Battery management system and method for performing passive balancing on battery cells in series-connected battery pack

Abstract

The present disclosure relates to a battery management system, method for performing passive balancing of battery cells in a battery pack connected in series. An example battery management system includes a battery pack, a battery management integrated circuit, and a battery management controller. The battery management integrated circuit includes a discharge circuit for each battery cell, the discharge circuit having a shared balancing resistor connected to an adjacent battery cell. The battery management controller is electrically coupled to the battery management integrated circuit and is configured to identify a minimum charge battery cell; iteratively selecting a plurality of highest charge cells, where no two highest charge cells are adjacent, and where each highest charge cell of the plurality of highest charge cells is greater than a minimum charge cell plus an imbalance threshold; and activating a discharge activation switch associated with each of the highest charge cells.

Description

TECHNICAL FIELD

[0001] Embodiments of the present disclosure generally relate to passive charge balancing of battery cells, and more particularly to efficiently performing passive charge balancing of multiple battery cells in a series-connected battery pack simultaneously. BACKGROUND

[0002] Batteries undergo chemical reactions within battery cells to power various devices. Devices requiring additional power include multiple battery cells that are typically connected in series in a battery pack. Each battery cell in the battery pack exhibits unique characteristics, such as internal resistance of the battery cell, capacitance of the battery cell, operating temperature of the battery cell, aging characteristics of the battery cell, and the like. The unique characteristics of the battery cell can affect the rate at which the battery cell charges and discharges. Different charging and discharging rates between the battery cells of the battery pack can cause imbalanced conditions within the battery pack, negatively impacting the life and utilization of the battery pack.

[0003] The Applicant has recognized numerous technical challenges and difficulties associated with efficiently performing passive balancing of multiple battery cells. Through exerted efforts, ingenuity, and innovation, the Applicant has solved problems associated with balancing multiple battery cells simultaneously by developing the technical solutions embodied in the present disclosure described in detail below. SUMMARY

[0004] Various embodiments relate to example battery management systems, methods, and computer program products for managing passive charge balancing of a battery pack. A first example battery management system is provided. The example battery management system includes a battery pack, a battery management integrated circuit, and a battery management controller. The battery pack includes a plurality of battery cells electrically connected in series, each battery cell of the plurality of battery cells exhibiting a battery cell charge. The battery management integrated circuit includes a discharge circuit for each battery cell, the discharge circuit including a discharge enable switch and a shared balancing resistor, wherein the shared balancing resistor is electrically connected to an adjacent battery cell. The battery management controller is electrically coupled to the battery management integrated circuit, including one or more processors and one or more storage devices storing instructions that are operable, when executed by the one or more processors, to: identify a least charged battery cell of the plurality of battery cells, wherein the least charged battery cell exhibits a lowest battery cell charge of the plurality of battery cells; iteratively select a plurality of most charged battery cells, wherein no two most charged battery cells of the plurality of most charged battery cells are adjacent, and wherein each most charged battery cell of the plurality of most charged battery cells is greater than the least charged battery cell plus an imbalance threshold; and enable the discharge enable switch associated with each most charged battery cell of the plurality of most charged battery cells.

[0005] In some embodiments, the discharge enable switch associated with each of the plurality of highest charge battery cells is enabled until at least one of the plurality of highest charge battery cells is balanced with the least charge battery cell.

[0006] In some embodiments, the battery cells of the plurality of battery cells are balanced in instances in which the battery cell value of the battery cells is within an imbalance threshold of the least charge battery cell.

[0007] In some embodiments, the discharge enable switch is a field effect transistor and the battery management controller modifies a gate voltage at a gate of the field effect transistor to discharge the associated battery cell.

[0008] In some embodiments, the battery management controller is configured to monitor one or more electrical characteristics of each of the plurality of battery cells.

[0009] In some embodiments, the one or more electrical characteristics include at least one of a voltage of the battery cell, a charge of the battery cell, an ampere count of the battery cell, a remaining ampere hour count of the battery cell, and an energy remaining in the battery cell.

[0010] In some embodiments, the one or more electrical characteristics are determined by a pair of electrical connection pins on the battery management integrated circuit.

[0011] In some embodiments, a first electrical connection pin of the pair of electrical connection pins is electrically connected to an anode of the battery cell and a second electrical connection pin of the pair of electrical connection pins is electrically connected to a cathode of the battery cell.

[0012] In some embodiments, the discharge circuit for each battery cell includes a first balancing resistor electrically connected in series with the battery cell, the discharge enable switch, and a second balancing resistor, wherein the shared balancing resistor includes at least one of the first balancing resistor and the second balancing resistor.

[0013] In some embodiments, the battery management controller is further configured to generate a balancing activation map including a balancing activation entry for each of the plurality of battery cells, wherein the balancing activation entry includes: a battery cell identifier identifying the associated battery cell; a battery cell value indicating a battery cell charge of the associated battery cell; and an enable indicator indicating that the associated battery cell is to be discharged.

[0014] An example method for passively charge balancing a battery pack is also provided. The example method includes a plurality of series connected battery cells exhibiting battery cell charges, respectively, the method comprising: identifying, by a battery management controller electrically coupled to a battery management integrated circuit, a least charged battery cell of the plurality of battery cells, wherein the least charged battery cell exhibits a lowest battery cell charge of the plurality of battery cells; iteratively selecting a plurality of most charged battery cells, wherein no two most charged battery cells of the plurality of most charged battery cells are adjacent, and wherein each most charged battery cell of the plurality of most charged battery cells is greater than the least charged battery cell plus an imbalance threshold; and enabling a discharge enable switch associated with each most charged battery cell of the plurality of most charged battery cells, wherein each battery cell is electrically coupled to a discharge circuit comprising: the discharge enable switch and a shared balancing resistor, wherein the shared balancing resistor is electrically connected to an adjacent battery cell.

[0015] In some embodiments, the method can further include enabling the discharge enable switch associated with each most charged battery cell of the plurality of most charged battery cells until each most charged battery cell is balanced with the least charged battery cell.

[0016] In some embodiments, the battery cells are balanced in instances where the battery cell charge of the battery cells is within the imbalance threshold of the least charged battery cell.

[0017] In some embodiments, the discharge enable switch is a field effect transistor, and enabling the discharge enable switch further includes: modifying a gate voltage at a gate of the field effect transistor to discharge the associated battery cell.

[0018] In some embodiments, the method further includes monitoring one or more electrical characteristics of each battery cell of the plurality of battery cells by a pair of electrical connection pins on the battery management integrated circuit, wherein a first electrical connection pin of the pair of electrical connection pins is electrically connected to an anode of the battery cell and a second electrical connection pin of the pair of electrical connection pins is electrically connected to a cathode of the battery cell.

[0019] In some embodiments, the one or more electrical characteristics include at least one of a voltage of the battery cell, a battery cell charge, an ampere count of the battery cell, a remaining ampere hour count of the battery cell, and a remaining energy in the battery cell.

[0020] In some embodiments, the discharge circuit for each battery cell includes a first balancing resistor, the discharge enable switch, and a second balancing resistor electrically connected in series with the battery cell, wherein the shared balancing resistor includes at least one of the first balancing resistor and the second balancing resistor.

[0021] In some embodiments, the method further includes generating a balancing activation map including a balancing activation entry for each battery cell of the plurality of battery cells, wherein the balancing activation entry includes: a battery cell identifier identifying the associated battery cell; a battery cell value indicating a battery cell charge of the associated battery cell; and an enable indicator indicating that the associated battery cell is to be discharged.

[0022] An example computer program product for passively charge balancing a battery pack including a plurality of battery cells electrically connected in series is also provided. In some embodiments, the example computer program product includes at least one non-transitory computer-readable storage medium having computer-readable program code portions stored therein, the computer-readable program code portions including executable portions configured to: identify, by a battery management controller electrically coupled to a battery management integrated circuit, a least charged battery cell of the plurality of battery cells, wherein the least charged battery cell exhibits a lowest battery cell charge of the plurality of battery cells; iteratively select a plurality of most charged battery cells, wherein no two most charged battery cells of the plurality of most charged battery cells are adjacent, and wherein each most charged battery cell of the plurality of most charged battery cells is greater than the least charged battery cell plus an imbalance threshold; and enable a discharge enable switch associated with each most charged battery cell of the plurality of most charged battery cells, wherein each battery cell is electrically coupled to a discharge circuit including: the discharge enable switch and a shared balancing resistor, wherein the shared balancing resistor is electrically connected to an adjacent battery cell.

[0023] A second example battery management system is also provided. The second example battery management system includes a battery pack, a battery management integrated circuit, and a battery management controller. The battery pack includes a plurality of battery cells electrically connected in series, each battery cell exhibiting a battery cell charge. The battery management integrated circuit includes a discharge circuit for each battery cell, each discharge circuit including a discharge enable switch and a shared balancing resistor, where the shared balancing resistor is electrically connected to an adjacent battery cell. The battery management controller is electrically coupled to the battery management integrated circuit, including one or more processors and one or more storage devices storing instructions that are operable, when executed by the one or more processors, to: receive an optimization parameter; determine an optimization value for each battery cell of the plurality of battery cells based on the optimization parameter; identify a least charged battery cell of the plurality of battery cells, where the least charged battery cell exhibits a lowest battery cell charge of the plurality of battery cells; select a plurality of unbalanced battery cells from the plurality of battery cells based on the optimization parameter and the optimization value for each battery cell of the plurality of battery cells, where the plurality of unbalanced battery cells does not include the least charged battery cell, where no two unbalanced battery cells of the plurality of unbalanced battery cells are adjacent, and where a battery cell charge of each unbalanced battery cell of the plurality of unbalanced battery cells is greater than the least charged battery cell plus an unbalance threshold; and enable the discharge enable switch associated with each unbalanced battery cell of the plurality of unbalanced battery cells.

