Cell balance device and power supply device

Abstract

To provide a cell balance device capable of securing a minimum value of a cell balance current while suppressing increase in a mounting area and cost, and a power supply device.SOLUTION: A cell balance device includes: a plurality of discharge circuits that is configured as a series circuit of a switching element and a variable resistor whose resistance value increases due to increase in temperature and being connected in parallel to each of a plurality of battery cells constituting a battery; a first voltage detection circuit configured to detect a cell voltage of each of the plurality of battery cells; a second voltage detection circuit configured to detect a voltage across each of the plurality of switching elements; and a control unit configured to perform ON / OFF control of the switching element so as to equalize a plurality of cell voltages based on the cell voltage. When a voltage across both terminals of the switching element exceeds a predetermined threshold value by the ON / OFF control, the control unit suppresses decrease in a discharge current by switching a control method from the ON / OFF control to duty control.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a cell balancing device and a power supply device. [Background technology]

[0002] Patent Document 1 below discloses a cell balancing device that can perform appropriate cell balancing with simple control. This cell balancing device includes multiple discharge circuits that can discharge multiple battery cells and a control unit that controls the multiple discharge circuits, and the multiple discharge circuits are first discharge circuits that include a discharge resistor unit in which a PTC thermistor is inserted and a switch that switches the discharge resistor unit between a conductive state and a non-conductive state, and the control unit switches the switch based on the voltage state of the multiple battery cells.

[0003] In this cell balancing device, the PTC thermistor has the property that its internal resistance increases significantly when it reaches or exceeds the Curie temperature. Therefore, even if the temperature rises with discharge, the increase in the resistance value of the PTC thermistor is suppressed until the temperature reaches the Curie temperature, allowing a large discharge current to flow. Furthermore, as the temperature rises above the Curie temperature with discharge, the resistance value of the PTC thermistor gradually increases, gradually reducing the discharge current, thereby suppressing heat generation. Therefore, this cell balancing device enables appropriate cell balancing with simple control. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-108412 Summary of the Invention [Problem to be solved by the invention]

[0005] The cell balancing device described above can adjust the discharge current (cell balancing current) according to the temperature of the PTC thermistor, but by connecting a resistor in parallel to each PTC thermistor, the rate at which the cell voltage drops is suppressed, i.e., the cell balancing current is kept at a minimum value. However, there are concerns that such a cell balancing device will increase the mounting area and cost.

[0006] The present invention has been made in view of the above-described circumstances, and aims to provide a cell balancing device and a power supply device that can ensure a minimum value of the cell balancing current while suppressing increases in mounting area and costs. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention provides, as a first solution related to a cell balancing device, a plurality of discharge circuits configured as series circuits of switching elements and variable resistors whose resistance value increases with temperature rise and connected in parallel to each of a plurality of battery cells constituting a battery, a first voltage detection circuit that detects the cell voltages of each of the plurality of battery cells, a second voltage detection circuit that detects the voltages across each of the plurality of switching elements, and a control unit that controls the on / off of the switching elements so as to equalize the plurality of cell voltages based on the cell voltages, wherein when the on / off control causes the voltages across the switching elements to exceed a predetermined voltage threshold, the control unit switches the control method from the on / off control to the duty control, thereby suppressing a decrease in the discharge current that functions as a cell balancing current.

[0008] The present invention provides a second solution related to the cell balancing device according to the first solution, in which the control unit evaluates the amount of discharge by calculating an integrated value of the cell balancing current.

[0009] The present invention provides a third solution related to the cell balance device according to the first or second solution, in which the control unit executes the duty control with a duty ratio that suppresses a decrease in the discharge current when the voltage between both ends exceeds the voltage threshold.

[0010] The present invention employs, as a solution relating to a power supply device, a solution comprising the cell balance device according to any one of the first to third solutions and the battery. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a cell balancing device and a power supply device that can ensure a minimum value of the cell balancing current while suppressing increases in mounting area and costs. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a block diagram showing the configuration of a cell balance device and a power supply device according to an embodiment of the present invention; [Figure 2] 4 is a flowchart illustrating an operation of the cell balance devices according to an embodiment of the present invention. [Figure 3] FIG. 4 is a characteristic diagram showing the operation of the cell balance devices according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1, the power supply device according to this embodiment includes a cell balance device A and a battery B. Starting with battery B, the battery B in this embodiment includes a plurality of battery cells C1 to C12 as shown in the figure. In this embodiment, the battery B will be described as being composed of 12 battery cells C1 to C12 as an example, but the number of battery cells C1 to C12 is not limited to 12.

