Balancing control for distributed low voltage systems with bidirectional converters

Abstract

A vehicle includes a battery pack and performs a method of balancing an electric quantity in the battery pack. The battery pack includes a first module group coupled to a first low voltage bus, a second module group coupled to a switch, a third module group coupled to a second low voltage bus, and a processor. The processor is configured to couple the second module group to the first low voltage bus via the switch in a first configuration during a first phase of the cycle to transfer power between the first module group and the second module group, and to couple the second module group to the second low voltage bus via the switch in a second configuration during a second phase of the cycle to transfer power between the first module group and the second module group. Therefore, electric quantity is transferred between the second module group and the third module group, so that the electric quantity in the battery pack is balanced.

Description

Technical Field

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

[0002] Electric vehicles operate using an electrical system having a battery pack. The battery pack includes a plurality of module groups, each module group having battery modules. The battery pack supplies power to both high-voltage loads (such as a motor, etc.) and low-voltage loads (such as a radio, dashboard, etc.). During vehicle operation, the state of charge of each module group can vary, resulting in a deviation 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. Accordingly, it is desirable to provide a system and method for balancing the state of charge between multiple module groups. Summary of the Invention

[0003] In one exemplary embodiment, a method for balancing the charge in a battery pack is disclosed. A first module group is coupled to a first low-voltage bus. A second module group is coupled to a switch. A third module group is coupled to a second low-voltage bus. The second module group is coupled to the first low-voltage bus via the switch in a first configuration during a first phase of a cycle to transfer charge between the first module group and the second module group. The second module group is coupled to the second low-voltage bus via the switch in a second configuration during a second phase of the cycle to transfer charge between the second module group and the third module group, thereby balancing the charge in the battery pack.

[0004] In addition to one or more of the features described herein, the method further includes determining a balancing current for transferring charge by minimizing a cost function that includes the sum of the squares of the charge differences over a finite cycle horizon and the sum of the squares of the balancing currents.

[0005] In addition to one or more of the features described herein, the method further includes determining a balancing current that minimizes the impact of the balancing module group on at least one of a first low-voltage load on the first low-voltage bus and a second low-voltage load on the second low-voltage bus.

[0006] In addition to one or more of the features described herein, the method further includes imposing constraints on the cost function and updating the constraints for each cycle.

[0007] In addition to one or more of the features described herein, the first module group includes a first plurality of module groups, and the third module group includes a second plurality of module groups.

[0008] In addition to one or more features described herein, the number of module groups in the first plurality of module groups is based on the power level in the low voltage bus coupled to the module group.

[0009] In addition to one or more features described herein, the period of the cycle is fixed.

[0010] In another exemplary embodiment, a battery pack for a vehicle is disclosed. The battery pack includes a first module group coupled to a first low voltage bus, a second module group coupled to a switch, a third module group coupled to a second low voltage bus, and a processor. The processor is configured to couple the second module group to the first low voltage bus via the switch in a first configuration during a first phase of the cycle to transfer electrical energy between the first module group and the second module group, and to couple the second module group to the second low voltage bus via the switch in a second configuration during a second phase of the cycle to transfer electrical energy between the second module group and the third module group, thereby balancing the electrical energy in the battery pack.

[0011] In addition to one or more features described herein, the processor is further configured to determine a balancing current for transferring the electrical energy by minimizing a cost function that includes the sum of the squares of the electrical energy differences over a finite cycle range and the sum of the squares of the balancing currents.

[0012] In addition to one or more features described herein, the processor is further configured to determine a balancing current to minimize the effect of the balancing module on at least one of a first low voltage load on the first low voltage bus and a second low voltage load on the second low voltage bus.

[0013] In addition to one or more features described herein, the processor is further configured to impose constraints on the cost function and update the constraints for each cycle.

[0014] In addition to one or more features described herein, the first module group includes a first plurality of module groups, and the third module group includes a second plurality of module groups.

