JPWO2015133401A1 - Control unit, storage battery system, battery cell balance method and program - Google Patents

Abstract

The control unit includes a plurality of battery cells connected to each other, an auxiliary storage element electrically connected to each battery cell, and a switch that switches a connection state between each battery cell and the auxiliary storage element. In the storage battery system provided, the operation of the switch can be controlled, and (i) a cell other than the battery cell to be balanced among the plurality of battery cells and the auxiliary storage element are connected to the storage battery system. A cell balance operation for switching the first connection state to be performed and (ii) a second connection state in which the battery cell to be balanced and the auxiliary power storage element are connected to equalize the voltage of the battery cell; Prior to the cell balance operation, a precharge operation for charging the auxiliary power storage element in the first connection state is performed.

Description

  The present invention relates to a storage battery system having a plurality of battery cells, a battery cell balance method, a program, and the like. In particular, the present invention relates to a control unit, a storage battery system, a battery cell balance method, and a program capable of more efficiently balancing cells between battery cells in an active manner.

  In recent years, storage battery systems combining a plurality of battery cells have come to be used in various fields as power sources for so-called hybrid cars and electric vehicles, and as power storage devices for home use and commercial facilities. In such a system in which a plurality of battery cells are connected, the capacity and voltage of each battery cell may gradually become unbalanced with use. One reason for this is that the electrical characteristics of all the battery cells or the environment during charging / discharging (for example, temperature variations) cannot be made uniform.

  As a method for eliminating such battery cell imbalance, an active cell balance method using a storage element such as a capacitor or an inductance has been proposed. As a conventional method, a method of charging / discharging a power storage element at a certain period is known (for example, Patent Document 1). Moreover, the method etc. which change the ratio of charging / discharging time period and charging / discharging time according to the voltage difference of a battery cell are also known (for example, cited reference 2).

Japanese Patent No. 3458740 Japanese Patent No. 4181104

  However, in the method as described in the above document, the state of charge of the power storage element is not considered when performing the cell balance operation. In other words, since the cell balance operation is performed under a predetermined condition that is uniformly set regardless of the storage state, the charge transfer from the storage element to the target battery cell is efficient especially in the initial stage of cell balance. (The details will be described later with reference to the drawings).

  Accordingly, an object of the present invention is to provide a control unit, a storage battery system, a battery cell balance method, and a program capable of more efficiently balancing cells between battery cells in an active manner.

In order to achieve the above object, a control unit according to an embodiment of the present invention is as follows:
1. In a storage battery system comprising: a plurality of battery cells connected to each other; an auxiliary storage element electrically connected to each of the battery cells; and a switch that switches a connection state between each of the battery cells and the auxiliary storage element. A control unit capable of controlling the operation of the switch,
In the storage battery system,
(I) a first connection state in which cells other than the battery cell to be balanced among the plurality of battery cells and the auxiliary power storage element are connected; and (ii) the battery cell to be balanced and the auxiliary power storage element. A cell balance operation for switching the second connection state to be connected to make the voltage of the battery cell uniform,
Prior to the cell balance operation, a pre-charging operation for charging the auxiliary storage element in the first connection state;
A control unit that is configured to cause

(Definition of terms)
“Battery cell” basically refers to an individual storage battery constituting an assembled battery, and in some cases includes a module including a plurality of storage batteries.
The timing of the “pre-charge operation” may be immediately before the cell balance operation (including the case where the “cell balance operation” is performed continuously to the “pre-charge operation”), or the pre-charge operation is performed in advance. The cell balance operation may be performed after that.
The “parameter relating to the charging state” refers to a parameter that can determine how much charging has progressed based on the parameter. For example, the current flowing through the auxiliary power storage element, the voltage of the auxiliary power storage element, or the charging time may be used.
The “steady state in which the charging current and the discharging current of the auxiliary storage element are substantially balanced” means not only a state in which the charging current and the discharging current are completely balanced but also a state in which they are substantially balanced (for example, charging of the auxiliary storage element). The rate of time change of the average value of the current and / or discharge current, or a state in which the difference is smaller than a certain threshold value).
The “cell balance operation” is not necessarily limited to one in which the “first connection state” and the “second connection state” are alternately performed.

