Inter-module battery balancing using minimal cell voltage selecting battery submodules

Abstract

For each battery pack sub-module of a plurality of battery pack sub-modules, a voltage associated with a battery in the battery pack sub-module is received, where each battery pack sub-module of the plurality of battery pack sub-modules includes a plurality of batteries. A battery pack sub-module is selected based at least in part on the received voltage, and a set of one or more loads is configured that draw power from the selected battery pack sub-module and are not powered by any other of the plurality of battery pack sub-modules, such that the set of loads at least temporarily does not draw power from the selected battery pack sub-module.

Description

[0001] This application is a divisional application, and the name of the invention of the parent case is "Inter-module battery pack balancing for selecting battery pack submodules to power a load using minimum battery voltage", the application date is April 23, 2019, and the application number is 201980063484.5. Background Art

[0002] New aircraft that are all-electric are being developed. Because of differences in how battery packs tend to be designed (e.g., battery packs in aircraft must satisfy the Federal Aviation Administration (which may have more concerns about single points of failure and levels of redundancy than the National Highway Traffic Safety Administration) and / or how vehicles are used, as all-electric aircraft are developed, there may be some battery pack-related issues that were not previously exposed with electric vehicles that are exposed. New technologies to detect, mitigate, and / or avoid such battery pack-related issues in all-electric aircraft (or other vehicles) would be desirable. BRIEF DESCRIPTION OF THE DRAWINGS

[0003] Various embodiments of the invention are disclosed in the following detailed description and accompanying drawings.

[0004] Figure 1 is a flow chart illustrating an embodiment of an inter-module balancing process.

[0005] Figure 2 is a diagram illustrating an embodiment of a battery system including battery submodules connected together in series, wherein each battery submodule includes batteries connected together in series.

[0006] Figure 3A is a diagram illustrating an embodiment of a battery submodule without a cover thereon.

[0007] Figure 3B is a diagram illustrating an embodiment of a battery submodule without a cover thereon.

[0008] Figure 4 is a flow chart illustrating an embodiment of an inter-module balancing process, including by shutting down electronics.

[0009] Figure 5 is a flow chart illustrating an embodiment of an inter-module balancing process including drawing power from unselected battery pack submodules by configuring a collection of electronics.

[0010] Figure 6 is a diagram illustrating an embodiment of cell voltages in a battery submodule in a battery system.

[0011] Figure 7is a flow chart illustrating an embodiment of a process for selecting a battery pack submodule using a voltage threshold.

[0012] Figure 8 is a flow chart illustrating an embodiment of a process for selecting a battery pack submodule using a maximum of a voltage threshold and a minimum battery voltage.

[0013] Fig. 9 is a flow chart illustrating an embodiment of a process for selecting a battery pack submodule using a maximum of a voltage threshold and a maximum battery voltage.

[0014] Fig. 10A is a diagram illustrating an embodiment in which balancing is performed both before and after charging.

[0015] Fig. 10B is a diagram illustrating an embodiment in which balancing is performed only after charging.

[0016] Fig.11 is a flow chart illustrating an embodiment of a process for deciding when to perform balancing relative to a charging process. DETAILED DESCRIPTION

[0017] The present invention may be implemented in a variety of 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 a processor, such as a processor configured to execute instructions stored on a memory coupled to the processor and / or provided by the memory. In this specification, these implementations or any other form that the present invention may take may be referred to as techniques. In general, the order of steps of the disclosed processes may be changed within the scope of the present invention. Unless otherwise stated, components such as processors or memories described as being configured to perform tasks may be implemented as general components that are temporarily configured to perform tasks at a given time or as specific components manufactured to perform tasks. As used herein, the term "processor" refers to one or more devices, circuits, and / or processing cores that are configured to process data such as computer program instructions.

[0018] The following is a schematic diagram of the principles of the present invention. Figure 1 A detailed description of one or more embodiments of the present invention is provided. The present invention is described in conjunction with such embodiments, but the present invention is not limited to any embodiment. The scope of the present invention is limited only by the claims, and the present invention includes many alternatives, modifications and equivalents. In order to provide a thorough understanding of the present invention, many specific details are set forth in the following description. These details are provided for illustrative purposes, and the present invention can be practiced according to the claims without some or all of these specific details. For the sake of clarity, technical materials known in the technical field related to the present invention are not described in detail to avoid unnecessarily obscuring the present invention.

[0019] Various embodiments of techniques for balancing battery submodules in a battery system are described herein. In some embodiments, a voltage associated with a battery in a battery submodule is received for each battery submodule in a plurality of battery submodules (e.g., connected in series), wherein each battery submodule in the plurality of battery submodules includes a plurality of batteries (e.g., connected in series). A battery submodule is selected from the plurality of battery submodules based at least in part on the received voltage. A collection of one or more loads (e.g., electronic devices or other power consumers) that draw power from the selected battery submodule and are not powered by any other battery submodule in the plurality of battery submodules is configured such that the collection of one or more loads does not draw power from the selected battery submodule at least temporarily.

[0020] In some applications, the technique is used to select which battery pack submodules do not (e.g., at least temporarily) supply standby or draw power to corresponding electronic devices, while the primary load (e.g., a lift fan in an all-electric aircraft) does not draw energy from the battery pack system. In the long run, if the process is performed, the battery pack submodules will be more balanced (e.g., where more balanced battery pack submodules perform better) than if the process is not performed and / or permanent damage to the battery pack submodules can be avoided.

[0021] Figure 1 is a flow chart illustrating an embodiment of an inter-module balancing process. In some embodiments, the process is performed by and / or on a battery pack system having a plurality of submodules connected together in series, wherein each battery pack submodule further comprises a plurality of batteries connected together in series.

[0022] At 100, for each of a plurality of battery submodules, a voltage associated with a battery in the battery submodule is received, wherein each of the plurality of battery submodules includes a plurality of batteries. In one example, a battery system is used to power an all-electric aircraft. For a variety of reasons, a battery system for powering an aircraft may consist of a plurality of battery submodules connected in series. For example, by connecting a plurality of battery submodules in series to form an overall battery system, the battery submodules may be easily replaced as needed or when needed, and relatively high voltages (e.g., about several hundred volts required for a lift fan) and lower voltages (e.g., about a single volt required for avionics and / or electronic devices) are available at the same time. In contrast, when the battery system includes (more) monolithic battery packs, these desirable characteristics and / or features do not exist. An exemplary battery system is described in more detail below, comprising battery submodules (connected in series), which in turn include batteries (also connected in series).

