Cell balance adjustment method and cell balance adjustment device

Abstract

To put an active system cell balance adjusting technique to practical use by eliminating its defects.SOLUTION: There is provided a cell balance adjustment method of a battery unit 3 mounted on a vehicle 1 as a power supply for traveling. When the active cell balance adjustment control is executed and the state of charge of the cell group 20 is not uniform, the cell balance adjustment control is executed independently of the state of use and non-use of the vehicle 1.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The disclosed technology relates to a cell balancing method and a cell balancing device for an in-vehicle battery unit. [Background technology]

[0002] In recent years, hybrid vehicles and electric vehicles, which have become increasingly popular, are equipped with high-voltage (e.g., 300V) battery units as a power source for driving. A battery unit is generally made up of a large number of unit cells (cells) connected in series, each cell being made of a lithium-ion battery or other battery with a voltage of several volts.

[0003] It should be noted that the term "cell" in this specification is not limited to a single battery (cell), but also includes a cell in which a plurality of cells are connected in parallel.

[0004] Even if the battery units are charged and discharged in the same way, the state of charge (SOC) of each cell will not be the same due to individual differences, which means that differences will occur in the voltage of each cell.

[0005] If the battery is charged with a voltage difference between each cell, when the cell with the highest voltage reaches full charge (SOC 100%), charging must be stopped to prevent that cell from overcharging. 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 battery's original capacity.

[0006] Therefore, technology to equalize the charge state of the cells (cell balancing technology) has been put into practical use so that the battery's original power can be used. This technology is generally divided into passive and active methods, and the passive method is the most widely used.

[0007] In the passive method, in order to make each cell's state of charge the same, the charge amount of the other cells is adjusted to match the charge amount (minimum charge amount) of the cell with the least charge amount. In other words, any power exceeding the minimum charge amount of the other cells is discharged and discarded. In this way, the charge amount of all cells is adjusted to the minimum charge amount, and the charge amount of all cells is controlled so that they are fully charged with an equalized state of charge.

[0008] The passive method has the advantage of simple circuitry and control, and low cost. This has led to the passive method being put into practical use. However, it has the disadvantage of high energy loss because the power is discarded. The passive method also has the disadvantage that it assumes that the cell capacity of each cell is the same, and it cannot resolve differences in the state of charge due to variations in cell capacity.

[0009] In contrast, the active system transfers power from highly charged cells to less charged cells, thereby equalizing the state of charge of all cells. Therefore, the active system has less energy loss.

[0010] On the other hand, active systems tend to have complex circuits and controls. Active systems typically require a circuit to connect cells, and by switching the connection state between cells with a voltage difference, a predetermined regulated current flows. Therefore, if the number of cells is large, the number of electronic components increases accordingly.

[0011] Furthermore, when the regulated current is large, the electronic components must have corresponding performance, which in turn increases the component size. Therefore, the active method has the drawback of being expensive and large, and has not yet been put to practical use.

[0012] An example of an active cell balancing technique is disclosed in Patent Document 1. This technique aims to overcome the above-mentioned drawbacks of the active method and to quickly equalize the cell voltages. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-223058 Summary of the Invention [Problem to be solved by the invention]

[0014] In the technology of Patent Document 1, the current that flows when equalizing the voltage between cells (cell balancing current) is set to approximately 10 A to 50 A (paragraph 0093 of the specification). The size of electronic components that can handle 50 A is large. If such electronic components are mounted on a board in units of the number of cells, the cost, size, weight, etc. will be excessive. Therefore, it is difficult to put the technology of Patent Document 1 into practical use, and there is still room for improvement.

[0015] Therefore, this specification discloses a technology that not only can eliminate the drawbacks of the active cell balance adjustment technology, but also enables its practical application. [Means for solving the problem]

[0016] One of the techniques disclosed relates to a cell balance adjustment method for a battery unit that includes a cell group consisting of a plurality of cells connected in series and is mounted on a vehicle as a power source for driving the vehicle.

[0017] The cell balancing method transfers power by passing a predetermined adjustment current between predetermined cells having a voltage difference, and performs active cell balancing control to equalize the state of charge of the cell group, and when the state of charge of the cell group is uneven, performs the cell balancing control independently of whether the vehicle is in use or not.

[0018] According to this cell balancing method, when the charge states of the cells are uneven, active cell balancing control is performed independently of whether the vehicle is in use or not, that is, not only when the vehicle is keyed in and powered on, but also when the vehicle is keyed off and powered off (such as when parked).

[0019] The inventors of the present invention have noticed that in actual use, it is extremely rare for a battery to go from fully charged to completely discharged through continuous discharge. Taking this into consideration, it is not necessary to perform cell balance adjustment control in accordance with the charging and discharging of the battery unit as in the past, and it is sufficient to equalize the charge states of all cells just before the battery unit reaches a fully discharged state.

[0020] Based on this concept, unlike conventional methods, the adjustment current value can be set as small as that of the passive method, allowing the use of small electronic components. This eliminates the drawbacks of active cell balancing technology and makes it possible to put it into practical use. A compact, high-performance in-vehicle cell balancing device can be realized at low cost.

[0021] When the battery unit is in a state where it can be charged or discharged, the execution of the cell balance adjustment control may be started.

[0022] Although cell balance adjustment control may be performed constantly, in that case power is still required even when the charge states of the cells are equalized, resulting in unnecessary power consumption. In contrast, this method can reduce unnecessary power consumption.

[0023] When the states of charge of the cell groups become uniform while the vehicle is not in use, the execution of the cell balance adjustment control may be stopped.

[0024] In this way, cell balance adjustment control is performed for a necessary and sufficient period, thereby making it possible to reduce unnecessary power consumption.

[0025] It is also possible to calculate an average charge / discharge current value, which is the time average value of the charge / discharge current that flows to charge or discharge the battery unit during a continuous predetermined period, including both periods when the vehicle is in use and when it is not in use, until the charge state of the battery unit goes from the upper limit to the lower limit, estimate a maximum width of variation in cell capacity that can occur in the cell group, calculate a reference adjustment current value that serves as a reference for the adjustment current based on the maximum width of variation in cell capacity and the average charge / discharge current value, and set a range of the adjustment current that is allowable in the cell balance adjustment control based on the reference adjustment current value.

[0026] According to this method, it is possible to appropriately and specifically set the value of the small adjustment current required to equalize the state of charge of all the cells just before the battery unit reaches a fully discharged state.

[0027] If the predetermined period further includes a period during which the battery unit is charged by an external power source, the average charge / discharge current value may be calculated using absolute values ​​of currents that flow both during charging and discharging.

