Inter-module battery balancing using minimum cell voltage to select battery sub-module to power load

Abstract

To provide a new technique of detecting, relaxing, and / or avoiding a problem related to a battery in a whole electrically-driven aircraft (or the other transportation means).SOLUTION: The present invention relates to each battery sub-module in a plurality of battery sub-modules, where a voltage related to a cell in each battery sub-module is received, and each battery sub-module in the plurality of battery sub-modules contains a plurality of cells. Each battery sub-module is selected based at least in part on the received voltages, and a set of one or more loads, which draws power from the selected battery sub-module and is not powered by any other battery sub-module in the plurality of battery sub-modules, is configured so that the set of loads at least temporarily does not draw power from the selected battery sub-module.SELECTED DRAWING: Figure 1

Description

[Background technology]

[0001] New types of aircraft are being developed that are all-electric. Due to differences in how batteries tend to be designed (e.g., aircraft batteries must satisfy the Federal Aviation Administration, which may have greater concerns about single points of failure and degrees of redundancy compared to the National Highway Traffic Safety Administration) and / or how the vehicles are used, there may be some battery-related issues that have not previously been exposed with electric vehicles but are becoming apparent as all-electric aircraft are developed. New techniques for detecting, mitigating, and / or avoiding such battery-related issues in all-electric aircraft (or other vehicles) would be desirable.

[0002] Various embodiments of the present invention are disclosed in the following detailed description and the accompanying drawings. [Brief explanation of the drawings]

[0003] [Figure 1] 1 is a flow chart illustrating one embodiment of a process for inter-module balancing. [Figure 2] 1 is a diagram illustrating an embodiment of a battery system including battery sub-modules connected in series, each battery sub-module including cells connected in series. [Figure 3A] 1 is a diagram showing an embodiment of an uncapped battery submodule. [Figure 3B] 1 is a diagram illustrating an embodiment of a covered battery submodule. [Figure 4] 10 is a flow chart illustrating an embodiment of a process for inter-module balancing that includes turning off electronics. [Figure 5]10 is a flowchart illustrating an embodiment of a process for inter-module balancing that includes configuring a set of electronics to draw power from a non-selected battery sub-module. [Figure 6] 1 is a diagram illustrating an example of cell voltages in a battery submodule in a battery system. [Figure 7] 10 is a flowchart illustrating one embodiment of a process for selecting battery sub-modules using voltage thresholds. [Figure 8] 10 is a flowchart illustrating one embodiment of a process for selecting battery sub-modules using a voltage threshold and a maximum value of minimum cell voltages. [Figure 9] 10 is a flowchart illustrating an embodiment of a process for selecting a battery sub-module using a voltage threshold and a maximum value of maximum cell voltage. [Figure 10A] 1 is a diagram illustrating an embodiment in which balancing is performed both before and after charging. [Figure 10B] 1 is a diagram illustrating an embodiment in which balancing is performed only after charging. [Figure 11] 10 is a flow chart illustrating one embodiment of a process for determining when to perform balancing on a charging process. DETAILED DESCRIPTION OF THE INVENTION

[0004] The present invention may be implemented in numerous ways, including as a process, an apparatus, a system, a composition of matter, a computer program product embodied on a computer-readable storage medium, and / or as a processor, such as a processor configured to execute instructions stored in and / or provided by a memory coupled to the processor. These implementations, or any other form the present invention may take, may be referred to herein as techniques. In general, the order of steps in disclosed processes may be varied within the scope of the present invention. Unless otherwise noted, components, such as a processor or memory, described as configured to perform a task may be implemented as general components temporarily configured to perform the task at a given time, or as specific components manufactured to perform the task. As used herein, the term "processor" refers to one or more devices, circuits, and / or processing cores configured to process data, such as computer program instructions.

[0005] A detailed description of one or more embodiments of the present invention is provided below along with accompanying figures that illustrate the principles of the invention. While the present invention will be described in connection with such embodiments, the invention is not limited to any particular embodiment. The scope of the present invention is limited only by the claims, and the present invention encompasses numerous alternatives, modifications, and equivalents. In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. These details are provided for the purpose of example, and the present invention may be practiced according to the claims without some or all of these specific details. For the purposes of clarity, technical material known in the art related to the present invention has not been described in detail so as not to unnecessarily obscure the present invention.

[0006] Various embodiments of techniques for balancing battery sub-modules in a battery system are described herein. In some embodiments, balancing is performed by receiving, for each battery sub-module in a plurality of battery sub-modules (e.g., connected in series with one another), a voltage associated with a cell in that battery sub-module, where each battery sub-module in the plurality of battery sub-modules includes a plurality of cells (e.g., connected in series with one another). A battery sub-module is selected from the plurality of battery sub-modules based at least in part on the received voltage. A set of one or more loads (e.g., electronic devices or other power consumers) that draw power from the selected battery sub-module and are not powered by other battery sub-modules in the plurality of battery sub-modules is configured such that the set of one or more loads at least temporarily does not draw power from the selected battery sub-module.

[0007] In some applications, this technique is used to select which battery sub-modules will not (e.g., at least temporarily) provide standby or standby power to corresponding electronics while a primary load (e.g., a lift fan in an all-electric aircraft) is not drawing power from the battery system. In the long run, if this process is performed, the battery sub-modules will be more balanced than if the process were not performed (e.g., a more balanced battery sub-module will perform better), and / or permanent damage to the battery sub-modules may be avoided.

[0008] 1 is a flowchart illustrating one embodiment of a process for inter-module balancing. In some embodiments, the process is performed by and / or on a battery system having multiple sub-modules connected in series with each other, each battery sub-module in turn including multiple cells connected in series with each other.

