GB2608577A

GB2608577A - Battery management system

Info

Publication number: GB2608577A
Application number: GB2102111.8A
Authority: GB
Inventors: Chambon Sebastien; Ansermet Didier; Özmen Linda; Henzer Kevin
Original assignee: Eaton Intelligent Power Ltd
Current assignee: Eaton Intelligent Power Ltd
Priority date: 2021-02-15
Filing date: 2021-02-15
Publication date: 2023-01-11
Anticipated expiration: 2041-02-15
Also published as: GB2608577B; GB202102111D0

Abstract

Battery management system and method, with a means for measuring a parameter indicative of a performance of a plurality of battery modules 104 with battery cells. Module switches 106 electrically connect/disconnect respective battery modules. A controller 108, in an output voltage supply mode, controls each module switch to connect/disconnect the respective battery module to generate an output voltage V, the controlling based on the parameters measured and a target output voltage signal. A polarity control switch changes a polarity of the output voltage in response to signals from the controller based on the target output voltage signal. The module switches and the polarity control switch form a switching assembly. The polarity control switch has polarity switches S1, S2 that are controlled by signals 112-1, 112-2 from the controller to produce an AC output that is approximately sinusoidal. The parameter may be the state of health. Preferably, second life batteries are used.

Description

Battery Management System

Field.

This relates to battery management system for controlling battery charge and discharge/voltage supply, and a battery pack system comprising the same.

Background

It is desirable to reuse batteries or battery modules, where possible, for environmental and cost reasons. For example, battery modules from electric vehicles can be repurposed for use with other electric vehicles or with solar cell or photovoltaic modules, or for use in power walls, etc. Such "second life" batteries can each have a different capacity (capacity is how much energy is stored in the battery) and state of health (an indication of the general condition, or long term capability, of the battery), and it may be necessary to balance the differing battery capabilities in order to provide the desired output voltage from a battery pack in a reliable manner, or to be able to charge the battery pack effectively.

The capacity of a battery pack comprising multiple battery cells is determined by the weakest cell (the one with the lowest capacity, or worst state of health), Once the weakest cell is depleted, the entire pack is effectively depleted. Passive balancing is known, which attempts to handle discrepancies in battery cell capacity by discharging high capacity cells into a resistor so that all cells have the same state of charge. Such an approach can be low cost, but it can waste significant amounts of energy and efficiency, particularly for second life batteries, which often have a large disparity in terms of capability or state of health. Another approach can be to rank each cell in order that cells of the same state of health are included together when forming battery packs. However, this approach is slow and expensive, and does not account for changes in the state of health over time.

3o An improved battery management system is therefore desirable, particularly for implementation with second life batteries.

Summary

In a first aspect, a battery management system is provided in accordance with independent claim 1. In a second aspect, a battery pack system is provided, the battery pack system comprising the battery management system and a battery pack comprising plurality of battery modules, each battery module comprising one or more battery cells.

Described herein is a battery management system, comprising: means for measuring, for each of a plurality of battery modules, each battery module comprising one or more battery cells, a parameter indicative of a performance of the battery module; a plurality of module switches, each module switch configured to electrically connect or disconnect a respective one of the plurality of battery modules; a controller configured, in an output voltage supply mode of operation, to control each module switch to electrically iv connect or disconnect the respective battery module to generate an output voltage, the controlling based on the parameters measured for each of the plurality of battery modules and a target output voltage signal; and a polarity control switch configured to change a polarity of the output voltage, the controller further configured to control the polarity switch based on the target output voltage signal. The plurality of module /5 switches and the polarity control switch can be considered to form a "switching assembly", although the respective switches may not be logically linked and/or may be independently operated by the controller.

By controlling both an amplitude and a polarity of an output voltage, an AC output may be produced by a battery pack, without the need for intermediate electronics or processing of the output. A simpler, quicker, and more efficient battery management system may therefore be provided which can make more effective use of battery modules. A more efficient battery pack may therefore be provided. This can be of particular importance when using second life batteries, which can have a large disparity za in state of health and therefore can lead to more inefficiencies than new batteries.

For example, the controller may be configured to control the switching assembly to approximate a sinusoidal output voltage, or to produce a substantially sinusoidal output voltage. In other examples, any suitable target output waveform may be approximated, depending on the desired application for the system.

Optionally, the controller is further configured, in a charge mode of operation, to control each module switch to electrically connect or disconnect the respective battery module, the controlling based on the parameter measured for each of the plurality of battery modules and an input voltage signal. Optionally, the controller is further configured to control the polarity switch based on the input voltage signal. This allows the input voltage signal used for charging to have a variable (i.e. both positive and negative) polarity. Optionally, the input voltage signal is a sinusoidal input voltage signal. Optionally, any other input voltage signal may be used.

