Low cost balance control of distributed low voltage systems supporting multiple low voltage buses

Abstract

A vehicle includes an electrical system for balancing a state of charge in a battery pack. An electrical system includes a plurality of module groups. The switch array includes a plurality of switches. Each switch is coupled to a respective group of modules. The switch may be in one of a first state in which the module group is connected to the first low voltage bus, a second state in which the module group is connected to the second low voltage bus, and a third state in which the module group is disconnected from both the first low voltage bus and the second low voltage bus. The array is placed in a first phase of an operational mode in which at least one switch is in one of a first state and a second state, and is cycled through the phase of the mode to balance charging between the plurality of module groups.

Description

Technical Field

[0001] The present disclosure relates to an electrical system in a vehicle, and in particular, to a system and method for balancing the state of charge between battery modules of a battery pack of the vehicle by controlling the configuration of switches between the battery pack and one or more low voltage loads of the vehicle. Background Art

[0002] An electric vehicle is operated using an electrical system having a battery pack. The battery pack includes a plurality of module groups, each module group having a plurality of battery modules. The battery pack provides power to both high voltage loads (such as motors, etc.) and low voltage loads (such as radios, dashboards, etc.). During operation, the state of charge of each module group may vary, resulting in deviations between the states of charge of the module groups of the battery pack. As the states of charge diverge, the operation of the electrical system degrades. Therefore, it is desirable to provide a system and method for balancing the states of charge between a plurality of module groups. Summary of the invention

[0003] In an exemplary embodiment, a method of balancing the state of charge between module groups of a battery pack of a vehicle is disclosed. For each module group, the module group is connected to a corresponding switch of a switch array, wherein the corresponding switch is configured to be in one of a first state, a second state, and a third state, wherein the module group is connected to a first low voltage bus, the module group is connected to a second low voltage bus, and the module group is disconnected from both the first low voltage bus and the second low voltage bus in the third state. The switch array is placed in a configuration in which at least one switch is in one of a first state and a second state, wherein the configuration defines a first stage of a mode of operation of the switch array. Cycling through the mode to balance the state of charge between the module groups.

[0004] In addition to one or more features described herein, the method also includes regulating the duration of the phase of the mode to passively balance the state of charge between the module groups.

[0005] In addition to one or more features described herein, the method also includes changing a mode of operation of the switch array.

[0006] In addition to one or more features described herein, a module stack includes a plurality of battery modules and further includes connecting each battery module of the module stack to a corresponding switch via a unidirectional direct current (DC / DC) converter.

[0007] In addition to one or more features described herein, wherein cycling through the pattern further comprises performing a cyclic permutation of a configuration of the switch array.

[0008] In addition to one or more features described herein, the respective switch is one of a single switch and a switch pair including a first switch for controlling connection to the first low voltage bus and a second switch for controlling connection to the second low voltage bus.

[0009] In addition to one or more features described herein, the module groups include at least three module groups.

[0010] In another exemplary embodiment, an electrical system for a vehicle is disclosed. The electrical system includes a plurality of module groups, a switch array, and a processor. The switch array includes a plurality of switches, each switch coupled to a module group in the plurality of module groups, and configured to be in one of a first state connecting the module group to a first low voltage bus, a second state connecting the module group to a second low voltage bus, and a third state in which the module group is disconnected from both the first low voltage bus and the second low voltage bus. The processor is configured to place the switch array in a configuration in which at least one switch is in one of a first state and a second state, wherein the configuration defines a first stage of a mode of operation of the switch array, and cycles through the mode to balance the state of charge between the plurality of module groups.

[0011] In addition to one or more features described herein, the processor is configured to adjust the duration of the phases of the mode to passively balance the state of charge between the module groups.

[0012] In addition to one or more features described herein, the processor is configured to change a mode of operation of the switch array.

[0013] In addition to one or more features described herein, the module stack includes a plurality of battery modules, each battery module of the module stack being connected to a corresponding switch via a unidirectional direct current (DC / DC) converter.

[0014] In addition to one or more features described herein, the processor is configured to cycle through the patterns by performing a cyclic permutation of a configuration of the switch array.

[0015] In addition to one or more features described herein, the respective switch is one of a single switch and a switch pair including a first switch for controlling connection to the first low voltage bus and a second switch for controlling connection to the second low voltage bus.

[0016] In addition to one or more features described herein, the plurality of module groups includes at least three module groups.

