Cross-Reference to Related Applications

[0001] This application claims the benefit under 35 U.S.C. §119 of application No. 63/188,799, filed 14 May 2021 , and entitled ENERGY CELL MANAGEMENT SYSTEM AND Method, which is hereby incorporated herein by reference for all purposes.

Technical Field

[0002] The present disclosure relates to electrical management systems and electrical management methods. More particularly, the present disclosure relates to management systems and management methods for energy cells.

Background

[0003] Electrical energy may be stored in energy cells, for example electrochemical cells, capacitors, super capacitors, and/or fuel cells. Multiple energy cells may be combined into a cell pack to provide the voltage, current, capacity, and/or power required for a given application.

[0004] Cell packs may be used in a variety of applications, for example portable consumer electronics, electric vehicles, hybrid-electric vehicles, off-grid power storage, satellites, aerospace equipment, robotics, electrical grid load balancing, emergency backup devices, and the like.

[0005] To provide the voltage, current, capacity, and/or power required by different applications of cell packs, multiple cells may be electrically connected in series and/or parallel within a cell pack. For example, an individual cell may provide a direct current (DC) voltage of between 1.2 and 4.2 volts (V), whereas some high-voltage applications may require a supply voltage higher than the voltage of an individual cell, for example of between 12 V and 600 V. To deliver the supply voltage required by such high-voltage applications, multiple cells may be electrically connected in series, where the voltage of multiple series connected cells is equal to the sum of the voltage of the cells.

[0006] Similarly, an individual cell may provide a peak current of between 50 milliamps (mA) and 30 amps (A). Some high-current applications may require a supply current higher than the peak current of an individual cell, for example 100 A or more. To deliver the supply current required by such high-current applications, a plurality of cells may be electrically connected in parallel to provide a supply current equal to the sum of the current of each individual cell.

[0007] A cell pack may be designed for a specific application, wherein a number of cells are electrically connected in series and/or parallel to provide the voltage, current, capacity,

1 and/or power required for the specific application. In addition, a cell pack may comprise control electronics for monitoring and/or controlling the cells in the cell pack.

[0008] A cell pack designed for a particular application may be unusable for another application. The specific configuration of cells within a cell pack determines the supply voltage and peak current of the cell pack. Accordingly, the cell pack cannot be used for any application that requires a different supply voltage or a higher peak current. Furthermore, any control electronics are typically designed for the particular application, and another application may require different control electronics. For example, one application of a cell pack may require monitoring of an output voltage of the cell pack, whereas another application of a cell pack may require monitoring of an output current of the cell pack. As such, a cell pack typically cannot be used for an application other than that for which it was designed.

[0009] Multiple cell packs may be electrically connected in series and/or parallel to provide a higher supply voltage and/or peak current. However, a cell pack may contain components that limit the number of cell packs that may be electrically connected in series and/or parallel. For example, a cell pack may contain a disconnect switch designed to electrically isolate a cell in the cell pack if the current drawn from the cell exceeds a limit. The disconnect switch may have a maximum voltage relative to a common electrical ground, after which the disconnect switch is no longer able to electrically isolate the cell. For example, the disconnect switch may comprise a metal-oxide-semiconductor field-effect transistor (MOSFET) wherein the MOSFET may operate as an open-circuit (electrically isolating) up to a maximum voltage, and as a closed-circuit (electrically conducting) above the maximum voltage. Accordingly, the number of cell packs which may be connected together may be limited by the maximum voltage of such a disconnect switch, as each additional cell pack increases the voltage relative to the common ground.

[0010] Each cell in a cell pack may have a slightly different energy capacity. The differences in capacity may be due to differences in materials and/or manufacturing of each cell. Furthermore, the capacity of each cell in a cell pack may change differently over operation of the cell pack due to differences in materials, manufacturing, use and/or environment between cells in the cell pack.

[0011] During discharge of a cell pack, typically the cell with the lowest capacity will discharge first. Once fully discharged, any further attempt to discharge a discharged cell may damage the cell. Accordingly, once the lowest capacity cell in the cell pack is discharged, the cell pack should no longer be discharged. Therefore, the capacity of a cell pack is limited by the lowest capacity cell in the cell pack.

2 [0012] Similar to discharging a cell pack, the charging capacity of a cell pack is limited by the lowest capacity of a cell in the cell pack because a cell may be damaged by attempting to further charge a fully charged cell. Accordingly, charging of a cell pack should stop once the lowest capacity cell in a cell pack is fully charged.

[0013] To address the limitations that result from cells in a cell pack having different capacities, control electronics comprising a battery management system may be used. A battery management system may be used for various purposes, including to bypass fully charged and/or discharged cells and/or to transfer charge between cells.

[0014] A battery management system typically comprises electronics for monitoring the cells in a cell pack and controlling electrical connections between each cell in the cell pack. Monitoring a cell may include measuring a voltage and/or a current of the cell. By measuring the voltage and current of a cell, the power of a cell may be determined. By measuring the power of a cell over time, the energy discharged or stored by the cell may be determined.

[0015] Connecting a battery management system to a cell pack comprising multiple cells may pose difficulties. Where multiple cells are connected in series, the voltage between each cell and a reference voltage will increase with each cell. Typically, control electronics operate at low voltage, for example below 12 V. Some high-voltage applications may require cell packs with an output voltage of up to 120 V. As such, directly connecting control electronics designed to operate at 12 V to a cell pack operating at 120 V may damage the control electronics, and/or the control electronics may not operate.

[0016] There is a general desire for an energy cell management system and method which addresses one or more of the above limitations in the prior art, and/or is reconfigurable for different applications.

[0017] The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.

Summary

[0018] The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above- described problems have been reduced or eliminated, while other embodiments are directed to other improvements.

3 [0019] One aspect of the invention provides an energy cell management system, the system comprising; a plurality of cell management modules each comprising three switches; a control system comprising one or more controllers; and a first output terminal and a second output terminal; wherein each of the cell management modules is electrically connected to at least one other of the cell management modules; the first output terminal is electrically connected to a first one of the cell management modules; the second output terminal is electrically connected to a second one of the cell management modules; and the control system is configured to operate the switches of the cell management modules and electrically connect the cell management modules between the first output terminal and the second output terminal in one of two or more configurations.

[0020] In some embodiments, the three switches of each module respectively comprise a first transistor, a second transistor, and a third transistor, and each of the cell management modules comprises: a first module terminal electrically connected to a first cell terminal and the first transistor; a second module terminal electrically connected to a second cell terminal, the second transistor, and the third transistor; a third module terminal electrically connected to the first transistor and the second transistor; and a fourth module terminal electrically connected to the third transistor.

[0021] In some embodiments, the first transistor comprises a first MOSFET; the second transistor comprises a second MOSFET; the third transistor comprises a third MOSFET; the first module terminal is electrically connected to a drain of the first transistor; the second module terminal is electrically connected to a source of the second transistor and to a drain of the third transistor; the third module terminal is electrically connected to a source of the first transistor and to a drain of the second transistor; and the fourth module terminal is electrically connected to a source of the third transistor.

[0022] In some embodiments, each switch may further comprise a gate driver. A gate driver may comprise a power amplifier configured to receive a control signal and provide a high- current driver signal for a MOSFET gate, of appropriate voltage to fully turn on or turn off the MOSFET.

[0023] One aspect of the invention provides a method of discharging a plurality of energy cells with an energy cell management system comprising a plurality of cell management modules electrically connected to the cells, the method comprising; operating the modules to electrically connect the cells to each other in parallel and to a load in series; and operating the modules to electrically connect at least two of the cells to each other and to the load in series.

4 [0024] In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following detailed descriptions.

Brief Description of the Drawings

[0025] Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive.

[0026] Figures 1 A and 1 B are schematic diagrams of cell management systems according to example embodiments of the present invention.

[0027] Figure 1C is a schematic diagram of a method performed by a cell management system according an example embodiment of the present invention.

[0028] Figure 2A is a schematic diagram of a cell management module according to an example embodiment of the present invention.

[0029] Figure 2B is a schematic diagram of two cell management modules as depicted in Fig. 2A.

[0030] Figures 3A to 3D are schematic diagrams of cell management systems according to example embodiments of the present invention.

[0031] Figures 4A to 4C are schematic diagrams of cell management modules according to example embodiments of the present invention.

[0032] Figures 5A to 5B are schematic diagrams of cell management modules according to example embodiments of the present invention.

[0033] Figure 5C is a schematic diagram of two cell management modules as depicted in Fig. 5B.

[0034] Figures 6A to 6E are schematic diagrams of multiple cell management modules according to example embodiments of the present invention.

