Battery module

Abstract

A battery module is described. The battery module comprises n cells including a first cell, wherein n is a non-zero positive integer. For each cell the battery module comprises a first switching element coupled to a positive terminal of the cell, and a second switching element coupled to a negative terminal of the cell, the first and second switching elements being coupled. The battery module further comprises a first inductor jointly coupled to the first and second switching elements corresponding to the first cell, a third switching element coupled between the first inductor and a positive terminal of the battery module, the coupling between the first inductor and the third switching element forming a first node, a fourth switching element coupled between the first node and a negative terminal of the battery module, wherein the coupling between the fourth switching element and the negative terminal of the battery module forms a second node, and the second switching element corresponding to the nth cell and the negative terminal of the nth cell are jointly coupled to the second node, and a capacitor coupled between the negative and positive terminals of the battery module.

Description

[0001] Batery Module

[0002] Field

[0003] The present invention relates to a battery module and a batteiy pack which includes the batteiy module. The present invention also relates to a method of operating the batteiy pack.

[0004] Background

[0005] Batteiy packs having a high voltage output are required in many applications, for example in electric vehicles.

[0006] Typical battery packs incorporate many cells in series. This introduces a problem of the batteiy pack being limited by the weakest cell (the cell having the lowest usable capacity or power capability, for example).

[0007] Some known battery packs attempt to solve this problem by incorporation of a cell balancing system having either a centralised architecture (a system addressing all cells) or a modular architecture (many systems each address a group / module of cells). Examples of battery packs incorporating a modular architecture are described in A. Fares et al.: “Optimising the structure of a cascaded modular battery system for enhancing the performance of battery packs” , The 9th International Conference on Power Electronics, Machines and Drives (2018), and in Y. Li “A Module-Integrated Distributed Battery Energy Storage and Management System” , IEEE TRANSACTIONS ON POWER ELECTRONICS (2016), and also in N. Mukheijee et al.: “Analysis and Comparative Study of Different Converter Modes in Modular Second- Life Hybrid Battery Energy Storage Systems” IEEE JOURNAL OF EMERGING AND SELECTED TOPICS IN POWER ELECTRONICS (2016). However, these known batteiy packs have several drawbacks. Summary

[0008] According to a first aspect of the present invention, there is provided a battery module comprising n cells including a first cell, wherein n is a non-zero positive integer. For each cell the battery module comprises a first switching element coupled to a positive terminal of the cell, and a second switching element coupled to a negative terminal of the cell, the first and second switching elements being coupled. The battery module further comprises a first inductor jointly coupled to the first and second switching elements corresponding to the first cell, a third switching element coupled between the first inductor and a positive terminal of the battery module, the coupling between the first inductor and the third switching element forming a first node, a fourth switching element coupled between the first node and a negative terminal of the batteiy module, wherein the coupling between the fourth switching element and the negative terminal of the battery module forms a second node, and the second switching element corresponding to the nth cell and the negative terminal of the nth cell are jointly coupled to the second node, and a capacitor coupled between the negative and positive terminals of the battery module.

[0009] The battery module may help to provide improved fault tolerance. The first and second switching elements may be selectively operable to control a current through their corresponding cell. For example, the first and second switching elements may be controlled to adjust a duty cycle of the current through the corresponding cell. The third and fourth switching elements may be selectively operable, in co-operation with the first and second switching elements, to control an output voltage of the battery module and / or to control current bypassing of the batteiy module.

[0010] Thus, the operation of the batteiy module may be adjusted to account for a state of health of the battery module, or other battery modules connected to it.

[0011] The battery module may comprise a single cell.

[0012] Wherein n is greater than 1, and wherein for each cell not including the nthcell: the negative terminal of the cell and the second switching element corresponding to the cell may be jointly coupled to the first and second switching elements of the proceeding cell, such that the second switching elements of each cell are connected in series.

[0013] The non-zero integer n may be between 5 and 15.

[0014] Typically, the battery module may consist of 10 cells. The number of cells may depend on the particular application of the batteiy pack which contains the battery module.

[0015] At least one cell of the n cells may have a usable capacity different to the other cells.

[0016] Each of the first, second, third, and / or fourth switching elements may be a semiconductor switch.

[0017] The semiconductor switch may be a transistor, such as an Insulated Gate Bipolar Transistor (IGBT).

[0018] The semiconductor switch may be a n-channel MOSFET or a p-channel MOSFET.

[0019] The first and second switching elements may be selectively operable such that the current bypasses the corresponding cell.

[0020] The first and second switching elements may be selectively operable to control the current through the corresponding cell according to a state of health of the corresponding cell.

[0021] The state of health may include a usable capacity of the corresponding cell.

[0022] The state of health may include a power capability of the corresponding cell. One or more cells may be bypassed within the same battery module.

[0023] The power capability may depend, at least in part, on the internal resistance of the cell.

[0024] The batteiy module may further comprise a second inductor, a fifth switching element coupled to the second inductor to form a third node, a sixth switching element coupled between the third node and the second node, wherein the second inductor and the fifth switching element are coupled across the first inductor and the third switching element.