[0009] At 100, for each battery sub-module in the plurality of battery sub-modules, a voltage associated with the cells in that battery sub-module is received, and each battery sub-module in the plurality of battery sub-modules includes a plurality of cells. In one example, the battery system is used to power an all-electric aircraft. For various reasons, the battery system powering the aircraft may consist of multiple battery sub-modules connected in series with each other. For example, by having multiple battery sub-modules connected in series with each other to form the overall battery system, the battery sub-modules can be easily replaced as needed or desired, and relatively high voltages (e.g., on the order of several hundred volts required by the lift fan) and lower voltages (e.g., on the order of a few volts required by avionics and / or electronics) may be simultaneously available. In contrast, these desirable properties and / or characteristics are not present when the battery system comprises a(n) monolithic battery. An exemplary battery system including battery sub-modules (connected in series with each other), which in turn include cells (also connected in series with each other), is described in more detail below.

[0010] At 102, a battery sub-module is selected from the plurality of battery sub-modules based at least in part on the received voltage. For example, the selected battery sub-module may be selected because it is undesirable for the battery sub-module to continue to power one or more loads (e.g., electronic devices, motors, solenoids, etc.) operating on the selected battery sub-module. In some embodiments, more than one battery sub-module is selected. Some examples of how the selection may be performed are described in more detail below.

[0011] At 104, a set of one or more loads that draw power from a selected battery sub-module and are not powered by any other battery sub-module in the plurality of battery sub-modules is configured such that the set of one or more loads at least temporarily does not draw power from the selected battery sub-module. As described in more detail below, in some embodiments, the loads include electronic devices that are turned off such that they no longer draw (e.g., standby) power from the selected and / or associated battery sub-module. Alternatively, electronic devices associated with a selected battery sub-module may be configured such that they draw power from some other battery sub-module other than the selected one.

[0012] Conceptually and / or generally, the above process attempts to balance voltage levels in various sub-modules and / or cells by selectively allowing some (if not all) battery sub-modules to provide power to associated loads, e.g., during some dormant or stationary state in which the aircraft (or other loads) are not consuming significant amounts of power, which reduces voltage levels in sub-modules and / or cells (e.g., better equipped and / or in a better state to provide power) so that voltage levels in selected sub-modules and / or selected cells may be preserved.

[0013] In one example of why balancing is important and / or useful, if balancing were not performed (e.g., according to the process of FIG. 1), some battery sub-modules in the battery system would permanently fail if the battery system were left unused for approximately 20 days. This is entirely possible if the battery system is used in an aircraft. For example, a pilot could fly the aircraft to some remote location with no charging stations, where the aircraft would sit unused for approximately 20 days, and the batteries would not be charged during that time. Or the aircraft could be left in a hangar for an extended period of time, and thus maintenance requiring human intervention would be significantly inconvenient.

[0014] Another benefit of keeping battery submodules balanced is that for batteries with series submodules, balancing increases the battery's capacity because the battery's capacity is determined by the smallest capacity cell. This is because discharging the battery below its minimum capacity would damage it. Along the same lines, keeping submodules balanced reduces the time it takes the battery to charge because, in a balanced state, the cells are uniform and have a higher voltage than in an unbalanced state. Finally, maintaining a balanced battery can increase the overall lifespan of the battery. Cells with reduced voltage may deteriorate more quickly than their neighbors, and when one of the constituent cells of a submodule reaches a critical point of deterioration, the submodule must be replaced. Furthermore, in embodiments that allow submodules to be discharged in parallel, submodules of different voltages will deliver different currents to the load, and submodules that must deliver excess current will experience accelerated degradation. The process of Figure 1 can be repeated as needed or desired. For example, when non-selected battery sub-modules provide power, the voltage levels stored in those cells and / or battery sub-modules decrease, resulting in different voltage levels and, therefore, different degrees and / or states of imbalance. In one example, the battery sub-module selected in step 102 does not provide power for (for example) 15 minutes during step 104, after which the process of Figure 1 is repeated with updated voltages. As a result, different battery sub-modules may be selected in step 102 to no longer provide power, at least temporarily, to their corresponding electronics.

[0015] In some embodiments, the exemplary balancing process described above is performed when the primary load (e.g., a lift fan in an all-electric aircraft) is not drawing power. For example, the draw by the primary load on the battery system can change very rapidly, and therefore it may be difficult and / or expensive to sample the battery system fast enough to accurately determine what state the battery system is in when the primary load is drawing power. For this reason, it may be simpler and / or easier to perform balancing when the primary load is off.

[0016] In some embodiments, the exemplary balancing process described above is performed before and / or after charging of the battery system is performed. For example, balancing a battery system before charging of the battery system (e.g., according to the process of FIG. 1) may aid in the charging process itself by repairing or otherwise reducing large imbalance(s) between the battery sub-modules (e.g., that may be undesirable during the charging process). If balancing is performed after the battery system is charged (e.g., according to the process of FIG. 1), small imbalance(s) between the battery sub-modules may be repaired or otherwise reduced.

[0017] It may be helpful to describe an exemplary battery system that implements the process of Figure 1. The following diagram describes one such exemplary battery system.

[0018] 2 is a diagram illustrating an example of a battery system including battery submodules connected in series, each containing cells connected in series with one another. In this example, the battery system is used to power an all-electric aircraft.

[0019] In this example, there are M battery sub-modules, namely a first battery sub-module (200a), a second battery sub-module (200b), and an Mth battery sub-module (200c), which are connected in series to generate a high voltage power supply (e.g., on the order of several hundred volts) to power a high voltage load (202), such as an aircraft lift fan.