[0035] Figure 7 is a schematic diagram of a cell management module and a controller according to an example embodiment of the present invention [0036] Figures 8A to 8C are schematic diagrams of cell configurations according to example embodiments of the present invention.

[0037] Figures 9A to 9C are schematic diagrams of cell management modules according to example embodiments of the present invention.

[0038] Figures 10A and 10B are each schematic diagrams of two cell management modules according to example embodiments of the present invention.

[0039] Figure 11 A is a schematic diagram of a cell management module and a controller according to an example embodiment of the present invention.

5 [0040] Figures 11 B and 11C are schematic diagrams of three cell management modules as depicted in Fig. 11A.

Description

[0041] Throughout the following description specific details are set forth in order to provide a more thorough understanding to persons skilled in the art. However, well-known elements may not have been shown or described in detail to avoid unnecessarily obscuring the disclosure. Accordingly, the description and drawings are to be regarded in an illustrative, rather than a restrictive, sense.

[0042] Some embodiments of the present invention provide a cell management module for an energy cell. A plurality of cell management modules may be electrically connected together and to one or more controllers to provide a cell management system. Each module of the system may be electrically connected to an energy cell, and the system may be electrically connected to a load and/or a source. The cell management system may be operated to configure electrical connections between the energy cells and the load/source. [0043] The cell management system may be operated to configure the electrical connections between the energy cells to:

• provide a certain voltage across a load;

• provide a current through a load up to a maximum output current;

• electrically isolate one or more cells from one or more of a load, a source, and each other;

• transfer charge between two or more cells; and/or

• electrically connect one or more cells in parallel and/or series to a source.

[0044] Figure 1A depicts an example embodiment of the present invention comprising a plurality of cell management modules 10-1 , 10-2 and 10-3 (collectively cell management modules 10) and a control system comprising controller 12. Controller 12 is configured to control cell management modules 10. Cell management modules 10 and controller 12 form cell management system 100.

[0045] Each of cell management modules 10 is electrically connected to a respective one of cells 14-1 , 14-2 and 14-3 (collectively cells 14). Cell management modules 10 are electrically connected to each other and to load 16. Load 16 may be any apparatus or combination of apparatus that draws electrical power from cells 14.

[0046] In some embodiments, a source may be connected to cell management modules 10 instead of load 16. The source may be used to charge one or more of cells 14. In some embodiments, a source and a load, or an apparatus capable of alternatively acting as a

6 source and a load, may be connected to cell management system 100 to alternatively draw power from cells 14 and charge cells 14.

[0047] System 100 may comprise a first output terminal and a second output terminal, and load/source 16 maybe electrically connected to system 100 by the first and the second output terminals.

[0048] Controller 12 is configured to operate cell management modules 10. Cell management modules 10 are operable to electrically connect cells 14 to load 16 in one of a plurality of configurations. The plurality of configurations may include two or more of:

• cells 14 connected in series with each other and in series with load 16;

• cells 14 connected in parallel with each other and in series with load 16;

• two of cells 14 connected in parallel with each other, and connected in series with a third of cells 14 and load 16;

• two of cells 14 connected in series with each other and in series with load 16;

• two of cells 14 connected in parallel with each other and in series with load 16;

• one of cells 14 connected in series with load 16; and

• two of cells 14 connected in parallel with each other and electrically isolated from a third of cells 14 and load 16.

[0049] Each configuration of cells 14 may have certain advantages, disadvantages, and/or be applicable for certain applications. For example, connecting two or more of cells 14 in series with each other and load 16 may provide a higher voltage to load 16 then when cells 14 are connected in parallel with each other and in series with load 16. Connecting two or more of cells 14 in parallel with load 16 may provide a higher current to load 16 then when cells 14 are connected in series with one another and load 16. Connecting two of cells 14 in parallel with each other may be used to balance charge between the two of cells 14.

[0050] Figure 1 B depicts an example embodiment of cell management system 100 wherein cell management modules 10-1 , 10-2 and 10-3 are respectively controlled by a control system comprising controllers 13-1 , 13-2 and 13-4 (collectively controllers 13). Controllers 13 may each be communicatively coupled to communication bus 15. Controllers 13 may communicate with each other to control cell management modules 10.

[0051] In some embodiments, one of controllers 13 is a primary controller, and the others of controllers 13 are secondary controllers. The primary controller may provide control information to the secondary controllers, and the secondary controllers may provide monitoring and/or status information to the primary controller.

[0052] One or more of controllers 12, 13 may be configured to perform one or more methods for switching between two configurations of cells 14 and load 16. Figure 1C

7 depicts example method 101 for switching from a configuration of cells 14 connected in series with each other and in series with load 16 to a configuration of cells 14 connected in parallel with each other and in series with load 16. Method 101 may comprise:

• step 102, electrically isolating cells 14 from load 16;

• step 104, electrically isolating cell 14-1 from cell 14-2, and electrically isolating cell 14-2 from cell 14-3;

• step 106, electrically connecting cell 14-1 to cell 14-2 in parallel, and electrically connecting cell 14-2 to cell 14-3 in parallel; and

• step 108, electrically connecting cells 14 to load 16 in series.

[0053] Figure 2A depicts an example embodiment of cell management module 10-1 , wherein cell management module 10-1 is connected to cell 14-1. One or more other cell management modules 10 of cell management system 100 may be similar or identical to cell management module 10-1.

[0054] Cell 14-1 is electrically connected to first cell terminal 18A and to second cell terminal 18B. When cell 14-1 is charged, cell 14-1 generates an electrical potential between first cell terminal 18A and second cell terminal 18B. Cell terminal 18A may be a positive cell terminal, and cell terminal 18B may be a negative cell terminal such that cell 14-1 generates a positive voltage when the voltage is measured from cell terminal 18B to cell terminal 18A.

[0055] Cell management module 10-1 comprises switches 20A, 20B and 20C (collectively switches 20) and module terminals 22A, 22B, 22C and 22D (collectively module terminals 22). A plurality of cell management modules may be connected by module terminals 22. [0056] Two cell management modules may be connected in series by connecting module terminals 22C and 22D of a first cell management module respectively to module terminals 22A and 22B of a second cell management module. Additional cell management modules may be connected in series by connecting module terminals 22A and 22B of subsequent cell management modules respectively to module terminals 22C and 22D of antecedent cell management modules.

[0057] Two cell management modules may be connected in parallel by connecting module terminals 22A and 22D of a first cell management module respectively with module terminals 22A and 22D of a second cell management module. Additional cell management modules may be connected in parallel by connecting module terminals 22A and 22D of subsequent cell management modules respectively to module terminals 22A and 22D of antecedent cell management modules.

8 [0058] Figure 2B depicts two cell management modules 10-1 and 10-2 connected in series by module terminals 22. Module terminal 22C-1 of first cell management module 10-1 is connected to module terminal 22A-2 of second cell management module 10-2 and module terminal 22D-1 of first cell management module 10-1 is connected to module terminal 22B- 2 of second cell management module 10-2.

[0059] Any further number of cells may be electrically connected to cells 14-1 and 14-2 by connecting additional cell management modules to either of cell management modules 10- 1 and 10-2, wherein the additional cell management modules are connected to the additional cells.

[0060] By selectively opening and closing switches 20, cell management modules 10-1 and 10-2 may electrically connect cells 14-1 and 14-2 in various configurations between module terminal 22A-1 and module terminal 22C-2 and/or module terminal 22D-2.

[0061] Figure 3A depicts cell management modules 10-1 , 10-2 and 10-3 connected to each other and to load 16 in series. Load 16 is connected to module terminal 22A-1 of cell management module 10-1 and module terminal 22D-3 of cell management module 10-3. Module terminal 22A-1 may be a first output terminal of system 100, and module terminal 22D-3 may be a second output terminal of system 100.

[0062] In some embodiments, cell management module 10-1 may be referred to as a first cell management module, cell management module 10-3 may be referred to as a last cell management module, and cell management module 10-2 may be referred to as an intervening cell management module.

[0063] Each of cells 14 is respectively connected to one of cell management modules 10 with a same polarity. The same polarity means that each of cells 14 generates either a positive or a negative voltage as measured from cell terminal 18A to cell terminal 18B of each of cells 14.

[0064] Figure 3A depicts switches 20 of cell management modules 10. Each of switches 20 is controlled by controller 12. Switches 20 may be selectively opened and closed by controller 12 to electrically connect cells 14 in two or more configurations to load 16.

[0065] Figures 3B and 3C depict two configurations of switches 20, wherein a switch labelled “0” indicates an open switch, and a switch labelled “1” indicates a closed switch.

