Cell balancing circuit and battery device

Abstract

To provide a cell balancing circuit that can continuously perform cell balancing operations on each battery cell connected in series. [Solution] A cell balance circuit 100 controls the cell balance between a battery cell 11 that generates a cell voltage V1 and a battery cell 12 connected in series with the battery cell 11 that generates a cell voltage V2, and comprises a voltage divider circuit 103 that outputs a divided voltage Vd1 which is the average voltage of the battery cell 11 and the battery cell 12, a differential voltage-current converter 101 that discharges a cell balance current Ib1 generated according to the voltage difference obtained by subtracting the cell voltage V2 from the divided voltage Vd1 from the battery cell 11, and a differential voltage-current converter 102 that discharges a cell balance current Ib2 generated according to the voltage difference with the positive and negative reversed from the battery cell 12.

Description

Technical Field

[0001] The present invention relates to a cell balance circuit and a battery device.

Background Art

[0002] There is a battery pack in which a plurality of rechargeable secondary battery cells are connected in series. The cell voltages of the plurality of battery cells in the battery pack are not the same, for example, due to manufacturing variations of the battery cells, variations in the self-leakage current of the battery cells, etc. Also, each cell voltage may vary depending on the environmental temperature. Furthermore, as this battery pack deteriorates as it repeatedly charges and discharges, the state of deterioration (SOH: State of Health) becomes different for each battery cell, and a deviation occurs in the cell voltage of each battery cell. As the deterioration progresses, the cell voltage of the battery cell becomes higher during charging but lower during discharging.

[0003] When the cell voltages of each battery cell are significantly different, if a charge-discharge control circuit is connected to each battery cell, the battery cell with a high cell voltage will immediately become overcharged and charging will stop when charging, and the battery cell with a low cell voltage will immediately become overdischarged and discharging will stop when discharging. Therefore, there is a risk that efficient charge and discharge cannot be achieved. In order to adjust the balance of the cell voltages of each battery cell in such a battery pack, various proposals have been made.

[0004] For example, a battery pack control device has been proposed that measures the cell voltage of each battery cell with an ADC (Analog to Digital Converter) and performs calculations with a signal processing circuit such as an MPU (Micro Processing Unit) to equalize the cell voltages of each battery cell (see Patent Document 1). Also, a voltage adjustment device for a battery pack has been proposed that selectively discharges battery cells with a voltage higher than the average voltage of the battery pack using a comparator, and finally equalizes the cell voltages of all battery cells (see Patent Document 2). Furthermore, a voltage balance correction circuit has been proposed that uses a comparator to form a negative feedback loop that makes the potential difference between the average voltage of two adjacent battery cells and the intermediate voltage of the two battery cells zero, and discharges the battery cell with the higher voltage when a voltage difference occurs (see Patent Document 3). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2015 / 029283 [Patent Document 2] Japanese Patent Publication No. 2000-83327 [Patent Document 3] Japanese Patent Publication No. 2010-63264 [Overview of the project] [Problems that the invention aims to solve]

[0006] One aspect of the present invention aims to provide a cell balancing circuit that can perform cell balancing operations by current control for each battery cell connected in series. [Means for solving the problem]

[0007] The cell balancing circuit in one embodiment of the present invention is A cell balancing circuit for controlling the cell balance between 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, A first voltage divider circuit that outputs a first voltage divider which is the average voltage of the first battery cell and the second battery cell, A first differential voltage-current converter discharges a first cell balance current, generated according to the voltage difference obtained by subtracting the second cell voltage from the first divided voltage, from the first battery cell. A second differential voltage-current converter discharges a second cell balance current generated in accordance with the voltage difference with reversed positive and negative polarity from the second battery cell, It has. [Effects of the Invention]

[0008] According to one aspect of the present invention, a cell balancing circuit can be provided that can perform cell balancing operations on each battery cell connected in series by current control. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a circuit diagram showing a battery device (during discharge) using a cell balance circuit according to the first embodiment of the present invention. [Figure 2] Figure 2 is a graph showing the cell balance current-voltage difference characteristics of a differential voltage-current converter in the first embodiment of the present invention. [Figure 3] Figure 3 is a graph showing the cell balance current-voltage difference characteristics of a differential voltage-current converter in the first embodiment of the present invention. [Figure 4] Figure 4 is a graph showing the cell balance current-voltage difference characteristics of a differential voltage-current converter in the first embodiment of the present invention. [Figure 5] Figure 5 is a circuit diagram showing a battery device (during charging) using a cell balance circuit according to the first embodiment of the present invention. [Figure 6] Figure 6 is a circuit diagram showing a battery device (when open) using a cell balance circuit according to the first embodiment of the present invention. [Figure 7] Figure 7 is a circuit diagram showing a battery device (during discharge) using a cell balance circuit according to a second embodiment of the present invention. [Figure 8] Figure 8 is a circuit diagram showing a battery device (during charging) using a cell balance circuit according to a second embodiment of the present invention. [Figure 9] Figure 9 is a circuit diagram showing a battery device (when open) using a cell balance circuit in a second embodiment of the present invention. [Figure 10] Figure 10 is a circuit diagram showing a battery device (during discharge) using a cell balance circuit according to a third embodiment of the present invention. [Figure 11] FIG. 11 is a circuit diagram showing a battery device (during charging) using the cell balance circuit in the third embodiment of the present invention. [Figure 12] FIG. 12 is a circuit diagram showing a battery device (during discharge) using the cell balance circuit in the third embodiment of the present invention. [Figure 13] FIG. 13 is a circuit diagram showing a battery device (during discharge) using the cell balance circuit in the fourth embodiment of the present invention. [Figure 14] FIG. 14 is a circuit diagram showing a battery device (during charging) using the cell balance circuit in the fifth embodiment of the present invention. [Figure 15] FIG. 15 is a schematic diagram showing an example of a battery device using a plurality of the cell balance circuits of FIG. 14. [Figure 16] FIG. 16 is a schematic diagram showing a battery device using a plurality of conventional cell balance circuits.