[0024] In some embodiments, the optimization value represents a quantification of the unbalanced battery cell with respect to the optimization parameter.

[0025] In some embodiments, the battery management controller is further configured to: generate a set of valid combinations, where the set of valid combinations includes all possible combinations of the unbalanced battery cells selected for discharging.

[0026] In some embodiments, the battery management controller is further configured to: select the combination from the set of valid combinations based on the optimization value associated with each unbalanced battery cell in the combination.

[0027] In some embodiments, the optimization parameter indicates that the selection of the plurality of unbalanced battery cells from the plurality of battery cells is optimized to reduce a time.

[0028] In some embodiments, the plurality of unbalanced battery cells is selected to minimize a number of balancing iterations.

[0029] In some embodiments, the plurality of unbalanced battery cells is selected to maximize a number of unbalanced battery cells that includes the plurality of unbalanced battery cells. BRIEF DESCRIPTION OF DRAWINGS

[0030] Reference will now be made to the drawings. In certain embodiments described herein, components illustrated in the drawings can or can not be present. Some embodiments can include components beyond those illustrated in the drawings.

[0031] Figure 1 An example battery pack including multiple battery cells is illustrated in accordance with example embodiments of the present disclosure.

[0032] Figure 2 An unbalanced battery pack during charging and discharging is illustrated in accordance with example embodiments of the present disclosure.

[0033] Figure 3 An example battery pack balancing process is illustrated in accordance with example embodiments of the present disclosure.

[0034] Figure 4 A block diagram of an example battery management system is illustrated in accordance with example embodiments of the present disclosure.

[0035] Figure 5 A block diagram of an example architecture of a battery management controller is illustrated in accordance with example embodiments of the present disclosure.

[0036] Figure 6 An example embodiment of a battery management system is illustrated in accordance with example embodiments of the present disclosure.

[0037] Figure 7 An example process for balancing multiple battery cells in a battery pack is illustrated in accordance with example embodiments of the present disclosure.

[0038] Figure 8 An example embodiment of an example process for balancing multiple battery cells in a battery pack is depicted in accordance with example embodiments of the present disclosure.

[0039] Figure 9 An example balancing activation map is depicted in accordance with example embodiments of the present disclosure.

[0040] Figure 10 An example battery cell charge in multiple battery cells is illustrated in accordance with example embodiments of the present disclosure.

[0041] Figure 11 An example process for balancing multiple battery cells in a battery pack is illustrated in accordance with example embodiments of the present disclosure.

[0042] Figure 12 An additional example embodiment of an example process for balancing multiple battery cells in a battery pack is depicted in accordance with example embodiments of the present disclosure.

[0043] Figure 13An example battery cell charge in a plurality of battery cells is illustrated in accordance with example embodiments of the present disclosure. DETAILED DESCRIPTION

[0044] Example embodiments now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the application of the present disclosure are shown. Indeed, the embodiments of the present disclosure can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.

[0045] Various example embodiments address technical problems associated with a plurality of battery cells in a passively balanced battery pack. As understood by those skilled in the art to which the present disclosure pertains, there are many example scenarios in which a user can desire to passively balance battery cells in a battery pack.

[0046] Generally, batteries (e.g., lithium-ion batteries, lithium-polymer batteries, nickel-cadmium batteries, etc.) can experience chemical reactions within the battery cells to power various devices. Devices requiring additional power can contain a plurality of battery cells typically connected in series in a battery pack. The battery pack is typically required to be used continuously repeatedly, including repeated charging and discharging of the battery cells within the battery pack. Each battery cell in the battery pack exhibits unique characteristics. Certain characteristics of the battery cells, such as internal resistance of the battery cell, capacity of the battery cell, operating temperature of the battery cell, aging characteristics of the battery cell, etc., can affect the rate at which the battery cell charges and discharges.

[0047] Different charging and discharging rates between the battery cells of the battery pack can cause unbalanced conditions within the battery pack. Unbalanced conditions arise when the battery cell charge (e.g., the energy or capacity of the battery cell) of the battery cells that make up the battery pack varies from cell to cell. During cell imbalance, the battery cells of the battery pack generally have variable capacities and are at different state-of-charge levels. In the absence of any battery balancing or redistribution, a number of problems can arise. For example, during discharging, the battery pack will stop supplying power when the battery cell with the lowest capacity (e.g., the least charged battery cell) is empty. Thus, the lower capacity battery cells will shorten the battery life of the entire battery pack. Additionally, during charging, the battery cell with the highest battery cell charge (e.g., the most charged battery cell) will reach full charge sooner than the battery cells with lower battery cell charges. When the most charged battery cell reaches full charge, the battery gauge will trigger, stopping the charging of the battery pack. Thus, the lower charged battery cells never reach full charge. This situation is undesirable as it results in underutilization of the total battery pack potential.

[0048] To restore balance to the battery pack, a battery management system can implement a cell balancing process. A battery pack, including several cells connected in series, is considered balanced when all of the battery cells have the same battery cell charge within a threshold, such as an imbalance threshold. Cell balancing improves the overall performance and longevity of the battery pack. Cell balancing processes can include active cell balancing or passive cell balancing. Active cell balancing redistributes stored energy among the battery cells. For example, energy is drained from battery cells with higher battery cell charge and used to charge battery cells with lower battery cell charge. Active cell balancing takes full advantage of the available energy in the battery pack. However, active cell balancing requires additional circuitry, such as charge storage components and / or dedicated DC-DC converters, such as capacitors and inductors, to transfer energy among the battery cells. The additional circuitry can be bulky and expensive.

[0049] Passive cell balancing involves reducing the battery cell charge of high-energy battery cells of the battery pack. The energy in all of the battery cells can be reduced to the level of the least charged battery cell. By reducing the battery cell charge to the level of the least charged battery cell, the battery cells of the battery pack are set to a balanced state. Typically, the battery cell charge of a high-energy battery cell can be reduced by exposing the battery cell to a load, such as a balancing resistor. By causing current to flow out of the battery cell and through the balancing resistor, the excess battery cell charge of the high-charged battery cell can be reduced.

[0050] In some examples, each battery cell of the battery pack can be connected to a dedicated load circuit. The dedicated load circuit can enable a user to selectively individually consume energy from the battery cell. Individually consuming battery cells can be both time consuming and inefficient. Additionally, the dedicated load circuit architecture can require additional circuitry, such as a dedicated load circuit for each battery cell in the battery pack and dedicated pins and electronic components for measuring the voltage, charge, and / or amperage of the battery cell. The additional circuitry can be particularly problematic in battery packs used within limited space requirements and / or low-cost products.

[0051] The various example embodiments described herein utilize various techniques to efficiently perform passive charge balancing for a plurality of battery cells in a battery pack. For example, a battery management system according to the present disclosure can include a battery management controller and a battery management system integrated circuit (IC) electrically coupled to each cell of the battery pack. The battery management system IC can include a discharge circuit for each battery cell in the battery pack, where each discharge circuit includes at least a discharge enable switch and a shared balancing resistor. Additionally, the battery management controller can be configured to selectively enable one or more discharge circuits associated with a battery cell by enabling the discharge enable switch corresponding to the battery cell.

[0052] A battery management controller can be configured to select battery cells for discharge in an efficient manner. A battery management system IC includes a discharge circuit for each battery cell, and each discharge circuit includes at least one shared balancing resistor. Utilizing one or more shared balancing resistors to implement the battery management system IC reduces the circuitry and size of the battery management system IC. However, the shared balancing resistors can impose certain limitations on the selection of battery cells for discharge. For example, two adjacent battery cells that share a shared balancing resistor can not be discharged simultaneously. Accordingly, the battery management controller can be configured to select battery cells for discharge according to one or more techniques to provide efficient charge balancing of the battery pack.

[0053] One example embodiment described herein utilizes a heuristic approach to select one or more battery cells for simultaneous discharge. For example, a battery management controller can be configured to iteratively select a plurality of highest charged battery cells. The heuristic approach can identify a least charged battery cell and a first highest charged battery cell, where the least charged battery cell is not selected for discharge, the first highest charged battery cell is selected for discharge, and a cell adjacent to the first highest charged battery cell is not selected for discharge. Selection of the remaining highest charged battery cells can continue until all battery cells are designated for discharge or not. This process can continue until the battery pack is balanced.

[0054] Another example embodiment described herein utilizes an optimization approach to select an optimal combination of battery cells designated for discharge or not from all combinations of possible techniques, where the selection is made to optimize an optimization parameter. The optimization approach employed by the battery management controller can operate according to programmed parameters, such as identifying and designating highest charged battery cells for discharge, and identifying and designating least charged battery cells for not discharge. Additionally, two adjacent battery cells cannot be selected for discharge. The optimization approach performs the selection of battery cells until the battery pack is balanced.

[0055] As a result of the example embodiments described herein and in some examples, the effectiveness of the passive charge balancing performed by the battery management system is greatly improved. The passive charge balancing performed according to the principles described herein can greatly improve the speed and efficiency at which the battery pack is balanced. This improvement can improve the performance and longevity of the battery pack.