[0023] At 102, a battery submodule is selected from a plurality of battery submodules based at least in part on the received voltage. For example, the selected battery submodule may have been selected because it is undesirable for the battery submodule to continue to supply power to one or more loads (e.g., electronics, motors, solenoids, etc.) that are running off the selected battery submodule. In some embodiments, more than one battery submodule is selected. Some examples of how the selection may be performed are described in more detail below.

[0024] At 104, a set of one or more loads that draw power from the selected battery submodule and are not powered by any other battery submodule in the plurality of battery submodules are configured such that the set of one or more loads at least temporarily does not draw power from the selected battery submodule. As will be described in more detail below, in some embodiments, the loads include (one or more) electronic devices that are turned off such that they no longer draw (e.g., draw) power from the selected and / or associated battery submodule. Alternatively, (one or more) electronic devices associated with the selected battery submodule may be configured such that they draw power from some other battery submodule other than the selected battery submodule.

[0025] Conceptually and / or generally, the above process attempts to balance the voltage levels in the various submodules and / or batteries by selectively permitting some (but not all) battery pack submodules to provide power to associated loads, such as during some stationary or dormant states where the aircraft (or other load) is not consuming a large amount of power. This pulls the voltage level in the submodule and / or battery down (e.g., which is better equipped and / or in a better state to provide power), so that the voltage level in the selected submodule and / or selected battery can be maintained.

[0026] In one example of why balancing is important and / or useful, if balancing is not performed (e.g., as per Figure 1 process), then if the battery system is left alone for ~20 days, some of the battery submodules in the battery system will fail permanently. This is entirely possible if the battery system is used in an aircraft. For example, a pilot can drive the aircraft to some remote place without a charging station, where the aircraft is left idle for ~20 days and the battery pack is not charged during this period. Alternatively, the aircraft may be placed in a hangar for a long period of time, so maintenance requiring manual intervention will be quite inconvenient.

[0027] Another benefit of keeping the submodules of a battery pack balanced is that it increases the capacity of the battery pack, due to the fact that for a battery pack that includes submodules in series, the capacity of the battery pack is driven by the smallest capacity cell. This is because discharging the battery pack below its minimum capacity will damage it. Likewise, keeping the submodules balanced reduces the time it takes to charge them because in a balanced state, the cells will be at a uniform and higher voltage than in an unbalanced state. Finally, maintaining a balanced battery pack can increase its overall lifespan. A cell with reduced voltage may degrade faster than its neighboring cells, and when one of the component cells of a submodule reaches a critical point of degradation, the submodule must be replaced. Furthermore, in embodiments that allow submodules to be discharged in parallel, submodules of different voltages will contribute different currents to their loads, and submodules that must contribute excess current will experience accelerated degradation. The battery pack may be repeated as desired or where desired. Figure 1 For example, in the event that the unselected battery submodules provide power, the voltage levels stored in those cells and / or battery submodules will drop, resulting in different voltage levels and, thus, different degrees and / or states of imbalance. In one example, the battery submodules selected in step 102 are not powered for 15 minutes during step 104 (as an example), after which the process is repeated with updated voltage levels. Figure 1 As a result, at step 102, different battery pack submodules may be selected to at least temporarily no longer power their corresponding electronic devices.

[0028] 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 of the primary load on the battery system may change very quickly, and thus it may be difficult and / or expensive to sample the battery system quickly 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.

[0029] In some embodiments, the exemplary balancing process described above is performed before and / or after charging of the battery system is performed. For example, by balancing the battery system before charging of the battery system occurs (e.g., according to Figure 1 process), can help the charging process itself by fixing or otherwise reducing (large) imbalances between battery pack submodules, if any (which may be undesirable during the charging process, for example). Figure 1 If the process) is performed after the battery system is charged, then small imbalances between the battery submodules can be fixed or otherwise reduced.

[0030] Describe execution Figure 1 An exemplary battery system for the process may be helpful. The following figure depicts one such exemplary battery system.

[0031] Figure 2 is a diagram illustrating an embodiment of a battery system including battery submodules connected together in series, wherein each battery submodule includes batteries connected together in series. In this example, the battery system is used to power an all-electric aircraft.

[0032] In this example, there are M battery submodules: a first battery submodule (200a), a second battery submodule (200b), and an Mth battery submodule (200c), wherein the battery submodules are connected in series. This produces a high voltage power supply (e.g., on the order of hundreds of volts) that powers a high voltage load (202), such as a lift fan of an aircraft.

[0033] Each battery pack submodule further includes N batteries connected in series. For example, the first battery pack submodule (200a) includes a first battery (204a), a second battery (204b), an (N-1)th battery (204c) and an Nth battery (204d). The voltage across each battery pack submodule in this example is about tens of volts. In this example, there are 36 battery pack submodules and 12 batteries per battery pack submodule. The following figure shows an exemplary battery pack submodule.

[0034] Figure 3A is an illustration of an embodiment of a battery pack submodule that does not have a cover thereon. In the example shown, the battery pack submodule includes a battery layer (300) that is interlaced with an insulating (e.g., flame retardant) layer (302). In this example, the battery is a pouch cell that performs better when pressure (e.g., ~3–5 PSI) is applied. More specifically, by applying pressure to the pouch cell, the cycle life of the pouch cell can be extended. As such, the battery pack submodule is packaged by a metal can (304) that applies pressure on the contained pouch cell.

[0035] Each of the cells has two terminals (306) extending upward from the cell: a positive terminal and a negative terminal. The terminals are connected together so that the cells are electrically connected together in series. For example, see Figure 2 .

[0036] Figure 3Bis a diagram illustrating an embodiment of a battery submodule without a cover thereon. In this example, a cover (350) has been attached to the battery submodule such that only a single positive connection and a single negative connection are exposed. In the above described examples where the battery system is included in an aircraft, each battery submodule can be physically and electrically connected together within the aircraft such that individual battery submodules can be swapped out and replaced as needed or if desired.