[0028] According to this method, it is possible to set the range of the adjustment current required to correct unevenness in the state of charge of the cells that may occur when the battery unit is charged by an external power source.

[0029] The range of the regulated current may be set to be equal to or greater than 40 mA and equal to or less than 1200 mA.

[0030] If the adjustment current is set within this range, an active circuit can be configured using electronic components with performance comparable to that of a passive circuit.

[0031] The charging current may be reduced to a current value equal to or less than the adjusted current when the state of charge of the battery unit reaches an upper limit due to charging or immediately before that.

[0032] This allows the cells to be fully charged even if there is variation in cell capacity among the cells.

[0033] The cell group may be configured using any cells without adjusting the width of variations in cell capacitance during manufacturing.

[0034] This makes it possible to omit the quality control process that occurs due to variations in cell manufacturing, thereby reducing costs and man-hours.

[0035] Another disclosed technique relates to a cell balancing device for a battery unit that includes a cell group formed by connecting a plurality of cells in series and is mounted on a vehicle together with the battery unit as a power source for driving the vehicle.

[0036] The cell balancing device includes an active cell balancing unit that transfers power by flowing a predetermined adjustment current between predetermined cells having a voltage difference to equalize the state of charge of the cell group, and a control unit that controls the cell balancing unit. When the state of charge of the cell group is uneven, the control unit operates the cell balancing unit independently of whether the vehicle is in use or not.

[0037] As described above, the cell balancing device can overcome the drawbacks of the active cell balancing technology.

[0038] The adjustment current may be set in a range of 40 mA to 1200 mA, and the cell balance adjustment unit may be configured with electronic components that correspond to the range of the adjustment current.

[0039] This makes it possible to construct an active circuit using electronic components with performance comparable to that of a passive circuit.

[0040] The entire cell group may be 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, and the cell balance adjustment unit may be arranged for each processing target group and may include a plurality of capacitors connected via switches to the positive and negative sides of each of the cells, and cell voltage comparison means capable of comparing the voltages of each of the cells, and the control unit may control each of the switches based on the detection value of the cell voltage comparison means to perform a capacitor charging process in which the capacitor is connected to both ends of each of the processing target groups to charge the capacitor, 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.

[0041] This configuration allows the use of a flying capacitor system, which is particularly advantageous in terms of cost and size among active systems, and therefore allows the device to be made smaller at lower cost. [Effects of the Invention]

[0042] The disclosed technology can overcome the drawbacks of active cell balancing technology and make it possible to put it into practical use, thereby enabling the realization of a compact, high-performance in-vehicle cell balancing device at low cost. [Brief explanation of the drawings]

[0043] [Figure 1] FIG. 1 is a schematic diagram illustrating an application example of the disclosed technology. [Figure 2A] FIG. 2 is an explanatory diagram of a cell balance adjustment control method (passive method). [Figure 2B] FIG. 2 is an explanatory diagram of a cell balance adjustment control method (active method). [Figure 3A] FIG. 1 is an explanatory diagram of a conventional active system. [Figure 3B] FIG. 10 is an explanatory diagram of voltage changes when the cell capacity is different. [Figure 4] FIG. 1 is an explanatory diagram of a disclosed technology. [Figure 5] FIG. 10 is an explanatory diagram of a technique for achieving full charging. [Figure 6] 1 is an explanatory diagram of a conventional problem related to variations in cell capacitance during manufacturing and the disclosed technology; [Figure 7A] FIG. 10 is an explanatory diagram of a conventional switch control method (comparison example). [Figure 7B] FIG. 10 is an explanatory diagram of an improved switch control method. [Figure 8] FIG. [Figure 9] FIG. 10 is a circuit diagram for reference in explaining a control example. [Figure 10] 10 is a flowchart of an example of control. [Figure 11] This is a diagram corresponding to the main steps in Figure 10. [Figure 12] FIG. 10 is a diagram for explaining the effect of the improved circuit. DETAILED DESCRIPTION OF THE INVENTION

[0044] The disclosed technology will be described below, however, the following description is merely exemplary in nature.

[0045] <In-vehicle battery unit> An application example of the disclosed technology (cell balancing method and cell balancing device) is shown in Figure 1. The disclosed technology is targeted at battery units mounted on vehicles that run on electric power, such as electric vehicles and hybrid vehicles.

[0046] The vehicle 1 shown in Fig. 1 is an electric vehicle. The vehicle 1 is equipped with a high-voltage battery unit 3 as a power source for driving the vehicle 1. The battery unit 3 is connected to a motor 1a via an inverter and a converter (not shown). The motor 1a is driven by the power supplied from the battery unit 3, and the vehicle 1 runs on this power.

[0047] The vehicle 1 is equipped with a charge / discharge control device (so-called OBC) 1b. The charge / discharge control device 1b has a charging outlet 1c provided on a panel of the vehicle 1. The battery unit 3 can be charged by connecting a plug 100 of an external power source to this outlet 1c.

[0048] The battery unit 3 includes, inside a battery case, a plurality of modules 30, a cell balance adjustment unit 31, and a battery management unit 32. The battery management unit 32 constitutes a "control unit" of the technology disclosed herein, and the cell balance adjustment unit 31 and the battery management unit 32 constitute a "cell balance adjustment device" of the technology disclosed herein.

[0049] Each module 30 has a plurality of cells 2 connected in series. That is, a single module 30 is made up of a plurality of (for example, several to several tens of) cells 2 connected in series. The illustrated cells 2 are single cells with a voltage of several volts, such as lithium ion batteries.

[0050] These multiple modules 30 are connected in series so as to be able to output a high voltage. In this way, the battery unit 3 includes a cell group 20 configured by connecting a large number (for example, about 100) of cells 2 in series. Note that the modules 30 are not essential. The battery unit 3 may also be configured by directly connecting a large number of cells 2 in series.

[0051] The positive and negative ends of the cell group 20 are connected to terminals 33 of the battery case. A pair of input / output cables 34 for charging or discharging the battery unit 3 are connected to the terminals 33.

[0052] The battery management unit 32 is a system that ensures the proper functioning of the battery unit 3. The battery management unit 32 is electrically connected to the charge / discharge control device 1b, and cooperates with an external power source to control the adjustment of the charging current, the start and stop of charging, etc. The battery management unit 32 also performs control such as permitting or prohibiting charging / discharging of the battery unit 3 based on the temperature and state of charge (SOC) of the battery unit 3.

[0053] The cell balance adjustment unit 31 is electrically connected to each cell 2 of each module 30, and performs active cell balance adjustment control as described below. The cell balance adjustment unit 31 includes a cell voltage monitoring unit that detects and monitors the voltage of each cell 2. The cell voltage monitoring unit constitutes the cell voltage comparison means 11, which will be described later.