[0056] Referring now to Figure 1 An example series-connected battery pack 100 is provided. As Figure 1The depicted, series-connected battery pack 100 includes a plurality of battery cells 102a to 102f. Each battery cell 102a to 102d includes a cathode terminal 110a to 110d and an anode terminal 112a to 112d. Each battery cell 102a to 102d is electrically coupled in series with adjacent battery cells 102a to 102d via series connectors 104a to 104c, which electrically connect the cathode terminal (e.g., cathode terminal 110a) of battery cell 102a to the anode terminal (e.g., anode terminal 112b) of the adjacent battery cell 102a to 102d. Although depicted as including four battery cells 102a to 102d, the battery pack 100 may include any number of battery cells 102a to 102d, such as dozens, hundreds, or even thousands of battery cells 102a to 102d.

[0057] like Figure 1 The illustrated example series-connected battery pack includes multiple battery cells 102a to 102d. Battery cells 102a to 102d are any electrochemical devices that generate electrical energy using chemical reactions. The chemical reactions within battery cells 102a to 102d may involve the transfer of ions between positively charged electrodes (e.g., cathode terminals 110a to 110d) and negatively charged electrodes (e.g., anode terminals 112a to 112d). When battery cells 102a to 102d supply power to a load, the electron flow from anode terminals 112a to 112d to cathode terminals 110a to 110d generates a current flowing from cathode terminals 110a to 110d to anode terminals 112a to 112d. Battery cells 102a to 102d may contain any of a variety of chemical compositions (e.g., lithium nickel manganese cobalt oxide, lithium iron phosphate, etc.). Battery cells 102a to 102d can take any form, including but not limited to cylindrical cells, prismatic cells, pouch cells, etc.

[0058] Battery cells 102a to 102d can exhibit battery cell charge. The battery cell charge of battery cells 102a to 102d is any representation of the electrical energy capacity generated by a particular battery cell 102a to 102d. The battery cell charge of battery cells 102a to 102d can be determined by measuring the voltage of battery cells 102a to 102d and equalizing the measured voltage with the capacity, for example, by comparing the measured voltage with the voltage of battery cells 102a to 102d at full capacity and the voltage of battery cells 102a to 102d at full discharge. The battery cell charge of battery cells 102a to 102d can be determined by measuring one or more electrical characteristics of battery cells 102a to 102d, such as voltage, charge, ampere number, remaining ampere-hours, and / or remaining energy in battery cells 102a to 102d.

[0059] As Figure 1 Further depicted, the example series-connected battery pack 100 includes a plurality of series connectors 104a-c. The series connectors 104a-c are any electrically conductive material configured to electrically couple the cathode terminal 110a-d of one or more battery cells 102a-d in the battery pack 100 to the anode terminal 112a-d of another battery cell 102a-d. Electrically coupling a plurality of battery cells 102a-d in series increases the available voltage that the battery pack 100 can provide.

[0060] Referring now to Figure 2 When discharging 220a and charging 220b, the unbalanced battery pack 220 including a plurality of battery cells 102a-d is depicted as being in an unbalanced state, each battery cell exhibiting a battery cell charge 226a-d.

[0061] As Figure 2 depicted, the battery pack 220 can include a plurality of battery cells 102a-d, each battery cell exhibiting a unique battery cell charge 226a-d. As described with respect to Figure 1 the battery cell charge 226a-d is any representation of the capacity of a particular battery cell 102a-d to generate electrical energy, and can be determined by measuring one or more electrical properties of the battery cell 102a-d, such as voltage, charge, amperage, remaining amp-hours, and / or energy remaining in the battery cell 102a-d.

[0062] As Figure 2 depicted, the unbalanced battery pack 220 of battery cells includes a least-charged battery cell 222 and a most-charged battery cell 224. The least-charged battery cell 222 includes one or more battery cells 102a-d that include the lowest battery cell charge 226a-d relative to the other battery cells 102a-d that make up the battery pack 220. For example, Figure 2 The depicted battery cell 102d exhibits the lowest battery cell charge 226d of any of the battery cells 102a-d, and is therefore the least-charged battery cell 222. In contrast, the most-charged battery cell 224 includes one or more battery cells 102a-d that include the highest battery cell charge 226a-d relative to the other battery cells 102a-d that make up the battery pack 220. Figure 2 The depicted battery cell 102b exhibits the highest battery cell charge 226d of any of the battery cells 102a-d, and is therefore the most-charged battery cell 224.

[0063] AsFigure 2 Further depicted, in instances where the battery pack is discharging 220a, the battery pack will stop supplying power when the least charged cell 222 is fully discharged. Thus, the discharging battery pack can stop supplying power even though there is still energy within the battery cells 102a-c of the battery pack. As Figure 2 depicted, the energy of the unbalanced battery pack can not be fully utilized.

[0064] Similarly, as Figure 2 depicted, in instances where the battery pack is charging 220b, the battery pack will stop charging when the most charged cell 224 is fully charged. Thus, the battery pack can stop charging even though the battery cells 102a, 102c, 102d are not fully charged. As Figure 2 depicted, the available capacity of the unbalanced battery pack can not be fully utilized.

[0065] Referring now to Figure 3 , an example passive battery balancing process 330 is depicted. Generally, the passive battery balancing process 330 includes identifying the least charged cell 222 based on the cell charge 226a-e of each of the battery cells 102a-f that make up the battery pack. The battery management system can utilize the cell charge 226a-e of the least charged cell 222 to determine a cell charge minimum level 334, indicating a target cell charge 226a-e for each of the battery cells 102a-f in the battery pack.

[0066] As Figure 3 depicted, each of the battery cells 102a-e is electrically coupled to a balancing resistor 332a-e to facilitate the discharge of excess energy in the battery cells 102a-e that is above the cell charge minimum level 334. During the passive battery balancing process 330, the battery cells 102a-e having a cell charge 226a-e above the cell charge minimum level 334 (e.g., battery cells 102b-e) are selected for discharge. To discharge the selected battery cells 102b-e, a current 338b-e is enabled from the battery cells 102b-d and through the balancing resistors 332b-e. The current 338b-e through the balancing resistors 332b-e begins to discharge the excess cell charge 226b-e in the battery cells 102b-e selected for discharge.

[0067] During the passive battery balancing process 330, the battery cells 102b-102e are allowed to discharge until the battery cell charges 226a-226e are within an imbalance threshold of the battery cell charge minimum level 334. The imbalance threshold is any data or value that indicates a minimum deviation of the battery cell charges 226a-226e from the battery cell charge minimum level 334. In some embodiments, the imbalance threshold can be a fixed value (e.g., 1 millivolt). In some embodiments, the imbalance threshold can be relative to the battery cell charge minimum level 334 (e.g., ±5%). In instances where the difference in the battery cell charges 226a-226e of one or more battery cells 102a-102e of the battery pack exceeds the imbalance threshold, the battery pack is considered imbalanced.

[0068] As Figure 3 Further depicted, when the battery cell charges 226a-226e of each of the battery cells 102a-102b are within the imbalance threshold, a balanced battery pack 336 is obtained.

[0069] Referring now to Figure 4 An example battery management system 440 is provided. As Figure 4 depicted, the example battery management system 440 includes a battery management controller 442 electrically coupled to a battery management system IC 444. Additionally, the battery management system IC 444 is electrically coupled to each battery cell 102a-102d that makes up the battery pack 100. As Figure 4 Further depicted, the battery management system IC 444 includes a discharge circuit 446a-446d for each battery cell 102a-102d that makes up the battery pack 100.

[0070] As Figure 4 depicted, the battery management system 440 includes a battery management controller 442. The battery management controller 442 includes one or more processors configured to receive input data related to the state of the battery pack 100 and take action based on the state of the battery pack 100. For example, the battery management controller 442 can control charging of the battery pack, monitor and alarm based on charge levels, monitor the battery pack 100 for overcharging / undercharging, and perform other similar tasks related to the management and health of the battery pack 100.

[0071] Additionally, the battery management controller 442 can be configured to perform passive charge balancing based on the electrical characteristics of the battery cells 102a-102d of the battery pack 100. For example, as Figure 4As depicted, the battery management controller 442 is electrically coupled to the battery management system IC 444. The battery management system IC 444 enables the battery management controller 442 to monitor electrical characteristics related to the cell charge of each battery cell 102a-d. In instances where the battery pack 100 becomes unbalanced (e.g., one or more battery cells 102a-d deviate from the lowest level of cell charge 334 beyond the unbalance threshold), the battery management controller 442 can select one or more battery cells 102a-d to discharge. Further, to perform the discharge, the battery management controller 442 can enable the discharge circuit 446a-d of the associated battery cell 102a-d, allowing excess energy in the battery cell 102a-d to discharge until the cell charge of the battery cell 102a-d is within the unbalance threshold of the lowest level of cell charge. With respect to Figure 5 An example architecture of the battery management system 440 is further described.

[0072] As Figure 4 Further depicted, the example battery management system 440 includes a battery management system IC 444. The battery management system IC 444 is any circuitry, including hardware and / or software, configured to facilitate interfacing between the battery management controller 442 and the battery cells 102a-d of the battery pack 100. The battery management system IC 444 can provide one or more electrical connections enabling the battery management controller 442 to monitor electrical characteristics of the battery cells 102a-d that make up the battery pack 100. For example, the battery management system IC 444 can enable the battery management controller 442 to monitor the voltage, charge, amperage, amp-hours, energy, or other similar electrical characteristics of the battery cells 102a-d.

[0073] The battery management system IC 444 also includes a discharge circuit 446a-d for each battery cell 102a-d of the battery pack 100. The discharge circuit 446a-d is any combination of circuitry, including hardware and / or software, configured to discharge excess charge in the corresponding battery cell 102a-d. The discharge circuit 446a-d is also configured to include a discharge enable switch and a shared balancing resistor.