[0037] Back to Figure 2 , each battery submodule (200a-200c) has a collection of electronic devices (206a-206c) associated with the battery submodule and powered by the battery submodule (e.g., even when the aircraft is not flying and the high voltage load (202) is not consuming power). For example, the first collection of electronic devices (206a) is powered by the first battery submodule (200a), the second collection of electronic devices (206b) is powered by the second battery submodule (200b), and the Mth collection of electronic devices (206c) is powered by the Mth battery submodule (200c). For simplicity and to maintain the readability of the figure, voltage converters (e.g., which step down the voltage generated by the battery submodule to the voltage level expected by the electronic device) are not shown herein, but can be used as needed or where needed.

[0038] 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 within the associated battery submodules over time. In some embodiments, the battery management system monitors and / or tracks the voltage of each of the cells in the associated battery submodules over time. The electronics controller (208) controls the various electronics (206a-206c) in a manner described in more detail below.

[0039] This type of battery pack arrangement may be more suitable for aircraft applications than for automotive applications. For example, the Federal Aviation Administration may have very strict requirements when it comes to redundancy and / or potential single points of failure. By arranging multiple battery pack submodules in series with backup connections not shown, the overall battery pack system can still operate and output a high voltage signal for the high voltage load (202) even if one of the battery pack submodules fails. In contrast, the National Highway Traffic Safety Administration may not be as concerned about redundancy and / or potential single points of failure because if the battery pack fails, the car can just glide and pull over to the curb to the shoulder, while the aircraft will crash. For these and other reasons, battery pack systems for electric vehicles tend to be more monolithic (e.g., having relatively few battery pack submodules and / or relatively few batteries per battery pack submodule compared to battery pack systems for aircraft).

[0040] Due to slight differences between various cells and various battery submodules, the voltages across the cells and battery submodules are not exactly the same. Furthermore, due to the configuration shown herein, when the high voltage load (202) is off and the electronic devices (206a-206c) are on (e.g., when the aircraft is powered off), the battery submodules with less charge will be powered more than the battery submodules with more charge (e.g., if inter-module balancing is not performed, Figure 1 ). To use an analogy, the rich ones (submodules) remain rich and the poor ones (submodules) remain poor. To solve this problem, the electronic device controller 208 (e.g., including a BMS controller) executes Figure 1 balancing process.

[0041] In the context of this example system, when the electronics controller (208) decides to execute Figure 1 During the process, initiate Figure 1 Step 100. As described above, balancing may be performed before and / or after charging, but (eg, for simplicity and / or to avoid expensive sampling equipment) balancing is not performed while a high voltage load is drawing power from the battery system.

[0042] once Figure 1 At the beginning of the process, the electronic device controller (208) sends a signal to each set of electronic devices (206a-206c) to send back one or more voltages associated with the batteries in the associated battery pack submodule. For example, the voltage sent back to the electronic device controller can be the minimum (e.g., lowest) voltage of all the batteries in the battery pack submodule, sometimes referred to as the minimum battery voltage in this document (e.g., for a given battery pack submodule). In some other embodiments, in addition to and / or in place of the minimum battery voltage, some other type of battery voltage (e.g., as a maximum battery voltage or an intermediate or average battery voltage) is sent to the electronic device controller. Using the voltages received from the electronic devices (206a-206c), the electronic device controller selects at least one set of electronic devices. In one example, the electronic device with the global minimum battery voltage (e.g., the controller picks the minimum of the minimum battery voltages) is selected (e.g., because if the battery with the minimum battery voltage is below a certain threshold and / or unrecoverable battery voltage level, continuing to draw power from the battery pack submodule may permanently damage the battery pack submodule). This is Figure 1 An example of step 102 in FIG.

[0043] In this example, there are two paths between each set of electronic devices (206a-206c) and the electronic device controller (208). One path is used for communication and / or control, and the other path is used for power. The latter incorporates switches for interrupting power from a given battery pack submodule and / or set of electronic devices to the electronic device controller. The control and / or communication paths are always connected and available (e.g., to allow the controller to interrogate the battery voltage and control the state of the aforementioned switches in response to the voltage measurement).

[0044] The electronics controller then configures the selected electronic device so that it does not draw power from its associated battery submodule (e.g., to the extent possible, since there is typically some level of power draw even when the item 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 component) so that power from a given battery submodule is not sent upstream to the electronics controller (208). For example, even if the electronic device 206a is in power minimization mode and is not providing any power to the controller (208), the controller (208) may still query the battery management system 206a to obtain its voltage, etc. This may be desirable in applications where it is desirable to keep the electronics accessible. For example, as described above, the battery management system tracks and / or monitors metrics associated with the associated battery submodule and / or the batteries therein. It may be desirable to keep track of such metrics and / or measurements, for example by obtaining power from another battery submodule. These are how this may be performed Figure 1 Some examples of step 104 in FIG.

[0045] Without balancing, one or more of the battery pack submodules may be irreparably damaged in as little as ~20 days. For example, if the voltage level of a cell drops below a certain voltage level, and power continues to be drawn from that cell, the cell will be irreparably damaged, and as a result the entire battery pack submodule will need to be replaced.

[0046] The following figures describe some of the examples described above more generally and / or formally in flow charts.

[0047] Figure 4 is a flow chart illustrating an embodiment of an inter-module balancing process, including by shutting down electronics. Figure 4 and Figure 1 Related, and for convenience, related steps are indicated by similar or identical reference numerals.

[0048] At 100, for each battery pack submodule in a plurality of battery pack submodules, a voltage associated with a battery in the battery pack submodule is received, wherein each battery pack submodule in the plurality of battery pack submodules includes a plurality of batteries. Figure 2 An electronic device controller (208) receives at least one voltage from each electronic device (206a-206c), wherein each received voltage is associated with a battery in a corresponding or associated battery pack submodule (200a-200c).

[0049] At 102, a battery submodule is selected from a plurality of battery submodules 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, a plurality of battery submodules are selected.

[0050] At 104a, a set of one or more loads that draw power from the selected battery submodule and are not powered by any other battery submodule in the plurality of battery submodules are configured so that the set of one or more loads do not draw power from the selected battery submodule at least temporarily, including by configuring the set of loads that draw power from the selected battery submodule to be turned off. For example, if a selected Figure 2 If the first battery submodule (200a) is powered off, the load controller 208 may configure the set of first loads 206a so that they are powered off and do not draw power from the first battery submodule (200a).