Embodiments for Carrying Out the Invention

[0010] The present invention is based on the finding that in a battery pack control device such as that in Patent Document 1, communication between the ADC and the MPU and the operation of the MPU are required, so it must be started constantly or periodically, resulting in a large consumption current. Also, in a method of discharging a cell balance current determined by an external resistance value by a switch operation like this battery pack control device, a sequence for switching between even cells and odd cells in the cell balance operation is required, and adjacent battery cells cannot be controlled simultaneously, so the efficiency may be low. Furthermore, in order to obtain a sufficient voltage balance effect in the cell balance operation only during charging or startup, a cell balance current of the order of 100 mA is required, and the scale of the circuit for discharging such a large current becomes large.

[0011] Furthermore, the present invention is based on the finding that, in voltage adjustment devices and voltage balance correction circuits such as those described in Patent Documents 2 and 3, if a high-precision comparator with a small offset error is not used, unnecessary cell balance current may be discharged. Moreover, if cell balance operation is performed using a comparator at all times when a load is driven, the cell balance operation, which is intended to bring degraded battery cells closer to the battery capacity of healthy battery cells, ends up bringing healthy cells closer to degraded cells, which may reduce the battery capacity of healthy battery cells.

[0012] Therefore, the cell balancing circuit in one embodiment of the present invention has two differential voltage-current converters for two battery cells. The first differential voltage-current converter discharges a first cell balancing current from the first battery cell, which is generated according to the voltage difference obtained by subtracting the second cell voltage from a first divided voltage, which is the average cell voltage of the two battery cells. The second differential voltage-current converter discharges a second cell balancing current from the second battery cell, which is generated according to the voltage difference with the positive and negative values ​​reversed. As a result, the cell balancing circuit in one embodiment of the present invention can discharge the cell balancing current by controlling the current according to the voltage difference, thereby enabling cell balancing operation that equalizes the cell voltage.

[0013] The embodiments for carrying out the present invention will be described in detail below with reference to the drawings. In drawings, identical components are denoted by the same reference numeral, and redundant explanations may be omitted.

[0014] (First embodiment) Figure 1 is a circuit diagram showing a battery device (during discharge) using a cell balance circuit according to the first embodiment of the present invention. As shown in Figure 1, the battery device 10 includes a battery cell 11, a battery cell 12, and a cell balancing circuit 100. The battery cells 11 and 12 are connected in series as a battery pack. The battery device 10 further has an external positive terminal EB+ and an external negative terminal EB-, and during discharge, a load LD is connected between the external positive terminal EB+ and the external negative terminal EB-. During discharge, the battery device 10 discharges battery cells 11 and 12 to the load LD, driving the load LD. A discharge current Id flows through the main current path P to which the battery cells 11 and 12 and the load LD are connected.

[0015] The battery cell 11 is a lithium-ion battery. This battery cell 11 generates a cell voltage V1 depending on the charge / discharge state and degradation state. The battery cell 11 is formed from a battery 11a and an internal resistor 11b. The battery 11a generates a predetermined open-circuit voltage depending on the charge and discharge state. The internal resistance 11b includes solution resistance, charge transfer resistance, active material bulk resistance, contact resistance, etc., and its resistance value increases as it deteriorates.

[0016] The charging voltage of battery cell 11 can be expressed as shown in equation (1) below. Charging voltage = Open-circuit voltage + Resistance of internal resistance 11b × Charging current ... (1) The discharge voltage of the battery cell 11 can be expressed as shown in equation (2) below. Discharge voltage = Open-circuit voltage - Resistance of internal resistance 11b × Discharge current ... (2) From equations (1) and (2), the cell voltage V1 of battery cell 11 increases during charging but decreases during discharging as degradation progresses.

[0017] The battery cell 11 may be referred to as the "first battery cell," and the cell voltage V1 may be referred to as the "first cell voltage."

[0018] Battery cell 12, like battery cell 11, is a lithium-ion battery. This battery cell 12 generates a cell voltage V2 depending on the charge / discharge state and degradation state. Battery cell 12 is formed from a battery 12a and an internal resistor 12b. Battery 12a generates a predetermined open-circuit voltage depending on the charge / discharge state. The internal resistance 12b, like internal resistance 11b, increases in resistance as it degrades.

[0019] The charging voltage of battery cell 12 can be expressed as shown in equation (3) below. Charging voltage = Open-circuit voltage + Resistance of internal resistance 12b × Charging current ... (3) The discharge voltage of battery cell 12 can be expressed as shown in equation (4) below. Discharge voltage = Open-circuit voltage - Resistance of internal resistance 12b × Discharge current ... (4) From equations (3) and (4), the cell voltage V2 of battery cell 12 increases during charging but decreases during discharging as degradation progresses.

[0020] Note that battery cell 12 may be referred to as the "second battery cell," and cell voltage V2 may be referred to as the "second cell voltage."

[0021] Therefore, if the degradation rates of battery cell 11 and battery cell 12 differ, the internal resistance values ​​will differ, which may result in a voltage difference between cell voltage V1 and cell voltage V2. If this voltage difference becomes large, and each battery cell is connected to a separate charge / discharge control circuit, when charging the battery pack of battery cells 11 and 12, the charge / discharge control circuit will determine that the degraded battery cell with the higher cell voltage is overcharged. As a result, charging will be stopped before the battery cell with the lower cell voltage is fully charged. Similarly, 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. As a result, discharging will be stopped before the battery cell with the higher cell voltage is fully discharged. This may lead to inefficient charging and discharging.

[0022] Therefore, the cell balancing circuit 100 compares the average voltage of cell voltages V1 and V2 with cell voltage V2, and discharges a cell balancing current from battery cell 11 or battery cell 12 according to the voltage difference. As a result, the cell balancing circuit 100 can perform cell balancing operations for each battery cell by current control, regardless of whether it is during charging, discharging, or open-circuiting.