[0025] The fifth and sixth switching elements may be selectively operable, in combination with the third and fourth switching elements, to control the output voltage of the battery module and / or to control current bypassing of the batteiy module.

[0026] According to a second aspect of the present invention, there is provided a batteiy pack comprising a plurality of battery module units, each unit comprising a batteiy module according to the first aspect, a module controller for controlling the battery module, wherein the batteiy module units are connected in series or in parallel. The battery pack further comprises a batteiy management system, BMS, for communicating with each module controller. The battery pack may be operated to account for cell or batteiy module failure and to account for mismatching in cell or battery module usable capacity.

[0027] The BMS may be configured to communicate with the plurality of module controllers via a Controlled Area Network bus.

[0028] Each module controller may be configured to transmit information indicating a state of health of the corresponding batteiy module to the BMS.

[0029] The state of health of the batteiy module may include an indication of the state of health of each cell within the battery module.

[0030] The state of health of a given cell may include a usable capacity and / or power capability of that cell. The state of health of the battery module may include an indication of the number of failed cells within the battery module.

[0031] The state of health of the battery module may further include a type of failure of the failed cell. Types of failure include activation of the cell’s equipped detection devices (if present), and dendrite formation (which risks internal short circuits and thermal runaway). A state of health of the batteiy module may further include a temperature reading of the battery module. The BMS may be configured to transmit at least one control signal to at least one module controller according to a voltage output requirement and / or power requirement of the battery pack.

[0032] The batteiy pack may be for use in electric vehicles. The battery pack may be for use in any battery-powered stationary application.

[0033] The BMS may be configured to transmit at least one control signal to at least one module controller according to a state of health of one of the batteiy modules. For example, the BMS may be configured to cause the current to bypass a given battery module in response to a determination that the temperature of the given batteiy module exceeds a threshold temperature.

[0034] The power of the battery pack may refer to the charging or discharging power.> The BMS may be configured to transmit at least one control signal to at least one module controller for adjusting the charging / discharging power of one or more batteiy modules to help ensure state of charge balance and / or thermal balance between the batteiy modules. According to a third aspect of the present invention, there is provided a first method of operating the battery pack according to the second aspect, the method comprising determining an operational state of a given cell within the battery module, and in response to a determination that the given cell has failed or is at risk of failure, selectively controlling the first and second switching elements corresponding to the given cell such that the current bypasses the given cell.

[0035] One or more cells within the same battery module may be bypassed.

[0036] The method may further comprise, after bypassing the given cell, selectively controlling the third and fourth switching elements to adjust the voltage output of the battery module. The method may further comprise, after bypassing the given cell, determining a remaining usable capacity of the battery module, transmitting information including the remaining usable capacity of the batteiy module to the BMS, and the BMS transmitting at least one control signal to at least one module controller, wherein the at least one control signal depends on a required voltage output of the batteiy module corresponding to the at least one module controller.

[0037] The at least one control signal may include a plurality of control signals for adjusting a voltage output of each batteiy module.

[0038] The information may further include the remaining usable capacity of each cell and / or the number of cells which have failed or are at risk of failure. The transmitted information may include the state of charge of the battery module. The transmitted information may include other indicators of the state of health of the batteiy module.

[0039] The transmitted information may include a state of charge of the battery module and module temperature.

[0040] According to a fourth aspect of the present invention, there is provided a second method of operating the batteiy pack according to the second aspect, the method comprising determining a usable capacity of a cell within the battery module, and in response to the determination, selectively controlling the first and second switching elements of each cell within the batteiy module to adjust the current through each cell.

[0041] The method may further comprise, after adjusting the current through each cell, selectively controlling the third and fourth switching elements to adjust the voltage output of the battery module.

[0042] The method may further comprise after adjusting the current through each cell, determining a usable capacity of the battery module, transmitting information including the usable capacity of the battery module to the BMS, and the BMS transmitting at least one control signal to at least one module controller, wherein the at least one control signal depends on a required voltage output of the batteiy module corresponding to the at least one module controller.

[0043] The transmitted information may include the state of charge of the battery module. The transmitted information may include other indicators of the state of health of the batteiy module.

[0044] The transmitted information may include a state of charge of the battery module and module temperature.

[0045] According to a fifth aspect of the present invention, there is provided a battery module comprising at least one cell and converter circuitry connected to the at least one cell, wherein the converter circuitry comprises a pair of switching elements addressing each cell. The pair of switching element are operable to control a current through the cell and the converter circuitry is operable, in cooperation with the pair of switching elements, to control a voltage output of the battery module and / or current bypassing of the battery module.

