Cell balance adjustment method and cell balance adjustment device for series secondary battery

Abstract

To solve a problem of a flying capacitor ACB circuit.SOLUTION: In a cell balance adjustment method for equalizing the charged states of cells 2 in a secondary battery 3, all of the cells 2 constituting the secondary battery 3 are divided into a plurality of treatment target groups 4, with some of the cells 2 overlapping between the adjacent treatment target groups 4. The method includes a capacitor charging step of charging a capacitor 8 by connecting the capacitor 8 to both ends of the treatment target group 4, and a capacitor discharging step of connecting a specific treatment target cell included in the treatment target group 4 to the capacitor 8 and discharging the charge, thereby charging the treatment target cell.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The disclosed technology relates to a cell balancing method and a cell balancing device suitable for a drive battery for an electric vehicle or the like. [Background technology]

[0002] High-voltage (e.g., several hundred volts) drive batteries installed in hybrid vehicles, electric vehicles, and the like are generally made up of a large number of unit cells, such as lithium-ion batteries with a voltage of several volts, connected in series.

[0003] Even if the battery is charged and discharged in the same way, the state of charge of each cell will not be the same due to individual differences. In other words, there will be differences in the voltage of each cell. If the battery is charged while there are differences in the voltage of each cell, when the cell with the highest voltage becomes fully charged (SOC 100%), charging must be stopped to prevent that cell from being overcharged. At this time, the other cells have not yet reached full charge, so even if the battery is charged, the amount of power that can actually be used will be significantly lower than the original amount of power of the battery.

[0004] Therefore, technology to equalize the charge state of the cells (cell balance adjustment technology) has been put into practical use so that the original amount of electric power of the battery can be used. Generally, such technology is divided into passive and active methods.

[0005] In the passive method, in order to make each cell have the same state of charge, the charge of the other cells is adjusted to match the charge of the least charged cell (minimum charge). In other words, the power of the other cells that exceeds the minimum charge is discharged and discarded, adjusting them to the minimum charge and equalizing the state of charge of all cells. In the case of the passive method, the circuit and control are simple and can be implemented at low cost, but it has the disadvantage of high energy loss.

[0006] In contrast, the active method transfers power from a cell with a high charge to a cell with a low charge. By doing so, the charge of each cell is adjusted to an average charge, and the charge state of all cells is made uniform. Therefore, with the active method, there is little energy loss, but the circuits and controls tend to be complicated. Therefore, the active method has the disadvantage of being high cost and large in size, and in reality it has not yet been put to practical use.

[0007] Various types of circuits that perform cell balancing using this active method (also known as ACB circuits for short) have been proposed, including the half-bridge inductor method and the transformer method. Among these, the ACB circuit (flying capacitor ACB circuit) that uses a capacitor that can be separated from the circuit (flying capacitor) is superior in that it has few drawbacks in terms of cost and size, and is relatively easy to control.

[0008] On the other hand, the flying capacitor ACB circuit has the problem that it takes time to perform the equalization process. In other words, in the flying capacitor ACB circuit, the power of the cell with the most charge is charged to the flying capacitor, and then the power of the flying capacitor is charged to the cell with the least charge. By doing so, the charge state of each cell is equalized.

[0009] In this type of power transfer via a capacitor, as the charge states of the cells become more equal and the voltage difference between the cells becomes smaller, the current flowing through the capacitor also becomes smaller, so it takes a very long time for the voltage to converge, which makes the equalization process take a long time.

[0010] Techniques have also been proposed to solve the problems associated with such flying capacitor ACB circuits.

[0011] For example, Patent Document 1 discloses a state-of-charge adjusting device that includes a capacitor C (corresponding to a flying capacitor) connected via a switch to both the positive and negative sides of each cell. In this state-of-charge adjusting device, a cell group consisting of two or more predetermined cells is connected to the capacitor C for charging, and then the cell with the smallest charge is connected to the capacitor C to equalize the states of charge of each cell.

[0012] Patent Document 2 discloses an energy storage device equipped with multiple capacitors (corresponding to flying capacitors) connected via switches to both the positive and negative sides of each cell. This energy storage device uses both an active method of equalizing the voltage of each cell by charging and discharging the capacitors, and a passive method of discharging the capacitors using switches to equalize the charge state of each cell. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] JP 2007-43788 A [Patent Document 2] JP 2015-37339 A Summary of the Invention [Problem to be solved by the invention]

[0014] In the technology of Patent Document 1, the capacitor C is charged with the voltages of multiple cells, so the current flowing through the capacitor C does not decrease even if the charge state of each cell becomes more equal. Therefore, the time for each equalization process can be shortened. However, since there is only one capacitor C, the equalization process must be repeated, and it takes time to equalize all the cells. Moreover, the control is complicated, as it is necessary to perform a discharge time estimation process, and the burden of calculation processing is large.

[0015] In the technology of Patent Document 2, since there are individual differences in the switches, it is difficult to discharge stably. Moreover, since a passive method is also used, the problem of energy loss still remains.

[0016] Here, we present a technology that can effectively solve these problems even in a basic flying capacitor ACB circuit by devising a switch control method. [Means for solving the problem]

[0017] One of the techniques disclosed is a cell balance adjustment method for equalizing the states of charge of a secondary battery configured by connecting a plurality of cells in series.

[0018] All of the cells constituting the secondary battery are divided into a plurality of processing target groups each consisting of at least two or more consecutive cells, with some of the cells overlapping between adjacent processing target groups.

[0019] The cell balance adjustment method is characterized by including a capacitor charging step of charging a capacitor by connecting the capacitor to both ends of the processing target group, and a capacitor discharging step of connecting the capacitor to a predetermined processing target cell included in the processing target group and discharging the charge of the capacitor to charge the processing target cell.

