Device capable of being connected to a battery pack and method of detecting imbalance between battery cells

Abstract

This invention relates to a device capable of connecting to a battery pack and a method for detecting imbalance between battery cells. The device may provide a fuel gauge circuit for detecting and determining the imbalance of a battery pack having two battery cells connected in series, using only the positive and negative terminals of the battery pack.

Description

Technical Field

[0001] The present invention relates to a device capable of being connected to a battery pack and a method for detecting imbalance between two battery cells connected in series. Background Technology

[0002] Battery-powered systems may include battery packs with two or more battery cells connected in series. In some cases, the battery cells may be unbalanced, which can lead to hazardous operating conditions such as overcharging and over-discharging. Conventional systems require a connection point between two battery cells to monitor the voltage of each cell. However, this configuration requires additional circuitry and increases the cost of the system. Summary of the Invention

[0003] The present invention relates to a device capable of being connected to a battery pack and a method for detecting imbalance between two battery cells connected in series.

[0004] The technical problem addressed by this invention is that conventional systems for detecting battery cell imbalance require a connection point between two battery cells to monitor the voltage of each cell. This configuration requires additional circuitry and increases the cost of the system.

[0005] Various embodiments of this technology can provide methods and apparatus for detecting battery cell imbalance. The apparatus can provide a fuel gauge circuit for detecting and determining the imbalance of a battery pack having two series-connected battery cells using only the positive and negative terminals of the battery pack.

[0006] According to a first aspect, an apparatus capable of being connected to a battery pack is provided, wherein the battery pack includes a first battery cell connected in series with a second battery cell and has a first terminal and a second terminal. The apparatus includes: a fuel gauge circuit configured to be connected to the first terminal and the second terminal, and includes: a voltage detector configured to measure the total voltage of the battery pack; a memory configured to store first battery characteristic data indicating a relationship between open-circuit voltage and capacity; and a processor communicating with the voltage detector and the memory and configured to detect imbalances between the series-connected battery cells, the detection of imbalances including: determining a first capacity based on the measured total voltage and the first battery characteristic data; calculating a first actual resistance of the battery pack using the measured total voltage and a first load current; determining whether the calculated first actual total resistance is equal to a theoretical resistance; calculating a second actual resistance of the battery pack using the measured total voltage and the second load current; and calculating a second capacity of the first battery cell and a third capacity of the second battery cell using the calculated first actual resistance, the calculated second actual resistance, and a set of formulas.

[0007] In one embodiment, the memory is further configured to store second battery characteristic data indicating the relationship between capacity, internal resistance, and current; and wherein a theoretical resistance is selected from the second battery characteristic data.

[0008] In one implementation, determining the first capacity includes selecting a capacity corresponding to the measured total voltage from first battery characteristic data.

[0009] In one embodiment, the set of formulas includes: a first function describing the curve of a first resistance versus capacitance under a first current parameter; and a second function describing the curve of a second resistance versus capacitance under a second current parameter.

[0010] In one implementation, the set of formulas includes a formula that describes the total capacity as the sum of the second and third capacities.

[0011] According to a second aspect, a method for detecting imbalance between two series-connected battery cells includes: measuring the total voltage of the series-connected battery cells; determining a capacity based on the measured total voltage and first battery characteristic data; calculating a first actual resistance of the series-connected battery cells using the measured total voltage and a first load current; obtaining a theoretical resistance based on the determined capacity; determining whether the calculated first actual total resistance is equal to the theoretical resistance; generating a first signal if the calculated first actual total resistance is equal to the theoretical resistance, wherein the first signal indicates that the series-connected battery cells are balanced; and generating a second signal if the calculated first actual total resistance is not equal to the theoretical resistance, wherein the second signal indicates that the series-connected battery cells are unbalanced.

[0012] In one implementation, the first battery characteristic data includes data indicating the relationship between open-circuit voltage and capacity.