[0014] This battery B is an in-vehicle secondary battery, such as a well-known lithium-ion battery. That is, this battery B is mounted on the vehicle and discharges by supplying stored low-voltage DC power to a load also mounted on the vehicle. Also, this battery B is charged by regenerative power supplied from the vehicle or DC power (power dedicated to charging) supplied from an external charger.

[0015] As shown in the figure, multiple battery cells C1 to C12 are connected in series and are unit batteries that make up battery B. That is, of the multiple battery cells C1 to C12, the first battery cell C1 has its negative electrode connected to the positive electrode of the second battery cell C1, and its positive electrode connected to a load as the positive electrode of battery B.

[0016] The second battery cell C2 has its negative electrode connected to the positive electrode of the third battery cell (not shown), and its positive electrode connected to the negative electrode of the first battery cell C1. (Omitted) Furthermore, the twelfth battery cell C12 has its negative electrode connected to the load as the negative electrode of battery B, and its positive electrode connected to the negative electrode of the eleventh battery cell (not shown).

[0017] These battery cells C1 to C12 have cell voltages V1 to V12 (voltage between electrodes) that correspond to their state of charge. Each cell voltage V1 to V12 varies depending on the state of charge of battery B, i.e., the state of charge of each battery cell C1 to C12. Furthermore, each battery cell C1 to C12 is charged by a charging voltage applied between the positive and negative electrodes of battery B, but is not necessarily charged uniformly due to variations in battery characteristics, etc.

[0018] That is, the state of charge of each cell voltage V1 to V12 inevitably varies. Such variation in the state of charge is one of the factors that accelerates the deterioration of battery B. As will be described in detail later, the cell balancing device A according to this embodiment corrects and equalizes the variation in the state of charge of each cell voltage V1 to V12.

[0019] Next, a cell balance device A according to this embodiment will be described. As shown in the figure, the cell balance device A includes a plurality of discharge circuits H1 to H12, a plurality of cell voltage detection circuits D1 to D12, a microcomputer M, and an isolation element Z.

[0020] As shown in the figure, the plurality of discharge circuits H1 to H12 are provided corresponding to the plurality of battery cells C1 to C12, and are configured as a plurality of series circuits each made up of switching elements T1 to T12 and variable resistors R1 to R12. That is, the plurality of discharge circuits H1 to H12 are connected in parallel to the corresponding battery cells C1 to C12.

[0021] For example, a first discharge circuit H1 is provided corresponding to a first battery cell C1 and is connected in parallel to the first battery cell C1. A second discharge circuit H2 is provided corresponding to a second battery cell C2 and is connected in parallel to the second battery cell C2. (Omitted) A twelfth discharge circuit H12 is provided corresponding to a twelfth battery cell C12 and is connected in parallel to the twelfth battery cell C12.

[0022] As shown in the figure, the multiple switching elements T1 to T12 are field-effect transistors (three-terminal elements), and their on (conducting) / off (non-conducting) states are controlled based on gate signals input from the microcomputer M. The multiple variable resistors R1 to R12 are two-terminal elements having resistance-temperature characteristics that change their resistance value with temperature. Details of these resistance-temperature characteristics will be described later, but the resistance values ​​of the multiple variable resistors R1 to R12 increase with increasing temperature in a specific temperature range.

[0023] For example, the first discharge circuit H1 is provided corresponding to the first battery cell C1 among the multiple battery cells C1 to C12 and is connected in parallel to the first battery cell C1. The second discharge circuit H2 is provided corresponding to the second battery cell C2 and is connected in parallel to the second battery cell C2. (Omitted) The twelfth discharge circuit H12 is provided corresponding to the twelfth battery cell C12 and is connected in parallel to the twelfth battery cell C12.

[0024] The first discharge circuit H1 is a first series circuit composed of a first switching element T1 and a first variable resistor R1. That is, the first switching element T1 has a drain terminal connected to the positive electrode of the first battery cell C1, a source terminal connected to one end of the first variable resistor R1, and a gate terminal connected to the first control output terminal of the microcomputer M. The first variable resistor R1 has one end connected to the source terminal of the first switching element T1 and the other end connected to the negative terminal of the first battery cell C1.

[0025] The second discharge circuit H2 is a second series circuit composed of a second switching element T2 and a second variable resistor R2. That is, the second switching element T2 has a drain terminal connected to the positive electrode of the second battery cell C2, a source terminal connected to one end of the second variable resistor R2, and a gate terminal connected to the second control output terminal of the microcomputer M. The second variable resistor R2 has one end connected to the source terminal of the second switching element T2 and the other end connected to the negative terminal of the second battery cell C2.

