Reconfigurable battery management system

Abstract

The invention relates to a battery control system comprising a circuit module with a pair of output terminals. The circuit module has a plurality of cell modules selectively connectable in a series configuration with the output terminals to provide the target output voltage on the output terminals, each cell module comprising at least one battery cell, a switching circuit configured to selectively operate in two or more states. The states include a state whereby the at least one cell is bypassed from the series string; and a state whereby the at least one cell is connected in series with the series string. A controller is configured to provide the target output voltage based on selective control of the operation state of each switching circuit of each cell.

Description

[0001] Reconfigurable Battery Management System

[0002] Technical Field

[0003] The invention generally relates to the control of energy storage modules typically containing battery cells in an energy storage system, and in particular relates to control of energy storage modules to improve voltage output generation and improve efficiency.

[0004] Background Art

[0005] Energy storage systems for applications such as full electric vehicles, hybrid electric vehicles, and stationary energy storage in grid connected or off grid applications, frequently include an arrangement of multiple energy storage cell units.

[0006] Each cell unit is limited by its functional mechanism and design to provide an output voltage within a certain range depending on its state of charge and operating conditions. Each cell unit is also limited by its functional mechanism and design to provide a certain maximum charge storage capability, depending on the operating conditions. Electrically connecting cell units in series increases the maximum achievable output voltage, therefore decreasing the magnitude of current required to supply a given power output. This increases the system efficiency as ohmic losses increase with current magnitude. Electrically connecting cell units in parallel increases the maximum achievable storage capacity for a given cell unit capacity and storage system output voltage level.

[0007] The individual cell units inevitably display some differences in terms of charge storage capacity, internal resistance, and other performance related factors. Even before entering their operating life, cell units inevitably have differences caused by manufacturing tolerances that allow for certain variations in cell units during manufacturing with even the most advanced state of the art manufacturing processes. Throughout the operating life, variations in cell unit performance degradation conditions or profiles further contribute to these differences. In applications in which used cell units are recycled for reuse, the cell units can be associated with notable performance differences, particularly if the cell units have been exposed to different usage profiles. Utilising cell units with different specifications can also contribute to cell unit differences.

[0008] Publications including US10573935B2 propose a new approach to balancing the performance of multiple energy storage cell units in an energy storage system. The approach involves balancing a battery by allowing each individual cell unit to be included or bypassed when connected in series via bypass / include MOSFET switches when the battery is in operation. This publication also reports novel layouts that have unique advantages. Publications US20210265710A1 and US11264812B2 further improved on US10573935B2 by adding more layouts that allow the altering of polarity of an energy storage system without requiring an inverter or an H-bridge. This allows the energy storage system to act as a multi-level inverter without requiring an H-bridge or a converter or an inverter.

[0009] Such systems are used in multi-level inverters or reconfigurable battery systems (or reconfigurable energy storage systems) which typically contain a large number of battery modules or cells (nodes), and even more number of switches to control these nodes. The cells are connected in series to produce a desired output voltage. The control scheme must enable selection of which nodes to connect in series and which nodes to bypass based on load requirements and balancing requirements.

[0010] However, there is an ongoing issue with such multi-cell systems whereby managing the load applied to any one cell and its environmental conditions is important to the longevity of cells within the system. It is therefore an object of the invention to improve upon the aforementioned issues of the prior art, or at least provide the public with a useful choice. Other objects will be apparent to those skilled in the art.

[0011] Summary of the Invention

[0012] In one aspect the invention relates to a battery control system comprising: a circuit module comprising a pair of output terminals configured to provide a target output voltage, the module comprising: a string of cell modules, each cell module comprising: a first terminal and a second terminal, at least one cell, a switching circuit configured to: connect the first terminal to the second terminal thereby bypassing the at least one cell, or connect the at least one cell between the first terminal and the second terminal; and a controller configured to control the switching of one or more cell modules to target the circuit module output voltage.

[0013] In one aspect the invention relates to a battery control system comprising: a circuit module comprising a pair of output terminals, the circuit module comprising: a plurality of cell modules selectively connectable in a series configuration with the output terminals to provide the target output voltage on the output terminals, each cell module comprising: at least one battery cell; a switching circuit configured to selectively operate in two or more states, the states comprising: a state whereby the at least one cell is bypassed from the series string; and a state whereby the at least one cell is connected in series with the series string; and a controller configured to provide the target output voltage based on selective control of the operation state of each switching circuit of each cell.

[0014] In some embodiments, the controller is configured to: control the switching circuit of one or more cell modules to meet the target circuit module output voltage by a combination of: the series connection of one or more cell modules with the output terminals; and modulation of the state of the switching circuit at least one cell module, relative to the state of the series connection of one or more cell modules, such that the target voltage is substantially provided at the circuit module output terminals.

[0015] In some embodiments, the controller is configured to: determine a set of cell modules for series connection to meet the target output voltage within a predefined time increment; and control the switching circuit of one or more cell modules comprising a combination of: a series connection of one or more cell modules with the output terminals, and modulation, within the predefined time increment, of the switching state of at least one cell module such that the output voltage is substantially provided at the circuit module output terminals.

[0016] In some embodiments, the controller is configured to: determine the target circuit module output voltage and control a modulation duty cycle of the modulation of the switching state of at least one cell module based on the target circuit module output voltage.

[0017] In some embodiments, the controller is configured to: control the switches of one or more cell modules to meet the target circuit module output voltage by a combination of: series connection of one or more cell modules with the output terminals, and modulation of the switching state of at least one cell module such that the target voltage is substantially met at the circuit module output terminals.

[0018] In some embodiments, the controller is configured to: determine a set of cell modules for series connection to meet a target output voltage within a predefined time increment, control the switches of the set of cell modules comprising a combination of: series connection of one or more cell modules with the output terminals, and modulation, within the predefined time increment, of the switching state of at least one cell module such that the output voltage is substantially targeted at the circuit module output terminals.

[0019] In some embodiments, the voltage target is defined by time varying amplitude and phase, and the controller is configured to control, at predetermined time intervals, the series connection of one or more cell modules and the modulation of the switching state overtime based on the time varying amplitude and phase.

[0020] In some embodiments, the controller is further configured to determine cell data from each at least one cell of each cell module comprising one or more of: voltage, state of charge, temperature, age, measured service life, predicted service life, rate of temperature change, internal resistance, position in a series arrangement, state of health, charge current ability, discharge current ability; and determine a rank for each cell module based on the determined cell data.

[0021] In some embodiments, the rank is determined based on a determination of which cell modules are contributing to the output voltage; and wherein the rank is determined by comparison to other contributing cell modules.

[0022] In some embodiments, the controller is further configured to determine cell data parameters from each the at least one cell of each cell module comprising one or more of: voltage, state of charge, temperature, age, measured service life, predicted service life, rate of temperature change, internal resistance, position in a series arrangement, state of health, and determine a rank for each cell module based on a weighted combination of two or more determined cell data parameters.

[0023] In some embodiments, the controller is further configured to: determine the target circuit module output voltage; and control the modulation duty cycle of the switching state of at least one cell module to meet the target circuit module output voltage.

[0024] In some embodiments, the controller is further configured to: determine the target circuit module output voltage; and control the modulation duty cycle of the switching state of a cell module based on the determined rank to meet the target circuit module output voltage.

[0025] In some embodiments, the controller is further configured to: determine the target circuit module output voltage and, based on the determined rank of each cell module: prioritise a higher modulation duty cycle of the switching state to those cell modules with a higher rank and / or a lower modulation duty cycle of the switching state to those cell modules with a lower rank.

[0026] In some embodiments, the controller is further configured to: determine the target circuit module output voltage; and control the modulation duty cycle of the switching state of two or more cell modules to meet the target voltage.

[0027] In some embodiments, the controller is further configured to: determine the target circuit module output voltage, determine a weighting factor attributing a modulation duty cycle priority to each cell module based on the determined rank, and control the modulation duty cycle of the switching state of each ranked cell module based on the weighting factor.

[0028] In some embodiments, the weighting factor defines an even distribution across the ranked cell modules.

[0029] In some embodiments, the weighting factor defines a nonlinear distribution across the ranked cell modules.

[0030] In some embodiments, the system comprises multiple cell modules, and controller is configured to: determining a cell module balance target voltage, and identify one or more cell modules have a voltage higher than the cell module balance target voltage, and based on the identified one or more cell modules: prioritise a higher modulation duty cycle of the switching state to those cell modules with a higher voltage and / or a lower modulation duty cycle of the switching state to remaining / unidentified cell modules.

[0031] In some embodiments, the controller is configured to determine the difference between: the sum of the one or more cell modules, and the target output voltage; then for the switching circuit of at least one cell module, control the modulation duty cycle based on the determined voltage difference.

[0032] In some embodiments, the controller is further configured to: determine the target circuit module output voltage, determine the output voltage, determine the difference between the output voltage and the target voltage, then, based on the difference: adjust the weighting factor attributing the modulation duty cycle priority to each cell module based on the determined rank, and control the modulation duty cycle of the switching state of each ranked cell module based on the weighting factor.

[0033] In some embodiments, the controller is further configured to, for each modulated cell: determine the difference magnitude between a current cell module rank and a new cell module rank; adjust the modulation duty cycle of the switching state of each ranked cell module based on difference magnitude.

[0034] In some embodiments, the controller is further configured to, for each modulated cell: determine one or more cell parameters comprising the voltage, state of charge, temperature, age, measured service life, predicted service life, rate of temperature change, internal resistance, position in a series arrangement, state of health of each cell module, charge current ability, discharge current ability; and adjust the modulation duty cycle of the switching state of each ranked cell module based on determined one or more cell parameters. In some embodiments, adjusting the modulation duty cycle of the switching state is further based on a scaler multiplier.

[0035] In some embodiments, adjusting the modulation duty cycle of the switching state is dependent on the rank of each cell module.

[0036] In some embodiments, the controller is further configured to: determine the target circuit module output voltage, map the weighting factor to the modulation duty cycle priority to each cell module based on the determined rank, and control the modulation duty cycle and / or frequency of the switching state of each ranked cell module based on the weighting factor.

[0037] In some embodiments, the controller is further configured to: measure the voltage at the output terminals, and adjust one or more modulation parameters for any one or more cell modules based on the measured voltage.

[0038] In some embodiments, the controller is further configured to measure the voltage output from a cell module, and adjust one or more modulation parameters for any one or more cell modules based on the measured cell module output voltage.

[0039] In some embodiments, the switching circuit comprises a plurality of switches having a set of switching states, the switching states comprising: a first state whereby the switches are configured to bypass the at least one cell; or a second state whereby the switches are configured to connect the at least one cell in series between the first terminal and second terminal.

[0040] In some embodiments, the system comprises two or more cell processors are configured to: determine the cell data for one or more cells under control of each cell processor; communicate the determined cell data to one or more other cell processors, wherein at least one cell processor is configured to determine the rank of each cell from received and determined cell data, and communicate the rank to one or more other cell processors.

[0041] In some embodiments, the system comprises two or more cell processors, each configured to: determine the cell data for one or more cells under control of each cell processor; communicate the determined cell data to one or more other cell processors; and wherein each cell processor is configured to determine the rank of each cell from received and determined cell data; and each cell processor is configured to operate the respective switching circuit according to the determined rank.

[0042] In some embodiments, the controller further comprises: one or more cell processors operatively configured to control the switching state of one or more cell modules, and a central processor, wherein the central processor and one or more cell processors are configured to communicate via a first communication channel.

[0043] In some embodiments, the first communication channel comprises a channel adapted for transmission of a synchronisation signal.

[0044] In some embodiments, the first communication channel is a dedicated synchronisation channel. Wherein the communication channel between the central processor and cell processor comprises an update frequency lower than the modulation base frequency.

[0045] In some embodiments, each of the one or more cell processors are configured to communicate to one or more other cell processors via a second communication channel.

[0046] In some embodiments, the one or more cell processors are configured to control the modulation of the switching circuit at a rate higher than the communication rate of the communication channel.