[0017] In yet another exemplary embodiment, a vehicle is disclosed. The vehicle includes a plurality of module groups, a switch array, and a processor. The switch array includes a plurality of switches, each switch coupled to a module group in the plurality of module groups, and configured to be in one of a first state connecting the module group to a first low voltage bus, a second state connecting the module group to a second low voltage bus, and a third state in which the module group is disconnected from both the first low voltage bus and the second low voltage bus. The processor is configured to place the switch array in a configuration in which at least one switch is in one of the first state and the second state, wherein the configuration defines a first stage of a mode of operation of the switch array and cycles through the mode to balance the state of charge between the plurality of module groups.

[0018] In addition to one or more of the features described herein, the processor is further configured to adjust phase durations of phases of the mode to passively balance the state of charge between the module groups.

[0019] In addition to one or more features described herein, the processor is configured to change a mode of operation of the switch array.

[0020] In addition to one or more features described herein, the module stack includes a plurality of battery modules, each battery module of the module stack being connected to a corresponding switch via a unidirectional direct current (DC / DC) converter.

[0021] In addition to one or more features described herein, the processor is configured to cycle through the patterns by performing a cyclic permutation of a configuration of the switch array.

[0022] In addition to one or more features described herein, the respective switch is one of a single switch and a switch pair including a first switch for controlling connection to the first low voltage bus and a second switch for controlling connection to the second low voltage bus.

[0023] The above features and advantages and other features and advantages of the present disclosure are apparent from the following detailed description when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Other features, advantages and details appear, by way of example only, from the following detailed description, which refers to the accompanying drawings, in which:

[0025] Figure 1 A vehicle according to an exemplary embodiment is shown;

[0026] Figure 2 A circuit diagram showing an electrical system of a vehicle in an illustrative embodiment;

[0027] Figure 3A high-level schematic diagram showing the power circuit of an electrical system;

[0028] Figure 4 For illustrative purposes, the P 1 P 1 P 2 Cycle through the stages of the pattern;

[0029] Figure 5 For illustrative purposes, the P 1 P 2 Cycle of the various stages of the X-mode;

[0030] Figure 6 is a graph of state of charge versus time;

[0031] Figure 7 is a graph of stage duration versus time;

[0032] Figure 8 is a graph of the number of modes over time; and

[0033] Fig. 9 is a graph of bus current versus time. DETAILED DESCRIPTION

[0034] The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate the same or corresponding parts and features.

[0035] According to an exemplary embodiment, Figure 1 An embodiment of a vehicle 10 is shown that includes a body 12 that at least partially defines an occupant compartment 14. The body 12 also supports various vehicle subsystems, including a propulsion system 16, as well as other subsystems for supporting the functions of the propulsion system 16 and other vehicle components, such as a braking subsystem, a suspension system, a steering subsystem, etc.

[0036] The vehicle 10 may be an electric vehicle (EV), a hybrid vehicle, or any other vehicle. In an embodiment, the vehicle 10 is an electric vehicle including a plurality of motors and / or a drive system. The vehicle 10 may be a car, a truck, a van, a bus, a motorcycle, or other types of vehicles. Any number of drive units may be included, such as one or more drive units for applying torque to the front wheels (not shown) and / or the rear wheels (not shown). The drive unit is controllable to operate the vehicle 10 in various operating modes, such as a normal mode, a high-performance mode (where additional torque is applied), an all-wheel drive ("AWD"), a front-wheel drive ("FWD"), a rear-wheel drive ("RWD"), etc.

[0037] For example, the propulsion system 16 is a multi-drive system, which includes a front drive unit 20 for driving the front wheels and a rear drive unit for driving the rear wheels. The front drive unit 20 includes a front motor 22 and a front inverter 24 (e.g., a front power inverter module or FPIM), as well as other components such as a cooling system. The left rear drive unit 30L includes a left rear motor 32L and a left rear inverter 34L. The right rear drive unit 30R includes a right rear motor 32R and a right rear inverter 34R. The front inverter 24, the left rear inverter 34L, and the right rear inverter 34R (e.g., a power inverter unit or PIM) each convert the direct current (DC) power from the high voltage (HV) battery system 40 into a multi-phase (e.g., two-phase, three-phase, six-phase, etc.) alternating current (AC) power to drive the front motor 22, the left rear motor 32L, and the right rear motor 32R.