An open switch acts as an open circuit when a voltage is applied across the switch, wherein the current through the open switch is at or near zero, and the voltage across the open switch is at a maximum. A closed switch acts as a closed circuit when a voltage is applied across the switch, wherein the voltage across the closed switch is at or near zero, and the current through the closed switch is at a maximum.

9 [0066] Figure 3B depicts switches 20 configured to connect cells 14 to each other and to load 16 in series. All switches 20 are open except for switches 20B-1 , 20B-2 and 20C-3. [0067] By closing switch 20B-1 and opening switches 20C-1 and 20A-2, an electrical connection is formed between second cell terminal 18B-1 and first cell terminal 18A-2. By closing switch 20B-2 and opening switches 20C-2 and 20A-3, an electrical connection is formed between second cell terminal 18B-2 and first cell terminal 18A-3. By closing switch 20C-3 and opening switch 20B-3, an electrical connection is formed between second cell terminal 18B-3 and module terminal 22D-3.

[0068] Because each of cells 14 is connected to each of cell management modules 10 with the same polarity, providing a path between the second cell terminal of a module and the first cell terminal of a subsequent module connects the cells of the modules in series. Therefore, in the configuration depicted in figure 3B, the voltage generated between module terminals 22A-1 and 22D-3 is the sum of the voltage of each of cells 14, and the current through load 16 is equal to the current through each of cells 14.

[0069] Figure 3C depicts switches 20 configured to connect cells 14 to each other in parallel and to load 16 in series. Switches 20A-1 , 20C-1 , 20A-2, 20C-2 and 20C-3 are closed, and switches 20B-1 , 20B-2, 20A-3 and 20B-3 are open.

[0070] By closing switches 20A-1 and 20A-2 and opening switches 20B-1 , 20B-2 and 20A- 3, an electrical connection is formed between module terminal 22A-1 and first cell terminals 18A of cells 14. By closing switches 20C-1 , 20C-2 and 20C-3 and opening switches 20B-1 , 20B-2 and 20B-3, an electrical connection is formed between module terminal 22D-3 and second cell terminals 18B of cells 14.

[0071] Because each of cells 14 is connected to each of cell management modules 10 with the same polarity, providing a first path between each of first cell terminals 18A of each of cells 14 and a second path between each of second cell terminals 18B of cells 14 connects cells 14 in parallel. Therefore, in the configuration depicted in figure 3C, the voltage generated between module terminals 22A-1 and 22D-3 is equal to the voltage of one of cells 14, and the current through load 16 is equal to the sum of the current through each of cells 14.

[0072] Figures 3A to 3D depict a system comprising three cell management modules. Any number of cell management modules may be connected to each other, and the switches of the cell management modules may be configured to connect cells connected to the cell management modules in any combination of series and/or parallel by configuring the switches of each cell management module as described above.

10 [0073] Where a cell management system comprises multiple cell management modules, one or more components of the first and last cell management modules in the cell management system may be unnecessary. For example, switches 20A-3 and 20B-3 are open in both of the series configuration and the parallel configuration respectively depicted in Figures 3B and 3C. Therefore, switches 20A-3 and 20B-3 may be unnecessary.

[0074] Similarly, switch 20C-3 is closed in both configurations depicted in Figures 3B and 3C. Switch 20C-3 must be closed to connect load 16 to cell management modules 10, because one of the connections between load 16 and cell management modules 10 is to module terminal 22D-3, and the only path between module terminal 22D-3 and cell management modules 10 is through switch 20C-3. If switch 20C-3 is open, then load 16 cannot be connected to any of cells 14. Therefore, switch 20C-3 may be unnecessary. [0075] Figure 3D depicts an embodiment of cell management system 100, wherein unnecessary components are omitted from cell management modules 10-1 and 10-3. Module terminal 22B-1 is omitted from cell management module 10-1. Module terminal 22C-3 and switches 20A-3, 20B-3 and 20C-3 are omitted from cell management module 10-3. Omitting such unnecessary components may reduce the cost, complexity, and form factor of cell management system 100. Omitting unnecessary components such as module terminals 22B-1 and 22C-3 may additionally reduce the likelihood of installation error, as there are only two module terminals of management system 100 that may be connected to load 16.

[0076] Controller 12 is configured to control switches 20. In some embodiments, controller 12 comprises a microcontroller, and a control input of each of switches 20 is connected to an output of the microcontroller. The microcontroller may switch each of switches 20 between open and closed by transmitting a signal from the respective output of controller 12 to each of switches 20. The microcontroller may be connected to the switches by a control circuit. The control circuit may comprise additional components to aid in switching switches 20.

[0077] Controller 12 may further comprise sensors for measuring one or more of current and voltage at one or more points in cell management modules 10.

[0078] Controller 12 may be configured to draw power from one or more of cells 14, or be externally powered.

[0079] In some embodiments, cell management system 100 comprises a plurality of controllers. Where cell management system 100 comprises a plurality of controllers, the controllers may be configured to communicate with each other. For example, one controller may be configured as a primary controller, and one or more other controllers may be

11 configured as secondary controllers. Each secondary controller may be configured to receive control signals from the primary controller, and switch the switches connected to the respective secondary controller according to the control signals received from the primary controller.

[0080] In some embodiments, cell management system 100 comprises a plurality of identical controllers. Cell management system 100 may comprise identical controllers to simplify construction and configuration of cell management system 100.

[0081] In some embodiments, cell management system 100 comprises two or more different controllers. For example, a primary cell management module may comprise a more powerful controller, and one or more secondary cell management modules may comprise less powerful controllers. A more powerful controller may be a controller with more inputs and/or outputs, a faster processor, and/or more memory than a less powerful controller.

[0082] The maximum voltage across one or more of cells 14 of cell management system 100 may be within an operating voltage range of controller 12. For example, the operating voltage range of controller 12 may be 20V, and the maximum voltage across one or more of cells 14 may be below 20 V. Where the voltage across one or more of cells 14 is within the operating voltage range of controller 12, one or more inputs and/or outputs of controller 12 may be electrically connected directly to one or more of cell management modules 10 corresponding to cells 14.

[0083] Where the maximum voltage across one or more of cells 14 is outside of the operating voltage range of controller 12, one or more inputs and/or outputs of controller 12 may be electrically connected to one or more of cell management modules 10 by one or more electrical isolators and/or voltage shifters.

[0084] Controller 12 may be electrically connected to a module to measure one or more of: a voltage between the two cell terminals of the module, a voltage between one of the cell terminals and another point in cell management system 100, a voltage between one of the cell terminals and a reference potential, and a current through one of the cell terminals. The reference potential may be an electrical ground, or the voltage at any other point in cell management system 100.

[0085] In some embodiments, each controller has two communication channels, wherein each communication channel comprises one or more terminals for receiving and transmitting electrical signals. One of the two communication channels may be configured for communication with one or more controllers at a higher voltage relative to a reference potential than the controller (a high-voltage channel), and the other of the two

12 communication channels may be configured for communication with one or more controllers at a lower voltage relative to a reference potential than the controller (a low- voltage channel).

[0086] A controller may comprise a level-shifter between the two communication channels. The level-shifter translates signals within a first voltage range from a first of the communication channels into signals within a second voltage range on a second of the communication channels. For example, the level-shifter may translate a signal on the low- voltage channel into a signal on the high-voltage channel by raising the voltage of the signal on the low-voltage channel. The level-shifter may translate a signal on the high- voltage channel into a signal on the low-voltage channel by lowering the voltage of the signal on the high-voltage channel.

[0087] In some embodiments, the level-shifter is configured to translate signals by shifting the voltage of the signals by a voltage in the range of 0 volts to 12 volts.

[0088] In some embodiments, each controller has three or more communication channels: one high-voltage communication channel, one low-voltage communications channel, and one or more communications channels that do not translate signals to another voltage. [0089] Controller 12 may be configured to operate switches 20 and change the configuration of switches 20 from one configuration to a second configuration. For example, controller 12 may change the configuration of switches 20 from a series configuration (as depicted in figure 3B) to a parallel configuration (as depicted in figure 3C).

[0090] Controller 12 may be configured to change the configuration of switches 20 from one configuration to another configuration without creating an open circuit between module terminals 22A-1 and 22D-3, and/or without creating a short circuit between any of first cell terminals 18A and second cell terminals 18B of any one cell.

[0091] In some embodiments, controller 12 is configured to change the configuration of switches 20 from series to parallel by:

• opening switch 20B-1 ;

• opening switch 20B-2;

• opening switch 20C-3;

• closing switch 20A-1 ;

• closing switch 20C-1 ;

• closing switch 20A-2;

• closing switch 20C-2; and

• closing switch 20C-3.