[0015] In addition to one or more features described herein, the number of module groups in the first plurality of module groups is based on the power level in the low voltage bus coupled to the module group.

[0016] In addition to one or more features described herein, the period of the cycle is fixed.

[0017] In yet another exemplary embodiment, a vehicle is disclosed. The vehicle includes a battery pack and a processor. The battery pack includes a first module group coupled to a first low voltage bus, a second module group coupled to a switch, and a third module group coupled to a second low voltage bus. The processor is configured to couple the second module group to the first low voltage bus via the switch in a first configuration during a first stage of a cycle to transfer electrical energy between the first module group and the second module group, and to couple the second module group to the second low voltage bus via the switch in a second configuration during a second stage of the cycle to transfer electrical energy between the second module group and the third module group, thereby balancing the electrical energy in the battery pack.

[0018] In addition to one or more of the features described herein, the processor is further configured to determine a balancing current for transferring electrical energy by minimizing a cost function that includes the sum of squares of electrical energy differences over a finite cycle range and the sum of squares of the balancing current.

[0019] In addition to one or more of the features described herein, the processor is further configured to determine a balancing current that minimizes the impact on at least one of a first low voltage load on the first low voltage bus and a second low voltage load on the second low voltage bus of a balancing module group.

[0020] In addition to one or more of the features described herein, the processor is further configured to impose constraints on the cost function and update the constraints for each cycle.

[0021] In addition to one or more of the features described herein, the first module group includes a first plurality of module groups, and the third module group includes a second plurality of module groups.

[0022] In addition to one or more of the features described herein, the number of module groups in the first plurality of module groups is based on the power level in the low voltage bus coupled to the module group.

[0023] The above features and advantages of the present disclosure, as well as other features and advantages, 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 only by way of example in the following detailed description, which refers to the accompanying drawings, in which:

[0025] Figure 1 An embodiment of a vehicle according to an exemplary embodiment is shown;

[0026] Figure 2 A high-level schematic diagram of an electric drive system of the vehicle is shown;

[0027] Figure 3Shows a detailed circuit diagram of the electrical system of a vehicle in an illustrative embodiment;

[0028] Figure 4 Shows the switching cycle of the electrical system in one embodiment;

[0029] Figure 5 Is a graph of the state of charge over time;

[0030] Figure 6 Shows a graph of the module current over time;

[0031] Figure 7 Shows a graph of the balancing current over time; and

[0032] Figure 8 Shows a graph of the regulator current over time. DETAILED DESCRIPTION

[0033] 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 denote the same or corresponding components and features.

[0034] According to an exemplary embodiment, Figure 1 Shows an embodiment of a vehicle 10 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, and 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, and the like.

[0035] The vehicle 10 can be an electric vehicle (EV), a hybrid vehicle, or any other vehicle. In one embodiment, the vehicle 10 is an electric vehicle that includes multiple motors and / or drive systems. The vehicle 10 can be a car, a truck, a van, a bus, a motorcycle, or other type of motor vehicle. Any number of drive units can 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 units are controllable to operate the vehicle 10 in various operating modes, such as a normal mode, a high-performance mode (where additional torque is applied), all-wheel drive (“AWD”), front-wheel drive (“FWD”), rear-wheel drive (“RWD”), and the like.

[0036] For example, the propulsion system 16 is a multi-drive system that 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 electric 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 electric motor 32L and a left rear inverter 34L. The right rear drive unit 30R includes a right rear electric 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., power inverter units or PIMs) each convert direct current (DC) power from a high voltage (HV) battery system 40 into polyphase (e.g., two-phase, three-phase, six-phase, etc.) alternating current (AC) power to drive the front electric motor 22, the left rear electric motor 32L, and the right rear electric motor 32R.

[0037] As Figure 1 shown, the drive system features separate electric motors. However, the embodiments are not limited thereto. For example, instead of separate motors, multiple drives can be provided by a single machine having physically independent multiple sets of windings.

