Cell equalization circuit and storage battery device

Abstract

The invention provides a cell equalization circuit capable of always performing cell equalization operation on each battery cell connected in series, and a storage battery device. A cell equalization circuit (100) for controlling cell equalization between a battery cell (11) that generates a cell voltage (V1) and a battery cell (12) that is connected in series with the battery cell (11) and that generates a cell voltage (V2) is provided with: a voltage division circuit (103) that outputs a divided voltage (Vd1) that is the average voltage of the battery cells (11, 12); a differential voltage / current converter (101) for discharging a cell equalization current (Ib1) from the battery cell (11), the current (Ib1) being generated on the basis of a voltage difference obtained by subtracting the cell voltage (V2) from the divided voltage; and a differential voltage / current converter (102) that discharges a cell equalization current (Ib2) from the battery cells (12), the current (Ib2) being generated in accordance with a voltage difference after positive and negative reversal.

Description

Technical Field

[0001] This invention relates to a cell balancing circuit and a battery device. Background Technology

[0002] There exists a battery pack consisting of multiple rechargeable battery cells connected in series. The voltage of each cell in the battery pack varies due to factors such as manufacturing variations and self-leakage current variations. Furthermore, the cell voltages can sometimes differ due to ambient temperature. Consequently, as the battery pack undergoes repeated charge-discharge cycles and degradation intensifies, the state of health (SOH) of each cell becomes different, causing deviations in the cell voltages. As degradation progresses, the cell voltage increases during charging but decreases during discharging.

[0003] If the cell voltages of the battery cells differ significantly, and each cell is connected to a separate charge / discharge control circuit, the cell with the higher voltage will immediately reach overcharge and stop charging during charging, and the cell with the lower voltage will immediately reach over-discharge and stop discharging during discharging. Therefore, efficient charging and discharging may not be possible.

[0004] Various solutions have been proposed to balance the cell voltage of each cell in this type of battery pack.

[0005] For example, a battery pack control device is proposed, which uses an analog-to-digital converter (ADC) to measure the cell voltage of each battery cell and uses a microprocessor (MPU) and other signal processing circuits to perform calculations to make the cell voltage of each battery cell uniform (see Patent Document 1).

[0006] In addition, a voltage adjustment device for a battery pack is proposed, which uses a comparator to selectively discharge battery cells with voltages higher than the average voltage of the battery pack, ultimately making the cell voltages of all battery cells equal (see Patent Document 2).

[0007] Furthermore, a voltage equalization correction circuit is proposed, which forms a negative feedback loop through a comparator to make the potential difference between the average voltage of two adjacent battery cells and the intermediate voltage of the two battery cells zero. When a voltage difference is generated, the battery cell with the higher cell voltage is discharged (see Patent Document 3).

[0008] [Existing technical documents]

[0009] [Patent Literature]

[0010] [Patent Document 1] International Publication No. 2015 / 029283

[0011] [Patent Document 2] Japanese Patent Application Publication No. 2000-83327

[0012] [Patent Document 3] Japanese Patent Application Publication No. 2010-63264 Summary of the Invention

[0013] [The problem the invention aims to solve]

[0014] In one aspect of the invention, the object is to provide a cell balancing circuit that can perform cell balancing operations on battery cells connected in series by current control.

[0015] [Technical means to solve the problem]

[0016] One embodiment of the battery cell equalization circuit of the present invention is as follows:

[0017] A cell balancing circuit for controlling cell balancing of a first battery cell that generates a first cell voltage and a second battery cell connected in series with the first battery cell that generates a second cell voltage, comprising:

[0018] The first voltage divider circuit outputs a first voltage divider voltage, which is the average voltage of the first battery cell and the second battery cell.

[0019] A first differential voltage-to-current converter discharges a first cell balancing current from the first battery cell, the first cell balancing current being generated based on the voltage difference between the first voltage divider and the second cell voltage; and

[0020] The second differential voltage-current converter discharges the second cell equalization current from the second battery cell, the second cell equalization current being generated based on the voltage difference after reversing the positive and negative polarities.

[0021] [The effects of the invention]

[0022] According to one aspect of the present invention, a cell balancing circuit can be provided, which can perform cell balancing operations on battery cells connected in series by current control. Attached Figure Description

[0023] Figure 1 This is a circuit diagram showing a battery device (during discharge) using the cell balancing circuit of the first embodiment of the present invention.

[0024] Figure 2 This is a graph showing the cell balancing current-voltage difference characteristics of the differential voltage-current converter according to the first embodiment of the present invention.

[0025] Figure 3 This is a graph showing the cell balancing current-voltage difference characteristics of the differential voltage-current converter according to the first embodiment of the present invention.

[0026] Figure 4 This is a graph showing the cell balancing current-voltage difference characteristics of the differential voltage-current converter according to the first embodiment of the present invention.

[0027] Figure 5 This is a circuit diagram showing a battery device (during charging) using the cell balancing circuit of the first embodiment of the present invention.

[0028] Figure 6 This is a circuit diagram showing a battery device (open circuit) using the cell balancing circuit of the first embodiment of the present invention.

[0029] Figure 7 This is a circuit diagram showing a battery device (during discharge) using the cell balancing circuit of the second embodiment of the present invention.

[0030] Figure 8 This is a circuit diagram showing a battery device (during charging) using the cell balancing circuit of the second embodiment of the present invention.

[0031] Figure 9 This is a circuit diagram showing a battery device (in open circuit mode) using the cell balancing circuit of the second embodiment of the present invention.

[0032] Figure 10 This is a circuit diagram showing a battery device (during discharge) using the cell balancing circuit of the third embodiment of the present invention.

[0033] Figure 11 This is a circuit diagram showing a battery device (during charging) using the cell balancing circuit of the third embodiment of the present invention.

[0034] Figure 12 This is a circuit diagram showing a battery device (open circuit) using the cell balancing circuit of the third embodiment of the present invention.

[0035] Figure 13 This is a circuit diagram showing a battery device (during discharge) using the cell balancing circuit of the fourth embodiment of the present invention.

[0036] Figure 14 This is a circuit diagram showing a battery device (during charging) using the cell balancing circuit of the fifth embodiment of the present invention.

[0037] Figure 15 This indicates that multiple [items] were used. Figure 14A schematic diagram of an example of a battery device with a cell balancing circuit.

[0038] Figure 16 This indicates that multiple [items] were used. Figure 14 A schematic diagram of another example of a battery device with a cell balancing circuit.