[0023] The cell balance circuit 100 has terminals connected to both ends of battery cells 11 and 12, and adjusts the balance by discharging a cell balance current corresponding to the voltage difference between battery cells 11 and 12. This cell balance circuit 100 includes a differential voltage-current converter 101, a differential voltage-current converter 102, and a voltage divider circuit 103. The cell balance circuit 100 also includes terminals VDD, VSS, VC1, VC2, CB1, and CB2.

[0024] Terminal VDD is the power supply terminal of the cell balance circuit 100 and is connected to the positive terminal of the battery cell 11. Terminal VSS is the GND terminal of the cell balance circuit 100 and is connected to the negative terminal of the battery cell 12.

[0025] The voltage divider circuit 103 outputs divided voltages obtained by dividing the voltage applied across its terminals. The voltage divider circuit 103 consists of resistors 103a and 103b connected in series. Resistors 103a and 103b have the same resistance value. One end of this voltage divider circuit 103 is connected to terminal VC1, and the other end is grounded.

[0026] Terminal VC1 is connected to the positive terminal of the battery cell 11 via resistor R1a. One end of capacitor C1 is also connected to terminal VC1, and the other end of capacitor C1 is grounded. Terminal VC2 is connected to the negative terminal of battery cell 11 and the positive terminal of battery cell 12 via resistor R2a. One end of capacitor C2 is also connected to terminal VC2, and the other end of capacitor C2 is grounded. Note that resistors R1a and R2a have the same resistance value.

[0027] 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 the battery cell 11 respectively, also have the same resistance value. As a result, the voltage divider circuit 103 outputs a divided voltage Vd1 which is the average voltage of the cell voltages V1 and V2. The voltage divider circuit 103 may be referred to as the "first voltage divider circuit," and the divided voltage Vd1 may be referred to as the "first divided voltage."

[0028] The differential voltage-current converter 101 outputs a current from its output terminal corresponding to the difference in voltages input to the non-inverting input terminal and the inverting input terminal, respectively. The differential voltage-current converter 101 has a non-inverting input terminal connected to the output terminal of the voltage divider circuit 103, and an inverting input terminal connected to terminal VC2. Furthermore, the differential voltage-current converter 101 has an input terminal connected to terminal CB1 and an output terminal connected to terminal CB2.

[0029] Terminal CB1 is connected to the positive terminal of the battery cell 11 via resistor R1b and is connected to one end of the differential voltage-current converter 101. 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 the differential voltage-current converter 101.

[0030] Therefore, the differential voltage-current converter 101 discharges a cell balance current Ib1 from the battery cell 11, which is generated according to the voltage difference obtained by subtracting the cell voltage V2 from the divided voltage Vd1. The differential voltage-current converter 101 may be referred to as the "first differential voltage-current converter," and the cell balance current Ib1 may be referred to as the "first cell balance current."

[0031] Figure 2 is a graph showing the cell balance current-voltage difference characteristics of a differential voltage-current converter in the first embodiment of the present invention. In Figure 2, the cell balance current-voltage difference characteristics of the differential voltage-current converter 101 are shown by a solid line. In this graph, the vertical axis represents the cell balance current Ib1, and the horizontal axis represents the voltage difference (Vd1-V2) obtained by subtracting the cell voltage V2 from the voltage divider voltage Vd1.

[0032] As shown in Figure 2, the differential voltage-current converter 101 does not discharge the cell balance current Ib1 when the voltage difference (Vd1-V2) is less than +V1a. When the voltage difference (Vd1-V2) is greater than or equal to +V1a and less than or equal to +V1b, the differential voltage-current converter 101 increases the cell balance current Ib1 as this voltage difference increases, and keeps the cell balance current Ib1 constant in the range where this voltage difference is greater than +V1b.

[0033] Returning to Figure 1, the differential voltage-current converter 102, like the differential voltage-current converter 101, outputs a current from its output terminal corresponding to the difference in voltages input to the non-inverting input terminal and the inverting input terminal, respectively. The differential voltage-current converter 102 has a non-inverting input terminal connected to terminal VC2, and an inverting input terminal connected to the output terminal of the voltage divider circuit 103. Furthermore, the differential voltage-current converter 102 has an input terminal connected to terminal CB2, and an output terminal connected to terminal VSS.

[0034] Therefore, the differential voltage-current converter 102 discharges a cell balance current Ib2 from the battery cell 12, which is generated according to the voltage difference obtained by subtracting the voltage divider voltage Vd1 from the cell voltage V2. In other words, the differential voltage-current converter 102 discharges a cell balance current Ib2 from the battery cell 12, which is generated according to the voltage difference obtained by reversing the positive and negative signs of the voltage difference input to the non-inverting and inverting input terminals of the differential voltage-current converter 101. The differential voltage-current converter 102 may be referred to as the "second differential voltage-current converter," and the cell balance current Ib2 may be referred to as the "second cell balance current."

[0035] Figure 3 is a graph showing the cell balance current-voltage difference characteristics of a differential voltage-current converter in the first embodiment of the present invention. In Figure 3, the cell balance current-voltage difference characteristics of the differential voltage-current converter 102 are shown by a dashed line. In this graph, the vertical axis represents the cell balance current Ib2, and the horizontal axis represents the voltage difference (Vd1-V2) obtained by subtracting the voltage divider voltage Vd1 from the cell voltage V2.

[0036] As shown in Figure 3, the differential voltage-current converter 102 keeps the cell balance current Ib2 constant when the voltage difference (Vd1-V2) is less than -V2b. When the voltage difference (Vd1-V2) is greater than or equal to -V2b and less than or equal to -V2a, the differential voltage-current converter 102 decreases the cell balance current Ib2 as this voltage difference increases, and does not discharge the cell balance current Ib2 when this voltage difference is greater than -V2a.