[0020] That is, in this cell balance adjustment method, all of the cells constituting the secondary battery are divided into a plurality of processing target groups each consisting of at least two or more consecutive cells, and the cells are divided so as to overlap between adjacent processing target groups.

[0021] In this state, the capacitor is charged by connecting it to both ends of the group to be processed. That is, the capacitor is charged with the voltage of all and a plurality of cells that make up the group to be processed. Then, a specific cell to be processed included in the group to be processed is connected to the capacitor, and the cell to be processed is charged by discharging the charge. That is, a part and one of the cells that make up the group to be processed is charged by discharging the high charge of the capacitor.

[0022] As a result, even if the charge state becomes uniform, the current flowing through the capacitor does not decrease, so the charge and discharge process can be completed in a short time. Since power is transferred between cells, energy loss can also be reduced.

[0023] Moreover, since each processing group includes some overlapping cells, the charged state of all the cells constituting the secondary battery can be made uniform.

[0024] The cell to be treated is preferably a low-voltage cell having the lowest voltage in the group to be treated.

[0025] This allows the cell balance to be adjusted most efficiently.

[0026] The processing group may be composed of two of the cells. In this case, the capacitor charging step and the capacitor discharging step may be repeated until the voltage magnitude relationship between one low-voltage side cell corresponding to the low-voltage cell and the other high-voltage side cell is reversed.

[0027] In this way, there is no need to detect the voltage of each cell. It is sufficient to be able to compare the voltages of two cells relatively, and no advanced detectors or calculations are required. This allows for reduced material costs and a more compact device.

[0028] The capacitor charging step and the capacitor discharging step may be repeated until a difference in voltage between the cells included in each of the processing target groups becomes equal to or less than a predetermined value.

[0029] In the case where the group to be processed is made up of three or more cells, this makes it possible to equalize the state of charge of the cells.

[0030] The capacitor charging step and the capacitor discharging step may be repeated continuously while the secondary battery is in use, which also makes it possible to equalize the state of charge of the cells.

[0031] The capacitor charging step and the capacitor discharging step may be repeated alternately at a cycle of 1 kHz to 1 MHz.

[0032] This allows the cell balance adjustment device to be made compact and low cost while suppressing harmonic noise.

[0033] Another disclosed technique relates to a cell balancing device for equalizing the states of charge of a secondary battery configured by connecting a plurality of cells in series.

[0034] All of the cells constituting the secondary battery are divided into a plurality of processing target groups each consisting of at least two or more consecutive cells, with some of the cells overlapping between adjacent processing target groups.

[0035] The cell balance adjustment device includes a plurality of capacitors arranged for each of the processing target groups and connected to the positive and negative sides of each of the cells via switches, a cell voltage comparison means capable of comparing the voltages of each of the cells, and a control means for controlling each of the switches based on the detection values ​​of the cell voltage comparison means.

[0036] The control means executes a capacitor charging process in which the capacitor is charged by connecting the capacitor to both ends of each of the processing target groups, and a capacitor discharging process in which the capacitor is connected to a predetermined processing target cell included in each of the processing target groups, and the capacitor is discharged to charge the processing target cell.

[0037] That is, this cell balancing apparatus executes the above-mentioned cell balancing method, and therefore a valuable cell balancing apparatus can be realized at low cost and put into practical use. Effect of the Invention

[0038] The disclosed technology can be applied to conventional flying capacitor ACB circuits, and the problems can be effectively solved simply by changing the switch control method. As a result, it is possible to obtain only the advantages of the flying capacitor ACB circuit, which has little energy loss, few drawbacks in cost and size, and is relatively easy to control. Therefore, a valuable cell balancing device can be realized at low cost and put into practical use. [Brief description of the drawings]

[0039] [Figure 1] FIG. 13 is a diagram for explaining a control method for switches in a conventional flying capacitor ACB circuit (comparative example). [Diagram 2] 1 is a diagram for explaining a control method for a switch in a flying capacitor ACB circuit to which the disclosed technology is applied (embodiment); FIG. [Diagram 3] 1 is a diagram showing a flying capacitor ACB circuit to which the disclosed technology can be applied; [Figure 4] FIG. 2 is a block diagram showing the relationship of the main components of the cell balancing device. [Diagram 5] FIG. 4 is a circuit diagram for reference in explaining an example of control by a control unit. [Figure 6] 4 is a flowchart showing a flow of main processes executed by a control unit. [Figure 7] FIG. 7 is a diagram corresponding to the main steps of the processing in FIG. 6. [Figure 8] FIG. 1 is a diagram for explaining the effect of the disclosed technology. [Figure 9] FIG. 13 is a diagram showing another flying capacitor ACB circuit to which the disclosed technology can be applied. [Figure 10A] 4 is a flowchart showing a flow of main processes executed by a second control means. [Figure 10B] 10B is a flowchart continuing from FIG. 10A. [Figure 11A] FIG. 10C is a diagram corresponding to the main steps of the process of FIGS. 10A and 10B. [Figure 11B] This is a continuation of Figure 11A. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] The disclosed technology will now be described, however, the following description is merely exemplary in nature.

[0041] <Basic features of the technology to be disclosed> Prior to the detailed description of the embodiments, the basic features of the disclosed technology will be described. Fig. 1 illustrates, as a comparative example, a switch control method (conventional SW method) in a conventional flying capacitor ACB circuit. Fig. 2 illustrates a switch control method (improved SW method) in a flying capacitor ACB circuit to which the disclosed technology is applied.

[0042] The circuit shown at the top of each figure shows the basic part of the flying capacitor ACB circuit (the part corresponding to the two cells V1 and V2 connected in series). In both the conventional SW method and the improved SW method, the circuit structure is the same.