[0046] Brief Description of Drawings

[0047] Certain embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which:

[0048] Figure i schematically illustrates a batteiy pack; Figure 2 is a circuit diagram of a first batteiy module;

[0049] Figure 3 is a circuit diagram of a second battery module;

[0050] Figure 4 is a process flow diagram of a first example method of operating a battery pack;

[0051] Figure 5 is a process flow diagram of a second example method of operating a batteiy pack;

[0052] Figure 6a is a first plot of module voltage out against time;

[0053] Figure 6b is a first plot of cell current against time;

[0054] Figure 7a is a second plot of module voltage against time;

[0055] Figure 7b is a second plot of cell current against time; Figure 8a is a third plot of module voltage against time; and

[0056] Figure 8b is a third plot of cell current against time.

[0057] Detailed Description of Certain Embodiments

[0058] In the following, like parts are denoted by like references.

[0059] The present application is concerned with a battery module and a battery pack into which the battery module is incorporated. The topology of the battery module may help to provide improved fault tolerance. Furthermore, the batteiy pack is operable to account for cell or batteiy module failure and to account for mismatching in cell or batteiy module usable capacity.

[0060] Referring to Figure 1, a battery pack 1 connected across a load 2 is shown. The battery pack 1 may be incorporated into an electric vehicle, such as an electric aircraft. Thus, the load 2 may be an electric motor. However, as will be hereinafter explained, the batteiy pack 1 is suitable for a variety of applications.

[0061] The batteiy pack includes a battery management system 3 (BMS) and one or more batteiy module units 4 (or “unit” 4). The battery module units 4 are connected in series or in parallel. Each batteiy module unit 4 includes a module controller 6 and a battery module 7 (or “module” 7) . The BMS is configured to communicate with each of battery modules 7 within the units 4 via a communication bus 5. The communication bus 5 used will depend on the application of the battery pack i. The communication bus 5 may be a Controlled Area Network bus.

[0062] The BMS 3 is configured to transmit control signals to each of the module controllers 6 for adjusting the voltage output of the batteiy modules 7. Adjusting the voltage output of the modules 7 in this way has the effect of adjusting the power share between the modules 7. Each module controller 6 is configured to transmit information relating to the battery module 7 to the BMS 3. The information includes a state of health of the batteiy module 7, as will be hereinafter explained.

[0063] The battery pack 1 need not be connected across the load 2 directly. For example, the batteiy pack 1 may be connected across a DC bus of a power system (not shown). When connected across the DC bus, the batteiy pack 1 may be configured to charge from the DC bus (in a “charging mode”) and / or discharge to the DC bus (in a “discharging mode”) according to the operational control of the power system. In this way, the batteiy pack 1 may be bidirectional. In the charging mode, the batteiy pack 1 receives power from the DC bus. In the discharging mode, the battery pack 1 provides power to the DC bus. Referring also to Figure 2, a first battery module 7, 71 is shown. The first battery module 7i is an example module 7 which may be incorporated into the batteiy pack 1.

[0064] The batteiy module 7 includes one or more cells 8 for providing the voltage output of the module 7. The cells 8 may be lithium-ion cells. The batteiy module 7 further includes a pair of switching elements 9 addressing each cell 8. As will be hereinafter explained, the pair of switching elements 9 may be selectively controlled to adjust the current (charging and / or discharging current) through the cell 8 and / or -in the event of complete or part failure of the cell 8— direct the current to bypass the cell 8. By providing separate pairs of switching elements for each cell 8, the cells do not share the same current. In this way, the current through each cell 8 can be independently adjusted.

[0065] The batteiy module 7 may include one cell 8. Preferably, the battery module 7 includes a plurality of cells 8, for example between 5 and 10 cells. The number of cells used may be selected according to the power output requirement of the battery pack 1. The switching elements 9 may be semiconductor switches. Examples of semiconductor switches include an Insulated Gate Bipolar Transistor (IGBT) and a Metal-Oxide- Semiconductor Field-Effect Transistor (MOSFET). The switching elements 9 used may be selected according to the particular application of the battery pack 1.

[0066] The pair of switching elements 9 form part of converter circuitiy integrated into the batteiy module 7. As will be explained in more detail hereinafter, the converter circuitiy is connected to the one or more cells 8 such that the voltage output of the battery module 7 may be stepped up and / or stepped down to satisfy one or more conditions or requirements placed on the battery pack 1. Furthermore, the converter circuitry may be configured to direct the current to bypass the battery module 7.

[0067] The first battery module 7, 71 includes n cells 8, where n is a non-zero positive integer. The switching elements 9 of the first batteiy module 71 are n-channel MOSFETS. Alternately, p-channel MOSFETS may be used; in which case, the controlling scheme (described hereinafter) applied to the switching elements 9 during operation would be modified for p-channel MOSFETS. As shown in Figure 2, each cell 8 of the first battery module 71 is coupled to a pair of n- channel MOSFETs 9, herein referred to as a first switching element 9, 91 and a second switching element 9, 92. The positive terminal of each cell 8 is coupled to the drain terminal of the first switching element 91 and the negative terminal of each cell is coupled to the source of the second switching element 92. The drain and the source of the second and first switching elements 92, 9i, respectively, are coupled. In this way, the pair of switching elements 9 92 are arranged such that they may be selectively controlled to modify the duty cycle of the current through the corresponding cell 8.