[0047] In some embodiments, the central processor is configured to communicate the target voltage to one or more cell processors, and in response, each cell processor is configured to control the state of their one or more cell modules and / or the modulation. In some embodiments, the central processor is configured to update the target voltage at a first frequency, and the modulation base frequency is at least twice the time increment.

[0048] In some embodiments, the central processor is configured to send a synchronisation signal operable to control the timing of the switching circuit and to thereby target a new output voltage, and one or more cell processors are configured to control a switching state of the switching circuit when a synchronisation signal is received.

[0049] In some embodiments, the system further comprises a low-pass filter connected between the string of cell modules and an output terminal.

[0050] In some embodiments, the predefined time increment represents an interval at which the target output voltage (or data indicative thereof) is updated. The target output voltage is based on an ideal output voltage which mimics a time varying voltage such as a mains voltage waveform of around 110 or 240V. The time increment will often have some level of tolerance involved before it departs too far from what voltage might match a mains sine shaped waveform. The tolerance may be for time interval before which a cell module is added or removed from the series string of cells and may be for the voltage level itself. The tolerance may be expressed in terms of voltage, time, or percentage difference from voltage and time. In some embodiments, the predefined time increment represents an interval at which the rank determination is updated. In some embodiments, the modulation duty cycle represents a cell contribution duty to the target output voltage based on the rank of the cell.

[0051] In some embodiments, the system is a reconfigurable battery system. In some embodiments, the modulation base frequency is at least 1 .25, 1.5, or 2 times faster the time increment. In some embodiments, the modulation comprises PWM or PDM. In some embodiments, the voltage target comprises a DC voltage reference. In some embodiments, the voltage target comprises an AC voltage reference. In some embodiments, the voltage target comprises a stepwise approximation of an AC sinusoidal voltage waveform reference. In some embodiments, the voltage target comprises a time varying DC voltage. In some embodiments, the voltage target comprises a substantially 50Hz or 60Hz waveform.

[0052] In another aspect the invention relates to an electric vehicle comprising the system according to any former statement, the vehicle comprising: a motor controller configured to determine motor demand data; wherein the controller is configured to determine the circuit module output voltage based on the demand data.

[0053] In another aspect the invention relates to an electric vehicle charging system comprising the system according to any former statement, the charging system comprising: one or more charger connection points, each point configured to connect with an electric vehicle; a charge controller configured to receive a signal containing charging requirement data of an electric vehicle connected with one charger connection point; wherein the controller is configured to determine the circuit module output voltage based on the charging requirement data.

[0054] In some embodiments, the invention relates to any one or more of the above statements in combination with any one or more of any of the other statements. Other aspects of the invention may become apparent from the following description which is given by way of example only and with reference to the accompanying drawings.

[0055] The entire disclosures of all applications, patents and publications, cited above and below, if any, are hereby incorporated by reference. This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

[0056] To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting. The term "and / or" referred to in the specification and claim means "and" or "or", or both. The term "comprising" as used in this specification and claims means "consisting at least in part of. When interpreting statements in this specification and claims which include that term, the features, prefaced by that term in each statement all need to be present but other features can also be present. Related terms such as "comprise" and "comprised" are to be interpreted in the same manner.

[0057] As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms “includes,” “comprises,” “including,” and / or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present.

[0058] Brief description of the drawings

[0059] The invention can be better understood with reference to the following drawings. The elements of the drawings are not necessarily to scale relative to each other, emphasis instead being placed upon clearly illustrating the principles of the invention. Furthermore, like reference numerals designate corresponding parts throughout the several views.

[0060] Figure 1 shows an exemplary control structure for an energy storage system which is typical of a multi-level inverter or a reconfigurable battery system.

[0061] Figures 2A and 2B show an exemplary battery system which includes a plurality of battery cell modules, a central controller for controlling the operation of the battery cell modules, and an output module for measuring and validating the output from the battery cell modules 102, and or processing the output to provide a desired output voltage profile.

[0062] Figure 3 shows a diagram of steps undertaken by a controller implementing modulated control and series connection control of a switching circuit based on a determined rank of cells in a reconfigurable battery system.

[0063] Figure 4 shows a table outlining exemplary duty cycle difference profiles based on an AC time varying waveform.

[0064] Figure 5 / 1 shows an overview of step B2 of the controller.

[0065] Figure 6 shows an example of an ideal AC waveform where 9V voltage target from a simplified 12V peak.

[0066] Figure 7 illustrates the contributions of five cells to generate an AC waveform where cell one contributes the longest duration and cell five the shortest duration.

[0067] Figure 8A and 8B show tables of profile information including different DCD profiles differences which can be used to control the use of cells over time or controls the usage of cells to more use some cells disproportionately more than others.

[0068] Figure 9 show an alternative embodiment where cell usage is determined by the DCD alone.

[0069] Figure 10A to 10C show cell contribution profiles including a linear, a less aggressive non-linear profile, and a more aggressive non-linear profile respectively.

[0070] Figure 11 shows an example of a more aggressive balancing profile (hence involving more cells) can lead to a better fit on an ideal AC sinusoidal waveform which reduces harmonics.

[0071] Figure 12 shows linear DCD profile embodiments and non-linear DCD profile embodiments.

[0072] Figure 13 shows an exemplary profile for implementation by the controller based on adaptive DCD / BWF

[0073] Figure 14 shows an example of what such an adaptive DCD could look like over time.

[0074] Figure 15A and B show an example based on PWM modulation.

[0075] Figure 15C and D shows an example of PDM based modulation.

[0076] Figure 16 shows a table comparing cell contribution differences.

[0077] Figure 17 shows an example of rounded PDM contributions based on rank is shown in the table. Figure 18A to 18D show examples of PDM and PWM based modulation compared with a prior art approach which does not incorporate modulation.

[0078] Figures 19A to 19D demonstrate that the PWM based modulation of this embodiment has an advantage over PDM based modulation.

[0079] Figures 20A to 20D demonstrate that the PWM based modulation of this embodiment has an advantage over PDM based modulation. Detailed Description of Exemplary Embodiments

[0080] Exemplary methods, devices, assemblies and systems are described herein. It should be understood that the word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment or feature described herein as “exemplary” or “illustrative” is not necessarily to be construed as preferred or advantageous over other embodiments or features. More generally, the embodiments described herein are not meant to be limiting. It will be readily understood that certain aspects of the disclosed systems and methods can be arranged and combined in a wide variety of different configurations, all of which are contemplated herein.

[0081] In this specification, the terms “energy storage module”, "battery cell unit", "cell unit" or “cell module” are generally intended to refer to a module which can store an electrical charge and can refer to an individual battery cell or a block of cells connected in parallel, or a multitude of individual battery cells or blocks of parallel cells or a mix of cells connected in series and / or parallel. Where the terms battery cell, cell or cell unit is used, equally applicable are battery module, module, cell module or module unit, where a module may contain one or more cells in series and / or in parallel.

[0082] In this specification, the term “energy storage module” may also refer to a block of cells connected in parallel and / or series and which further includes circuit components such as fuses, resistors, passively controlled diodes, capacitors or inductors are connected in series and / or parallel with individual cells. The term “energy storage unit”, “storage unit”, “battery cell unit” or “cell unit” may also refer to non-battery energy storage elements such as fuel cells and supercapacitors.

[0083] In some embodiments, the energy storage modules may be designed to include one or more energy storage units enabling a charge capacity of at least 10Ah, 20Ah 40Ah, 60Ah, 100Ah, 200Ah, or 400Ah ampere hours. In some embodiments, the plurality of energy storage units may comprise a first and a second energy storage unit, with the first energy storage unit having a charge capacity that is substantially larger than the charge capacity of the second energy storage unit.

[0084] Embodiments of the invention discussed in this specification relate to a battery control system comprising a circuit module comprising a pair of output terminals configured to provide a target output voltage. The module comprises a string of cell modules and may be referred to as a reconfigurable battery system. Such cell modules typically each cell module comprise a first terminal and a second terminal, at least one cell, and a switching circuit configured to connect the first terminal to the second terminal thereby bypassing the at least one cell, or connect the at least one cell between the first terminal and the second terminal. In this way, the cell module may contain any number of cells in series, or parallel, or a combination of series and parallel, and the switching circuit controls the connection of any one of those cells to the cell terminals. For example, in a reconfigurable battery system is common for the switching circuit to control the connection of those cells to the terminals or for the terminals to be connected such that the cells are bypassed. Other cell configurations are possible, such as the switching circuit configurations which reverse the polarity of cells within the cell module. Polarity control may be provided by, for example, H-Bridge or 2n+2 inverted H-Bridge circuit topologies. A controller is configured to control the switching of one or more cell modules to target the circuit module output voltage.

[0085] The term controller as used in this specification will most commonly be used to describe the functions of one or more processing devices such as microprocessors but will also include other computations devices or discrete logic circuits. The term controller also includes a combination of multiple processing devices. A controller will typically feature output pins which are operably connected to switching devices to control the state of that switching device. For example, the pin of a microprocessor may be connected to the gate of a MOSFET switching device. The controller provides control functionality of the system such as the determination of a target voltage, and the output signals required to operate the switching circuit of one or multiple cell modules to generate the target output voltage.

[0086] The target voltage will be determined on the basis of the output voltage requirement for the system. For example, in some embodiments, the system provides a mains output voltage which may be a sinusoidal 110 to 240V signal at 50 to 60Hz. Other examples include DC voltage applications such as would be found in an electric vehicle (EV), EV charging device, or other more general DC application. As such, the target output voltage may be time varying or time static. A reconfigurable battery system is most often found with lithium-based cells and as such the cell voltage is typically operated between 2.5 and 4.2V per cell. This cell voltage range means that the output voltage is typically only able to step based on voltage of the cell i.e., steps of 2.5-4.2V, depending on the voltage of a connected cell at any time. Other battery technologies or voltage source technologies may dictate other voltage steps. Embodiments of the invention relate to improving this step control by the inclusion of modulation of the switching state of any one or more cell modules such that, typically when combined with a filter, a much smaller output voltage step can be achieved. Other advantages are also possible such as having control over the load applied to a cell over time. Load application can be based on, for example, determinations of cell performance.

[0087] Accordingly, in some embodiments, the controller is configured to control the switches of one or more cell modules to meet the target circuit module output voltage by a combination of: series connection of one or more cell modules with the output terminals, and modulation of the switching state of at least one cell module such that the target voltage is substantially met at the circuit module output terminals. In this way, at least one cell is able to contribute a fraction of the full cell voltage to the total output voltage of the series combination of cells. Modulation duty as applied by the controller, for example, will allow control of the voltage contribution of the modulated cell or cells.

[0088] In some embodiments, the controller is configured to determine a set of cell modules for series connection to meet a target output voltage within a predefined time increment, control the switches of the set of cell modules comprising a combination of: series connection of one or more cell modules with the output terminals, and modulation, within the predefined time increment, of the switching state of at least one cell module such that the output voltage is substantially targeted at the circuit module output terminals. The predefined time increment is typically determined based on the type of voltage waveform the system is intended to provide. For AC main voltage generation, the time increment is typically based on a determination of the target output voltage for incremental time periods. For example, where the peak voltage of the AC mains is 240v, the controller is configured to determine how many cells are required to be configured in series to meet the target. If all cells are at 4V, for example, then 240 / 4 = 60 cells to be connected in series at the peak amplitude of the waveform. The number of cells to be connected in series would be determined by the voltage of those cells and the voltage of the waveform at any point in time. Accordingly, the controller is configured to determine the voltage of cells for possible connection to the output.

[0089] Therefore, the voltage target is defined by time varying amplitude and phase, and the controller is configured to control, at predetermined time intervals, the series connection of one or more cell modules and the modulation of the switching state over time based on the time varying amplitude and phase. The predetermined intervals may be determined by steps of available cell voltage compared to the required voltage at phase increments of the waveform.