[0037] Figure 4 is a graph showing the cell balance current-voltage difference characteristics of a differential voltage-current converter in the first embodiment of the present invention. This Figure 4 shows the cell balance current-voltage difference characteristics of the differential voltage-current converters 101 and 102 shown in Figures 2 and 3 in the same graph. As shown in Figure 4, a dead band is provided in the cell balance current-voltage difference characteristic in the range where the voltage difference is between -V2a and +V1a. This dead band is a dead zone in which the differential voltage-current converters 101 and 102 do not discharge the cell balance currents Ib1 and Ib2 when the voltage difference is small and close to zero. This makes it possible to avoid unstable operation in which the differential voltage-current converters 101 and 102 discharge the cell balance current Ib2 immediately after discharging the cell balance current Ib1.

[0038] Furthermore, in the combination of differential voltage-current converters 101 and 102, the cell balance currents Ib1 and Ib2 are not discharged simultaneously. Therefore, no loss occurs near terminal CB2 due to the cancellation of cell balance currents Ib1 and Ib2, and this risk is further reduced by this deadband.

[0039] Furthermore, the differential voltage-current converters 101 and 102 are configured with upper limits so that the cell balance currents Ib1 and Ib2 remain constant when the absolute value of the voltage difference (Vd1-V2) is greater than a predetermined value. This prevents the discharge of a large amount of cell balance current, allowing the device to operate at its rated capacity and keeping heat generation low.

[0040] Figure 5 is a circuit diagram showing a battery device (during charging) using a cell balance circuit according to the first embodiment of the present invention. As shown in Figure 5, during charging, the charger CG is connected between the external positive terminal EB+ and the external negative terminal EB-. During charging, the battery device 10 charges battery cells 11 and 12, which are connected in series with the charger CG. A charging current Ic flows through the main current path P to which battery cells 11, 12 and the charger CG are connected. The cell balancing circuit 100 performs cell balancing operation even during charging by comparing the divided voltage Vd1 and the cell voltage V2, thereby discharging the cell balancing current Ib1 or cell balancing current Ib2.

[0041] Figure 6 is a circuit diagram showing a battery device (when open) using a cell balance circuit according to the first embodiment of the present invention. As shown in Figure 6, when the circuit is open, nothing is connected between the external positive terminal EB+ and the external negative terminal EB-. Therefore, no current flows through the main current path P to which the battery cells 11 and 12 are connected. Even when the cell balance circuit 100 is open, it performs cell balance operation by comparing the divided voltage Vd1 with the cell voltage V2, thereby discharging a cell balance current Ib1 or cell balance current Ib2 from the battery cells 11 and 12.

[0042] Thus, the cell balance circuit 100 compares the average voltage of cell voltages V1 and V2 with cell voltage V2, regardless of whether it is during charging, discharging, or opening, and discharges a cell balance current from battery cell 11 or battery cell 12 according to the voltage difference. As a result, the cell balancing circuit 100 can perform cell balancing operations for each battery cell by current control, regardless of whether it is during charging, discharging, or opening. Furthermore, because the cell balancing circuit 100 continuously performs cell balancing operations over a long period of use, the degradation state of each battery cell becomes less likely to differ, eliminating the need to discharge a large cell balancing current and thus extending the lifespan of the battery pack.

[0043] (Second embodiment) Figure 7 is a circuit diagram showing a battery device (during discharge) using a cell balance circuit according to a second embodiment of the present invention. As shown in Figure 7, the cell balance circuit 200 in the second embodiment is the same as the cell balance circuit 100 in the first embodiment, except that it further includes a current monitoring circuit 104 and a switching element SW1. Also, the battery device 20 in the second embodiment is the same as the battery device 10 in the first embodiment, except that it further includes a current sense resistor Rs. Here, we will describe the current sense resistor Rs, the current monitoring circuit 104, and the switching element SW1, which are components added from the first embodiment.

[0044] The current sense resistor Rs has one end connected to the negative terminal of the battery cell 12 and the other end connected to the external negative terminal EB-.

[0045] The current monitoring circuit 104 is connected across the current sense resistor Rs and monitors the current value flowing through the current sense resistor Rs, i.e., the current value flowing through the main current path P, to determine whether the battery device 20 is in the discharge, charging, or open-circuit state. When the current monitoring circuit 104 determines that a discharge is occurring, 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 converters 101 and 102. To prevent voltage differences from occurring, the cell balancing operation is stopped.

[0046] The switching element SW1 is turned on and off by a signal output from the current monitoring circuit 104. When the switching element SW1 is turned on, it short-circuits the non-inverting input terminal and inverting input terminal of the differential voltage-current converters 101 and 102 so that no voltage difference occurs between them, and when it is turned off, it opens up.

[0047] In this way, the cell balancing circuit 200 stops the cell balancing operation by turning on the switching element SW1 when the current monitoring circuit 104 determines that discharge is occurring, thereby maintaining the overall capacity of the battery pack without unnecessarily reducing the battery capacity of healthy battery cells.

[0048] Figure 8 is a circuit diagram showing a battery device (during charging) using a cell balance circuit according to a second embodiment of the present invention. As shown in Figure 8, during charging, the charger CG is connected between the external positive terminal EB+ and the external negative terminal EB-. A charging current Ic flows through the main current path P to which the battery cells 11 and 12 and the charger CG are connected, and the current monitoring circuit 104, which determines that charging is in progress, turns off the switching element SW1. Then, the cell balancing circuit 200 performs a cell balancing operation by comparing the divided voltage Vd1 and the cell voltage V2 and discharging either the cell balancing current Ib1 or the cell balancing current Ib2.

[0049] Figure 9 is a circuit diagram showing a battery device (when open) using a cell balance circuit in a second embodiment of the present invention. As shown in Figure 9, the current monitoring circuit 104 turns off the switching element SW1 when it determines that nothing is connected between the external positive terminal EB+ and the external negative terminal EB- and that no current is flowing. Then, the cell balancing circuit 200 performs a cell balancing operation by comparing the voltage divider voltage Vd1 and the cell voltage V2 and discharging the cell balancing current Ib1 or cell balancing current Ib2.

[0050] In this way, the cell balancing circuit 200 turns on the switching element SW1 when the current monitoring circuit 104 determines that discharge is occurring, thereby preventing the cell balancing operation from being performed. This allows the overall capacity of the battery pack to be maintained without unnecessarily reducing the battery capacity of healthy battery cells.