[0074] The discharge enable switch is any switching mechanism configured to enable current to flow from a corresponding battery cell 102a-d through one or more load elements, including one or more shared balancing resistors. The discharge enable switch can be controlled by the battery management controller 442. Thus, in instances where the battery management controller 442 selects a battery cell 102a-d for discharge, the battery management controller 442 can enable the discharge enable switch to perform the discharge of the selected battery cell 102a-d. In some embodiments, the discharge enable switch can include a transistor device, such as a field effect transistor (FET), a metal oxide semiconductor FET (MOSFET), a bipolar junction transistor (BJT), or other similar switching device.

[0075] The shared balancing resistor includes any resistive element that is electrically coupled to two adjacent battery cells 102a-d and includes at least a portion of the discharge circuit of each of the adjacent battery cells 102a-d. In some embodiments, the battery management system IC 444 can share electrical components and / or electrical connectors, such as electrical connection pins, between one or more adjacent battery cells 102a-d. The shared electrical components reduce the size and cost of the battery management system IC 444. Reducing the size and cost can be particularly important for products with strict size limitations and / or low cost products. Sharing electrical components of the discharge circuits 446a-d with adjacent battery cells 102a-d can result in certain limitations of the passive balancing process. For example, sharing a shared balancing resistor between the discharge circuits of adjacent battery cells 102a-d can prevent the battery management controller 442 from simultaneously selecting two adjacent cells for discharge, as the increased current in the electrical components can damage the electrical components. With respect to Figure 6 Example embodiments of a discharge circuit including a discharge enable switch and a shared balancing resistor are further described.

[0076] Reference is now made to Figure 5 , Figure 5 A block diagram of an example apparatus that can be specially configured in accordance with at least one example embodiment of the present disclosure is illustrated. Specifically, Figure 5 A battery management controller 442 in accordance with at least one example embodiment of the present disclosure is illustrated. The battery management controller 442 includes a processor 552, a data storage medium 556, input / output circuitry 554, and communication circuitry 558. In some embodiments, the battery management controller 442 is configured to execute and perform one or more operations described herein using one or more of the set of circuitry 552, 556, 554, and / or 558.

[0077] Generally, the term computing entity (or referring to an "entity" other than a user) device, system, and / or the like used interchangeably herein can refer to, for example, one or more computers, computing entities, desktop computers, mobile phones, tablet computers, phablets, notebook computers, laptop computers, distributed systems, items / devices, terminals, servers or server networks, blades, gateways, switches, processing devices, processing entities, set-top boxes, relays, routers, network access points, base stations, and / or any combination of devices or entities suitable for performing the functions, operations, and / or processes described herein. Such functions, operations, and / or processes can include, for example, sending, receiving, operating on, processing, displaying, storing, determining, creating / generating, monitoring, evaluating, comparing, and / or the like used interchangeably herein. In one embodiment, these functions, operations, and / or processes can be performed on data, content, information, and / or the like used interchangeably herein. In this regard, the battery management controller 442 embodies a particular, specially-configured computing entity that is transformed to implement the specific operations described herein and provide the particular advantages associated therewith, as described herein.

[0078] While the components are described in relation to functional limitations, it should be understood that particular implementations necessarily include the use of particular computing hardware. It should also be understood that, in some embodiments, certain components described herein include similar or generic hardware. For example, in some embodiments, both circuitry collections utilize the same processor(s), network interface(s), storage medium(s), etc. to perform their associated functions, such that each circuitry collection does not require duplicative hardware. Accordingly, the use of the term "circuitry" used herein in relation to the apparatus components described herein should be understood to include the particular hardware configured to perform the functions associated with the particular circuitry described herein.

[0079] In particular, the term "circuitry" should be broadly interpreted to include hardware and, in some embodiments, software for configuring the hardware. For example, in some embodiments, "circuitry" includes processing circuitry, storage media, network interfaces, input / output devices, etc. Alternatively or additionally, in some embodiments, other elements of the battery management controller 442 provide or supplement the functionality of another particular circuitry collection. For example, in some embodiments, the processor 552 provides processing functionality to any circuitry collection, the data storage media 556 provides storage functionality to any circuitry collection, the communication circuitry 558 provides network interface functionality to any circuitry collection, etc.

[0080] In some embodiments, the processor 552 (and / or co-processor or secondary processor or any other processing circuitry associated with the processor) is in communication with a data storage medium 556 via a bus for passing information among the components of the battery management controller 442. In some embodiments, the data storage medium 556 is non-transitory, for example, and can include one or more volatile and / or non-volatile memories. In other words, in some embodiments, the data storage medium 556 includes or embodies electronic storage devices (e.g., computer readable storage medium). In some embodiments, the data storage medium 556 is configured to store information, data, content, applications, instructions, etc. for enabling the battery management controller 442 to perform various functions in accordance with example embodiments of the present disclosure.

[0081] The processor 552 can be implemented in numerous ways, with the various embodiments of the example embodiments described herein being illustrative only. Thus, for example, in some example embodiments, the processor 552 includes one or more processing devices configured to independently execute. Additionally or alternatively, in some embodiments, the processor 552 includes one or more processor(s) configured in a serial, parallel, or other configuration via a bus to implement independent execution, pipelining, and / or multi-threading of instructions. The use of the terms “processor” and “processing circuitry” should be understood to encompass single core processors, multi-core processors, multiple processors, and / or one or more remote or “cloud” processors that are external to the battery management controller 442.

[0082] In example embodiments, the processor 552 is configured to execute instructions stored in the data storage medium 556 or otherwise accessible to the processor. Alternatively, or additionally, in some embodiments, the processor 552 is configured to execute hard coded functionality. Thus, whether configured by hardware or software methods, or by a combination thereof, the processor 552 represents an entity capable of performing operations according to embodiments of the present disclosure as variously described herein. Alternatively, or additionally, as another example in some example embodiments, when the processor 552 is embodied as an executor of software instructions, the instructions specifically configure the processor 552 to perform the algorithms in specific operations described herein. In some embodiments, the processor 552 includes or is embodied by a CPU, microprocessor, etc. that executes computer coded instructions stored in a non-transitory data storage medium 556, for example.

[0083] In some embodiments, the battery management controller 442 includes input / output circuitry 554 that provides output to the user and, in some embodiments, receives an indication of a user input. In some embodiments, the input / output circuitry 554 is in communication with the processor 552 to provide such functionality. The input / output circuitry 554 can include one or more (symbolic) user interfaces and, in some embodiments, a display including an interface(s) presented to a user via an electronic interface, web interface, application interface, user device, backend system, etc. In some embodiments, the input / output circuitry 554 also includes a keyboard, a mouse, a joystick, a touchpad, a touch screen, soft keys, a microphone, a speaker, or other input / output mechanisms. The processor 552 and / or input / output circuitry 554 including a processor can be configured to control one or more functions of one or more user interface elements via computer program instructions (e.g., software and / or firmware) stored on memory accessible to the processor, such as the data storage medium 556, etc. In some embodiments, the input / output circuitry 554 includes or utilizes a user-facing application to provide input / output functionality to a client device and / or other display associated with a user. In some embodiments, the input / output circuitry 554 includes hardware, software, firmware, and / or combinations thereof that facilitate simultaneous display of particular data via a plurality of different devices.

[0084] In some embodiments, the battery management circuitry 442 includes communication circuitry 558. The communication circuitry 558 includes any components, such as devices or circuitry implemented in hardware or a combination of hardware and software, that are configured to receive and / or transmit data from / to a network and / or any other device, circuitry, or module in communication with the battery management controller 442. In this regard, in some embodiments, the communication circuitry 558 includes, for example, a network interface for implementing communication with a wired or wireless communication network. Additionally or alternatively, in some embodiments, the communication circuitry 558 includes one or more network interface cards, antennas, buses, switches, routers, modems, and supporting hardware, firmware, and / or software, or any other devices suitable for implementing communication via one or more communication networks. Additionally or alternatively, the communication circuitry 558 includes circuitry for interacting with the antenna(s) and / or other hardware or software to transmit signals via the antenna(s) or to process received signals from the antenna(s). In some embodiments, the communication circuitry 558 is capable of transmitting and / or receiving data to and / or from a client device, a capture device, and / or other external computing devices in communication with the battery management controller 442.

[0085] Additionally or alternatively, in some embodiments, two or more of the set of circuitry 552-558 are combinable. Alternatively or additionally, in some embodiments, one or more of the set of circuitry performs some or all of the functionality associated with the description of another component. For example, in some embodiments, two or more of the set of circuitry 552-558 are combined as a single module implemented in hardware, software, firmware, and / or combinations thereof. Similarly, in some embodiments, one or more of the set of circuitry are combined with the processor 552 such that the processor 552 performs one or more operations described above with respect to each of these sets of circuitry 554-558.

[0086] Referring now to Figure 6 , an example battery management system 440 is provided. As Figure 6 depicted, the example battery management system 440 includes a battery management controller 442 that is electrically coupled to a discharge enable switch 664a-664d of each discharge circuit 446a-446d that make up the battery management system IC 444. As Figure 6 further depicted, each discharge circuit 446a-446d is electrically connected to a corresponding battery cell 102a-102d of the example battery pack 110. Further, each discharge circuit 446a-446d includes at least one shared balancing resistor 662a-662c, with each of the outermost discharge circuits 446a, 446d including a balancing resistor 332a, 332b.