[0039] Explanation of icon numbers

[0040] 10, 20, 30, 40, 50, 60, 70: Battery storage devices

[0041] 11: Battery cell (first battery cell)

[0042] 11a, 12a, 13a: Batteries

[0043] 11b, 12b, 13b: Internal resistance

[0044] 12: Battery cell (second battery cell)

[0045] 13: Battery cell (third battery cell)

[0046] 100, 200, 300, 400, 500, 500a, 500b: Cell balancing circuit

[0047] 101: Differential Voltage-to-Current Converter (First Differential Voltage-to-Current Converter)

[0048] 102: Differential voltage-current converter (second differential voltage-current converter)

[0049] 103: Voltage divider circuit (first voltage divider circuit)

[0050] 103a, 103b, 107a, 107b, R1a, R1b, R2a, R2b, R3a, R3b: Resistors

[0051] 104: Current monitoring circuit

[0052] 105: Differential voltage-current converter (third differential voltage-current converter)

[0053] 106: Differential Voltage-to-Current Converter (Fourth Differential Voltage-to-Current Converter)

[0054] 107: Voltage divider circuit (second voltage divider circuit)

[0055] 108: Differential Voltage-to-Current Converter

[0056] 109: Current Mirror Circuit (First Current Mirror Circuit)

[0057] 110: Current mirror circuit (second current mirror circuit)

[0058] 111, 112: Charging termination voltage detection unit

[0059] 113, 114: Logic circuits

[0060] 115: Diagnostic Circuit

[0061] 116: Equalization Detection Department (First Equalization Detection Department)

[0062] 117: Equalization Detection Department (Second Equalization Detection Department)

[0063] 118: Buffer

[0064] 119a, 119b: Battery cell packs

[0065] C1, C2, C3: Capacitors

[0066] CB1, CB2, CB3, CBE, CBEI, CBEO, ERR, VC1, VC2, VC3, VDD, VSS: terminals

[0067] CG: Charger

[0068] EB+: External positive extremum

[0069] EB-: External negative extreme

[0070] FMC12, FMC21, VBC1, VBC2: Signals

[0071] Ib1: Cell balancing current (first cell balancing current)

[0072] Ib2: Cell balancing current (second cell balancing current)

[0073] Ib3: Cell balancing current (third cell balancing current)

[0074] Ib4: Cell balancing current (fourth cell balancing current)

[0075] Ic: Charging current

[0076] Id: Discharge current

[0077] LD: Load

[0078] P: Main current path

[0079] Rs: Current sensing resistor

[0080] V1: Cell voltage (first cell voltage)

[0081] V2: Cell voltage (second cell voltage)

[0082] V3: Cell voltage (third cell voltage)

[0083] Vd1: Voltage divider (first voltage divider)

[0084] SW1, SW2, SW3, SW4: Switching elements Detailed Implementation

[0085] This invention is based on the following insight: In battery pack control devices such as those in Patent Document 1, communication between the ADC and MPU, and MPU operations, necessitate constant or periodic startup, leading to increased current consumption. Furthermore, in battery pack control devices like those described, where cell equalization current, determined by an external resistor value, is discharged via switching, the cell equalization process requires switching the sequence of even-numbered and odd-numbered cells, making it impossible to simultaneously control adjacent cells, sometimes resulting in lower efficiency. Moreover, to achieve sufficient voltage equalization during cell equalization operations only during charging or startup, a cell equalization current on the order of 100 mA is required, necessitating a larger circuit size to handle such a large discharge current.

[0086] Furthermore, this invention is based on the following insight: In voltage regulation devices or voltage equalization correction circuits such as those in Patent Documents 2 and 3, if a high-precision comparator with small offset error is not used, useless cell equalization current may sometimes be discharged. Moreover, if a comparator is always used for cell equalization during load driving, the cell equalization operation used to bring degraded battery cells closer to the battery capacity of healthy battery cells may cause healthy cells to approach degraded cells, thus sometimes reducing the battery capacity of healthy battery cells.

[0087] Therefore, in one embodiment of the present invention, the cell balancing circuit has two differential voltage-to-current converters for two battery cells. A first differential voltage-to-current converter discharges a first cell balancing current from the first battery cell, the first cell balancing current being generated based on the voltage difference obtained by subtracting the second cell voltage from a first voltage divider, which is the average cell voltage of the two battery cells. A second differential voltage-to-current converter discharges a second cell balancing current from the second battery cell, the second cell balancing current being generated based on the voltage difference after reversing the positive and negative polarities.

[0088] Therefore, the cell balancing circuit of one embodiment of the present invention can discharge the cell balancing current by controlling the current corresponding to the voltage difference, thereby enabling cell balancing operation to achieve uniform cell voltage.

[0089] Hereinafter, the methods for carrying out the present invention will be described in detail with reference to the accompanying drawings.

[0090] Furthermore, in the accompanying drawings, the same symbols are used to label the same components, and sometimes repeated descriptions are omitted.

[0091] (First Implementation)

[0092] Figure 1 This is a circuit diagram showing a battery device (during discharge) using the cell balancing circuit of the first embodiment of the present invention.

[0093] like Figure 1 As shown, the battery device 10 includes battery cells 11 and 12, and a cell balancing circuit 100. Battery cells 11 and 12 are connected in series as a battery pack. The battery device 10 also has an external positive terminal EB+ and an external negative terminal EB-, and a load LD is connected between the external positive terminal EB+ and the external negative terminal EB- during discharge.

[0094] During discharge, battery cells 11 and 12 discharge to the load LD in the battery storage device 10, driving the load LD. The discharge current Id flows in the main current path P that connects battery cells 11, battery cells 12 and the load LD.

[0095] The battery cell 11 is a lithium-ion battery. The battery cell 11 generates a cell voltage V1 according to the charge / discharge state and the degradation state. In addition, the battery cell 11 is formed by a battery 11a and an internal resistor 11b.

[0096] The battery 11a generates a specified open-circuit voltage according to the charge and discharge state. The internal resistance 11b includes solution resistance, charge transfer resistance, active material bulk resistance, contact resistance, etc., and the resistance value increases with deterioration.

[0097] The charging voltage of battery cell 11 can be shown as shown in the following formula (1).

[0098] Charging voltage = open-circuit voltage + resistance value of internal resistor 11b × charging current ···(1)

[0099] The discharge voltage of battery cell 11 can be shown as shown in the following formula (2).

[0100] Discharge voltage = Open-circuit terminal voltage - Resistance value of internal resistor 11b × Discharge current ···(2)

[0101] According to equations (1) and (2), the cell voltage V1 of battery cell 11 will increase during charging as the degradation intensifies, but will decrease during discharging.

[0102] In addition, the battery cell 11 is sometimes referred to as the "first battery cell", and the cell voltage V1 is sometimes referred to as the "first cell voltage".

[0103] Battery cell 12, like battery cell 11, is a lithium-ion battery. The battery cell 12 generates a cell voltage V2 depending on its charge / discharge state and degradation state. Furthermore, battery cell 12 is formed by a battery 12a and an internal resistor 12b.