[0054] The battery management unit 32 is also electrically connected to the cell balance adjustment unit 31, and controls the operation of the cell balance adjustment unit 31. For example, the battery management unit 32 issues instructions to start and stop the execution of cell balance adjustment control.

[0055] <Cell balance adjustment control method> Two cell balancing control methods (passive and active) for equalizing the state of charge of cells 2 are outlined below. Figures 2A and 2B show simplified diagrams of a cell group 20. As mentioned above, the cell group 20 is made up of a large number of cells 2, but here the cell group 20 is represented by two cells C1 and C2.

[0056] The rectangles for cells C1 and C2 represent the cell capacity, and the dots represent the state of charge (SOC) of cells C1 and C2. Cells C1 and C2 have the same cell capacity. Cell C1 has a higher charge amount and voltage than cell C2.

[0057] As shown in the upper diagram of Figure 2A, in the passive method, the charge amount of the other cells (C1) in the cell group 20 is adjusted to match the cell (C2) with the lowest state of charge. That is, the other cell C1 is connected to a discharge circuit DCC including a resistor and discharged until it reaches the charge amount of C2. This makes it possible to equalize the state of charge of all cells 2 even if the state of charge of cells 2 becomes uneven during charging and discharging. By equalizing the state of charge of all cells 2 and charging them, the battery unit 3 can be fully charged (SOC = 100%: upper limit of state of charge).

[0058] In the passive method, it is sufficient to discharge each cell 2 individually to equalize the charge amount, so a discharge current of several tens to several hundred mA is sufficient. Since the voltage of each cell 2 is only several volts, the resistance of the discharge circuit DCC can also be small. The semiconductor switch of the discharge circuit DCC can also be of a correspondingly low power type.

[0059] Therefore, the passive method has the advantage that the circuitry and control required to perform cell balancing adjustment control are simple and low cost. This has led to the passive method being put into practical use. However, it has the disadvantage of high energy loss due to the waste of power.

[0060] In addition, the passive method selects the cell with the lowest state of charge from all the cells and discharges the other cells accordingly, which is a disadvantage in that the voltage of each cell must be monitored with high accuracy.

[0061] Furthermore, in the case of the passive system, there is a disadvantage that the decrease in the amount of power of the battery unit 3 caused by the difference in cell capacity cannot be improved.

[0062] For example, as shown in the lower diagram of Figure 2A, suppose the cell capacity of cell C2 is 10% lower than that of cell C1. Even in this case, by performing passive cell balance adjustment control and adjusting the state of charge of all cells 2 during the charging process, the battery unit 3 can be fully charged. In other words, when approaching full charge, the cell with the smallest cell capacity can be discharged to adjust the state of charge.

[0063] On the other hand, when the battery unit 3 discharges as the vehicle 1 travels, the cell C2 with the lowest voltage is the first to reach the lower discharge limit voltage and enter a fully discharged state (SOC = 0%: lower limit of the state of charge). At this time, cell C1 has 10% power remaining and cannot discharge any more. The power cannot be used up. Therefore, the decrease in the amount of power in the battery unit 3 caused by the difference in cell capacity cannot be improved.

[0064] On the other hand, in the active system, as shown in the upper diagram of Figure 2B, a predetermined adjustment current is passed between predetermined cells 2 of a cell group 20 that have a voltage difference, thereby transferring power and equalizing the state of charge of the cell group 20. That is, by passing a predetermined adjustment current between cells C1 and C2, power is transferred from cell C1, which has more power, to cell C2, which has less power. In this way, the states of charge of these cells C1 and C2 are equalized.

[0065] Therefore, with the active method, the state of charge of the cell group 20 can be equalized with little energy loss. Even if the state of charge of the cells 2 becomes uneven during charging or discharging, the state of charge of all the cells 2 can be equalized, and the battery unit 3 can be fully charged, which is the upper limit of the state of charge.

[0066] Furthermore, in the case of the active method, as shown in the lower diagram of Figure 2B, before the lowest voltage cell C2 reaches the lower discharge limit voltage first, power can be transferred from cell C1 to equalize the state of charge. This allows all cells to reach a fully discharged state without any remaining power. The power can be used up.

[0067] This also applies when there is a difference in cell capacity. Therefore, the active method has the advantage that it is not affected by the difference in cell capacity, unlike the passive method.

[0068] As circuits for performing active cell balancing control, methods such as the half-bridge inductor method, the transformer method, and the capacitor (flying capacitor) method have been proposed (these circuits are well known and therefore will not be described here). Since each circuit requires the implementation of electronic components in accordance with the number of cells, active cell balancing devices have the disadvantages of being more complex in structure than passive methods, as well as being high in cost and excessively large in size.

[0069] (Conventional active cell balancing control) Like the passive method, the active cell balance adjustment control (hereinafter also simply referred to as cell balance adjustment control) proposed so far is also premised on performing cell balance adjustment in accordance with the charging and discharging of the battery unit 3. Therefore, rapid adjustment in real time is required, as in the technology of Patent Document 1.

[0070] As a result, the regulated current also becomes larger, so the electronic components are required to have corresponding performance and become excessively large in size. As a result, the active type is significantly larger in cost and size than the passive type, and has not yet been put to practical use.

[0071] FIG. 3A shows an example of the charge and discharge current of the battery unit 3. The battery unit 3, which is the power source for driving, is required to have a large output, so the discharge current is also large. Charging is also required to be completed in a short time, so the charge current is also large. For example, when charging from an external power source, it is known that it takes about half a day of charging (so-called normal charging) with AC 200V, 15A power to fully charge from a completely discharged state.

[0072] In the case of the illustrated battery unit 3, a maximum discharge current and charge current of approximately 150 A flows due to the power running and regeneration of the vehicle 1 (the sign of the charge / discharge current I is opposite for charging and discharging). In other words, while the vehicle 1 is running, a large current of 100 A or more flows through each cell.

[0073] Assume that there is a variation in cell capacity (BCC) among the cell group 20 constituting the battery unit 3, and the variation width (ΔBCC) is 10%. In FIG. 3A, the cell capacity of cell C1 corresponds to 100%, and the cell capacity of cell C2 corresponds to 90%.

[0074] In this case, as shown in the lower left diagram of Fig. 3A, even if the battery unit 3 is fully charged, a difference in the state of charge occurs between cells C1 and C2 due to the difference in cell capacity. From this state, charging and discharging of the battery unit 3 begins, and cell balance adjustment control is executed accordingly.