[0013] In one embodiment, obtaining the theoretical resistance includes retrieving the theoretical resistance from second battery characteristic data, wherein the second battery characteristic data includes data indicating the relationship between capacity, internal resistance, and current; and measuring the total voltage of the battery includes measuring the voltage difference between a first terminal of a series-connected battery cell and a second terminal of a series-connected battery cell.

[0014] In one embodiment, the method further includes determining a mismatch, which includes: calculating a second actual resistance of the series-connected battery cells using the measured total voltage and a second load current; and calculating the capacity of each series-connected battery cell using the calculated first actual resistance, the calculated second actual resistance, and a set of formulas; wherein the set of formulas includes: a first function describing a curve of first resistance versus capacity with a first current parameter; and a second function describing a curve of second resistance versus capacity with a second current parameter.

[0015] In one embodiment, the method further includes: setting a first actual resistance equal to a first function; setting a second actual resistance equal to a second function; and solving for the capacity of one of the series-connected battery cells.

[0016] The technical effect achieved by this invention is to provide a system that detects imbalance in a battery cell with two batteries by measuring the voltage at the two terminals of the battery cell, without requiring a third connection point between the two batteries. Attached Figure Description

[0017] The present invention can be more fully understood by referring to the specific embodiments when considered in conjunction with the following exemplary drawings. Throughout the following drawings, similar reference numerals are used to refer to similar elements and steps in the various drawings.

[0018] Figure 1 This is a block diagram of a system according to an exemplary embodiment of the present technology;

[0019] Figures 2A to 2B The charging of a battery pack with two balanced battery cells is illustrated.

[0020] Figures 3A to 3B The discharge of a battery pack with two balanced battery cells is shown as a representative example.

[0021] Figures 4A to 4B The charging of a battery pack with two unbalanced battery cells is illustrated representatively.

[0022] Figures 5A to 5B The discharge of a battery pack with two unbalanced battery cells is illustrated representatively.

[0023] Figure 6 This is a flowchart illustrating an exemplary embodiment of the present technology for detecting and determining an imbalance between two series-connected battery cells;

[0024] Figure 7 This is a graph showing the open-circuit voltage value as a function of capacity according to an exemplary embodiment of the present technology;

[0025] Figure 8 This is a table showing the capacity values ​​and corresponding resistance values ​​under two different load conditions, according to an exemplary embodiment of the present technology; and

[0026] Figure 9 This is from an exemplary embodiment of the present technology. Figure 8 A graph of the values ​​in the table. Detailed Implementation

[0027] This technology can be described in terms of functional block components and various processing steps. Such functional blocks can be implemented by any number of components configured to perform specified functions and achieve various results. For example, this technology can employ various voltage sensors, current sensors, coulomb counters, logic gates, timers, memory devices, signal converters, semiconductor devices such as transistors and capacitors, etc., capable of performing multiple functions.

[0028] The methods and apparatus for detecting battery cell imbalance according to various aspects of this technology can be operated in conjunction with any suitable battery-powered electronic system and / or device, such as "smart devices," wearable devices, consumer electronics, portable devices, medical devices, gaming systems, etc. See also Figure 1 As shown in Figure 2, the exemplary system 100 can be integrated into an electronic device (not shown) powered by a rechargeable battery pack 105, such as an electric drill. The battery pack 105 may include any number of battery cells connected in series. In an exemplary embodiment, the battery pack 105 may include a first battery cell 120 connected in series with a second battery cell 125. The first battery cell 120 and the second battery cell 125 may include lithium-ion battery cells or any other type of rechargeable battery. The battery pack 105 may include a first terminal 155 (e.g., a positive terminal) and a second terminal 160 (e.g., a negative terminal). The first battery cell 120 may be directly connected to the first terminal 155, and the second battery cell 125 may be directly connected to the second terminal 160. The system 100 may also include a fuel gauge circuit 110 and a charger 115.

[0029] Charger 115 can be configured to control the charging and discharging of battery pack 105. Charger 115 can be connected to battery pack 105 and can initiate charging and discharging operations in the direction of fuel gauge circuit 110. Charger 115 may include any circuitry and / or systems suitable for controlling the current supplied to a load (not shown) and the current applied to battery pack 105 for the purpose of charging battery pack 105.