[0068] As hereinbefore explained, the first batteiy module 71 includes n cells 8. The first and second switching elements 9 92, which address the first cell 8, 81 of the n cells 8, are jointly coupled to a first inductor 10, 10i. In other words, the first inductor lOi is jointly coupled to the drain of the second switching element 92 and the source of the first switching element 91. For each of the cells 8 from the second cell 82 to the nthcell 8n, the pair of switching elements 9 addressing those cells 8 are jointly coupled to the preceding second switching element 92 and cell 8 (as shown in Figure 2). Thus, the second switching elements 92 (of each cell 81 to 8n) are connected in series.

[0069] By way of illustration, for the second cell 82: the source of the first switching element 91 and the drain of the second switching element 92 are jointly coupled to the source of the second switching element 92, which addresses the first cell 8 and the negative terminal of the first cell 81. Likewise, the negative terminal of the second cell 82 and source of the second switching element 92, which addresses the second cell 82, are jointly coupled to the source of the first switching element 91 addressing the third cell 83 and the drain of the second switching element 92 addressing the third cell 83.

[0070] The first inductor lOi is further coupled to the source of a third switching element 9, 93(this coupling forming a first node, Nt). The drain of the third switching element 93is coupled to a positive terminal 11 of the battery module 7. The drain of a fourth switching element 9, 94is coupled between the first inductor lOi and the source of the third switching element 93.

[0071] As will be hereinafter explained, the third and fourth switching elements 93, 94may be selectively operable to control an output voltage of the battery module 7 and / or to control current bypassing of the battery module 7.

[0072] To control the current to bypass the battery module 7, in one example the third and fourth switching elements 93, 94are both switched ON. In another example, the third switching element 93is switched ON and all second switching elements 92 are switched ON.

[0073] The source of the fourth switching element 94is jointly coupled to a negative terminal

[0074] 12 of the batteiy module 7 (forming a second node, N2) and the negative terminal of the nthcell and the source of the second switching element 92 addressing the nthcell.

[0075] The first battery module 71 further includes a capacitor 13 coupled between the positive terminal 11 and the negative terminal 12 of the battery module 71.

[0076] Alternatively, the first batteiy module 71 may include a single cell 8. In this case, the first and second switching elements 9 92 are jointly coupled to the first inductor lOi, as hereinbefore described. The negative terminal of the single cell 8 and the source of the second switching element 92 are jointly coupled to the fourth switching element 94and the negative terminal 12, as hereinbefore described. According to this alternative topology, the first inductor lOi is coupled to the negative terminal 12 and fourth switching element 94via the second switching element 92.

[0077] The circuit elements of the first battery module 71 hereinbefore described, namely the switching elements 9, the first inductor lOi, and the capacitor 13, form part of the converter circuitry of the first battery module 71. The type of circuit elements used in the first battery module 71 may depend on the application of the battery pack 1. The capacitor 13 may take the form of a ceramic capacitor, electrolytic capacitor, or a film capacitor. The capacitor 13 may take the form of a supercapacitor, for example to form a hybrid energy storage system. The first inductor 10 may take the form of a wire-wound inductor having a ferrite or powdered iron core.

[0078] Referring also to Figure 3, a second battery module 7, 72 is shown. The second battery module 72 is an example module 7 which may be incorporated into the batteiy pack 1. The second batteiy module 72 has the same topology as the first battery module 71. However, the second battery module 72 includes additional circuit elements incorporated into the converter circuitry, as will now be explained.

[0079] The second batteiy module 72 includes a duplicate of the current channel formed by the first inductor 10, lOi and the third and fourth switching elements 93, 94(herein also referred to as the “original current channel”). The duplicate channel is formed by a second inductor to2, a fifth switching element 95, and a sixth switching element 96. The circuit elements of the duplicate current channel are arranged in the same way as the counterpart circuit element in the original current channel.

[0080] As shown in Figure 3, the second inductor to2is coupled, with the first inductor lOi, to the first and second switching elements 92, 93addressing the first cell 81. The drain of the fifth switching element 95is coupled to the positive terminal 11. The source of the sixth switching element 96 is jointly coupled to the negative terminal of the nthcell and the source of the second switching element 92 addressing the nthcell. The second inductor to2and the source of the fifth switching element 95are coupled (forming a third node, N3). The drain of the sixth switching element 96 is coupled to the third node N3.

[0081] In this way, the current is split between the original current channel and the duplicate current channel. This topology may help to improve efficiency and / or provide greater fault tolerance in the batteiy module 7, particularly in high power applications, such as those involving power levels of 3 kW or more.

[0082] The duplicate channel is operated in the same way as the original current channel. The duplicate channel can be activated in parallel to the original channel to share the current at high power peaks, or it can be activated as a replacement for the original current channel if the original channel fails. In an example in which both channels are working in parallel, the switching signals of the two channels can be phase-shifted to reduce the voltage ripple.