[0038] like Figure 1 As shown, the drive system features a single motor. However, embodiments are not limited thereto. For example, instead of a single motor, multiple drives may be provided by a single machine having physically separate sets of windings.

[0039] Also like Figure 1 As shown, the drive system is configured so that the front motor 22 drives the front wheels (not shown), and the left rear motor 32L and the right rear motor 32R drive the rear wheels (not shown). However, the embodiments are not limited to this, as there can be any number of drive systems and / or motors at various locations (e.g., a motor driving each wheel, dual motors for each axle, etc.). In addition, the embodiments are not limited to dual drive systems, as the embodiments can be used with vehicles having any number of motors and / or power inverters.

[0040] In the propulsion system 16, the front drive unit 20, the left rear drive unit 30L, and the right rear drive unit 30R are electrically connected to a battery system 40. The battery system 40 may also be electrically connected to other electrical components (also referred to as "electrical loads"), such as vehicle electronics (e.g., via an auxiliary power module or APM 42), heaters, cooling systems, etc. The battery system 40 may be configured as a rechargeable energy storage system (RESS).

[0041] In one embodiment, the battery system 40 includes a plurality of individual battery assemblies, each of which can be charged independently and can be used to independently power one or more drive systems. For example, the battery system 40 includes a first battery assembly, such as a first battery pack 44 and a second battery pack 46 connected to the front inverter 24. The first battery pack 44 includes a plurality of battery modules 48, and the second battery pack 46 includes a plurality of battery modules 50. Each battery module 48, 50 includes a plurality of individual battery cells (not shown).

[0042] Each of the front motor 22 and the left rear motor 32L and the right rear motor 32R is a three-phase motor having a three-phase motor winding. However, the embodiments described herein are not limited thereto. For example, the motor may be any multi-phase machine supplied by a multi-phase inverter, and the drive unit may be implemented using a single machine having an independent winding set.

[0043] The battery system 40 and / or the propulsion system 16 include a switch system having various switch devices for controlling the operation of the first battery pack 44 and the second battery pack 46, and selectively connecting the first battery pack 44 and the second battery pack 46 to the front drive unit 20, the left rear drive unit 30L, and the right rear drive unit 30R. The switch device can also be operated to selectively connect the first battery pack 44 and the second battery pack 46 to the charging system. The charging system can be used to charge the first battery pack 44 and the second battery pack 46, and / or supply power from the first battery pack 44 and / or the second battery pack 46 to charge another energy storage system (e.g., vehicle-to-vehicle (V2V) and / or vehicle-to-everything (V2X) charging). The charging system includes one or more charging modules. For example, a first onboard charging module (OBCM) 52 is electrically connected to a charging port 54 for charging and charging from an AC system or device (such as a public AC power supply). A second OBCM 53 may be included for DC charging (e.g., DC fast charging or DCFC).

[0044] In an embodiment, the switch system includes a first switch device 60 and a second switch device 62, wherein the first switch device 60 selectively connects the first battery pack 44 to the front inverter 24, the left rear inverter 34L, and the right rear inverter 34R, and the second switch device 62 selectively connects the second battery pack 46 to the front inverter 24, the left rear inverter 34L, and the right rear inverter 34R. The switch system also includes a third switch device 64 (also referred to as a "battery switch device") for selectively connecting the first battery pack 44 to the second battery pack 46 in series.

[0045] Any of a variety of controllers may be used to control the functions of the vehicle's electrical system, including the battery system 40, the switch system, the drive unit, etc. The controller 65 includes any suitable processing device or unit, and may use an existing controller, such as a drive system controller, a RESS controller, and / or a controller in the drive system. For example, a controller 65 may be included to control the switch and drive control operations as discussed herein.

[0046] The controller 65 may include processing circuitry that may include an application specific integrated circuit (ASIC), electronic circuitry, a processor (shared, dedicated, or group) and memory executing one or more software or firmware programs, combinatorial logic circuitry, and / or other suitable components that provide the described functionality. According to one or more embodiments detailed herein, the controller 65 may include a non-transitory computer-readable medium storing instructions that, when processed by one or more processors of the controller 65, implement a method of balancing charging between various battery modules of a vehicle during operation of a low voltage load.