[0090] In some embodiments, the controller is further configured to determine cell data from each at least one cell of each cell module comprising one or more of: voltage, state of charge, temperature, age, measured service life, predicted service life, rate of temperature change, internal resistance, position in a series arrangement, state of health, charge current ability, discharge current ability; and determine a rank for each cell module based on the determined cell data. As mentioned, the ability to modulate cells allows a cell to be controlled to connect to a load for less time than an unmodulated cell. Accordingly, there are advantages in unloading some cells over others. The cell data is used to inform which cells would be favourably unloaded against others. Simple examples include where one cell is hotter, or has less voltage compared to another cell. When the system has many cells, cell data for those cells allows ranking and therefore prioritisation of some cells to be loaded more than others.

[0091] In some embodiments, the rank is determined based on a determination of which cell modules are contributing to the output voltage; and wherein the rank is determined by comparison to other contributing cell modules. When cells are connected to a load, their cell data will often change over time. For example, heat or internal resistance will cause the properties of a cell to change over time. Accordingly, it is advantageous to determine cell data from those cells connected to a load (contributing to an output voltage). Rank information can be based on that cell data to be more accurate or reliable.

[0092] In some embodiments, cell data points are combined to determine the rank of a cell over others. The combination may be based on various methods including which cell data takes priority over others. For example, cell temperature is often more important for a cell rank determination than other cell data points. Accordingly, in some embodiments, the controller is further configured to determine cell data parameters from each the at least one cell of each cell module comprising one or more of: voltage, state of charge, temperature, age, measured service life, predicted service life, rate of temperature change, internal resistance, position in a series arrangement, state of health, and determine a rank for each cell module based on a weighted combination of two or more determined cell data parameters.

[0093] In some embodiments the controller is further configured to determine the target circuit module output voltage; and control the modulation duty cycle of the switching state of at least one cell module to meet the target circuit module output voltage. This means that more than one cell may be subject to modulation in a series string of cells. In this way, the contribution of multiple cells can be controlled based on the resolution of the modulation. The resolution of the modulation may be determined based on processor operation speeds, control loop speeds, communication speeds and whether switching losses are to be mitigated within the switching devices.

[0094] In some embodiments, the controller is further configured to determine the target circuit module output voltage; and control the modulation duty cycle of the switching state of a cell module based on the determined rank to meet the target circuit module output voltage. Where there are many cells configured in series, the rank of each cell can determine the contribution, and therefore the modulation duty cycle, to the output voltage.

[0095] In some embodiments, the controller is further configured to determine the target circuit module output voltage and, based on the determined rank of each cell module, prioritise a higher modulation duty cycle of the switching state to those cell modules with a higher rank and / or a lower modulation duty cycle of the switching state to those cell modules with a lower rank. In this way, those cells which are prioritised may have a different duty cycle applied compared to a selection of lower ranked cells. The prioritisation may further include a nonlinear distribution of contribution, based on the modulation duty cycle, such that higher ranked cells are disproportionately loaded compared to lower ranked cells.

[0096] In some embodiments, the controller is further configured to determine the target circuit module output voltage, determine a weighting factor attributing a modulation duty cycle priority to each cell module based on the determined rank, and control the modulation duty cycle of the switching state of each ranked cell module based on the weighting factor. The weighing factor is a factor which represents the level of disproportionality which may be spread across modulated cells. The weighting factor often represents a variable in a mathematical representation of contribution distribution across multiple cells. The variable may simply be altered based on ongoing cell data measurements by the controller.

[0097] In some embodiments, the controller is configured to balance the voltage of multiple cells in a series string of cells by determining a cell module balance target voltage, and identify one or more cell modules have a voltage higher than the cell module balance target voltage, and based on the identified one or more cell modules: prioritise a higher modulation duty cycle of the switching state to those cell modules with a higher voltage and / or a lower modulation duty cycle of the switching state to remaining / unidentified cell modules. In this way, the higher prioritised cells are loaded more than the lower such that their capacity is used at a higher rate. Control of the duty cycle of each cell allows a cell balance target voltage to be converged on. Accordingly, in some embodiments the controller is configured to measure individual cells voltages and adjust the applied modulation duty cycle to converge those cell voltages to a cell balancing target. The balancing target may evolve overtime such as a group of cells collectively are discharged.

[0098] In some embodiments, the controller is configured to implement a feedback loop whereby the output voltage of the circuit is measured, and any difference between the output voltage and the target voltage is used to control a change in the modulation duty cycle applied to one or more cells. Accordingly, the controller is further configured to: determine the target circuit module output voltage, determine the output voltage, determine the difference between the output voltage and the target voltage, then, based on the difference: adjust the weighting factor attributing the modulation duty cycle priority to each cell module based on the determined rank, and control the modulation duty cycle of the switching state of each ranked cell module based on the weighting factor. The controller may measure the output voltage of the circuit and make adjustments to the modulation duty cycle, or the output voltage from one or more individual cells, or a combination of these measurements.

[0099] Modulation of the switching circuit and thereby cell voltage contributions to a total output voltage is most advantageous when the controller is distributed and comprises multiple processors. In a distributed controller system, some processors may operate at higher speeds than others. One particular system is where there is a master or central processor controlling the synchronisation of cell switching, and a cell level processor controlling the switching circuit of one or more cell modules. Often, the central processor is bandwidth limited and is unable to control modulation of cell modules directly without overloading the processor and causing issues with the synchronisation of cell switching functions. Accordingly, in some embodiments, the system comprises two or more cell processors are configured to: determine the cell data for one or more cells under control of each cell processor; communicate the determined cell data to one or more other cell processors, wherein at least one cell processor is configured to determine the rank of each cell from received and determined cell data, and communicate the rank to one or more other cell processors. In some embodiments, the system comprises two or more cell processors, each configured to: determine the cell data for one or more cells under control of each cell processor; communicate the determined cell data to one or more other cell processors; and wherein each cell processor is configured to determine the rank of each cell from received and determined cell data; and each cell processor is configured to operate the respective switching circuit according to the determined rank. Cell level processors can undertake less time-sensitive tasks as will be discussed in further detail below.

[0100] Overview of electronic structure - switched cell circuits

[0101] In some embodiments, there is a system where energy storage modules are selectively connected in series as may be required to produce a desired output voltage. This system may be referred to as a reconfigurable battery system.

[0102] In some embodiments, an electronic assembly supports electronic switching components that are selectively operated to enable connection or bypass of any one or more battery cell units from a series arrangement. The operation may further entail selective bypass and reconnection, where bypassing a battery cell from a series arrangement is performed in a reversible way such that the battery cell can thereafter be selectively reconnected to the series arrangement. Selective bypassing of cells from a series arrangement achieves different connection states and allows variation, for example, in the output voltage of the series arrangement. Operation of the electronic switching components is possible during charging and / or discharging of one or more battery cell units in the series arrangement.

[0103] Where there are three battery cell units, the connection states may include a first state in which the first battery cell unit and the second battery cell unit are electrically connected in series and the third battery cell unit is bypassed; a second state in which the first battery cell unit and the third battery cell unit are electrically connected in series and the second battery cell unit is bypassed; and a third state in which the second battery cell unit and the third battery cell unit are electrically connected in series and the first battery cell unit is bypassed.

[0104] Where there are four battery cell units, the states may include the above three states, as well as a fourth state in which the first battery cell unit, the second battery cell unit and the fourth battery cell unit are electrically connected in series and the third battery cell unit is bypassed; and a fifth state in which the first battery cell unit, the second battery cell unit, the third battery cell unit and the fourth battery cell unit are electrically connected in series.

[0105] By controlling the number of cell units connected in series, the electronic assembly may be able to control the resulting voltage at the outputs of one or a multitude of electronic assemblies.

[0106] In some embodiments, the electronic assembly supports electronics components that are operated in such a way that in addition to connecting or bypassing any of a number of battery cell units from a series arrangement, individual battery cell units or groups of battery cell units can additionally be inverted. In one control state, such an electronic assembly may have a first output terminal with a comparatively positive voltage potential in respect to a second output terminal. In a second control state, such an electronic assembly may have the first output terminal with a comparatively negatively voltage potential in respect to a second output terminal. Inversion of the battery cell outputs may be performed by circuit arrangements such as an H-bridge circuit.

[0107] In some embodiments, the switching components may be operated in such a way that multiple battery cell units are series-connected while one or more battery cell units are connected to a resistive element for the purpose of discharging these one or more battery cell units or reducing the charging of these one or more battery cell units. In another embodiment, the switching components on the electronic assembly may be operated in such a way that multiple battery cell units are series- connected while one or more battery cell units are connected to an energy transfer element for the purpose of transferring energy from a first cell unit to one or more other cell units, or to transfer energy from one or more other cell units to the first cell unit. The energy transfer elements could for example include one or more of capacitors, inductors, transformers, DC / DC converters and / or batteries.

[0108] Harmonics

[0109] Embodiments of the invention are directed to the control of an output voltage profile from a series connection of energy storage modules closely fits a time varying waveform such as a sinusoid. In particular, the embodiments are directed to the mitigation of harmonics being generated when series cells are switched. Switching series connected cells causes the generation of harmonics in several ways: First, the switching action creates a square wave voltage waveform with sharp transitions that contain high-frequency components, including odd and even harmonics; Second, the output voltage waveform is typically not a pure sinusoidal waveform, which also contributes to the generation of harmonics. It is here that a better “fit” of a waveform reduces harmonics by a closer match of a sinusoidal waveform.

[0110] One example is an ideal AC sinusoidal waveform such as a mains voltage. However, the closeness of the fit is limited by the voltage values of the connected cells. For example, when the cells are near full SoC their voltages are higher which puts a limit on the degree of “fit” on the ideal AC sinusoidal waveform, leading to undesirable level of harmonics.

[0111] Control structure

[0112] Figure 1 shows an exemplary energy storage system control structure which is typical of a multi-level inverter or a reconfigurable battery system. In the depicted system, there is a controller configured to operate one or more energy storage devices.

[0113] The system also comprises a distributed arrangement of communication channels operable to control the switching devices of each energy storage module. In the exemplary system, communication channels are separated into those with “real-time” signals which are typically time sensitive and relate to precision timing of events, and “soft- time” signals. A real time signal is also typically communicated to all energy storage modules from a single source, whereas a soft-time signal is typically sent from multiple sources.

[0114] Separate channels for high and low speed communication signals are useful in instances where the communication speed limitations of a system cause delay in time sensitive signal arrival times. In a reconfigurable battery system, causes are typically due to having too many nodes to control, line delays, or requiring large computations to determine operational parameters. Any such factor will cause a limitation on how much harmonics can be reduced without increasing the communication speed (typically involving much costlier hardware such as microprocessors and communications devices).

[0115] In a reconfigurable battery system, real-time signals include the control signals which are used to operate the switching devices to make and break cell connections. Such real-time signals are therefore those that must be transmitted at high speed for the reconfigurable battery system connect and disconnect battery modules without short circuiting any cells or inadvertently disconnecting the output voltage. A gate control signal for a MOSFET in a reconfigurable battery system is one example of a real-time signal which requires micro or nano second precision. A control message that is broadcast to all cells to control connection and disconnection of energy storage modules belongs in this category. In some embodiments, a real time signal is therefore transmitted on the depicted High Speed Communication bus channel.

[0116] In a reconfigurable battery system, soft-time signals are signals are not time-critical to the functionality. Examples of soft time signals are those containing date relating to temperature, voltage, current, SOC and SOH, and other battery parameters or environmental data. In some embodiments, a soft-time signal is therefore transmitted on the Low-Speed Communication bus depicted. One example of a low-speed communication bus is a UART communication channel which might operate to communicate data at rates of up to a few seconds. A further example of a soft-time signal includes data representing a rank of the energy storage module and data representing an update of the rank.

