module is excluded.

Next, a method of estimating the reflux current of each battery module will be described. Hereinafter, a method of estimating the return current using the equivalent circuit shown in FIG. 7 will be described. In addition, V1 to Vn represent the voltage of each battery module M1 to Mn. R1 to Rn represent the resistance (internal resistance + wiring resistance) of each battery module M1 to Mn. C1 to Cn represent an estimated value of the reflux current of each battery module M1 to Mn generated when the battery modules M1 to Mn are connected in parallel. n represents the number of battery modules included in the battery system 100.

In the equivalent circuit shown in FIG. 7, the following voltage-related equations and current-related equations are obtained.

By summarizing these relational expressions, the following simultaneous equations can be obtained.

This simultaneous equation is expressed by a matrix operation as shown below.

Therefore, the reflux currents C1 to Cn of the battery modules M1 to Mn are represented by the following equations.

As described above, the reflux currents C1 to Cn of each battery module are calculated from the resistors R1 to Rn of each battery module and the voltages V1 to Vn of each battery module. Here, the resistors R1 to Rn of each battery module are known in this embodiment and are stored in advance in a memory (not shown). Therefore, the control unit 10 can estimate the recirculation currents C1 to Cn of each battery module by acquiring the measured values of the voltages V1 to Vn of each battery module using the voltage sensor V.

In the equivalent circuit shown in FIG. 7, when the maximum drive current of the load 300 is K, the maximum drive currents D1 to Dn of each battery module M1 to Mn may be calculated by the following equation. Further, the maximum regenerative currents E1 to En of each battery module M1 to Mn can also be obtained by the same calculation formula.

<Variation 1>
In the examples shown in FIGS. 3 to 5, the allowable return current value is set for each battery module in consideration of variations in the characteristics (for example, the resistance value of the internal resistance) of the battery modules 1a to 1n due to manufacturing errors and the like. It is calculated. However, when the variation in the characteristics of the battery modules 1a to 1n is sufficiently small, the permissible return current value common to all the battery modules may be set. For example, by dividing the maximum operating current of the load 300 by the number of battery modules included in the battery system 100, the maximum operating current of the battery modules common to each battery module is calculated. Then, by subtracting the maximum operating current of the battery module from the allowable current value, the allowable return current value common to each battery module can be obtained.

FIG. 8 shows a variation of a method for determining the necessity of voltage equalization processing. In this example, the permissible return current value common to each battery module is set. TH5 represents the permissible recirculation current value for discharge, and TH6 represents the permissible recirculation current value for charging.

In this case, the control unit 10 estimates the reflux current of each battery module. Then, when the estimated value of the recirculation current of one or more battery modules exceeds the permissible recirculation current value (TH5, TH6), the control unit 10 executes the voltage equalization process. On the other hand, if the estimated value of the recirculation current of all the battery modules is equal to or less than the permissible recirculation current value (TH5, TH6), the control unit 10 does not execute the voltage equalization process. In the example shown in FIG. 8, the recirculation currents C1 and C4 are both smaller than the permissible recirculation current value TH5, and the recirculation currents C2 and C3 are both smaller than the permissible recirculation current value TH6. Therefore, the control unit 10 does not execute the voltage equalization process.

<Variation 2>
When the change in the internal resistance of the battery module is small, the reflux current may be estimated based on the minimum value of the internal resistance. In this case, the minimum resistance value of the internal resistance may be set for each temperature range (for example, every 5 degrees).

<Variation 3>
The inrush current to the battery module increases as the internal resistance of the battery module decreases. Therefore, if the return current is estimated based on the minimum value of the internal resistance, it is determined on the safety side whether or not the voltage equalization process is executed. Here, using the equivalent circuit shown in FIG. 7, the return current is estimated based on the minimum value of the internal resistance. In the following calculation, R represents the minimum value among R1 to Rn.

In this case, in the equivalent circuit shown in FIG. 7, the following voltage-related equations and current-related equations are obtained.

Here, the reflux current C1 of the battery module M1 is obtained. First, the voltage relational expression is transformed as follows.

By adding these equations, the following equations are obtained.

Then, by substituting the above-mentioned current-related equation, the following equation is obtained.

Therefore, the reflux current C1 of the battery module M1 is expressed by the following equation. Further, the reflux currents C2 to Cn of the battery modules M2 to Mn can also be obtained by the same method.

As described above, the reflux currents C1 to Cn of each battery module are calculated from the resistance R of the battery module and the voltages V1 to Vn of each battery module. Here, the resistance R of the battery module is stored in advance in a memory (not shown). Therefore, the control unit 10 can estimate the recirculation currents C1 to Cn of each battery module by acquiring the measured values of the voltages V1 to Vn of each battery module using the voltage sensor V. According to this method, the calculation for estimating the recirculation current becomes easier than the method using the resistance value of each battery module individually, and whether or not the voltage equalization process is executed is determined on the safety side. Is done.

1 (1a to 1n) Battery module 10 Control unit 100 Battery system 300 Load

Claims (4)

A battery system with multiple battery modules
A voltage sensor that measures the voltage of each of the plurality of battery modules, and
An electric circuit that connects the plurality of battery modules in series or in parallel,
A control unit that controls the electric circuit is provided.
The control unit
For each battery module, calculate the permissible return current value based on the difference between the predetermined permissible current value and the maximum operating current determined by the internal resistance.
Based on the voltages of the plurality of battery modules measured by the voltage sensor, the recirculation current generated when the plurality of battery modules are connected in parallel is estimated for each battery module.
When the estimated return current exceeds the corresponding permissible recirculation current value in one or more battery modules, among the one or more battery modules, until there is no battery module in which the estimated recirculation current exceeds the corresponding permissible recirculation current value. Exclude at least one from
It is characterized in that the connection circuit is controlled so that the remaining battery modules are connected in parallel when there are no battery modules whose estimated return current exceeds the corresponding allowable return current value. Battery system. When the estimated return current exceeds the corresponding allowable return current value in one or more battery modules, the control unit excludes the battery module having the largest estimated return current among the one or more battery modules. The battery system according to claim 1, wherein the battery system is characterized by the above. The control unit excludes the battery module having the highest voltage or the battery module having the lowest voltage when the estimated value of the recirculation current exceeds the corresponding permissible recirculation current value in one or more battery modules. The battery system according to 1. In the procedure of excluding the battery modules from the one or more battery modules, the number of remaining battery modules when the estimated value of the recirculation current exceeds the corresponding permissible recirculation current value is a predetermined threshold. The battery system according to any one of claims 1 to 3, wherein the control unit controls the connection circuit so that the remaining battery modules are connected in parallel.

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