[0043] That is, the flying capacitor ACB circuit includes a plurality of branch wirings Lb connected to the positive and negative sides of each of the cells V1, V2, a plurality of switches S1 to S4 arranged on each of the branch wirings Lb, and a capacitor C (a so-called flying capacitor) connected to both the positive and negative sides of each of the cells V1, V2 via the switches S1 to S4. Note that, in a normal state, each of the switches S1 to S4 is turned OFF (a state in which no current is passed) (a so-called normally open state).

[0044] Here, we assume that cell V1 has a higher voltage than cell V2 (V1>V2). In this case, in the conventional SW method, as shown in the upper left diagram of Figure 1, switches S1 and S3 are turned ON (conductive state) so that cell V1, which has a higher voltage, is connected to capacitor C. This causes current Ic to flow as shown by the dashed line, transferring charge from cell V1 to capacitor C, and capacitor C is charged.

[0045] 1, instead of the switches S1 and S3, the switches S2 and S4 are turned on so that the cell V2 with the lower voltage is connected to the capacitor C. This causes a current Ic to flow as shown by the dashed line, transferring charge from the capacitor C to the cell V2, and charging the cell V2.

[0046] In the conventional switching method, the switches S1 to S4 are controlled so that such an operation is repeated.

[0047] The lower part of each figure shows a time chart corresponding to the operation shown above. As shown in the lower left diagram of Figure 1, when the voltage difference between cell V2 and cell V1 is large (V1>V2), the voltage difference is applied to capacitor C, so the current Ic flowing through capacitor C is also relatively large. Therefore, the charge states of both cells V1 and V2 are equalized relatively quickly.

[0048] Then, as shown in the lower right diagram of Figure 1, when the voltage difference between cells V2 and V1 becomes smaller (V1 ≒ V2), the current Ic flowing through capacitor C also becomes smaller accordingly. As the charge states of cells V1 and V2 become more equalized, the difference becomes smaller, so the equalization of the charge states of cells V1 and V2 becomes slower. Theoretically, the voltages of cells V1 and V2 never become completely equal, but rather converge exponentially. Therefore, with the conventional SW method, it takes a long time to equalize the charge states.

[0049] 2, switches S1 and S4 are turned on so that both cells V1 and V2 are connected to capacitor C. This causes current Ic to flow as shown by the dashed lines, transferring charge from cells V1 and V2 to capacitor C, and capacitor C is charged.

[0050] 2, instead of the switches S1 and S4, the switches S2 and S4 are turned on so that the cell V2 with the lower voltage is connected to the capacitor C. This causes a current Ic to flow as shown by the dashed line, transferring charge from the capacitor C to the cell V2, and charging the cell V2.

[0051] In the improved SW method, the switches S1 to S4 are controlled so that such an operation is repeated.

[0052] As shown in the lower left diagram of Figure 2, when the voltage difference between cell V2 and cell V1 is large (V1>V2), the total voltage of both cells V1 and V2 is applied to capacitor C, so the current Ic flowing through capacitor C is relatively large regardless of the voltage difference. Therefore, the charge states of both cells V1 and V2 are equalized relatively quickly.

[0053] Thus, as shown in the lower right diagram of Figure 2, even if the voltage difference between cells V2 and V1 becomes smaller (V1 ≒ V2), the total voltage of both cells V1 and V2 is applied to capacitor C as before (about twice the voltage of the conventional SW method), so the current Ic flowing through capacitor C remains large. Even if the charge states of both cells V1 and V2 become more equal, the current Ic does not decrease, so the charge states of both cells V1 and V2 are more quickly equalized. Therefore, with the improved SW method, the charge state equalization process can be completed in a short time.

[0054] <First embodiment of the disclosed technology> 3 shows a flying capacitor ACB circuit (first circuit 10) to which the disclosed technology can be applied. Note that the disclosed technology can be applied to any flying capacitor ACB circuit, and the first circuit 10 is an example thereof.

[0055] Hybrid cars, electric cars, and other electrically powered vehicles are equipped with a high-voltage battery 3 (secondary battery) as a power source for driving the vehicle, which is configured by connecting many cells 2 in series, as shown in Fig. 3. Fig. 3 shows a portion (five cells 2) of the battery 3 (first cell 2a to fifth cell 2e). The first circuit 10 has the same configuration for all the cells 2, so the other portions are not shown.

[0056] Although not shown in the drawings, such a battery 3 is provided with a dedicated controller for controlling the power thereof. The first circuit 10 is built into such a controller in order to equalize the states of charge of the cells 2. Specifically, most of the cell balancing device 1 in this embodiment is configured as a single semiconductor chip including the first circuit 10, and can be used by being mounted on a board of the controller.

[0057] A group of cells 2 constituting the battery 3 is divided into a plurality of groups (processing target groups 4) each consisting of at least two or more consecutive cells 2 (two in this example). In Fig. 3, the group is divided into a first processing target group 4a, a second processing target group 4b, a third processing target group 4c, and a fourth processing target group 4d.

[0058] These processing target groups 4 overlap with each other in a portion of the cell 2 (here, one cell 2) between adjacent processing target groups 4. For example, the first processing target group 4a and the second processing target group 4b overlap with each other in the second cell 2b. The second processing target group 4b and the third processing target group 4c overlap with each other in the third cell 2c. The third processing target group 4c and the fourth processing target group 4d overlap with each other in the fourth cell 2d.

[0059] The first circuit 10 is composed of a plurality of branch wirings 5, a plurality of connecting wirings 6, a plurality of switches 7, a plurality of capacitors 8, etc. for the battery 3. As shown in Fig. 3, these components are conceptually arranged so as to extend along the series of cells 2 (for convenience, the first circuit 10 will be described below with reference to Fig. 3).

[0060] One end of each branch wiring 5 is connected to a portion between the positive electrode side of one cell 2 connected in series and the negative electrode side of the other cell 2. The other end of each branch wiring 5 branches into two and is connected to one end of two switches 7, 7.