[0075] In this case, if cell balance adjustment control is performed without delaying the charging and discharging, the charge states of cells C1 and C2 can be maintained in a balanced state until the cells reach a fully discharged state, as shown in the lower right diagram of Figure 3A, and the power of battery unit 3 can be used up.

[0076] Figure 3B shows an example of the voltage changes of cells C1 and C2 during charging and discharging. Since cells C1 and C2 are connected in series, the value of the charging and discharging current I is the same. Here, the following relationship exists between the voltage and time changes ΔV and Δt of cell 2, the charging and discharging current I, and the cell capacity BCC:

[0077] ΔV=I / BCC*Δt···Equation (1): / indicates division and * indicates multiplication (same below).

[0078] Therefore, if the cell capacity BCC of cell C2 is 90% of the cell capacity BCC of cell C1, the voltage change ΔV2 of cell C2 is 10% greater than the voltage change ΔV1 of cell C1 (ΔV1:ΔV2=1:1.1).

[0079] Therefore, in order to charge both cells C1 and C2 evenly without delay while keeping up with the charging and discharging, it is necessary to reduce the current flowing through cell C2 by 10%. If the maximum charging and discharging current I is 150A, then 10% of that, or 15A, must be reduced from cell C2. In active cell balancing control, this current corresponds to the adjustment current.

[0080] As mentioned above, the charge / discharge current of the battery unit 3 is large, and therefore the regulating current, which is 10% of that current, is also large. Therefore, in the case of an active system, the electronic components that make up the circuit are required to have corresponding performance, and their size is inevitably excessive.

[0081] (Active cell balancing control of the disclosed technology) As described above, in the prior art, it was considered necessary to perform cell balance adjustment control in accordance with the charging and discharging of the battery unit 3 so that the battery unit 3 could use its original amount of power and the charged state of all cells 2 could be made uniform even when continuous charging and discharging were performed both from a fully discharged state to a fully charged state and from a fully charged state to a fully discharged state.

[0082] In contrast, the inventors have noticed that in actual use, it is extremely rare for a battery to go from fully charged to completely discharged through continuous discharge, and that in most cases, the battery is charged (top-up charged) just before it reaches a fully discharged state.

[0083] From this perspective, the inventors have considered that it is not necessary to perform cell balance adjustment control in accordance with the charging and discharging of the battery unit 3, and that it is sufficient if the charge states of all the cells 2 are equalized just before the battery unit 3 reaches a fully discharged state. They have also found that when the charge states of the cell group 20 are uneven, it is sufficient to perform cell balance adjustment control independently of whether the vehicle 1 is in use or not (non-real-time adjustment).

[0084] An example of this non-real-time adjustment is shown in Figure 4. Figure 4 shows the passage of a predetermined period of time from when the battery unit 3 is fully charged (SOC = 100%), and visualizes the daily changes in the charge and discharge current of the battery unit 3. There is variation in cell capacity (ΔBCC = 10%).

[0085] The battery management unit 32 may operate constantly and execute the cell balance adjustment control before the start of the predetermined period. For example, as will be described later, the battery management unit 32 may execute the cell balance adjustment control constantly unless the vehicle 1 is in a dead battery state.

[0086] In this case, however, the cell balance adjustment unit 31 continues to operate even if the charge states of the cells 2 are equalized, resulting in unnecessary power consumption. Therefore, it is preferable to start the execution of cell balance adjustment control when the battery unit 3 is in a state where it can be charged or discharged.

[0087] For example, when the vehicle 1 is keyed in and its power is turned on, there is a high possibility that the vehicle 1 will start running. Therefore, execution of the cell balance adjustment control may be started at that timing. Also, when the plug 100 of the external power supply is connected to the outlet 1c, there is a high possibility that the battery unit 3 will be charged. Therefore, execution of the cell balance adjustment control may be started at that timing.

[0088] Then, when the states of charge of the cell group 20 become uniform while the vehicle 1 is not in use, the execution of the cell balance adjustment control can be stopped. In this way, the cell balance adjustment unit 31 operates for a necessary and sufficient period of time, thereby reducing unnecessary power consumption.

[0089] As an example, the distance that vehicle 1 can travel from a fully charged state is 300 km. In the example of Fig. 4, it is assumed that vehicle 1 travels a total of 300 km on the Nth day, and battery unit 3 reaches a fully discharged state. Therefore, in this case, it is sufficient that the state of charge of all cells 2 is equalized by the time vehicle 1 finishes traveling on the Nth day.

[0090] The predetermined continuous period includes both periods of use (periods during which the vehicle 1 is keyed in and powered on, and the vehicle 1 is running or idling) and periods of non-use (periods during which the vehicle 1 is keyed off and powered off, and the vehicle 1 is parked and completely at rest).

[0091] That is, on the first and second days, vehicle 1 is driven twice intermittently, and this period is a period of use. The rest of the period is a period of non-use, as vehicle 1 is not in use. On the third day, vehicle 1 is not in use, and the entire day is a period of non-use. On the N-1th day and the Nth day, vehicle 1 is used once, and this period includes both a period of use and a period of non-use.

[0092] During such a series of periods in which the vehicle 1 is in use and not in use, the battery management unit 32 controls the cell balance adjustment unit 31 to operate as long as the states of charge of the cell group 20 are uneven. This allows the cell balance adjustment control to be performed independently of whether the vehicle 1 is in use or not.

[0093] This allows the value of the regulating current to be set in a different way than before.

[0094] Specifically, the charge / discharge current average value is calculated, which is the time average value of the charge / discharge current that flows to charge or discharge the battery unit 3 during a continuous predetermined period, including both periods when the vehicle 1 is in use and when it is not in use, until the charge state of the battery unit 3 goes from the upper limit to the lower limit.

[0095] The maximum variation width of the cell capacitance that can occur in the cell group 20 is also estimated. Then, based on the maximum variation width of the cell capacitance and the average charge / discharge current, a reference adjustment current value that serves as a reference for the adjustment current is calculated, and based on the reference adjustment current value, a range of the adjustment current that is allowable in the cell balance adjustment control is set.

[0096] In this method, the charge / discharge current used to set the adjustment current value is not the maximum value during charging / discharging, but the time average value (average charge / discharge current value) of these periods.Then, a reference adjustment current value that serves as the reference for the adjustment current is calculated based on the following relational expression.

[0097] Reference adjustment current value = average charge / discharge current value * maximum variation width of cell capacity (Equation 2).