[0117] In some embodiments, there is reconfigurable battery system with a controller which comprises a combination of processing devices such as two or more microprocessor devices. In a distributed system such as depicted in Figure 1 , the controller comprises a first processor (central processing device or central controller) in communication with a number of local processors (cell level processing devices or cell controllers). The central controller is in communication with the cell controllers via the high-speed communication channel and is configured to send timing related control signals via that channel. The cell controllers are in communication with other cell controllers via the low-speed communication channel. Reference within this specification to the controller refers to a control function which may take place at the central or local processing level. Reference to cell controller or central controller refers to a control function which takes place at the cell level or central level of the system structure respectively.

[0118] In this specification, reference to the high-speed channel is intended to mean a communication bus configured to support at least timing signals, whereas a low-speed channel is intended to refer to a communication bus configured to support the transmission of cell data.

[0119] Communication between the central controller and the local controllers (all each cell unit / node) and communication speed as the speed at which a control message can potentially be updated to a new number (e.g., 2 to 3). Communication speed directly determined by communication cycle, a communication speed of 1 kHz therefore has a communication cycle of 1 millisecond. A control cycle is the rate at which each cell modulation can be controlled, and thus control cycle is not necessarily the same as the control message speed or the communication speed. In most implementations, the communication speed surpasses the time required to process cell ranks since ranking happens in soft time (e.g., every 1 or 2 seconds), and communication speed happens in real-time (e.g., 10kHz or higher).

[0120] Modulation control of switching circuit of energy storage module

[0121] Embodiments of the invention relate to a battery control system comprising a circuit module comprising a pair of output terminals, the module comprising a string of cell modules, each cell module comprising at least one cell and a switching circuit configured to define a switching state of the cell module including a cell bypass state and a cell series connection state. The battery control system further comprises a controller configured to control the switches of one or more cell modules to meet a target circuit module output voltage. The target output voltage is typically dictated to by the application of the battery control system and might be, for example, a mains voltage supply, an electric vehicle motor control or similar. The controller is configured to operate the switching circuit by a combination of series connection of one or more cell modules with the output terminals, and modulation of the switching state of at least one cell module. The series connection and modulation together allow control of an output voltage that substantially meets a target voltage.

[0122] In circumstances where the target voltage is time varying and / or lies between the voltage thresholds that series connected cells can provide, the modulation of the switching circuit enables the output to reach a target between the voltage thresholds. In this way, a target voltage is substantially met at the circuit module output terminals, and further, the generated harmonics are reduced to further improve system efficiency.

[0123] In embodiments of the invention, series connection of a desired number of cell modules is selected to meet a voltage target and the connections take place at predetermined time increments. The time increments may be even, fixed, or dynamic. One example of dynamic time increments may be predetermined but unequal increments such as may be ideal for the shape of a time varying waveform the output is intended to approximate. Modulation of the series connection of one or more cell modules takes place within that time increment. In this way: series cell connections take place at a first frequency, or such as may be determined by a first-time increment, and modulated cell connections take place at a second higher frequency, or such as may be determined by a second shorter time increment. In some embodiments, the second frequency is at least ten times the first frequency.

[0124] In some embodiments, modulation of the switching circuit comprises application of pulse width modulation (PWM) to the switching circuit of any one or more energy storage modules. The PWM parameters typically include modulation of the duty cycle, or a fixed duty cycle together with a modulated base frequency, or both.

[0125] In some embodiments, modulation of the switching circuit comprises application of pulse density modulation (PDM) to the switching circuit of any one or more energy storage modules. The PDM parameters typically include time increments where pulses can be applied or not such that over a time span the number of pulses can be varied to fill any ratio of the time increment. In some embodiments, many pulses are combined to produce a combination of longer and shorter pulses within a time increment.

[0126] In some embodiments, a combination of PWM and PDM modulation techniques is applied to the switching circuits. For example, by combination of a PDM pulse with a PWM pulse within a time increment. This method may be preferred in some embodiments where pulse on / off instances applied to one cell module may be desirable to align with pulse on / off instances of another cell module.

[0127] Note that the modulation or switching resolution is based on the circuit and control hardware. In some circumstances, it is not advantageous to control switching at a rate which introduces significant switching losses. To manage switching losses, considerations of how often to control a switch state may include, for example, combining pulses in a pulse density approach. The resolution is the lowest effective voltage of the lowest ranked cell since that produces the smallest step.

[0128] In one exemplary embodiment, a PDM based modulation is implemented according to a principle of minimising switching losses, and here, pulses in the pulse density are combined into one pulse within a predetermined time increment. In a varied exemplary embodiment, a PDM based modulation is implemented where pulses are combined into two pulses within a predetermined time increment. In a varied exemplary embodiment, a PDM based modulation is implemented where pulses are combined into three pulses within a predetermined time increment. In a varied exemplary embodiment, a PDM based modulation is implemented where pulses are combined into four pulses within a predetermined time increment. In a varied exemplary embodiment, a PDM based modulation is implemented where pulses are combined into any one of one to four pulses within a predetermined time increment.

[0129] Figures 2A and 2B show an exemplary battery system 100 which includes a plurality of battery cell modules 102, a central controller 104 for controlling the operation of the battery cell modules 102, and an output module 106 for measuring and validating the output from the battery cell modules 102, and or processing the output to provide a desired output voltage profile. The output profile may be determined based on user inputs, or the voltage requirements of a device or appliance to be powered by the battery system 100.

[0130] In some embodiments, the central controller 104 determines a set of control parameters to control the battery cell modules 102 based on input parameters retrieved from the battery cell modules 102 such as the present voltage, maximum charged voltage, and minimum discharged voltage for each battery cell module 102, as well as voltage values for the overall battery system 100. Each battery cell module 102 includes a cell controller 108 for communicating with the central controller 104. Any suitable communication protocol may be used. In one embodiment, the central controller 104 communicates with the cell controllers 108 on each of the battery cell module 102 as well as the output module 106 using I2C protocol.

[0131] The control parameters determine when and how each battery cell module 102 operates at any given point in time. In particular, the control parameters include duty cycle and time shift as explained in further detail below. In some embodiments, the battery cell modules include a processor configured to control the local module, other modules, and / or share information with other modules for operation. In some embodiments, any one of the above control functions are shared between the central controller 104 and the controller of a battery cell module 102.

[0132] Each battery cell module 102 further includes a battery cell unit 110 and a switching assembly 112. The switching assembly 112 comprises transistors 114 to selectively connect or disconnect (or bypass) the battery cell unit 110, and a switch control circuit for controlling the transistors 114. In one embodiment, two power transistors (i.e., MOSFETs) are used for each switching assembly 112, one MOSFET for connecting the battery cell unit 110 and one for disconnecting the battery cell unit 110, for example, in a ‘half-bridge’ circuit configuration. The output of all connected battery cell modules 102 are electrically connected in series. Some further examples configurations of switching assemblies and cell units are described in PCT application no. PCT / AU2016 / 050917, the entire contents of which are incorporated herein by reference.

[0133] In the embodiment of Figure 2B, the output module 107 includes a set of output switches 125, one a more voltage and current measurement sensors (not shown), and further includes an LC low pass filter 118 for smoothing out the accumulated voltage and current output of the battery cell modules 102. The LC filter 118 is used to provide further stabilisation of the battery system output by reducing voltage variations and / or current spikes caused by switching of battery cell units 110. The filter is also operable to smooth any modulated cell switching and produce a substantially averaged cell voltage which closely approximates the modulation duty cycle. The corner frequency of the filter is selected based on modulation frequencies of the switch circuit. In some embodiments, the filter has a corner frequency above the modulation base frequency of the switch circuit. In some embodiments, the corner frequency of the filter is at least one octave higher than the base frequency of the switch circuit. In some embodiments, the filter is a single pole circuit. However, in alternative embodiments the filter may have more than one filter stages, such as a two or three pole circuit. A higher number of poles means the corner frequency of the filter can be closer to the base frequency of the switch circuit modulation, however, the cost of additional or larger capacitor components, the level of harmonic or modulation suppression, and the response speed of the filter may define what is the optimum filter circuit.

[0134] The output controller 116 communicates with the central controller 104 and interfaces with the sensors and transistors 125. The transistors 125 can be used to disconnect the entire battery system 100 from an electrical device or appliance (not shown), either when instructed to do so by the central controller 104, or when the sensors on the output module 107 show a current or voltage that is outside expected operating thresholds.

[0135] In some embodiments, the controller is configured to implement PDM based modulation, including a modulation where the pulses are within a cycle. This means a cell can be turned on for a full control cycle and off in the next full control cycle. In some embodiments, the cell level controller is configured to control pulsing of the cell connection in the series string of cells.

[0136] Figure 15A shows an example based on PWM modulation and Figure 15C shows an example of PDM based modulation. In the example shown by Figure 15C, cells are connected at 100% duty cycle and with various pulse frequencies to mimic a similar effect to variable PWM duty cycles. In some embodiments, the central controller is configured to instruct the location controller to apply a pulsing frequency based on cell rank. In the example of Figure 15C, there are 10 control cycles within a 1ms time increment, the cell contributions are therefore as follows:

[0137] For example, Rank 1 could be 100% rank 2 could be 90% thereby producing a PDM based Cell Contribution Difference (CCD) profile as shown in Figure 4 is shown in Figure 16. For a control cycle time iteration of 0.1 ms, over a period of 1 ms, there can be 0 - 10 pulses. Which means the CCD can only be 10% or above. Meaning the smallest difference between ranks is 10%. In some embodiments when a Balancing Weight Factor (BWF) is used, the resultant CCD profile and thus the cell contributions assigned to adjacent ranks has to be rounded up or down to the nearest multiple of 10%. For example, for a BWF of 0.75 used, the initial calculation of CCD between ranks is 15%, but since pulsing can only achieve CCD of multiples of 10%, the actual CCD assigned or used will have to be either 10% or 20%. An example of rounded PDM contributions based on rank is shown in the table of Figure 17.

[0138] Note that rounding can be avoided by careful selection of the length of time increment or by combination of two or mor time increments. For example, a cell contribution of 85% can be achieved using full cycle pulsing with 17 pulses in a time window increment of 20 control cycles, or 2 communication cycles 1 ms of each. However, this will result in larger harmonics and current ripple due to a longer pulse width. Having to apply a fixed pulsing frequency over a window of 2 communication cycles is also less flexible than being able apply 2 different pulsing frequencies over the 2 communication cycles.

[0139] Another notable difference between PWM embodiment and PDM based cell contributions is how small the pulse period can be using the same communication speed and the same control speed. The PWM based contribution enables a smaller pulse period which provides a smaller current ripple and lower harmonics. The PWM based contribution also allows for finer control of the frequency of the current pulse that the cells experience. This may allow manipulation of the cell impedance and gain benefits such as extended cell life and less heat generation.

[0140] Figure 18 shows examples of PDM and PWM based modulation compared with a prior art approach which does not incorporate modulation. Observable is the relationship between communication speed, control cycle, and their effects on the resolution of the stepwise approximation on the ideal AC sinusoidal waveform.

[0141] Rank

[0142] The rate of use of any battery cell in a system will depend on many factors including parameters of the battery cell itself and environmental parameters. In some embodiments, cells are ranked according to what might be considered the order of cells which should be utilised the most. The rank of any one cell can also change overtime based on the cell performance and changing environmental conditions. Cell data is used to determine the rank of a cell in a group of cells and cell data will typically include one or more of: voltage, current delivery, capacity, state of charge, temperature, age, measured service life, predicted service life, temperature, rate of temperature change, internal resistance, position in a series arrangement, state of health, and / or cell pressure. This list is merely exemplary and other factors may also be included as desired by a system operator to determine a rank of cells in a system.

[0143] In some embodiments, the reconfigurable battery system comprises two or more cell processors are configured to determine the cell data for one or more cells under control of each cell processor and communicate the determined cell data to one or more other cell processors. In such an embodiment, at least one cell processor is configured to determine the rank of each cell from received and determined cell data and communicate the rank to one or more other cell processors. However, in other embodiments, each cell controller is configured to determine the rank of each energy storage module under control, since each cell controller will determine the rank of all cells based on the received call data.