[0104] Battery 12a generates a specified open-circuit voltage according to its charge / discharge state. Similarly, internal resistor 12b increases in resistance as it deteriorates, just like internal resistor 11b.

[0105] The charging voltage of battery cell 12 can be shown as shown in the following formula (3).

[0106] Charging voltage = open-circuit voltage + resistance value of internal resistor 12b × charging current ···(3)

[0107] The discharge voltage of battery cell 12 can be shown as shown in the following formula (4).

[0108] Discharge voltage = Open-circuit terminal voltage - Resistance value of internal resistor 12b × Discharge current ···(4)

[0109] According to equations (3) and (4), the cell voltage V2 of battery cell 12 will increase during charging as the degradation intensifies, but will decrease during discharging.

[0110] In addition, battery cell 12 is sometimes referred to as "second battery cell", and cell voltage V2 is sometimes referred to as "second cell voltage".

[0111] Therefore, if the degradation progress of battery cells 11 and 12 differs, the resistance values ​​of their internal resistors will differ, sometimes resulting in a voltage difference between cell voltage V1 and cell voltage V2. If this voltage difference becomes large, when each battery cell is connected to a charge / discharge control circuit, during the charging of the battery pack containing battery cells 11 and 12, the charge / discharge control circuit will determine that the degraded battery cell with the higher cell voltage is overcharged. Thus, charging will stop when the battery cell with the lower cell voltage is not fully charged. Furthermore, when discharging the battery pack, the charge / discharge control circuit will determine that the degraded battery cell with the lower cell voltage is over-discharged. Thus, discharging will stop when the battery cell with the higher cell voltage is not fully discharged. Therefore, efficient charge / discharge may not be possible.

[0112] Therefore, the cell balancing circuit 100 compares the average voltage of cell voltage V1 and cell voltage V2 with cell voltage V2, and discharges the cell balancing current from battery cell 11 or battery cell 12 according to the voltage difference.

[0113] Therefore, the cell balancing circuit 100 can perform cell balancing operations on each battery cell through current control, regardless of whether it is charging, discharging, or open-circuit operation.

[0114] In the cell balancing circuit 100, each terminal is connected to the two ends of battery cell 11 and battery cell 12. Adjustment is achieved by discharging a cell balancing current corresponding to the voltage difference between battery cell 11 and battery cell 12. The cell balancing circuit 100 includes a differential voltage-to-current converter 101, a differential voltage-to-current converter 102, and a voltage divider circuit 103. Additionally, the cell balancing circuit 100 includes terminals VDD, VSS, VC1, VC2, CB1, and CB2.

[0115] Terminal VDD is the power supply terminal of the cell balancing circuit 100, which is connected to the positive terminal of the battery cell 11.

[0116] Terminal VSS is the ground (GND) terminal of the cell balancing circuit 100, which is connected to the negative terminal of the battery cell 12.

[0117] The voltage divider circuit 103 outputs a divided voltage after dividing the voltage applied to both ends.

[0118] In the voltage divider circuit 103, resistors 103a and 103b are connected in series. Resistors 103a and 103b have the same resistance value. One end of the voltage divider circuit 103 is connected to terminal VC1, and the other end is grounded.

[0119] Terminal VC1 is connected to the positive terminal of battery cell 11 via resistor R1a. Additionally, one end of capacitor C1 is connected to terminal VC1, and the other end of capacitor C1 is grounded.

[0120] Terminal VC2 is connected between the negative terminal of battery cell 11 and the positive terminal of battery cell 12 via resistor R2a. Additionally, one end of capacitor C2 is connected to terminal VC2, and the other end of capacitor C2 is grounded.

[0121] Furthermore, resistors R1a and R2a have the same resistance value.

[0122] Therefore, resistors 103a and 103b have the same resistance value, and resistors R1a and R2a, which are connected from terminals VC1 and VC2 to the positive and negative terminals of battery cell 11 respectively, have the same resistance value. Consequently, the voltage divider circuit 103 outputs a divided voltage Vd1, which is the average voltage of cell voltage V1 and cell voltage V2.

[0123] In addition, the voltage divider circuit 103 is sometimes referred to as the "first voltage divider circuit", and the voltage divider voltage Vd1 is sometimes referred to as the "first voltage divider voltage".

[0124] The differential voltage-to-current converter 101 outputs a current from its output terminal that corresponds to the difference between the voltages input to the non-inverting input terminal and the inverting input terminal, respectively.

[0125] The non-inverting input terminal of the differential voltage-to-current converter 101 is connected to the output terminal of the voltage divider circuit 103, and the inverting input terminal is connected to terminal VC2. Additionally, the input terminal of the differential voltage-to-current converter 101 is connected to terminal CB1, and the output terminal is connected to terminal CB2.

[0126] Terminal CB1 is connected to the positive terminal of battery cell 11 via resistor R1b and is connected to one end of differential voltage-current converter 101.

[0127] Terminal CB2 is connected between the negative terminal of battery cell 11 and the positive terminal of battery cell 12 via resistor R2b, and is connected to the other end of differential voltage-current converter 101.

[0128] Therefore, the differential voltage-current converter 101 discharges the cell equalization current Ib1 from the battery cell 11, and the cell equalization current Ib1 is generated based on the voltage difference obtained by subtracting the cell voltage V2 from the voltage divider voltage Vd1.

[0129] In addition, the differential voltage-current converter 101 is sometimes referred to as the "first differential voltage-current converter", and the cell balancing current Ib1 is sometimes referred to as the "first cell balancing current".

[0130] Figure 2 This is a graph showing the cell balancing current-voltage difference characteristics of the differential voltage-current converter according to the first embodiment of the present invention. Figure 2 The solid line in the graph represents the cell balancing current-voltage difference characteristic of the differential voltage-current converter 101. In the graph, the vertical axis represents the cell balancing current Ib1, and the horizontal axis represents the voltage difference (Vd1-V2) after subtracting the cell voltage V2 from the voltage divider voltage Vd1.

[0131] like Figure 2 As shown, the differential voltage-to-current converter 101 does not discharge the cell balancing current Ib1 when the voltage difference (Vd1-V2) is less than +V1a. Furthermore, when the voltage difference (Vd1-V2) is greater than +V1a and less than +V1b, the differential voltage-to-current converter 101 increases the cell balancing current Ib1 as the voltage difference increases, and keeps the cell balancing current Ib1 constant when the voltage difference is greater than +V1b.

[0132] return Figure 1 Similarly, the differential voltage-to-current converter 102 outputs a current from its output terminal that corresponds to the difference between the voltages input to the non-inverting input terminal and the inverting input terminal, respectively.