[0020] Each battery submodule, in turn, includes N cells connected in series with one another. For example, the first battery submodule (200a) includes a first cell (204a), a second cell (204b), an (N-1)th cell (204c), and an Nth cell (204d). The voltage across each battery submodule in this example is on the order of tens of volts. In this example, there are 36 battery submodules and 12 cells per battery submodule. The following diagram shows an exemplary battery submodule:

[0021] FIG. 3A is a diagram illustrating one embodiment of an uncapped battery submodule. In the illustrated example, the battery submodule includes layers of cells (300) interleaved with layers of insulating material (302, e.g., flame-retardant). In this example, the cells are resistant to pressure (e.g., about 0.21-0.35 kgf / cm). 2 The pouch cells perform better when subjected to pressure (3-5 PSI). More specifically, the cycle life of the pouch cells can be extended by applying pressure to the pouch cells. Therefore, the battery sub-module is encased in a metal can (304) that applies pressure to the contained pouch cells.

[0022] Each cell has two tabs (306) extending upward from the cell, a positive tab and a negative tab. The tabs are connected to each other so that the cells are electrically connected in series with each other. See, for example, Figure 2.

[0023] 3B is a diagram showing one embodiment of a capped battery sub-module. In this example, the cap (350) is attached to the battery sub-module so that only a single positive connection and a single negative connection are exposed. In the above-described example where the battery system is included in an aircraft, the battery sub-modules may be physically and electrically connected to each other within the aircraft so that a single battery sub-module can be swapped out and replaced as needed or desired.

[0024] Returning to FIG. 2 , each battery sub-module (200a-200c) has a set of electronics (206a-206c) associated with it and powered by that battery sub-module (e.g., even when the aircraft is not flying and the high-voltage load (202) is not consuming power). For example, a first set of electronics (206a) is powered by the first battery sub-module (200a), a second set of electronics (206b) is powered by the second battery sub-module (200b), and an Mth set of electronics (206c) is powered by the Mth battery sub-module (200c). For simplicity and to maintain readability of the diagram, voltage converters (e.g., to step down the voltage generated by the battery sub-modules to a voltage level expected by the electronics) are not shown herein, but may be used if needed or desired.

[0025] The electronics (206a-206c) in this example include a battery management system (BMS) that monitors and / or records metrics and / or measurements associated with the cells in the associated battery sub-module over time. In some embodiments, the BMS monitors and / or tracks the voltage of each of the cells in the associated battery sub-module over time. The electronics controller (208) controls the various electronics (206a-206c) in a manner described in more detail below.

[0026] This type of battery configuration may be better suited for aircraft applications compared to automotive applications. For example, the Federal Aviation Administration may have very strict requirements regarding redundancy and / or potential single points of failure. By configuring multiple battery sub-modules in series with backup connections (not shown), if one of the battery sub-modules fails, the entire battery system can still operate and output a high-voltage signal for the high-voltage load (202). In contrast, the National Highway Traffic Safety Administration may be less concerned about redundancy and / or potential single points of failure because if a battery fails, the aircraft would crash, whereas the car could simply coast and pull over. For these and other reasons, battery systems for electric vehicles tend to be more monolithic (e.g., relatively fewer battery sub-modules and / or relatively fewer cells per battery sub-module compared to battery systems for aircraft).

[0027] Due to slight differences between the various cells and the various battery sub-modules, the voltages across the cells and battery sub-modules may not all be the same. Furthermore, with the configurations shown herein, while the high-voltage load (202) is off and the electronics (206a-206c) are on (e.g., when the aircraft is powered down), the battery sub-modules with less charge are used to provide more power than the battery sub-modules with more charge (e.g., if inter-module balancing is not performed, one example of which is illustrated in FIG. 1). Metaphorically, the rich (sub-modules) remain rich, and the poor (sub-modules) remain poor. To address this, the electronics controller 208 (including, for example, a BMS controller) performs the balancing process of FIG. 1.

[0028] In the context of this exemplary system, step 100 of Figure 1 begins when the electronics controller (208) decides to execute the process of Figure 1. As explained above, balancing may be performed before and / or after charging, but (e.g., for simplicity and / or to avoid costly sampling equipment) balancing is not performed when high voltage loads are drawing power from the battery system.

[0029] 1 begins, the electronics controller (208) signals each set of electronics (206a-206c) to transmit back one or more voltages associated with the cells in the associated battery sub-module. For example, the voltage transmitted back to the electronics controller may be the minimum (e.g., lowest) voltage of all cells in that battery sub-module, sometimes referred to herein as the minimum cell voltage (e.g., for a given battery sub-module). In some other embodiments, some other type of cell voltage is transmitted to the electronics controller in addition to and / or instead of the minimum cell voltage (e.g., as a maximum cell voltage or a median or average cell voltage). Using the voltages received from the electronics (206a-206c), the electronics controller selects at least one set of electronics. In one example, the electronic device with the global minimum cell voltage is selected (e.g., the controller picks the lowest of the minimum cell voltages) (e.g., because continuing to draw power from the battery sub-module may permanently damage the battery sub-module if the cell with the minimum cell voltage falls below a threshold and / or irrecoverable cell voltage level). This is one example of step 102 in FIG. 1 .

[0030] In this example, there are two paths between each set of electronics (206a-206c) and the electronics controller (208): one path for communication and / or control, and the other path for power supply. The latter incorporates a switch to interrupt power from a given battery sub-module and / or set of electronics to the electronics controller. The control and / or communication path is always connected and available (e.g., to allow the controller to query cell voltages and control the state of the aforementioned switches in response to voltage measurements).