[0038] Also as Figure 1 shown, the drive system is configured such that the front electric motor 22 drives the front wheels (not shown), and the left rear electric motor 32L and the right rear electric motor 32R drive the rear wheels (not shown). However, the embodiments are not limited thereto, as any number of drive systems and / or motors can be present at various locations (e.g., motors driving each wheel, dual motors for each axle, etc.). Additionally, 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.

[0039] 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 the battery system 40. The battery system 40 can 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 can be configured as a rechargeable energy storage system (RESS).

[0040] In one embodiment, the battery system 40 includes a plurality of separate battery components, where each battery component can be independently charged and can be used to independently power one or more drive systems. For example, the battery system 40 includes a first battery component, such as a first battery pack 44 connected to the front inverter 24, and a second battery pack 46. 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).

[0041] Each of the front electric motor 22, the left rear electric motor 32L, and the right rear electric 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 can be any polyphase machine supplied by a polyphase inverter, and the drive unit can be implemented using a single machine having independent sets of windings.

[0042] The battery system 40 and / or the propulsion system 16 includes a switching system having various switching 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 switching devices 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, the first on-board charging module (OBCM) 52 is electrically connected to the charging port 54 for charging from and charging to an AC system or device (such as a utility AC power supply). A second OBCM 53 can be included for DC charging (e.g., DC fast charging or DCFC).

[0043] In one embodiment, the switching system includes a first switching device 60 and a second switching device 62. The first switching 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. The second switching 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 switching system further includes a third switching device 64 (also referred to as a "battery switching device") for selectively connecting the first battery pack 44 in series with the second battery pack 46.

[0044] Any of a variety of controllers can be used to control the functions of the vehicle's electrical system, including the battery system 40, the switching system, the drive unit, etc. The controller 65 includes any suitable processing device or unit and can use existing controllers, such as a drive system controller, a RESS controller, and / or a controller in the drive system. For example, a controller 65 can be included for controlling the switching and drive control operations as discussed herein.

[0045] The controller 65 may include processing circuitry, which may include an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or grouped) that executes one or more software or firmware programs, and memory, combinational 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 the power among various battery modules of the vehicle during operation of a low-voltage load.

[0046] The vehicle 10 further includes a computer system 55 that includes one or more processing devices 56 and a user interface 58. The computer system 55 may communicate with the charging system controller, for example, to provide commands thereto in response to user input. The various processing devices, modules, and units may communicate with each other via a communication device or system, such as a controller area network (CAN) or a transmission control protocol (TCP) bus.

[0047] As shown herein, the vehicle 10 is an electric vehicle. In alternative embodiments, the vehicle 10 may be an internal combustion engine vehicle fueled by gasoline, diesel, etc., a hybrid vehicle powered in part or in whole by electricity, etc.

[0048] 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, etc. The electrical load may be a high-voltage load or a low-voltage load, and the battery system 40 (e.g., one or more of the first battery pack 44 and the second battery pack 46) may provide high voltage to the high-voltage load and low voltage to the low-voltage load. According to one or more embodiments described herein, high voltage may refer to, but is not limited to, 100 volts, 250 volts, 400 volts, 500 volts, 650 volts, 800 volts, 1000 volts, etc. Low voltage may refer to, but is not limited to, 12V, 48V, etc. 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.

[0049] Figure 2Shows a high - level schematic diagram 200 of the electric drive system of vehicle 10. The high - level schematic diagram 200 shows a battery pack 202, a DC converter array 204, and a low - voltage power grid 206. The battery pack 202 has a plurality of module groups 208a, 208b, 208c arranged in series along a high - voltage bus (HV bus 210). Each module group 208a, 208b, 208c includes a plurality of battery modules (not shown). The DC converter array 204 includes a plurality of DC / DC converters 212a, 212b, 212c. For illustrative purposes, three module groups are shown. The DC / DC converters can be bidirectional converters.