[0133] The non-inverting input terminal of the differential voltage-to-current converter 102 is connected to terminal VC2, and the inverting input terminal is connected to the output terminal of the voltage divider circuit 103. Additionally, the input terminal of the differential voltage-to-current converter 102 is connected to terminal CB2, and the output terminal is connected to terminal VSS.

[0134] Therefore, the differential voltage-to-current converter 102 discharges the cell balancing current Ib2 from the battery cell 12. This cell balancing current Ib2 is generated based on the voltage difference obtained by subtracting the divider voltage Vd1 from the cell voltage V2. In other words, the differential voltage-to-current converter 102 discharges the cell balancing current Ib2 from the battery cell 12, and this cell balancing current Ib2 is generated based on the voltage difference obtained by reversing the positive and negative values ​​of the voltage difference input to the non-inverting input terminal and the inverting input terminal of the differential voltage-to-current converter 101.

[0135] In addition, the differential voltage-current converter 102 is sometimes referred to as the "second differential voltage-current converter", and the cell balancing current Ib2 is sometimes referred to as the "second cell balancing current".

[0136] Figure 3 This is a graph showing the cell balancing current-voltage difference characteristics of the differential voltage-current converter according to the first embodiment of the present invention. Figure 3 The cell balancing current-voltage difference characteristic of the differential voltage-current converter 102 is represented by a dashed line. In the graph, the vertical axis represents the cell balancing current Ib2, and the horizontal axis represents the voltage difference (Vd1-V2) after subtracting the divider voltage Vd1 from the cell voltage V2.

[0137] like Figure 3 As shown, the differential voltage-to-current converter 102 keeps the cell balancing current Ib2 constant when the voltage difference (Vd1-V2) is less than -V2b. Furthermore, when the voltage difference (Vd1-V2) is above -V2b and below -V2a, the differential voltage-to-current converter 102 reduces the cell balancing current Ib2 as the voltage difference increases; and when the voltage difference is greater than -V2a, it prevents the cell balancing current Ib2 from discharging.

[0138] Figure 4 This is a graph showing the cell balancing current-voltage difference characteristics of the differential voltage-current converter according to the first embodiment of the present invention. Figure 4 Shown in the same chart Figure 2 and Figure 3 The cell balancing current-voltage difference characteristics of the differential voltage-current converter 101 and differential voltage-current converter 102 shown.

[0139] like Figure 4As shown, in the cell balancing current-voltage difference characteristic, a dead zone is set in the range where the voltage difference is above -V2a and below +V1a. The dead zone is a quiet area where the differential voltage-current converter 101 and differential voltage-current converter 102 do not discharge the cell balancing current Ib1 and cell balancing current Ib2 when there is a small voltage difference near 0.

[0140] Therefore, the unstable operation of differential voltage-current converter 101 and differential voltage-current converter 102, which discharges the cell equalization current Ib2 immediately after discharging the cell equalization current Ib1, can be avoided.

[0141] Furthermore, in the combination of differential voltage-to-current converter 101 and differential voltage-to-current converter 102, the cell balancing current Ib1 and cell balancing current Ib2 will not discharge simultaneously. Therefore, no losses will occur near terminal CB2 where the cell balancing current Ib1 and cell balancing current Ib2 cancel each other out, and the dead zone further reduces these concerns.

[0142] In addition, the differential voltage-current converter 101 and the differential voltage-current converter 102 are provided with upper limits so that when the absolute value of the voltage difference (Vd1-V2) is greater than a specified value, the cell balancing current Ib1 and the cell balancing current Ib2 are kept constant.

[0143] Therefore, rated operation can be performed without excessive cell equalization current discharge, and heat generation can be kept low.

[0144] Figure 5 This is a circuit diagram showing a battery device (during charging) using the cell balancing circuit of the first embodiment of the present invention.

[0145] like Figure 5 As shown, during charging, a charger CG is connected between the external positive terminal EB+ and the external negative terminal EB-.

[0146] During charging, the battery storage device 10 uses a charger CG to charge battery cells 11 and 12, which are connected in series. A charging current Ic flows in the main current path P connecting battery cells 11, 12, and the charger CG.

[0147] During charging, the cell balancing circuit 100 also performs cell balancing by comparing the divided voltage Vd1 with the cell voltage V2 and discharging either the cell balancing current Ib1 or the cell balancing current Ib2.

[0148] Figure 6 This is a circuit diagram showing a battery device (open circuit) using the cell balancing circuit of the first embodiment of the present invention.

[0149] like Figure 6 As shown, in the open circuit state, there is no connection between the external positive terminal EB+ and the external negative terminal EB-. Therefore, no current flows in the main current path P connecting battery cells 11 and 12.

[0150] When the cell balancing circuit 100 is open, it also performs cell balancing by comparing the voltage divider Vd1 with the cell voltage V2, causing the cell balancing current Ib1 or the cell balancing current Ib2 to discharge from the battery cell 11 and the battery cell 12.

[0151] Thus, regardless of whether it is charging, discharging, or open-circuit, the cell balancing circuit 100 will compare the average voltage of cell voltage V1 and cell voltage V2 with cell voltage V2, and discharge the cell balancing current from battery cell 11 or battery cell 12 according to the voltage difference.

[0152] Therefore, the cell balancing circuit 100 can perform cell balancing operations on each battery cell through current control, regardless of whether it is charging, discharging, or in an open-circuit state. Furthermore, since the cell balancing circuit 100 continuously performs cell balancing operations during long-term use, the degradation state of each battery cell is less likely to become different, thus eliminating the need for large cell balancing current discharges and achieving a longer lifespan for the battery pack.

[0153] (Second Implementation)

[0154] Figure 7 This is a circuit diagram showing a battery device (during discharge) using the cell balancing circuit of the second embodiment of the present invention.

[0155] like Figure 7 As shown, the cell balancing circuit 200 of the second embodiment is the same as the cell balancing circuit 100 of the first embodiment, except that it also includes a current monitoring circuit 104 and a switching element SW1. Furthermore, the battery device 20 of the second embodiment is the same as the battery device 10, except that it also includes a current sensing resistor Rs as in the battery device 10 of the first embodiment.

[0156] Here, the current sensing resistor Rs, the current monitoring circuit 104, and the switching element SW1, which are additional structures compared to the first embodiment, will be described.

[0157] One end of the current sensing resistor Rs is connected to the negative terminal of battery cell 12, and the other end is connected to the external negative terminal EB-.

[0158] The current monitoring circuit 104 is connected to both ends of the current sensing resistor Rs through terminals CSP and CSN. By monitoring the current value flowing in the current sensing resistor Rs, i.e. the current value flowing in the main current path P, it determines whether the battery device 20 is discharging, charging, or open-circuit.