[0051] (Third embodiment) Figure 10 is a circuit diagram showing a battery device using a cell balancing circuit in a third embodiment of the present invention. As shown in Figure 10, the cell balance circuit 300 of the third embodiment is the same as the cell balance circuit 200 except that it further includes a battery cell 13, a voltage divider circuit 107, differential voltage-current converters 105 and 106, and a switching element SW2. Here, we will describe the battery cell 13, the voltage divider circuit 107, and the differential voltage-current converters 105 and 106, which are components added from the second embodiment.

[0052] Battery cell 13, like battery cells 11 and 12, is a lithium-ion battery. This battery cell 13 is connected in series with battery cells 11 and 12 in the main current path P and generates a cell voltage V3 depending on the charge / discharge state and degradation state. Battery cell 13 is formed by a battery 13a and an internal resistor 13b. Battery 13a generates a predetermined open-circuit voltage depending on the charge / discharge state. The internal resistance 13b includes solution resistance, charge transfer resistance, active material bulk resistance, contact resistance, etc., and its resistance value increases as it degrades.

[0053] The voltage divider circuit 107, like the voltage divider circuit 103, outputs divided voltages obtained by dividing the voltage applied across its terminals. The voltage divider circuit 107 consists of resistors 107a and 107b connected in series. Resistors 107a and 107b have the same resistance value. One end of this voltage divider circuit 107 is connected to terminal VC2, and the other end is grounded. Note that resistor R3a has the same resistance value as resistors R1a and R2a.

[0054] Therefore, since resistors 107a and 107b have the same resistance value, the voltage divider circuit 107 outputs a divided voltage Vd2 which is the average voltage of the cell voltages V2 and V3. The voltage divider circuit 107 is sometimes referred to as the "second voltage divider circuit," and the divided voltage Vd2 is sometimes referred to as the "second divided voltage."

[0055] Similar to the differential voltage-current converter 101, the differential voltage-current converter 105 outputs a current from its output terminal corresponding to the difference in voltages input to the non-inverting input terminal and the inverting input terminal, respectively. The differential voltage-current converter 105 has its non-inverting input terminal connected to the output terminal of the voltage divider circuit 107, and its inverting input terminal connected to terminal VC3. Furthermore, the differential voltage-current converter 105 has its input terminal connected to terminal CB2, and its output terminal connected to terminal CB3.

[0056] Terminal VC3 is connected to the negative terminal of battery cell 12 and the positive terminal of battery cell 13 via resistor R3a. One end of capacitor C3 is also connected to terminal VC3, and the other end of capacitor C3 is grounded. 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 the differential voltage-current converter 105.

[0057] Therefore, this differential voltage-current converter 105 discharges a cell balance current Ib3 from the battery cell 12, which is generated according to the voltage difference obtained by subtracting the cell voltage V3 from the divided voltage Vd2. The differential voltage-current converter 105 may be referred to as the "third differential voltage-current converter," and the cell balance current Ib3 may be referred to as the "third cell balance current."

[0058] Similar to the differential voltage-current converter 102, the differential voltage-current converter 106 outputs a current from its output terminal corresponding to the difference in voltages input to the non-inverting input terminal and the inverting input terminal, respectively. The differential voltage-current converter 106 has its non-inverting input terminal connected to terminal VC3, and its inverting input terminal connected to the output terminal of the voltage divider circuit 107. Furthermore, the differential voltage-current converter 106 has its input terminal connected to terminal CB3, and its output terminal connected to terminal VSS.

[0059] Therefore, this differential voltage-current converter 106 discharges a cell balance current Ib4 from the battery cell 12, which is generated according to the voltage difference obtained by subtracting the divided voltage Vd2 from the cell voltage V3. The differential voltage-current converter 106 may be referred to as the "fourth differential voltage-current converter," and the cell balance current Ib4 may be referred to as the "fourth cell balance current."

[0060] Switching element SW2, like switching element SW1, is switched on and off by a signal output from current monitoring circuit 104. When switching element SW2 is on, it short-circuits the non-inverting input terminal and inverting input terminal of differential voltage-current converters 105 and 106 so that no voltage difference occurs, and when it is off, it opens up.

[0061] Figure 11 is a circuit diagram showing a battery device (during charging) using a cell balancing circuit according to a third embodiment of the present invention. As shown in Figure 11, during charging, the charger CG is connected between the external positive terminal EB+ and the external negative terminal EB-. A charging current Ic flows through the main current path P to which the battery cells 11, 12, 13 and the charger CG are connected, and the current monitoring circuit 104, which determines that charging is in progress, turns off the switching elements SW1 and SW2. The cell balancing circuit 300 then compares the divided voltage Vd1 with the cell voltage V2 and the divided voltage Vd2 with the cell voltage V3. Based on this comparison result, the cell balancing circuit 300 discharges the cell balancing currents Ib1 or Ib2 and Ib3 or Ib4 to perform the cell balancing operation.

[0062] Figure 12 is a circuit diagram showing a battery device (when open) using a cell balance circuit according to a third embodiment of the present invention. As shown in Figure 12, the current monitoring circuit 104 turns off the switching element SW1 when it determines that nothing is connected between the external positive terminal EB+ and the external negative terminal EB- and that no current is flowing. Then, the cell balancing circuit 300 compares the divided voltage Vd1 with the cell voltage V2 and also compares the divided voltage Vd2 with the cell voltage V3. Based on the results of this comparison, the cell balancing circuit 300 discharges the cell balancing current Ib1 or cell balancing current Ib2 and the cell balancing current Ib3 or cell balancing current Ib4 to perform the cell balancing operation.

[0063] In this way, even with three battery cells, the cell balancing circuit 300 compares the battery voltages of adjacent battery cells and discharges a cell balancing current from battery cells 11, 12, and 13 according to the voltage difference. In battery cell 12, cell balancing currents Ib2 and Ib3 are added together.