  ADVANTAGE OF THE INVENTION According to this invention, the storage battery system, the battery cell balance method, and program which can take the cell balance between battery cells more efficiently by an active system are provided.

It is a block diagram showing typically an example of a storage battery system concerning one form of the present invention. It is a graph which shows the charging current of the capacitor at the time of switching by a fixed period (initial stage). It is a graph which shows the charging current of the capacitor at the time of switching by a fixed period (the last stage and a steady state). It is a figure which shows a circuit model (charge to a capacitor). It is a figure which shows a circuit model (charge to an object battery cell). It is a flowchart of an example of a cell balance method. It is a flowchart of the other example of the cell balance method. It is a flowchart of the further another example of the cell balance method. It is a result which shows transition of the average balance current at the time of applying the method of this embodiment and changing the charge time of the capacitor of cell balance initial stage.

  Next, embodiments of the present invention will be described in detail with reference to the drawings. The configuration described below is merely an example of the present invention, and the specific configuration can be changed as appropriate. FIG. 1 shows an example of a storage battery system according to an embodiment of the present invention.

[System configuration]
The storage battery system 1 of FIG. 1 includes battery cells 15a to 15d (hereinafter also simply referred to as battery cells 15) connected in series and a circuit configuration for equalizing the voltages of the battery cells 15a to 15d. Yes. Specifically, an auxiliary storage element 25 that can be electrically connected to each battery cell 15 and a plurality of switches SW (details below) for switching the connection state between each battery cell 15 and the auxiliary storage element 25. I have. The storage battery system 1 further includes a monitor unit 31 that measures the voltage and the like of each battery cell 15 and a control unit 35 that is electrically connected thereto.

  Although the battery cell 15 is not specifically limited, For example, secondary batteries, such as a lithium ion battery, may be sufficient. In FIG. 1, a cylindrical shape is shown as an example, but naturally, it may be a thin battery with a laminate and may be a lithium ion secondary battery. In FIG. 1, four battery cells 15 are arranged in series. However, the number is not limited to this, and the number of battery cells 15 can be changed to any number of two, three, or five or more.

  As the auxiliary power storage element 25, a power storage element such as a capacitor or a transformer can be used. Of course, one or a plurality of auxiliary power storage elements 25 may be provided. In the present embodiment, as will be described later, the cell balance condition is determined based on the voltage value and / or current value of the auxiliary power storage element 25. Therefore, the auxiliary power storage element 25 is also provided with means (not shown) for measuring voltage and / or current.

As the switches SW, first switch groups SW1a to SW1e and second switch groups SW2a to SW2d are provided. By appropriately turning on / off these switches, the following states are set:
(I) A first connection state in which cells (for example, 15b to 15d) other than the battery cells to be balanced among the plurality of battery cells 15a to 15d are connected to the auxiliary storage element 25.
(Ii) A second connection state in which a battery cell (15a in one example) to be balanced and the auxiliary storage element 25 are connected.

  On / off of each of the switches SW1a to 1e and SW2a to 2d is controlled by the control unit 35. The control unit 35 may be, for example, a microcomputer having one or more processors and a memory. Or the control unit 35 may be comprised with the electric circuit. Control of the switch SW may be, for example, PWM (Pulse Width Modulation) control of the semiconductor switching element.

  The control unit 35 may have a display device such as a display in some cases. A program is installed in the memory of the control unit 35, and according to the program, one or more processors are configured to realize various functions of the storage value system, cell balance operation (detailed below), and the like. Also good.

  The monitor unit 31 has a function as a voltmeter that can measure the voltage of each battery cell 15. Moreover, you may grasp | ascertain the other state of a battery cell. The control unit 35 is electrically connected to the monitor unit 31 and performs various arithmetic processes based on the detection result (monitoring result). Conventionally known methods can be used for such battery cell state monitoring and arithmetic processing based on the monitoring (for example, whether or not to start a cell balance operation).