[0087] As Figure 6 depicted, the example battery management system 440 includes a discharge circuit 446a-446d for each battery cell 102a-102d of the battery pack. The discharge circuit 446a includes a first resistor, a discharge enable switch 664a-664d, and a second resistor electrically connected in series. The first resistor is also electrically connected to a first terminal of the battery cell 102a-102d, and the second resistor is electrically connected to a second terminal of the battery cell 102a-102d. For example, the discharge circuit 446a associated with the battery cell 102a includes the battery cell 102a, a balancing resistor 332a, a discharge enable switch 664a, and a shared balancing resistor 662a electrically connected in series. Thus, in instances where the discharge enable switch 664a is enabled by the battery management controller 442, current flows through the discharge circuit 446a to discharge excess charge from the battery cell 102a.

[0088] The discharge circuit 446b associated with the battery cell 102b includes the battery cell 102b, the shared balancing resistor 662a, the discharge enable switch 664b, and the shared balancing resistor 662b electrically connected in series. Thus, in instances where the discharge enable switch 664b is enabled by the battery management controller 442, current flows through the discharge circuit 446b, discharging excess charge from the battery cell 102b.

[0089] The discharge circuit 446c associated with the battery cell 102c includes the battery cell 102c, the shared balancing resistor 662b, the discharge enable switch 664c, and the shared balancing resistor 662c electrically connected in series. Thus, in instances where the discharge enable switch 664c is enabled by the battery management controller 442, current flows through the discharge circuit 446c, discharging excess charge from the battery cell 102c.

[0090] The discharge circuit 446d associated with the battery cell 102d includes the battery cell 102d, the shared balancing resistor 662c, the discharge enable switch 664d, and the shared balancing resistor 332b electrically connected in series. Thus, in instances where the discharge enable switch 664d is enabled by the battery management controller 442, current flows through the discharge circuit 446d, discharging excess charge from the battery cell 102d.

[0091] As Figure 6 depicted, each discharge circuit 446a-446d includes at least one shared balancing resistor 662a-662c between adjacent battery cells 102a-102d. Utilizing shared balancing resistors 662a-662c between adjacent battery cells 102a-102d can reduce the size, cost, and complexity of the battery management system IC 444. However, the shared balancing resistors 662a-662c prevent adjacent battery cells 102a-102d from being discharged simultaneously, as enabling the discharge enable switches 664a-664d of two adjacent battery cells 102a-102d would increase the current flowing through the electrical components of the battery management system IC 444, potentially damaging the electrical components.

[0092] As Figure 6 further depicted, each discharge circuit 446a-446d includes a discharge enable switch 664a-664d. While depicted as a MOSFET, the discharge enable switches 664a-664d can include any switching device configured to be enabled based on one or more electronic signals sent by the battery management controller 442. As Figure 6As depicted, the battery management controller 442 can cause a voltage change at the gate of the discharge enable switches 664a-664d. The voltage change can enable current to flow through the source and drain of the discharge enable switches 664a-664d, thereby causing the associated battery cells 102a-102d to discharge.

[0093] Referring now to Figure 7 An example process 700 is provided for iteratively selecting non-adjacent highest charged battery cells for passively balancing a plurality of battery cells (e.g., battery cells 102) in a battery pack (e.g., battery pack 100). In block 702, a battery management controller (e.g., battery management controller 442) identifies a least charged battery cell (e.g., least charged battery cell 222) of a plurality of battery cells, where the least charged battery cell exhibits a lowest battery cell charge (e.g., battery cell charge 226) of the plurality of battery cells. As described herein, the battery management controller can utilize a battery management system IC to monitor one or more electrical characteristics of each of the battery cells, such as voltage, charge, amperage, amp-hours, energy, etc. In instances of battery pack imbalance, the battery management controller can identify the battery cell exhibiting the lowest battery cell charge.

[0094] In block 704, the battery management controller can iteratively select a plurality of highest charged battery cells, where no two highest charged battery cells of the plurality of highest charged battery cells are adjacent, and where each highest charged battery cell of the plurality of highest charged battery cells is greater than the least charged battery cell plus an imbalance threshold. To efficiently perform passive balancing of the battery pack, the battery management controller can first select a battery cell exhibiting a highest battery cell charge that is above a lowest level of battery cell charge (e.g., lowest level of battery cell charge 334) plus the imbalance threshold. Once a battery cell is selected for discharging, discharging operations of one or more battery cells adjacent to the selected battery cell must be disabled.

[0095] The iterative selection of the plurality of highest charged battery cells continues with all remaining battery cells that have not been selected for discharging or removed from consideration for discharging. For example, if a remaining highest charged battery cell has a battery cell charge that is above the lowest level of battery cell charge plus the imbalance threshold, the remaining highest charged battery cell of the plurality of battery cells is added to the plurality of highest charged battery cells and selected for discharging.

[0096] The iterative selection of the remaining highest charged battery cells to the plurality of highest charged battery cells continues until all battery cells are selected for discharging or designated not to discharge.

[0097] In block 706, the battery management controller enables a discharge enable switch (e.g., discharge enable switch 664) associated with each of the plurality of highest state-of-charge cells, where each cell is electrically coupled to a discharge circuit (e.g., discharge circuit 446), and each discharge circuit includes: a discharge enable switch and a shared balancing resistor (e.g., shared balancing resistor 662), where the shared balancing resistor is electrically connected to an adjacent cell. Iteratively selecting the remaining highest state-of-charge cells can result in selecting a plurality of highest state-of-charge cells for discharge. The battery management controller can enable the discharge enable switch of the discharge circuit associated with each of the plurality of highest state-of-charge cells. The battery management controller can discharge the plurality of highest state-of-charge cells simultaneously until one or more of the plurality of highest state-of-charge cells is within the imbalance threshold of the lowest state-of-charge cell level.

[0098] Process 700 can be repeated for any remaining imbalanced cells. Iteratively selecting non-adjacent highest state-of-charge cells and discharging the non-adjacent highest state-of-charge cells simultaneously with process 700 can enable efficient passive balancing of a battery pack.

[0099] Referring now to Figure 8 , an example flow diagram is provided that depicts a process 800 for iteratively selecting non-adjacent highest state-of-charge cells for passive balancing of a plurality of cells (e.g., cells 102) in a battery pack (e.g., battery pack 100).

[0100] In block 802, a battery management controller (e.g., battery management controller 442) initializes a balancing activation map.

[0101] Referring to Figure 9 , an example balancing activation map 990 is provided. As Figure 9 depicted, balancing activation map 990 includes a plurality of balancing activation entries 998, each entry associated with a cell in a battery pack. Balancing activation entries 998 include a cell identifier 992, which is configured to identify each cell. Cell identifier 992 can be any data or value configured to uniquely identify a cell. For example, cell identifier 992 can be a pin number on a battery management system IC (e.g., battery management system IC 444) associated with a cell. In some embodiments, sequential cell identifiers 992 can correspond to adjacent cells.

[0102] The balance activation entry 998 of the balance activation map 990 also includes a cell value 994. The cell value 994 can include any data or value configured to represent a cell charge of a battery cell. For example, the cell value 994 can indicate a measured voltage of a battery cell or indicate a battery state of charge in percentage.

[0103] The balance activation entry 998 of the balance activation map 990 also includes an enable indicator 996. The enable indicator indicates whether the battery cell identified by the battery cell identifier 992 is selected for discharging or designated not to discharge. For example, the enable indicator 996 can include a Boolean value, such as a single bit, where a ‘1’ indicates the battery cell is selected for discharging and a ‘0’ indicates the battery cell is not selected for discharging.

[0104] Referring now to Figure 10 , an example battery pack 1000 is provided. As Figure 10 depicted, the example battery pack includes five battery cells 1000a-1000e. Each battery cell includes a measured cell charge 226 measured in millivolts. As Figure 10 shown, the third battery cell (battery cell 1000c) is the highest charged cell 224 and the fifth battery cell (battery cell 1000e) is the least charged cell 222.

[0105] Returning to Figure 8 , the battery management controller can initialize the balance activation map by creating a balance activation entry for each battery cell in the battery pack and determining a battery cell identifier to uniquely identify the battery cell. Additionally, the battery management controller can set a cell value for each battery cell in the balance activation map. Further, the battery management controller can set the enable indicator of each balance activation entry to a value indicating the battery cell is not selected for discharging or designated not to discharge (e.g., ‘-1’).

[0106] For example, for Figure 10The depicted example battery pack 1000, the cell identifiers can be initialized in a sequential order, 1000a is '1', 1000b is '2', 1000c is '3', 1000d is '4', and 1000e is '5'. Additionally, the cell values can be set to the measured voltage (in millivolts) of each cell; 1000a (e.g., cell identifier 1) is 3873, 1000b (e.g., cell identifier 2) is 3872, 1000c (e.g., cell identifier 3) is 3877, 1000d (e.g., cell identifier 4) is 3873, and 1000e (e.g., cell identifier 5) is 3863. Further, the enable indicators of each balancing activation entry in the balancing activation map can be set to '-1', indicating that the cell is not selected for discharge or designated not to discharge.

[0107] In block 804, the battery management controller identifies the least charged cell and sets the enable indicator for the associated balancing activation entry to 0, indicating that the corresponding cell is designated not to discharge. As Figure 9 As depicted, based on the example battery pack 1000 of Figure 10 , the fifth cell (1000e) is identified as the least charged cell and the enable indicator 996 for the balancing activation entry of the fifth cell (e.g., cell identifier 992 is 5) is set to 0.