[0064] Furthermore, similar to the cell balance circuit 200, the cell balance circuit 300 turns on the switching element SW1 when the current monitoring circuit 104 determines that discharge is occurring, thereby preventing the cell balance operation from being performed. This allows the overall capacity of the battery pack to be maintained without unnecessarily reducing the battery capacity of healthy battery cells.

[0065] In this example, the cell balancing circuit 300 performed a cell balancing operation for three battery cells. However, it can also perform cell balancing operations for four or more battery cells by adding the configurations introduced in the second embodiment as the number of battery cells increases.

[0066] (Fourth embodiment) Figure 13 is a circuit diagram showing a battery device (during discharge) using a cell balance circuit according to the fourth embodiment of the present invention. The cell balance circuit 400 of the fourth embodiment is the same as the cell balance circuit 100, except that it has a differential voltage-current converter 108 and current mirror circuits 109 and 110 instead of differential voltage-current converters 101 and 102.

[0067] Here, we will describe a differential voltage-current converter 108 and current mirror circuits 109 and 110, which are alternative configurations to the differential voltage-current converters 101 and 102 of the first embodiment.

[0068] The differential voltage-current converter 108 outputs current from its two output terminals corresponding to the difference in voltages input to the non-inverting input terminal and the inverting input terminal, respectively. The differential voltage-current converter 108 has a non-inverting input terminal connected to the output terminal of the voltage divider circuit 103, and an inverting input terminal connected to terminal VC2. In addition, one output terminal of the differential voltage-current converter 108 is connected to the current mirror circuit 109, and the other output terminal is connected to the current mirror circuit 110.

[0069] The current mirror circuit 109 discharges a cell balance current Ib1 from the battery cell 11 that corresponds to the current generated from one output terminal of the differential voltage-current converter 108. The current mirror circuit 110 discharges a cell balance current Ib2 from the battery cell 12, corresponding to the current generated from another output terminal of the differential voltage-current converter 108. The current mirror circuit 109 may be referred to as the "first current mirror circuit," and the current mirror circuit 110 may be referred to as the "second current mirror circuit."

[0070] Therefore, the differential voltage-current converter 108 generates a supply current according to the voltage difference obtained by subtracting the cell voltage V2 from the divided voltage Vd1, and the current mirror circuits 109 and 110 discharge cell balance currents Ib1 and Ib2 from the battery cells 11 and 12 according to the supply current. Specifically, consider the case where the amplification factor of the current mirror circuit 109 is 1,000 times, and the battery voltage of battery cell 11 is higher than that of battery cell 12. In this case, as shown in Figure 13, a supply current of 1 μA is passed from the differential voltage-current converter 108 to the current mirror circuit 109, causing a cell balance current Ib1 of 1 mA to be discharged from battery cell 11 through the current mirror circuit 109.

[0071] As a result, the cell balance circuit 400 of the fourth embodiment can have the same functionality as the cell balance circuit 100 of the first embodiment, and can discharge a larger cell balance current.

[0072] (Fifth embodiment) Figure 14 is a circuit diagram showing a battery device (during charging) using a cell balance circuit according to a fifth embodiment of the present invention. The cell balance circuit 500 of the fifth embodiment further includes charge termination voltage detection units 111, 112, logic circuits 113, 114, diagnostic circuit 115, balance detection units 116, 117, and buffer 118 in addition to the cell balance circuit 400. Otherwise, the cell balance circuit 500 is the same as the cell balance circuit 400. Here, we will describe the components added from the fourth embodiment: the charge termination voltage detection units 111 and 112, the logic circuits 113 and 114, the diagnostic circuit 115, the balance detection units 116 and 117, and the buffer 118.

[0073] The charge termination voltage detection unit 111 detects the charge termination voltage of the battery cell 11. The charge termination voltage is a voltage value determined to ensure safe charging. One end of the charge termination voltage detection unit 111 is connected to terminal VC1, and the other end is connected to terminal VC2. When the charge termination voltage detection unit 111 detects that the charging voltage of the battery cell 11 has reached the charge termination voltage, it outputs a signal VBC1 to the logic circuit 113.

[0074] The charge termination voltage detection unit 112 detects the charge termination voltage of the battery cell 12. One end of the charge termination voltage detection unit 112 is connected to terminal VC2, and the other end is connected to terminal VSS. When the charge termination voltage detection unit 112 detects that the charge voltage of the battery cell 12 has reached the charge termination voltage, it outputs a signal VBC2 to the logic circuit 113.

[0075] The logic circuit 113 outputs the results of a logical operation based on the input signals VBC1 and VBC2 as signals FMC12 and FMC21 to the logic circuit 114 and the differential voltage-current converter 108, respectively. Specifically, the logic circuit 113 performs logical operations to output signals FMC12 and FMC21, which indicate whether the charging voltage of either or both of the battery cells 11 and 12 has reached or not reached the charging termination voltage.

[0076] Furthermore, the differential voltage-current converter 108 switches the supply of current to the current mirror circuits 109 and 110 on and off in accordance with the signals FMC12 and FMC21 input from the logic circuit 113. Specifically, the differential voltage-current converter 108 discharges cell balance currents Ib1 and Ib2 corresponding to the voltage difference between battery cell 11 and battery cell 12 when both the charging voltages of battery cell 11 and 12 have reached the charging termination voltage. The differential voltage-current converter 108 also discharges cell balance currents Ib1 and Ib2 corresponding to the voltage difference between battery cell 11 and battery cell 12 when both the charging voltages of battery cell 11 and 12 have not reached the charging termination voltage. Furthermore, if only the charging voltage of battery cell 11 has reached the charging termination voltage, the differential voltage-current converter 108 discharges the maximum output cell balance current Ib1 regardless of the voltage difference. If only the charging voltage of battery cell 12 has reached the charging termination voltage, the differential voltage-current converter 108 discharges the maximum output cell balance current Ib2.