[About cell balance]
By the way, when using the some battery cell 15 like the system of FIG. 1, the balance and capacity | capacitance of each battery cell may arise. As a cell balance method for correcting the unbalance and making the voltage of each battery cell uniform, a “passive method” and an “active method” are broadly known.

  The “passive method” uses a resistor and a switch provided in a detour, bypasses a battery cell having a high voltage to a resistor connected in parallel to the battery cell, and discharges the voltage, thereby equalizing the voltage. It is intended. On the other hand, in the “active method”, a plurality of battery cells are divided into a battery cell group having a high voltage and a battery cell to be balanced having a low voltage, and (i) the battery cell group having a high voltage is sub-storage element. And charging the auxiliary power storage element by connecting to the battery, and (ii) connecting the auxiliary power storage element and the battery cell to be balanced and moving the charge to the battery cell, thereby making the voltage uniform Is intended.

  Of the two methods described above, the “active method” cell balance method is advantageous from the viewpoint of energy efficiency. However, the conventional general active cell balance method basically switches the two connection states at a constant period, and thus has the following problems. Hereinafter, a description will be given with reference to FIGS. Hereinafter, the auxiliary power storage element will be described as a capacitor.

  FIG. 2A is a graph showing the charging current of the capacitor when switching is performed at a constant period (T = 2s in one example) (initial stage of cell balance). The horizontal axis indicates time, and the vertical axis indicates the current value of the charging current. As can be seen from this graph, the initial value of the cell balance (that is, for a while after the start of the cell balance operation, the current value is on the positive side, and the charging current is significantly larger than the discharging current from the capacitor. The current value gradually shifts to the minus side as time passes, and when the state finally reaches a state as shown in FIG 2B, the charging current and discharging current from the capacitor are balanced. It becomes a steady state.

  That is, in the method of switching at a constant cycle as described above, a sufficient amount is not stored in the capacitor at the initial stage of cell balance as shown in FIG. 2A, and the state where charging is prioritized over discharging continues for a while. . Therefore, in this state, the amount of charge moving from the capacitor to the battery cell to be balanced is small and the charging efficiency is low, and as a result, the time until the cell balance is finally completed becomes long.

  Therefore, in the present embodiment, in order to solve such problems and improve the charging efficiency of the battery cells at the initial stage of cell balance, the following cell balance method is performed. The basic technical idea of the method described below is that (i) first, a certain amount of charge is stored in the capacitor (auxiliary storage element) prior to the initial stage of cell balance or cell balance operation, and (ii) as an example Then, after a steady state in which the charging current and the discharging current of the auxiliary power storage element are substantially balanced is obtained, the switching is made to periodic switching (not necessarily limited to a certain period).

  By doing so, charging can be performed efficiently immediately after the start of cell balance (details will be described later with reference to FIG. 5 and the like). As a reference parameter, a case where it is based on a current flowing through a capacitor, a case where it is based on a voltage of the capacitor, a case where it is based on time, or the like is assumed. Hereinafter, it demonstrates in order.

(Controlled by current)
3A and 3B are circuit models of the system of FIG. FIG. 4A is an example of a flowchart in the case of performing cell balance based on the current flowing through the capacitor.

  First, in step S1 of FIG. 4A, the voltage value of each battery cell 15 is acquired (step S1). Specifically, it may be performed by the control unit 35 reading the value measured by the monitor unit 31.

  Next, in step S2, the maximum value of the cell voltage difference is detected (step S2). Thereafter, in step S3, it is determined whether or not a cell balance operation is necessary (step S3). For example, the control unit 35 may compare the voltage values of the battery cells 15 and determine whether or not the maximum value of the difference exceeds a predetermined reference value. When the maximum value of the difference exceeds a predetermined reference value, the control unit 35 determines that the cell balance operation is necessary.

  In addition, if description about the determination whether a cell balance operation | movement is required is added, this determination is not necessarily limited to what is based on a voltage difference. This determination may be made based on some parameter indicating a difference in the charging state of each battery cell, a predetermined threshold value, and the like. As a specific example, it may be determined whether or not a parameter value (for example, a percentage display) representing a state of charge calculated from a charge / discharge history is shifted to a predetermined threshold value or more. . Various methods including a known method can be used for determining whether or not the cell balance operation is necessary.