13 [0092] In some embodiments, the above steps are performed sequentially, for example such that switch 20C-3 is opened before switch 20A-1 is closed.

[0093] To avoid creating a short circuit between cell terminals 18A and 18B or an open circuit between the module terminals, the timing of the transition of switches from open to closed and/or closed to open should be made as close to simultaneous as can be practically achieved. However, it may not be possible to transition switches from open to closed and/or closed to open sufficiently simultaneous to avoid creating undesirable circuit states. Undesirable circuit states may include creating a short circuit between any two cell terminals 18A and 18B or the same cell, and creating an open circuit between module terminals 22A-1 and 22D-3.

[0094] Some embodiments of controller 12 implement a break-before-make switching method to prevent creating a short circuit and attending current shoot-through when changing states. In a break-before-make switching method, closed switches are opened before opened switches are closed.

[0095] To avoid creating an open circuit between the module terminals of a module, some embodiments of a cell management module may comprise a switch which conducts when biased in a certain polarity, regardless of the control signal to the switch.

[0096] Examples switches that conduct when biased in a certain polarity include MOSFETs and diodes. An example of a switch that requires a control input to conduct in either direction includes two MOSFETs connected in series.

[0097] In some embodiments, each of switches 20 comprises a MOSFET. In some embodiments, P-channel MOSFETs can also be used in place of N-channel MOSFETs, or a single switch may be constructed from a combination of N-channel and P-channel MOSFETs.

[0098] Some embodiments of switches 20 comprise two MOSFETs, where the two MOSFETs are connected in series by either their source terminals or their drain terminals. [0099] In some embodiments of cell management module 10, at least switches 20A and 20C are configured to always conduct when forward-biased, ensuring current is not interrupted. Such switches may be implemented by adding a diode electrically connecting in parallel, thereby providing an electrical path in one direction through the diode. Such switches may also be implemented by one or more MOSFETs, as a MOSFET operates as a diode when a positive voltage is applied from the drain to the source of the MOSFET. To reduce cost and complexity, switches comprising a single MOSFET may suffice.

[0100] Where a switch comprises a single MOSFET, a bypass diode may still be desirable, in particular to support failsafe operation in the event that the MOSFET becomes damaged.

14 If an external bypass diode is provided for one or more switches, the bypass diode may be selected to have low leakage current. Leakage current is the current through a reverse- biased diode, which may drain a cell.

[0101] In some embodiments, a switch comprises a bypass diode and an ideal-diode controller. The ideal-diode controller closes the MOSFET (or other component comprising the switch) whenever a forward voltage is present across the diode.

[0102] Some loads may require a constant, or slowly-changing input voltage. A slowly- changing voltage may be a voltage with a frequency less than or equal to 1 hertz (Hz). For such applications, controller 12 may be configured to control cell management modules 10 and provide a slowly-changing voltage to a load by connecting two or more of cell management modules 10 one at a time and in series to the load.

[0103] Where cell management modules are configured for such applications, switches 20 may have one or more of low-impedance, high-current capacity, and/or low gate capacitance. In one or more embodiments:

• one or more of switches 20 have an impedance in the range of 0.1 milliohms to 10 milliohms when closed;

• one or more of switches 20 have a peak current capacity in the range of 10 amps to 100 amps when closed; and/or

• one or more of switches 20 have a gate capacitance in the range of 1 nanofarad to 20 nanofarads.

[0104] In some embodiments, an “open” switch may have a resistance of more than 100 megaohms. In some embodiments, a “closed” switch may have a resistance of less than 10 milliohms.

[0105] In some embodiments, one or more of switches 20 switches from open to closed, and/or from closed to open, within 0.1 milliseconds.

[0106] In some embodiments, cell management modules may be reconfigured to respond to changes in a load. For example, one or more cell management modules may reconfigure between series and parallel configurations to provide a supply voltage and/or current to a load. A controller may be configured to measure an impedance of a load, and configure one or more cell management modules to provide a requisite current to the load. For example, cells configured in series may be reconfigured in parallel to sustain a threshold level of current to a lower resistance load. A controller may be configured to measure the impedance of a load by measuring the voltage across the load and the current through the load, and calculating the impedance from the measured voltage and current.

15 [0107] In some embodiments, a controller is configured to reconfigure multiple cells from a parallel configuration to a series configuration by reconfiguring the connection of one cell at a time from parallel to series, thereby ramping up an output voltage. The controller may initially configure the cells in parallel, and then reconfigure one cell at a time in series, until a threshold output voltage is reached. In some embodiments, the controller may transition between all cells connected in parallel to two or more cells connected in series within 100 milliseconds.

[0108] Some loads may have large input capacitances, for example due to large input capacitors. When such loads are initially powered, the large input capacitance may draw a large current, thereby leading to current surges, electrical sparks, and/or voltage overshoot. Power systems may use inrush limiters to reduce the likelihood of current surges, electrical sparks, and/or voltage overshoot. Inrush limiters may comprise an input resistor to reduce input current until the input capacitance is charged. However, such input resistors dissipate power through heat, typically wasting power. By gradually ramping up the supply voltage, the inrush current and/or voltage overshoot may be lower than not gradually ramping up the supply voltage, without the need for additional components such as an inrush limiter.

[0109] In some embodiments, the controller may provide an application program interface (API) for receiving control information. The control information may comprise information about a load (e.g. impedance of the load, current requirement of the load, power requirement of the load, etc.), and/or information on configuration of the cells (e.g. a specific configuration of cells in parallel and/or series). The API may receive general operating information such as nominal load impedance, safety shutdown thresholds, and discharge limits. Data may be received from the API, for example data on cell discharging, cell charging, and/or error conditions.

[0110] In some embodiments, further components such as a DC-DC converter may be connected between the load and cell management modules. The further components may communicate with the controller and provide control information to the controller, for example through the API of the controller.

[0111] Figures 4A to 4C depict various embodiments of a cell management modules comprising alternative arrangements of switches 20.

[0112] In some embodiments, switches 20 comprise one or more MOSFETs. A MOSFET comprises a drain terminal, a source terminal, and a gate terminal. When a threshold voltage is applied between the gate and the source of an N-channel MOSFET, a current can flow between the drain and the source of the MOSFET. When a voltage less than the threshold voltage is applied between the gate and the source of an N-channel MOSFET,

16 current may flow from the source to the drain, with a voltage loss of about 0.8 volts from the source to the drain.

[0113] In a P-channel MOSFET, current may flow from the drain to the source of the MOSFET with a voltage loss of about 0.8 volts from the drain to the source.

[0114] Figure 5A depicts an embodiment of a cell management module, wherein switches 20 comprise N-channel MOSFETs.

[0115] A switch comprising an n-channel MOSFET is electrically closed when the voltage at the gate of the MOSFET is higher than the voltage at the source of the MOSFET. The higher the voltage between the gate and the source of the MOSFET, the faster the switch will close and the lower the resistance of the switch once closed. Some MOSFETs may require a voltage difference in the range of 2 volts to 5 volts between the gate and the source to close effectively.

[0116] Where one or more of switches 20 comprise N-channel MOSFETs, a gate of each MOSFET may be electrically connected to a higher voltage than a source of each MOSFET to close the MOSFET. For example, where switch 20B comprises a MOSFET, cell terminal 18A is a positive cell terminal and cell terminal 18B is a negative cell terminal, a source of MOSFET 20B may be connected to cell terminal 18B and a gate of MOSFET 20B may be connected to cell terminal 18A. By connecting the source of MOSFET 20B to negative cell terminal 18B and the gate of MOSFET 20B to positive cell terminal 18A, a positive voltage is applied from the gate of MOSFET 20B to the source of MOSFET 20B. The positive voltage between the gate of MOSFET 20B and the source of MOSFET 20B allows MOSFET 20B to be switched between open and closed without having to otherwise power MOSFET 20B.

[0117] Figure 5B depicts an embodiment of cell management module 10 wherein switch 20B comprises a MOSFET, and switches 20A and 20C each comprise a diode. A diode may function as a passive one-way switch, whereby the diode operates as a closed circuit when forward-biased, and an open circuit when reverse-biased. A diode is forward-biased when an anode of the diode is at a higher voltage than a cathode of the diode and reverse- biased when the cathode of the diode is at a higher voltage than the anode of the diode. [0118] Switches 20A and 20C may comprise diodes to reduce the cost, complexity, and/or form factor of modules 10. However, switches 20A and/or 20C comprising diodes may reduce overall efficiency due to the forward conduction losses through the diodes. Furthermore, using switches 20A and 20C comprising diodes may reduce the flexibility of modules 10, as cells 14 may be connected in only one of two different configurations between module terminals 22 due to the only configurable switch being switch 20B.