[0051] Figure 5 is a flow chart illustrating an embodiment of a process of inter-module balancing, including by configuring a collection of electronics to draw power from unselected battery pack submodules. Figure 5 and Figure 1 Related, and for convenience, related steps are indicated by similar or identical reference numerals.

[0052] At 100 , for each battery submodule of a plurality of battery submodules, a voltage associated with a battery in the battery submodule is received, wherein each battery submodule of the plurality of battery submodules includes a plurality of batteries.

[0053] At 102, a battery submodule is selected from a plurality of battery submodules based at least in part on the received voltage. As described above, in some embodiments, the plurality of battery submodules are selected (e.g., because the plurality of battery submodules are in a poor power supply state and / or may be irreparably damaged if they continue to supply power and are therefore selected).

[0054] At 104b, a collection of one or more loads that draw power from a selected battery pack submodule and are not powered by any other battery pack submodule among the plurality of battery pack submodules are configured such that the collection of one or more loads at least temporarily does not draw power from the selected battery pack submodule, including by configuring the collection of loads that draw power from the selected battery pack submodule to draw power from an unselected battery pack submodule.

[0055] In some applications, shutting down electronics is undesirable. Figure 2 In an example of a battery management system, the electronics include a battery management system that tracks and / or monitors the health and / or other metrics of the battery submodules and / or cells, and it is important and / or desirable to track this information at all times. For example, for an aircraft, the aircraft may be shut down during the week and only fly on weekends. The battery management system should operate throughout the week so that any poor battery submodules can be identified and / or the aircraft not permitted to fly as needed or if desired.

[0056] As described above, in some embodiments, a battery submodule is selected from a plurality of battery submodules in order to prevent the cells in the battery submodule from being drawn down to a voltage level at which irreparable damage occurs (e.g., and the entire battery submodule must be replaced). The following figures describe some exemplary battery voltages and exemplary techniques for selecting a battery submodule using those battery voltages.

[0057] Figure 6 1 is a diagram illustrating an embodiment of battery voltages in a battery submodule in a battery system. In this example, there are M battery submodules, and each battery submodule has N batteries, with Figure 2 In the illustrated diagram, the x-axis shows the battery pack index (defined by the battery pack submodule number and the battery number within the battery pack submodule), and the y-axis shows the battery voltage of the corresponding battery. Group 600 shows the battery voltage of the battery in the first battery pack submodule, group 602 shows the battery voltage of the battery in the second battery pack submodule, and group 604 shows the battery voltage of the battery in the Mth battery pack submodule.

[0058] For simplicity and ease of explanation, assume that there exists a threshold (606) represents a voltage level below which, if power continues to be drawn from the battery (e.g., standby or power draw when the aircraft is shut down), the battery will be permanently damaged. For example, battery pack 2,1 (610) and battery pack 2,N (612), both in the second battery pack submodule (602), are at V threshold (606) or at V threshold(606) below. To ensure that power is no longer drawn from this battery submodule, a second battery submodule (e.g., Figure 1 102 in step 102) and a corresponding set of electronic devices (e.g., Figure 2 206b) will be configured so that they no longer receive power from the second battery pack submodule (e.g., Figure 2 200b) in draws power.

[0059] Briefly return to Figure 2 It would be desirable if the electronics controller (208) could receive the battery voltage of only some of the cells in each battery submodule, rather than having to receive the battery voltage of all of the cells in a given battery submodule. This would, for example, reduce the amount of traffic or communication exchanged between the electronics controller (208) and the low level electronics (206a-206c).

[0060] In one example, the minimum cell voltage from each battery pack submodule is sent to an electronics controller or other block that makes the selection. For example, the corresponding electronics controller (e.g., a battery pack management system) can make the selection and only upload the minimum cell voltage to the electronics controller (e.g., a BMS controller). Figure 6 In the example of FIG. 1 , this would mean selecting the cell voltage of cell 1, (N-1) (620) and sending it to the electronics controller, which is the minimum cell voltage in the first battery pack submodule (600). For the second battery pack submodule (602), the minimum cell voltage is the cell voltage of cell 2, 1 (610) and would be selected and sent to the electronics controller. For the Mth battery pack submodule (604), the minimum cell voltage is the cell voltage of cell M, N (622) and would be selected and sent to the electronics controller.

[0061] In some embodiments, Figure 1 At step 102 in the embodiment, a battery pack submodule is selected using a threshold voltage. For example, if any battery pack submodule has a threshold voltage between V threshold (606) or less, the battery submodule is selected so that its corresponding electronic device does not continue to draw power from the battery submodule. Figure 6 , only the second battery submodule (602) will be selected. As such, the corresponding electronic devices will be configured to at least temporarily not draw power from the second battery submodule (e.g., either by shutting down the second set of electronic devices or supplying power from some other battery submodule).

[0062] In some embodiments, the above steps are performed first (e.g., wherein the minimum cell voltage from each battery pack submodule is compared to a certain voltage threshold, such as Vthreshold (606) for comparison). Then, from V threshold In the above pool of battery submodules, the n battery submodules having the n largest values ​​of the (remaining) minimum cell voltages are used to (at least temporarily) provide power, while the other battery cell modules (including those having the n largest values ​​of the (remaining) minimum cell voltages) are used to (at least temporarily) provide power. threshold Those below the minimum cell voltage) do not provide power (at least temporarily). This pulls n battery submodules down, which makes those battery submodules more balanced relative to the other battery submodules.

[0063] For example, in Figure 6 In the example, the Mth battery submodule (604) generally has a much higher cell voltage than the rest of the battery submodules. By pulling the cell voltage of the Mth battery submodule (604) down, this can help pull down the Mth battery submodule (604), i.e., the high-end outlier, without irreparably damaging the second battery submodule (602), i.e., the low-end outlier. In other words, the first check or test (e.g., comparing the minimum cell voltage to V threshold comparison) ensures nothing is faulty or damaged, and (e.g., draws power from the n largest values ​​of n battery pack submodules with the smallest cell voltage) the second check or test is a performance oriented selection (e.g., it does a better job of balancing than some other selection techniques, and balanced battery pack submodules are good for performance).