[0061] When looking at a certain cell 2, the other end of the switch 7 connected to the positive electrode side of the cell 2 via the branch wiring 5 is connected to the other end of the switch 7 connected to the negative electrode side of the cell 2 via the branch wiring 5 by a connecting wiring 6. Circuits with such a configuration are repeatedly arranged along the series of cells 2 to form a series of continuous circuits 9.

[0062] Two such continuous circuits 9 are arranged symmetrically with respect to the series of cells 2. Capacitors 8 are connected alternately between two adjacent connecting wires 6, 6 of both of these continuous circuits 9. That is, one capacitor 8 is arranged for each processing target group 4.

[0063] For example, in one (left) continuous circuit 9, a capacitor 8 (first capacitor 8a) is connected between the connecting wiring 6 corresponding to the first cell 2a and the connecting wiring 6 corresponding to the second cell 2b. Similarly, a capacitor 8 (third capacitor 8c) is connected between the connecting wiring 6 corresponding to the third cell 2c and the connecting wiring 6 corresponding to the fourth cell 2d.

[0064] In the other (right) continuous circuit 9, a capacitor 8 (second capacitor 8b) is connected between the connecting wiring 6 corresponding to the second cell 2b and the connecting wiring 6 corresponding to the third cell 2c. Similarly, a capacitor 8 (fourth capacitor 8d) is connected between the connecting wiring 6 corresponding to the fourth cell 2d and the connecting wiring 6 corresponding to the fifth cell 2e.

[0065] In addition to the first circuit 10, the cell balancing apparatus 1 also has a cell voltage comparing means 11 and a control means 12. Figure 4 shows a block diagram illustrating the relationship between these main components of the cell balancing apparatus 1.

[0066] The cell voltage comparison means 11 is a means capable of comparing the voltages of each of the cells 2. For example, in a conventional controller, a voltage monitoring device is normally installed to monitor the voltage of each cell 2 for abnormalities. The voltage monitoring device is equipped with a mechanism for detecting the voltage of each of the cells 2 with high accuracy. Therefore, by utilizing this mechanism, it is possible to obtain the voltage (absolute value) of each of the cells 2 and compare the magnitude of the voltage of each of the cells 2. In this case, the cell voltage comparison means 11 can be configured using an existing controller.

[0067] If there is no voltage monitoring device, it is not necessary to detect the voltage of each cell 2. The cell voltage comparison means 11 only needs to compare the relative magnitude relationship of the voltages of the cells 2. Therefore, a highly accurate voltage detection mechanism is not necessary, and the cell voltage comparison means 11 can be configured with a simple circuit. For example, the cell voltage comparison means 11 may be a comparator.

[0068] That is, most of the control means 12 can be configured with a predetermined circuit including the above-mentioned first circuit 10 and cell voltage comparing means 11 using resistors, comparators, capacitors, etc. Therefore, if the circuit is built into a chip, the cell balancing device 1 can be made smaller and can be easily incorporated into a controller. The control means 12 is configured to control each of the switches 7 with a predetermined operation based on the detection value of the cell voltage comparing means 11.

[0069] (Example of control by control means) Next, with reference to Figs. 5 to 7, a specific example of control executed by the control means 12 in relation to the above-mentioned first circuit 10 to equalize the states of charge of the cells 2 of the battery 3 will be described.

[0070] Fig. 5 shows the first circuit 10. In Fig. 5, for the sake of convenience, the cell 2, the switch 7, the capacitor 8, and the processing target group 4 are each given a reference symbol for distinguishing them from each other instead of a numerical reference symbol. Fig. 6 is a flow chart showing the flow of main processes executed by the control means 12. Fig. 7 is a diagram for explaining the charge state of each cell corresponding to the main steps of the process.

[0071] 7(a) shows the initial state of charge of each cell. In this control example, the initial state of charge of each cell is: first cell V1>fourth cell V4>third cell V3>second cell V2.

[0072] As shown in Fig. 6, first, the control means 12 turns on the switches S1, S4, S5, S8, S9, and S12 (step S1). As a result, in the first processing group G1, the first cell V1 and the second cell V2 are connected to the first capacitor C1 via the switches S1 and S4 (corresponding to both ends of the first processing group G1). In the second processing group G2, the second cell V2 and the third cell V3 are connected to the second capacitor C2 via the switches S5 and S8. In the third processing group G3, the third cell V3 and the fourth cell V4 are connected to the third capacitor C3 via the switches S9 and S12.

[0073] As a result, charges are transferred from the first cell V1 and the second cell V2 to the first capacitor C1, and the first capacitor C1 is charged. Similarly, charges are transferred from the second cell V2 and the third cell V3 to the second capacitor C2, and the second capacitor C2 is charged. Charges are transferred from the third cell V3 and the fourth cell V4 to the third capacitor C3, and the third capacitor C3 is charged. As a result, as shown by the arrows in FIG. 7(a), the charge amount of each cell decreases according to its discharge state.

[0074] At this time, as described above, the total voltage of the two cells in each processing group is applied to the capacitor. Therefore, regardless of the charge state of the cell, the current flowing through each capacitor is maintained at a large state, so that the charging and discharging converges in a short time. In consideration of the time required for the convergence, the control means 12 has a predetermined capacitor charging time tj (e.g., 50 μs) set to be longer than that time. The control means 12 judges whether the capacitor charging time tj has elapsed (step S2).

[0075] Then, when it is determined that the capacitor charging time tj has elapsed, the control means 12 compares the magnitude relationship of the voltages of the first cell V1 and the second cell V2 based on information from the cell voltage comparison means 11 (step S3). As a result, if the voltage of the first cell V1 is higher than that of the second cell V2 (the first cell V1 corresponds to the high-voltage cell, and the second cell V2 corresponds to the low-voltage cell, and so on below), the switch S2 and the switch S4 are turned ON (step S4) to connect the first capacitor C1 and the second cell V2. If the voltage of the second cell V2 is higher than that of the first cell V1, the switch S1 and the switch S3 are turned ON (step S5) to connect the first capacitor C1 and the first cell V1.