[0030] The fuel gauge circuit 110 can be configured to detect an imbalance between the first battery cell 120 and the second battery cell 125. For example, the fuel gauge circuit 110 can be configured to detect an imbalance based on the total voltage V. PACKThe first capacity is determined using the first battery characteristic data and the total voltage V. PACK The first actual resistance R of battery pack 105 is calculated using the first load current. PACK1 And determine the calculated first actual total resistance R. PACK1 Is it equal to the theoretical resistance R? TH1 If the calculated first actual total resistance R PACK1 Equal to theoretical resistance R TH1 If so, then the first battery cell 120 and the second battery cell 125 are considered to be balanced. If the calculated first actual total resistance R... PACK1 Not equal to the theoretical resistance R TH1 If the first battery cell 120 and the second battery cell 125 are unbalanced, the fuel gauge circuit 110 can set the usage range of the battery pack 105 to less than 100% based on the degree of imbalance. Alternatively, the fuel gauge circuit 110 can perform a battery balancing operation to balance the first battery cell 120 and the second battery cell 125.

[0031] The fuel gauge circuit 110 may be further configured to determine the mismatch between the first battery cell 120 and the second battery cell 125. For example, the fuel gauge circuit 110 may be configured to use the total voltage and the second load current to calculate the second actual resistance R of the battery pack 105. PACK2 and using the calculated first actual resistance R PACK1 The calculated second actual resistance R PACK2 A set of formulas are used to calculate the second capacity of the first battery cell 120 and the third capacity of the second battery cell 125.

[0032] In an exemplary embodiment, the fuel gauge circuit 110 can detect imbalance and determine the amount of imbalance by monitoring only the first terminal 155 and the second terminal 160 of the battery pack 105.

[0033] The fuel gauge circuit 110 may include a method for measuring the total voltage V of the battery pack 105. PACK Voltage detector 140. Total voltage V PACK It is the sum of the voltage of the first battery 120 and the voltage of the second battery cell 125. The voltage detector 140 can be connected to the first terminal 155 and the second terminal 160 and may include any circuitry and / or device suitable for measuring the voltage difference between the two points.

[0034] The fuel gauge circuit 110 may include a current sensor 145 for sensing or otherwise measuring the current of the battery pack 105. The current sensor 145 may include any circuitry and / or devices suitable for measuring the current of the battery 101. For example, the current sensor 145 may operate in conjunction with a sensing resistor 165, wherein the current sensor 145 measures the voltage across the sensing resistor 165 to determine the current.

[0035] The fuel gauge circuit 110 may also include a memory 135 configured to store known battery characteristic data. For example, the memory 135 may store first battery characteristic data indicating the relationship between open-circuit voltage and capacity (e.g., ...). Figure 7 (As shown). For example, the first battery characteristic data can be stored in a lookup table or other suitable form. Generally, battery capacity can be expressed as a percentage and referred to as relative state of charge (RSOC). In various embodiments, the first battery cell 120 and the second battery cell 125 have the same first battery characteristic data.

[0036] The memory 135 may also store second battery characteristic data indicating the relationship between capacity, internal resistance, and current (e.g., such as...). Figure 8 (As shown). Second battery characteristic data can be stored in a lookup table or other suitable format.

[0037] The fuel gauge circuit 110 may also include a processor 150 configured to receive various measured battery data, such as total voltage V. PACK and current I DD The processor 150 can also communicate with the memory 135, such as retrieving or receiving known battery characteristic data. The processor 150 can be configured to perform various operations to determine whether battery cells 120, 125 are balanced, and if unbalanced, to determine the imbalance. For example, the processor 150 can be configured to determine a first capacity based on the total voltage and first battery characteristic data, using the total voltage V. PACK The first actual resistance of the battery pack 105 is calculated using the first load current, and it is determined whether the calculated first actual total resistance is equal to the theoretical resistance.