[0098] During powering and regeneration associated with the running of the vehicle 1, a charge / discharge current flows through the battery unit 3. At this time, the charge / discharge current of the battery unit 3 moves from an upper limit state of charge to a lower limit state of charge as the vehicle 1 runs, so the average value of the charge / discharge current is generally in the discharging direction.

[0099] Therefore, the reference adjustment current value may be calculated from the time average value of the charge / discharge current.

[0100] On the other hand, when the battery unit 3 is charged by an external power source, the state of charge of the cells 2 also becomes uneven. The direction of the current flowing through the battery unit 3 due to charging at this time is the charging direction, which is opposite to the direction of the charge / discharge current flowing through the battery unit 3 when the vehicle 1 is running.

[0101] The current value in the discharging direction and the current value in the charging direction have opposite signs. Therefore, if the calculation includes the period during which the battery unit 3 is charged by an external power source during a specified period, the average value of the charge and discharge currents with different signs will be calculated, and it is possible that the reference adjustment current value will become extremely small.

[0102] In contrast, if the average charge / discharge current is calculated using the absolute value of the current flowing during both charging and discharging, an appropriate reference adjustment current value can be obtained even when external charging and driving states are mixed.

[0103] Here, the maximum variation in cell capacitance is the maximum variation in cell capacitance that can occur in the cell group 20. Differences in cell capacitance include differences in cell capacitance that exist from the beginning due to variations during manufacturing, and differences in cell capacitance that occur later due to quality deterioration over time, etc.

[0104] This is the maximum variation in cell capacity including both of these, and is the maximum variation allowed after the quality assurance period of the battery unit 3 has elapsed. The maximum variation in cell capacity is estimated from experiments, sample data, etc. In the case of lithium-ion batteries, the maximum variation in cell capacity is, for example, about 10% (in the following explanation, this value will be used as the maximum variation in cell capacity).

[0105] As described above, the maximum value of the charge / discharge current of the battery unit 3 reaches 150 A. In contrast, the average value of the charge / discharge current of the battery unit 3 when driving in the known WLTC mode is, for example, 12 A. If periods when the vehicle 1 is not in use are also included, the average value of the charge / discharge current becomes even smaller.

[0106] For example, if vehicle 1 drives for 25 minutes twice in WLTC mode in one day, the average charge / discharge current during that period is calculated as 12A * 25 minutes * 2 times / 24 hours ≒ 400mA. Substituting this value into the above-mentioned formula (2), the reference adjustment current value is obtained as 400mA * 10% = 40mA.

[0107] Let us assume that there is no period of non-use of the vehicle 1 and the vehicle is continuously driven in the WLTC mode. In this case, the average charge / discharge current of the battery unit 3 is, as described above, 12 A, for example. By substituting this value into the above-described formula (2), the reference adjustment current value is obtained as 12 A * 10% = 1200 mA.

[0108] In other words, in this case, the adjustment current can be set in the range of 40 mA to 1200 mA. This allows the cell balance adjustment unit 31 to be configured using small electronic components equivalent to those used in passive systems. This eliminates the drawbacks of active cell balance adjustment technology, making it possible to put it into practical use. A compact, high-performance on-board cell balance adjustment device can be realized at low cost.

[0109] The battery management unit 32 and the cell balance adjustment unit 31 may be powered by the battery unit 3, or may be powered by a low-voltage (12V) power supply system used for electrical components and controls of the vehicle 1.

[0110] This prevents the state of charge of the cell group 20 from becoming uneven due to discharge of the battery unit 3. As long as the vehicle 1 does not reach a so-called dead battery state, it becomes possible to constantly execute the cell balance adjustment control. The cell balance adjustment control can be executed completely independently of the battery unit 3.

[0111] As described above, the cell balance adjustment control is executed throughout the use and non-use periods of the vehicle 1. During the use period of the vehicle 1, the battery units 3 are charged and discharged, which increases the unevenness of the state of charge of each cell 2. Even when charging is performed, the unevenness of the state of charge of each cell 2 increases.

[0112] On the other hand, during periods when the vehicle 1 is not in use, the battery unit 3 is not charged or discharged, which promotes uniformity of the state of charge of each cell 2. In practice, the period when the vehicle 1 is not in use is usually longer than the period when the vehicle 1 is in use. If this is the case, the longer the specified period, the more uniform the state of charge will be.

[0113] During the period when the state of charge of the battery unit 3 is between the upper limit (fully charged state) and the lower limit (fully discharged state), there is no problem even if the state of charge of the cell group 20 is uneven. In an actual vehicle 1, this state is almost always the case.

[0114] In an actual vehicle 1, it is considered unlikely that the power supply of the battery unit 3 will be completely depleted, as the vehicle will be unable to travel. Even in such a case, as shown in the lower diagram of Figure 4, if the state of charge of the cell group 20 is equalized just before the state of charge of the battery unit 3 reaches its lower limit, all cells 2 can be made to reach a fully discharged state without any remaining power. The power can be used up. The vehicle can travel to its limit.

[0115] On the other hand, just before the battery unit 3 reaches a fully charged state through charging, a cell 2 with a smaller cell capacity may reach its upper limit first, making it impossible to charge the other cells 2. In response to this, it is preferable to reduce the charging current to a value equal to or lower than the current value corresponding to the adjustment current when or just before the state of charge of the battery unit 3 reaches its upper limit through charging.

[0116] This will be explained in detail with reference to Figure 5. In this example, we assume that the battery is being charged from a fully discharged state to a fully charged state. The graph in the middle of Figure 5 illustrates the change over time in the charging current I and the voltage V of each cell 2 during the charging process.

[0117] As shown in the upper diagram of Figure 5, the cells C1-C8 that make up the cell group 20 have varying cell capacities. At the start of charging (t=0), the state of charge of each cell 2 is uniform. When charging begins from that state, the voltage V of each cell 2 rises accordingly. At this time, the charging current I1 is constant.

[0118] As the battery approaches full charge (t=t1), the cell C8, which has the smallest cell capacity, reaches its upper limit. The other cells C1-C7 have not yet reached their upper limit. To prevent overcharging of cell C8, charging is stopped. Therefore, the other cells C1-C7 cannot be charged any further.

[0119] Therefore, the charging current is reduced to a value equal to or less than the current value corresponding to the adjustment current so that the cell balance adjustment control is performed above the charging current. Here, the value of the charging current is reduced from I1 to I2, which is sufficiently smaller than I1.

[0120] As a result, as shown in the lower diagram of Figure 5, power can be transferred from cell C8, whose state of charge is near or at its upper limit, to the other cells C1-C7, even if the state of charge exceeds the charge of the other cells C1-C7. When the other cells C2 approach or reach their upper limit, the same process is repeated. This allows all cells C2 to be fully charged, even if there is variation in cell capacity among the cells C1-C8 that make up the cell group 20. This allows the battery unit 3 to be fully charged, ensuring the battery unit's inherent power capacity.