[0026] (Omitted) The twelfth discharge circuit H12 is a twelfth series circuit composed of a twelfth switching element T12 and a twelfth variable resistor R12. That is, the twelfth switching element T12 has a drain terminal connected to the positive electrode of the twelfth battery cell C12, a source terminal connected to one end of the twelfth variable resistor R12, and a gate terminal connected to a twelfth control output terminal of the microcomputer M. The twelfth variable resistor R12 has one end connected to the source terminal of the twelfth switching element T12 and the other end connected to the negative terminal of the twelfth battery cell C12.

[0027] The plurality of cell voltage detection circuits D1 to D12 are provided corresponding to the plurality of battery cells C1 to C12, similar to the plurality of discharge circuits H1 to H12 described above, and detect the cell voltages V1 to V12 of the corresponding battery cells C1 to C12, respectively. These plurality of cell voltage detection circuits D1 to D12 output the plurality of cell voltages V1 to V12 to the microcomputer M.

[0028] That is, each of the plurality of cell voltage detection circuits D1 to D12 has three input terminals, of which the first input terminal is connected to the positive terminal of the corresponding battery cell C1 to C12, the second input terminal is connected to the negative terminal of the corresponding battery cell C1 to C12, and the third input terminal is connected to the source terminal of the switching element T1 to T12 of the discharge circuit H1 to H12 provided in the corresponding battery cell C1 to C12.

[0029] Each of the plurality of cell voltage detection circuits D1 to D12 has two output terminals, each of which is connected to a plurality of (24) input terminals provided in the microcomputer M.

[0030] For example, for the first cell voltage detection circuit D1, the first input terminal is connected to the positive terminal of the first battery cell C1, the second input terminal is connected to the negative terminal of the first battery cell C1, and the third input terminal is connected to the source terminal of the first switching element T1 provided in the first battery cell C1.

[0031] As for the second cell voltage detection circuit D2, the first input terminal is connected to the positive terminal of the second battery cell C2, the second input terminal is connected to the negative terminal of the second battery cell C2, and the third input terminal is connected to the source terminal of the second switching element T2 provided in the second battery cell C2.

[0032] (Omitted) As for the 12th cell voltage detection circuit D12, the first input terminal is connected to the positive terminal of the 12th battery cell C12, the second input terminal is connected to the negative terminal of the 12th battery cell C12, and the third input terminal is connected to the source terminal of the 12th switching element T12 provided in the 12th battery cell C12.

[0033] Furthermore, the plurality of cell voltage detection circuits D1 to D12 detect the voltage across each of the switching elements T1 to T12, i.e., the voltage between the drain terminal and the source terminal, as switch voltages Vs1 to Vs12 for the discharge circuits H1 to H12 provided in the corresponding battery cells C1 to C12. These plurality of cell voltage detection circuits D1 to D12 output the plurality of switch voltages Vs1 to Vs12 to the microcomputer M.

[0034] These cell voltage detection circuits D1 to D12 correspond to the first voltage detection circuits in the present invention that detect the cell voltages V1 to V12 of the plurality of battery cells C1 to C12, respectively. Also, these cell voltage detection circuits D1 to D12 correspond to the second voltage detection circuits in the present invention that detect the voltages across the plurality of switching elements T1 to T12 as SW voltages Vs1 to Vs12, respectively.

[0035] The microcomputer M is an integrated circuit equipped with a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), input / output circuits, etc. The CPU of the microcomputer M executes a control program stored in advance in the ROM using the RAM, thereby controlling the on / off of multiple switching elements T1 to T12 so as to equalize multiple cell voltages V1 to V12.

[0036] That is, the microcomputer M processes the multiple cell voltages V1 to V12 and the voltages Vs1 to Vs12 across the SW input from the multiple cell voltage detection circuits D1 to D12 based on a control program, thereby controlling the on / off of the multiple switching elements T1 to T12 at a predetermined cycle or duty controlling them at a predetermined duty ratio.

[0037] As will be described in detail later, the microcomputer M optimally performs equalization control (cell balance control) on the multiple battery cells C1 to C12 by switching between on / off control at a predetermined cycle and duty control at a predetermined duty ratio for the multiple switching elements T1 to T12. Such a microcomputer M corresponds to the control unit in the present invention.