[0050] Each DC / DC converter is connected across the corresponding module group of the battery pack 202. For example, the first DC / DC converter 212a is connected across the first module group 208a, the second DC / DC converter 212b is connected across the second module group 208b, and the third DC / DC converter 212c is connected across the third module group 208c. The first wire 224 connects the positive terminal of the first DC / DC converter 212a to the HV bus 210 at the outer end of the first module group 208a. The second wire 226 connects the negative terminal of the first DC / DC converter 212a and the positive terminal of the second DC / DC converter 212b to the HV bus 210 between the first module group 208a and the second module group 208b. The third wire 228 connects the negative terminal of the second DC / DC converter 212b and the positive terminal of the third DC / DC converter 212c to the HV bus 210 between the second module group 208b and the third module group 208c. The fourth wire 230 connects the negative terminal of the third DC / DC converter 212c to the HV bus 210 at the outer end of the third module group 208c.

[0051] The low - voltage power grid 206 includes a first low - voltage bus 214, a second low - voltage bus 216, and a switch 218. The first low - voltage bus 214 includes a first low - voltage load 220, and the second low - voltage bus 216 includes a second low - voltage load 222. The first low - voltage load 220 is electrically connected to the first module group 208a via the first low - voltage bus 214 and the first DC / DC converter 212a. The second low - voltage load 222 is electrically connected to the third module group 208c via the second low - voltage bus 216 and the third DC / DC converter 212c.

[0052] The fixed terminal 217 of switch 218 is connected to the second module group 208b via the second DC / DC converter 212b. The configurable terminal of switch 218 can be placed in a first configuration or a second configuration. In the first configuration, the second module group 208b is electrically connected to the first low-voltage bus 214 and, thus, is also electrically connected to the first module group 208a via the DC / DC converter 212a. This configuration allows a first transfer current to flow between the first module group 208a and the second module group 208b. If the first electrical quantity on the first module group 208a is different from the second electrical quantity of the second module group 208b, then this first transfer current allows the transfer of electrical quantity between the first module group and the second module group to balance the first electrical quantity and the second electrical quantity.

[0053] In the second configuration, the second module group 208b is electrically connected to the second low-voltage bus 216 and, thus, is electrically connected to the third module group 208c via the DC / DC converter 212c. This configuration allows a second transfer current to flow between the second module group 208b and the third module group 208c. If the second electrical quantity on the second module group 208b is different from the third electrical quantity of the third module group 208c, then this second transfer current allows the transfer of electrical quantity between the second module group and the third module group to balance the second electrical quantity and the third electrical quantity.

[0054] By flipping the switch 218 between the first configuration and the second configuration, the electrical quantity can be balanced among all the module groups.

[0055] It should be understood that in an alternative embodiment, the low-voltage power grid 206 may include more than two low-voltage buses (and low-voltage loads), and each low-voltage bus is associated with a module group for supplying power to the low-voltage load. Since one module group (e.g., the second module 208b) acts as a buffer module for transferring electrical quantity, the number of modules is one more than the number of low-voltage buses. In another embodiment, the first module group 208a may represent a first plurality of module groups, and the third module group 208c may represent a second plurality of module groups. The second module group 208b may act as a buffer module group for transferring electrical quantity between the first plurality of module groups and the second plurality of module groups via a switch. The number of module groups in the plurality of module groups may be based on the power level in the low-voltage buses connected to the module groups.

[0056] Figure 3 A detailed circuit diagram 300 of the electrical system of the vehicle 10 in an illustrative embodiment is shown. The detailed circuit diagram 300 includes a battery pack 202, a DC / DC converter array 204, and a low-voltage power grid 206.

[0057] For illustrative purposes, the low - voltage power grid 206 includes a first low - voltage power grid 302 and a second low - voltage power grid 304. The first low - voltage power grid 302 includes a first low - voltage load 220 and a first load regulator 306. A first load current i LV1 flows through the first low - voltage load 220. The first load regulator 306 outputs a first regulator current i reg LV1 for the DC / DC converter to regulate the voltage of the first low - voltage power grid 302. The second low - voltage power grid 304 includes a second low - voltage load 222 and a second load regulator 308. A second load current i LV2 flows through the second low - voltage load 222. The second load regulator 308 outputs a second regulator current i reg LV2 for the DC / DC converter to regulate the voltage of the second low - voltage power grid 304.