[0031] The electronics controller then configures the selected electronic device so that it does not draw power from its associated battery sub-module (e.g., to the extent possible, since there is typically some level of standby power consumption even when the thing is “turned off”). In some embodiments, the electronics controller turns off the selected electronic device to achieve this goal. Alternatively, in some other embodiments, the electronics controller configures the selected electronic device (and / or any other components) so that power from a given battery sub-module is not sent to the upstream electronics controller 208. For example, even if an electronic device 206a is in a power minimization mode and is not providing power to the controller 208, the controller 208 can still query the battery management system 206a about the electronic device's voltage, etc. This may be desirable in applications where it is desirable to keep the electronic device accessible. For example, as described above, the battery management system tracks and / or monitors metrics associated with the associated battery sub-module and / or cells therein. It may be desirable to continue tracking such metrics and / or measurements, for example, by drawing power from another battery sub-module. These are some examples of how step 104 in FIG. 1 may be performed.

[0032] Without balancing, one or more of the battery sub-modules can become irreparably damaged in as little as about 20 days. For example, if power continues to be drawn from a cell when its voltage level drops below a certain voltage level, the cell will become irreparably damaged, resulting in the need to replace the entire battery sub-module.

[0033] The following figures more generally and / or formally describe in flow chart form some of the examples described above.

[0034] Figure 4 is a flow chart illustrating one embodiment of a process for inter-module balancing, including turning off electronics. Figure 4 relates to Figure 1, and for convenience, related steps are indicated using similar or identical reference numbers.

[0035] In 100, for each battery sub-module in the plurality of battery sub-modules, a voltage associated with a cell in that battery sub-module is received, and each battery sub-module in the plurality of battery sub-modules includes a plurality of cells. For example, in FIG. 2, the electronics controller (208) receives at least one voltage from each of the electronics (206a-206c), and each received voltage is associated with one cell in the corresponding or associated battery sub-module (200a-200c).

[0036] At 102, a battery sub-module is selected from the plurality of battery sub-modules based at least in part on the received voltage. Some examples of how the selection may be performed are described in more detail below. In some embodiments, multiple battery sub-modules are selected.

[0037] In 104a, a set of one or more loads that draw power from a selected battery sub-module and are not powered by any other battery sub-module in the plurality of battery sub-modules may be configured to at least temporarily not draw power from the selected battery sub-module, including configuring the set of loads that draw power from the selected battery sub-module to be turned off. For example, if the first battery sub-module (200a) in FIG. 2 is selected, the load controller 208 may configure the first set of loads 206a to be turned off and not draw power from the first battery sub-module (200a).

[0038] 5 is a flow chart illustrating an embodiment of a process for inter-module balancing, including configuring a set of electronics to draw power from a non-selected battery sub-module. FIG. 5 relates to FIG. 1, and for convenience, related steps are indicated using similar or identical reference numerals.

[0039] At 100, for each battery sub-module in the plurality of battery sub-modules, a voltage associated with the cells in that battery sub-module is received, and each battery sub-module in the plurality of battery sub-modules includes a plurality of cells.

[0040] At 102, a battery sub-module is selected from the plurality of battery sub-modules based at least in part on the received voltage. As discussed above, in some embodiments, the plurality of battery sub-modules is selected (e.g., because if the plurality of battery sub-modules continued to provide power, the plurality of battery sub-modules would become insufficient to provide power and / or would be irreparably damaged and therefore are selected).

[0041] In 104b, a set of one or more loads that draw power from a selected battery sub-module and are not powered by any other battery sub-module in the plurality of battery sub-modules is configured to at least temporarily not draw power from the selected battery sub-module, including configuring the set of loads that draw power from the selected battery sub-module to draw power from a non-selected battery sub-module.

[0042] In some applications, it is not desirable to turn off the electronics. In the example of FIG. 2, the electronics include a battery management system that tracks and / or monitors the health and / or other metrics of the battery sub-modules and / or cells, and it is important and / or desirable to keep track of that information at all times. For example, in the case of an aircraft, the aircraft may be powered down during the week and only flown on weekends. The battery management system should operate throughout the week so that a faulty battery sub-module can be identified and / or the aircraft will not be allowed to fly if necessary or required.

[0043] As described above, in some embodiments, a battery sub-module is selected from multiple battery sub-modules to prevent the cells in that battery sub-module from being pulled down to a voltage level where irreparable damage occurs (and, for example, the entire battery sub-module must be replaced). The following diagram describes some example cell voltages and example techniques for using those cell voltages to select a battery sub-module.

[0044] FIG. 6 is a diagram illustrating one example of cell voltages in battery submodules in a battery system. In this example, there are M battery submodules and N cells per battery submodule, consistent with the example of FIG. 2. In the graph shown, the x-axis represents cell index (defined by the battery submodule number and the cell number within that battery submodule), and the y-axis represents the cell voltage of the corresponding cell. Group 600 represents cell voltages for cells in the first battery submodule, group 602 represents cell voltages for cells in the second battery submodule, and group 604 represents cell voltages for cells in the Mth battery submodule.

[0045] For the sake of brevity and ease of explanation, V thresholdAssume that there is a voltage level, represented by (606), below which a cell will be permanently damaged if power (e.g., standby power or standby power when the aircraft is powered down) continues to be drawn from the cell. For example, Cell 2,1 (610) and Cell 2,N (612) are both in the second battery sub-module (602) and V threshold (606) or below. To ensure that power is no longer drawn from that battery sub-module, a second battery sub-module will be selected (e.g., in step 102 of FIG. 1) and the corresponding set of electronic devices (e.g., 206b in FIG. 2) will be configured such that they no longer draw power from the second battery sub-module (e.g., 200b in FIG. 2).

[0046] Returning briefly to Figure 2, it would be desirable if the electronics controller (208) could receive cell voltages for only a few cells per battery sub-module, instead of having to receive cell voltages for all cells in a given battery sub-module. This would reduce the amount of traffic or communication exchanged between the electronics controller (208) and the lower-level electronics (206a-206c), for example.