[0159] When the current monitoring circuit 104 determines that a discharge has occurred, it turns on the switching element SW1 and short-circuits the non-inverting input terminal and the inverting input terminal of the differential voltage-current converter 101 and the differential voltage-current converter 102 to prevent the generation of a voltage difference and thus stop the cell balancing operation.

[0160] The switching element SW1 is turned on / off according to the signal output from the current monitoring circuit 104. When the switching element SW1 is turned on, it is short-circuited so that no voltage difference is generated between the non-inverting input terminal and the inverting input terminal of the differential voltage-current converter 101 and the differential voltage-current converter 102; when it is turned off, it is open-circuited.

[0161] Thus, when the current monitoring circuit 104 determines that the battery is discharging, the cell balancing circuit 200 turns on the switching element SW1 to stop the cell balancing operation, thereby maintaining the overall capacity of the battery pack without unnecessarily reducing the capacity of healthy battery cells.

[0162] Figure 8 This is a circuit diagram showing a battery device (during charging) using the cell balancing circuit of the second embodiment of the present invention.

[0163] like Figure 8 As shown, during charging, a charger CG is connected between the external positive terminal EB+ and the external negative terminal EB-. A charging current Ic flows in the main current path P connecting battery cell 11, battery cell 12, and charger CG. The current monitoring circuit 104, which determines that charging is in progress, disconnects the switching element SW1. Then, the cell balancing circuit 200 compares the divided voltage Vd1 with the cell voltage V2, discharging either the cell balancing current Ib1 or the cell balancing current Ib2 to perform cell balancing.

[0164] Figure 9 This is a circuit diagram showing a battery device (in open circuit mode) using the cell balancing circuit of the second embodiment of the present invention.

[0165] like Figure 9As shown, when the current monitoring circuit 104 determines that there is no connection and no current flowing between the external positive terminal EB+ and the external negative terminal EB-, it disconnects the switching element SW1. Then, the cell balancing circuit 200 performs cell balancing by comparing the divided voltage Vd1 with the cell voltage V2 and discharging either the cell balancing current Ib1 or the cell balancing current Ib2.

[0166] Thus, when the current monitoring circuit 104 determines that the battery is discharging, the cell balancing circuit 200 turns on the switching element SW1 without performing cell balancing, thereby maintaining the overall capacity of the battery pack without unnecessarily reducing the capacity of healthy battery cells.

[0167] (Third implementation method)

[0168] Figure 10 This is a circuit diagram showing a battery device 30 (during discharge) using the cell balancing circuit of the third embodiment of the present invention.

[0169] like Figure 10 As shown, the cell balancing circuit 300 of the third embodiment is the same as the cell balancing circuit 200 except that it also includes the battery cell 13, voltage divider circuit 107, differential voltage-current converter 105, differential voltage-current converter 106 and switching element SW2.

[0170] Here, the battery cell 13, voltage divider circuit 107, differential voltage-current converter 105, and differential voltage-current converter 106, which are additional structures compared to the second embodiment, will be described.

[0171] Battery cell 13, like battery cells 11 and 12, is a lithium-ion battery. Battery cell 13 is connected in series with battery cells 11 and 12 on the main current path P, and its cell voltage V3 is generated according to the charge / discharge state and degradation state. Furthermore, battery cell 13 is formed by a battery 13a and an internal resistor 13b.

[0172] Battery 13a generates a specified open-circuit voltage according to the charge / discharge state. The internal resistance 13b includes solution resistance, charge transfer resistance, active material bulk resistance, contact resistance, etc., and the resistance value increases with degradation.

[0173] Like voltage divider circuit 103, voltage divider circuit 107 outputs a divided voltage after dividing the voltage applied to both ends.

[0174] In the voltage divider circuit 107, resistors 107a and 107b are connected in series. Resistors 107a and 107b have the same resistance value. One end of the voltage divider circuit 107 is connected to terminal VC2, and the other end is grounded.

[0175] Furthermore, the resistance value of resistor R3a is the same as that of resistors R1a and R2a.

[0176] Therefore, since the resistance values ​​of resistors 107a and 107b are the same, the voltage divider circuit 107 outputs a voltage divider voltage Vd2, which is the average voltage of cell voltage V2 and cell voltage V3.

[0177] In addition, the voltage divider circuit 107 is sometimes referred to as the "second voltage divider circuit", and the voltage divider voltage Vd2 is sometimes referred to as the "second voltage divider voltage".

[0178] The differential voltage-to-current converter 105, like the differential voltage-to-current converter 101, outputs a current from its output terminal corresponding to the difference between the voltages input to the non-inverting input terminal and the inverting input terminal, respectively.

[0179] The non-inverting input terminal of the differential voltage-to-current converter 105 is connected to the output terminal of the voltage divider circuit 107, and the inverting input terminal is connected to terminal VC3. Additionally, the input terminal of the differential voltage-to-current converter 105 is connected to terminal CB2, and the output terminal is connected to terminal CB3.

[0180] Terminal VC3 is connected between the negative terminal of battery cell 12 and the positive terminal of battery cell 13 via resistor R3a. Additionally, one end of capacitor C3 is connected to terminal VC3, and the other end of capacitor C3 is grounded.

[0181] Terminal CB3 is connected between the negative terminal of battery cell 12 and the positive terminal of battery cell 13 via resistor R3b, and is connected to the other end of differential voltage-current converter 105.

[0182] Therefore, the differential voltage-current converter 105 discharges the cell balancing current Ib3 from the battery cell 12, and the cell balancing current Ib3 is generated based on the voltage difference obtained by subtracting the cell voltage V3 from the voltage divider voltage Vd2.

[0183] In addition, the differential voltage-current converter 105 is sometimes referred to as the "third differential voltage-current converter", and the cell balancing current Ib3 is sometimes referred to as the "third cell balancing current".

[0184] Similarly to the differential voltage-current converter 102, the differential voltage-current converter 106 outputs a current from its output terminal that corresponds to the difference between the voltages input to the non-inverting input terminal and the inverting input terminal, respectively.

[0185] The non-inverting input terminal of the differential voltage-to-current converter 106 is connected to terminal VC3, and the inverting input terminal is connected to the output terminal of the voltage divider circuit 107. Additionally, the input terminal of the differential voltage-to-current converter 106 is connected to terminal CB3, and the output terminal is connected to terminal VSS.

[0186] Therefore, the differential voltage-current converter 106 discharges the cell balancing current Ib4 from the battery cell 12, and the cell balancing current Ib4 is generated based on the voltage difference after subtracting the voltage divider voltage Vd2 from the cell voltage V3.

[0187] In addition, the differential voltage-current converter 106 is sometimes referred to as the "fourth differential voltage-current converter", and the cell balancing current Ib4 is sometimes referred to as the "fourth cell balancing current".