[0144] In some embodiments, combinations of cell data may be used to determine a cell rank. For example, a rank for each energy storage module may be determined based on a weighted combination of two or more determined parameters in the cell data.

[0145] In some embodiments, the rank of the energy storage modules determines whether the module is to be connected or bypassed from the circuit, and whether a module should be modulated. In one exemplary embodiment, the central controller is configured to determine a number of cells which should be connected in series based on a target output voltage. A determination of the target output voltage may be indicated by output control data such as the target voltage, or number of cells for connection, or a rank number which indicated a threshold where a number of cells to reach that threshold are to be connected. The cell controller is configured to receive the output control data and operate the switching circuit accordingly.

[0146] Target voltage definitions

[0147] In some embodiments, there is a target voltage which is an effective output voltage. For example, a voltage measured at the output of a reconfigurable battery system. The output voltage may be subject to one or more filters which act to smooth the voltage waveform. Such filters are typically used to modify a modulated voltage, or modulated voltage component, or high frequency time varying voltage or voltage component, and produce a smooth voltage or low frequency time varying voltage. In some embodiments, the target voltage is determined from a measured output voltage, i.e., in a closed loop. In some embodiments, the target voltage is predetermined based on known output voltage. In some embodiments, the voltage target is stored in a database. In some embodiments, the voltage is determined based on a modelled time varying waveform and a particular time or phase increment of that waveform. In some embodiments, the target voltage is a combination of one or more cell voltages and one or more modulated cell voltages. In some embodiments, the target voltage

[0148] Figure 3 shows an example of steps undertaken by a controller implementing modulated control and series connection control of a switching circuit based on a determined rank of cells in a reconfigurable battery system. The modulated control allows variable output voltage and power delivery from one or more energy storage units thus enabling finer control of a target output voltage. Accordingly, the variability may in turn depend on the rank of the cell where the modulated control is applied. It should also be noted from the depicted steps that not all steps occur on the same time scale, and that some steps may occur before other steps. For example, steps A1-A4 may be determined at a comparatively high speed (such as at an update rate of 1 kHz), whereas steps B1-B3 may occur at comparatively low speed (such as 1 Hz).

[0149] Steps A1-A4

[0150] With regard to the following steps, communication between the central controller and the local controllers and communication speed is referred to as the speed at which a control message can potentially be updated. The communication speed is directly determined by communication cycle where a communication speed of 1 kHz has a communication cycle of 1 millisecond. Control cycle means the rate at which each cell can be controlled to be on or off or modulated. A Control cycle speed is not necessarily the same as the control message speed or the communication speed since the switching control may be operated directly by a cell controller.

[0151] Step A1 : The central controller determines the target output voltage for a next communication cycle. For example, if a desired output is a time varying AC sinusoid, then a target voltage will be determined by the voltage at the particular phase increments in the sinusoid.

[0152] Figure 4 and Figure 6 show an example of an ideal AC waveform where 9V voltage target from a simplified 12V peak in order to more readily illustrate the embodiment. Note that in the control cycle frequency is deliberately low for the purpose of simpler illustration of the invention concepts. In actual implementation control cycle frequencies are typically higher than the 50 or 60hz AC waveform, for example 20 kHz or 50 kHz or higher.

[0153] Step A2: The central controller transmits a control message (for example a number between 0 to 6 representing the number of cells to be connected in series to reach a target voltage) to the local cell controllers. The cell controllers receive the control message and compare with stored rank information to thereby determine whether the cell is to be connected or bypassed from the series connection of cells. For example, the particular cells in the number of cells to be connected is determined by the rank of each cell, where the lowest ranked cells are prioritised for connection. If the rank of the cell module is lower than or equal to the control message the cell should be connected, or if it were higher, the cell should be bypassed.

[0154] In response to this target output voltage, the controller sends a message to all battery modules. The message contains a number of battery modules which have to assume a predetermined switching state or merely a target output voltage. At the local controller, on the basis of a comparison between the control message which is sent by the controller and the specific ranking, a switching state, which is to be assumed based on the received state or target voltage, is defined in each of the battery modules and is finally assumed by each of the battery modules in order to provide the required output voltage.

[0155] In some embodiments, the control message contains the desired output voltage. In other embodiments, the control message contains a number of battery modules which have to assume a particular switching state. Other control messages containing data directing a target voltage are possible.

[0156] In some embodiments, the control message is broadcast by the central controller to each of the cell controllers. In some embodiments, the control message is sent from the central controller only to a first cell controllers, and the first cell controller receiving the control message is configured to transmit the control message to a second and any further cell controllers.

[0157] Note that the example of 0 - 6 as the control message is used for this step. This is a simplification as 0-6 works for the positive half of the AC sine wave only. For the second / negative half of the AC sine wave, this number could be between -6 to 0, and the negative sign is received by local controllers as an instruction to reverse their polarities to achieve a negative output voltage, if each cell is capable of such a reversal. Alternatively, the negative sign instructs an H-bridge at the end of a string of included cells to configure the switches to invert the polarity of the total output voltage.

[0158] Step A3: Each cell controller is configured to compare a received the control message (from Step A2) against the rank or target determined for that local unit. Each cell controller is configured to output signals operable to configure the switching circuit to include or bypass the cell unit(s) based on the comparison. However, the switches do not assume their determined states until step A4 as it is important that the switching state only changes in response to a synchronisation signal that all cell controllers are configured to receive.

[0159] Step A4: Each cell controller is configured to receive the control message (from Step A2) and apply any modulation to the switching circuit. This step produces the output voltage.

[0160] In some embodiments, the control message is transmitted at a communication speed which may or may not necessarily at the frequency of a control cycle loop (e.g. 50 kHz). In some embodiments, the control message is updated at each communication cycle but may not be updated at each control cycle. The rate of updates will be dependent on any communication speed limitation between a central controller and cell controllers.

[0161] In Figure 6, the communication cycle is 1 ms and thus the communication speed is 1 kHz, whereas the control cycle is 0.1ms and thus the control frequency is 10kHz. One limitation of the control cycle update rate is that the modulation parameters (duty cycle and / or base frequency) will be fixed between updates. In an example where modulation is not utilised and 9V is the desired output voltage, cells five and six are included which sums a 7.6V output voltage, and the control message is two for the communication cycle.

[0162] In an example where modulation is not utilised and 9V is the desired output voltage, cells may be modulated between 0 and 100% of their output voltage (depending on the step resolution as determined by the ability of the cell controller or switching circuit to generate the modulation resolution). Where a cell output is modulated, cells four, five and six are included which sums to an output voltage of 8.99V, and the control message is 3 for the control cycle.

[0163] Steps B1-B3

[0164] Referring again to Figure 3B:

[0165] Step B1 : Each local controller is configured to measure the voltage of the cell or cells under control. In some embodiments, this step is repeated at a rate faster than the cell control update rate and may be performed at a rate useful for determining any particular cell property useful for at least cell ranking purposes.

[0166] Step B2: The controller ranks all available cells according to their measured voltages or preferred ranking parameters as discussed earlier. Note that this step does not need to occur within a control cycle, ranking is usually determined and updated at a much slower rate than control cycle frequency.

[0167] Note that the number of available cells may be determined based on battery parameters which indicate useable or usable cells. One example of an unusable cell is a cell which is outside a predetermined criterion. In one exemplary embodiment, a cell which has exceeded a temperature limit is excluded from a selection of available cells and therefor either not ranked or ranked low such that its use is limited or excluded. Cells determined to be undesirable may later become desirable again if the relevant parameters are improved on such as by being within the predetermined criterion. Figure 5 outlines various considerations which may be used for cell ranking by the controller including one or more, or a combination, weighted combination, or trade-off between factors.

[0168] Step B3: The controller determines a modulation profile to be applied to one or more cells.

[0169] Note on the sequential order of these steps: It is not strictly required that these steps occur in the exact order as shown above. The steps are sequentially described for illustration purposes. For example, in Step B3 the central controller receives or determines duty cycles for each rank (and thus available cells), this step can take place even before Step A1 and can be arbitrarily set via user input. At Step A2, the sending of the control messages can also take place in any other step as it is constantly occurring and does not require information from other steps. For example, Step B3 can happen all at the same time to arrive at a Duty Cycle Difference profile that satisfies a plurality of constraints which may be appliable at Step B3.

[0170] Therefore, in some embodiments, the controller is configured to determine the target circuit module output voltage and control the modulation duty cycle and / or frequency of the switching state of at least one cell module to meet the target circuit module output voltage.

[0171] In some embodiments, the controller is further configured to determine the target circuit module output voltage and control the modulation duty cycle and / or frequency of the switching state of a cell module based on the determined rank to meet the target circuit module output voltage.

[0172] In some embodiments, the controller is further configured to determine the target circuit module output voltage and, based on the determined rank of each cell module, prioritise a higher modulation duty cycle and / or frequency of the switching state to those cell modules with a higher rank and a lower modulation duty cycle of the switching state to those cell modules with a lower rank.

[0173] In some embodiments, the controller is further configured to determine the target circuit module output voltage and control the modulation duty cycle and / or frequency of the switching state of two or more cell modules to meet the target voltage. In some embodiments, the controller is further configured to determine the target circuit module output voltage, determine a (balanced) weighting factor attributing a modulation duty cycle priority to each cell module based on the determined rank, and control the modulation duty cycle and / or frequency of the switching state of each ranked cell module based on the weighting factor. The weighting factor defines a distribution across the ranked cell modules. In some embodiments, the distribution is even across all cells. In other embodiments, the distribution is nonlinear distribution across the ranked cell modules. In some embodiments, the distribution is dynamically adjusted across available cells based on cell data such as may be referenced for cell rank determinations.

[0174] In some embodiments, the target voltage comprises a time incrementing target voltage having discrete voltage levels for each time increment, and the modulation comprises a modulation base frequency time greater than the time increment. For example, the modulation base frequency is at least 1 .25, 1 .5, or 2 times faster the time increment. In some embodiments, the time increment is limited by the speed at which the central processor is configured to update the target output voltage or rank information indicative of how many cells should be connected in series and therefore substantially the target output voltage.

[0175] Further details of determining modulation duty cycle and / or frequency for each ranked cell module is discussed below.

[0176] Modulation profile

[0177] The modulation profile is based on a number of considerations and the profile itself can be applied to one or more cell modules in a reconfigurable battery system.

[0178] In some embodiments, the modulation profile is based on a duty cycle difference (DCD) profile. In such embodiments, the controller determines a DCD between cell modules with adjacent ranks thereby defining the duty cycle for each rank required to reach the target voltage. Figure 4 shows a table detailing examples of a Duty Cycle Difference profiles.

[0179] In some embodiments, the BWF is applied to all cell modules. In other embodiments, the BWF is applied to a selection of cells. In some embodiments, a selection of cells is determined based on cell rank or cell parameters indicating some cells require more or less loading than other cells. In some embodiments, the controller applies a balancing weight factor (BWF) of between 0 to 1. To utilise all cells, the BWF should be non-zero so that the lowest ranked available cell is not assigned a 0% modulation duty cycle.

[0180] One exemplary calculation of the Duty Cycle Difference is as follows: DCD = (1 / (Total number of cells -1)) x 0.75 (BWF) x 100%

[0181] Therefore, for 6 cells, the example DCD = 15% for each cell.

[0182] Note that there can be many alternative ways of working out the DCD, such as an alternative equation, or simply setting a fixed DCD arbitrarily based on a user input. The DCD merely indicates there is a difference in modulation data between ranks.

[0183] In some embodiments, the controller is further configured to measure the voltage at the output terminals, and adjust one or more modulation parameters for any one or more cell modules based on the measured voltage. In one exemplary embodiment, the controller is configured to measure the output voltage once modulation of one of more cell modules occurs. The measured voltage may be higher or lower than the target voltage due to cell performance variation or other environmental factors. The controller is configured to adjust the modulation of one or more cell modules based on any measured difference, by, for example, adjusting one ore more modulation parameters. If the output voltage is below the target voltage, the controller could increase the modulation duty cycle of one or more cell modules. Conversely, if the output voltage is above the target voltage, the controller could decrease the modulation duty cycle of one or more cell modules.