[0047] In one example, the minimum cell voltage from each battery sub-module is sent to an electronics controller or other block making the selection. For example, each electronics controller (e.g., a battery management system) may make this selection and upload only the minimum cell voltage to the electronics controller (e.g., a BMS controller). In FIG. 6, this would mean selecting the cell voltage (620) for cell 1, (N-1), which is the minimum cell voltage in the first battery sub-module (600), and sending it to the electronics controller. For the second battery sub-module (602), the minimum cell voltage would be the cell voltage (610) for cell 2,1, and that cell voltage would be selected and sent to the electronics controller. For the Mth battery sub-module (604), the minimum cell voltage would be the cell voltage (622) for cell M,N, and that cell voltage would be selected and sent to the electronics controller.

[0048] In some embodiments, the battery sub-modules are selected in step 102 of FIG. 1 using threshold voltages. For example, if any of the battery sub-modules is V threshold If a battery sub-module has a minimum cell voltage below (606), then that battery sub-module will be selected so that its corresponding electronics do not continue to draw power from that battery sub-module. For the example cell voltages shown in Figure 6, only the second battery sub-module (602) would be selected. Thus, the corresponding electronics would be configured to at least temporarily not draw power from the second battery sub-module (e.g., by either turning off the second set of electronics or drawing power from some other battery sub-module).

[0049] In some embodiments, the above steps are performed first (e.g., the minimum cell voltage from each battery sub-module is V threshold (606) and then Vthreshol From the pool of battery sub-modules that were above d, the n battery sub-modules with the n largest (remaining) minimum cell voltages are used to power (at least temporarily), while the other battery sub-modules (V threshold (including battery sub-modules with minimum cell voltages below ) will not provide power (at least temporarily). This will pull down n battery sub-modules, thereby making them more balanced relative to the other battery sub-modules.

[0050] In FIG. 6, for example, the Mth battery sub-module (604) generally has a much higher cell voltage compared to the remaining battery sub-modules. By lowering the cell voltage of the Mth battery sub-module (604), this can help lower the Mth battery sub-module (604), i.e., the high-end outlier, without irreparably damaging the second battery sub-module (602), i.e., the low-end outlier. In other words, the first inspection or test (e.g., setting the minimum cell voltage to V threshold ) ensures that nothing is faulty or broken, and the second inspection or test (e.g., drawing power from the n battery sub-modules with the n largest minimum cell voltages) is a performance-oriented selection (e.g., the selection will balance better than some other selection techniques, and the balanced battery sub-modules will perform better).

[0051] In some embodiments, V thresholdNo battery sub-module has a minimum cell voltage below (606). In some such embodiments, the maximum cell voltage from each battery sub-module is obtained, and the m battery sub-modules with the m largest maximum cell voltages provide power (at least temporarily), while the remaining battery sub-modules do not provide power (at least temporarily). In this situation, no battery sub-module is in danger of being permanently damaged if that battery sub-module continues to provide power, and therefore, using the maximum cell voltage from each cell is a better way to balance the sub-modules (e.g., even better than using the largest minimum cell voltage). In the context of this type of balancing, it is always beneficial to draw power from higher voltage sub-modules rather than lower voltage sub-modules.

[0052] These examples are more generally and / or formally described in the following flow charts: Suitable techniques may be implemented in various applications and / or embodiments.

[0053] 7 is a flowchart illustrating an example process for selecting battery sub-modules using voltage thresholds. In some embodiments, battery sub-modules are selected in step 102 of FIG. 1 using the example process described herein. In this example, receiving a voltage in step 100 of FIG. 1 includes receiving a minimum cell voltage for each battery sub-module in a plurality of battery sub-modules connected in series with one another, such that a plurality of minimum cell voltages are received.

[0054] At 700, the minimum cell voltages are compared to voltage thresholds to identify any battery sub-modules with minimum cell voltages that do not exceed the voltage thresholds. For example, in FIG. 6, the minimum cell voltage (620) for cell 1, (N-1), the minimum cell voltage (610) for cell 2, (N-1), and the minimum cell voltage (622) for cell M, (N-1) are V threshold(606). In that example, the only cell with a minimum cell voltage that does not exceed the voltage threshold is cell 2,1 (610).

[0055] At 702, any of the identified battery sub-modules having a minimum cell voltage that does not exceed the voltage threshold is selected. Continuing the example from FIG. 6, the second battery sub-module (602) would be selected. Accordingly, the corresponding electronics would be configured so that they do not, at least temporarily, draw power from the second battery sub-module (602). The second battery sub-module (602) is fragile and could be permanently damaged if the battery sub-module (602) continued to draw power.

[0056] Depending on the design objectives and / or constraints, an appropriate technique for making the selection may be used. For example, the process of Figure 7 is relatively simple. In some applications, the process of Figure 7 is used to make the selection when other, more complex processes offer negligible performance improvements.

[0057] 8 is a flowchart illustrating an embodiment of a process for selecting battery sub-modules using a voltage threshold and a maximum value of minimum cell voltages. In some embodiments, battery sub-modules are selected in step 102 of FIG. 1 using the exemplary process described herein. In this example, receiving a voltage in step 100 of FIG. 1 includes receiving a minimum cell voltage such that multiple minimum cell voltages are received for each battery sub-module in multiple battery sub-modules connected in series with one another.

[0058] At 800, the plurality of minimum cell voltages are compared to a voltage threshold to identify any battery sub-modules having a minimum cell voltage that does not exceed the voltage threshold. For example, see FIG. 6, where the second battery sub-module (602) has a minimum cell voltage (610) that does not exceed the voltage threshold (606).

[0059] At 802, one or more maximum values ​​are selected from the plurality of minimum cell voltages to obtain one or more maximum values ​​of the minimum cell voltages. For example, in Figure 6, the minimum cell voltages include the voltage (620) for cell 1,(N-1), the voltage (610) for cell 2,1, and the voltage (622) for cell M,N, with the maximum of those voltages being the voltage (622) for cell M,N. For simplicity and ease of explanation, it will be assumed in this example of step 802, and thereafter in step 804, that only one maximum value is selected.