[0038] Processor 150 may be configured to store the set of formulas and use them to determine the capacity of the first battery cell 120 and the capacity of the second battery cell 125. The set of formulas may include a first function and a second function, the first function describing the curve of a first resistance versus capacity at a first current parameter (e.g., ...). Figure 9 The curve shown as a solid line in the middle), this second function describes the curve of the second resistance versus capacitance at the second current parameter (e.g., Figure 9 (The curve is shown as a dashed line in the image). For example, at the first current parameter (e.g., 1C load), the function of the first curve can be described by the following equation: y = 98(6-log2.9 (x)), and at the second current parameter (e.g., 0.5C load), the function of the second curve can be described by the following equation: y = 102(5-log 3.2 (1.4x)). The first and second current parameters can be defined by C-rate, where C-rate is a measure of the rate at which the battery is charging or discharging, and is defined as the current through the battery divided by the theoretical current consumption when the battery will deliver its nominal rated capacity in one hour. At a 1C load, battery pack 105 should be able to provide 1A to the load for one hour, and at a 0.5C load, battery pack 105 should be able to provide 500mA to the load for two hours. Processor 150 may also store a formula that describes the total capacity as the sum of the second and third capacities (i.e., total capacity = second capacity + third capacity).

[0039] Processor 150 may be further configured to determine the loss of measurement. For example, processor 150 may be configured to use the measured total voltage V PACK The second actual resistance of the battery pack 105 is calculated using the second load current, and the calculated first actual resistance R is used. PACK1 The calculated second actual resistance R PACK2 The formulas are used to calculate the second capacity of the first battery cell 120 and the third capacity of the second battery cell 125.

[0040] The fuel gauge circuit 110 may also include a load control circuit 130 configured to operate in conjunction with the charger 115 to control the charging and discharging operations of the battery pack 105. For example, the load control circuit 130 may ensure that the battery pack 105 receives a current of 1A, 500mA, or any other desired current. If the battery pack 105 is charging, the load control circuit 130 may signal to the charger 115 to instruct the charger 115 to provide a specific charging current level to the battery pack 105. In an exemplary embodiment, the load control circuit 130 may be responsive to the processor 150. For example, the load control circuit 130 may adjust the current of the battery pack 105 to a desired level based on whether the fuel gauge circuit 110 is performing balance / imbalance detection. The load control circuit 130 may include any circuitry and / or devices suitable for interfacing between the fuel gauge circuit 110 and the charger 115 and providing current level commands to the charger 115.

[0041] Generally speaking, and referring to Figures 2 and 3, when the two series-connected batteries are balanced, the charging of battery cells 120 and 125 results in each battery cell being charged to 100% capacity (e.g., as shown in Figures 2 and 3). Figures 2A to 2B(As shown). Furthermore, when the series-connected battery cells 120 and 125 are balanced, the discharge of battery cells 120 and 125 causes each battery cell to discharge at the same rate, such that each battery cell discharges to 0% capacity (e.g., as shown). Figures 3A to 3B (As shown).

[0042] In contrast, and referring to Figures 4 and 5, when the two series-connected battery cells 120 and 125 are unbalanced, charging results in one battery cell being charged to 100%, while the other battery cell is less than 100% (e.g., as shown in Figures 4 and 5). Figures 4A to 4B (As shown). Furthermore, when the series-connected battery cells 120 and 125 are unbalanced, the discharge of the battery cells causes one cell to discharge to 0%, while the other cell discharges to more than 0% (e.g., as shown). Figures 5A to 5B (As shown).

[0043] In various implementations, the battery pack 105 is used to cover the combined capacity of the two battery cells 120 and 125. Its usability is maximized when the battery cells 120 and 125 are balanced. However, its usability is limited when the battery cells 120 and 125 are unbalanced.