  Next, in step S4, switching conditions (charging conditions) for cell balance are determined (step S4). The determination of the charging condition will be described with reference to the circuit models of FIGS. 3 (A) and 3 (B). Here, the capacitance of the capacitor is C, the resistance due to the circuit element is R, the voltage of each battery cell is Vi (i = 1 to 4), and the voltage of the cell 4 (corresponding to the battery cell 15d in FIG. 1) is Assume that it is in the lowest state.

When charge / discharge switching of the capacitor is performed at the period T, the steady state can be formulated under the condition that the charge current of the capacitor and the balance current from the capacitor to the battery cell are balanced. In other words, the storage element current i _ter , the storage element voltage V _ter , and the time required for charging t _ter when the capacitor is charged from the state of 0 until the steady state is established can be expressed as follows. Yes (R is the internal resistance of the circuit):

  here,

である。

It is.

In the case of the control by the capacitor current, the current i _ter is determined, and the cell balance operation is performed accordingly (steps S5 and S6). The determination of the current i _ter may be performed by the control unit 35 performing a calculation based on the above formula.

In step S7, the control unit 35, the current i of the capacitor is a judgment of whether or not reached to the current _{i ter,} continues to charge the capacitor to reach the current _{i ter} (step S8), and the current _{i ter} reach After that, go to the next step.

  In step S8, a normal cell balance operation (for example, switching is performed at a constant period) is performed (step S8). Conventionally known techniques may be used for the switching timing and the operation end timing in this step.

  As described above, in such a method, at the initial stage of cell balance, first, a charge is stored in the capacitor so that a steady state of charge / discharge current of the capacitor is obtained, and then the switching is performed periodically. Therefore, the efficiency at the initial stage of cell balance can be improved, and as a result, the time required to complete cell balance can be shortened.

(Controlled by voltage)
As in the flowchart shown in FIG. 4B, it is also possible to perform control based on the capacitor voltage. In this case, the capacitor voltage V _ter is determined in step S5, and in step S7, it is determined whether or not the capacitor voltage V has reached the voltage V _ter and the capacitor charging at the initial stage of cell balance may be performed. Other operations and control can be performed in the same manner as in the case of control with the current.

(Controlled by time)
Instead of the current and voltage of the capacitor, it is possible to control based on time as in the flowchart shown in FIG. 4C. In this case, the time t _ter is determined in step S5, and in step S7, it is determined whether or not the capacitor charging time t at the initial stage of cell balance has reached the time t _ter . Other operations and control can be performed in the same manner as in the case of control with the current.

The current reference control, the voltage reference control, and the time reference control as described above may be used alone or in appropriate combination. Also, in FIGS. 4A to 4C, it is determined whether or not the current value i, the voltage value V, and the time t reach the storage element current i _ter , the storage element voltage V _ter , and the time t _ter required for charging, respectively. Although an example of performing is shown, the threshold value in this determination does not necessarily need to be exactly i _ter , V _ter , t _ter , an approximate value of these values, or a value of 90% or more of these values, for example, 80% It is good also as the above value or a value 70% or more.

  In the above description, calculation based on mathematical expressions has been described. However, when calculation is difficult, determination of charging conditions is not necessarily performed by calculation. It is also possible to set a charging condition that can realize a steady state based on actual measurement. In the present invention, at the initial stage of cell balance, first, it is not necessarily limited to a specific calculation process as long as it can be in a steady state in which the charging current and discharging current of the auxiliary storage element are substantially balanced. It is not a thing.

FIG. 5 is a result showing the transition of the average balance current when the method of the present embodiment is applied and the capacitor charging time t ₁ at the initial stage of cell balance is changed to 2 s, 5 s, and 10 s. The horizontal axis is time (sec), and the vertical axis is the average balance current value. The current value is standardized with a steady state value of 1.