[0060] At 804, any identified battery sub-modules having a minimum cell voltage that does not exceed the voltage threshold, as well as battery sub-modules that do not correspond to one of the maximum minimum cell voltages, are selected. For example, the second battery sub-module (602) would be selected because it has a minimum cell voltage (610) that does not exceed the voltage threshold (606). The first battery sub-module (600) also does not correspond to the maximum minimum cell voltage, and therefore, the first battery sub-module would also be selected. In other words, the first battery sub-module (600) and the second battery sub-module (602) would not need to provide power (at least temporarily), while the Mth battery sub-module (604) would provide power (e.g., during the time period). Intuitively, this makes sense because the Mth battery sub-module (604) tends to have a higher cell voltage compared to the other battery sub-modules.

[0061] In some applications, the process of FIG. 8 is used instead of the process of FIG. 7 because it allows for better and / or faster balancing compared to FIG. 7, without the need to obtain additional cell voltages for each battery sub-module (e.g., according to FIG. 9).

[0062] 9 is a flowchart illustrating an embodiment of a process for selecting battery sub-modules using voltage thresholds and maximum values ​​of maximum cell voltages. In some embodiments, battery sub-modules are selected in step 102 of FIG. 1 using the exemplary process described herein. In this example, receiving voltages in step 100 of FIG. 1 includes receiving minimum and maximum cell voltages, such that a plurality of minimum and maximum cell voltages are received for each battery sub-module in a plurality of battery sub-modules connected in series with one another.

[0063] At 900, the plurality of minimum cell voltages are compared to a voltage threshold to identify any battery sub-modules having minimum cell voltages that do not exceed the voltage threshold. See, for example, FIG. 6.

[0064] At 902, it is determined whether there is a battery sub-module with a minimum cell voltage that does not exceed the voltage threshold. For example, for the cell voltages shown in Figure 6, the determination would be "yes" because the minimum cell voltage (610) for cells 2 and 1 does not exceed the voltage threshold (606). In this example, the process would then proceed to step 802 in Figure 8.

[0065] However, if the determination in step 902 is "no" (e.g., because all of the minimum cell voltages exceed the voltage threshold), one or more maximum values ​​are selected from the plurality of maximum cell voltages to obtain one or more maximum values ​​of the maximum cell voltages in 904. For example, the plurality of maximum cell voltages in Figure 6 includes the cell voltage for cell 1,2 (630), the cell voltage for cell 2,(N-1) (632), and the cell voltage for cell M,1 (634). If only one maximum value is selected, the maximum value of the maximum cell voltages would be the cell voltage for cell M,1 (634).

[0066] At 906, a battery sub-module that does not correspond to one of the maximum maximum cell voltage values ​​is selected. In other words, the battery sub-module that corresponds to the maximum maximum cell voltage value will provide power (at least temporarily) for a period of time. Continuing with the example from above, the Mth battery sub-module will provide power (at least temporarily), while the other battery sub-modules will not provide power (at least temporarily).

[0067] In some applications, this technique requires the use of both minimum and maximum cell voltages, which allows for best and / or faster balancing, but requires more information to be exchanged between the (local) electronics (e.g., battery management system) and the electronics controller (e.g., BMS controller). Depending on the specific design goals and / or constraints of a particular application, an appropriate technique may be selected. For example, if performance is important and more and / or additional exchanges are an acceptable trade-off, the process of FIG. 9 may be used.

[0068] As explained above, in some embodiments, balancing is performed before and / or after charging. The following figures describe some example scenarios in which balancing is performed both before and after charging, as well as only after charging.

[0069] FIG. 10A is a diagram illustrating one embodiment in which balancing is performed both before and after charging. In the illustrated example, the battery system has a large imbalance between various battery sub-modules and / or between the cells underlying those battery sub-modules at time 0. For example, assume that the BMS controller calculates an imbalance metric representing the degree or amount of imbalance in the battery system and that the metric is relatively high and / or exceeds a certain imbalance threshold. As discussed above, it is important that the battery system be balanced (e.g., sufficiently) before charging. Thus, in this example, a first pass of balancing is performed at 1000 (e.g., according to any of the balancing techniques discussed above). For example, some battery sub-modules provide power to various electronic devices in the system, while other battery sub-modules do not provide power for a certain predefined amount of time and / or until a certain desired imbalance metric is reached.

[0070] A first pass or iteration of balancing is then performed at 1000 before the battery system is charged at 1002 .

[0071] After charging (1002) is complete, there may still be some imbalance in the battery system (e.g., carried over from the end of the first balancing pass) and / or additional imbalances may have been introduced by the charging process. Therefore, a second pass or iteration of balancing (e.g., by any of the techniques described above) is performed at 1004, but this time to address smaller and / or minor imbalances in the battery system.

[0072] FIG. 10B is a diagram illustrating an embodiment in which balancing is performed only after charging. In this example, the battery system has a relatively small amount or degree of imbalance between the battery sub-modules (and / or underlying cells) when the entire process begins. In other words, at time 0, the battery sub-modules are sufficiently balanced so that charging can be performed immediately (e.g., without having to first perform a balancing process). As previously described, the BMS controller may have determined an imbalance metric and compared the imbalance metric to a threshold to conclude that the battery system is sufficiently balanced to proceed with charging. Thus, charging (1050) is performed immediately at time=0. After charging is completed, balancing (1052) is performed (e.g., according to any of the techniques described above) to address any relatively small and / or minor imbalances present in the battery system at that time.

[0073] A third possible scenario (not shown here for simplicity) is to perform balancing before charging, but not after charging.