[0121] <Issues related to variations in cell capacity> As mentioned above, one of the causes of variations in cell capacity is variations that occur during the manufacturing of the cells 2. Because the cells 2 are mass-produced, variations in cell capacity that occur during manufacturing are unavoidable. In response to this, all cells 2 of the battery unit 3 installed in each vehicle 1 are required to have a cell capacity greater than or equal to a predetermined value in order to guarantee predetermined performance.

[0122] As shown in the upper left diagram of Figure 6, the cell capacity of mass-produced cells 2 shows a predetermined distribution with respect to its average value BCCavg. From the perspective of performance guarantee, cells 2 with a predetermined cell capacity or greater are selected. Furthermore, the average cell capacity BCCavg varies from production lot to production lot, and cell quality may also vary, although within the appropriate range. Cell quality affects the degree of degradation that causes subsequent variations in cell capacity.

[0123] Therefore, currently, the cells 2 that make up one battery unit 3 are selected from the same manufacturing lot, and the cell capacity of each cell 2 is measured and the range of variation in cell capacity is adjusted so that passive cell balance adjustment control can be performed appropriately.

[0124] Specifically, cells 2 whose cell capacity falls within a predetermined range (BCCmin or more and BCCmax or less) are selected from the same production lot, and these cells 2 are distributed to the battery units 3 to be installed in each vehicle 1 to form the cell group 20. However, such quality control is an excessive burden.

[0125] In contrast, when the disclosed technology is applied, it is preferable to configure the cell group 20 using any cells 2 without adjusting the cell capacity variation range. That is, as shown in the lower diagram of Figure 6, by performing active cell balance adjustment control, as described above, even if there is variation in cell capacity, it is possible to equalize the state of charge of the cells 2, that is, to bring the cell capacity closer to its average value BCCavg.

[0126] Therefore, without considering variations in production lots or cell capacity, any cells 2 selected from multiple production lots can be distributed to the battery units 3 to be installed in each vehicle 1 to form a cell group 20. Because conventional quality control can be omitted, significant cost and labor reductions can be achieved.

[0127] <Example of a suitable cell balance adjustment unit> The cell balance adjustment unit 31 can be applied to any of the conventional circuits described above as long as it performs active balance adjustment control. However, from the viewpoint of cost and size, a capacitor-based circuit (specifically, a flying capacitor-based circuit: a flying capacitor ACB circuit) is preferable.

[0128] However, the conventional switching control method for a flying capacitor ACB circuit (conventional switching method) has a problem in that the equalization process takes a long time. To address this problem, the present inventors have developed a new switching control method (improved switching method) that can solve this problem by devising a switch control method. A flying capacitor ACB circuit that employs this improved switching method is suitable for the cell balance adjustment unit 31.

[0129] Before describing the specific structure of the cell balance adjustment unit 31 using the improved SW method, the differences between the switch control methods (conventional SW method and improved SW method) will be explained using Figures 7A and 7B. Note that in the following description, V may be used as the symbol for a cell in relation to the symbol for a capacitor.

[0130] The circuit shown at the top of each figure represents the basic part of the flying capacitor ACB circuit (the part corresponding to the two cells V1 and V2 connected in series). The circuit structure is the same in both the conventional SW method and the improved SW method.

[0131] 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 these 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 these switches S1 to S4. Note that, under normal conditions, each of the switches S1 to S4 is turned OFF (non-conductive) (a so-called normally open state).

[0132] 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 7A, 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 charging capacitor C.

[0133] 7A, switches S2 and S4 are turned on instead of switches S1 and S3 so that cell V2, which has a lower voltage, is connected to capacitor C. This causes current Ic to flow as shown by the dashed line, transferring charge from capacitor C to cell V2 and charging cell V2.

[0134] In the conventional SW method, the switches S1 to S4 are controlled so that such an operation is repeated.

[0135] 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 7A, when the voltage difference between cell V2 and cell V1 is large (V1>V2), that voltage difference is applied to capacitor C, and 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.

[0136] As shown in the lower right diagram of Figure 7A, as the voltage difference between cells V2 and V1 decreases (V1 ≒ V2), the current Ic flowing through capacitor C also decreases. As the charge states of cells V1 and V2 become more equal, the difference between them decreases, slowing the equalization of the charge states of cells V1 and V2. 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 for the charge states to become equal.

[0137] In contrast, in the improved SW method, as shown in the upper left diagram of Fig. 7B, 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 line, transferring charge from cells V1 and V2 to capacitor C and charging it.

[0138] 7B, instead of switches S1 and S4, switches S2 and S4 are turned on so that cell V2, which has a lower voltage, is connected to capacitor C. This causes current Ic to flow as shown by the dashed line, transferring charge from capacitor C to cell V2 and charging cell V2.

[0139] In the improved SW method, the switches S1 to S4 are controlled so that such an operation is repeated.

[0140] As shown in the lower left diagram of Figure 7B, 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.

[0141] As shown in the lower right diagram of Figure 7B, 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 (approximately twice the voltage of the conventional SW method), so the current Ic flowing through capacitor C remains large. Even as the states of charge of both cells V1 and V2 become more equal, the current Ic does not decrease, so the state of charge of both cells V1 and V2 is more quickly equalized. Therefore, the improved SW method allows the state of charge equalization process to be completed in a short time.

[0142] (Specific example of cell balance adjustment unit) Fig. 8 shows a specific example (improved circuit 10) of the main part of the cell balance adjustment unit 31. Fig. 8 shows a part (five cells 2) of the cell group 20 (first cell 2a to fifth cell 2e). The improved circuit 10 has the same configuration for all cells 2, so other parts are not shown.

[0143] The cell group 20 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. 8, 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.

[0144] These processing target groups 4 overlap with each other in part of the cells 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.

[0145] The improved circuit 10 is configured with a plurality of branch wirings 5, a plurality of connecting wirings 6, a plurality of switches 7, a plurality of capacitors 8, etc. for this cell group 20. As shown in FIG. 8, these components are conceptually arranged so as to extend along the series of cells 2 (for convenience, the improved circuit 10 will be described below based on FIG. 8).

[0146] One end of each branch wiring 5 is connected to a location between the positive electrode side of one serially connected cell 2 and the negative electrode side of the other serially connected cell 2. The other end of each branch wiring 5 branches into two and is connected to one end of two switches 7, 7.