[0064] In some embodiments, there is no minimum battery voltage at V threshold (606) the following battery submodules. In some such embodiments, the maximum cell voltage from each battery submodule is obtained, and the m battery submodules having the m maximum values ​​of the maximum cell voltage provide power (at least temporarily), while the remaining battery submodules do not provide power (at least temporarily). In this case, if the battery submodule continues to provide power, there is no danger of the battery submodule being permanently damaged, and thus using the maximum cell voltage from each cell is an even better way to balance the submodules (e.g., even better than using the maximum value of the minimum cell voltage). In such a balanced situation, it is always more beneficial to draw power from a higher voltage submodule than from a lower voltage submodule.

[0065] These examples are more generally and / or formally described in the flowcharts below.In various applications and / or embodiments, appropriate techniques may be performed.

[0066] Figure 7 is a flow chart illustrating an embodiment of a process for selecting a battery pack submodule using a voltage threshold. Figure 1At step 102 in the example process described herein, a battery pack submodule is selected. In this example, Figure 1 Receiving a voltage at step 100 in includes receiving a minimum battery voltage for each battery pack submodule in a plurality of battery pack submodules connected together in series, thereby receiving a plurality of minimum battery voltages.

[0067] At 700, a plurality of minimum cell voltages are compared to a voltage threshold to identify any battery pack submodules having a minimum cell voltage that does not exceed the voltage threshold. Figure 6 In the example, the minimum battery voltage of battery 1, (N-1) (620), battery 2, 1 (610) and battery M, N (622) is compared with V threshold (606) A comparison is made. In this example, the only battery with a minimum battery voltage that does not exceed the voltage threshold is battery 2,1 (610).

[0068] At 702, any of the identified battery pack submodules having a minimum battery voltage that does not exceed a voltage threshold is selected. Figure 6 In the example of , the second battery submodule (602) will be selected. As such, the corresponding electronic devices will be configured so that they do not draw power from the second battery submodule (602), at least temporarily. The second battery submodule (602) is vulnerable and may be permanently damaged if it continues to draw power.

[0069] Depending on the design goals and / or constraints, appropriate techniques can be used to make the selection. For example, Figure 7 In some applications, if other more complex procedures provide only minimal performance improvements, Figure 7 The process is used to make the selection.

[0070] Figure 8 is a flow chart illustrating an embodiment of a process for selecting a battery pack submodule using a maximum of a voltage threshold and a minimum battery voltage. Figure 1 At step 102 in the example process described herein, a battery pack submodule is selected. In this example, Figure 1 Receiving a voltage at step 100 in includes receiving a minimum battery voltage for each battery pack submodule in a plurality of battery pack submodules connected together in series, such that a plurality of minimum battery voltages are received.

[0071] At 800, a plurality of minimum cell voltages are compared to a voltage threshold to identify any battery pack submodules having a minimum cell voltage that does not exceed the voltage threshold. Figure 6, wherein the second battery pack submodule (602) has a minimum battery voltage (610) that does not exceed a voltage threshold (606).

[0072] At 802, one or more maximum values ​​are selected from a plurality of minimum battery voltages to obtain one or more maximum values ​​of the minimum battery voltage. Figure 6 , the minimum battery voltages include the voltages of battery 1, (N-1) (620), battery 2, 1 (610), and battery M, N (622), and the maximum of those is the voltage of battery M, N (622). For simplicity and ease of explanation, it is assumed that only one maximum value is selected in this example of step 802 and subsequently at step 804.

[0073] At 804, any of the identified battery submodules having a minimum cell voltage that does not exceed the voltage threshold are selected, as well as those battery submodules that do not correspond to one of the maximum values ​​of the minimum cell voltage. For example, the second battery submodule (602) will be selected because it has a minimum cell voltage (610) that does not exceed the voltage threshold (606). Moreover, the first battery submodule (600) does not correspond to the maximum value of the minimum cell voltage, and therefore the first battery submodule will also be selected. In other words, the first battery submodule (600) and the second battery submodule (602) will not have to provide power (at least temporarily), while the Mth battery submodule (604) will provide power (e.g., during the time period in question). Intuitively, this makes sense because the Mth battery submodule (604) tends to have a higher cell voltage than the other battery submodules.

[0074] In some applications, use Figure 8 process rather than Figure 7 process, because Figure 7 It can achieve better and / or faster balancing than conventional battery packs, but without having to obtain additional battery voltages for each battery pack submodule (e.g., according to Fig. 9 ).

[0075] Fig. 9 is a flow chart illustrating an embodiment of a process for selecting a battery pack submodule using a maximum of a voltage threshold and a maximum battery voltage. Figure 1 At step 102 in the example process described herein, a battery pack submodule is selected. In this example, Figure 1 Receiving voltages at step 100 includes receiving a minimum battery voltage and a maximum battery voltage for each battery pack submodule in a plurality of battery pack submodules connected together in series, such that a plurality of minimum battery voltages and a plurality of maximum battery voltages are received.

[0076] At 900, a plurality of minimum cell voltages are compared to a voltage threshold to identify any battery pack submodules having a minimum cell voltage that does not exceed the voltage threshold. Figure 6 .

[0077] At 902, it is determined whether there are any battery pack submodules with a minimum battery voltage that does not exceed a voltage threshold. Figure 6 , the decision would be "yes" because the minimum battery voltage of battery 2,1 (610) does not exceed the voltage threshold (606). In this example, the process would then proceed to Figure 8 Step 802 in .

[0078] However, if the decision at step 902 is "no" (e.g., because all minimum battery voltages exceed the voltage threshold), then at 904, one or more maximum values ​​are selected from the plurality of maximum battery voltages to obtain one or more maximum values ​​of the maximum battery voltage. Figure 6 The multiple maximum battery voltages in include the battery voltages of battery 1,2 (630), battery 2,(N-1) (632), and battery M,1 (634). If only one maximum value is selected, the maximum value of the maximum battery voltages will be the battery voltage of battery M,1 (634).

[0079] At 906, those battery submodules that do not correspond to one of the maximum values ​​of the maximum cell voltage are selected. In other words, the battery submodules corresponding to the maximum value of the maximum cell voltage will provide power for a period of time (at least temporarily). Continuing with the example from above, the Mth battery submodule will provide power (at least temporarily), while the other battery submodules will not provide power (at least temporarily).