[0083] As hereinbefore explained, the charging / discharging current through a given cell 8 of the battery module 7 may be adjusted or directed to bypass the cell 8. Furthermore, the converter circuity is configured to both step-up and step-down the voltage output of the batteiy module 7 and to direct the current to bypass the battery module 7. As will be hereinafter explained, the voltage output of the battery module 7 may be adjusted to control its power share, relative to the other modules 7, according to a given command from the BMS 3.

[0084] By providing converter circuity at each module 7 within the pack 1, individual cells 8 and / or module 7 can be bypassed in the event of failure. Thus, the batteiy pack 1 has improved fault tolerance compared to conventional batteiy packs.

[0085] As will be hereinafter illustrated, the batteiy pack 1 according to the present application is controllable to adjust the power sharing between each cell 8 / batteiy module 7 within the battery pack 1. Specifically, the power output of each cell 8 / battery module 7 can be individually and independently adjusted. In this way, the batteiy pack 1 has a “modular” design. This functionality helps to address mismatching in the usable capacity between cells 8 or between battery modules 7 without requiring additional balancing circuitry (as would be the case in conventional batteiy packs). Thus, the batteiy pack 1 can operate under a large degree of mismatching in usable capacity between cells 8 / batteiy modules 7, even when faulty or failed cells 8 / battery modules 7 are present.

[0086] For this reason, partial replacement for components within the battery pack 1 are more feasible than for conventional battery packs. The replacement batteiy modules, which have a higher state of health compared to the original, degraded battery modules, can be controlled to output a greater proportion of the total power output of the battery pack 1— to ensure balanced conditions. Furthermore, the batteiy pack 1 according to the present application is particularly suitable for second-life utilization. The functionality of the battery pack 1 can help to reduce the cost of second-life utilization by removing the need for disassembly of the modules 7, assessments, repairs, matching / grouping, and rebuilding of the battery pack 1. This is because, as previously mentioned, the battery pack 1 can operate with a large degree of mismatching in usable capacity between cells 8 / battery modules 7, even when faulty or failed cells 8 / battery modules 7 are present.

[0087] As will be herein after explained, the battery pack 1 is configured to determine a state of health of one or more cells 8 and / or one or more battery modules 7.

[0088] Indicators of a cell’s 8 state of health include its voltage output, temperature, usable capacity, and power capability (which is determined by the value of its internal resistance). The battery pack 1 may be configured to determine one, some, or all of these indicators.

[0089] Depending on the state of health indicators to determine, each battery module unit 4 may include voltage measurement circuitry (not shown) arranged to measure the voltage output of each cell 8 and temperature sensor circuitry (not shown) arranged to measure the temperature of each cell 8. The voltage measurement circuity and the temperature sensor circuitry are in communication with the module controller 6. Thus, the module controller 6 may be configured to determine the voltage output of each cell 8 and the temperature of each cell 8.

[0090] The module controller 6 may also be configured to determine the power capability of a cell 8 by determining the internal resistance of the cell 8. The module controller 6 may be further configured to determine the usable capacity of a cell 8. The usable capacity may be determined by considering the operating window parameters defined by the specific application, for example the minimum and maximum operating voltage, or the depth of discharge etc.

[0091] Indicators of a battery module’s 7 state of health include the number of failed cells 8 within the module 7, the usable capacity of the module 7, the power capability of each cell 8, and the temperature of the module 7. Thus, the temperature sensor circuitiy (not shown) may be arranged to measure the temperature of the cells within the whole of the module 7.

[0092] The module controller 6 may be configured to determine the usable capacity of the module 7 by determining the usable capacity of each cell 8 in the module 7. Failure of a cell 8 is determined by determining its operational state— as will now be described.

[0093] Methods of operation

[0094] As will now be explained, the battery pack 1 may be operated to account for changes in a state of health of one or more batteiy modules 7 and / or the cells 8. Referring to Figure 4, a first example method of operating the batteiy pack 1 will now be described. This method is outlined in reference to the first battery module 71 merely by way of example.

[0095] According to the first example method, the charging / discharging current is directed to bypass a given cell 8. The given cell 8 may be a failed cell or at risk of failure, for example due to overvoltage, undervoltage, and / or over temperature conditions.

[0096] Firstly, the operational state of the given cell 8 in the battery module 7 is determined (step S1.1).

[0097] Determining the operational state of the given cell 8 may involve determining the cell’s 8 state of health and / or measuring other cell parameters. The given cell 8 is either bypassed or remains connected depending on its operational state. Its operational state indicates that the given cell 8 has failed or is at risk of failure. In response to a determination that the given cell 8 does not need to be bypassed (step Si.2), the given cell 8 continues to be monitored until a threshold operational state is passed (in other words, until the given cell 8 fails or is at risk of failure). In response to a determination that the given cell 8 needs to be bypassed (step S1.2), the module controller 6 corresponding to the first battery module 71 transmits control signals to the first and second switching elements 92 for directing the current to bypass the given cell 8 (step S1.3). In other words, the control signals turn the first switching element 91 OFF and the second switching element 62 ON continuously such that no current flows through the given cell 8 and the charging / discharging current through the other cells 8 of the module 7 is not interrupted. This ON / OFF switching scheme is for when the switching elements 91, 92 are n-channel MOSFETs.