[0077] Thus, in addition to the functions of the cell balance circuit 400, the cell balance circuit 500 discharges the maximum output cell balance current via the differential voltage-current converter 108 when at least one of the battery cells 11 and 12 exceeds the charging termination voltage during charging. In other words, as shown in the graph in Figure 4, the cell balance circuit 500 discharges the cell balance current Ib1 or cell balance current Ib2 at its maximum output, and returns to its original state when both battery cells 11 and 12 exceed the charging termination voltage.

[0078] The logic circuit 114 outputs the result of a logic operation based on the two voltages input to the differential voltage-current converter 108 (the divided voltage Vd1 and the voltage at terminal VC2), as well as the signals FMC12 and FMC21 output by the logic circuit 115, to the diagnostic circuit 115. Specifically, the logic circuit 114 performs logical operations to determine two states: whether or not a cell balancing operation is necessary, and whether or not the charging voltage of battery cells 11 and 12 has reached the charging termination voltage. The logic circuit 114 outputs the result of the logical operations to the diagnostic circuit 115.

[0079] The diagnostic circuit 115 outputs an error signal from terminal ERR based on the result of the logic operation performed by the logic circuit 114. Specifically, the diagnostic circuit 115 outputs an error signal from terminal ERR when the voltage difference between battery cell 11 and battery cell 12 becomes extremely large and the cells are in an unbalanced state. As will be described later, the diagnostic circuit 115 outputs an error signal from terminal ERR based on the signals output by the balance detection units 116 and 117. In other words, the diagnostic circuit 115 outputs an error signal to the outside if it diagnoses that either the current mirror circuit 109 or the current mirror circuit 110 is abnormal, based on the detection results of the balance detection unit 116 and the balance detection unit 117.

[0080] The balance detection unit 116 is connected between terminals VC1 and CB1 and detects whether or not cell balancing is being performed. In other words, it compares the cell voltage of the battery cell 11 with the input voltage of the current mirror circuit 109 and detects the operating state of the current mirror circuit 109. When the balance detection unit 116 detects an abnormality in the operation of the current mirror circuit 109, it outputs a signal to the diagnostic circuit 115. The balance detection unit 117 is connected between terminals VC2 and CB2 and detects whether or not cell balancing is being performed. In other words, it compares the cell voltage of the battery cell 12 with the input voltage of the current mirror circuit 110 and detects the operating state of the current mirror circuit 110. When the balance detection unit 117 detects an abnormality in the operation of the current mirror circuit 110, it outputs a signal to the diagnostic circuit 115. The balance detection unit 116 may be referred to as the "first balance detection unit," and the balance detection unit 117 may be referred to as the "second balance detection unit."

[0081] Buffer 118 is through which signals output from terminal CBEO to another cell balancing circuit pass.

[0082] The switching element SW3 is connected between one output terminal of the differential voltage-current converter 108 and the current mirror circuit 109. The switching element SW4 is connected between the other output terminal of the differential voltage-current converter 108 and the current mirror circuit 110.

[0083] When the cell balance circuit 500 is in conjunction with another cell balance circuit, a signal from the other cell balance circuit is input to terminal CBEI, which is an external signal input, and a signal is output to the other cell balance circuit via buffer 118 from terminal CBEO. Specifically, when an off signal is input to terminal CBEI from another cell balance circuit, the switching elements SW3 and SW4 of the cell balance circuit 500 are turned off, and the cell balance function is stopped. The diagnostic circuit 115 outputs an error signal to the outside if any balance detection unit detects that any current mirror circuit is discharging the cell balance current even though an off signal has been input to terminal CBEI from another cell balance circuit. Furthermore, when an ON signal is input to terminal CBEI from another cell balancing circuit, the cell balancing circuit 500 activates its cell balancing function by turning on switching elements SW3 and SW4. The cell balancing circuit 500 can activate or deactivate the cell balancing function by switching the switching elements of another cell balancing circuit on or off based on the signal output from terminal CBEO.

[0084] Next, two examples of embodiments of the battery device of the present invention are shown. Figure 15 is a schematic diagram showing an example of a battery device using multiple cell balancing circuits as shown in Figure 14. As shown in Figure 15, the battery device 60 is connected so that the battery cells of battery cell groups 119a and 119b are balanced by series-connected cell balancing circuits 500a and 500b. Each of the battery cell groups 119a and 119b consists of six battery cells connected in series. Furthermore, the cell balance circuits 500a and 500b are connected by terminal CBE (terminal CBEI + terminal CBEO) and can be operated in conjunction with each other. This allows the cell balancing circuits 500a and 500b to be connected with simple wiring.

[0085] Furthermore, since there is one differential voltage-current converter in the cell balancing circuits 500a and 500b for every two adjacent battery cells, the cell balancing current is not added for the top and bottom battery cells in the same battery cell group. As a result, the top and bottom battery cells in each battery cell group have a smaller cell balancing current and take longer to balance compared to the other battery cells. This can be compensated for by the differential voltage-current converter 108 shown in Figures 13 and 14, which discharges a battery cell at maximum output when any of the battery cells exceeds the charging termination voltage. Furthermore, the connection method shown in Figure 16 allows the time required for balancing to be equalized within the battery device.

[0086] Figure 16 is a schematic diagram showing another example of a battery device using multiple cell balancing circuits as shown in Figure 14. Figure 16 shows a battery device in which multiple battery cell groups form a battery pack. In the battery device 70 shown in Figure 16, for example, the bottommost battery cell of the battery cell group 119a is connected so that both cell balancing circuit 500a and cell balancing circuit 500b perform cell balancing operations.

[0087] This connection allows the cell balancing circuits 500a and 500b to perform a cell balancing operation in the bottommost battery cell of the battery cell group 119a, thereby summing the cell balancing currents. As a result, the battery device 70 can equalize the time required for balancing within the battery device.

[0088] As described above, the cell balancing circuit in one embodiment of the present invention includes a first differential voltage-current converter that discharges a first cell balancing current generated in accordance with the voltage difference obtained by subtracting the second cell voltage from the first divided voltage from the first battery cell. Furthermore, this cell balancing circuit further includes a second differential voltage-current converter that discharges a second cell balancing current generated in accordance with the voltage difference obtained by subtracting the first divided voltage from the second cell voltage from the second battery cell. This allows for cell balancing to be performed on each battery cell connected in series by current control.