[0047] The vehicle 10 also includes a computer system 55 including one or more processing devices 56 and a user interface 58. The computer system 55 can communicate with the charging system controller, for example, to provide commands thereto in response to user input. The various processing devices, modules, and units can communicate with each other via a communication device or system, such as a controller area network (CAN) or a transmission control protocol (TCP) bus.

[0048] As shown herein, the vehicle 10 is an electric vehicle. In alternative embodiments, the vehicle 10 may be an internal combustion vehicle fueled by gasoline, diesel, etc., a hybrid vehicle partially or fully powered by electricity, etc.

[0049] As described herein, the vehicle may include one or more electrical loads powered by one or more batteries. Exemplary loads include, but are not limited to, motors, lights, infotainment devices, electronic control units, climate control systems, and the like. The electrical loads may be high voltage loads or low voltage loads, and the battery system 40 (e.g., one or more of the first battery pack 44 and the second battery pack 46) may provide a high voltage to the high voltage loads and a low voltage to the low voltage loads. According to one or more embodiments described herein, the high voltage may refer to, but is not limited to, 100 volts, 250 volts, 400 volts, 500 volts, 650 volts, 800 volts, 1000 volts, and the like. The low voltage may refer to, but is not limited to, 12V, 48V, and the like. To support these low voltage loads, the vehicle 10 may include at least one DC / DC converter to convert DC power from a higher voltage to a lower voltage, as disclosed herein.

[0050] Figure 2A circuit diagram of an electrical system 200 of a vehicle 10 in an illustrative embodiment is shown. The electrical system 200 includes a grid system 202, a power circuit 204, a switch array 206, and a control circuit 208. The grid system 202 includes various low-voltage loads of the vehicle 10. The power circuit 204 includes various electrical components for providing power to the low-voltage loads. The switch array 206 includes switches that control the connection between the electrical components of the power circuit 204 and the low-voltage loads of the grid system 202. As disclosed herein, the switch array 206 can also be used to balance the charge between the electrical components of the power circuit 204. The control circuit 208 can be a processor that operates one or more algorithms for controlling the operation of the electrical components of the switch array 206.

[0051] For illustrative purposes, the power grid system 202 includes a first low voltage power grid 210 and a second low voltage power grid 212. In other embodiments, more than two voltage power grids may be included in the power grid system 202. The first low voltage power grid 210 includes a first low voltage load 214 and a first load regulator 216. The second low voltage power grid 212 includes a second low voltage load 218 and a second load regulator 220.

[0052] The power circuit 204 includes a battery pack 222 and a DC converter array 224. The battery pack 222 includes a plurality of module groups 226a, 226b, 226c. Each module group 226a, 226b, 226c includes a plurality of battery modules. For illustrative purposes, a first module group 226a, a second module group 226b, and a third module group 226c are shown. However, it should be understood that in various embodiments, any plurality of module groups may be included in the battery pack 222. The module groups 226a, 226b, 226c are wired in series with each other along a high-voltage bus 228. Each module group 226a, 226b, 226c includes an associated module balancing controller 230a, 230b, 230c. Each module balancing controller (e.g., module balancing controller 230a) is used to balance the state of charge (SOC) between the battery modules of the associated module group (e.g., module group 226a). The module balancing controllers 230a, 230b, 230c may receive a signal indicating the first load regulator current (i reg LV1 ), the second load regulator current (i reg LV2 ) and a feedback signal of the estimated state of charge.

[0053] The DC converter array 224 includes DC converter groups 232a, 232b, 232c. Each DC converter group is associated with a corresponding module group. (For example, the first DC converter group 232a is associated with the first module group 226a). Each DC converter group includes a plurality of DC / DC converters (such as DC converters 234a, 234b, 234c), wherein the primary end of each DC / DC converter is coupled to a corresponding module of the associated module group (for example, module group 226a). Each DC / DC converter is a unidirectional converter.

[0054] The switch array 206 includes a plurality of switch groups 236a, 236b, 236c. Each switch group is associated with a corresponding DC converter group. For example, the switch group 236a is connected to the secondary side of the DC converter group 232a. The switch group may include a plurality of switches. For example, the first switch group 236a includes a first switch 238a (U 1 ) and the second switch 238b (Z 1 ). The first switch U 1 Controls the connection between the first DC converter group 226a and the first low-voltage grid 210. The second switch Z 1 The connection between the first DC converter group 226 a and the second low-voltage grid 212 is controlled.