[0098] The following step (step S1.4) of the first example method may be performed to ensure that the power output requirement of the module 7 is nevertheless satisfied after the given cell 8 is bypassed.

[0099] The module controller 6 transmits control signals to the third and fourth switching elements 93, 94for adjusting the duty cycle of current through the converter circuitry. As a result, the voltage output of the module 7 is increased to meet the pre-failure voltage output level (step S1.4).

[0100] The following steps (steps S1.5 to S1.7) of the first example method may be performed to adjust the power sharing between the modules 7 within the battery pack 1.

[0101] Either after or simultaneously with step S1.4, the module controller 6 determines a usable capacity of the module 7. The module controller 6 may also determine other indicators of the state of health of the module 7. The module controller 6 then transmits the information, including the usable capacity, to the BMS 3 (step S1.5).

[0102] In response to the information transmitted in step S1.5, the BMS 3 generates and transmits control signals to one or more module controllers 6 within the batteiy pack 1 (step S1.6). These control signals are for adjusting the voltage output of the one or more modules 7. The voltage output of the one or more modules 7 are adjusted (step S1.7) such that i) the battery pack 1 maintains the required voltage output (which may be pre-set by the application of the batteiy pack 1) and ii) a balanced state of charge among all the batteiy modules 7 within the battery pack 1 is maintained. Thus, the cells 8 of the batteiy module 7 in which the given cell 8 was bypassed are prevented from discharging too quickly (i.e. before the other modules 7 have discharged).

[0103] In step S1.7, the voltage output of the module 7 in which the given cell 8 was bypassed may be adjusted in additional to some or all of the other modules 7.

[0104] Referring also to Figure 5, a second example method of operating the battery pack 1 will now be described. This method is outlined in reference to the first batteiy module 71 merely by way of example. According to the second example method, the charging / discharging current through one or more cells 8 within a given battery pack 1 is adjusted to account for the usable capacity of a given cell 8 within the given batteiy pack 1.

[0105] In other words, and as hereinbefore explained, the second example method addresses mismatching in usable capacity between cells 8 within the same battery pack 1 and between different battery packs 1 without requiring additional balancing circuitry.

[0106] First, a usable capacity of the given cell 8 is determined (step S2.1). The usable capacity of other cells 8 within the same module 7 may be determined.

[0107] In response to the determination in step S2.1, the charging / discharging current of each cell 8 within the module 7 is adjusted (step S2.2). The charging / discharging current is adjusted by selectively controlling the first and second switching elements 92 of each cell 8 such that the duty cycle of the current is adjusted.

[0108] Step S2.2 may occur if, for example, the usable capacity of the given cell 8 is bellow a threshold value and / or a mismatch in usable capacity between the given cell 8 and the other cells 8 within the module 7 is above a threshold value. Each cell 8 is adjusted according to a percentage of the total current of the module 7. For cells 8 with a higher usable capacity, the duty cycle of their charging / discharging current is adjusted such that these cells 8 are supplied with a greater percentage of the total current of the module 7.

[0109] The following step (step S2.3) of the second example method may be performed to ensure that the power output requirement of the module 7 is nevertheless satisfied after the currents of each cell 8 are adjusted. The module controller 6 transmits control signals to the third and fourth switching elements 93, 94for adjusting the duty cycle of current through the converter circuitry. As a result, the voltage output of the module 7 is increased to meet the pre-failure voltage output level (step S2.3). The following steps (steps S2.4 to S2.6) of the second example method may be performed to adjust the power sharing between the modules 7 within the batteiy pack 1. Steps S2.4 to S2.6 are the same as steps S1.4 to S1.6 of the first example method.

[0110] Thus, steps S2.4 to S2.6 enables the battery pack 1 to maintain the required voltage output and maintains the balance in the state of charge among all the battery modules

[0111] 7. Thus, a battery module 7 with a reduced usable capacity relative to the other modules 7 does not prematurely discharge.

[0112] The battery pack 1 according to the present application may be operated in other ways.

[0113] For example, in a scenario in which a battery module 7 is replaced (e.g. due to failure), the BMS may adjust the power sharing between the replacement batteiy module 7 and the original battery modules 7. As the replacement battery module 7 is new, it has greater usable capacity compared to the original battery modules 7. Thus, the BMS may generate and transmit control signals to some or all of the module controllers 6 such that i) the voltage output and hence the power share of the replacement battery module 7 is increased, and ii) the voltage output and hence the power share of at least some of the original battery modules 7 is decreased. In this way, the battery pack 1 is operated to maintain the required voltage output of the battery pack 1 whilst maintaining the balance in the state of charge among all the batteiy modules 7. Simulation data

[0114] Referring now to Figures 6a, 6b, 7a, 7b, 8a, and 8b, simulation data illustrating the functionality of the battery pack 1 according to the present application will now be described.