17 [0119] Figure 5C depicts an embodiment of cell management system 100 comprising two cell management modules 10-1 and 10-2, wherein cell management modules 10-1 and 10- 2 each comprise a MOSFET and two diodes. Load 16 may be connected to cell management system 100 between module terminal 22A-1 and module terminal 22D-2. [0120] Load 16 may be electrically connected in series to cells 14 by closing switch 20B-1. When switch 20B-1 is closed, the voltage at the anode of diode 20A-1 is equal to the voltage at cell terminal 18B-1. The voltage at the cathode of diode 20A-1 is equal the voltage at cell terminal 18A-1. Thereby, diode 20A-1 is reverse-biased, and operates as an open circuit.

[0121] When switch 20B-1 is closed, the voltage at the cathode of diode 20C-1 is equal to the voltage at cell terminal 18A-2. The voltage at the anode of diode 20C-1 is equal to the voltage at cell terminal 18B-2. Thereby diode 20C-1 is reverse-biased, and operates as an open circuit.

[0122] Because diodes 20A-1 and 20C-1 operate as open circuits when switch 20B is closed, cells 14 may be electrically connected in series between module terminals 22A-1 and 22D-2 by closing switch 20B.

[0123] The voltage at the cathode of diode 20C-2 is equal to the voltage at cell terminal 18B-2. When a load is connected between module terminals 22A-1 and 22D-2, the voltage at the anode of diode 20C-2 is equal to the sum of the voltages of cells 14, less the voltage drop across the load. If the voltage drop across the load is less than the sum of the voltages of cells 14, diode 20C-2 will be forward-biased, and operate as a closed circuit. [0124] If a source is connected between terminals 22A-1 and 22D-2 and the source has higher voltage than the sum of the voltages of cells 14, then cells 14 will be charged by the source.

[0125] Load 16 may be electrically connected in parallel with cells 14 by opening switch 20B-1. When switch 20B-1 is open, current flows through diode 20C-2 and then through one or both of: cell 14-2 in series with diode 20A-1 ; and diode 20C-1 in series with cell 14- 1. Accordingly, cells 14 are electrically connected in parallel to load 16.

[0126] If cells 14-1 and 14-2 have equal charges, current will flow equally through cell 14-2 in series with diode 20A-1 and diode 20C-1 in series with cell 14-1. If one of cells 14-1 and 14-2 has a higher charge, then a higher current will flow through the cell with a higher charge.

[0127] In some embodiments of cell management system 100, cell management modules 10 are connected in parallel, for example to increase energy storage and/or current capacity of cell management system 100. Figure 6A depicts an embodiment of cell

18 management system 100 comprising cell management modules 10-1 and 10-2 connected in parallel to power bus 60 (comprising conductors 62).

[0128] Power bus 60 comprises first conductor 62A connected to module terminals 22A, second conductor 62B connected to module terminals 22B, third conductor 62C connected to module terminals 22C, and fourth conductor 62D connected to module terminals 22D. [0129] Connecting modules 10 in parallel by power bus 60 may have advantages over connecting modules 10 in series (for example as in Fig. 3C) and configuring the modules in parallel. For example, where modules 10 are connected in series and configured in parallel, the current through each module 10 is equal to the sum of the current of all cells in the system. Therefore, the maximum current of the system is limited by the maximum current capacity of certain components in a single module, for example one or more switches and/or terminals of a single module.

[0130] Where modules 10 are connected in parallel, the current through each cell management module is equal to only the current of the cell associated with the cell management module. The current through the power bus is equal to sum of the current of all cells in the system. Therefore, the maximum current of a system comprising a power bus is limited by the maximum current of the power bus, and not by the maximum current of any one cell management module. Accordingly, the maximum current of a system with parallel connected modules and comprising a power bus can be increased by replacing or expanding the power bus, as opposed to in a system with series connected modules or a system with parallel connected modules without a power bus, where the modules must be replaced to increase the current of the system.

[0131] Some embodiments may omit one or more of conductors 62.

[0132] Figure 6B depicts three cell management modules connected in parallel by power bus 60, and load 16 connected between first conductor 62A and third conductor 62C of power bus 60.

[0133] Figure 6C depicts switches 20 configured to connect cells 14 in parallel with each other and in series with load 16. In figure 6C, switches labelled “0” are open and switches labelled “1” are closed. Cell terminals 18A are electrically connected to first conductor 62A, and through first conductor 62A to load 16. Closed switches 20B electrically connect cell terminals 18B to third conductor 62C, and through third conductor 62C to load 16.

[0134] Open switches 20A electrically isolate first conductor 62A from third conductor 62C, thereby preventing a short circuit between any of cell terminals 18A and any of cell terminals 18B. Switches 20C may be open or closed.

19 [0135] Some embodiments of cell management system 100 comprise a plurality of cell management modules connected to each other in series and parallel.

[0136] Figure 6D depicts an embodiment of a cell management system comprising six cell management modules 10-1 to 10-6 respectively connected to cells 14-1 to 14-6. Paris of cell management modules 10 are connected to each other in series (specifically: 10-1 to 10-2, 10-3 to 10-4, 10-5 to 10-6) to form three pairs of series connected modules. The three pairs of series connected modules are connected to each other in parallel by power bus 60. Load 16 is connected to power bus 60 of the cell management system.

[0137] Figure 6E depicts an embodiment of a cell management system comprising two sets of three cell management modules. Cell management modules 14-1 , 14-3 and 14-5 are connected to each other in parallel by first power bus 66A, and cell management modules 14-2, 14-4 and 14-6 are connected to each other in parallel be second power bus 66B. The two sets of modules are connected to each other and to load 16 in series.

[0138] A cell management module may be embodied as a discrete physical product, or multiple modules might be combined into a single package, for example a single circuit board, for a larger-scale application. One or more power buses and/or communication buses may also be incorporated into the package of each module, allowing multiple modules to be directly connected to each other without the need for additional components. [0139] In some embodiments, multiple cell management modules may be combined into meshes of modules. A mesh of modules may comprise groups of modules connected in series or parallel. A module mesh may comprise a power bus connected to only some of the modules in the mesh. For example, the modules in a series connected group of modules may be connected to each other, and only the first and last modules in the group of modules may be connected to the power bus. These design decisions will typically be driven by particular application demands, or heterogeneous cell performance characteristics.

[0140] Cells 14 may comprise any element or combination of elements capable of storing and discharging electrical energy. For example, cells 14 may comprise one or more electrochemical batteries and/or one or more capacitors. Cell 14 may comprise further electrical elements to assist in charging/discharging, for example one or more capacitors, inductors, diodes, protection elements, fuses, and/or other circuit elements. In some embodiments, one or more of cells 14 comprises between one and twelve similarly constructed electrochemical cells.

[0141] In some embodiments, one or more of cells 14 are one or more distinct components from cell management modules 10, and cell management modules 10 are electrically

20 connected to cells 14. In some embodiments, one or more of cells 14 are integrated with cell management modules 10, and one or more of cells 14 and cell management modules 10 are combined into a single component. Where one or more of cells 14 are integrated with cell management modules 10, cells 14 may be removable from cell management modules 10 so to be replaceable.

[0142] In some embodiments, one or more of cells 14 may be charged by one or more others of cells 14, and/or an external power source. Where one or more of cells 14 are charged by a power source, the power source may be connected to modules 10 in place of load 16.

[0143] To charge a cell with a power source, the voltage of the power source must be greater than the voltage of the cell. If a power source is connected to multiple cells connected to each other in series, then the voltage of the power source must be greater than the combined voltage of the cells to charge the cells.

[0144] Modules may be configured to connect their associated cells in parallel to a power source for charging of the cells. For example, series connected modules may be configured to drive a load in series, and change to a parallel configuration for charging. By configuring the cells in parallel, the cells may be charged by a voltage too low to charge the cells if they were configured in series. Accordingly, parallel-configuring cells may be charged by a voltage higher than the highest voltage of any single cell and lower than the sum of the voltage of any two cells. Therefore, cells configured in parallel may be charged by a lower source voltage than cells configured in series.

[0145] In some embodiments, cells may be charged by one or more of: an external battery, a generator, a solar cell, a USB host device, and an electrical grid.

[0146] Where switches 20 comprise bypass diodes or MOSFETs, a sufficient reverse voltage will cause the modules to recharge in series. For example, in the embodiment of a cell management module depicted in figure 5A, a power source connected between module terminals 22A and 22C will charge cell 14 if the voltage of the power source is greater than the voltage of cell 14.