[0108] In block 806, if the cell charge of the most charged cell is greater than the imbalance threshold plus the cell charge of the least charged cell, the battery management controller identifies the most charged cell and sets the enable indicator of the associated balancing activation entry to 1. Setting the enable indicator to 1 indicates that the corresponding cell is selected for discharge. As Figure 9 As depicted, based on the example battery pack 1000 of Figure 10 , the third cell (1000c) is identified as the most charged cell and the enable indicator 996 for the balancing activation entry of the third cell (e.g., cell identifier 992 is 3) is set to 1.

[0109] Additionally, the battery management controller sets the enable indicators of all cells adjacent to the most charged cell to 0, indicating that the corresponding cells are designated not to discharge. As Figure 9As depicted, since the battery cell identifiers in the balance activation mapping are sequential, adjacent battery cells are identified by sequential battery cell identifiers. Therefore, the second battery cell (1000b) and the fourth battery cell (1000d) are identified as adjacent battery cells, and the enable indicator 996 for the balance activation entries for the second battery cell (e.g., battery cell identifier 992 is 2) and the fourth battery cell (e.g., battery cell identifier 992 is 4) is set to 0.

[0110] In block 808, the battery management controller checks for any additional unbalanced battery cells that have not yet been selected for discharge or designated as not to be discharged. An unbalanced battery cell is any battery cell whose cell charge is at least greater than the cell charge of the least charged battery cell by an imbalance threshold. In instances where no additional unbalanced battery cells are specified, process 800 returns to block 806. In instances where no unspecified unbalanced battery cells exist, process 800 continues in block 810.

[0111] like Figure 9 The description is based on Figure 10 In the example battery pack 1000, the first battery cell (1000a) is not specified (e.g., the battery cell is not selected for discharge or specified as not to discharge) and is unbalanced. Therefore, process 800 will return to box 806 and set the enable indicator 996 for the balance activation entry for the first battery cell (e.g., battery cell identifier 992 is 1) to 1.

[0112] In box 810, cell balancing operation begins based on the balance activation map. The battery management controller can refer to the balance activation map to determine which one or more battery cells to select for discharge. The battery management controller can also enable the discharge enable switch (e.g., discharge enable switch 664) associated with each battery cell identified in the balance activation map. Enabling the discharge enable switch of the discharge circuit (e.g., discharge circuit 446) associated with the battery cell will allow additional charge within the battery cell to discharge. The battery management controller can monitor the electrical characteristics of the battery cells during discharge. Once at least one of the multiple highest-charged battery cells is balanced (e.g., the battery cell charge is within the imbalance threshold of the lowest battery cell charge level), the cell balancing operation for the selected cells terminates. For any remaining unbalanced cells, the process can be repeated. Figure 8 The process is depicted in the flowchart 800. This process may continue until all battery cells within the battery pack are balanced.

[0113] Now for reference Figure 11An example process 1100 for balancing one or more battery cells (e.g., battery cell 102) in a battery pack (e.g., battery pack 100) based on an optimization parameter is provided. In block 1102, a battery management controller (e.g., battery management controller 442) is configured to receive an optimization parameter. The optimization parameter includes one or more data constructs indicative of one or more characteristics to optimize during passive charge balancing. In one non-limiting example, the optimization parameter can be a total passive charge balancing time, and thus, the selection of battery cells to discharge is determined based on reducing the total time to perform passive charge balancing. In another non-limiting example, the optimization parameter can indicate a number of passive charge balancing iterations. Thus, the selection of battery cells to discharge is determined based on the number of passive charge balancing iterations that can be performed to complete passive charge balancing. Another optimization parameter can relate to the technology or chemistry of the battery cells that make up the battery pack. For example, based on the battery cell technology or chemistry, the performance of the battery cells can last longer. Thus, in another non-limiting embodiment, a metric based on the chemistry or technology of the battery cells that make up the battery pack can be used to monitor / balance the least stable battery cells. In another non-limiting example, the optimization parameter can represent a state of health of the battery cells. For example, the optimization parameter indicates those battery cells that can be performing the worst due to premature aging. Additional optimization parameters can include reducing total power consumption, reducing wasted charge discharged from the power cell, optimizing battery life, etc.

[0114] In block 1104, the battery management controller determines an optimization value for each battery cell of the plurality of battery cells based on the optimization parameter. The optimization value is any data value representative of a characteristic of the associated battery cell with respect to the optimization parameter. For example, in some embodiments, the optimization value can be a battery cell charge. In instances where the battery cell charge is used as the optimization value, the selection of battery cells can be optimized based on time, number of iterations, wasted charge, total power consumption. In some instances, the optimization values of the battery cells can be weighted. In some embodiments, the optimization value can be based on multiple characteristics of the battery cell. For example, the battery cell can include various internal chemistries. The optimization value can be configured based on the chemistry of the battery and another electrical parameter, such as the battery cell charge.

[0115] In block 1106, the battery management controller identifies a least charged battery cell (e.g., least charged battery cell 222) of the plurality of battery cells, where the least charged battery cell exhibits a lowest battery cell charge of the plurality of battery cells. The least charged battery cell can be used to determine a battery cell charge low level (e.g., battery cell charge low level 334) indicative of a battery charge level of the least charged battery cell of the group of battery cells. Any battery cell having a battery charge level greater than the battery cell charge low level plus an imbalance threshold is considered imbalanced.

[0116] In block 1108, the battery management controller identifies a highest charged battery cell (e.g., highest charged battery cell 224) of the plurality of battery cells, where the highest charged battery cell exhibits a highest battery cell charge of the plurality of battery cells. In some embodiments, the highest charged battery cell can be selected for automatic discharge during the first discharge iteration. In such embodiments, the highest charged battery cell is added to the plurality of unbalanced battery cells, and one or more battery cells adjacent to the highest charged battery cell are designated as not to be discharged. In some embodiments, the process 1100 can continue without identifying the highest charged battery cell.

[0117] In block 1110, the battery management controller selects a plurality of unbalanced battery cells from the plurality of battery cells based on the optimization parameter and the optimization value of each battery cell of the plurality of battery cells, where the plurality of unbalanced battery cells does not include the least charged battery cell, where no two unbalanced battery cells of the plurality of unbalanced battery cells are adjacent, and where each unbalanced battery cell of the plurality of unbalanced battery cells has a battery cell charge greater than the least charged battery cell plus an unbalance threshold. The battery management controller can select the plurality of unbalanced battery cells based on the optimization value of each battery cell of the plurality of battery cells and the unbalance classification of the battery cells. As described herein, any battery cell having a battery cell charge greater than the battery cell charge minimum plus the unbalance threshold is considered unbalanced. The battery management controller is configured to select the unbalanced battery cells for discharge based on the optimization values associated with the unbalanced battery cells. Additionally, no two battery cells of the plurality of unbalanced battery cells can be adjacent. Further, the least charged battery cell is not included in the plurality of unbalanced battery cells.

[0118] The battery management controller can utilize any method to select the unbalanced battery cells based on the optimization values. For example, the battery management controller can generate all possible combinations of unbalanced battery cells (e.g., a set of valid combinations) that satisfy the selection criteria. The battery management controller can select the valid combination having the highest cumulative total optimization value, e.g., by accumulating the optimization values of the selected unbalanced battery cells. The battery management controller can select the valid combination having the highest average optimization value per battery cell, e.g., by accumulating the optimization values of the selected unbalanced battery cells and dividing by the number of selected unbalanced battery cells.

[0119] The battery management controller can also utilize an algorithm to select the plurality of unbalanced battery cells. For example, a genetic algorithm, simulated annealing, particle swarm optimization, ant colony optimization, fuzzy optimization, neural network based optimization, linear programming optimization techniques, etc. The optimization algorithm can be configured to select a set of unbalanced battery cells that does not include the least charged battery cell and does not include any adjacent battery cells, thereby optimizing an optimization value. The optimization value can include finding a combination of unbalanced battery cells that has a minimum total optimization value, a minimum average optimization value, a maximum total optimization value, and a maximum average optimization value, etc. In some embodiments, the optimization value can include a battery cell charge of each of the battery cells in the battery pack.

[0120] In some embodiments, the selection of the plurality of unbalanced battery cells can be optimized over the iterations of discharging. For example, the selection of the plurality of unbalanced battery cells can be optimized to minimize the number of iterations of discharging required to fully balance the battery pack. Further, the optimization algorithm can consider multiple iterations of discharging when optimizing the selection of the plurality of unbalanced battery cells with respect to the optimization parameter.

[0121] In block 1112, the battery management controller enables a discharge enable switch (e.g., discharge enable switch 664) associated with each of the plurality of unbalanced battery cells. Enabling the discharge enable switch of the discharge circuit (e.g., discharge circuit 446) associated with the battery cell will allow additional charge within the battery cell to be discharged. The battery management controller can monitor electrical characteristics of the plurality of unbalanced battery cells during discharging. Once at least one of the plurality of unbalanced battery cells is balanced (e.g., the battery cell charge is within an unbalance threshold of the lowest level of battery cell charge), the cell balancing operation of the selected cell terminates. The process 1100 can be repeated for any remaining unbalanced cells and continue until all of the battery cells within the battery pack are balanced.

[0122] Referring now to Figure 12 An example flow diagram is provided that depicts a process 1200 of selecting a plurality of unbalanced battery cells according to an optimization parameter.

[0123] In block 1202, the battery management controller (e.g., battery management controller 442) identifies a least charged battery cell (e.g., least charged battery cell 222). The identified least charged battery cell indicates a lowest level of battery cell charge (e.g., lowest level of battery cell charge 334), e.g., the battery cell charge of the least charged battery cell. The lowest level of battery cell charge enables the battery management controller to determine unbalanced battery cells. The lowest level of battery cell charge also provides a target battery cell charge for the battery cells to be discharged during passive charge balancing.

