Battery pack and method for balancing charge in a battery pack

Abstract

A vehicle includes a battery pack and performs a method for equalizing charge 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 a cycle to transfer charge 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 charge between the second module group and the third module group, thereby equalizing charge in the battery pack.

Description

INTRODUCTION

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

[0002] For background information, reference is made at this point to the documents US 2024 / 0 270 118 A1, DE 10 2023 122 996 A1, DE 10 2019 121 918 A1, US 2022 / 0 320 873 A1 and US 2021 / 0 028 503 A1, although the first two were not known on the priority date relevant here.

[0003] An electric vehicle is powered using an electrical system with a battery pack. The battery pack includes a plurality of module groups with battery modules contained therein. The battery pack supplies power to both high-voltage loads, such as the motor, etc., and low-voltage loads, such as the radio, dashboard, etc. During vehicle operation, the state of charge of each module group can vary, resulting in a divergence between the charge levels of the module groups of the battery pack. As the charge levels diverge, the functionality of the electrical system decreases. Accordingly, it is desirable to provide a system and method for balancing the charge levels across the plurality of module groups. SUMMARY

[0004] According to the invention, a method for equalizing charge in a battery pack is presented. A first group of modules is coupled to a first low-voltage bus. A second group of modules is coupled to a switch. A third group of modules is coupled to a second low-voltage bus. The second group of modules 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 group of modules and the second group of modules. The second group of modules 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 group of modules and the third group of modules and thereby equalize the charge in the battery pack.

[0005] In addition to one or more of the features described herein, the method further comprises determining a balancing current for transferring the charge by minimizing a cost function comprising a sum of the square of the charge differences and a sum of the square of the balancing currents over a finite cycle horizon.

[0006] In addition to one or more of the features described herein, the method further comprises determining the balancing currents that minimize an impact 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.

[0007] In addition to one or more of the features described herein, the method further comprises applying a condition to the cost function and updating the condition for each cycle.

[0008] In addition to one or more of the features described herein, the first module group comprises a first plurality of module groups, and the third module group comprises a second plurality of module groups. 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 a power level in low-voltage buses coupled to the module groups.

[0009] In addition to one or more of the features described here, a period of the cycle is specified.

[0010] According to the invention, a battery pack of a vehicle is further presented. The battery pack comprises 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 a cycle to transfer charge 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 charge between the second module group and the third module group, thereby balancing the charge in the battery pack.

[0011] In addition to one or more of the features described herein, the processor is further configured to determine a compensation current for transferring the charge by minimizing a cost function comprising a sum of the square of the charge differences and a sum of the square of the compensation currents over a finite cycle horizon.

[0012] In addition to one or more of the features described herein, the processor is further configured to determine the balancing currents to minimize an impact 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.

[0013] In addition to one or more of the features described herein, the processor is further configured to apply a condition to the cost function and update the condition for each cycle.

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

[0015] 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 a power level in low voltage buses coupled to the module groups.

[0016] In addition to one or more of the features described here, a period of the cycle is specified.

[0017] In 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 phase of a cycle to transfer charge 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 charge between the second module group and the third module group to thereby equalize the charge 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 charge by minimizing a cost function comprising a sum of the square of the charge differences and a sum of the square of the balancing currents over a finite cycle horizon.

[0019] In addition to one or more of the features described herein, the processor is further configured to determine the balancing currents that minimize an impact 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.

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

[0021] In addition to one or more of the features described herein, the first module group comprises a first plurality of module groups, and the third module group comprises 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 a power level in low voltage buses coupled to the module groups.

[0023] The foregoing features and advantages, as well as other features and advantages of the invention, will be readily apparent from the following detailed description taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Further features, advantages and details are listed only as examples in the following detailed description, which refers to the drawings in which: Fig. 1 shows an embodiment of a vehicle according to an exemplary embodiment; Fig. Figure 2 shows a high-level schematic representation of an electric drive system of the vehicle; Fig. 3 shows a detailed circuit diagram for the electrical system of the vehicle in an illustrative embodiment; Fig. 4 illustrates a switching cycle of the electrical system in one embodiment; Fig. Figure 5 is a graph of state of charge versus time; Fig. 6 shows a graph of the module current over time; Fig. 7 shows a graph of the compensating current over time; and Fig. 8 shows a diagram of the controller currents over time. DETAILED DESCRIPTION

[0025] The following description is given by way of example only. It should be understood that throughout the drawings, corresponding reference characters designate like or corresponding parts and features.