[0058] The battery pack 202 includes a plurality of module balance controllers 310a, 310b, 310c. Each module balance controller is associated with a corresponding module group (i.e., the module balance controller 310a is associated with the module group 208a). Each module balance controller is used to balance the state of charge (SOC) between the battery modules of its associated module. The module balance controllers 310a, 310b, 310c receive feedback signals indicating the first load regulator current (i reg LV1 ), the second load regulator current (i reg LV2 ) and the state of charge estimate, and balance the battery modules based on these signals, as disclosed herein.

[0059] The detailed circuit diagram 300 further depicts a control circuit 314 that controls the operation of the electrical system and specifically controls the operation of the switch 218. The control circuit 314 can be a processor that operates one or more algorithms (such as a balance control algorithm 316 and a state of charge estimation algorithm 318). The balance control algorithm 316 outputs a signal for controlling the configuration of the switch 218. In particular, the balance control algorithm 316 sends a signal that causes the switch 218 to flip between a first configuration and a second configuration. The switching occurs over a fixed time period (dT) and thus occurs at a fixed frequency (1 / dT).

[0060] The balance control algorithm 316 can also output a desired current that can be used as feedback for balancing the charge, as disclosed herein. The balance control algorithm 316 outputs commands for the balancing currents i i1 and i i21 to a first summing circuit 320. The first summing circuit 320 sums these currents with the first load regulator current (i regLV1 ) are added together, and the sum is sent to the module balancing controllers 310a, 310b, 310c. Similarly, the balancing control algorithm 316 will be used to balance the current i i3 and i i22 The command to balance the current is output to the second summing circuit 322. The second summing circuit 322 adds these currents to the second load regulator current (i reg LV2 ) and sends the sum to the module balancing controllers 310a, 310b, 310c.

[0061] The state of charge estimation algorithm 318 receives data from sensors that can measure the current at the module groups 208a, 208b, 208c or at individual battery modules within the module groups. The state of charge estimation algorithm 318 determines the state of charge based on these currents and outputs the state of charge value to the module balancing controllers 310a, 310b, 310c and the balancing control algorithm 316. Each module balancing controller 310a, 310b, 310c balances the state of charge between the battery modules of the selected module group. The balancing control algorithm 316 controls the configuration of the switch 218 based on the state of charge value.

[0062] Figure 4 Shows the switching cycle 400 of the electrical system in one embodiment. The switching cycle 400 includes a first stage 402 and a second stage 404. The first stage 402 shows the electrical system where the switch 218 connects the first module group 208a and the second module group 208b via the first low voltage bus 214. The second stage 404 shows the electrical system where the switch 218 connects the second module group 208b and the third module group 208c via the second low voltage bus 216. The electrical system cycles back and forth between the first stage 402 and the second stage 404 at a frequency of 1 / dT, where the electrical system lasts for half of the period (0.5*dT) in the first stage 402 and for half of the period (0.5*dT) in the second stage 404.

[0063] In the first stage 402, the balancing currents i i1 and i i21 are provided in the circuit. Current is supplied to the first DC / DC converter 212a Current is supplied to the second DC / DC converter 212b Current is supplied to the third DC / DC converter 212c

[0064] In the second stage 404, the balancing currents i i3 and i i22 are provided in the circuit. Current is supplied to the first DC / DC converter 212a, current is supplied to the second DC / DC converter 212b, current is supplied to the third DC / DC converter 212c.