[0188] Like switch element SW1, switch element SW2 is switched on / off according to the signal output from current monitoring circuit 104. When switch element SW2 is switched on, it is short-circuited so that no voltage difference is generated between the non-inverting input terminal and the inverting input terminal of differential voltage-current converter 105 and differential voltage-current converter 106; when switched off, it is open-circuited.

[0189] Figure 11 This is a circuit diagram showing a battery device (during charging) using the cell balancing circuit of the third embodiment of the present invention.

[0190] like Figure 11 As shown, during charging, a charger CG is connected between the external positive terminal EB+ and the external negative terminal EB-. A charging current Ic flows in the main current path P connecting battery cells 11, 12, 13, and the charger CG. The current monitoring circuit 104, which determines that charging is in progress, disconnects switching elements SW1 and SW2. Then, the cell balancing circuit 300 compares the divided voltage Vd1 with the cell voltage V2, and compares the divided voltage Vd2 with the cell voltage V3. Based on the comparison results, the cell balancing circuit 300 discharges the cell balancing currents Ib1, Ib2, Ib3, or Ib4 to perform cell balancing.

[0191] Figure 12 This is a circuit diagram showing a battery device (open circuit) using the cell balancing circuit of the third embodiment of the present invention.

[0192] like Figure 12 As shown, when the current monitoring circuit 104 determines that there is no connection and no current flowing between the external positive terminal EB+ and the external negative terminal EB-, it disconnects the switching element SW1. Then, the cell balancing circuit 300 compares the divided voltage Vd1 with the cell voltage V2, and compares the divided voltage Vd2 with the cell voltage V3. Based on the comparison results, the cell balancing circuit 300 discharges the cell balancing currents Ib1, Ib2, Ib3, or Ib4 to perform cell balancing.

[0193] Thus, even if there are three battery cells, the cell balancing circuit 300 can compare the battery voltages of adjacent battery cells and discharge cell balancing currents from battery cells 11, 12, and 13 based on the voltage difference. In battery cell 12, cell balancing currents Ib2 and Ib3 are added together.

[0194] In addition, similarly to the cell balancing circuit 200, when the current monitoring circuit 104 determines that the battery is discharging, the cell balancing circuit 300 turns on the switching element SW1 without performing cell balancing, thus maintaining the overall capacity of the battery pack without unnecessarily reducing the capacity of healthy battery cells.

[0195] Furthermore, although the cell balancing circuit 300 performs cell balancing for three battery cells, for four or more battery cells, cell balancing can also be performed by adding a structure relative to the second embodiment as the number of battery cells increases.

[0196] (Fourth Implementation)

[0197] Figure 13 This is a circuit diagram showing a battery device 40 (during discharge) using the cell balancing circuit of the fourth embodiment of the present invention.

[0198] The cell balancing circuit 400 of the fourth embodiment is the same as the cell balancing circuit 100, except that it has a differential voltage-current converter 108, a current mirror circuit 109, and a current mirror circuit 110 instead of a differential voltage-current converter 101 and a differential voltage-current converter 102 in the cell balancing circuit 100.

[0199] Here, the differential voltage-current converter 108, the current mirror circuit 109, and the current mirror circuit 110, which are alternatives to the differential voltage-current converter 101 and differential voltage-current converter 102 in the first embodiment, will be described.

[0200] The differential voltage-to-current converter 108 outputs a current from two output terminals corresponding to the difference between the voltages input to the non-inverting input terminal and the inverting input terminal, respectively.

[0201] The non-inverting input terminal of the differential voltage-to-current converter 108 is connected to the output terminal of the voltage divider circuit 103, and the inverting input terminal is connected to terminal VC2. In addition, one output terminal of the differential voltage-to-current converter 108 is connected to the current mirror circuit 109, and the other output terminal is connected to the current mirror circuit 110.

[0202] The current mirror circuit 109 discharges the cell balancing current Ib1 from the battery cell 11, the cell balancing current Ib1 corresponding to the current generated from an output terminal of the differential voltage-current converter 108.

[0203] The current mirror circuit 110 discharges the cell balancing current Ib2 from the battery cell 12, which corresponds to the current generated from another output terminal of the differential voltage-current converter 108.

[0204] In addition, the current mirror circuit 109 is sometimes referred to as the "first current mirror circuit", and the current mirror circuit 110 is sometimes referred to as the "second current mirror circuit".

[0205] Therefore, the differential voltage-to-current converter 108 generates a supply current based on the voltage difference obtained by subtracting the cell voltage V2 from the voltage divider voltage Vd1, and the current mirror circuits 109 and 110 discharge the cell balancing currents Ib1 and Ib2, which are corresponding to the supply current, from the battery cells 11 and 12.

[0206] Specifically, consider the case where the amplification of the current mirror circuit 109 is set to 1,000 times, and the battery voltage of battery cell 11 is higher than that of battery cell 12. In this case, such as Figure 13 As shown, a supply current of 1 μA flows from the differential voltage-to-current converter 108 to the current mirror circuit 109, thereby causing the current mirror circuit 109 to discharge a cell equalization current Ib1 of 1 mA from the battery cell 11.

[0207] Therefore, the cell balancing circuit 400 of the fourth embodiment can have the same function as the cell balancing circuit 100 of the first embodiment, and can discharge a larger cell balancing current.

[0208] (Fifth implementation method)

[0209] Figure 14 This is a circuit diagram showing a battery device 50 (when charging) using the cell balancing circuit of the fifth embodiment of the present invention.

[0210] The cell balancing circuit 500 of the fifth embodiment further includes, in addition to, a charging termination voltage detection unit 111, a charging termination voltage detection unit 112, a logic circuit 113, a logic circuit 114, a diagnostic circuit 115, an balancing detection unit 116, a balancing detection unit 117, and a buffer 118, which are the same as those in the cell balancing circuit 400.

[0211] Here, the charging termination voltage detection unit 111, charging termination voltage detection unit 112, logic circuit 113, logic circuit 114, diagnostic circuit 115, equalization detection unit 116, equalization detection unit 117, and buffer 118, which are additional structures compared to the fourth embodiment, will be described.

[0212] The charging termination voltage detection unit 111 detects the charging termination voltage of the battery cell 11. The charging termination voltage is a voltage value specified for safe charging. One end of the charging termination voltage detection unit 111 is connected to terminal VC1, and the other end is connected to terminal VC2. When the charging termination voltage detection unit 111 detects that the charging voltage of the battery cell 11 has reached the charging termination voltage, it outputs a signal VBC1 to the logic circuit 113.

[0213] The charging termination voltage detection unit 112 detects the charging termination voltage of the battery cell 12. One end of the charging termination voltage detection unit 112 is connected to terminal VC2, and the other end is connected to terminal VSS. When the charging termination voltage detection unit 112 detects that the charging voltage of the battery cell 12 has reached the charging termination voltage, it outputs a signal VBC2 to the logic circuit 113.