[0080] In some applications, this technique enables optimal and / or faster balancing, but requires the use of both the minimum and maximum cell voltages, which requires more information to be exchanged between the (local) electronics (e.g., battery pack 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 tradeoff, then Fig. 9 process.

[0081] As described above, in some embodiments, balancing is performed before and / or after charging. The following figures describe some example scenarios where balancing is performed before and after charging and only after charging.

[0082] Fig. 10Ais a diagram illustrating an embodiment of performing balancing before and after charging. In the example shown, the battery pack system has a major imbalance between the various battery pack submodules and / or their underlying cells at time 0. For example, assume that the BMS controller calculates an imbalance metric representing the degree or amount of imbalance in the battery pack system, and the metric is relatively high and / or above a certain imbalance threshold. As described above, it is important that the battery pack system is (e.g., fully) balanced before charging. As such, in this example, a first pass of balancing is performed at 1000 (e.g., in accordance with any of the balancing techniques described above). For example, some battery pack submodules will provide power to various electronic devices in the system, while other battery pack submodules provide power for some predetermined amount of time and / or until some desired imbalance metric is reached.

[0083] Then, after a first pass or iteration of balancing is performed at 1000 , the battery pack system is charged at 1002 .

[0084] After charging (1002) is complete, some degree of imbalance may still exist in the battery system (e.g., extending from the end of the first balancing pass) and / or additional imbalances may have been introduced by the charging process. As such, a second pass or iteration of balancing is performed at 1004 (e.g., according to any of the techniques described above), but this time to address smaller and / or lesser imbalances in the battery system.

[0085] Fig. 10B is a diagram illustrating an embodiment in which balancing is performed only after charging. In this example, when the overall process begins, the battery pack system has a relatively small amount or degree of imbalance between the battery pack submodules (and / or base cells). In other words, at time 0, the battery pack submodules are sufficiently balanced that charging can be performed immediately (e.g., without having to run a balancing process first). As before, the BMS controller may have determined an imbalance metric and compared it to a threshold value in order to conclude that the battery pack system is sufficiently balanced to continue charging. As such, charging is performed immediately at time = 0 (1050). After charging is complete, balancing is performed (1052) (e.g., according to any of the techniques described above) to resolve the relatively small and / or smaller imbalances that exist in the battery pack system at the time.

[0086] A third possible scenario (not shown here for simplicity) is to perform balancing before charging but not after charging.

[0087] The following diagram describes the above example more generally and / or formally in a flow chart.

[0088] Fig.11 is a flow chart illustrating an embodiment of a process for determining when to perform balancing relative to a charging process. In some embodiments, the process is performed by Figure 2The BMS controller 208 in the embodiment is executed.

[0089] At 1100, an imbalance metric associated with the degree of imbalance between battery pack submodules in a plurality of battery pack submodules is determined. An example of an imbalance metric is the difference between the maximum battery state of charge and the minimum battery state of charge within the battery pack, referred to herein as RANGE(SOC). Another metric in this example is the amount of imbalance that can be handled within the duration of a single charge (), referred to herein as maxImbalance. To put it bluntly, if RANGE(SOC)>maxImbalance, balancing before charging would be beneficial. If balancing is not completed before charging, the battery pack will be charged until the maximum voltage cell reaches the maximum cell voltage threshold (where going above this threshold will damage the battery pack). At this point, the battery pack will still be unbalanced, and all high voltage cells will need to be depleted until they reach the same voltage as the minimum voltage cell. Thereafter, another charge will be performed until the now balanced battery pack reaches the maximum cell voltage.

[0090] This is not really a problem if the aircraft remains attached to the charger for very long periods of time. In this case, the battery pack can be trickle charged and remain full while the battery pack balances itself. However, in high throughput environments (e.g., aircraft out-of-group or shared-use applications) where the aircraft needs to spend minimal time on the charger, it is beneficial to pre-balance the battery pack (e.g., because the battery pack does not need to be connected to the charger during this time).

[0091] Note that maxImbalance is actually a variable, and 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 are occurring at a set rate, the logic follows that if less than 1.25 hours' worth of balancing is required, then charging should proceed, or otherwise be completed without fear of downtime. Otherwise, if it is desired to minimize time on the charger, then there will be a benefit from pre-balancing. If only 0.5 hours' worth of charge is required (i.e., the aircraft is only partially discharged), then the threshold becomes correspondingly smaller.

[0092] 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 larger degree or amount of imbalance in the battery system, and an imbalance metric with a smaller value corresponds to a smaller degree or amount of imbalance in the battery system. In other words, the imbalance threshold is used to decide whether the battery system is sufficiently charged to begin charging immediately, or whether some balancing needs to be performed first.

[0093] If the imbalance metric exceeds the imbalance threshold at 1102 (e.g., the battery pack system is not balanced enough for charging), then pre-charge balancing is performed at 1104. For example, any of the balancing techniques described above (e.g., Figure 1 ). After performing pre-charge balancing at 1104 , the plurality of battery pack submodules are charged at 1106 .

[0094] If the imbalance metric does not exceed the imbalance threshold at 1102 (eg, the battery system is sufficiently balanced for charging), then the plurality of battery submodules are charged at 1106 (eg, without first performing balancing at step 1104 ).

[0095] In some embodiments, after charging the battery pack submodules at step 1106, post-charge balancing is performed at 1108 (e.g., using any of the above-described balancing techniques, such as Figure 1 Alternatively, the post-charge balancing step at 1108 may be skipped (eg, because the degree or amount of imbalance in the battery system after charging does not warrant iterations of balancing).

[0096] Although the foregoing embodiments have been described in some detail for the purpose of clarity of understanding, the invention is not limited to the details provided. There are many alternative ways to implement the invention. The disclosed embodiments are illustrative and non-restrictive.

Claims

1. A system comprising: A plurality of battery pack submodules, wherein: A plurality of battery submodules are electrically connected in series to provide power to a primary load; Each battery pack submodule includes a plurality of batteries electrically connected in series; and A controller configured to: Selecting one or more battery pack submodules from a plurality of battery pack submodules includes: Obtaining at least one voltage from each battery submodule; and selecting one or more battery submodules based at least in part on the obtained voltage, wherein the plurality of battery submodules include at least one unselected battery submodule; wherein each selected battery submodule is coupled to a secondary load; Those secondary loads in one or more selected battery pack submodules are configured to draw power from at least one unselected battery pack submodule so that when (1) the multiple battery pack submodules are not providing power to the main load, or (2) the multiple battery pack submodules are not being charged, the secondary loads coupled to the selected battery pack submodules do not, at least temporarily, consume power from the multiple batteries in the selected battery pack submodules.