[0147] Where the voltage of the power source is greater than the voltage of cell 14, module terminal 22A is at voltage V1 , cell terminal 18B is at voltage V2, and module terminal 22C is at voltage V3, wherein V1 > V2 > V3. Because V2 > V3, the voltage of the source of MOSFET 20B is greater than the voltage of the drain of MOSFET 20B, and MOSFET 20B is forward biased. When MOSFET 20B is forward biased, MOSFET 20B operates as a closed switch and conducts between module terminal 22C and cell terminal 18B. As such, MOSFET 20B forms an electrical connection between module terminal 22C and cell

21 terminal 18B, and thereby cell 14 will be charged by the power source connected between module terminals 22A and 22C.

[0148] A controller may monitor the state of charge, charge history, temperature, and/or overall condition or health of one or more cells. This information may be communicated between module controllers, such that a controller can assess the overall energy remaining one or more other modules, and compare the state of charge of the cell connected to its module relative to the state of charge of cells in one or more other modules, and in particular preceding and/or antecedent modules. Furthermore, one or more controllers may receive such information from all other modules in a cell management system, and determine a total state of charge for the system. The total system charge may be stored and/or provided to external systems. Additionally, individual cell charges may be used by one or more controllers to reconfigure connection of modules in the system, and transfer charge from cells with greater charge to cells with lower charge, while maintaining the power requirements of the load.

[0149] Where one or more of cells 14 are charged by one or more others of cells 14, charge may be transferred between cells to balance charge between cells.

[0150] One or more algorithms may be used for charge balancing multiple cells connected in series. One example of such an algorithm is to have at least one redundant cell above the minimum number of series cells required to maintain a supply voltage. The redundant cell is placed electrically in parallel with a preceding or antecedent cell for a period of time to balance a charge between the two cells, after which the modules are reconfigured so that the parallel connection is moved to between two other cells, changing the identity of the redundant cell, and repeating the process of charge balancing.

[0151] Figures 8A and 8B depict a redundant cell being used to balance charge within a cell management system. Other features of the cell management system are omitted for clarity. Figure 8A depicts cell 14-1 in parallel with cell 14-2, and cells 14-1 and 14-2 in series with the others of cells 14. Figure 8B depicts cell 14-2 in parallel with cell 14-3, and cells 14-2 and 14-3 in series with the others of cells 14. Figure 8C depicts all of cells 14 in series.

[0152] In some embodiments, the controller may be configured to monitor the charge of each cell in the system, and place two cells in parallel to balance the load between the two cells. For example, the controller may be configured to periodically measure the charge of each cell in the system, and if the difference between the charge of the highest charged cell and the charge of the lowest charged cell exceeds a threshold, perform a charge balancing method.

22 [0153] A cell with a higher charge typically has a higher voltage than a cell with a lower charge. As such, when two cells are connected in parallel, charge is transferred from the higher voltage cell to the lower voltage cell. Rotating the cells of a system through a parallel configuration with each other ensures that some threshold amount of charge sharing between all cells takes place, preventing a difference in charge between any two cells from exceeding a threshold. Two or more redundant cells may be used to increase charge balancing between cells in a system, thereby lowering the threshold difference in charge between any two cells in the system.

[0154] One or more further algorithms may use state-of-charge information exchanged between controllers. For example, a lowest-state-of-charge cell in a system may be placed in parallel with a redundant cell for a longer period of time than other cells in the system, and thereby increasing the amount of charge that is balanced between it and another cell, and reducing a rate by which the cell is discharged relative to other cells in the system, until another cell in the system becomes the new lowest-state-of-charge cell and is subsequently placed in parallel with another cell. The opposite procedure may be performed during charging, with the highest-state-of-charge cell spending a longer time configured in parallel with a preceding or antecedent cell.

[0155] As a decreasing state of charge causes the total voltage of a system to decrease, the redundant cells can be added back into the series chain to maintain the nominal output voltage for as long as possible, as shown in Figure 8C.

[0156] In addition to charge balancing, connections between cells may be set according to exchanged information to prevent localized temperature increases (for example, by reducing current through cells experiencing elevated temperatures), or to perform other performance optimizations. A cell may have a safety threshold, for example a maximum current and/or temperature. When the system detects that a safety threshold of a cell is being neared, the module corresponding to the cell can reconfigure the connections with other modules in the system to maintain operation of the cell within the safety threshold of the cell. For example, when discharging into a resistive load, if the current through a cell approaches its maximum safe discharge level, it can be moved into a parallel configuration, thereby reducing its current; conversely, when charging from a voltage source, if the charge current approaches the maximum safe level, cells can be reconfigured into a series configuration to reduce the charging current. The safer configuration may depend on the characteristics of the load, which advantageously can be communicated to the module controllers via their API to ensure the appropriate response.

23 [0157] Battery design often attempts to design all cells in a battery to be as similar as possible, such that the minimum amount of charge balancing is needed. The use of modules as described herein allows an alternative approach, where dissimilar battery chemistries may be placed in series with each other, allowing a mix of high-capacity and high-pulse-discharge power sources.

[0158] After extended periods of use or when used to power certain types of loads, cells in series can end up with unbalanced states of charge, which can manifest as different cell voltages. When the cells are subsequently connected in parallel, the current that flows between the cells resulting from differences in cell voltages may exceed the rated charge or discharge current capacity of the cells. For example, a fully charged lithium-ion cell tends to have a voltage of 4.2 V, and a discharged lithium-ion cell may have a voltage of 2.8 V, so the voltage difference between module terminals of a fully charged lithium-ion cell and a fully discharged lithium-ion cell is 1.4 V. The internal resistance of such cells may be very low, such as 0.02 ohms. If such cells are directly connected in parallel, a current of 35 amps will flow between the cells. Typically, such a cell may be have a rated recharge current of 1 amp and a rated discharge current of 10 amps, so such a direct parallel connection could damage both cells.

[0159] One solution is to operate the system to only permit parallel connections to be made between cells that have voltages that are sufficiently similar that balancing currents are within a safe limit, such as 40 mV. If cell loads are balanced or charge transfer between cells occurs sufficiently often, this condition may be maintained. Cells may be automatically placed in parallel by the controller when their voltage difference begins to approach the safe limit. However, these measures also restrict the ability of modules in a system to be reconfigured, as some module configurations may become unavailable depending on the state of charge of the cells.

[0160] Another option is, during discharge, to bypass cells that have the lowest state of charge, and, during recharge, to bypass cells that have the highest state of charge. However, this limits the maximum discharge and recharge power capability of cells in a system, and as the full current is handled by only a fraction of the cells, the resistive losses during charge and discharge are increased. A cell may be bypassed by electrically connecting a preceding module with an antecedent module.

[0161] An alternative solution is to add a current-limiting circuit to limit current during recharge of a cell. Figure 9A depicts an embodiment of cell management module 90 wherein the current-limiting circuit comprises power resistor 121 , and Figures 9B and 9C

24 respectively depict cell management modules 92 and 94 wherein the current-limiting circuit comprises inductor 122. Modules 90, 92 and 94 are each recharged by source 96.

[0162] Modules 90, 92 and 94 may operate in one of two modes: a recharge-current-limited mode, and a recharge-current-unlimited mode.

[0163] In the recharge-current-unlimited mode, switches 110 and 111 are closed, thereby respectively bypassing resistor 121 and transistor 122, and cell 14 in each module is electrically connected to source 96.

[0164] In the recharge-current-limited mode, switch 110 is open and switch 111 is closed until a difference in charge between cells in a system is within operable limits. In the resistive embodiment shown in Figure 9A, power resistor 121 has a resistance that limits the recharge current to a safe threshold when exposed to the maximum expected voltage difference, such as 1.5 ohms, and switch 120 is kept closed unless the recharge current can be disconnected.

[0165] Once lower charge cells in a system have been charged to within a threshold of all other cells in the system, switches 110 may be closed thereby bypassing resistor 121 and placing the cell in recharge-current-unlimited mode.

[0166] In the inductive current-limiting method shown in Figures 9B and 9C, switch 120 is closed until the recharge current through inductor 122 reaches a threshold. Switch 120 is then opened for a duration of recharging. The recharge current recirculates through diode 123. This method has reduced power loss compared with the resistive method.

[0167] As depicted in figure 6C, all of switches 20A are open, and all of switches 20B are closed. Therefore, to configure switches as in figure 6C, switches 20A may be controlled together, and switches 20B may be controlled together. For example, a first output of a controller may control all of switches 20A, and a second output of the controller may control all of switches 20B. Where multiple switches are controlled by a single controller output, the controller output may be connected to the switches through a communication bus.