[0184] In some embodiments, the controller is configured to measure the output voltage from one or more modulated cell modules and adjust a modulation parameter of that cell module based on any measured difference between the output voltage and a target voltage. In some embodiments, the controller is configured to compare a measured output voltage to a target output voltage, and adjust the modulation duty cycle of any one or more cell modules only if a determined difference is above a threshold voltage. In some embodiments, the threshold voltage is dependent on the load connected to the output of the reconfigurable battery system.

[0185] A smaller BWF means there is smaller spread between duty cycles which may be applied to cell modules with adjacent ranks. Conversely, a higher the BWF produces a higher Duty Cycle Difference profile. If the BWF is too high, and thus if the Duty Cycle Difference profile is too large, the total voltage that can be provided by the inclusion of all the available cells may be lower than required since some cells are directed for modulation at a low duty cycle, thereby relinquishing some voltage potential from that cell. In this case, more cells are required to achieve a target output voltage. For example, in Figures 4 and Figure 6, if the BWF is higher than 0.75, even if all 6 cells are included, a 12V target voltage cannot be reached.

[0186] In some embodiments, the controller is configured to determine the maximum BWF for a target output voltage, and control the cell modules by limiting the BWF accordingly. In some embodiments, the controller is configured to measure the maximum output voltage of a reconfigurable battery system, and determine a maximum BWF based on a maximum target output voltage. For example, the controller can check if the BWF is too high by measuring the output of all summed cell module voltages and determining if the sum is at greater than or equal to a peak target voltage. If the sum is less than a desired target peak output voltage, step B3 can be repeated until a constraint is converged upon which satisfies an ideal BWF for a maximum peak target output voltage. In some embodiments, other constraints are applied and in this specification the process of determining other constraints is referred to as the “DCD / BWF optimisation step”.

[0187] Duty Cycle Difference (DCD) Profiles (Step B3)

[0188] Figures 8A and 8B shows tables of profile information including different DCD profiles differences which can be used to control the use of cells over time or controls the usage of cells to more use some cells disproportionately more than others. Cells which are used more is generally part of a more aggressive profiles refer to a higher BWF. Figure 8A shows a highest ranked cell may have 100% duty cycle (when connected) and the lowest ranked cell with rank 6 may have just 5% duty cycle (when connected). This increases the disparity between higher ranked cells and lower ranked cells such that the contribution of cells to the output is controlled to converge the SOC or capacity. Figure 8B shows lower ranked cells have similar duty cycles to the higher ranked cells.

[0189] A higher BWF may be desirable for cell balancing. For example, where one cell has a higher voltage it may be desirable to include that cell in the switched series connection most often. Accordingly, in some embodiments, cell parameters are used to determine a desired BWF which may be applied.

[0190] A lower BWF may be desirable to minimise connected cells. In the examples of Figures 8A and Figure 8B, the a more aggressive profile of Figure 8A requires more cells (in this example, 3 cells) are required to achieve the same target output voltage (or the best possible fit to the target output voltage) compared to a less aggressive profile of Figure 8B which results in less cells (in this example, 2 cells) being required to achieve the same target output voltage. This is because a more aggressive profile leads to more disparity between Duty Cycles assigned to adjacent ranks and thus contribution by cells drop off more steeply at lower ranks. And vice versa for a less aggressive profile such as that shown by Figure 8B.

[0191] More cells being connected may be desirable for reasons including heat distribution aging the cells more evenly to provide an improved battery system longevity. However, if some cells age faster than others due to overuse or heat exposure, potentially these cells would die before others, and once a threshold number of cells are determined unavailable or unfit for use either the entire battery is out of commission or maintenance needs to be performed in the battery. Therefore, the optimum BWF may be an evolving target based on determined cell health parameters and priorities.

[0192] One exemplary application is an electric vehicle battery charging or other similar high charge current environment where charging a battery to 100% capacity means faster charging since a high level of precision is required in such scenarios to maintain performance while minimising damage caused by over-charging in the process of balancing at 100% or in the process of charging to 100%. A more aggressive BWF profile can better achieve this due to using lower ranked cells (when ranking is based at least partially on voltage or Soc) at lower duty cycles, and thus not having as many overshoots and the subsequent over-corrections in the process of balancing at 100% SoC (of the entire battery) or charging to 100% SoC (of the entire battery). On the other hand, with a less aggressive BWF profile, the lower ranked cells have similar duty cycles to the higher ranked cells, in this case balancing may be achieved more slowly given the same precision requirement. A more aggressive profile is useful in applications in which charge / discharge happens at a very high current such as fast charging of an EV with a very high current, or fast discharging with high current spikes such as a motor drive application. The rate of balancing should ideally match the rate of charge or discharge. This indicates that where there is a need to discharge a battery in 20 minutes, balancing at a much faster rate is required compared to discharging a battery in 2 hours.

[0193] Conversely, less cells being involved may lead to more efficient battery usage as there’s less voltage potential drop across cell terminals, this is especially significant when the current drawn from the battery is high such as a sudden EV acceleration, or when cells are less healthy or older with higher internal resistances. During acceleration in an EV, the battery experiences an increase in current draw and a decrease in voltage, which can cause the battery to become less efficient. The voltage and current behaviour of an EV battery during acceleration is dependent on the specific design and components of the battery system, as well as the power demand of the vehicle. The increase in current draw causes the voltage of the battery to drop due to the internal resistance of the battery, and the exact relationship between the current draw and voltage drop will vary depending on the specific design and construction of the battery, as well as the operating conditions.

[0194] Less cells being involved also means there are more available redundant cells in the case of certain cells hitting 0% SOCs first or having faults such as a thermal run-away of cells that need to be shut off. Therefore, a less aggressive profile tends to improve system reliability, and it is rare for an application to require an overly aggressive balancing factor.

[0195] Figure 9A and 9B show an alternative embodiment where cell usage is determined by the DCD alone. The DCD may be a linear difference, or a non-linear cell. A nonlinear DCD profile means that the difference between adjacent ranks is not fixed through all the ranks. A nonlinear profile can be desirable when a linear profile would involve too many cells to achieve target output voltages, such as the peak AC voltage.

[0196] Figures 10A, 10B and 10C show DCD profiles including a linear, a less aggressive non-linear profile, and a more aggressive non-linear profile respectively. The linear profile of Figure 10A has a drawback where the voltage output from lower ranked cells drops off very quickly such the total output voltage may be reduced even with all the cells connected. In such scenarios, the non-linear DCD profile of Figure 10B may overcome this issue through use of higher ranked cells, such as rank 1 or 2, being used at or near 100%, whereas cells that are lowest in rank such as rank 5 or 6 can be used a lot less, at close to 0%.

[0197] The nonlinear DCD has a benefit of requiring less cells to achieve target output voltage and also using low ranked cells less than with a linear profile. This may be desirable due to cell temperatures being too high or the SOC too low, but where they are still required by the circuit to meet a desired target output voltage.

[0198] To ensure the system can meet a target output voltage, the sum of connected cell voltages as a function of their modulation frequency must be greater than the target voltage. In some embodiments, the controller is configured to control the duty cycle variation by the ratio of number of cells and the target output voltage. For example, a limited number of cells which may barely meet a target voltage requirement with all the cells on 100% will not be able to have much DCD.

[0199] Different types of non-linear profiles may be appropriate for different scenarios, Figure 10A shows a nonlinear profile in which higher ranks stay near 100% for longer until dropping off quickly at the lowest ranks. Figure 10C shows a non-linear profile in which duty cycles start dropping off sharply at the highest ranks.

[0200] A less aggressive non-linear profile is desirable for providing a lot of output power since duty cycles directly correlate with power output, and particularly when a relatively high level of power output with a relative fewer number of cells is desired. A more aggressive non-linear profile curve is desirable when less output power output or when more cell involvement is desired where no cell is heavily loaded.

[0201] In some embodiments, the controller is configured to control dynamic cell contributions. For example, a dynamic DCD and / or BWF. A dynamic duty cycle modified from a static duty cycle derived from any DCD profile can be calculated with the following exemplary formula:

[0202] When Rb > Rl, dd = ( Rb - Rl)*c+dl and set dd = 1 if dd>1 Where: dd is the dynamic duty, Rb is the broadcasted rank, Rl is the local rank, c is a coefficient to scale difference in rank to [0,1], and dl is the static duty cycle derived from a linear DCD profile updated in step B3.

[0203] This equation modifies the current cell contribution based on the difference between the current and new ranks and based on a scale variable (c) which can be used to set the rate at which cell contributions are changed. Numeric examples are as follows: dl = 25%

[0204] Rb = 10

[0205] Rl = 3

[0206] C = 0.5 dl = 25%

[0207] Rb = 4

[0208] Rl = 3

[0209] C = 0.5 dd = ((4 - 3) * 0.5) + 25% = 50%

[0210] For a dynamic duty cycle, the top-ranked cells will have increasing contribution thereby to provide more voltage until they reach a 100% contribution. The drawback is that there would be an increased processing demand from the controller to compute the number of required cells to meet a target voltage.

[0211] Producing an output voltage profile that more closely matches the ideal AC sinusoidal waveform voltage output reduces harmonics in a multi-level inverter or reconfigurable battery system. Figure 11 shows an example of a more aggressive balancing profile (hence involving more cells) can lead to a better fit on an ideal AC sinusoidal waveform which reduces harmonics. In this example, the controller is configured to dynamically control the contribution of cells at an update rate which allows a close match with the target output voltage. A constraint on the ability of the controller to control cell connections and contributions is that the total output voltage from all available cells after duty cycles are applied must be higher than the required maximum peak voltage of the AC waveform (typically 240V in North America, and 230V in Europe). Having at least some redundant cells is also very important for system reliability and system longevity. This curtails the ability of the controller to provide significant contributions of some cells over others, that is, the profile cannot be overly aggressive. This constraint puts a limit on how large the DCD or the BWF can or should be.

[0212] Trade-off (DCD / BWF optimisation Step B3 - determining a DCD profile)

[0213] For the above explained reasons, there is a trade-off between having an aggressive profile, from having a larger DCD or a larger BWF, versus having a less aggressive profile, from having a lower DCD or a lower BWF. Figure 12 illustrates this concept and is a detailed inspection of Step B3 in Figure 3B. Figure 12 left shows linear DCD profile embodiments, whereas Figure 12 right shows nonlinear DCD profile embodiments.

[0214] In an exemplary embodiment, an equation that is used as an algorithm to work out the DCD to be used is shown below: Starting point DCD (arbitrarily set as 10%) X [((0.5-1.5) Fit + (0.5-1 .5) speed of precise balancing + (0.5-1 .5) More cells for even spread of temperature / 3] * [((0.5-1 .5) comm speed limitation + (0.5-1 .5) less cells desired due to ‘typically high current application + (0.5-1 .5) less cells to be used due to availability or wanting more redundancy) / 3] = the actual DCD.

[0215] In this embodiment, a fixed value / factor is set if the battery is used at high current frequently (such as EV race cars). In other embodiments this factor might be a time varying value. In another embodiment, an equation that is used as an algorithm to work out the BWF to be used is shown below:

[0216] Starting point BWF (arbitrarily set as 0.75) * [((0.5 to 1 ,5)Fit + (0.5 to 1 ,5)speed of precise balancing + (0.5 to 1 ,5)More cells for even spread of temperature / 3] X [ ((0.5 to 1 .5)comm speed limitation + (0.5 to 1 ,5)less cells desired due to ‘typically high current application + (0.5 to 1 ,5)less cells to be used due to availability or wanting more redundancy) / 3] = The actual BWF.

[0217] There can be a number of other formulae / equations which achieves the same essence of the DCD I BWF optimisation step (step B3) shown in Figure 12.

[0218] In making determinations of cell contributions to be applied to cells, there are factors which must prioritise or present limitations. Accordingly, in some embodiments, the controller is configured to determine cell contributions first based on limitations and second based on priorities. Limitations include:

[0219] • the maximum desired output voltage (maximum target output voltage); and

[0220] • the maximum control frequency.