[0089] Although the battery cell in each embodiment is a lithium-ion battery, it is not limited to lithium-ion batteries; any battery capable of charging and discharging will suffice. Furthermore, in the second and third embodiments, the current sense resistor Rs was assumed to have one end connected to the negative terminal of the battery cell 12 and the other end connected to the external negative terminal EB-, but it is sufficient if the current monitoring circuit 104 can determine the state of the battery cell. Specifically, the current sense resistor Rs only needs to be connected in series with the main current path P. Furthermore, in each embodiment, the voltage divider circuit outputs a divided voltage that is the average voltage of the two cell voltages, but the divided voltage may be adjusted as appropriate by changing the resistance value of the voltage divider resistor. [Explanation of Symbols]

[0090] 10, 20, 30, 40, 50, 60, 70 Battery Units 11. Battery cell (first battery cell) 12 Battery cells (second battery cells) 13. Battery cell (third battery cell) 100, 200, 300, 400, 500 cell balancing circuit 101 Differential Voltage-Current Converter (First Differential Voltage-Current Converter) 102 Differential Voltage-Current Converter (Second Differential Voltage-Current Converter) 103 Voltage divider circuit (first voltage divider circuit) 104 Current monitoring circuit 105 Differential Voltage-Current Converter (Third Differential Voltage-Current Converter) 106 Differential Voltage-Current Converter (Fourth Differential Voltage-Current Converter) 107 Voltage divider circuit (second voltage divider circuit) 108 Differential Voltage Current Converter 109 Current Mirror Circuit (First Current Mirror Circuit) 110 Current Mirror Circuit (Second Current Mirror Circuit) 111, 112 Charging termination voltage detection unit 113, 114 Logic Circuits 115 Diagnostic Circuit 116 Balance detection unit (first balance detection unit) 117 Balance detection unit (second balance detection unit) 118 buffers 119a, 119b battery cell group CG charger Ib1 Cell balance current (first cell balance current) Ib2 Cell balance current (second cell balance current) Ib3 Cell balance current (third cell balance current) Ib4 Cell balance current (fourth cell balance current) IC charging current ID discharge current P Main current path V1 Cell voltage (Voltage of the first cell) V2 Cell voltage (second cell voltage) V3 Cell voltage (Third cell voltage) SW1, SW2, SW3, SW4 switching elements LD load

Claims

1. A cell balancing circuit for controlling the cell balance between 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, A first voltage divider circuit that outputs a first voltage divider which is the average voltage of the first battery cell and the second battery cell, A first differential voltage-current converter discharges a first cell balance current, generated according to the voltage difference obtained by subtracting the second cell voltage from the first voltage divider, from the first battery cell. A second differential voltage-current converter discharges a second cell balance current generated in accordance with the voltage difference with reversed positive and negative polarity from the second battery cell, A cell balance circuit characterized by having the following features.

2. The cell balancing circuit according to claim 1, wherein the first differential voltage-current converter and the second differential voltage-current converter do not discharge the cell balancing current in a predetermined range including zero voltage difference.

3. The cell balancing circuit according to claim 1, wherein the differential voltage-current converter maintains a constant cell balancing current in a range where the absolute value of the voltage difference is greater than a predetermined value.

4. A current monitoring circuit is connected across a current sense resistor that is connected in series with the main current path, and monitors the current value flowing through the current sense resistor to determine whether the battery cell is in the discharge, charging, or open state. A switching element that turns on and off based on a signal output from the current monitoring circuit, short-circuits to prevent the voltage difference from occurring when it is on, and does not short-circuit to create the voltage difference when it is off, It further possesses, The cell balancing circuit according to claim 1, wherein the current monitoring circuit turns on the switching element when it determines that it is discharging, and turns off the switching element when it determines that it is charging or open.

5. A first current mirror circuit discharges a current corresponding to the supply current from the first differential voltage-current converter as the first cell balance current from the first battery cell, A second current mirror circuit discharges a current corresponding to the supply current from the second differential voltage-current converter as the second cell balance current from the second battery cell, The cell balancing circuit according to claim 1, further comprising the above.

6. A first balance detection unit compares the first cell voltage with the input voltage of the first current mirror circuit and detects the operating state of the first current mirror circuit, A second balance detection unit compares the second cell voltage with the input voltage of the second current mirror circuit and detects the operating state of the second current mirror circuit, A diagnostic circuit that outputs an error signal to the outside if it diagnoses that either the first current mirror circuit or the second current mirror circuit is abnormal, based on the detection results of the first balance detection unit and the detection results of the second balance detection unit, The cell balancing circuit according to claim 5, further comprising the above.

7. The device further includes an external signal input terminal to which an off signal is input to stop the discharge of the first cell balance current and the second cell balance current. When the OFF signal is input to the external signal input terminal, The balance detection unit detects that the cell balance current is being discharged, The diagnostic circuit outputs the error signal to the outside, as described in claim 6.

8. When a third battery cell that generates a third cell voltage is connected in series with the negative terminal side of the second battery cell, A second voltage divider circuit that outputs a second voltage divider which is the average voltage of the second battery cell and the third battery cell, A third differential voltage-current converter discharges a third cell balance current, generated according to the voltage difference obtained by subtracting the third cell voltage from the second voltage divider, from the second battery cell. A fourth differential voltage-current converter discharges a fourth cell balance current, generated in accordance with the voltage difference with reversed positive and negative polarity, from the third battery cell. It further possesses, The cell balancing circuit according to claim 1, wherein the second cell balancing current and the third cell balancing current are added together in the second battery cell.

9. A first battery cell that generates a first cell voltage, A second battery cell is connected in series with the first battery cell and generates a second cell voltage, A cell balancing circuit according to any one of claims 1 to 8, A battery device characterized by having at least one of the following.

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