[0115] The data shown in Figures 6a and 6b correspond to a simulation of the battery module

[0116] 7 (“simulated battery module” 7) having four cells 8 (first, second, third, and fourth cells 8) with mismatched usable capacity (i.e. the first cell has higher capacity compared to other three cells) . As will now be explained, this data demonstrates how the battery pack 1 engages in active power management to perform active energy balancing and to maintain module 7 functionality when multiple cells 8 within a module 7 fail.

[0117] Figure 6a shows a plot of output voltage, Vo, of the batteiy module 7 varying against time. Figure 6b shows a plot of current for each cell, II, 12, 13, I4, varying against time.

[0118] Each plot corresponds to the same time period.

[0119] The simulation starts with active energy balancing by increasing the current share of the first cell 8 that has a higher usable capacity compared to other cells 8 within the module 7.

[0120] At time 1 - 0.25 s, the fourth cell 8 of the simulated battery module 7 fails and thus the plot of I4 falls to I = o. As hereinbefore described, the current through the remaining cells 8 is adjusted (shown by an increase in plots II to I3) to counteract the failed call. This adjustment enables the battery module 7 to maintain a constant output voltage; only a minor fluctuation in plot Vo is observed at the time of failure of the fourth cell 8.

[0121] A similar variation in the plots of Figures 6a and 6b is seen when an additional two cells

[0122] 8 fail. At time t « 0.50 s and t « 0.75 s, the third and fourth cells 8 fail respectively. This results in a respective increase in current of the first cell 8 (shown by respective increases in plot II). From t ~ 0.25 s, the output voltage of the battery module 7 is maintained— aside from brief fluctuations at the time of cell failure.

[0123] The simulation data of Figures 6a and 6b demonstrate how the battery pack 1 according to the present invention can maintain a required voltage output level of the batteiy module 7 whilst performing active energy balancing even when cells 8 fail. The data shown in Figures 7a and 7b correspond to a simulation of a battery pack 1 (“simulated battery pack” 1) having two batteiy modules 7 (first battery module 7 and second battery module 7). The first batteiy module 7 has four cells 8 (first to fourth cells 8) which have the same usable capacity and the second batteiy module 7 has four cells 8 (fifth to eighth cells 8) with once cell (eighth cell) having lower usable capacity.

[0124] Figure 7a shows plots of output voltages of the first battery module 7, VM1, the second batteiy module 7, VM2, and their combined output voltage, VC (in other words, the voltage output of the simulated batteiy pack 1). Figure 7b shows a plot of current for each cell in the first battery module, II, 12, 13, I4, and the second battery module, I5, 16, I7, 18, varying against time. Each plot corresponds to the same time period.

[0125] The simulation starts with active energy balancing by significantly reducing the current share of the eighth cell 8 which has a reduced usable capacity compared to other cells 8 within the two modules 7.

[0126] At t ~ 0.5 s, the eighth cell 8 fails and thus the plot of 18 in Figure 7b falls to I = o. This causes an initial drop in current of the remaining cells 8 in the second module 7, before the current in these cells increases to a value below the current value before the eight cell 8 failed (shown by an increase in plots I5, 16, 17 just after t « 0.5 s).

[0127] As hereinbefore described, the converter circuity of the second module 7 is controlled to adjust the current of the remaining cells 8 in the second module 7. Likewise, the current of the cells 8 in the first module 7 are adjusted (shown by an increase in plots Il to I4 after the eighth cell 8 fails) by increasing its voltage output (shown by an increase in plot VMi after the eighth cell 8 fails) to increase its power share, allowing the second module 7 to reduce its output voltage and hence its power share, to perform active energy balancing whilst maintain the pack’s output voltage at the pre-set value. Aside from a slight fluctuation at t ~ 0.5 s, the voltage output of the simulated batteiy pack 1 is maintained.

[0128] The simulation data in Figures 7a and 7b demonstrate how the batteiy pack 1 according to the present invention can adjust the voltage output of a batteiy module 7 and perform energy balancing whilst maintaining the pack’s output voltage at the pre-set value when another battery module 7 experiences cell failure. The data in Figures 8a and 8b correspond to the same simulation as Figures 7a and 7b, but illustrates a scenario in which the second module 7 fails completely. The second batteiy module 7 fails at t ~ 0.5 s. After this time, the voltage output of the first module 7 is adjusted (by adjustment of the current applied to the first to fourth cells 8) such that this module 7 provides the total voltage output of the simulated batteiy pack 1. Modifications

[0129] It will be appreciated that various modifications may be made to the embodiments hereinbefore described. Such modifications may involve equivalent and other features which are already known. Features of one embodiment may be replaced or supplemented by features of another embodiment.

[0130] Although claims have been formulated in this application to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel features or any novel combination of features disclosed herein either explicitly or implicitly or any generalization thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention. The applicant hereby gives notice that new claims may be formulated to such features and / or combinations of such features during the prosecution of the present application or of any further application derived therefrom.