[0221] The maximum output voltage sets or limits the minimum sum of total duty cycles. The maximum control frequency defines limits the resolution of the modulation duty due to a limitation on how quickly the switching state can change without causing failure or degradation.

[0222] In some embodiments, the limitations are predefined and provided to the controller as the basis for further determinations. In some embodiments, the controller is configured to determine one or both limitations based on data derived from the system. For example, a method of determining cell duty cycles includes starting with a linear applied modulation duty cycle to all cells. The method further includes evolving the applied modulation duty cycle in a stepwise manner based on rank or other factors, such that the duty cycle of each cell departs from a linear application to other form. Cell characteristics and total output voltage for data provided to the controller as part of a feedback loop. The controller is thereby configured to use the data in the feedback loop to inform whether to continue or revert any stepwise change in cell contribution.

[0223] The requirement for feedback-controlled changes to cell contribution is generally lessened where nonlinear cell contributions are determined. However, feedback may be applied in circumstances where cell contributions may need to be adapted or optimised over time.

[0224] Adaptive DCD / BWF

[0225] Some of the constraints discussed above and shown in Figure 12 are time-varying constraints. For example, during an EV vehicle’s acceleration, there’s a sudden increase in current. During acceleration, the electric motor requires a large amount of current to produce the necessary torque for acceleration. This results in a high current draw from the battery. On the other hand, during steadystate driving at a constant speed on level ground, the power demand is relatively low and the current draw from the battery is also low. The current draw may also be low during regenerative braking, where the electric motor acts as a generator to convert the kinetic energy of the vehicle back into electrical energy to be stored in the battery. Overall, the current draw from the battery varies depending on the driving conditions and the power demand of the electric motor.

[0226] Another example of a time varying constraint is the number of cells that are required to be connected at the peak of an AC waveform, factoring in desire to have several redundant cells. An example calculation is if cells are fully charged at 4.2V, to achieve 270V peak AC voltage only 64 cells are needed to be connected, as they gradually discharge the number is increased until 100 cell units are connected at 2.7V each to provide 270V output (64 x 4.2 = 270V), when the cells are almost fully discharged. Therefore, more cells will need to be connected in series as the cells discharge. If 20 redundant cells are needed, then 120 cells are required. If the DCD or BWF strategy is applied, most cells will operate at less than 100% duty cycle, if the controller determines that 110 cells are required to be connected in series after applying modulation, and yet there are 120 cells available with 20 planned redundant cells, then the DCD or the BWF can be decreased until only 100 cells are required to be connected. The ability to quickly and precisely balance the cells is therefore improved by having more cells in the battery system because an aggressive profile (large DCD / BWF numbers) reduces lower ranked cells’ effective voltages substantially more than a smaller DCD / BWF value.

[0227] It’s also worth noting that not all cells may be available at all times and the number of cells that are available at each point in time may not stay constant. For example, using the example in Figure 4, cell 1 was unusable (such as being too hot or the voltage is too low or would become too low), so the controller is configured to temporarily disable use of that cell. Such thresholds may be predetermined by the controller to impose one or more variables on the number of cells that are available for use. This constraint is also shown in Figure 12.

[0228] Figure 13 left shows an exemplary profile for implementation by the controller based on adaptive DCD / BWF. There is an inverse correlation between the current demand and the ideal DCD / BWF for the constraint. It is also shown that the relationship does not necessarily need to be a linear one. It may be that some of the constraints listed in Figure 12 are time dependent and some are not. In some embodiments, the controller is configured to implement an algorithm based on an ideal dynamic DCD / BWF for each instant in time incorporating a trade-off between time varying and time constant constraints. Figure 14 shows an example of what such an adaptive DCD could look like over time.

[0229] In an exemplary embodiment, the controller is configured to implement a mathematical relationship to determine the adaptive DCD as a function of time. In other embodiments, an adaptive BWF can be worked out using a similar equation, where :

[0230] Dynamic DCD = Stating DCD (e.g. 10%) * ((Better Fit factor (e.g. 0.5 to 1 ,5)(t) + Speed of precise balancing factor© + more spread of temperature factor© + any other factors)) I (the number of factors)) * ((low comm speed factor© + higher current factor + availability or redundancy factor© + any other factors) I number of factors). And:

[0231] Dynamic BWF = Stating BWF (e.g. 75%) * ((Better Fit factor (e.g. 0.5 to 1 .5)© + Speed of precise balancing factor© + more spread of temperature factor© + any other factors)) I (the number of factors)) * ((low comm speed factor© + higher current factor + availability or redundancy factor© + any other factors) I number of factors).

[0232] To implement any one or more of the above-described control strategies, the controller is configured to determine the lowest effective voltage. For example, this may be from the lowest ranked cell. The lowest cell voltage provides the smallest voltage step when not being modulated. The resolution (defined by the lowest effective voltage of the lowest ranked call) determines how closely your stepwise output voltage profile can approximate the ideal AC sinusoidal waveform and thus minimise harmonics.

[0233] The example outlined by Figure 19 shows six cells and a minimum cell voltage of 2.3V. To improve the ability to meet a target voltage below requiring a resolution below 2.3V in a rank based distributed gate driving communication scheme, the contribution of one or more included cells needs to be less than 100%. This can be achieved, for example, by assigning different contributions to different cells based on their ranks. Such a way is possible if some cells can contribute at less than 100%, via one of the below methods:

[0234] Firstly, the control cycle is reduced such that the control frequency is faster than the communication speed. In the example of Figure 19A, the control cycle is 10% the duration of a communication cycle - the control cycle is 0.1 ms and the communication cycle is 1 ms. For any given cell, for example cell 1 (measured at 2.3V), reducing the control cycle to be less than the communication cycle enables the cell to be turned ON or OFF multiple times, note that the control cycle needs to be less than 50% of the communication cycle for the cell to be turned on once and turned off once within the communication cycle, enabling the effective voltage of cell 1 to be either 2.3V, 1.15V or 0V within the 1 ms communication cycle. Further reducing the control cycle duration achieves an even higher resolution. In the example of Figure 19A, the control cycle is 10% of the communication cycle providing 2.3V x 10% = 0.23V. Secondly, modulation of any one or more cell modules to provide a contribution between 0% to 100% such as shown in Figure 19. Figure 20 demonstrates that the PWM based modulation of this embodiment has an advantage over PDM based modulation. When the control cycle is 10% of the communication cycle, or 100% of the communication cycle, does not limit the resolution of the system as a cell can be on with 10% duty cycle even when the control cycle is the same as the communication cycle. Thus, as shown in Figure 20A and 20B, an effective voltage of 85% of the measured voltage of a cell can be achieved when the control cycle is 0.1 ms as shown in Figure 19A, or if when the control cycle is 1 ms as shown in Figure 20B.

[0235] Note that there is no benefit to having a communication speed being faster than the control speed. If the communication cycle is 1 ms and control cycle is 1.1ms for example, when the control message is updated from 3 (at 9.0ms) to 2 (at 10.0ms), the configuration of the cells (how many cells are included or bypassed) cannot be updated in time to reflect the change in the control message since the update can only happen at 1.1 ms, leading to the cells configuration remaining unchanged despite the control message requesting for a change.

[0236] Where environmental realities have a slow communication speed, having a control speed that is at least twice as fast (and preferably faster to enable more levels) as the communication speed provides a PDM based modulation which is a combination of: a. Being able to assign cell contribution other than 0% and 100% which in turn enables b. Assigning different contributions to differently ranked cells. And it is the combination of a and b that allows a rank based distributed gate driving communication scheme to achieve better harmonics than the prior art approach.

[0237] And given a slow communication speed or a slow control speed, PWM modulation provides a combination of: a. Being able to assign duty cycles between 0% to 100% which in turn enables b. Assigning different duty cycles to differently ranked cells. And it is the combination of a and b that allows a rank based distributed gate driving communication scheme to achieve better harmonics than the prior art approach.

[0238] Both modulation techniques described reduce harmonics further when the communication speed or the control speed puts a limit on how closely the stepwise voltage output approximates an ideal AC sinusoidal waveform. In summary, the embodiments of the invention add more resolution without changing control speed, so if the communication is slow, they can help improve output quality without having to improve communication.

[0239] Figure 6 also shows the output voltage waveform of the invention compared to a waveform prior art as may be observed at the output of the reconfigurable battery system. In a multi-level inverter, the voltage output of a cell is not typically a pure sinusoidal waveform, instead containing harmonic distortion that can cause problems in the load that the inverter is driving. Issues caused by harmonics include increased electromagnetic interference (EMI), reduced efficiency, and increased stress on the power semiconductor devices and other components. To mitigate these issues, a filter is typically used to smooth out the output waveform and reduce the level of harmonic distortion. Harmonic distortion is reduced by a closer fit to an ideal AC waveform.

[0240] Harmonics in a multi-level inverter are caused by the high frequency switching of the power semiconductor devices that are used to generate the output voltage waveform. In a multi-level inverter, the output voltage is typically synthesised from a series of voltage levels, each of which is generated by a separate set of power semiconductor devices. The devices are switched on and off at high frequencies to create the desired voltage waveform which can contain a significant amount of harmonic content.

[0241] The high-frequency switching of the power semiconductor devices causes the generation of harmonics in several ways. First, the switching action creates a square wave voltage waveform with sharp transitions that contain high-frequency components, including odd and even harmonics. Second, the output voltage waveform is typically not a pure sinusoidal waveform, which also contributes to the generation of harmonics. It is here that a better “fit” of a pure sinusoidal waveform reduces harmonics by matching the pure sinusoidal waveform closely. Another benefit of higher voltage resolution derived from the use of modulation is that it is more precise and potentially faster to fully charge a battery pack especially at high current, such as found in fast charging or EV acceleration applications. For example, in high current applications such as fast charging or EV acceleration, cells charging or discharging inherently causes significant mismeasurement or inaccurate estimation of parameters such as voltages or SoC levels, due to high cell impedance leading to voltage potential that causes such errors. Voltage over potential affects battery performance by reducing the efficiency of a battery meaning that the actual voltage output of a battery is lower than its theoretical or nominal voltage. These errors take time to correct and thus the system takes longer in a process of overshoot and overcorrection to hit a precise SoC target - for example when trying to fully charge an EV battery to 100% capacity / SoC. This is especially a problem when charging as over-charging damages the battery. Overcharging and over discharging are both harmful to batteries, especially lithium-ion batteries. They can reduce the battery lifetime, damage the battery components, and create a safety hazard. However, overcharging is generally considered worse than over discharging because it can cause more severe damage to the battery cells, such as plating, gas generation, thermal runaway, and even fire or explosion. By implementing modulation to cell contributions, and by allowing lower ranked cells (when rank partially or fully based on Voltage or SoC) be used to a less than higher ranked cells, more precise balancing is possible, and this leads to less errors and thus improves the battery performance, life and safety while also potentially increasing especially the speed or charging an EV battery to 100% while minimising damage caused by overcharging.

[0242] Precise balancing is possible since smaller steps and thus effectively lower load on the lower ranked cells are possible, the balancing process involves less overshoots and less estimation error for SoC (or measurement error of voltages). For a specified balancing precision requirement that is relatively high (such as a requirement that all cells be balanced within 10% or 5% of one another), balancing is achieved faster.

[0243] Another benefit is that given a slow communication speed or a slow control speed the modulation enables assignment of duty cycles between 0% to 100%. Modulation also allows different duty cycles to be assigned duty cycles to differently ranked cells. And it is the combination of modulation and application of different duty cycles to different cells that allows a rank based distributed gate driving communication scheme to achieve better harmonics than the prior art approach. Harmonics are further reduced when the communication speed or the control speed puts a limit on how closely the stepwise voltage output approximates an ideal AC sinusoidal waveform.