[0065] The average power on the first module group 208a at a given time step k+1 is related to the average power at the previous time step k, as shown in equation (1):

[0066]

[0067] where q 1 (k+1) is the state of charge at the first module group 208a at time step k+1, q 1 (k) is the state of charge at time step k, h HV is the reciprocal of the capacitance of the battery pack 202, i i1 is the balancing current along the first low voltage bus 214 during the first stage 402, i HV is the current along the high voltage bus, and is the first regulator current from the first load regulator 306. The parameter dT is the duration or period of the switching cycle.

[0068] Similarly, the average power on the second module 208b is shown in equation (2):

[0069]

[0070] where q 2 (k+1) is the state of charge at the second module group 208b at time step k+1, q 2 (k) is the state of charge at time step k, i 21 is the balancing current between the first module group 208a and the second module group 208b during the first stage 402. i 22 is the second balancing current between the second module group 208b and the third module group 208c during the second stage 404, and i LV2 reg is the second regulator current from the second load regulator 308.

[0071] Similarly, the average power on the third module 208c is shown in equation (3):

[0072]

[0073] where q 3 (k+1) is the state of charge of the third module group 208c at time step k+1, q 3(k) is the state of charge at time step k, and i i3 is the current from the third module group 208c.

[0074] Operate switch 218 to minimize the cost function that includes J quadratic costs over a finite cycle range N, as shown in Equation (4):

[0075]

[0076] where the term y(k) is the square of the difference in state of charge across module groups 208a - 208c, as shown in Equation (5):

[0077] y(k) = (q 1 (k) - q 2 (k)) 2 + (q 2 (k) - q 3 (k)) 2 + (q 3 (k) - q 1 (k)) 2 Equation (5)

[0078] And the term R u (k) is the sum of the squares of the balancing currents, as shown in Equation (6):

[0079]

[0080] The quadratic cost J can be minimized using constraints that are selected to avoid damaging the battery pack 202. The constraints can be updated at each cycle or time step k. Exemplary constraints are shown in Equations (7) - (9):

[0081]

[0082]

[0083]

[0084] where is the maximum possible current through module x, is the minimum possible current through module x, is the maximum current allowed by the DC / DC converter in either current direction.

[0085] The balancing currents can be selected to minimize the effect of the balancing of the module groups on the low voltage load detected at the LV regulator, as shown in Equations (10) - (11):

[0086]

[0087]

[0088] where V 1 is the voltage of the first module group 208a, V 2 is the voltage of the second module group 208b, V 3 is the voltage of the third module group 208c, V LV1 is the voltage of the first low voltage bus 214, V LV2 is the voltage of the second low voltage bus 216.

[0089] Figure 5 is the graph 500 of the state of charge over time. Time is shown along the horizontal axis in seconds (s), and the normalized SOC is shown along the vertical axis, where a value of SOC = 1 refers to a fully charged module and SOC = 0 is a fully discharged module. The SOC of the modules is initially balanced (i.e., the same SOC at time t = 0 seconds). The modules are operated without using the charge balancing operations disclosed herein until approximately time t = 3900 seconds. Over time, the SOC of the modules diverges, as shown by the divergence between the first SOC 502 of the first module group 208a, the second SOC 504 of the second module group 208b, and the third SOC 506 of the third module group 208c. At time t = 3900 seconds, the charge balancing operations disclosed herein are implemented. The first SOC 502, the second SOC 504, and the third SOC 506 quickly converge to the same value (i.e., within about 500 seconds).

[0090] Figure 6 shows the graph 600 of the module current over time. The module current is the sum of the high voltage bus current and the selected balancing current. Time is shown along the horizontal axis in seconds, and the module current is shown along the vertical axis in amperes (A). From the initial time to the time when the balancing operations disclosed herein are implemented (about t = 3900 seconds), the current through the module groups is the same. After t = 3900 seconds, the current of each module is different, as shown by the first current curve 602 (first module group 208a), the second current curve 604 (second module group 208b), and the third current curve 606 (third module group 208c).