2. The system according to claim 1, wherein: Each secondary load is powered using a lower voltage than the primary load.

3. The system according to claim 1, wherein: At least one secondary load coupled to the battery pack submodule includes a battery management system that monitors a plurality of batteries in the battery pack submodule.

4. The system according to claim 1, wherein: Selecting one or more battery submodules is based at least in part on a plurality of minimum battery voltages including a minimum battery voltage from each of the plurality of battery submodules.

5. The system according to claim 1, wherein: Selecting one or more battery submodules is based at least in part on a plurality of maximum battery voltages including a maximum battery voltage from each of the plurality of battery submodules.

6. The system according to claim 1, wherein: Select one or more battery pack submodules including: for each battery submodule in the plurality of battery submodules, comparing the minimum cell voltage to a voltage threshold to identify any battery submodule having a minimum cell voltage that does not exceed the voltage threshold; and One or more of those battery pack submodules are selected that have a minimum cell voltage that does not exceed a voltage threshold.

7. The system according to claim 1, wherein: The controller is also configured to: determining an imbalance metric associated with a degree of imbalance between battery submodules in the plurality of battery submodules; determining whether the imbalance measure exceeds an imbalance threshold; In response to determining that the imbalance metric exceeds an imbalance threshold, performing pre-charge balancing; and After performing pre-charge balancing, the plurality of battery pack submodules are charged.

8. The system according to claim 7, wherein: Pre-charge balancing includes configuring those secondary loads in one or more selected battery pack submodules to draw power from at least one unselected battery pack submodule so that when (1) the multiple battery pack submodules are not providing power to the primary load, or (2) the multiple battery pack submodules are not being charged, the secondary loads coupled to the selected battery pack submodules do not, at least temporarily, consume power from the multiple batteries in the selected battery pack submodules.

9. The system of claim 1, further comprising: An electric aircraft including one or more lift fans, wherein the electric aircraft is powered by a plurality of battery submodules, wherein a primary load includes the one or more lift fans.

10. The system according to claim 1, wherein: Each secondary load includes one or more of an electronic device, a motor, or a solenoid.

11. The system according to claim 1, wherein: The controller is configured to balance voltage levels of the plurality of battery pack submodules.

12. A method comprising: Selecting one or more battery pack submodules from a plurality of battery pack submodules includes: obtaining at least one voltage from each battery pack submodule; and One or more battery submodules are selected based at least in part on the obtained voltage, wherein: A plurality of battery submodules are electrically connected in series to provide power to a primary load; Each battery pack submodule includes a plurality of batteries electrically connected in series; wherein the plurality of battery submodules include at least one unselected battery submodule; wherein each selected battery submodule is coupled to a secondary load; and Those secondary loads in one or more selected battery pack submodules are configured to draw power from at least one unselected battery pack submodule so that when (1) the multiple battery pack submodules are not providing power to the main load, or (2) the multiple battery pack submodules are not being charged, the secondary loads coupled to the selected battery pack submodules do not, at least temporarily, consume power from the multiple batteries in the selected battery pack submodules.

13. The method according to claim 12, wherein: Each secondary load is powered using a lower voltage than the primary load.

14. The method according to claim 12, wherein: At least one secondary load coupled to the battery pack submodule includes a battery management system that monitors a plurality of batteries in the battery pack submodule.

15. The method according to claim 12, wherein: Selecting one or more battery submodules is based at least in part on a plurality of minimum battery voltages including a minimum battery voltage from each of the plurality of battery submodules.

16. The method according to claim 12, wherein: Selecting one or more battery submodules is based at least in part on a plurality of maximum battery voltages including a maximum battery voltage from each of the plurality of battery submodules.

17. The method according to claim 12, wherein: Select one or more battery pack submodules including: for each battery submodule in the plurality of battery submodules, comparing the minimum cell voltage to a voltage threshold to identify any battery submodule having a minimum cell voltage that does not exceed the voltage threshold; and One or more of those battery pack submodules are selected that have a minimum cell voltage that does not exceed a voltage threshold.

18. The method according to claim 12, further comprising: determining an imbalance metric associated with a degree of imbalance between battery submodules in the plurality of battery submodules; determining whether the imbalance measure exceeds an imbalance threshold; In response to determining that the imbalance metric exceeds an imbalance threshold, performing pre-charge balancing; and After performing pre-charge balancing, the plurality of battery pack submodules are charged.

19. The method according to claim 12, wherein: Pre-charge balancing includes configuring those secondary loads in one or more selected battery pack submodules to draw power from at least one unselected battery pack submodule so that when (1) the multiple battery pack submodules are not providing power to the primary load, or (2) the multiple battery pack submodules are not being charged, the secondary loads coupled to the selected battery pack submodules do not, at least temporarily, consume power from the multiple batteries in the selected battery pack submodules.

20. The method according to claim 12, wherein: Each secondary load includes one or more of an electronic device, a motor, or a solenoid.

21. A system comprising: A plurality of battery pack submodules, wherein: A plurality of battery submodules are electrically connected in series to provide power to a primary load; Each battery pack submodule includes a plurality of batteries electrically connected in series; and Each battery pack submodule also includes a battery management system that monitors the plurality of batteries in the battery pack submodule; and A controller configured to: Selecting one or more battery pack submodules from a plurality of battery pack submodules includes: Obtaining at least one voltage from each battery submodule; and selecting one or more battery submodules based at least in part on the obtained voltage; and Shut down those battery management systems in one or more selected battery pack submodules so that when (1) the multiple battery pack submodules are not providing power to the main load, and (2) the multiple battery pack submodules are not being charged, the battery management systems in one or more selected battery pack submodules do not, at least temporarily, consume power from the multiple batteries in the one or more selected battery pack submodules.

22. The system of claim 21, wherein: Selecting one or more battery submodules is based at least in part on a plurality of minimum battery voltages including a minimum battery voltage from each of the plurality of battery submodules.