[0168] In another embodiment, modules connected in parallel may each have their own controller. As all parallel-connected modules must change state synchronously, the controllers must be capable of coordinating their state-transition times.

[0169] Some embodiments of cell management system 100 may comprise communications lines, hardware triggers, and calibrated time delays to aid in synchronizing switching of switches 20.

[0170] Figure 7 depicts an example embodiment of a cell management module comprising controller and a communication bus. The communication bus comprises first wire 41 and

25 second wire 42. First and second wires 41 and 42 may be connected to communications terminals of one or more modules, for example communications terminals 52 and 53. [0171] Terminals 52 and 53 may be connected to a terminal, for example a positive terminal, of a cell respectively by resistors 50 and 51. Resistors 50 and 51 may comprise resistors of a moderately high impedance, for example 100 kQ. Where minimal to no current is drawn through resistors 50 and/or 51 , the respective voltage of terminals 52 and/or 53 is at or near the voltage of the positive terminal. Thereby, terminals 52 and 53 are driven to the voltage of the positive terminal.

[0172] Terminal 52 is actively driven down to the potential of terminal 13 by any module where any of switches 15, 16 or 17 are closed. OR gate 54 is connected to a control input of switches 15, 16 or 17. When any of switches 15, 16 or 17 are closed, OR gate 54 closes switch 55. When switch 55 is closed, an electrical path is formed between terminal 52 and terminal 13, thereby equalizing the potential between terminals 52 and 13, which is at the potential of the second cell terminal.

[0173] Terminal 53 is driven low by any module that is initiating a change of state between a series configuration of switches in the module and a parallel configuration of switches in the module. Accordingly, any module may provide a signal to the other modules in the system that a transition is underway and cause each other module to open the respective switches 15, 16 and 17 in each module. Once the switches of the final module in the system are opened, the OR gates 54 of all modules may close switch 55, and terminal 52 will no longer equal the potential of terminal 13. Once terminal 52 is no longer equal to the potential of terminal 13, switches 15, 16 and 17 in each module may be closed.

[0174] Two modules may be connected by connecting terminals 10 and 11 of one module respectively with terminals 12 and 13 of a second module.

[0175] In some embodiments, the control input of one or more switches in a module may be connected to a communication terminal of the module. Modules may be connected to each other and/or a controller by the communication terminal of the modules. In some embodiments, the communications channels may carry signals comprising one or more of: RS-232, RS-422, RS-423, RS-485, universal asynchronous receiver-transmitter (UART), inter-integrated circuit (I2C), serial peripheral interface (SPI), universal serial bus (USB), optical, Ethernet, and radio-frequency signals, and various combinations thereof.

[0176] One or more of the communications channels may implement a fan-out, one-to- many, or many-to-many communication topologies, for example I2C, SPI, and USB. Such topologies may be used for communication between a plurality of parallel-connected modules over a shared bus.

26 [0177] Where multiple modules communicate over a single bus, one or more modules may need to be galvanically isolated from the bus. Where multiple modules are configured in series, the voltage may be too high between some of the modules to connect all of the modules directly to the bus. For example, the voltage of a cell may be 5 V. The maximum voltage of signals on a communication bus may be up to 12 V. Therefore, if three cells are connected in series, the voltage of the third cell will be 15 V, which is higher than the maximum voltage of the communications bus. Therefore, the third cell (and any further series connected cells) would need to be connected to the communications bus by a galvanic isolator, for example by radio, optical, capacitive, or magnetic coupling.

[0178] In some embodiments, the modules are connected to communicate in a daisy-chain, meaning connected to communicate with only adjacent modules. By connecting the modules in a daisy-chain, the voltage difference between two modules is limited to the voltage of a single module. If the voltage of a single module is within the operating range of the communications bus, additional galvanic isolation components are not required. If galvanic isolation is not provided, fault protection (such as current-limiting resistors, fuses, and/or zener diodes) may be used to prevent an electrical fault resulting in a cascading short circuit along the daisy chain.

[0179] Some embodiments may comprise a differential signalling method such as RS-485. In such a differential signalling method, the common-voltage difference does not corrupt data transmission.

[0180] In a preferred embodiment, the controller comprises an ultra-low-power microcontroller such as a Tl MSP430 provided by Texas Instruments™, an EFM32 provided by Silicon Labs™, or an STM32L provided by STMicroelectronics™.

[0181] In some embodiments, controller 12 comprises a microcontroller with an active power consumption of less than 10 mW, and including power management sleep modes, a long-time-average power consumption that may be below 0.1 mW in a typical use case. A single 18650 battery cell may have an energy capacity of 40 kJ, and could run such a processor for over 10 years. In practice, the self-discharge of the cell will greatly exceed the power draw from the processor, therefore the power draw of the microcontroller may not practically affect the capacity of the cell.

[0182] The use of a programmable microcontroller allows for firmware control of the functionality and state management of the module, including not only the power electronics, but also state-of-charge history, communications, power-on and power-off routines, LEDs, temperature, and other functions. However, it is not a strict requirement and the basic

27 functionality can be implemented using only simple hardware if necessary, or an independent or centralized control system.

[0183] In some embodiments, the controller of a module is powered by the cell in its respective module. A high-efficiency DC-DC step-down converter may be used to match the cell’s voltage, which may be at least 2.5 V, to the power requirement of the controller, which may be lower, for example, between 1.8 and 2 V.

[0184] In some embodiments of cell management system 100, cell management modules 10 are configured to be powered even if a cell of the respective module is no longer capable of powering the cell management module. For example, where a cell fails or is discharged below a level sufficient to power a controller and/or switches of a module, a backup power supply may be needed to operate the module’s processor and switches. [0185] Back up power may be provided by another parallel-connected module, or an adjacent series-connected module.

[0186] In some embodiments, two or more cell management modules may be electrically connected other than by module terminals 22 or in addition to module terminals 22. For example, a controller and/or one or more switches of a cell management module may be electrically connected to a controller and/or one or more switches of another cell management module.

[0187] Figure 10A depicts an embodiment of system 100 that includes two cell management modules 10-1 and 10-2, wherein controller 12-2 of module 10-2 and controller 12-1 of module 10-1 are both powered by cell 14-1. Dashed lines 30A and 30B depict the electrical connections between controller 12-1 and controller 12-2.

[0188] Controller 12-2 may be electrically connected to module 10-1 when cell 14-2 is incapable of powering controller 12-2, for example, when cell 14-2 is discharged or malfunctioning.

[0189] In some embodiments, one or more cell management modules 10 comprise a boost converter, and the boost converter is connected to power the electronics (e.g. switches, controller, etc.) of another module.

[0190] Figure 10B depicts an embodiment of system 100 that includes two cell management modules 10-1 and 10-2, wherein controller 12-1 of module 10-1 is electrically connected to cell 14-2 of module 10-2. Dashed lines 32A and 32B depict the electrical connections between controller 12-1 and cell 14-2. Controller 12-1 may be electrically connected to module 10-2 when cell 14-1 is incapable of powering controller 12-1 , for example, when cell 14-1 is discharged or malfunctioning.

28 [0191] In some embodiments, controller 12-1 may be configured to measure or estimate the charge of cell 14-1 and receive power from cell 14-2 when the charge of cell 14-1 falls below a threshold.

[0192] N-channel MOSFETs conduct between the drain and source of the MOSFET (i.e. a closed switch or a closed MOSFET) when the voltage from the source to the gate of the MOSFET (the source-gate voltage) is above a threshold, typically 2 V. The gate of the MOSFET must be at a higher voltage than the source of the MOSFET for the MOSFET to conduct between the source and the drain of the MOSFET. If the source-gate voltage of the MOSFET is below the threshold, the MOSFET will not conduct.

[0193] Not only must the source-gate voltage be above the threshold for an n-channel MOSFET to conduct, but the speed at which the MOSFET transitions from open to closed, and the impedance of the MOSFET when closed is a function of the source-gate voltage. Therefore, the speed at which a MOSFET transitions from open to closed and the impedance of the MOSFET when closed may both be increased by increasing the source- gate voltage of the MOSFET.

[0194] While the voltage of a cell may vary over time, a cell may generate only a single voltage at a time. As such, if components of a cell management module are solely powered by the module cell, and require more than one voltage, a voltage converter or charge pump may be included in the module to provide a voltage other than that provided by the cell. [0195] For example, to generate the source-gate voltage required to close one or more MOSFETs of a module, a higher voltage than the cell voltage must be applied to the gate of a MOSFET which is connected by its source to the positive cell terminal. Furthermore, even if the source of a MOSFET is at the potential of the negative cell terminal, the MOSFET may operate more efficiently if the gate of the MOSFET is electrically connected to a potential even higher than the potential of the positive cell terminal. The potential at the gate of a MOSFET may be increased by electrically connecting the MOSFET gate to the positive cell module terminal of an adjacent series connected module.