[0076] Next, the control means 12 similarly compares the magnitude relationship of the voltages of the second cell V2 and the third cell V3 (step S6). If the result shows that the voltage of the second cell V2 is greater than that of the third cell V3, the control means 12 turns on the switches S6 and S8 (step S7) to connect the second capacitor C2 to the third cell V3. If the voltage of the third cell V3 is greater than that of the second cell V2, the control means 12 turns on the switches S5 and S7 (step S8) to connect the second capacitor C2 to the second cell V2.

[0077] Next, the control means 12 similarly compares the magnitude relationship of the voltages of the third cell V3 and the fourth cell V4 (step S9). If the result shows that the voltage of the third cell V3 is greater than that of the fourth cell V4, the switch S10 and the switch S12 are turned ON (step S10) to connect the third capacitor C3 to the fourth cell V4. If the voltage of the fourth cell V4 is greater than that of the third cell V3, the switch S9 and the switch S11 are turned ON (step S11) to connect the third capacitor C3 to the third cell V3.

[0078] In this control example, as shown in (b) of Fig. 7, since the voltage of the first cell V1 is higher than that of the second cell V2, the first capacitor C1 and the second cell V2 are connected (step S4). As a result, as shown by the arrow in (b) of Fig. 7, charge is transferred from the first capacitor C1 to the second cell V2, and the second cell V2 is charged.

[0079] In this case, the cell with the relatively low voltage corresponds to the “cell to be processed.” Therefore, in this case, the second cell V2 corresponds to the cell to be processed.

[0080] Similarly, as shown in Fig. 7(c), since the voltage of the second cell V2 is greater than that of the third cell V3, the second capacitor C2 and the third cell V3 (corresponding to the cell to be processed) are connected (step S7). As a result, as shown by the arrow in Fig. 7(c), charge is transferred from the second capacitor C2 to the third cell V3, and the third cell V3 is charged.

[0081] Furthermore, as shown in (d) of Fig. 7, since the voltage of the fourth cell V4 is greater than that of the third cell V3, the third capacitor C3 and the third cell V3 (corresponding to the cell to be processed) are connected (step S11). As a result, as shown by the arrow in (d) of Fig. 7, charge is transferred from the third capacitor C3 to the third cell V3, and the third cell V3 is charged.

[0082] In consideration of the time required for the discharge of the capacitor to converge, a predetermined capacitor discharge time th (e.g., 50 μs) longer than the time is set in the control means 12. The control means 12 determines whether the capacitor discharge time th has elapsed (step S12).

[0083] Then, when it is determined that the capacitor discharge time th has elapsed, the control means 12 determines whether the magnitude relationship between the voltages of the first cell V1 and the second cell V2 has been reversed (step S13). For example, in this control example, since the voltage of the first cell V1 before processing is higher than that of the second cell V2, it is determined whether the voltage of the second cell V2 has become equal to or higher than the voltage of the first cell V1 (essentially, this corresponds to determining whether the two voltages have been substantially equalized).

[0084] As a result, when it is determined that the magnitude relationship between the voltages of the first cell V1 and the second cell V2 has been inverted, the control means 12 further determines whether or not the magnitude relationship between the voltages of the second cell V2 and the third cell V3 has been inverted (step S14). For example, in this control example, since the voltage of the third cell V3 before processing is higher than that of the second cell V2, it is determined whether or not the voltage of the second cell V2 has become equal to or higher than the voltage of the third cell V3.

[0085] As a result, when it is determined that the magnitude relationship between the voltages of the second cell V2 and the third cell V3 has been inverted, the control means 12 further determines whether or not the magnitude relationship between the voltages of the third cell V3 and the fourth cell V4 has been inverted (step S15). For example, in this control example, since the voltage of the fourth cell V4 before processing is higher than that of the third cell V3, it is determined whether or not the voltage of the third cell V3 has become equal to or higher than the voltage of the fourth cell V4.

[0086] If it is determined that the voltage relationship between the first cell V1 and the second cell V2 has not been inverted (No in step S13), if it is determined that the voltage relationship between the second cell V2 and the third cell V3 has not been inverted (No in step S14), or if it is determined that the voltage relationship between the third cell V3 and the fourth cell V4 has not been inverted (No in step S15), the process returns to step S1 and the series of processes are repeated. That is, the series of processes are repeated until the cell voltage relationship is inverted in all groups to be processed.

[0087] In this control example, the magnitude relationship of the cell voltages is inverted in the second processing target group G2, but the magnitude relationship of the cell voltages is not inverted in the other processing target groups, so the processing is executed again from step S1. Specifically, as shown in FIG. 7(e), the processing is executed starting from the capacitor charging processing.

[0088] At this time, since each group to be processed includes some overlapping cells, the states of charge of the first cell V1 to the fourth cell V4 are more uniform than initially. Therefore, by repeating this process, the states of charge of the first cell V1 to the fourth cell V4 are uniformed. In this way, by repeating a series of processes until the magnitude relationship of the cell voltages is reversed in all groups to be processed of the battery 3, the states of charge of all the cells constituting the battery 3 can be uniformed in a short time.

[0089] It should be noted that steps S1 and S2 here correspond to the capacitor charging step in the cell balancing method, and also correspond to the capacitor charging process of the cell balancing adjustment device 1. Steps S3 to S12 correspond to the capacitor discharging step in the cell balancing method, and also correspond to the capacitor discharging process of the cell balancing adjustment device 1.

[0090] Furthermore, the order of steps S3 to S5, S6 to S8, and S9 to S11 is not limited to this and may be any order. Similarly, the order of steps S13, S14, and S15 is not limited to this and may be any order.