[0044] During operation, and see also Figures 1 to 8 The system 100 can be configured to detect an imbalance between the first battery cell 120 and the second battery cell 125. In an exemplary embodiment, the fuel gauge circuit 110 can measure the total voltage V of the series-connected battery cells. PACK (600) (For example, voltage detector 140 can measure the total voltage V) PACK The capacity (605) is determined based on the measured total voltage and first battery characteristic data (e.g., the processor 150 may retrieve the corresponding total voltage V from the memory 135). PACK (Capacity value); using the measured total voltage V PACK and the first load current I DD For example, 1A can be used to calculate the first actual resistance R of a battery pack connected in series. PACK1 (610) (For example, processor 150 can use Ohm's law based on the measured total voltage V) PACK The first actual resistance R is calculated using the load current. PACK1 :R PACK1 =V PACK / I DD The theoretical resistance R is obtained based on the determined capacitance. TH1 (615) (For example, processor 150 may retrieve the theoretical resistance R corresponding to the capacity from memory 135) TH1 Determine the calculated first actual total resistance R. PACK1Is it equal to the theoretical resistance (620) (e.g., processor 150 can determine the first actual total resistance R) PACK1 With theoretical resistance R TH1 (Comparison); if the calculated first actual total resistance equals the theoretical resistance, a first signal is generated, indicating that the series-connected battery cells are balanced (625) (e.g., processor 150 may generate the first signal and transmit it to load control circuit 130); and if the calculated first actual total resistance is not equal to the theoretical resistance, a second signal is generated, indicating that the series-connected battery cells are unbalanced (e.g., processor 150 may generate the second signal and transmit it to load control circuit 130). In the event that battery cells 120, 125 are unbalanced, fuel gauge circuit 110 may activate conventional battery balancing technology (640).

[0045] In various embodiments, system 100 may be further configured to determine the misalignment between battery cells 120, 125. In an exemplary embodiment, fuel gauge circuit 110 may use the measured total voltage V PACK The second actual resistance R of the series-connected battery pack is calculated using a second load current such as 500mA. PACK2 (630) (For example, processor 150 can use Ohm's law based on the measured total voltage V) PACK The second actual resistance R is calculated using the load current. PACK2 ); and using the calculated first actual resistance R PACK1 The calculated second actual resistance R PACK2 A set of formulas is used to calculate the capacity (635) of each series-connected battery cell. This set of formulas may include functions such as y = 98(6-log...). 2.9 (x)) and y = 102(5-log 3.2 (1.4x)), where y is the resistance of the battery cell and x is the capacity. The function can be determined based on the specific resistance of the battery cell versus its capacity characteristics, and the relationship can be established during testing when the battery cells are new. Alternatively, the combined resistance of two battery cells can be given as equal to the capacity x under the first load current. a The resistance of the first battery cell plus the capacity x b The resistance of the second battery cell (i.e., the combined resistance = 98(6-log)) 2.9 (x a ))+98(6-log 2.9 (x b It is also possible to specify that the combined resistance of two battery cells is equal to the capacity x under the second load current. a The resistance of the first battery cell plus the capacity x bThe resistance of the second battery cell (i.e., the combined resistance = 102(5-log)) 3.2 (1.4x a ))+102(5-log 3.2 (1.4x b The processor 150 can also retrieve a capacity value from the memory 135, which assumes that the battery cells 120, 125 are balanced. For example, the measured total voltage V PACK It can be 7.2V. In this case, if the battery cells are balanced, each battery cell will be 3.6V, corresponding to a capacity of 3.6V (e.g., using from...). Figure 7 The relational data is 20%. Therefore, in the equilibrium case, it follows (x a +x b ) / 2 = 20.

[0046] For example, suppose the first actual resistance R PACK1 It is 651Ω and the second actual resistance R PACK2 Given 460.8Ω, then:

[0047] 651 = 98(6-log) 2.9 (x a ))+98(6-log 2.9 (x b ))(Formula 1);

[0048] 460.8 = 102(5-log) 3.2 (1.4x a ))+102(5-log 3.2 (1.4x b (Formula 2); and

[0049] (x a +x b ) / 2=20 (Formula 3).