[0026] According to an exemplary embodiment, Fig. 1 illustrates an embodiment of a vehicle 10 including a vehicle body 12 that at least partially defines a passenger compartment 14. The vehicle 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 others.

[0027] The vehicle 10 may be an electric vehicle (EV), a hybrid vehicle, or other vehicle. In one embodiment, the vehicle 10 is an electric vehicle that includes multiple motors and / or drive systems. The vehicle 10 may be a car, a truck, a van, a bus, a motorcycle, or other vehicle. 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 to 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 (in which additional torque is applied), all-wheel drive ("AWD"), front-wheel drive ("FWD"), rear-wheel drive ("RWD"), and others.

[0028] The drive system 16 is, for example, a multi-drive system that includes a front drive unit 20 for driving the front wheels and rear drive units for driving the rear wheels. The front drive unit 20 includes a front electric motor 22 and a front inverter 24 (e.g., front power inverter module or FPIM), as well as other components such as a cooling system. A left rear drive unit 30L includes a left rear electric motor 32L and a left rear inverter 34L. A 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 conversion units or PIMs) each convert the DC power from a high-voltage battery system 40 into multi-phase (e.g., two-phase, three-phase, six-phase, etc.) DC power.) AC power to drive the front electric motor 22, the left rear electric motor 32L and the right rear electric motor 32R.

[0029] As in Fig. 1, the drive systems are equipped with separate electric motors. However, the configurations are not so limited. Instead of separate motors, for example, multiple drives can be provided by a single machine having multiple sets of physically independent windings.

[0030] As in Fig. 1, the drive systems are 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 configurations are not so limited, as there may be any number of drive systems and / or motors in various locations (e.g., one motor for each wheel, two motors per axle, etc.). Furthermore, the configurations are not limited to a dual drive system, as the configurations may be used with a vehicle having any number of motors and / or power converters.

[0031] In the drive 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 may also be 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, and others. The battery system 40 may be configured as a rechargeable energy storage system (RESS).

[0032] In one embodiment, the battery system 40 includes a plurality of separate battery assemblies, each battery assembly capable of being independently charged and used to independently power one or more propulsion systems. The battery system 40 includes, for example, a first battery assembly, 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 number of individual cells (not shown).

[0033] Each of the front electric motors 22, the left rear electric motor 32L, and the right rear electric motor 32R is a three-phase motor with three-phase motor windings. However, the configurations described here are not so limited. For example, the motors can be any multi-phase machines powered by multi-phase inverters, and the drive units can be implemented using a single machine with independent winding sets.

[0034] The battery system 40 and / or the drive 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 for 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 actuated to selectively connect the first battery pack 44 and the second battery pack 46 to a charging system. The charging system can be used to charge the first battery pack 44 and the second battery pack 46 and / or to supply power to 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 on-board charging module (OBCM) 52 is electrically connected to a charging port 54 for charging to and from an AC system or device, such as a utility AC power supply. A second OBCM 53 may be included for DC charging (e.g., DC fast charging or DCFC).

[0035] In one embodiment, the switching system includes a first switching device 60 that selectively connects the first battery pack 44 to the front inverter 24, the left rear inverter 34L, and the right rear inverter 34R, and a second switching device 62 that 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 also includes a third switching device 64 (also called a "battery switching device") for selectively connecting the first battery pack 44 to the second battery pack 46 in series.

[0036] Any of a variety of controllers may be used to control functions of the vehicle's electrical system, including the battery system 40, the switching system, the drive units, etc. A controller 65 includes any suitable processing device or unit and may utilize an existing controller, such as a drive system controller, a RESS controller, and / or controllers within the drive system. For example, a controller 65 may be included to control switching and drive control operations, as discussed herein.

[0037] The controller 65 may include processing circuitry, which may include an application-specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group), and memory executing one or more software or firmware programs, combinational logic circuitry, and / or other suitable components that provide the described functionality. 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 for balancing charge between various battery modules of the vehicle during operation of low-voltage loads, according to one or more embodiments recited herein.