Claims

Claims1. A battery module comprising : n cells including a first cell, wherein n is a non-zero positive integer, and wherein for each cell the batteiy module comprises: a first switching element coupled to a positive terminal of the cell; and a second switching element coupled to a negative terminal of the cell, the first and second switching elements being coupled; the battery module further comprising: a first inductor jointly coupled to the first and second switching elements corresponding to the first cell; a third switching element coupled between the first inductor and a positive terminal of the battery module, the coupling between the first inductor and the third switching element forming a first node; a fourth switching element coupled between the first node and a negative terminal of the battery module, wherein: the coupling between the fourth switching element and the negative terminal of the battery module forms a second node, and the second switching element corresponding to the nthcell and the negative terminal of the nthcell are jointly coupled to the second node; and a capacitor coupled between the negative and positive terminals of the batteiy module.

2. The batteiy module of claim 1, wherein n is greater than 1, and wherein: for each cell not including the nthcell: the negative terminal of the cell and the second switching element corresponding to the cell are jointly coupled to the first and second switching elements of the proceeding cell, such that the second switching elements of each cell are connected in series.

3. The battery module of claim 2, wherein n is between 5 and 15.

4. The batteiy module of claims 2 or 3, wherein at least one cell of the n cells has a usable capacity different to the other cells.

5. The batteiy module of any preceding claim, wherein each of the first, second, third, and / or fourth switching elements is a semiconductor switch.

6. The battery module of claim 5, wherein the semiconductor switch is a n-channel MOSFET or a p-channel MOSFET.

7. The batteiy module of any preceding claim, wherein the first and second switching elements are selectively operable such that the current bypasses the corresponding cell.

8. The batteiy module according to any preceding claim, wherein the first and second switching elements are selectively operable to control the current through the corresponding cell according to a state of health of the corresponding cell.

9. The batteiy module of claim 8, wherein the state of health includes a usable capacity of the corresponding cell.

10. The battery module of claims 8 or 9, wherein the state of health includes a power capability of the corresponding cell.

11. The batteiy module of any preceding claim, the batteiy module further comprising: a second inductor; a fifth switching element coupled to the second inductor to form a third node; a sixth switching element coupled between the third node and the second node; wherein the second inductor and the fifth switching element are coupled across the first inductor and the third switching element.

12. A battery pack comprising: a plurality of battery module units, each unit comprising: a batteiy module according to any one of claims 1 to 11; a module controller for controlling the battery module; wherein the batteiy module units are connected in series or in parallel; the batteiy pack further comprising a batteiy management system, BMS, for communicating with each module controller.13- The batteiy pack of claim 12, wherein the BMS is configured to communicate with the plurality of module controllers via a Controlled Area Network bus.

14. The batteiy pack of claims 12 or 13, wherein each module controller is configured to transmit information indicating a state of health of the corresponding batteiy module to the BMS.

15. The batteiy pack of claim 14, wherein the state of health of the battery module includes an indication of the state of health of each cell within the battery module.

16. The batteiy pack of claims 14 or 15, wherein the state of health of the batteiy module includes an indication of the number of failed cells within the battery module.

17. The battery pack of any of claims 12 to 16, wherein the BMS is configured to transmit at least one control signal to at least one module controller according to a voltage output requirement and / or power requirement of the battery pack.

18. A first method of operating the battery pack of any one of claims 12 to 17, the method comprising: determining an operational state of a given cell within the batteiy module; in response to a determination that the given cell has failed or is at risk of failure, selectively controlling the first and second switching elements corresponding to the given cell such that the current bypasses the given cell.

19. The first method of claim 18, the method further comprising, after bypassing the given cell: selectively controlling the third and fourth switching elements to adjust the voltage output of the battery module.

20. The first method of claims 18 or 19, the method further comprising, after bypassing the given cell: determining a remaining usable capacity of the battery module; transmitting information including the remaining usable capacity of the battery module to the BMS;the BMS transmitting at least one control signal to at least one module controller, wherein the at least one control signal depends on a required voltage output of the batteiy module corresponding to the at least one module controller.

21. The first method of claim 20, wherein the at least one control signal includes a plurality of control signals for adjusting a voltage output of each battery module.

22. The first method of claims 20 or 21, wherein the information further includes the remaining usable capacity of each cell and / or the number of cells which have failed or are at risk of failure.

23. A second method of operating the battery pack of any one of claims 12 to 17, the method comprising: determining a usable capacity of a cell within the batteiy module; in response to the determination, selectively controlling the first and second switching elements of each cell within the battery module to adjust the current through each cell.

24. The second method of claim 23, the method further comprising, after adjusting the current through each cell: selectively controlling the third and fourth switching elements to adjust the voltage output of the batteiy module.

25. The second method according to claims 23 or 24, the method further comprising: after adjusting the current through each cell, determining a usable capacity of the battery module; transmitting information including the usable capacity of the battery module to the BMS; the BMS transmitting at least one control signal to at least one module controller, wherein the at least one control signal depends on a required voltage output of the batteiy module corresponding to the at least one module controller.

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