[0050] Then, processor 150 can use formulas 1, 2, and 3 to solve for x. a and x b In this example, x a =10 and x b =30. This means that one battery cell has 10% capacity and the other battery cell has 30% capacity, and the cell imbalance gap is 20%. This also means that the usability of battery pack 105 is 80%. In the case of known battery cell imbalance, load control circuit 130 and charger 115 can operate together to prevent overcharging and over-discharging of battery cells 120, 125 (640) by limiting charging and discharging operations to be commensurate with the usability.

[0051] In the foregoing description, the technology has been described in conjunction with specific exemplary embodiments. The specific embodiments shown and described are for illustrative purposes only and are not intended to further limit the scope of the technology in any way. In fact, for the sake of brevity, conventional manufacturing, connection, fabrication, and other functional aspects of the methods and systems may not be described in detail. Furthermore, the connecting lines shown in the various figures are intended to represent exemplary functional relationships and / or steps between various components. In actual systems, multiple alternative or additional functional relationships or physical connections may exist.

[0052] The technology has been described in conjunction with specific exemplary embodiments. However, various modifications and variations may be made without departing from the scope of this technology. The descriptions and drawings are to be considered in an exemplary and non-limiting manner, and all such modifications are intended to be included within the scope of this technology. Therefore, the scope of the technology should be determined by the general embodiments described and their legally equivalent forms, rather than solely by the specific examples given above. For example, unless otherwise expressly stated, the steps listed in any method or process embodiment may be performed in any order, and are not limited to the explicit order provided in the specific examples. Furthermore, the components and / or elements listed in any apparatus embodiment may be assembled in various arrangements or otherwise configured to produce substantially the same results as this technology, and are therefore not limited to the specific configurations illustrated in the specific examples.

[0053] The beneficial effects, other advantages, and problem solutions have been described above for specific implementation schemes. However, any beneficial effect, advantage, problem solution, or any element that makes any specific beneficial effect, advantage, or solution appear or become more apparent should not be construed as a critical, required, or necessary feature or component.

[0054] The terms “comprising,” “including,” or any variations thereof are intended to refer to a non-exclusive inclusion, such that a process, method, article, composition, or apparatus that comprises a list of elements includes not only those listed but also other elements not expressly listed or inherent to such process, method, article, composition, or apparatus. Except for those not specifically referenced, other combinations and / or modifications of the above-described structures, arrangements, applications, proportions, elements, materials, or components used in the implementation of this technology may vary without departing from its general principles or be otherwise particularly suited to specific environments, manufacturing specifications, design parameters, or other operational requirements.

[0055] The present technology has been described above in conjunction with exemplary embodiments. However, changes and modifications may be made to the exemplary embodiments without departing from the scope of the present technology. These and other changes or modifications are intended to be included within the scope of the present technology, as set forth in the following claims.

[0056] According to a first aspect, an apparatus capable of being connected to a battery pack is provided, wherein the battery pack includes a first battery cell connected in series with a second battery cell and has a first terminal and a second terminal. The apparatus includes: a fuel gauge circuit configured to be connected to the first terminal and the second terminal, and includes: a voltage detector configured to measure the total voltage of the battery pack; a memory configured to store first battery characteristic data indicating a relationship between open-circuit voltage and capacity; and a processor communicating with the voltage detector and the memory and configured to detect imbalances between the series-connected battery cells, the detection of imbalances including: determining a first capacity based on the measured total voltage and the first battery characteristic data; calculating a first actual resistance of the battery pack using the measured total voltage and a first load current; determining whether the calculated first actual total resistance is equal to a theoretical resistance; calculating a second actual resistance of the battery pack using the measured total voltage and the second load current; and calculating a second capacity of the first battery cell and a third capacity of the second battery cell using the calculated first actual resistance, the calculated second actual resistance, and a set of formulas.

[0057] In one implementation, the memory is further configured to store second battery characteristic data indicating the relationship between capacity, internal resistance, and current.

[0058] In one implementation, the theoretical resistance is selected from the second battery characteristic data.