[0038] The vehicle 10 also includes a computer system 55 that includes one or more processing devices 56 and a user interface 58. The computer system 55 may, for example, communicate with the charging system controller to issue 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.

[0039] As illustrated here, vehicle 10 is an electric vehicle. In an alternative embodiment, vehicle 10 may be an internal combustion engine vehicle powered by gasoline, diesel, etc., or a hybrid vehicle powered entirely or partially by electric power, etc.

[0040] As described herein, a vehicle may include one or more electrical loads powered by one or more batteries. Example loads include, but are not limited to, motors, lights, infotainment devices, electronic control units, climate control systems, etc. 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 both high voltage for the high-voltage loads and low voltage for the low-voltage loads. According to one or more embodiments described herein, high voltage may refer to, but are not limited to, 100 volts, 250 volts, 400 volts, 500 volts, 650 volts, 800 volts, 1000 volts, etc. Low voltage may refer to, but are not limited to, 12 V, 48 V, etc.To support these low voltage loads, the vehicle 10, as disclosed herein, may include at least one DC / DC converter that converts the DC electrical power from the higher voltage to the lower voltage.

[0041] Fig. 2 shows a high-level schematic diagram 200 of an electric propulsion system of the vehicle 10. The high-level schematic diagram 200 shows a battery pack 202, an array 204 of DC-DC converters, and a low-voltage power grid 206. The battery pack 202 includes a plurality of module groups 208a, 208b, 208c arranged in series along a high-voltage (HV) bus 210. Each module group 208a, 208b, 208c includes a plurality of battery modules (not shown). The array 204 of DC-DC converters includes a plurality of DC-DC converters 212a, 212b, 212c. For illustrative purposes, three module groups are shown. The DC-DC converters may be bidirectional converters.

[0042] Each DC / DC converter is coupled across a respective module group of the battery pack 202. For example, a first DC / DC converter 212a is coupled across the first module group 208a, a second DC / DC converter 212b is coupled across the second module group 208b, and a third DC / DC converter 212c is coupled across the third module group 208c. A first conductive wire 224 connects a positive terminal of the first DC / DC converter 212a to the high-voltage bus 210 at an outer end of the first module group 208a. A second conductive wire 226 connects a negative terminal of the first DC / DC converter 212a and a positive terminal of the second DC / DC converter 212b to the high voltage bus 210 between the first module group 208a and the second module group 208b.A third conductor 228 connects a negative terminal of the second DC / DC converter 212b and a positive terminal of the third DC / DC converter 212c to the high-voltage bus 210 between the second module group 208b and the third module group 208c. A fourth conductive wire 230 connects a negative terminal of the third DC / DC converter 212c to the high-voltage bus 210 at an outer end of the third module group 208c.

[0043] The low-voltage network 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 coupled 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 coupled to the third module group 208c via the second low-voltage bus 216 and the third DC / DC converter 212c.

[0044] A fixed end 217 of the switch 218 is connected to the second module group 208b via the second DC / DC converter 212b. A configurable end of the switch 218 can be placed in either a first or a second configuration. In the first configuration, the second module group 208b is electrically coupled to the first low-voltage bus 214 and thus also to the first module group 208a via the DC / DC converter 212a. This configuration enables a first transfer current to flow between the first module group 208a and the second module group 208b. When a first charge on the first module group 208a differs from a second charge on the second module group 208b, this first transfer current enables charge transfer between the first module group and the second module group to balance the first charge with the second charge.

[0045] In the second configuration, the second module group 208b is electrically coupled to the second low-voltage bus 216 and thus to the third module group 208 via the DC / DC converter 212c. This configuration enables a second transfer current to flow between the second module group 208b and the third module group 208c. If the second charge on the second module group 208b differs from a third charge on the third module group 208c, this second transfer current enables a charge transfer between the second module group and the third module group to balance the second charge with the third charge.

[0046] By switching the switch 218 between the first configuration and the second configuration, the charge can be balanced across all module groups.

[0047] 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), with each low-voltage bus associated with a module group for providing power to the low-voltage load. Since one module group (e.g., the second module 208b) is used as a buffer module for charge transfer, the number of modules is one higher 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 serve as a buffer module group used to transfer charge between the first plurality of module groups and the second plurality of module groups via the switch.The number of module groups in the plurality of module groups may be based on a power level in the low-voltage buses coupled to the module groups.