[0147] When looking at a certain cell 2, the other end of the switch 7 connected to its positive electrode side via a branch wiring 5 is connected to the other end of the switch 7 connected to the negative electrode side of that cell 2 via a branch wiring 5 by a connecting wiring 6. Circuits with such a configuration are repeatedly arranged along the series of cells 2, thereby forming a series of continuous circuits 9.

[0148] 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 each of these continuous circuits 9. In other words, one capacitor 8 is arranged for each processing target group 4.

[0149] 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.

[0150] 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.

[0151] As described above, the cell balance adjustment unit 31 has a cell voltage monitoring unit that constitutes the cell voltage comparison means 11. The cell voltage comparison means 11 is a means that can compare the voltages of each of the cells 2. The battery management unit 32 controls each of the switches 7 in a predetermined manner based on the detected values ​​of the cell voltage comparison means 11. However, it is sufficient for the cell voltage comparison means 11 to be able to compare the relative magnitude relationship of the voltages of each of the cells 2.

[0152] (Example of battery management control) Next, with reference to FIGS. 9 to 11, a specific example of control executed by the battery management unit 32 in the improved circuit 10 described above to equalize the states of charge of the cells 2 in the cell group 20 will be described.

[0153] FIG. 9 shows an improved circuit 10. In FIG. 9, for ease of explanation, the cell 2, switch 7, capacitor 8, and processing group 4 are each assigned a symbol to distinguish them individually instead of a numerical symbol. FIG. 10 is a flowchart showing the flow of the main processing executed by the battery management unit 32. FIG. 11 is a diagram for explaining the state of charge of each cell corresponding to the main steps of the processing.

[0154] The initial state of charge of each cell is shown in Figure 11(a). In this control example, the initial state of charge of each cell is as follows: first cell V1 > fourth cell V4 > third cell V3 > second cell V2.

[0155] 10, first, the battery management unit 32 turns on the switches S1, S4, S5, S8, S9, and S12 (step S1). As a result, in the first processing target 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 target group G1). In the second processing target 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 target group G3, the third cell V3 and the fourth cell V4 are connected to the third capacitor C3 via the switches S9 and S12.

[0156] As a result, charge is transferred from the first cell V1 and the second cell V2 to the first capacitor C1, charging the first capacitor C1. Similarly, charge is transferred from the second cell V2 and the third cell V3 to the second capacitor C2, charging the second capacitor C2. Charge is transferred from the third cell V3 and the fourth cell V4 to the third capacitor C3, charging the third capacitor C3. As a result, the charge amount of each cell decreases according to its discharge state, as shown by the arrows in Figure 11(a).

[0157] 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 level, and charging and discharging converges in a short time. In consideration of the time required for convergence, the battery management unit 32 pre-sets a predetermined capacitor charging time tj (e.g., 50 μs) that is longer than that time. The battery management unit 32 determines whether the capacitor charging time tj has elapsed (step S2).

[0158] Then, when it is determined that the capacitor charging time tj has elapsed, the battery management unit 32 compares 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, respectively, and the same applies below), the battery management unit 32 turns on switches S2 and S4 (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 battery management unit 32 turns on switches S1 and S3 (step S5) to connect the first capacitor C1 and the first cell V1.

[0159] Next, the battery management unit 32 similarly compares the voltages of the second cell V2 and the third cell V3 (step S6). If the voltage of the second cell V2 is greater than that of the third cell V3, the battery management unit 32 turns on 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 battery management unit 32 turns on switches S5 and S7 (step S8) to connect the second capacitor C2 to the second cell V2.

[0160] Next, the battery management unit 32 similarly compares the voltages of the third cell V3 and the fourth cell V4 (step S9). If the voltage of the third cell V3 is greater than that of the fourth cell V4, the battery management unit 32 turns on switches S10 and S12 (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 battery management unit 32 turns on switches S9 and S11 (step S11) to connect the third capacitor C3 to the third cell V3.

[0161] In this control example, as shown in (b) of Fig. 11, the voltage of the first cell V1 is higher than that of the second cell V2, so the first capacitor C1 and the second cell V2 are connected (step S4). As a result, charge is transferred from the first capacitor C1 to the second cell V2, as shown by the arrow in (b) of Fig. 11, and the second cell V2 is charged.

[0162] In this case, the cell with a 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.

[0163] Similarly, as shown in Fig. 11(c), since the voltage of the second cell V2 is higher 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, charge is transferred from the second capacitor C2 to the third cell V3, as shown by the arrow in Fig. 11(c), and the third cell V3 is charged.

[0164] 11(d), since the voltage of the fourth cell V4 is higher 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 FIG. 11(d), charge is transferred from the third capacitor C3 to the third cell V3, and the third cell V3 is charged.

[0165] 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 that time is set in advance in the battery management unit 32. The battery management unit 32 determines whether the capacitor discharge time th has elapsed (step S12).

[0166] If it is determined that the capacitor discharge time th has elapsed, the battery management unit 32 determines whether the magnitude relationship between the voltages of the first cell V1 and the second cell V2 has reversed (step S13). For example, in this control example, the voltage of the first cell V1 before processing is higher than that of the second cell V2, so it determines 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).

[0167] If it is determined that the voltage relationship between the first cell V1 and the second cell V2 has reversed, the battery management unit 32 further determines whether the voltage relationship between the second cell V2 and the third cell V3 has reversed (step S14). For example, in this control example, the voltage of the third cell V3 before processing is higher than that of the second cell V2, so it determines whether the voltage of the second cell V2 has become equal to or higher than the voltage of the third cell V3.

[0168] If it is determined that the voltage relationship between the second cell V2 and the third cell V3 has reversed, the battery management unit 32 further determines whether the voltage relationship between the third cell V3 and the fourth cell V4 has reversed (step S15). For example, in this control example, the voltage of the fourth cell V4 before processing is higher than that of the third cell V3, so it determines whether the voltage of the third cell V3 has become equal to or higher than the voltage of the fourth cell V4.

[0169] If it is determined that the voltage magnitude relationship between the first cell V1 and the second cell V2 has not reversed (No in step S13), if it is determined that the voltage magnitude relationship between the second cell V2 and the third cell V3 has not reversed (No in step S14), or if it is determined that the voltage magnitude relationship between the third cell V3 and the fourth cell V4 has not reversed (No in step S15), the process returns to step S1 and repeats the series of processes. That is, the series of processes is repeated until the cell voltage magnitude relationship is reversed in all processing target groups.

[0170] In this control example, the magnitude relationship of the cell voltages is reversed in the second processing target group G2, but the magnitude relationship of the cell voltages is not reversed in the other processing target groups, so processing is executed again from step S1. Specifically, as shown in Figure 11(e), the process starts from the capacitor charging process.