[0059] In one embodiment, the total voltage is the sum of the first voltage of the first battery cell and the second voltage of the second battery cell.

[0060] In one implementation, determining the first capacity includes selecting a capacity corresponding to the measured total voltage from first battery characteristic data.

[0061] In one embodiment, the set of formulas includes: a first function describing the curve of a first resistance versus capacitance under a first current parameter; and a second function describing the curve of a second resistance versus capacitance under a second current parameter.

[0062] In one implementation, the set of formulas includes a formula that describes the total capacity as the sum of the second and third capacities.

[0063] According to a second aspect, a method for detecting imbalance between two series-connected battery cells includes: measuring the total voltage of the series-connected battery cells; determining a capacity based on the measured total voltage and first battery characteristic data; calculating a first actual resistance of the series-connected battery cells using the measured total voltage and a first load current; obtaining a theoretical resistance based on the determined capacity; determining whether the calculated first actual total resistance is equal to the theoretical resistance; generating a first signal if the calculated first actual total resistance is equal to the theoretical resistance, wherein the first signal indicates that the series-connected battery cells are balanced; and generating a second signal if the calculated first actual total resistance is not equal to the theoretical resistance, wherein the second signal indicates that the series-connected battery cells are unbalanced.

[0064] In one implementation, the first battery characteristic data includes data indicating the relationship between open-circuit voltage and capacity.

[0065] In one embodiment, obtaining the theoretical resistance includes retrieving the theoretical resistance from second battery characteristic data, wherein the second battery characteristic data includes data indicating the relationship between capacity, internal resistance, and current.

[0066] In one embodiment, measuring the total voltage of the battery includes measuring the voltage difference between the first terminal of the series-connected battery cells and the second terminal of the series-connected battery cells.

[0067] In one embodiment, the method further includes determining a miscalculation measure, which includes: calculating a second actual resistance of the series-connected battery cells using the measured total voltage and a second load current; and calculating the capacity of each series-connected battery cell using the calculated first actual resistance, the calculated second actual resistance, and a set of formulas.

[0068] In one embodiment, the set of formulas includes: a first function describing the curve of a first resistance versus capacitance under a first current parameter; and a second function describing the curve of a second resistance versus capacitance under a second current parameter.

[0069] In one embodiment, the method further includes: setting a first actual resistance equal to a first function; setting a second actual resistance equal to a second function; and solving for the capacity of one of the series-connected battery cells.

[0070] According to a third aspect, a system includes: a battery pack comprising: a first battery cell connected in series with a second battery cell; a first terminal directly connected to the first battery cell; and a second terminal directly connected to the second battery cell; and a fuel gauge circuit connected to the first and second terminals and configured to detect an imbalance between the first and second battery cells based on: the voltage difference between the first and second terminals; the internal resistance of the battery pack; and known battery characteristic data.

[0071] In one embodiment, the known battery characteristic data includes: first battery characteristic data indicating the relationship between open-circuit voltage and capacity; and second battery characteristic data indicating the relationship between capacity, internal resistance, and current.

[0072] In one embodiment, the fuel meter circuit includes a voltage detector configured to measure the voltage difference.

[0073] In one embodiment, the fuel gauge circuit includes a processor configured to detect imbalance, the imbalance detection including: determining a first capacity based on voltage difference and known battery characteristic data; calculating a first internal resistance of the battery pack using the voltage difference and a first load current; and determining whether the calculated first internal resistance is equal to the theoretical resistance.

[0074] In one embodiment, the processor is further configured to determine a miscalculation measure, the miscalculation measure comprising: calculating a second internal resistance of the battery pack using a voltage difference and a second load current; and calculating a second capacity of the first battery cell using: the calculated first internal resistance; the calculated second internal resistance; and a set of functions describing a curve of resistance versus capacity.

[0075] In one embodiment, the processor is further configured to calculate the third capacity of the second battery cell using the calculated second capacity and a formula that describes the total capacity of the battery pack as the sum of the second and third capacities.