[0055] The first switch U 1 and the second switch Z 1 can be placed in several configurations. In a first configuration, the first switch U 1 is in the on state, and the second switch Z 1 In the second configuration, the first switch U is in the disconnected state, thereby connecting the first module group to the first low-voltage grid 210, wherein the second low-voltage grid 212 is disconnected from the first module group. 1 is in the off state, and the second switch Z 1 In the third configuration, the first switch U is in the on state, thereby connecting the first module group 226a to the second low-voltage grid 212, wherein the first low-voltage grid 210 is disconnected from the first module group. 1 and the second switch Z 1 The first switch U is in the disconnected state, thereby disconnecting the first module group 226a from the first low-voltage power grid 210 and the second low-voltage power grid 212. When the balancing controller algorithm disclosed in this article is enabled, the first switch U 1 and the second switch Z 1 A similar configuration can be used for the switches U of the second switch group 236b. 2 and Z 2 and the switch U of the third switch group 236c 3 and Z 3 .

[0056] Control circuit 208 operates SOC balancing control algorithm 240, SOC estimation algorithm 242, and mode determination algorithm 244. SOC balancing algorithm 240 controls the configuration of switches of switch array 206 (ie, switches of first switch group 236a, second switch group 236b, and third switch group 236c).

[0057] The state of charge estimation algorithm 242 receives data from sensors that can measure current, voltage, and temperature at a module group or at individual battery modules within a module group. The state of charge estimation algorithm 242 can provide a state of charge value to a module balancing controller of the selected module group (i.e., the module balancing controller 230a of the first module group 226a), which performs actions to balance the charge between the battery modules of the selected module group. The state of charge estimation algorithm 242 can also provide the state of charge value to the charge balancing control algorithm 240, which controls the configuration of the switch array 206 based on the state of charge value.

[0058] The mode determination algorithm 240 receives input regarding the requirements of the low voltage load and outputs an operating mode and mode duration that can be used at the charge balancing algorithm 240 to control the configuration of the switch array 206. Figure 3 and Table 1 describe further discussion of the operating modes and mode durations.

[0059] Figure 3 Shows Figure 2 2 is a high-level schematic diagram 300 of the power circuit 204 of FIG. The high-level schematic diagram 300 shows the module groups 226a, 226b, 226c, the associated DC converter groups 232a, 232b, 232c and the associated switches 302a, 302b, 302c ( Figure 2 236a, 236b, 236c are equivalent representations of the switch groups 236a, 236b, 236c of the first module group 226a). For illustrative purposes, four battery modules 304a, 304b, 304c, 304d of the first module group 226a are shown. In various embodiments, any number of modules may be included in the module group. The switch groups 236a, 236b, 236c are each depicted as a single switch, which has the ability to be connected to the first low-voltage bus 306 associated with the first low-voltage power grid 210, to the second low-voltage bus 308 associated with the second low-voltage power grid 212, or to be in a neutral or disconnected state. For illustrative purposes, the first switch 302a is depicted as being connected to the first low-voltage bus 306 and is therefore in a state referred to as P 1 The second switch 302b is depicted as being connected to the second low voltage bus 308 and is therefore in a state referred to as P 2The third switch 302c is depicted as being disconnected from both the first low voltage bus 306 and the second low voltage bus 308 and is therefore in a state referred to as an X state. As a unit, the array including the first switch 302a, the second switch 302b, and the third switch 302c is referred to as a P state. 1 P 2 X-mode operation.

[0060] The switch mode consists of various stages that are executed in sequence. Each stage consists of switches in a specific configuration (e.g., P 1 P 2 X). Each stage is related to the previous stage by a cyclic permutation of the switch states. For example, Figure 3 The switch configuration shown (i.e., P 1 P 2 X) defines the first stage of the pattern. Therefore, the second stage includes 1 P 2 configured switches, and the third stage consists of a P 2 XP 1 The operation of this mode includes cycling from the first stage to the second stage to the third stage and then back to the first stage. The duration of the mode and the duration of the stage can be controlled by the mode determination algorithm 244.

[0061] Table 1 shows various patterns of switches and their associated phases. The state of charge balancing control algorithm 240 controls the configuration of the switch array 206 and adjusts the duration of each phase to balance the state of charge of the module groups.