[0214] The logic circuit 113 outputs the results of the logic operation based on the input signals VBC1 and VBC2 to the logic circuit 114 and the differential voltage-current converter 108 in the form of signals FMC12 and FMC21, respectively.

[0215] Specifically, the logic circuit 113 performs logical operations on the output signals FMC12 and FMC21, where signals FMC12 and FMC21 indicate that either or both of the charging voltages of battery cell 11 and battery cell 12 have reached or not reached the charging termination voltage.

[0216] In addition, the differential voltage-to-current converter 108 turns the supply current to the current mirror circuit 109 and the current mirror circuit 110 on / off according to the signal FMC12 and signal FMC21 input from the logic circuit 113.

[0217] Specifically, the differential voltage-to-current converter 108 discharges the cell balancing currents Ib1 and Ib2, corresponding to the voltage difference between battery cells 11 and 12, when both the charging voltages of battery cells 11 and 12 reach the charging termination voltage. Even when the charging voltages of battery cells 11 and 12 have not reached the charging termination voltage, the differential voltage-to-current converter 108 still discharges the cell balancing currents Ib1 and Ib2, corresponding to the voltage difference between battery cells 11 and 12. Furthermore, when only the charging voltage of battery cell 11 reaches the charging termination voltage, the differential voltage-to-current converter 108 discharges the maximum output cell balancing current Ib1 regardless of the voltage difference. When only the charging voltage of battery cell 12 reaches the charging termination voltage, the differential voltage-to-current converter 108 discharges the maximum output cell balancing current Ib2.

[0218] Thus, in addition to having the functions of the cell balancing circuit 400, the cell balancing circuit 500, during charging, when at least one of battery cells 11 and 12 reaches or exceeds the charging termination voltage, discharges the maximum output cell balancing current through the differential voltage-to-current converter 108. That is, in Figure 4 In the diagram shown, the cell balancing circuit 500 discharges the cell balancing current Ib1 or cell balancing current Ib2 at its maximum output saturation. When both battery cell 11 and battery cell 12 reach above the charging termination voltage, they return to their original state.

[0219] The logic circuit 114 outputs the result of logical operations on the two voltages (voltage divider Vd1 and voltage at terminal VC2) input to the differential voltage-current converter 108, and the signals FMC12 and FMC21 output by the logic circuit 113 to the diagnostic circuit 115.

[0220] Specifically, logic circuit 114 performs logical operations to determine whether cell balancing is required and whether the charging termination voltage of battery cells 11 and 12 has been reached. Logic circuit 114 outputs the result of the logical operations to diagnostic circuit 115.

[0221] The diagnostic circuit 115 outputs an error signal from the ERR terminal based on the result of logical operations performed by the logic circuit 114.

[0222] Specifically, when the voltage difference between battery cell 11 and battery cell 12 is extremely large and the cells are in an unbalanced state, the diagnostic circuit 115 outputs an error signal from the ERR terminal.

[0223] Furthermore, although described later, the diagnostic circuit 115 outputs an error signal from the ERR terminal based on the signals output by the equalization detection unit 116 and the equalization detection unit 117. That is, when the diagnostic circuit 115 diagnoses that either the current mirror circuit 109 or the current mirror circuit 110 is abnormal based on the detection results of the equalization detection unit 116 and the detection results of the equalization detection unit 117, it outputs an error signal to the outside.

[0224] The equalization detection unit 116 is connected between terminals VC1 and CB1 to detect whether cell equalization is being performed. Specifically, it compares the cell voltage of battery cell 11 with the input voltage of the current mirror circuit 109 to detect the operating state of the current mirror circuit 109. Then, when the equalization detection unit 116 detects an abnormality in the operation of the current mirror circuit 109, it outputs a signal to the diagnostic circuit 115.

[0225] The equalization detection unit 117 is connected between terminal VC2 and terminal CB2 to detect whether cell equalization is being performed. That is, it compares the cell voltage of battery cell 12 with the input voltage of current mirror circuit 110 to detect the operating state of current mirror circuit 110. Then, when the equalization detection unit 117 detects an abnormality in the operation of current mirror circuit 110, it outputs a signal to diagnostic circuit 115.

[0226] In addition, the equalization detection unit 116 is sometimes referred to as the "first equalization detection unit", and the equalization detection unit 117 is sometimes referred to as the "second equalization detection unit".

[0227] Buffer 118 allows signals from the CBEO terminal output to another cell equalization circuit to pass through.

[0228] The switching element SW3 is connected between one of the output terminals of the differential voltage-current converter 108 and the current mirror circuit 109.

[0229] Switching element SW4 is connected between another output terminal of differential voltage-current converter 108 and current mirror circuit 110.

[0230] When cooperating with another cell equalization circuit, the cell equalization circuit 500 inputs a signal from the other cell equalization circuit to terminal CBEI, which serves as an external signal input, and outputs a signal from terminal CBEO to the other cell equalization circuit via buffer 118. Specifically, when a disconnect signal is input from the other cell equalization circuit to terminal CBEI, switching elements SW3 and SW4 in the cell equalization circuit 500 are disconnected, and the cell equalization function stops. Furthermore, even though a disconnect signal is input from the other cell equalization circuit to terminal CBEI, if any equalization detection unit detects that any current mirror circuit is discharging the cell equalization current, the diagnostic circuit 115 outputs an error signal to the outside.

[0231] In addition, when a connection signal is input to terminal CBEI from another cell balancing circuit, switching elements SW3 and SW4 in cell balancing circuit 500 are turned on, and the cell balancing function is activated.

[0232] The cell balancing circuit 500 can turn on / off the switching element of another cell balancing circuit according to the signal output from the terminal CBEO, thereby enabling or stopping the cell balancing function.

[0233] Next, two examples of embodiments of the battery device of the present invention will be shown.

[0234] Figure 15 This indicates that multiple [items] were used. Figure 14 A schematic diagram of an example of a battery device with a cell balancing circuit.

[0235] like Figure 15 As shown, the battery device 60 is connected in series via cell balancing circuits 500a and 500b, so that the battery cells in battery cell groups 119a and 119b can perform cell balancing operations respectively. Each battery cell group 119a and 119b contains six battery cells connected in series.

[0236] In addition, the cell balancing circuit 500a and the cell balancing circuit 500b are connected via terminal CBE (terminal CBEI + terminal CBEO) and can cooperate.

[0237] Therefore, the cell balancing circuit 500a and the cell balancing circuit 500b can work together through simple wiring.