[0091] It is preferable that steps S1 and S2 (capacitor charging step or capacitor charging process) and steps S3 to S12 (capacitor discharging step or capacitor discharging process) are alternately repeated at a cycle of 1 kHz or more and 1 MHz or less.

[0092] The larger the capacitor, the fewer the number of times it needs to be charged and discharged, but the larger the capacitor will be and the higher the material costs will be. Therefore, making the capacitor smaller and increasing the number of times it needs to be charged and discharged is advantageous in terms of cost and size. However, increasing the number of times it needs to be charged and discharged generates harmonic noise.

[0093] As a result of the inventors' investigations, they found that it is most preferable to alternately repeat the charge and discharge processes at a cycle of 1 kHz to 1 MHz. Therefore, by alternately repeating the charge and discharge processes at the above-mentioned cycle, it is possible to make the cell balancing device 1 compact and low-cost while suppressing harmonic noise.

[0094] <Effects of the disclosed technology> A verification test was conducted to verify the effect of the improved SW method. In the verification test, a capacitor was used as a cell (alternative cell) instead of a lithium-ion battery, and six of the alternative cells were connected together to form a simulated battery. An experimental device equipped with the first circuit 10 described above was installed in the simulated battery, and the same control as in the above-mentioned control example was performed.

[0095] The results of the verification test are shown in Figure 8. The lower graph in Figure 8 shows the verification results of the improved SW method (Example). The upper graph in Figure 8 shows the results when passive cell balancing was performed on the same experimental device (Comparative Example). The vertical axis represents cell voltage (V) and the horizontal axis represents elapsed time (ms). The magnitude relationship of the voltages of cells V1 to V6 before processing is V1>V2>V3>V4>V5>V6.

[0096] As shown in the upper diagram of Figure 8, in passive cell balancing, the cells V1 to V5 are discharged according to the voltage of the cell V6, which has the lowest voltage. As a result, a loss of 54 mW occurred in this test, but the charge state of each cell was equalized in about 500 ms.

[0097] In contrast, as shown in the lower diagram of Figure 8, the improved SW method is based on active cell balancing, so each cell is charged and discharged so that it converges to an approximate average value. As a result, a loss of 2mW occurred in this test, and the charge state of each cell was equalized in about 500ms. Note that this 500ms is the value for a replacement cell with a very small capacity, and in the case of an actual cell, it would take, for example, about 5 hours.

[0098] In this way, by adopting the improved SW method, the process can be completed in a short time equivalent to that of passive cell balancing, and energy loss can be significantly reduced.

[0099] <Second embodiment of the disclosed technique> 9 shows a flying capacitor ACB circuit (second circuit 20) to which the disclosed technology can be applied. The second circuit 20 differs from the first circuit 10 in that a processing target group is composed of three cells 2.

[0100] Specifically, the first processing target group G1 is made up of the first cell V1 to the third cell V3, the second processing target group G2 is made up of the third cell V3 to the fifth cell V5, and the third processing target group G3 is made up of the fifth cell V5 to the seventh cell V7.

[0101] The second circuit 20 is also composed of a plurality of branch wirings 5, a plurality of connecting wirings 6, a plurality of switches 7, a plurality of capacitors 8, etc. As shown in Fig. 9, these components are conceptually arranged so as to extend along the series of cells 2 (hereinafter, for convenience, the second circuit 20 will be described based on Fig. 9).

[0102] The configurations of the branch wiring 5 and the switch 7 of the second circuit 20 are the same as those of the first circuit 10. The configurations of the connecting wiring 6 and the capacitor 8 of the second circuit 20 are different from those of the first circuit 10. That is, the connecting wiring 6 of the second circuit 20 is composed of a first connecting wiring 6a and a second connecting wiring 6b, and the capacitor 8 is connected between the first connecting wiring 6a and the second connecting wiring 6b.

[0103] Specifically, when looking at a certain processing group 4, of the two switches 7, 7 connected to the positive or negative side of each cell 2 included in that processing group 4 via branch wiring 5, one of them is connected to the first connecting wiring 6a, and the other is connected to the second connecting wiring 6b.

[0104] For example, in the first processing target group G1, the first, third, fifth, and seventh switches S1, S3, S5, and S7 are connected to the first connecting wire 6a, and the second, fourth, sixth, and eighth switches S2, S4, S6, and S8 are connected to the second connecting wire 6b. A first capacitor C1 is connected between the first connecting wire 6a and the second connecting wire 6b.

[0105] The cell balancing device 1 in the second embodiment also has a second cell voltage comparing means 21 and a second control means 22, in addition to the second circuit 20. The configuration of the cell balancing device 1 is similar to that of the first embodiment, and only the cell voltage comparing means 11 and control means 12 in Fig. 3 are replaced by the second cell voltage comparing means 21 and second control means 22, so their reference numerals are added in parentheses in Fig. 3 and their explanations are omitted.

[0106] The second control means 22 also consists of a predetermined circuit, most of which is made up of resistors, comparators, capacitors, etc. built into the chip, and includes the above-mentioned second circuit 20 and second cell voltage comparison means 21. The second control means 22 is configured to control each of the switches 7 with a predetermined operation based on the detection value of the second cell voltage comparison means 21.

[0107] (Example of control by the second control means) Next, with reference to Figures 9 to 11B, a specific control example executed by the second control means 22 in order to equalize the states of charge of the cells 2 of the battery 3 will be described with reference to the above-mentioned second circuit 20. Figure 9 shows the second circuit 20 to which the description will be referred.

[0108] Figures 10A and 10B are flow charts showing the flow of main processes executed by the second control means 22. Figures 11A and 11B are diagrams for explaining the state of the second circuit 20 and the state of charge of each cell corresponding to the main steps of the processes for the first processing target group G1.