[0038] The isolation element Z is a circuit element provided between the microcomputer M and the battery ECU (battery control device). That is, the isolation element Z is provided between the output terminal of the microcomputer M and the input terminal of the battery ECU, and electrically insulates the multiple cell voltages V1 to V12 input from the microcomputer M before outputting them to the battery ECU. Such an isolation element Z is, for example, a photocoupler or a pulse transformer.

[0039] Next, the operation of the cell balance device A according to this embodiment will be described in detail with reference to the flowchart shown in FIG.

[0040] This flowchart shows the cell balancing process executed by the microcomputer M based on a control program. This cell balancing process identifies battery cells (cells to be equalized) that have an excessively high charge amount compared to the others based on the multiple cell voltages V1 to V12 acquired by the microcomputer M from the multiple cell voltage detection circuits D1 to D12.

[0041] In this cell balancing process, the switching elements of the discharge circuits corresponding to the equalization target cells are turned on / off at a predetermined cycle to forcibly discharge the equalization target cells. The forced discharge reduces the charge amount of the equalization target cells, and the cells are brought to the same charge state as the other battery cells. This cell balancing process achieves equalization of the charge states of the multiple battery cells C1 to C12.

[0042] In the following, as an example, a case where the equalization target cell is the first battery cell C1 will be described. That is, a case where the first switching element T1 in the first discharge circuit H1 is set to the ON state to forcibly discharge the first battery cell C1 will be described.

[0043] Here, the first variable resistor R1 in the first discharge circuit H1 has a resistance value within a predetermined range defined by an upper limit and a lower limit in the temperature range of −20 to +160° C., as shown in the upper characteristic diagram of Fig. 3. The first variable resistor R1 also has a temperature characteristic in which the resistance value increases with temperature rise in a temperature range equal to or higher than temperature T0.

[0044] That is, as shown in the upper characteristic diagram of Figure 3, when the forced discharge of the first battery cell C1 causes its own temperature to rise and exceed temperature T0, the resistance value of the first variable resistor R1 increases, thereby reducing the discharge current Ih (cell balancing current) flowing through the first discharge circuit H1.

[0045] When the microcomputer M starts the cell balancing process for the first battery cell C1, it first acquires the voltage Vs1 across the first switch from the first cell voltage detection circuit D1 (step S1). Then, the microcomputer M determines whether the voltage Vs1 across the first switch exceeds a voltage threshold Er (step S2). This voltage threshold Er is pre-stored in the microcomputer M as control data.

[0046] If the determination in step S2 is "No," that is, if the voltage Vs1 across the first SW is equal to or lower than the voltage threshold Er, the microcomputer M performs normal control (step S3). That is, the microcomputer M maintains the ON state of the first switching element T1, which is set to the ON state by the ON / OFF control, that is, the discharging state of the first battery cell C1.

[0047] On the other hand, if the determination in step S2 is "Yes," the microcomputer M switches the control method of the first switching element T1 from on / off control to duty control (step S4). That is, when the discharge current Ih of the first battery cell C1 increases and the voltage Vs1 across the first SW rises to a level exceeding the voltage threshold Er, the microcomputer M performs duty control (PWM control) on the first switching element T1.

[0048] In this duty control (PWM control), the microcomputer M suppresses a decrease in the discharge current Ih (cell balancing current) of the first battery cell C1 by duty controlling the first switching element T1 with a duty ratio that can suppress a decrease in the discharge current Ih, that is, a duty ratio that exceeds 50% that can increase the discharge current Ih more than on / off control with a duty ratio of 50%.

[0049] Here, the state in which the voltage Vs1 across the first SW exceeds the voltage threshold Er is the state in which the resistance value of the first variable resistor R1 becomes the resistance value X, as shown in the upper characteristic diagram of FIG. 3, that is, the state in which the resistance value of the first variable resistor R1 has decreased to near the lower limit value of the usable range ΔL of the first variable resistor R1.

[0050] When the process of step S3 or step S4 is completed, the microcomputer M performs an OCV (Open Circuit Voltage) determination (step S5). This OCV determination evaluates the open circuit voltage (OCV) of the first battery cell C1 based on the first cell voltage V1, and evaluates the discharge amount of the first battery cell C1.

[0051] The method for evaluating the discharge amount of the first battery cell C1 is not limited to evaluating the open circuit voltage (OCV) of the first battery cell C1. For example, instead of evaluating the open circuit voltage of the first battery cell C1, the microcomputer M evaluates the SOC (State Of Charge) of the first battery cell C1 by calculating an integrated value of the discharge current Ih (cell balancing current) of the first battery cell C1.