[0238] Furthermore, in both cell balancing circuits 500a and 500b, one differential voltage-to-current converter exists in each pair of adjacent battery cells. Therefore, for the topmost and bottommost battery cells within the same cell group, the cell balancing current is not added together. Consequently, compared to other battery cells, the topmost and bottommost battery cells in each cell group have a smaller cell balancing current, resulting in a longer balancing time. In this respect... Figure 13 and Figure 14 The differential voltage-to-current converter 108 shown can be supplemented by discharging from the battery cell at maximum output when any of the battery cells reaches a charge termination voltage.

[0239] In addition, through Figure 16 The connection method shown allows the equalization time required to be equalized within the battery pack.

[0240] Figure 16 This indicates that multiple [items] were used. Figure 14A schematic diagram of another example of a battery storage device with a cell balancing circuit. Figure 16 The image shows a battery device that uses multiple battery cells to form a battery pack. Figure 16 The battery storage device 70 shown connects the battery cells of the bottom layer of battery cell group 119a (top layer of battery cell group 119b) to enable cell balancing operation between cell balancing circuit 500a and cell balancing circuit 500b. Furthermore, the battery storage device 70 connects the battery cells of the bottom layer of battery cell group 119b (top layer of battery cell group 119c) to enable cell balancing operation between cell balancing circuit 500b and cell balancing circuit 500c.

[0241] Through this connection, for example in the bottom layer of battery cells in battery cell group 119a, cell balancing circuits 500a and 500b perform cell balancing operations, thereby adding the cell balancing currents. Thus, the battery storage device 70 can equalize the time required for balancing within the battery storage device.

[0242] As described above, a cell balancing circuit according to one embodiment of the present invention includes a first differential voltage-to-current converter that discharges a first cell balancing current from a first battery cell. The first cell balancing current is generated based on the voltage difference obtained by subtracting the second cell voltage from a first voltage divider. Furthermore, the cell balancing circuit also includes a second differential voltage-to-current converter that discharges a second cell balancing current from a second battery cell. The second cell balancing current is generated based on the voltage difference obtained by subtracting the first voltage divider from the second cell voltage.

[0243] Therefore, cell balancing can be performed on the series-connected battery cells through current control.

[0244] Furthermore, the battery cell is a lithium-ion battery in each embodiment, but it is not limited to this; any battery capable of charging and discharging is acceptable.

[0245] In addition, in the second and third embodiments, one end of the current sensing resistor Rs is connected to the negative terminal of the battery cell 12, and the other end is connected to the external negative terminal EB-, but this is only necessary as long as the current monitoring circuit 104 can determine the state of the battery cell. Specifically, the current sensing resistor Rs only needs to be connected in series in the main current path P.

[0246] Furthermore, in each embodiment, the voltage divider circuit outputs a voltage divider voltage that is the average voltage of the two cell voltages, but the voltage divider voltage can also be adjusted by changing the resistance value of the voltage divider resistor.

Claims

1. A cell balancing circuit for controlling the cell balancing of a first battery cell generating a first cell voltage and a second battery cell connected in series with the first battery cell and generating a second cell voltage, the cell balancing circuit being characterized by having: The first voltage divider circuit outputs a first voltage divider voltage, which is the average voltage of the first battery cell and the second battery cell. A first differential voltage-to-current converter discharges a first cell balancing current from the first battery cell, the first cell balancing current being generated based on the voltage difference between the first voltage divider and the second cell voltage; and The second differential voltage-current converter discharges the second cell equalization current from the second battery cell, the second cell equalization current being generated based on the voltage difference after reversing the positive and negative polarities.

2. The cell balancing circuit according to claim 1, wherein, The first differential voltage-to-current converter and the second differential voltage-to-current converter do not discharge the first cell balancing current and the second cell balancing current when the voltage difference is within a specified range including 0.

3. The cell balancing circuit according to claim 1, wherein, When the absolute value of the voltage difference is greater than a specified value, the first differential voltage-current converter and the second differential voltage-current converter keep the cell balancing current constant.

4. The cell balancing circuit according to claim 1 further comprises: A current monitoring circuit is connected to both ends of a current sensing resistor connected in series in the main current path, monitors the current value flowing in the current sensing resistor, and determines whether the first battery cell or the second battery cell is in a discharging, charging, or open-circuit state; and The switching element is switched on / off according to a signal output from the current monitoring circuit. When switched on, it is short-circuited to prevent the voltage difference from being generated; when switched off, it is not short-circuited to generate the voltage difference. The current monitoring circuit turns on the switching element when it determines that the circuit is discharging, and turns off the switching element when it determines that the circuit is charging or open circuit.

5. The cell balancing circuit according to claim 1 further comprises: A first current mirror circuit makes a current corresponding to the supply current from the first differential voltage-to-current converter serve as the first cell equalization current for discharging from the first battery cell; and The second current mirror circuit makes the current corresponding to the supply current from the second differential voltage-current converter the second cell equalization current, and discharges from the second battery cell.

6. The cell balancing circuit according to claim 5 further comprises: The first equalization detection unit compares the voltage of the first cell with the input voltage of the first current mirror circuit to detect the operating state of the first current mirror circuit. The second equalization detection unit compares the voltage of the second cell with the input voltage of the second current mirror circuit to detect the operating state of the second current mirror circuit. as well as The diagnostic circuit outputs an error signal to the outside when it diagnoses either the first current mirror circuit or the second current mirror circuit as abnormal based on the detection results of the first equalization detection unit and the second equalization detection unit.

7. The cell balancing circuit according to claim 6 further comprises an external signal input terminal, wherein the external signal input terminal is used to input a disconnect signal that stops the discharge of the first cell balancing current and the second cell balancing current. When the disconnect signal is input to the external signal input terminal The first equalization detection unit and the second equalization detection unit detected the positive discharge of the cell equalization current. The diagnostic circuit outputs the error signal to the outside.

8. The cell balancing circuit according to claim 1, wherein, When the third battery cell, which generates the third cell voltage, is connected in series with the negative terminal side of the second battery cell, it also has the following characteristics: The second voltage divider circuit outputs a second voltage divider voltage, which is the average voltage of the second battery cell and the third battery cell. The third differential voltage-current converter discharges the third cell equalization current from the second battery cell. The third cell equalization current is generated based on the voltage difference obtained by subtracting the third cell voltage from the second voltage divider. as well as A fourth differential voltage-to-current converter discharges a fourth cell equalizing current from the third battery cell. This fourth cell equalizing current is generated based on the voltage difference after reversing the positive and negative polarities. In the second battery cell, the equalization current of the second cell is added to the equalization current of the third cell.

9. A battery storage device, characterized in that... At least have: The first battery cell generates the first cell voltage; The second battery cell is connected in series with the first battery cell and generates the second cell voltage; and The cell balancing circuit as described in any one of claims 1 to 8.

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