[0109] 11A(a) shows the initial state of charge of each cell in the first treatment target group G1. In this control example, the first cell V1>the second cell V2>the third cell V3.

[0110] As shown in Fig. 10A, first, the second control means 22 turns on the switches S1, S8, S9, S16, S17, and S24 (step S31). As a result, in the first processing target group G1, the first cell V1, the second cell V2, and the third cell V3 are connected to the first capacitor C1 via the switches S1 and S8. In the second processing target group G2, the third cell V3, the fourth cell V4, and the fifth cell V5 are connected to the second capacitor C2 via the switches S9 and S16. In the third processing target group G3, the fifth cell V5, the sixth cell V6, and the seventh cell V7 are connected to the third capacitor C3 via the switches S17 and S24.

[0111] As a result, in the first group G1 to be processed, a current Ic flows as shown by the dashed arrow in the left diagram of (a) of Fig. 11A, and charge is transferred from the first cell V1 to the third cell V3 to the first capacitor C1, and the first capacitor C1 is charged. Similarly, in the second group G2 to be processed, charge is transferred from the third cell V3 to the fifth cell V5 to the second capacitor C2, and the second capacitor C2 is charged. Similarly, in the third group G3 to be processed, charge is transferred from the fifth cell V5 to the seventh cell V7 to the third capacitor C3, and the third capacitor C3 is charged.

[0112] As a result, in the first processing group G1, the charge amount of each cell decreases according to its discharge state, as shown in the right diagram of Fig. 11A(a). Similarly, in the other processing groups, the charge amount of each cell decreases according to its discharge state.

[0113] At this time, the total voltage of the three cells in each processing group is applied to the capacitor. Therefore, regardless of the charge state of the cell, the current Ic flowing through each capacitor is maintained at a large state, so that charging and discharging converges in a short time. In the second control means 22, a predetermined capacitor charging time tj (e.g., 50 μs) that is longer than the time required for the convergence is set in advance, taking into account the time required for the convergence. The second control means 22 determines whether the capacitor charging time tj has elapsed (step S32).

[0114] If it is determined that the capacitor charging time tj has elapsed, the second control means 22 turns off the switches S1, S8, S9, S16, S17, and S24 (step S33). After that, the second control means 22 compares the magnitude relationship of the voltages of the cells included in each processing target group based on the information from the second cell voltage comparison means 21, and extracts the processing target cell.

[0115] In this case, any cell with a relatively low voltage in the group to be treated can be selected as the cell to be treated. However, it is preferable to select the cell with the lowest voltage (low voltage cell) as the cell to be treated. This allows for the most efficient cell balancing.

[0116] For example, in the first processing group G1, the third cell V3 has the lowest voltage, so it is extracted as the processing cell Vmin-a (step S34). Then, as shown in the left diagram of FIG. 11A(b), the switches S5 and S8 are turned ON (step S35) to connect the first capacitor C1 and the third cell V3.

[0117] As a result, a current Ic flows as shown by the dashed arrow in the left diagram of Fig. 11A(b), and charge is transferred from the first capacitor C1 to the third cell V3, charging the third cell V3. As a result, the voltage of the third cell V3 rises as shown in the right diagram of Fig. 11A(b).

[0118] Next, in the second processing target group G2, the cell with the lowest voltage among the third cell V3 to the fifth cell V5 is extracted as the processing target cell Vmin-b, and the switch connecting the processing target cell Vmin-b to the second capacitor C2 is turned ON (steps S36, S37).

[0119] Furthermore, in the third processing target group G3, the cell with the lowest voltage among the fifth cell V5 to the seventh cell V7 is extracted as the processing target cell Vmin-c, and the switch connecting the processing target cell Vmin-c to the third capacitor C3 is turned ON (steps S38, S39).

[0120] In the second control means 22, a predetermined capacitor discharge time th (e.g., 50 μs) longer than the time required for the capacitor discharge to converge is also set in advance, taking into consideration the time required for the capacitor discharge to converge. As shown in Fig. 10B, the second control means 22 determines whether the capacitor discharge time th has elapsed (step S40).

[0121] The second control means 22 is equipped with a function of estimating an average voltage Vavg of the multiple cells included in the processing target group before processing based on information from the second cell voltage comparison means 21, and storing the average voltage Vavg. The second control means 22 then compares the voltage of each cell with the average voltage Vavg so that the voltage of each cell falls within a predetermined range including the average voltage Vavg.

[0122] Specifically, the second control means 22 determines whether the voltages of the first cell V1, the second cell V2, and the third cell V3 in the first processing group G1 have reached their approximate average value Vavg-a (step S41). Similarly, in the second processing group G2, the second control means 22 determines whether the voltages of the third cell V3, the fourth cell V4, and the fifth cell V5 have reached their approximate average value Vavg-b (step S42). Similarly, in the third processing group G3, the second control means 22 determines whether the voltages of the fifth cell V5, the sixth cell V6, and the seventh cell V7 have reached their approximate average value Vavg-c (step S43).

[0123] In this process, it is sufficient to determine that the voltage difference between all cells included in each of the processing target groups is equal to or less than a predetermined value. Therefore, for any two cells included in each of the processing target groups, the determination of whether the magnitude relationship between the cells is reversed as in the control example of the first embodiment may be repeated for all cells, so that the voltage difference between the two cells is equal to or less than a predetermined value for all cells.

[0124] Then, the second control means 22 returns to step S31 and repeats the series of processes unless it is determined that the voltages of the cells included in all the groups to be processed have reached the approximate average value Vavg. That is, the series of processes is repeated until the voltages of the cells included in all the groups to be processed have reached the approximate average value Vavg.

[0125] For example, in the first processing target group G1, the first cell V1 and the second cell V2 are not substantially at Vavg-a as shown in the right diagram of Fig. 11A(b). Therefore, the second control means 22 executes the series of processes again from step S1 (No in step S41).