[0124] In block 1202, the battery management controller further identifies the highest charged battery cell. In some embodiments, the battery management controller can automatically select the highest charged battery cell for discharge. In instances where the highest charged battery cell is selected for discharge, one or more battery cells adjacent to the highest charged battery cell are designated for no discharge.

[0125] The battery management controller can utilize any mechanism to store data indicative of the least charged battery cell, the highest charged battery cell, and / or one or more battery cells adjacent to the highest charged battery cell. For example, the battery management controller can utilize a data structure such as a map, a list, a dictionary, a set, a bitmap, an array, or other similar structure. For example, in one embodiment, a pattern mask can be generated to record battery cells selected for discharge and battery cells designated for no discharge. One example pattern mask includes a sequence of enable indicators, each corresponding to an index of a battery cell in the battery pack. For example, a pattern mask utilizing a sequence of enable indicators can set a value to 1 to indicate a battery cell is selected for discharge, to 0 to indicate a battery cell is designated for no discharge, and to -1 to indicate a battery cell is neither selected for discharge nor designated for no discharge. In some embodiments, multiple pattern masks can be utilized, for example one to indicate battery cells selected for discharge and one to indicate battery cells designated for no discharge.

[0126] Referring now to Figure 13 , an example battery pack 1300 is provided. As Figure 13 depicted, the example battery pack includes five battery cells 1300a-1300e. Each battery cell includes a measured battery cell charge 226 measured in millivolts. As Figure 13 shown, the fifth battery cell (battery cell 1300e) is the highest charged battery cell 224 (3849 millivolts) and the fourth battery cell (battery cell 1300d) is the least charged battery cell 222 (3844 millivolts). In an instance where the imbalance threshold is 0.9 millivolts, all battery cells except the least charged battery cells (e.g. battery cells 1300a, 1300b, 1300c, 1300e) are imbalanced.

[0127] Returning to Figure 12 , in block 1202, the battery management controller identifies the highest charged battery cell based on Figure 13In the example battery pack 1300, the fourth battery cell (1300d) is identified as the least charged battery cell and the fifth battery cell (1300e) is identified as the most charged battery cell. The battery management controller can update one or more pattern masks to indicate that the fifth battery cell (1300e) is selected for discharging and the fourth battery cell (1300d) is designated as not discharging. Since the battery cell adjacent to the most charged battery cell is the least charged battery cell, no adjacent battery cell is designated as not discharging.

[0128] In block 1204, the battery management controller identifies all unbalanced battery cells. An unbalanced battery cell is any battery cell whose battery cell charge is above the minimum battery cell charge level plus the unbalance threshold. During the passive charge balancing process, the unbalanced battery cells can be selected for discharging. In some embodiments, the passive charge balancing process can continue until the battery cell charge of all unbalanced battery cells is within the unbalance threshold of the minimum battery cell charge level. The storage mechanism of the battery management controller can be updated to identify the unbalanced battery cells. For example, the pattern mask can be updated by setting the enable indicator associated with the index of a balanced battery cell to 0 to indicate that the balanced battery cell is not designated for discharging.

[0129] In Figure 13 In the example battery pack 1300, all battery cells except the least charged battery cells (e.g., battery cells 1300a, 1300b, 1300c, 1300e) are unbalanced, so no further updates to the pattern mask are needed.

[0130] In block 1206, the battery management controller iterates through all possible combinations of selected battery cells based on the designation of the least charged battery cell, the most charged battery cell, the battery cell adjacent to the most charged battery cell, and the identification of the unbalanced battery cells. In some examples, all possible combinations of selected battery cells are generated. The battery management controller can loop through the list of possible combinations and test the optimal solution. In each instance where there are still combinations of selected battery cells to consider, the process 1200 continues in block 1208. Once all possible combinations have been considered, the process 1200 continues in block 1216.

[0131] In block 1208, the battery management controller considers the next combination of selected battery cells by checking whether the selected battery cells comply with the adjacency rule. Thus, the battery management controller only considers combinations of selected battery cells that do not select two adjacent battery cells for discharging. In instances where the combination of selected battery cells includes selecting two adjacent battery cells for discharging, the process 1200 continues in block 1206. In instances where the combination of selected battery cells complies with the adjacency rule, the process 1200 continues in block 1210.

[0132] In block 1210, the battery management controller considers the next combination of selected battery cells by checking whether the selected battery cells comply with the balance and imbalance requirements. Thus, the battery management controller only considers combinations of selected battery cells where the battery cells selected for discharging are imbalanced, for example by comparing the battery cells selected for discharging to the imbalanced battery cells identified in block 1204. In instances where the combination of selected battery cells includes balanced battery cells, the process 1200 continues in block 1206. In instances where the combination of selected battery cells only includes imbalanced battery cells, the process 1200 continues in block 1212.

[0133] As described herein, the set of combinations that comply with the adjacency rule; the balance and imbalance requirements; and the designation of the least charged battery cell as not to discharge can refer to a set of valid combinations. The set of valid combinations includes all possible combinations of selected cells that comply with the established requirements. In some embodiments, the set of valid combinations can be determined in blocks 1206-1208.

[0134] In block 1212, the battery management controller calculates an optimal value for the combination. The optimal value for the combination can be determined based on the optimization value associated with each battery cell selected in the combination of selected battery cells. In one example embodiment, the optimal value for the combination of selected battery cells can be determined by accumulating the optimization values of the selected battery cells. For example, by performing a summation, such as:

[0135]

[0136] where V cell includes the optimization value for each battery cell k, Map includes an indicator of whether battery cell k is selected for discharging, N is the total number of battery cells, and Opt k is the optimal value for the combination of selected battery cells. In another embodiment, the average optimal value can be determined, for example, by performing an operation:

[0137]

[0138] For example, based on Figure 13For the example battery pack 1300 of

[0139] Opt k = 3846 + 3845 + 3850 = 11541

[0140] However, with the same Map

[10101] , the optimal value for the same combination of selected battery cells according to equation (2) is:

[0141]

[0142] Similarly, for the example battery pack 1300 based on Figure 13 a second combination of selected battery cells based on Map

[01001] in which the second battery cell (1300b) and the fifth battery cell (1300e) are selected for discharge, the optimal value according to equation (1) is:

[0143] Opt k = 3849 + 3850 = 7699

[0144] However, the optimal value for the second combination of selected battery cells according to equation (2) is:

[0145]

[0146] As described herein, any value can be assigned to each battery cell as an optimization value, representing the cost of the battery cell in the optimization function.

[0147] In block 1214, the optimal value determined for the combination of selected battery cells is compared to the stored best combination of selected battery cells. The best combination can be determined by comparing the optimal value of the current combination of selected battery cells to the optimal value of the stored best combination of selected battery cells. In some embodiments, the best combination of selected battery cells can be the combination of selected battery cells associated with the highest optimal value. In some embodiments, the best combination of selected battery cells can be the combination of selected battery cells associated with the lowest optimal value.

[0148] Continuing the above example, in instances where the battery management controller utilizes the cumulative optimum according to equation (1) in block 1214 and block 1214 considers the highest optimum to be the best combination, the first combination of selected battery cells exhibits a higher optimum (11541) than the second combination of selected battery cells (7699). Thus, in instances where the first combination of selected battery cells has previously been stored as the best combination, the battery management controller determines in block 1214 that the second combination of selected battery cells is not better, and the process 1200 continues operation in block 1206.

[0149] However, in instances where the battery management controller utilizes the average optimum according to equation (2) at block 1214, the first combination of selected battery cells exhibits a lower optimum (3847) than the second combination of selected battery cells (3849.5). Thus, in instances where the first combination of selected battery cells has previously been stored as the best combination, the battery management controller determines in block 1214 that the second combination of selected battery cells is better, and the process 1200 continues operation in block 1216.

[0150] In block 1216, the battery management controller stores the current combination of selected battery cells as the best combination of selected battery cells. In some embodiments, the combination of selected battery cells can be stored by a bit sequence of 1s and Os, where a 1 indicates that a battery cell having an associated index is selected for discharge, and a 0 indicates that a battery cell having an associated index is not selected for discharge.

[0151] In block 1216, the battery management controller initiates a cell balancing operation based on the best combination of selected battery cells according to the optimum. The battery management controller can reference the data structure representing the best combination of selected battery cells to determine one or more battery cells selected for discharge. The battery management controller can also enable a discharge enable switch (e.g., discharge enable switch 664) associated with each battery cell identified in the best combination of selected battery cells. Enabling the discharge enable switch of a discharge circuit (e.g., discharge circuit 446) associated with a battery cell will allow additional charge within the battery cell to be discharged. The battery management controller can monitor electrical characteristics of the battery cells during discharge. The cell balancing operation of the selected cells terminates once at least one of the plurality of highest charged battery cells is balanced (e.g., the battery cell charge is within an imbalance threshold of the lowest level of battery cell charge). The process 1200 can be repeated for any remaining imbalanced cells. This process can continue until all battery cells within the battery pack are balanced.

[0152] While the detailed description sets forth embodiments of the application, other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. For example, it will be appreciated that the principles of the application can be applied to any electronic device powered with a battery having multiple battery cells. For example, mobile electronic devices, such as laptop computers, mobile phones, tablet computers, cameras, etc.; appliances; power tools; electric vehicles; battery powered entertainment devices, etc.