[0052] When the process of step S5 is completed, the microcomputer M determines whether the OCV change amount ΔOCV of the open circuit voltage (OCV) of the first battery cell C1 has fallen below the OCV threshold value Fr (step S6). If the determination in step S6 is "Yes," the microcomputer M ends the cell balancing process.

[0053] On the other hand, if the determination in step S6 is "No," the microcomputer M repeats the processes from step S1 onward. That is, by repeating the series of processes from step S1 to S6 several times, the microcomputer M ends the cell balancing process when the OCV change amount ΔOCV for the first battery cell C1 falls below the OCV threshold value Fr.

[0054] The cell balance device A of this embodiment is configured as a series circuit of switching elements T1 to T12 and variable resistors R1 to R12 whose resistance value increases with an increase in temperature, and is equipped with a plurality of discharge circuits H1 to H12 respectively connected in parallel to a plurality of battery cells C1 to C12 constituting a battery B, a plurality of cell voltage detection circuits D1 to D12 (first voltage detection circuits) which detect the cell voltages V1 to V12 of the plurality of battery cells C1 to C12 respectively, a plurality of cell voltage detection circuits D1 to D12 (second voltage detection circuits) which detect the SW end voltages Vs1 to Vs12 (end voltages) of the plurality of switching elements T1 to T12 respectively, and a microcomputer M (controller) which performs on / off control or duty control of the switching elements T1 to T12 to equalize the plurality of cell voltages V1 to V12.

[0055] Furthermore, in the cell balance device A according to this embodiment, when the SW end-to-end voltages Vs1 to Vs12 (end-to-end voltages) of the switching elements T1 to T12 exceed a predetermined voltage threshold Er due to on / off control, the microcomputer M (controller) switches the control method of the switching elements T1 to T12 from on / off control to duty control, thereby suppressing a decrease in the discharge current Ih.

[0056] According to this embodiment, the control method of the multiple switching elements T1 to T12 is switched from on / off control to duty control to suppress a decrease in the discharge current Ih (cell balancing current), eliminating the need to connect a resistor in parallel to each of the multiple variable resistors R1 to R12 in order to ensure a minimum value for the discharge current Ih. Therefore, this embodiment can provide a cell balancing device A that can ensure a minimum value for the discharge current Ih while suppressing increases in mounting area and costs.

[0057] Furthermore, the microcomputer M (controller) in this embodiment evaluates the discharge amount by calculating the integrated value of the discharge current Ih (cell balancing current). According to this embodiment, it is possible to perform more accurate cell balancing processing for the multiple battery cells C1 to C12.

[0058] Furthermore, when the voltage across the switching elements T1 to T12 exceeds the voltage threshold Er, the microcomputer M (controller) in this embodiment performs duty control of the switching elements T1 to T12 with a duty ratio that suppresses a decrease in the discharge current Ih. According to this embodiment, it is possible to perform more accurate cell balancing for the multiple battery cells C1 to C12.

[0059] Furthermore, the power supply device according to this embodiment includes the cell balance device A according to this embodiment and the battery B. According to this embodiment, it is possible to provide a power supply device that can ensure a minimum value for the discharge current Ih while suppressing increases in mounting area and costs. [Explanation of symbols]

[0060] A Cell balance device B Battery C1~C12 battery cells D1 to D12 Cell voltage detection circuit (first voltage detection circuit, second voltage detection circuit) H1~H12 Discharge circuit R1~R12 variable resistors M microcomputer (control unit) T1~T12 switching elements Z isolation element

Claims

1. a plurality of discharge circuits each configured as a series circuit of a switching element and a variable resistor whose resistance value increases with an increase in temperature, the discharge circuits being connected in parallel to a plurality of battery cells constituting the battery; a first voltage detection circuit that detects the cell voltages of the plurality of battery cells; a second voltage detection circuit that detects the voltages across each of the plurality of switching elements; a control unit that performs on / off control or duty control of the switching elements so as to equalize the plurality of cell voltages based on the cell voltages, the control unit, when the voltage across the switching element exceeds a predetermined voltage threshold due to the on / off control, switches the control method from the on / off control to the duty control, thereby suppressing a decrease in discharge current.

2. 2. The cell balancing device according to claim 1, wherein the control unit evaluates a state of charge (SOC) by calculating an integrated value of the discharge current.

3. 3. The cell balancing device according to claim 1, wherein the control unit performs the duty control with a duty ratio that suppresses a decrease in the discharge current when the voltage between both ends exceeds the voltage threshold value.

4. A power supply device comprising: the cell balance device according to claim 1 or 2; and the battery.

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