[0048] Fig. 3 shows a detailed circuit diagram 300 for the electrical system of the vehicle 10 in an illustrative embodiment. The detailed circuit diagram 300 includes the battery pack 202, the DC / DC converter assembly 204, and the low-voltage power grid 206.

[0049] To illustrate, the low-voltage power grid 206 includes a first low-voltage grid 302 and a second low-voltage grid 304. The first low-voltage grid 302 includes the 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 LV1for DC / DC converters to regulate the voltage of the first low-voltage network 302. The second low-voltage network 304 includes the 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 DC / DC converters to regulate the voltage of the second low-voltage network 304.

[0050] The battery pack 202 includes a plurality of module balancing controllers 310a, 310b, 310c. Each module balancing controller is associated with a respective module group (i.e., module balancing controller 310a is associated with module group 208a). Each module balancing controller is used to balance the state of charge (SOC) between the battery modules of the associated module. The module balancing controllers 310a, 310b, 310c receive feedback signals that determine the first load regulator current (i reg LV1 ), the second load regulator current (i reg LV2 ) and an estimate of the state of charge, and balance the battery modules based on these signals as disclosed herein.

[0051] The detailed circuit diagram 300 further shows a control circuit 314 that controls the operation of the electrical system and, in particular, the operation of the switch 218. The control circuit 314 may be a processor that runs one or more algorithms, such as a balancing control algorithm 316 and a state of charge estimation algorithm 318. The balancing control algorithm 316 outputs a signal to control a configuration of the switch 218. In particular, the balancing control algorithm 316 sends a signal that switches the switch 218 between the first configuration and the second configuration. The switching occurs over a fixed period of time (dT) and thus at a fixed frequency (1 / dT).

[0052] The balancing control algorithm 316 may also output desired currents, which, as disclosed herein, may be used as feedback for balancing charges. The balancing control algorithm 316 issues commands to balance the currents i i1 and i i21 to a first summing circuit 320. The first summing circuit 320 adds these currents to the first load regulator current (i reg LV1 ) and sends the sum to the module balancing controllers 310a, 310b, 310c. Similarly, the balancing control algorithm 316 issues commands to balance the currents i i3 and i i22 to a 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.

[0053] 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 from these currents and outputs the state of charge values to the module balancing controllers 310a, 310b, 310c and to the balancing control algorithm 316. Each module balancing controller 310a, 310b, 310c balances the state of charge among 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 values.

[0054] Fig. 4 illustrates a switching cycle 400 of the electrical system in one embodiment. The switching cycle 400 includes a first phase 402 and a second phase 404. The first phase 402 shows the electrical system with the switch 218 connecting the first module group 208a and the second module group 208b via the first low-voltage bus 214. A second phase 404 shows the electrical system with the switch 218 connecting the second module group 208b and the third module group 208c via the second low-voltage bus 216. The electrical system oscillates between the first phase 402 and the second phase 404 at a frequency of 1 / dT, with the electrical system being in the first phase 402 for half of a period (0.5*dT) and in the second phase 404 for half of the period (0.5*dT).

[0055] In the first phase 402, the compensating currents i i1 and i 21provided in the circuit. The first DC / DC converter 212a is supplied with a current ii1+12iLV1reg i i1 The second DC / DC converter 212b is supplied with a current i21+12iLV1reg The third DC / DC converter 212c is supplied with a current iLV2reg supplied.

[0056] In the second phase 404, the compensating currents ii3 and i22 provided in the circuit. A current iLV1reg is supplied to the first DC / DC converter 212a, a current ii22+12iLV2reg is supplied to the second DC / DC converter 212b and a current ii3+12iLV2reg is supplied to the third DC / DC converter 212c. The average charge of the first module group 208a in a given time step k+1 is related to the average charge in the previous time step k, as shown in equation (1): q1(k+1)=q1(k)−hHV(ii1(k)+iHV(k)+34iLV1reg(k))dT where q1(k+1) is the charge state of the first module group 208a at time step k+1, q1(k) is the charge state at time step k, h HV is the reciprocal of the capacity of the battery pack 202, i i1 the compensating current along the first low-voltage bus 214 during the first phase 402 is i HV the current along the high voltage bus, and iLV1reg is the first regulator current from the first load regulator 306. The parameter dT is the duration or period of a switching cycle.