[0153] Within the appended claims, unless the word "means" is specifically used followed by the phrase "for...," it is not intended that the claim be interpreted under 35 U.S.C. 112, Sixth Paragraph.

[0154] The use of the terms "comprises", "comprising", "includes", "including" and the like are not intended to exclude the presence of other elements or steps. At the very least, such terms are to be construed to mean "consisting essentially of" or "consisting of", unless these phrases are specifically excluded. The terms "comprises", "comprising", "includes", "including" and the like mean "including, but not limited to". The use of the term "about" in relation to a given value means that the value is within a reasonable range of the given value, such as within 10% of the given value. The use of the term "optionally" in relation to an element of the embodiments means that the element is not required, or that the element is required, but not necessarily present.

Claims

1. A battery management system comprising: a battery pack comprising a plurality of battery cells electrically connected in series, each of the plurality of battery cells exhibiting a battery cell charge; a battery management integrated circuit comprising: a discharge circuit for each battery cell, the discharge circuit comprising: a discharge enable switch and a shared balancing resistor, wherein the shared balancing resistor is electrically connected to an adjacent battery cell; and a battery management controller electrically coupled to the battery management integrated circuit comprising one or more processors and one or more storage devices storing instructions that are operable when executed by the one or more processors to: identify a least charged battery cell of the plurality of battery cells, wherein the least charged battery cell exhibits a lowest battery cell charge of the plurality of battery cells; iteratively select a plurality of most charged battery cells, wherein no two most charged battery cells of the plurality of most charged battery cells are adjacent, and wherein each most charged battery cell of the plurality of most charged battery cells is greater than the least charged battery cell plus an imbalance threshold; and enable the discharge enable switch associated with each most charged battery cell of the plurality of most charged battery cells.

2. The battery management system of claim 1, wherein the discharge enable switch associated with each most charged battery cell of the plurality of most charged battery cells is enabled until at least one most charged battery cell of the plurality of most charged battery cells is balanced with the least charged battery cell.

3. The battery management system of claim 2, wherein a battery cell of the plurality of battery cells is balanced in instances where a battery cell value of the battery cell is within the imbalance threshold of the least charged battery cell.

4. The battery management system of claim 1, wherein the discharge enable switch is a field effect transistor, and wherein the battery management controller modifies a gate voltage at a gate of the field effect transistor to discharge an associated battery cell.

5. The battery management system of claim 1, wherein the battery management controller is configured to monitor one or more electrical characteristics of each battery cell of the plurality of battery cells.

6. The battery management system of claim 5, wherein the one or more electrical characteristics comprise at least one of: a voltage of a battery cell, a charge of the battery cell, an ampere count of the battery cell, a remaining ampere hour count of the battery cell, and an energy remaining in the battery cell.

7. The battery management system of claim 5, wherein the one or more electrical characteristics are determined by a pair of electrical connection pins on the battery management integrated circuit.

8. The battery management system of claim 7, wherein a first electrical connection pin of the pair of electrical connection pins is electrically connected to an anode of the battery cell, and a second electrical connection pin of the pair of electrical connection pins is electrically connected to a cathode of the battery cell.

9. The battery management system of claim 1, wherein the discharge circuit for each battery cell comprises a first balancing resistor electrically connected in series with the battery cell, the discharge enable switch, and a second balancing resistor, wherein the shared balancing resistor comprises at least one of the first balancing resistor and the second balancing resistor.

10. The battery management system of claim 1, wherein the battery management controller is further configured to: generate a balancing activation map comprising a balancing activation entry for each battery cell of the plurality of battery cells, wherein the balancing activation entry comprises: a battery cell identifier identifying an associated battery cell; a battery cell value indicating the battery cell charge of the associated battery cell; and an enable indicator indicating that the associated battery cell is to be discharged.

11. A method for passive charge balancing of a battery pack, the battery pack comprising a plurality of battery cells connected in series, the plurality of battery cells each exhibiting a battery cell charge, the method comprising: identifying, by a battery management controller electrically coupled to a battery management integrated circuit, a least charged battery cell of the plurality of battery cells, wherein the least charged battery cell exhibits a lowest battery cell charge of the plurality of battery cells; iteratively selecting a plurality of most charged battery cells, wherein no two most charged battery cells of the plurality of most charged battery cells are adjacent, and wherein each most charged battery cell of the plurality of most charged battery cells is greater than the least charged battery cell plus an imbalance threshold; and enabling a discharge enable switch associated with each most charged battery cell of the plurality of most charged battery cells, wherein each battery cell is electrically coupled to a discharge circuit, the discharge circuit comprising: a discharge enable switch and a shared balancing resistor, wherein the shared balancing resistor is electrically connected to an adjacent battery cell.

12. The method of claim 11, further comprising: enabling the discharge enable switch associated with each most charged battery cell of the plurality of most charged battery cells until each most charged battery cell is balanced with the least charged battery cell.

13. The method of claim 12, wherein in instances where a battery cell’s battery cell charge is within the imbalance threshold of the least charged battery cell, the battery cell is balanced.

14. The method of claim 11, wherein the discharge enable switch is a field effect transistor, and enabling the discharge enable switch further comprises: modifying a gate voltage at a gate of the field effect transistor to discharge an associated battery cell.

15. The method of claim 11, further comprising: monitoring one or more electrical characteristics of each battery cell of the plurality of battery cells by a pair of electrical connection pins on the battery management integrated circuit, ​ wherein a first electrical connection pin of the pair of electrical connection pins is electrically connected to an anode of a battery cell and a second electrical connection pin of the pair of electrical connection pins is electrically connected to a cathode of the battery cell.

16. The method of claim 15, wherein the one or more electrical characteristics comprise at least one of a voltage of a battery cell, a battery cell charge, an ampere count of the battery cell, a remaining ampere hour count of the battery cell, and a remaining energy in the battery cell.

17. The method of claim 11, wherein the discharge circuit for each battery cell comprises a first balancing resistor electrically connected in series with the battery cell, the discharge enable switch, and a second balancing resistor, wherein the shared balancing resistor comprises at least one of the first balancing resistor and the second balancing resistor.

18. The method of claim 11, further comprising: generating a balancing activation map comprising a balancing activation entry for each battery cell of the plurality of battery cells, wherein the balancing activation entry comprises: a battery cell identifier identifying an associated battery cell; a battery cell value indicating the battery cell charge of the associated battery cell; and an enable indicator indicating that the associated battery cell is to be discharged.

19. A computer program product for passive charge balancing of a battery pack comprising a plurality of battery cells electrically connected in series, the computer program product comprising at least one non-transitory computer-readable storage medium having computer-readable program code portions stored therein, the computer-readable program code portions comprising executable portions configured to: identify, by a battery management controller electrically coupled to a battery management integrated circuit, a least charged battery cell of the plurality of battery cells, wherein the least charged battery cell exhibits a lowest battery cell charge of the plurality of battery cells; iteratively select a plurality of most charged battery cells, wherein no two most charged battery cells of the plurality of most charged battery cells are adjacent, and wherein each most charged battery cell of the plurality of most charged battery cells is greater than the least charged battery cell plus an imbalance threshold; and enable a discharge enable switch associated with each most charged battery cell of the plurality of most charged battery cells, wherein each battery cell is electrically coupled to a discharge circuit, and each discharge circuit comprises: the discharge enable switch and a shared balancing resistor, wherein the shared balancing resistor is electrically connected to an adjacent battery cell.

20. A battery management system comprising: a battery pack comprising a plurality of battery cells electrically connected in series, each battery cell exhibiting a battery cell charge; a battery management integrated circuit comprising: a discharge circuit for each battery cell, each discharge circuit comprising: a discharge enable switch and a shared balancing resistor, wherein the shared balancing resistor is electrically connected to an adjacent battery cell; and ​ a battery management controller electrically coupled to the battery management integrated circuit, including one or more processors and one or more storage devices storing instructions that are operable when executed by the one or more processors to: receive an optimization parameter; determine an optimization value for each of the plurality of battery cells based on the optimization parameter; identify a least-charged battery cell of the plurality of battery cells, wherein the least-charged battery cell exhibits the lowest battery cell charge of the plurality of battery cells; select a plurality of unbalanced battery cells from the plurality of battery cells based on the optimization parameter and the optimization value for each of the plurality of battery cells, wherein the plurality of unbalanced battery cells does not include the least-charged battery cell, wherein no two unbalanced battery cells of the plurality of unbalanced battery cells are adjacent, and wherein the battery cell charge of each unbalanced battery cell of the plurality of unbalanced battery cells is greater than the least-charged battery cell plus an unbalance threshold; and enable the discharge enable switch associated with each unbalanced battery cell of the plurality of unbalanced battery cells.

21. The battery management system of claim 20, wherein the optimization value represents a quantification of the unbalanced battery cell with respect to the optimization parameter.

22. The battery management system of claim 21, wherein the battery management controller is further configured to: generate a set of valid combinations, wherein the set of valid combinations includes all possible combinations of unbalanced battery cells selected for discharge.

23. The battery management system of claim 22, wherein the battery management controller is further configured to: select a combination from the set of valid combinations based on the optimization value associated with each unbalanced battery cell of the combination.

24. The battery management system of claim 20, wherein the optimization parameter indicates that the selection of the plurality of unbalanced battery cells from the plurality of battery cells is optimized to reduce time.

25. The battery management system of claim 24, wherein the plurality of unbalanced battery cells is selected to minimize a number of balancing iterations.

26. The battery management system of claim 24, wherein the plurality of unbalanced battery cells is selected to maximize a number of unbalanced battery cells including the plurality of unbalanced battery cells.

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