[0062] Table 1

[0063] model# Phase 1 Phase 2 Phase 3 1 XXX XXX XXX 2 <![CDATA[XXP 1 ]]> <![CDATA[P 1 XX]]> <![CDATA[XP 1 X]]> 3 <![CDATA[XXP 2 ]]> <![CDATA[P 2 XX]]> <![CDATA[XP 2 X]]> 4 <![CDATA[XP 1 P 1 ]]> <![CDATA[P 1 XP 1 ]]> <![CDATA[P 1 P 1 X <!-- 6 -->]]> 5 <![CDATA[XP 2 P 2 ]]> <![CDATA[P 2 XP 2 ]]> <![CDATA[P 2 P 2 X]]> 6 <![CDATA[XP 1 P 2 ]]> <![CDATA[P 2 XP 1 ]]> <![CDATA[P 1 P 2 X]]> 7 <![CDATA[P 1 P 1 P 2 ]]> <![CDATA[P 2 P 1 P 1 ]]> <![CDATA[P 1 P 2 P 1 ]]> 8 <![CDATA[P 1 P 2 P 2 ]]> <![CDATA[P 2 P 1 P 2 ]]> <![CDATA[P 2 P 2 P 1 ]]> 9 <![CDATA[P 1 P 1 P 1 ]]> <![CDATA[P 1 P 1 P 1 ]]> <![CDATA[P 1 P 1 P 1 ]]> 10 <![CDATA[P 2 P 2 P 2 ]]> <![CDATA[P 2 P 2 P 2 ]]> <![CDATA[P 2 P 2 P 2 ]]>

[0064] For illustrative purposes, Figure 4 Depicted by P 1 P 1 P 2 The cycle 400 includes a first phase 402 (P 1 P 1 P 2 ), the second stage 404 (P 2 P 1 P 1 ) and Phase III 406 (P 1 P 2 P 1). In the first phase 402, the first module group 226a and the second module group 226b are both connected to the same bus (i.e., the first low-voltage bus 306), thereby allowing charge transfer and thus charge balancing between the first module group and the second module group. Similarly, in the second phase, the second module group 226b and the third module group 226c are both connected to the same bus (i.e., the first low-voltage bus 306), thereby allowing charge transfer and thus charge balancing between the second module group and the third module group. In the third phase, the third module group 226c and the first module group 226a are both connected to the same bus (i.e., the first low-voltage bus 306), thereby allowing charge transfer, thereby allowing charge balancing between the third module group and the first module group. Cycle through P 1 P 1 P 2 The modes regulate the distribution of power to the first low voltage bus 306 and the second low voltage bus 308 .

[0065] For illustrative purposes, Figure 5 Depicted by P 1 P 2 The cycle 500 of the phases of the X mode. The cycle 500 includes a first phase 502 (P 1 P 2 X), the second stage 504 (XP 1 P 2 ) and Phase III 506 (P 2 XP 1 ). In the first phase 502, the first module group 226a is connected to the first low voltage bus 306, and the second module group 226b is connected to the second low voltage bus 308. The third module group 226c is not connected to either bus. In the second phase, the second module group 226b is connected to the first low voltage bus 306, and the third module group 226c is connected to the second low voltage bus 308. The first module group 226a is not connected to either bus. In the third phase, the third module group 226c is connected to the first low voltage bus 306, and the first module group 226a is connected to the second low voltage bus 308. The second module group 226b is not connected to either bus. The cycle passes through P 1 P 2 The X-mode provides equal power to the first low voltage bus 306 and the second low voltage bus 308 .

[0066] Figure 66 is a graph of state of charge versus time. Time is shown in seconds along the abscissa and SOC is shown along the ordinate axis, where a value of SOC=1 refers to a fully charged module and SOC=0 is a fully discharged module. The SOCs of the modules are initially balanced (i.e., the same SOC at time t=5500 seconds). The modules are operated with equal stage durations until time t=0. Over time, the SOCs of the modules diverge, as shown by the divergence between the first SOC 602 of the first module group 226a, the second SOC 604 of the second module group 226b, and the third SOC 606 of the third module group 226c. At time t=0, the modified balancing operation disclosed herein is achieved. The first SOC 602, the second SOC 604, and the third SOC 606 quickly converge to the same value (i.e., within about 100 seconds).

[0067] Figure 7 700 is a graph of stage duration versus time. Time is shown in seconds along the abscissa, and stage duration is shown as a normalized value along the ordinate axis. From t=-5500 seconds to t=0 seconds, the duration of the stage is the same value (e.g., about 0.4). At time t=0, the duration of the stage is changed to induce equilibrium between the modules, as shown by first stage duration 702, second stage duration 704, and third stage duration 706.