[0057] Similarly, the average charge of the second module 208b is shown in equation (2): q2(k+1)=q2(k)−hHV(iI21(k)+ii22(k)+iHV(k)+14(iLV1reg(k)+iLV2reg(k))) where q2(k+1) is the charge state of the second module group 208b at time step k+1, q2(k) is the charge state at time step k, i 21 a compensating current between the first module group 208a and the second module group 208b during the first phase 402. i 22 is a second equalizing current between the second module group 208b and the third module group 208c during the second phase 404, and i LV2 reg is the second regulator current from the second load regulator 308.

[0058] Similarly, the average charge of the third module 208c is shown in equation (3): q3(k+1)=q3(k)−hHV(ii3(k)+iHV(k)+34iLV2reg(k))dT where q3(k+1) is the charge state of the third module group 208c at time step k+1, q3(k) is the charge state at time step k and i i3 the current from the third module group 208c.

[0059] The switch 218 is actuated to minimize a cost function comprising J quadratic costs over a finite cycle horizon N, as shown in equation (4): J=∑k=1N(y(k)+Ru(k)) where the term y(k) is a square of the differences in the charges of the module groups 208a-208c, as shown in equation (5): y(k)=(q1(k))2+(q2(k)−q3(k))2+(q3(k)−q1(k))2 and the term R u (k) is the sum of the squares of the compensating currents, as shown in equation (6): Ru(k)=R×∑j=13iij2(k)

[0060] The quadratic cost J can be minimized using conditions chosen to avoid damage to the battery pack 202. The conditions can be updated at each cycle or time step k. Example conditions are shown in equations (7)-(9): max(−i1max+iHV(k),−iDC1max(k))≤ii1(k)≤min(−i1min+iHV(k),−DC1max(k)) max(−i2max+iHV(k),−iDC2max(k))≤ii2j(k)≤min(−i2min+iHV(k),−iDC2max(k)) j=1,2 max(−i3max+iHV(k),−iDC3max(k))≤ii3(k)≤min(−i3min+iHV(k),−iDC3max(k)) where ixmax a maximum possible current through an x -tes -module is, ixmin a minimum possible current through an x -tes -Module is iDCxmax a maximum allowable current for DC / DC converters in each current direction.

[0061] The balancing current can be chosen so that the effect of balancing the module groups on the low-voltage loads, as detected by the low-voltage regulators, is as small as possible, as shown in equations (10)-(11): V1(k)VLV1(k)ii1(k)V2(k)VLV1(k)ii21(k)=0 V3(k)VLV2(k)ii3(k)V2(k)VLV2(k)ii22(k)=0 where V1 is the voltage of the first module group 208a, V2 is the voltage of the second module group 208b and V3 is the voltage of the third module group 208c, V LV1 the voltage of the first low-voltage bus 214 and V LV2 is the voltage of the second low voltage bus 216.

[0062] Fig. 5 is a graph 500 of state of charge versus time. The abscissa represents time in seconds (s), and the ordinate represents the normalized SOC, where SOC = 1 refers to a fully charged module and SOC = 0 refers to a fully discharged module. The SOCs of the modules are initially balanced (i.e., equal SOC at time t = 0 seconds). The modules are operated until approximately time t = 3900 seconds without the charge balancing disclosed herein being used. Over time, the SOCs of the modules diverge, 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 change balancing process disclosed herein is implemented. The first SOC 502, the second SOC 504 and the third SOC 506 soon converge to the same value (i.e., within approximately 500 seconds).

[0063] Fig. 6 shows a graph 600 of module current over time. The module current is the sum of the high-voltage bus current and a selected equalizing current. Time is indicated on the abscissa in seconds, and the module current is indicated on the ordinate in amperes. From the initial time until the equalizing process disclosed herein is implemented (approximately t = 3900 seconds), the current through the module groups is the same. After t = 3900 seconds, the current of each module differs, as illustrated 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).