23. The system of claim 21, wherein: Selecting one or more battery submodules is based at least in part on a plurality of maximum battery voltages including a maximum battery voltage from each of the plurality of battery submodules.

24. The system of claim 21, wherein: Select one or more battery pack submodules including: for each battery submodule in the plurality of battery submodules, comparing the minimum cell voltage to a voltage threshold to identify any battery submodule having a minimum cell voltage that does not exceed the voltage threshold; and One or more of those battery pack submodules are selected that have a minimum cell voltage that does not exceed a voltage threshold.

25. The system of claim 21, wherein: The controller is also configured to: determining an imbalance metric associated with a degree of imbalance between battery submodules in the plurality of battery submodules; determining whether the imbalance measure exceeds an imbalance threshold; and In response to determining that the imbalance metric exceeds the imbalance threshold: Perform pre-charge balancing, including by: Selecting one or more battery pack submodules from a plurality of battery pack submodules includes: Obtaining at least one voltage from each battery submodule; and selecting one or more battery submodules based at least in part on the obtained voltage; and shutting down those battery management systems in the one or more selected battery submodules so that the battery management systems in the one or more selected battery submodules do not, at least temporarily, consume power from the plurality of batteries in the one or more selected battery submodules when (1) the plurality of battery submodules are not providing power to the primary load, and (2) the plurality of battery submodules are not being charged; and After performing pre-charge balancing, the plurality of battery pack submodules are charged.

26. A method comprising: Selecting one or more battery pack submodules from a plurality of battery pack submodules includes: obtaining at least one voltage from each battery pack submodule; and One or more battery submodules are selected based at least in part on the obtained voltage, wherein: A plurality of battery submodules are electrically connected in series to provide power to a primary load; Each battery pack submodule includes a plurality of batteries electrically connected in series; and Each battery pack submodule also includes a battery management system that monitors the plurality of batteries in the battery pack submodule; and Shut down those battery management systems in one or more selected battery pack submodules so that when (1) the multiple battery pack submodules are not providing power to the main load, and (2) the multiple battery pack submodules are not being charged, the battery management systems in one or more selected battery pack submodules do not, at least temporarily, consume power from the multiple batteries in the one or more selected battery pack submodules.

27. The method according to claim 26, wherein: Selecting one or more battery submodules is based at least in part on a plurality of minimum battery voltages including a minimum battery voltage from each of the plurality of battery submodules.

28. The method according to claim 26, wherein: Selecting one or more battery submodules is based at least in part on a plurality of maximum battery voltages including a maximum battery voltage from each of the plurality of battery submodules.

29. The method according to claim 26, wherein: Select one or more battery pack submodules including: for each battery submodule in the plurality of battery submodules, comparing the minimum cell voltage to a voltage threshold to identify any battery submodule having a minimum cell voltage that does not exceed the voltage threshold; and One or more of those battery pack submodules are selected that have a minimum cell voltage that does not exceed a voltage threshold.

30. The method of claim 26, further comprising: determining an imbalance metric associated with a degree of imbalance between battery submodules in the plurality of battery submodules; determining whether the imbalance measure exceeds an imbalance threshold; and In response to determining that the imbalance metric exceeds the imbalance threshold: Perform pre-charge balancing, including by: Selecting one or more battery pack submodules from a plurality of battery pack submodules includes: Obtaining at least one voltage from each battery submodule; and selecting one or more battery submodules based at least in part on the obtained voltage; and shutting down those battery management systems in the one or more selected battery submodules so that the battery management systems in the one or more selected battery submodules do not, at least temporarily, consume power from the plurality of batteries in the one or more selected battery submodules when (1) the plurality of battery submodules are not providing power to the primary load, and (2) the plurality of battery submodules are not being charged; and After performing pre-charge balancing, the plurality of battery pack submodules are charged.

31. A computer program product implemented in a non-transitory computer readable storage medium and comprising computer instructions for: Selecting one or more battery pack submodules from a plurality of battery pack submodules includes: Obtaining at least one voltage from each battery submodule; and One or more battery submodules are selected based at least in part on the obtained voltage, wherein: A plurality of battery submodules are electrically connected in series to provide power to a primary load; Each battery pack submodule includes a plurality of batteries electrically connected in series; and Each battery pack submodule also includes a battery management system that monitors the plurality of batteries in the battery pack submodule; and Shut down those battery management systems in one or more selected battery pack submodules so that when (1) the multiple battery pack submodules are not providing power to the main load, and (2) the multiple battery pack submodules are not being charged, the battery management systems in one or more selected battery pack submodules do not, at least temporarily, consume power from the multiple batteries in the one or more selected battery pack submodules.

32. The computer program product of claim 31, wherein: Selecting one or more battery submodules is based at least in part on a plurality of minimum battery voltages including a minimum battery voltage from each of the plurality of battery submodules.

33. The computer program product of claim 31 , wherein: Selecting one or more battery submodules is based at least in part on a plurality of maximum battery voltages including a maximum battery voltage from each of the plurality of battery submodules.

34. The computer program product of claim 31 , wherein: Selecting one or more battery submodules includes: for each battery submodule in the plurality of battery submodules, comparing the minimum cell voltage to a voltage threshold to identify any battery submodule having a minimum cell voltage that does not exceed the voltage threshold; and One or more of those battery pack submodules are selected that have a minimum cell voltage that does not exceed a voltage threshold.

35. The computer program product of claim 31 , further comprising computer instructions for: determining an imbalance metric associated with a degree of imbalance between battery submodules in the plurality of battery submodules; determining whether the imbalance measure exceeds an imbalance threshold; and In response to determining that the imbalance metric exceeds the imbalance threshold: Perform pre-charge balancing, including by: Selecting one or more battery pack submodules from a plurality of battery pack submodules includes: Obtaining at least one voltage from each battery submodule; and selecting one or more battery submodules based at least in part on the obtained voltage; and shutting down those battery management systems in the one or more selected battery submodules so that the battery management systems in the one or more selected battery submodules do not, at least temporarily, consume power from the plurality of batteries in the one or more selected battery submodules when (1) the plurality of battery submodules are not providing power to the primary load, and (2) the plurality of battery submodules are not being charged; and After performing pre-charge balancing, the plurality of battery pack submodules are charged.

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