[0091] Figure 7A graph 700 showing the balance current over time is presented. Time is shown on the abscissa in seconds, and the balance current is shown on the ordinate in amperes. From the initial time to the time (about t = 3900 seconds) when the balance operation disclosed herein is implemented, the balance current passing through the module group is the same. After t = 3900 seconds, the current of each module is different, as shown by the first balance current curve 702 (the first module group 208a), the second balance current curve 704 (between the first module group 208a and the second module group 208b), the third balance current curve 606 (between the second module group 208b and the third module group 208c), and the fourth balance current curve 708 (the third module group 208c).

[0092] Figure 8 A graph 800 showing the regulator current over time is presented. Time is shown on the abscissa in seconds, and the regulator current is shown on the vertical axis in amperes. The first regulator current i reg LV1 is shown in the first curve 802 and the second regulator current i reg LV2 is shown in the second curve 804.

[0093] The terms "a" and "an" do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. Unless the context clearly dictates otherwise, the term "or" means "and / or". References to "aspect" throughout the specification mean that the particular elements (e.g., features, structures, steps, or characteristics) described in connection with that aspect are included in at least one aspect described herein, and may or may not be present in other aspects. Additionally, it should be understood that the described elements may be combined in any suitable manner in the various aspects.

[0094] 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, no intervening elements are present.

[0095] Unless otherwise stated herein, all test standards are the latest 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.

[0096] Unless otherwise defined, the 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 pertains.

[0097] While the foregoing disclosure has been described with reference to exemplary embodiments, those skilled in the art will understand that various changes can be made and elements thereof can be replaced with equivalents without departing from its scope. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the disclosure without departing from the basic scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiments disclosed, but that it will include all embodiments falling within its scope.

Claims

1. A method for balancing the charge in a battery pack; coupling the first module group to a first low voltage bus; coupling the second module group to the switch; coupling the third module group to the second low voltage bus; During a first phase of the cycle, coupling the second module group to the first low voltage bus via the switch in a first configuration to transfer power between the first module group and the second module group; as well as During a second phase of the cycle, the second module group is coupled to the second low voltage bus via the switch in a second configuration to transfer charge between the second module group and the third module group to balance the charge in the battery pack.

2. The method according to claim 1, further comprising determining a balancing current for transferring the charge by minimizing a cost function, the cost function comprising a sum of squares of charge differences over a limited cycle range and a sum of squares of the balancing current. 3 . The method of claim 2 , further comprising determining the balancing current that minimizes an effect of balancing the module group on at least one of a first low voltage load on the first low voltage bus and a second low voltage load on the second low voltage bus. 4 . The method of claim 1 , wherein the first module group comprises a first plurality of module groups and the third module group comprises a second plurality of module groups. 5 . The method of claim 4 , wherein the number of module groups in the first plurality of module groups is based on a power level in a low voltage bus coupled to the module groups.

6. A battery pack for a vehicle, comprising: a first module group coupled to a first low voltage bus; a second module group coupled to the switch; a third module group coupled to the second low voltage bus; A processor configured to: During a first phase of the cycle, coupling the second module group to the first low voltage bus via the switch in a first configuration to transfer power between the first module group and the second module group; as well as During a second phase of the cycle, the second module group is coupled to the second low voltage bus via the switch in a second configuration to transfer charge between the second module group and the third module group to balance the charge in the battery pack.

7. The battery pack according to claim 6, wherein the processor is further configured to determine a balancing current for transferring the charge by minimizing a cost function, the cost function comprising a sum of squares of charge differences over a limited cycle range and a sum of squares of the balancing currents.

8. The battery pack of claim 7, wherein the processor is further configured to determine the balancing current to minimize an effect of balancing the module groups on at least one of a first low voltage load on the first low voltage bus and a second low voltage load on the second low voltage bus. 9 . The battery pack of claim 6 , wherein the first module group comprises a first plurality of module groups, and the third module group comprises a second plurality of module groups.

10. The battery pack of claim 9, wherein the number of module groups in the first plurality of module groups is based on a power level in a low voltage bus coupled to the module groups.

Images