[0068] Figure 8 is a graph 800 of mode number versus time. Time is shown in seconds along the abscissa and mode number is shown along the ordinate (see column 1 of Table 1). Curve 802 shows the mode number at a given time and indicates transitions between modes as appropriate.

[0069] Fig. 9 900 is a graph of bus current over time. Time is shown in seconds along the abscissa and current is shown along the ordinate axis. Curve 902 shows the current along the first low voltage bus 306 (P1), and curve 904 shows the current along the second low voltage bus 308 (P2).

[0070] The terms "one" and "an" do not indicate a limitation of quantity, but rather indicate the presence of at least one of the referenced item. Unless the context clearly indicates otherwise, the term "or" means "and / or". References to "aspects" throughout the specification mean that a particular element (e.g., a feature, structure, step, or characteristic) described in conjunction with that aspect is included in at least one aspect described herein, and may or may not be present in other aspects. In addition, it should be understood that the described elements may be combined in any suitable manner in the various aspects.

[0071] When an element such as a layer, film, region, or substrate is referred to as being "on" another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" another element, there are no intervening elements present.

[0072] Unless otherwise indicated herein, all test standards are the most current standards in effect as of the filing date of this application or, if priority is claimed, the filing date of the earliest priority application in which the test standards appear.

[0073] Unless defined otherwise, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0074] Although the above disclosure has been described with reference to exemplary embodiments, it will be appreciated by those skilled in the art that various changes may be made and equivalents may be substituted for its elements without departing from its scope. In addition, many modifications may be made to adapt specific circumstances or materials to the teachings of the disclosure without departing from the basic scope of the disclosure. Therefore, it is intended that the disclosure is not limited to the specific embodiments disclosed, but will include all embodiments falling within its scope.

Claims

1. A method for balancing the state of charge between module groups of a battery pack of a vehicle, comprising: For each module group, connecting the module group to a corresponding switch of the switch array, wherein the corresponding switch is configured to be in one of a first state in which the module group is connected to a first low-voltage bus, a second state in which the module group is connected to a second low-voltage bus, and a third state in which the module group is disconnected from both the first low-voltage bus and the second low-voltage bus; placing the switch array into a configuration in which at least one switch is in one of the first state and the second state, wherein the configuration defines a first phase of a mode of operation of the switch array; and Cycling through the modes balances the state of charge between the groups of modules. 2 . The method of claim 1 , further comprising adjusting the duration of the phases of the mode to passively balance the state of charge between the module groups. 3 . The method of claim 1 , further comprising changing a mode of operation of the switch array.

4. The method according to claim 1, wherein: The module group includes a plurality of battery modules and further includes connecting each battery module of the module group to a corresponding switch via a unidirectional direct current (DC / DC) converter.

5. The method according to claim 1, wherein: The respective switch is one of: (i) a single switch; and (ii) a switch pair including a first switch for controlling a connection to a first low voltage bus and a second switch for controlling a connection to a second low voltage bus.

6. An electrical system for a vehicle, comprising: Multiple module groups; a switch array, the switch array comprising a plurality of switches, each switch coupled to a module group of the plurality of module groups and configured to be in one of a first state connecting the module group to a first low-voltage bus, a second state connecting the module group to a second low-voltage bus, and a third state disconnecting the module group from both the first low-voltage bus and the second low-voltage bus; as well as A processor configured to: placing the switch array into a configuration in which at least one switch is in one of the first state and the second state, wherein the configuration defines a first phase of a mode of operation of the switch array; as well as Cycling through the modes balances the state of charge among the plurality of module groups.

7. The electrical system according to claim 6, wherein: The processor is further configured to adjust the duration of the phases of the mode to passively balance the state of charge between the module groups.

8. The electrical system according to claim 6, wherein: The processor is also configured to change a mode of operation of the switch array.

9. The electrical system according to claim 6, wherein: The module group includes a plurality of battery modules, each battery module of the module group being connected to a corresponding switch via a unidirectional direct current (DC / DC) converter.

10. The electrical system of claim 6, wherein: The respective switch is one of: (i) a single switch; and (ii) a switch pair including a first switch for controlling a connection to a first low voltage bus and a second switch for controlling a connection to a second low voltage bus.

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