Claims

1. A device capable of being connected to a battery pack, wherein, The battery pack includes a first battery cell connected in series with a second battery cell, and has a first terminal and a second terminal, characterized in that the device includes: A fuel gauge circuit, configured to be connected to the first terminal and the second terminal, and the fuel gauge circuit includes: A voltage detector configured to measure the total voltage of the battery pack; A memory, configured to store first battery characteristic data indicating the relationship between open-circuit voltage and capacity; and A processor, which communicates with the voltage detector and the memory, and is configured to detect imbalances between the series-connected battery cells, the detection of imbalances between the series-connected battery cells including: The first capacity is determined based on the measured total voltage and the first battery characteristic data; The theoretical resistance is determined based on the first capacity; The first actual resistance of the battery pack is calculated using the measured total voltage and the first load current. Determine whether the calculated first actual resistance is equal to the theoretical resistance; If the first actual resistance is equal to the theoretical resistance, then it is determined that the series-connected battery cells are balanced; and If the first actual resistance is not equal to the theoretical resistance, then it is determined that the series-connected battery cells are unbalanced. The detection of this imbalance further includes: The second actual resistance of the battery pack is calculated using the measured total voltage and second load current; and The second capacity of the first battery cell and the third capacity of the second battery cell are calculated using the calculated first actual resistance, the calculated second actual resistance, and a set of formulas.

2. The apparatus according to claim 1, characterized in that, The memory is further configured to store second battery characteristic data indicating the relationship between capacity, internal resistance, and current; and wherein the theoretical resistance is selected from the second battery characteristic data.

3. The apparatus according to claim 1, characterized in that, Determining the first capacity includes selecting a capacity corresponding to the measured total voltage from the first battery characteristic data.

4. The apparatus according to claim 1, characterized in that, The set of formulas includes: The first function describes the curve of the first resistance versus capacitance under the condition of the first current parameter; and The second function describes the curve of the second resistance versus capacitance under the condition of the second current parameter.

5. The apparatus according to claim 1, characterized in that, The set of formulas includes a formula that describes the total capacity as the sum of the second capacity and the third capacity.

6. A method for detecting imbalance between two series-connected battery cells, characterized in that, include: Measure the total voltage of the series-connected battery cells; The capacity is determined based on the measured total voltage and the first battery characteristic data; The first actual resistance of the series-connected battery cells is calculated using the measured total voltage and the first load current. The theoretical resistance is obtained based on the determined capacitance; Determine whether the calculated first actual total resistance is equal to the theoretical resistance; If the calculated first actual total resistance is equal to the theoretical resistance, a first signal is generated, wherein the first signal indicates that the series-connected battery cells are balanced; as well as If the calculated first actual total resistance is not equal to the theoretical resistance, a second signal is generated, wherein the second signal indicates that the series-connected battery cells are unbalanced.

7. The method according to claim 6, characterized in that, The first battery characteristic data includes data indicating the relationship between open-circuit voltage and capacity.

8. The method according to claim 6, characterized in that: Obtaining the theoretical resistance includes retrieving the theoretical resistance from second battery characteristic data, wherein the second battery characteristic data includes data indicating the relationship between capacity, internal resistance, and current; and Measuring the total voltage of the series-connected battery cells includes measuring the voltage difference between the first terminal and the second terminal of the series-connected battery cells.

9. The method according to claim 6, characterized in that, The method further includes determining the loss measure, wherein determining the loss measure includes: The second actual resistance of the series-connected battery cells is calculated using the measured total voltage and second load current; and The capacity of each series-connected battery cell is calculated using the calculated first actual resistance, the calculated second actual resistance, and a set of formulas. The set of formulas mentioned above includes: The first function describes the curve of the first resistance versus capacitance under the condition of the first current parameter; and The second function describes the curve of the second resistance versus capacitance under the condition of the second current parameter.

10. The method according to claim 9, characterized in that, The method further includes: Set the first actual resistance to be equal to the first function; Set the second actual resistance to be equal to the second function; and Determine the capacity of one of the battery cells in the series-connected battery cells.

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