[0244] In a time varying waveform there are parts of the waveform near-zero which can be used to unload certain cells and achieve balancing functions (for example by using some cells more than others in a time varying voltage). Use of some cells more than other occurs by assigning different durations to different cells which contribute to different parts of the sine wave as part of a rank based distributed gate driving communication scheme.

[0245] Figure 7 illustrates the contributions of five cells to generate an AC waveform where cell one contributes the longest duration and cell five the shortest duration. Accordingly, in some embodiments the controller is configured to determine cell voltages, and rank the higher voltage cells higher such that their contribution is more than lower ranked cells. Due to higher ranked cells being used for longer durations, they will be depleted faster than other cells and therefore those cells with higher voltage will reduce more than those with a lower voltage. Accordingly, cell balancing target voltages can be achieved by ranking cells according to their voltage such that they converge toward the cell balance target voltage.

[0246] In some embodiments, the above-described reconfigurable battery system is part of an electric vehicle (EV). For example, the battery system is the primary power source for at least one electric motor of the electric vehicle. The EV has a motor controller configured to determine motor demand data. In some embodiments, the battery controller is configured to receive the motor demand data from the motor controller and determine at least a voltage target for the reconfigurable battery and therefore the circuit module output voltage based on that demand data. In some embodiments, the controller is configured to compare the demand to one or more cell data parameters, and control the series connection of select cells and the modulated contribution of some of those select cells based on the motor demand data. For example, for low motor torque demands, the controller may be configured to select cells ranked based on data indicating poor performance. For high motor torque demands, the controller may be configured to select cells ranked based on data indicating good performance. Further, in each circumstance, the controller is configured to apply modulation to the switching circuit of one or more cells which reduces the contribution of select low ranked cells in high motor torque demand applications. The cell contribution can be controlled by the modulation such that their poor cell performance mitigates issues such as excessive heat generation or low capacity. High motor torque applications are defined as those which require all or at least half of the cells from the possibly connected cells to be connected to the motor to meet the motor demand. Low motor torque applications are defined as those which require less than half of the cells from the possibly connected cells to be connected to the motor to meet the motor demand.

[0247] In some embodiments, the above-described reconfigurable battery system is part of an EV charging system. The charging system comprises one or more charger connection points, each point configured to connect with an electric vehicle. In one embodiment, the reconfigurable battery system is contained within the EV. In another embodiment, the reconfigurable battery system is contained within the charger infrastructure. In another embodiment, each of the charging system and the EV contain a separate reconfigurable battery system. In another embodiment, each of the charging system and the EV contain an integrated reconfigurable battery system whereby some cells are contained within the EV and some are contained in the charging system, and there are one or more controllers configured to mange one or more of the reconfigurable battery systems including cell modulation. In these embodiments, a charge controller is configured to receive a signal containing charging requirement data of an electric vehicle connected with one charger connection point. The charge controller is configured to determine the circuit module output voltage based on the charging requirement data. Accordingly, the target output voltage is be achieved through the use of varied cell contribution based on cell state modulation as described elsewhere.

[0248] From the foregoing, it will be appreciated that, although specific embodiments have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims and the elements recited therein. In addition, while certain aspects of the invention are presented below in certain claim forms, the inventors contemplate the various aspects of the invention in any available claim form.

Claims

Claims1 . A battery control system comprising: a circuit module comprising a pair of output terminals, the circuit module comprising: a plurality of cell modules selectively connectable in a series configuration with the output terminals to provide the target output voltage on the output terminals, each cell module comprising: at least one battery cell; a switching circuit configured to selectively operate in two or more states, the states comprising: a state whereby the at least one cell is bypassed from the series string; and a state whereby the at least one cell is connected in series with the series string; and a controller configured to provide the target output voltage based on selective control of the operation state of each switching circuit of each cell.

2. The system of claim 1 , wherein the controller is configured to: control the switching circuit of one or more cell modules to meet the target circuit module output voltage by a combination of: the series connection of one or more cell modules with the output terminals; and modulation of the state of the switching circuit at least one cell module, relative to the state of the series connection of one or more cell modules, such that the target voltage is substantially provided at the circuit module output terminals.

3. The system of claim 1 or claim 2, wherein the controller is configured to: determine a set of cell modules for series connection to meet the target output voltage within a predefined time increment; and control the switching circuit of one or more cell modules comprising a combination of: a series connection of one or more cell modules with the output terminals, and modulation, within the predefined time increment, of the switching state of at least one cell module such that the output voltage is substantially provided at the circuit module output terminals.

4. The system of claim 2 or claim 3, wherein the controller is further configured to determine the target circuit module output voltage and control a modulation duty cycle of the modulation of the switching state of at least one cell module based on the target circuit module output voltage.

5. The system of any one of claims 2 to 4, wherein the target voltage is defined by a time varying amplitude and phase, and the controller is configured to control, at predetermined time intervals, the series connection of one or more cell modules and the modulation of the switching state overtime based on the time varying amplitude and phase.

6. The system of any one of claims 1 to 5, wherein the controller is further configured to determine cell data from each at least one cell of each cell module comprising one or more of: voltage, state of charge, temperature, age, measured service life, predicted service life, rate of temperature change, internal resistance, position in a series arrangement, state of health, charge current ability, and discharge current ability; determine a rank for each cell module based on the determined cell data; and control the switching state of one or more cell modules based on the determined rank of one or more cell modules.

7. The system as claimed in claim 6, wherein the controller is further configured to determine the rank for each cell module based on a weighted combination of two or more determined cell data parameters.

8. The system of as claimed in claim 6 or claim 7, wherein the controller is further configured to control the modulation duty cycle based on the determined rank.

9. The system as claimed in claim 8, wherein the controller is further configured to determine the target circuit module output voltage and, based on the determined rank of each cell module, prioritise a higher modulation duty cycle of the switching state to those cell modules with a higher rank and / or a lower modulation duty cycle of the switching state to those cell modules with a lower rank.

10. The system as claimed in any one of claims 6 to 9, wherein the controller is further configured to determine the target circuit module output voltage and control the modulation duty cycle of the switching state of two or more cell modules to meet the target output voltage.11 . The system of any one of claims 6 to 10, wherein the controller is further configured to: determine the target circuit module output voltage; determine a weighting factor attributing a modulation duty cycle priority to each cell module based on the determined rank; and control the modulation duty cycle of the switching state of each ranked cell module based on the weighting factor.

12. The system of any claim 11 , wherein the weighting factor defines an even distribution across the ranked cell modules.

13. The system of claim 11 or claim 12, wherein the weighting factor defines a nonlinear distribution across the ranked cell modules.

14. The system of any one of claims 1 to 13, wherein the controller is configured to: determine a weighting factor assigning a cell contribution value to one or more cells; determine a number of cells for connection to meet the target output voltage; control the switching circuit each cell module comprising a combination of: the series connection of one or more cell modules with the output terminals, and modulation of the switching state of at least one cell module based on the weighting factor, such that the output voltage is substantially provided at the circuit module output terminals; determine a new weighting factor based on cell data and / or cell rank; and determine a new number of cells for connection to meet the target output voltage; and control the switching circuit each cell module such that the output voltage is substantially provided at the circuit module output terminals based on the new number of cells.

15. The system of any one of claims 4 to 14, wherein the controller is configured to: determine balance target voltage for each cell module, and identify one or more cell modules have a voltage higher than the cell module balance target voltage, and, based on the identified one or more cell modules: control the switching state of the identified cell modules with a higher modulation duty cycle than non-identified cell modules.

16. The system of any one of claims 4 to 15, claim, wherein the controller is configured to determine the difference between: the combined voltage of the one or more cell modules, and the target output voltage; then for the switching circuit of at least one cell module, control the modulation duty cycle based on the determined voltage difference.

17. The system of any one of claims 4 to 16, wherein the controller is further configured to: determine the target circuit module output voltage, determine the output voltage, determine the difference between the output voltage and the target voltage, then, based on the difference: adjust the weighting factor attributing the modulation duty cycle priority to each cell module based on the determined rank, and control the modulation duty cycle of the switching state of each ranked cell module based on the weighting factor.

18. The system of claim 17, wherein the controller is further configured to:determine the target circuit module output voltage; map the weighting factor to the modulation duty cycle priority to each cell module based on the determined rank; and control the modulation duty cycle of the switching state of each ranked cell module based on the weighting factor.

19. The system of any one or claims 4 to 18, wherein the controller is further configured to, for each modulated cell: determine the difference magnitude between a current cell module rank and a new cell module rank; and adjust the modulation duty cycle of the switching state of each ranked cell module based on difference magnitude.

20. The system of any one of claims 4 to 19, wherein the controller is further configured to, for each modulated cell: determine one or more cell parameters comprising the voltage, state of charge, temperature, age, measured service life, predicted service life, rate of temperature change, internal resistance, position in a series arrangement, state of health of each cell module, charge current ability, discharge current ability; and adjust the modulation duty cycle of the switching state of each ranked cell module based on determined one or more cell parameters.21 . The system of any one of claims 4 to 20, wherein the controller is further configured to: measure the voltage output from a cell module, and adjust a modulation duty cycle applied to any one or more cell modules based on the measured cell module output voltage.

22. The system as claimed in any one of claims 1 to 21 , wherein the controller comprises two or more cell processors, each configured to control a subset of the modules of the system, and each cell processor is configured to: determine cell data for one or more cells under control of each cell processor; communicate the determined cell data to one or more other cell processors; and wherein at least one cell processor is configured to determine the rank of each cell from communicated and determined cell data, and communicate the rank to one or more other cell processors.

23. The system as claimed in any one of claims 1 to 22, wherein the system comprises two or more cell processors, each configured to: determine cell data for one or more cells under control of each cell processor; communicate the determined cell data to one or more other cell processors; and wherein each cell processor is configured to determine the rank of each cell from communicated and determined cell data; and each cell processor is configured to operate the respective switching circuit according to the determined rank.

24. The system as claimed in any one of claims 1 to 23, wherein the controller comprises: one or more cell processors operatively configured to control the switching state of one or more cell modules, and a central processor, wherein the central processor and one or more cell processors are configured to communicate via a first communication channel.

25. The system as claimed in claim 24, wherein the first communication channel comprises a channel adapted for transmission of: a synchronisation signal; the target voltage data; and / or rank data comprising the number of cells ranked to thereby contribute to the target output voltage.

26. The system as claimed in claim 24 or claim 25, wherein the communication channel between the central processor and cell processor comprises an update frequency lower than the modulation base frequency.

27. The system of any one of claims 24 to 26, wherein each of the one or more cell processors are configured to communicate to one or more other cell processors via a second communication channel.

28. The system of any one of claims 24 to 27, wherein the one or more cell processors are configured to control the modulation of the switching circuit at a rate higher than the communication rate of the communication channel.

29. The system of any one of claims 24 to 28, wherein the central processor is configured to communicate the target voltage to one or more cell processors, and in response, each cell processor is configured to control the state of their one or more cell modules and / or the modulation.

30. The system of any one of claims 24 to 29, wherein the central processor is configured to update the target voltage or rank based cell contributions at a first frequency, and the modulation base frequency is faster the time increment.31 . The system of any one of claims 24 to 30, wherein the central processor is configured to send a synchronisation signal operable to control the timing of the switching circuit and to thereby target a new output voltage, and one or more cell processors are configured to control a switching state of the switching circuit when a synchronisation signal is received.

32. The system of any one of claims 24 to 31 , wherein the system further comprises a low-pass filter connected between the string of cell modules and an output terminal.

33. An electric vehicle comprising the system according to any one of claims 1 to 32, the vehicle comprising a motor controller configured to determine motor demand data; and wherein the controller is configured to determine the circuit module output voltage based on the motor demand data.

34. An electric vehicle charging system comprising the system according to any one of claims 1 to 32, the charging system comprising: one or more charger connection points, each point configured to connect with an electric vehicle; a charge controller configured to receive a signal containing charging requirement data of an electric vehicle connected with one charger connection point; and wherein the controller is configured to determine the circuit module output voltage based on the charging requirement data.

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