[0064] Fig. 7 shows a graph 700 of the equalizing current over time. Time is indicated on the abscissa in seconds, and the equalizing current is indicated on the ordinate in amperes. From the initial time until the equalizing process disclosed herein is implemented (approximately t = 3900 seconds), the equalizing current through the module groups is the same. After t = 3900 seconds, the current of each module differs, as shown by the first equalizing current curve 702 (first module group 208a), the second equalizing current curve 704 (between the first module group 208a and the second module group 208b), the third equalizing current curve 606 (between the second module group 208b and the third module group 208c), and the fourth equalizing current curve 708 (third module group 208c). Fig.Figure 8 shows a graph of the regulator currents over time. Time is given in seconds on the abscissa, and the regulator current is given in amperes on the ordinate. The first regulator current iregLV1 is shown in the first curve 802 and the second regulator current iregLV2 is shown in the second curve 804.

[0065] The terms "a / an" do not imply a quantity limitation, but denote the presence of at least one of the referenced subject matter. The term "or" means "and / or" unless the context clearly indicates otherwise. Throughout this specification, references to "an aspect" mean that a particular element (e.g., a feature, structure, step, or property) described in connection with the aspect is included in at least one of the aspects described herein and may or may not be present in other aspects. Furthermore, it is understood that the described elements in the various aspects may be combined in any suitable manner.

[0066] When an element, such as a layer, film, region, or substrate, is described as being "on" another element, it may be directly on top of the other element, or there may be intervening elements. Conversely, when an element is described as being "directly on" another element, there are no intervening elements.

[0067] Unless otherwise indicated herein, all examination standards are the most recent standard in effect on the filing date of this application or, if priority is claimed, the filing date of the earliest priority application in which the examination standard appears.

[0068] Unless otherwise defined, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

Claims

[1] Method for balancing charge in a battery pack (202); coupling a first module group (208a) to a first low voltage bus (214); Coupling a second module group (208b) to a switch (218); Coupling a third module group (208c) to a second low-voltage bus (216); coupling the second module group (208b) via the switch (218) in a first configuration to the first low-voltage bus (214) during a first phase of a cycle to transfer a charge between the first module group and the second module group (208b); and Coupling the second module group (208b) via the switch (218) in a second configuration during a second phase of the cycle to the second low voltage bus (216) to transfer the charge between the second module group (208b) and the third module group (208c) to thereby equalize the charge in the battery pack (202). [2] The method of claim 1, further comprising determining a balancing current for transferring charge by minimizing a cost function comprising a sum of the square of the charge differences and a sum of the square of the balancing currents over a finite cycle horizon. [3] The method of claim 2, further comprising determining the balancing currents that minimize an effect of balancing the module groups on at least one of a first low voltage load (220) on the first low voltage bus (214) and a second low voltage load (222) on the second low voltage bus (216). [4] The method of claim 1, wherein the first module group (208a) comprises a first plurality of module groups and the third module group (208c) 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 low voltage buses coupled to the module groups. [6] Battery pack (202) of a vehicle (10), comprising; a first module group (208a) coupled to a first low-voltage bus (214); a second module group (208b) coupled to a switch (218); a third module group (208c) coupled to a second low-voltage bus (216); a processor designed to: coupling the second module group (208b) via the switch (218) in a first configuration to the first low-voltage bus (214) during a first phase of a cycle to transfer a charge between the first module group (208a) and the second module group (208b); and Coupling the second module group (208b) via the switch (218) in a second configuration during a second phase of the cycle to the second low voltage bus (216) to transfer the charge between the second module group (208b) and the third module group (208c) to thereby equalize the charge in the battery pack (202). [7] The battery pack (202) of claim 6, wherein the processor is further configured to determine a balancing current for transferring the charge by minimizing a cost function comprising a sum of the square of the charge differences and a sum of the square of the balancing currents over a finite cycle horizon. [8] The battery pack (202) of claim 7, wherein the processor is further configured to determine the balancing currents to minimize an impact of balancing the module groups on at least one of a first low voltage load (220) on the first low voltage bus (214) and a second low voltage load (222) on the second low voltage bus (216). [9] The battery pack (202) of claim 6, wherein the first module group (208a) comprises a first plurality of module groups and the third module group (208c) comprises a second plurality of module groups. [10] The battery pack (202) of claim 9, wherein the number of module groups in the first plurality of module groups is based on a power level in low voltage buses coupled to the module groups.

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