[0126] Specifically, as shown in the left diagram of Fig. 11B(c), the first cell V1, the second cell V2, and the third cell V3 are connected to the first capacitor C1 via the switches S1 and S8, and the first capacitor C1 is charged. As a result, as shown in the right diagram of Fig. 11B(c), the charge amount of each cell decreases according to its discharge state.

[0127] After the capacitor charging time tj has elapsed, the second control means 22 turns off the switches S1, S8, etc. (step S33) and extracts the cell to be processed. Here, the second cell V2 has the lowest voltage, so the second cell V2 is extracted as the cell to be processed Vmin-a (step S34).

[0128] As shown in the left diagram of FIG. 11B(d), the switches S3 and S6 are turned on (step S35) to connect the first capacitor C1 to the second cell V2. This causes the voltage of the second cell V2 to rise, as shown in the right diagram of the same figure. As a result, the charge states of the first cell V1 to the third cell V3 included in the first processing target group G1 become more uniform than they were initially. By repeating this process, the voltages of the first cell V1 to the third cell V3 become approximately Vavg-a.

[0129] Since each group to be processed includes some overlapping cells, the average voltage Vavg of the cells included in each group to be processed eventually converges to a constant value and becomes the same value. Therefore, by repeating this process for all groups to be processed of the battery 3, the state of charge of all the cells constituting the battery 3 can be made uniform in a short time.

[0130] It should be noted that steps S31 and S32 here correspond to the capacitor charging step in the cell balancing method, and also correspond to the capacitor charging process of the cell balancing adjustment device 1. Steps S34 to S40 correspond to the capacitor discharging step in the cell balancing method, and also correspond to the capacitor discharging process of the cell balancing adjustment device 1.

[0131] Furthermore, the order of steps S34 and S35, steps S36 and S37, and steps S38 and S39 is not limited to this and may be any order. Similarly, the order of steps S41, S42, and S43 is not limited to this and may be any order.

[0132] The disclosed technology is not limited to the above-described embodiment, and includes various other configurations. For example, in the above-described embodiment, the processing target group is configured with two or three cells, but the processing target group may be configured with four or more cells. The number of overlapping cells is not limited to one, and may be two or more.

[0133] Also, the series of processes may be continuously and repeatedly executed without being stopped while the battery is being used.

[0134] That is, in the case of the first embodiment described above, after step S12, a series of processes is repeated from step S1, whereas in the case of the second embodiment described above, after step S40, a series of processes is repeated from step S31.

[0135] For example, in the second embodiment, if the charge states of the cells V1 to V3 in the first processing target group G1 before processing are V1: L (low), V2: H (high), and V3: M (medium), the voltages of these cells (V1, V2, V3) will change, for example, as follows: (L, H, M) → (M, H, L) → (L, H, M) → (M, H, L) → (L, M, H) → (H, L, M) → (M, H, L) → (L, M, H)...

[0136] In this way, the cell with the lowest voltage among the cells constituting the processing target group is continuously charged, so that a very small voltage difference can be achieved and a highly accurate and stable cell balance can be maintained. [Explanation of symbols]

[0137] 1 Cell balance adjustment device 2 Cell 4 Processing Group 7. Switch 8 Capacitor 10 1st circuit 11 Cell voltage comparison means 12 Control Means 20 2nd circuit 21 second cell voltage comparison means 22 Second control means

Claims

1. A cell balancing method for equalizing the states of charge of a secondary battery having a plurality of cells connected in series, comprising: all of the cells constituting the secondary battery are divided into a plurality of processing target groups each including at least two or more consecutive cells, with some of the cells overlapping between adjacent processing target groups; a capacitor charging step of charging a capacitor by connecting the capacitor to both ends of the processing target group; a capacitor discharging step of connecting a predetermined processing target cell included in the processing target group to the capacitor and discharging the charge of the capacitor to charge the processing target cell; 13. A cell balancing method comprising:

2. The cell balancing method according to claim 1 , The cell balancing method according to claim 1, wherein the target cell is a low-voltage cell having the lowest voltage among the target cells.

3. The cell balancing method according to claim 2, The processing group is composed of two of the cells, A cell balancing method comprising: repeating the capacitor charging step and the capacitor discharging step until a voltage magnitude relationship between a low-voltage side cell corresponding to the low-voltage cell and a high-voltage side cell corresponding to the low-voltage cell is reversed.

4. The cell balancing method according to claim 1 , A cell balancing method comprising: repeating the capacitor charging step and the capacitor discharging step until a difference in voltage between the cells included in each of the processing target groups becomes equal to or less than a predetermined value.

5. The cell balancing method according to claim 1 , The cell balancing method according to claim 1, wherein the capacitor charging step and the capacitor discharging step are continuously repeated while the secondary battery is in use.

6. The cell balancing method according to any one of claims 3 to 5, The cell balance adjustment method, wherein the capacitor charging step and the capacitor discharging step are alternately repeated at a cycle of 1 kHz to 1 MHz.

7. A cell balancing adjustment device for equalizing the states of charge of a secondary battery configured by connecting a plurality of cells in series, comprising: all of the cells constituting the secondary battery are divided into a plurality of processing target groups each including at least two or more consecutive cells, with some of the cells overlapping between adjacent processing target groups; A plurality of capacitors each arranged for each of the processing target groups and connected to a positive electrode side and a negative electrode side of each of the cells via a switch; A cell voltage comparison means for comparing the voltages of the cells; a control means for controlling each of the switches based on a detection value of the cell voltage comparison means; having The control means a capacitor charging process for charging the capacitor by connecting the capacitor to both ends of each of the processing target groups; a capacitor discharge process for connecting a predetermined processing target cell included in each of the processing target groups to the capacitor and discharging the charge of the capacitor to charge the processing target cell; A cell balancing adjustment device comprising:

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