[0171] At this time, because each processing target group 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 the series of processes until the magnitude relationship of the cell voltages is reversed in all processing target groups of the cell group 20, the states of charge of all cells constituting the cell group 20 can be uniformed in a short time.

[0172] Note that steps S1 and S2 correspond to the capacitor charging process of the cell balancing adjustment device, and steps S3 to S12 correspond to the capacitor discharging process of the cell balancing adjustment device.

[0173] Furthermore, the order of steps S3 to S5, steps S6 to S8, and steps 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.

[0174] 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.

[0175] The larger the capacitor, the fewer the number of charge / discharge cycles, but the larger the capacitor and the higher the material costs. Therefore, making the capacitor smaller and increasing the number of charge / discharge cycles is advantageous in terms of cost and size. However, increasing the number of charge / discharge cycles generates harmonic noise.

[0176] As a result of investigations, the inventors have found that it is most preferable to alternately repeat charge and discharge processes at a cycle of 1 kHz to 1 MHz. Therefore, by alternately repeating charge and discharge processes at the above-mentioned cycle, it is possible to suppress harmonic noise while making the cell balancing device compact and low-cost.

[0177] <Effects of the improved SW method> 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 (substitute cell) instead of a lithium-ion battery, and six of these substitute cells were connected together to form a simulated battery. An experimental device equipped with the above-mentioned improved circuit 10 was installed in the simulated battery, and control similar to the above-mentioned control example was performed.

[0178] The results of the verification test are shown in Figure 12. The bottom graph in Figure 12 shows the verification results of the improved SW method (Example). The top graph in Figure 12 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.

[0179] As shown in the upper diagram of Figure 12, in passive cell balancing, the cells V1 to V5 are discharged to match the voltage of 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.

[0180] In contrast, the improved SW method is based on active cell balancing, so charging and discharging are performed on each cell so that they converge to an approximate average value, as shown in the lower diagram of Figure 12. As a result, a loss of 2 mW occurred in this test, and the charge state of each cell was equalized in approximately 500 ms.

[0181] Note that this approximately 500 ms is a value for a replacement cell with a very small capacity, and in the case of an actual cell, it would take, for example, about five hours. However, as described above, the disclosed technology provides sufficient time for cell balance adjustment control. Therefore, it is believed that there is almost no impact.

[0182] The disclosed technology is not limited to the above-described embodiment, but includes various other configurations. For example, in the preferred example of the cell balance adjustment unit 31 described above, the processing target group is configured with two cells, but the processing target group may be configured with three or more cells. The number of overlapping cells is also not limited to one, and may be two or more. [Explanation of symbols]

[0183] 1 vehicle 2 cells 3 Battery Unit 4 Processing group 5 branch wiring 6 Connecting wiring 6a First connecting wire 6b Second connecting wire 7 Switch 8 Capacitors 9 Continuous Circuit 10 Improved circuit 11 Cell voltage comparison means 20 Cell Groups 30 modules 31 Cell balance adjustment unit 32 Battery management unit (control unit)

Claims

1. A cell balance adjustment method for a battery unit that includes a cell group consisting of a plurality of cells connected in series and is mounted on a vehicle as a power source for driving the vehicle, comprising: an active cell balancing control is performed to transfer power by flowing a predetermined adjustment current between predetermined cells having a voltage difference, thereby equalizing the state of charge of the cell group; a cell balancing method for performing the cell balancing control independently of whether the vehicle is in use or not when the states of charge of the cell groups are uneven;

2. The cell balancing method according to claim 1 , a cell balancing method that starts execution of the cell balancing control when the battery unit is in a state where it can be charged or discharged;

3. 3. The cell balancing method according to claim 1, The cell balancing method stops the execution of the cell balancing control when the states of charge of the cell groups become uniform while the vehicle is not in use.

4. The cell balancing method according to claim 1 , calculating a charge / discharge current average value, which is a time average value of a charge / discharge current flowing to charge or discharge the battery unit during a continuous predetermined period including both periods during which the vehicle is in use and periods during which the state of charge of the battery unit changes from an upper limit to a lower limit; estimating a maximum variation in cell capacitance that may occur in the group of cells; calculating a reference adjustment current value that serves as a reference for the adjustment current based on the maximum variation width of the cell capacity and the average charge / discharge current value; a cell balancing method for setting a range of the adjustment current allowed in the cell balancing control based on the reference adjustment current value;

5. The cell balancing method according to claim 4, a cell balancing method for calculating the average charge / discharge current value using absolute values ​​of currents flowing during both charging and discharging when the predetermined period further includes a period during which the battery unit is charged by an external power source;

6. The cell balancing method according to claim 4, The cell balance adjustment method, wherein the range of the adjustment current is set to 40 mA or more and 1200 mA or less.

7. The cell balancing method according to claim 1 , A cell balance adjustment method in which, when the state of charge of the battery unit reaches an upper limit due to charging or immediately before that, the charging current is reduced to a current value equal to or lower than the adjustment current.

8. The cell balancing method according to claim 1 , A cell balancing method for configuring the cell group using any cells without adjusting the width of variations in cell capacitance during manufacturing.

9. A cell balancing device for a battery unit including a cell group configured by connecting a plurality of cells in series, the cell balancing device being mounted on a vehicle together with a battery unit that serves as a power source for driving the vehicle, the device comprising: an active cell balancing unit that transfers power by flowing a predetermined adjustment current between predetermined cells having a voltage difference, thereby equalizing the state of charge of the cell group; a control unit that controls the cell balance adjustment unit; Equipped with When the states of charge of the cells are uneven, the control unit operates the cell balance adjustment unit independently of whether the vehicle is in use or not.

10. The cell balancing device according to claim 9, The cell balance adjustment device in which the adjustment current is set in a range of 40 mA to 1200 mA, and the cell balance adjustment unit is configured with electronic components that correspond to the range of the adjustment current.

11. The cell balancing device according to claim 10, All of the cell groups are divided into a plurality of processing target groups each consisting of at least two or more consecutive cells, with a portion of the cells overlapping between adjacent processing target groups, The cell balance adjustment unit 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; cell voltage comparison means for comparing the voltages of the cells; and The control unit By controlling each of the switches based on the detection value of the cell voltage comparison means, a capacitor charging process for charging the capacitor by connecting the capacitor to both end portions of each of the processing target groups; a capacitor discharge process in which a predetermined processing target cell included in each of the processing target groups is connected to the capacitor and the capacitor is discharged to charge the processing target cell; A cell balancing device that performs the above.

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