[0196] Figures 11A to 11C depict an embodiment of a cell management module 10, wherein controller 12 may be electrically connected to an adjacent module. Module 10 comprises module terminals 44A and 44B that may be used to electrically connect controller 12 to adjacent modules. Controller 12 may comprise a circuit for electrically connecting module terminal 44A to a control input of one or more of switches 20, for example a gate of switches 20 where switches 20 comprise MOSFETs.

[0197] Figure 11A depicts an embodiment of cell management module 10 comprising MOSFET 40 and diode 42. MOSFET 40 may be closed to electrically connect module

29 terminal 44A to module terminal 44B. Module terminal 44A may be connected to module terminal 44B to electrically connect a subsequent module to a preceding module.

[0198] Figures 11 B and 11C depict three cell management modules electrically connected by module terminals 44A and 44B.

[0199] Figure 11 B depicts modules 10-1 , 10-2 and 10-3 electrically connected in series, and controller 12-2 electrically connected to cell 14-1 and controller 12-3 electrically connected to cell 14-2. Accordingly, all of MOSFETs 40, 20A and 20C are open (source- gate voltage lower than the threshold), and MOSFETs 20B are closed (source-gate voltage above the threshold). Dashed lines 46 depict current flow between modules 10. Dashed line 46-1 depicts the electrical connection between controller 12-2 and cell 14-1.

[0200] Figure 11C depicts modules 10-1 and 10-2 connected in parallel with each other and in series with module 10-3. Dashed line 38 depicts current flow between modules 10. As modules 10-1 and 10-2 are connected in parallel, cells 14-1 and 14-2 are electrically connected in parallel. Switch 40-2 is closed to electrically connect controller 12-3 to cell 14- 1 , as depicted by dashed line 48-1.

[0201] In some embodiments, cell management system 100 comprises a plurality of cell management modules 10, wherein cell management modules 10 comprise a first module, a last module, and one or more intervening modules.

[0202] In some embodiments, modules may comprise one or more of: current-limiting fuses, temperature controllers, light-emitting diodes, electrostatic discharge prevention, current and voltage sensors. In addition to electrical connections between modules, additional ports and connections such as hydraulic channels can be included for water cooling systems or similar functionality.

[0203] Each of switches 20 may comprise one or more components, for example one or more transistors, electromechanical relays, solid-state relays, reed switches, and/or mechanical switches. Each of switches 20 may further comprise elements such as one or more bypass diodes, gate drivers, protection circuits, snubbers, decoupling capacitors, or soft-switching control circuits.

[0204] Unless the context clearly requires otherwise, throughout the description and the claims:

• “comprise”, “comprising”, and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”;

30 • “connected”, “coupled”, or any variant thereof, means any connection or coupling, either direct or indirect, between two or more elements; the coupling or connection between the elements can be physical, logical, or a combination thereof;

• “herein”, “above”, “below”, and words of similar import, when used to describe this specification, shall refer to this specification as a whole, and not to any particular portions of this specification;

• “or”, in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list;

• the singular forms “a”, “an”, and “the” also include the meaning of any appropriate plural [0205] Words that indicate directions such as “vertical”, “transverse”, “horizontal”, “upward”, “downward”, “forward”, “backward”, “inward”, “outward”, “vertical”, “transverse”, “left”, “right”, “front”, “back”, “top”, “bottom”, “below”, “above”, “under”, and the like, used in this description and any accompanying claims (where present), depend on the specific orientation of the apparatus described and illustrated. The subject matter described herein may assume various alternative orientations. Accordingly, these directional terms are not strictly defined and should not be interpreted narrowly.

[0206] Embodiments of the invention may be implemented using specifically designed hardware, configurable hardware, programmable data processors configured by the provision of software (which may optionally comprise “firmware”) capable of executing on the data processors, special purpose computers or data processors that are specifically programmed, configured, or constructed to perform one or more steps in a method as explained in detail herein and/or combinations of two or more of these. Examples of specifically designed hardware are: logic circuits, application-specific integrated circuits (“ASICs”), large scale integrated circuits (“LSIs”), very large scale integrated circuits (“VLSIs”), and the like. Examples of configurable hardware are: one or more programmable logic devices such as programmable array logic (“PALs”), programmable logic arrays (“PLAs”), and field programmable gate arrays (“FPGAs”)). Examples of programmable data processors are: microprocessors, digital signal processors (“DSPs”), embedded processors, graphics processors, math co-processors, general purpose computers, server computers, cloud computers, mainframe computers, computer workstations, and the like. For example, one or more data processors in a control circuit for a device may implement methods as described herein by executing software instructions in a program memory accessible to the processors.

31 [0207] Processing may be centralized or distributed. Where processing is distributed, information including software and/or data may be kept centrally or distributed. Such information may be exchanged between different functional units by way of a communications network, such as a Local Area Network (LAN), Wide Area Network (WAN), or the Internet, wired or wireless data links, electromagnetic signals, or other data communication channel.

[0208] For example, while processes or blocks are presented in a given order, alternative examples may perform routines having steps, or employ systems having blocks, in a different order, and some processes or blocks may be deleted, moved, added, subdivided, combined, and/or modified to provide alternative or subcombinations. Each of these processes or blocks may be implemented in a variety of different ways. Also, while processes or blocks are at times shown as being performed in series, these processes or blocks may instead be performed in parallel, or may be performed at different times.

[0209] In addition, while elements are at times shown as being performed sequentially, they may instead be performed simultaneously or in different sequences. It is therefore intended that the following claims are interpreted to include all such variations as are within their intended scope.

[0210] Features of the invention may also be provided in the form of a program product.

The program product may comprise any non-transitory medium which carries a set of computer-readable instructions which, when executed by a data processor, cause the data processor to execute a method of the invention. Program products according to the invention may be in any of a wide variety of forms. The program product may comprise, for example, non-transitory media such as magnetic data storage media including floppy diskettes, hard disk drives, optical data storage media including CD ROMs, DVDs, electronic data storage media including ROMs, flash RAM, EPROMs, hardwired or preprogrammed chips (e.g., EEPROM semiconductor chips), nanotechnology memory, or the like. The computer-readable signals on the program product may optionally be compressed or encrypted.

[0211] In some embodiments, the invention may be implemented in software. For greater clarity, “software” includes any instructions executed on a processor, and may include (but is not limited to) firmware, resident software, microcode, and the like. Both processing hardware and software may be centralized or distributed (or a combination thereof), in whole or in part, as known to those skilled in the art. For example, software and other modules may be accessible via local memory, via a network, via a browser or other

32 application in a distributed computing context, or via other means suitable for the purposes described above.

[0212] Where a component (e.g. a software module, processor, assembly, device, circuit, etc.) is referred to above, unless otherwise indicated, reference to that component (including a reference to a “means”) should be interpreted as including as equivalents of that component any component which performs the function of the described component (i.e., that is functionally equivalent), including components which are not structurally equivalent to the disclosed structure which performs the function in the illustrated exemplary embodiments of the invention.

[0213] Specific examples of systems, methods and apparatus have been described herein for purposes of illustration. These are only examples. The technology provided herein can be applied to systems other than the example systems described above. Many alterations, modifications, additions, omissions, and permutations are possible within the practice of this invention. This invention includes variations on described embodiments that would be apparent to the skilled addressee, including variations obtained by: replacing features, elements and/or acts with equivalent features, elements and/or acts; mixing and matching of features, elements and/or acts from different embodiments; combining features, elements and/or acts from embodiments as described herein with features, elements and/or acts of other technology; and/or omitting combining features, elements and/or acts from described embodiments.

[0214] Various features are described herein as being present in “some embodiments”. Such features are not mandatory and may not be present in all embodiments.

Embodiments of the invention may include zero, any one or any combination of two or more of such features. This is limited only to the extent that certain ones of such features are incompatible with other ones of such features in the sense that it would be impossible for a person of ordinary skill in the art to construct a practical embodiment that combines such incompatible features. Consequently, the description that “some embodiments” possess feature A and “some embodiments” possess feature B should be interpreted as an express indication that the inventors also contemplate embodiments which combine features A and B (unless the description states otherwise or features A and B are fundamentally incompatible).

[0215] It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions, omissions, and sub-combinations as may reasonably be inferred. The scope of the claims

33 should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.

34