In FIG. 5, t ₁ = 2s means that the capacitor charging time in the initial stage of cell balance is not particularly lengthened, and switching is performed at a period of T = 2s, for example. On the other hand, t ₁ = 5 s, 10 s means that the capacitor charging time at the initial stage of cell balance is set longer than the period of T = 2 s.

When only switching with a fixed period is performed (t ₁ = 2s), the rising curve of the balance current is gentle, and it can be seen that time is required to reach a steady state. On the other hand, when the capacitor is charged in the initial stage of cell balance (t ₁ = 5 s, 10 s), the current value is naturally zero until 5 s or 10 s, respectively, but thereafter the balance current curve is almost Compared to the case of rising vertically and t ₁ = 2s, a large balance current is obtained from the initial stage of cell balance. In particular, when t ₁ = 10 s, a more remarkable improvement effect was observed, and the charge transfer efficiency up to the steady state could be improved by 16% as compared with the case of only switching with a constant period.

This application discloses the following invention.
1. A plurality of battery cells (15) connected to each other, an auxiliary storage element (25) electrically connected to each of the battery cells, and a switcher for switching a connection state between each of the battery cells and the auxiliary storage element ( A control unit (35) capable of controlling the operation of the switch in a storage battery system (1) comprising:
In the storage battery system,
(I) a first connection state in which cells other than the battery cell to be balanced among the plurality of battery cells and the auxiliary power storage element are connected; and (ii) the battery cell to be balanced and the auxiliary power storage element. A cell balance operation for switching the second connection state to be connected to make the voltage of the battery cell uniform,
Prior to the cell balance operation, a pre-charging operation for charging the auxiliary storage element in the first connection state;
A control unit that is configured to cause

2. The control unit as described above, wherein the pre-charging operation is performed until a parameter related to a charging state reaches a predetermined threshold value.

3. The control unit according to claim 1 or 2, wherein the precharging operation is performed until a steady state is obtained in which a charging current and a discharging current of the auxiliary power storage element are substantially balanced.

4). The parameter for the state of charge is current,
The pre-charging operation is
The above description is performed until the current i flowing through the auxiliary storage element becomes the reference current i _ter based on the value of the current i _ter flowing through the auxiliary storage element until the steady state is obtained. Control unit.

5. The parameter relating to the state of charge is voltage,
The pre-charging operation is
The above description is performed until the voltage V of the auxiliary storage element becomes the reference voltage V _ter based on the value of the reference voltage V _ter of the same element when the auxiliary storage element is charged to a state where a steady state is obtained. Controller unit.

6). The parameter for the state of charge is time,
The pre-charging operation is
The control unit as described above, which is performed until the reference time t _ter is reached based on a value of a reference time t _ter necessary for charging the auxiliary power storage element to a state where a steady state can be obtained.

7). A plurality of battery cells connected to each other;
An auxiliary energy storage device electrically connected to each of the battery cells;
A switcher (switching circuit) for switching the connection state between each battery cell and the auxiliary storage element;
A control unit as described above;
A storage battery system comprising:

8). The storage battery system as described above, wherein the auxiliary storage element is a capacitor or a transformer.

9. The storage battery system as described above, wherein the battery cell is a lithium ion battery.

10. further,
The storage battery system according to the above, comprising voltage measuring means for measuring the voltage of the auxiliary storage element.

11. further,
The storage battery system according to the above, further comprising current measuring means for measuring a current flowing through the auxiliary power storage element.

12 In order to equalize the voltage of a plurality of battery cells connected to each other by cell balance operation,
(I) charging the auxiliary power storage element in a first connection state in which a cell other than the battery cell to be balanced and the auxiliary power storage element are connected among the plurality of battery cells; and (ii) the balance target A cell balance operation step of switching to a second connection state in which the battery cell and the auxiliary storage element are connected to charge the battery cell to be balanced;
Prior to the cell balance operation step, a pre-charge operation step of charging the auxiliary storage element in the first connection state;
A battery cell balance method.

13. The pre-charging operation step includes
The battery cell balancing method according to the above, which is performed until a parameter relating to a charging state reaches a predetermined threshold value.