[0074] The following figures explain the above examples more generally and / or formally in flow chart form.

[0075] 11 is a flow chart illustrating an embodiment of a process for determining when to perform balancing on a charging process. In some embodiments, the process is performed by the BMS controller 208 in FIG.

[0076] At 1100, an imbalance metric related to the degree of imbalance between battery sub-modules in the plurality of battery sub-modules is determined. One example of an imbalance metric is the difference between the maximum and minimum cell state of charge within a battery, referred to herein as RANGE(SOC). Another metric in this example is the amount of imbalance that can be handled over the duration of a single charge, referred to herein as maxImbalance. Straightforward, if RANGE(SOC) > maxImbalance, it would be beneficial to balance before charging. If balancing before charging was not performed, the battery would be charged until the maximum voltage cell reached a maximum cell voltage threshold (above which would damage the cell). At this point, the battery would still be unbalanced, and all high voltage cells would need to be depleted until they reached the same voltage as the minimum voltage cell. After this, another charge would be performed until the now-balanced battery reached its maximum cell voltage.

[0077] This is not really an issue if the aircraft is left attached to the charging station for an extremely long period of time. In this case, the batteries can be trickle charged and kept fully charged while the batteries themselves balance. However, in high-throughput environments (e.g., air taxi or shared use applications) where the time the aircraft spends on the charging station needs to be minimized, it is beneficial to pre-balance the batteries (e.g., because the batteries do not need to be connected to the charging station during that time).

[0078] Note that maxImbalance is actually a variable, not a fixed value. If the aircraft is fully discharged, it may nominally take 1.25 hours to charge. Since balancing can occur while charging and balancing occur at a set rate, logic dictates that if less than 1.25 hours' worth of balancing is required, charging should proceed or otherwise be performed without fear of downtime. Otherwise, if it is desired to minimize time on the charging device, it would be beneficial to perform balancing beforehand. If only 0.5 hours' worth of charging is required (i.e., the airplane was only partially discharged), the threshold would be correspondingly smaller.

[0079] At 1102, it is determined whether the imbalance metric exceeds an imbalance threshold. In this example, an imbalance metric with a larger value corresponds to a greater degree or amount of imbalance in the battery system, and an imbalance metric with a smaller value corresponds to a lesser degree or amount of imbalance in the battery system. In other words, the imbalance threshold is used to determine whether the battery system is sufficiently charged to begin charging immediately or whether some balancing needs to be performed first.

[0080] If the imbalance metric exceeds an imbalance threshold at 1102 (e.g., the battery system is not sufficiently balanced for charging), then pre-charging balancing is performed at 1104. For example, any of the balancing techniques described above (e.g., in FIG. 1) may be used. After pre-charging balancing is performed at 1104, the plurality of battery sub-modules are charged at 1106.

[0081] If the imbalance metric does not exceed the imbalance threshold at 1102 (e.g., the battery system is sufficiently balanced for charging), then the battery sub-modules are charged at 1106 (e.g., without first performing balancing at step 1104).

[0082] In some embodiments, after the battery sub-modules are charged in step 1106, post-charging balancing is performed in 1108 (e.g., using any of the balancing techniques described above, such as in FIG. 1). Alternatively, the post-charging balancing step in 1108 may be skipped (e.g., because the degree or amount of imbalance in the battery system after charging does not warrant repeated balancing).

[0083] Although the above embodiments have been described in some detail for purposes of clarity of understanding, the present invention is not limited to the details given. There are many alternative ways to implement the present invention. The disclosed embodiments are illustrative and not limiting.

Claims

1. A plurality of battery sub-modules; Controller and A system comprising: the plurality of battery sub-modules are electrically connected in series to provide power to a primary load; Each battery sub-module includes a plurality of cells electrically connected in series; each battery sub-module further including a battery management system that monitors the plurality of cells of that battery sub-module; the controller is configured to select one or more battery sub-modules from the plurality of battery sub-modules, including by obtaining at least one voltage from each battery sub-module and selecting one or more battery sub-modules based at least in part on the obtained voltages; powering down battery management systems in the one or more selected battery sub-modules, so that (1) the plurality of battery sub-modules are not providing power to the primary load, and (2) while the plurality of battery sub-modules are not charging, the battery management systems in the one or more selected battery sub-modules at least temporarily do not consume power from the plurality of cells in the one or more selected battery sub-modules; The system, wherein selecting the one or more battery sub-modules is based at least in part on a plurality of maximum cell voltages, including a maximum cell voltage from each battery sub-module in the plurality of battery sub-modules.

2. A plurality of battery sub-modules; Controller and A system comprising: the plurality of battery sub-modules are electrically connected in series to provide power to a primary load; Each battery sub-module includes a plurality of cells electrically connected in series; each battery sub-module further including a battery management system that monitors the plurality of cells of that battery sub-module; the controller is configured to select one or more battery sub-modules from the plurality of battery sub-modules, including by obtaining at least one voltage from each battery sub-module and selecting one or more battery sub-modules based at least in part on the obtained voltages; powering down battery management systems in the one or more selected battery sub-modules, so that (1) the plurality of battery sub-modules are not providing power to the primary load, and (2) while the plurality of battery sub-modules are not charging, the battery management systems in the one or more selected battery sub-modules at least temporarily do not consume power from the plurality of cells in the one or more selected battery sub-modules; the controller determines an imbalance metric related to a degree of imbalance between battery sub-modules in the plurality of battery sub-modules; determining whether the imbalance metric exceeds an imbalance threshold; In response to determining that the imbalance metric exceeds the imbalance threshold, selecting one or more battery sub-modules from the plurality of battery sub-modules, including by obtaining at least one voltage from each battery sub-module and selecting one or more battery sub-modules based at least in part on the obtained voltages; and performing pre-charge balancing, including powering down battery management systems in the one or more selected battery sub-modules, whereby (1) the plurality of battery sub-modules are not providing power to the primary load, and (2) the battery management systems in the one or more selected battery sub-modules at least temporarily do not consume power from the plurality of cells in the one or more selected battery sub-modules while the plurality of battery sub-modules are not being charged; performing pre-charge balancing and then charging the plurality of battery sub-modules; The system further comprises:

3. A method comprising selecting one or more battery sub-modules from a plurality of battery sub-modules, including by obtaining at least one voltage from each battery sub-module, and selecting one or more battery sub-modules based at least in part on the obtained voltages, the plurality of battery sub-modules are electrically connected in series to provide power to a primary load; Each battery sub-module includes a plurality of cells electrically connected in series; each battery sub-module further including a battery management system that monitors the plurality of cells of that battery sub-module; powering down the battery management systems in the one or more selected battery sub-modules, whereby (1) the plurality of battery sub-modules are not providing power to the primary load, and (2) the battery management systems in the one or more selected battery sub-modules at least temporarily do not consume power from the plurality of cells in the one or more selected battery sub-modules while the plurality of battery sub-modules are not charging; The method, wherein selecting the one or more battery sub-modules is based at least in part on a plurality of maximum cell voltages, including a maximum cell voltage from each battery sub-module in the plurality of battery sub-modules.

4. A method comprising selecting one or more battery sub-modules from a plurality of battery sub-modules, including by obtaining at least one voltage from each battery sub-module, and selecting one or more battery sub-modules based at least in part on the obtained voltages, the plurality of battery sub-modules are electrically connected in series to provide power to a primary load; Each battery sub-module includes a plurality of cells electrically connected in series; each battery sub-module further including a battery management system that monitors the plurality of cells of that battery sub-module; powering down the battery management systems in the one or more selected battery sub-modules, whereby (1) the plurality of battery sub-modules are not providing power to the primary load, and (2) the battery management systems in the one or more selected battery sub-modules at least temporarily do not consume power from the plurality of cells in the one or more selected battery sub-modules while the plurality of battery sub-modules are not charging; determining an imbalance metric related to a degree of imbalance between battery sub-modules in the plurality of battery sub-modules; determining whether the imbalance metric exceeds an imbalance threshold; In response to determining that the imbalance metric exceeds the imbalance threshold, selecting one or more battery sub-modules from the plurality of battery sub-modules, including by obtaining at least one voltage from each battery sub-module and selecting one or more battery sub-modules based at least in part on the obtained voltages; and performing pre-charge balancing, the pre-charge balancing including by powering down battery management systems in the one or more selected battery sub-modules, whereby (1) the plurality of battery sub-modules are not providing power to the primary load, and (2) the battery management systems in the one or more selected battery sub-modules at least temporarily do not consume power from the plurality of cells in the one or more selected battery sub-modules while the plurality of battery sub-modules are not being charged; performing pre-charge balancing and then charging the plurality of battery sub-modules; The method further comprises:

5. A computer program embodied on a non-transitory computer-readable storage medium, comprising: computer instructions, selecting one or more battery sub-modules from the plurality of battery sub-modules, including obtaining at least one voltage from each battery sub-module and selecting the one or more battery sub-modules based at least in part on the obtained voltages; the plurality of battery sub-modules are electrically connected in series to provide power to a primary load; Each battery sub-module includes a plurality of cells electrically connected in series; each battery sub-module further including a battery management system that monitors the plurality of cells of that battery sub-module; powering down the battery management systems in the one or more selected battery sub-modules, whereby (1) the plurality of battery sub-modules are not providing power to the primary load, and (2) the battery management systems in the one or more selected battery sub-modules at least temporarily do not consume power from the plurality of cells in the one or more selected battery sub-modules while the plurality of battery sub-modules are not charging; The computer program product, wherein selecting the one or more battery sub-modules is based at least in part on a plurality of maximum cell voltages, including a maximum cell voltage from each battery sub-module in the plurality of battery sub-modules.

6. A computer program embodied on a non-transitory computer-readable storage medium, comprising: computer instructions, selecting one or more battery sub-modules from the plurality of battery sub-modules, including obtaining at least one voltage from each battery sub-module and selecting the one or more battery sub-modules based at least in part on the obtained voltages; the plurality of battery sub-modules are electrically connected in series to provide power to a primary load; Each battery sub-module includes a plurality of cells electrically connected in series; each battery sub-module further including a battery management system that monitors the plurality of cells of that battery sub-module; powering down the battery management systems in the one or more selected battery sub-modules, whereby (1) the plurality of battery sub-modules are not providing power to the primary load, and (2) the battery management systems in the one or more selected battery sub-modules at least temporarily do not consume power from the plurality of cells in the one or more selected battery sub-modules while the plurality of battery sub-modules are not charging; determining an imbalance metric relating to a degree of imbalance between battery sub-modules in the plurality of battery sub-modules; determining whether the imbalance metric exceeds an imbalance threshold; In response to determining that the imbalance metric exceeds the imbalance threshold, selecting one or more battery sub-modules from the plurality of battery sub-modules, including by obtaining at least one voltage from each battery sub-module and selecting one or more battery sub-modules based at least in part on the obtained voltages; and performing pre-charge balancing, the pre-charge balancing including by powering off battery management systems in the one or more selected battery sub-modules, whereby (1) the plurality of battery sub-modules are not providing power to the primary load, and (2) the battery management systems in the one or more selected battery sub-modules at least temporarily do not consume power from the plurality of cells in the one or more selected battery sub-modules while the plurality of battery sub-modules are not being charged; performing pre-charge balancing and then charging the plurality of battery sub-modules; 20. A computer program product comprising:

Images