14 The pre-charging operation step,
The battery cell balance method according to the above, wherein the battery cell balance method is performed until a steady state is obtained in which a charging current and a discharging current of the auxiliary power storage element are substantially balanced.

15. A program for causing one or more processors (one or more computers) to perform the battery cell balancing method described above.

  Such a program may be stored in a storage area of the system. That is, an algorithm for performing the above method may be stored in the storage area.

1 Storage battery system 15a-15d Battery cell (storage battery, secondary battery)
25 Capacitor (auxiliary storage element)
31 Monitor 35 Control unit (control circuit)
SW1a ~ 1e, 2a ~ 2d switch

Claims (15)

In a storage battery system comprising: a plurality of battery cells connected to each other; an auxiliary power storage element electrically connected to each battery cell; and a switch that switches a connection state between each battery cell and the auxiliary power storage element. A control unit capable of controlling the operation of the switch,
In the storage battery system,
(I) a first connection state in which cells other than the battery cell to be balanced among the plurality of battery cells and the auxiliary power storage element are connected; and (ii) the battery cell to be balanced and the auxiliary power storage element. A cell balance operation for switching the second connection state to be connected to make the voltage of the battery cell uniform,
Prior to the cell balance operation, a pre-charging operation for charging the auxiliary storage element in the first connection state;
A control unit that is configured to cause   The control unit according to claim 1, wherein the precharging operation is performed until a parameter relating to a state of charge reaches a predetermined threshold value.   The control unit according to claim 1 or 2, wherein the precharging operation is performed until a steady state is obtained in which a charging current and a discharging current of the auxiliary power storage element are substantially balanced. The parameter for the state of charge is current,
The pre-charging operation is
The process is performed until the current i flowing through the auxiliary power storage element becomes the reference current i _ter based on the value of the current i _ter flowing through the auxiliary power storage element in a state where a steady state is obtained. The control unit according to 2 or 3. The parameter relating to the state of charge is voltage,
The pre-charging operation is
The process is performed until the voltage V of the auxiliary storage element becomes the reference voltage V _ter based on the value of the reference voltage V _ter of the same element when the auxiliary storage element is charged to a state where a steady state is obtained. Or the control unit of 3. The parameter for the state of charge is time,
The pre-charging operation is
4. The control unit according to claim 2, wherein the control unit is performed until the reference time t _ter is reached based on a value of a reference time t _ter necessary for charging the auxiliary power storage element to a state where a steady state is obtained. A plurality of battery cells connected to each other;
An auxiliary energy storage device electrically connected to each of the battery cells;
A switch for switching the connection state between each battery cell and the auxiliary storage element;
The control unit according to any one of claims 1 to 6,
A storage battery system comprising:   The storage battery system according to claim 7, wherein the auxiliary storage element is a capacitor or a transformer.   The storage battery system according to claim 7 or 8, wherein the battery cell is a lithium ion battery. further,
The storage battery system according to any one of claims 7 to 9, further comprising voltage measuring means for measuring a voltage of the auxiliary storage element. further,
The storage battery system according to any one of claims 7 to 10, further comprising a current measuring unit that measures a current flowing through the auxiliary power storage element. In order to equalize the voltage of a plurality of battery cells connected to each other by cell balance operation,
(I) charging the auxiliary power storage element in a first connection state in which a cell other than the battery cell to be balanced and the auxiliary power storage element are connected among the plurality of battery cells; and (ii) the balance target A cell balance operation step of switching to a second connection state in which the battery cell and the auxiliary storage element are connected to charge the battery cell to be balanced;
Prior to the cell balance operation step, a pre-charge operation step of charging the auxiliary storage element in the first connection state;
A battery cell balance method. The pre-charging operation step,
The battery cell balancing method according to claim 12, wherein the battery cell balancing method is performed until a parameter relating to a state of charge reaches a predetermined threshold value. The pre-charging operation step,
The battery cell balance method according to claim 12, wherein the battery cell balance method is performed until a steady state is obtained in which a charging current and a discharging current of the auxiliary storage element are substantially balanced.   The program for making a 1 or several processor implement the battery cell balance method as described in any one of Claims 12-14.

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