Optionally, the means for measuring a parameter indicative of a performance of the battery module comprises means for measuring a state of health, SOH, of the battery module. The module switches may therefore control the connection and disconnection of the modules on the basis of SOH. Optionally, the means for measuring a parameter indicative of a performance of the battery module comprises means for measuring a i() voltage across the battery module. The use of voltage may allow for a quicker estimate or indication of SOH than a direct SOH measurement, A quicker and more efficient battery management system may therefore be provided.

In some examples, the controller is configured to control each module. switch to i electrically connect or disconnect one or more of the plurality of battery modules in an order dependent on the voltage measured across each battery module. Optionally, in the output voltage supply mode of operation, the controller is configured to first connect a battery module having a highest measured voltage, and then connect one or more further battery modules in a descending order of measured voltage. This approach can cause connection of the "best" or highest capacity module when discharging (or supplying a voltage), so that the best module is used more than the worst" module. This can improve balancing of the battery system over time, since the different modules can reach a more equal state of health over repeated charge and discharge cycles.

Optionally, in the charge mode of operation, the controller is configured to first connect a battery module having a lowest measured voltage, and then connect one or more further battery modules in an ascending order of measured voltage. The "worst" cell can therefore be connected first when charging, which can help a more equal state of charge to be reached across the battery pack.

Optionally, the system further comprises a filter configured to receive the output voltage and generate a filtered output voltage. The use of a filter can help reduce or eliminate (help suppress) harmonics in the generated output signal.

Optionally, the battery management can further comprise a step up transformer. -4 -

Described herein is a battery pack system comprising: at least one battery management system of any preceding claim; and at least one battery pack, each battery pack comprising a plurality of battery modules, each battery module comprising one or more battery cells. There can be one battery management system per battery pack, or one battery management system for a plurality of battery packs. For example, a three-phase system may be provided comprising three battery packs and at least one battery management system (e.g. a three--phase system comprising the battery pack system described herein, wherein there are three battery packs). The battery management system or systems are arranged to control or manage the battery pack or battery packs.

In one example, the plurality of battery modules are arranged to form a string, wherein the polarity control switch is configured to switch a polarity of the string to change a polarity of the output voltage. In another example, the plurality of battery modules are i arranged to form two strings, each string having a different polarity, wherein the polarity control switch is configured to switch between the two strings to change a polarity of the output voltage. Other arrangements may be envisaged in order to provide the desired change in polarity of the output voltage signal.

Optionally, each battery module comprises four battery cells, two of the battery cells arranged in parallel and two of the battery cells arranged in series. Optionally, the one or more battery cells are second life battery cells.

Described herein is a photovoltaic energy system comprising one or more photovoltaic cells, and the battery pack system of any example described herein. Also described herein is an electric vehicle comprising the battery pack system of any example described herein. The battery modules in these implementations may comprise one or more second life battery cells.

A method of operating a battery management system to generate an output voltage is also provided. The method comprises: measuring, for each of a plurality of battery modules, each battery module comprising one or more battery cells, a parameter indicative of a performance of the battery module; and in an output voltage supply mode of operation: controlling each module switch of a plurality of module switches, each module switch configured to electrically connect or disconnect a respective one of the plurality of battery modules, to electrically connect or disconnect the respective -5 -battery module to generate the output voltage, the controlling based on the parameters measured for each of the plurality of battery modules and a target output voltage signal, and controlling, based on the target output voltage signal, a polarity control switch configured to change a polarity of the output voltage, wherein the plurality of module switches and the polarity control switch form a switching assembly.

Optionally, the parameter indicative of a performance of the battery module comprises a voltage across the battery module, and wherein controlling each module switch comprises: electrically connecting a battery module of the plurality of battery modules having a highest measured voltage; subsequently electrically connecting a battery module having a second highest measured voltage; subsequently electrically connecting one or more battery modules in a descending order of measured voltage with the output voltage approximates a maximum of the target output voltage; and once the output voltage is approximate to a maximum of the target output voltage, electrically disconnecting the connected battery modules in an ascending order of measured voltage.

Optionally, the method further comprises, in a charge mode of operation: controlling the plurality of module switches to electrically connect a battery module of the plurality of battery modules having a lowest voltage measured across then battery modules; and subsequently controlling the plurality of module switches to electrically connect one or more further battery modules in an ascending order of measured voltage.

It will be understood that any of the features described above with reference to the battery management system of the first aspect may be provided in any suitable combination, and in any suitable combination with features of the battery pack system provided herein. Moreover, any such features may be combined with any features of the method of operating the battery management system, or vice-versa, as appropriate.

3o Brief Description of the Drawings

The following description is with reference to the following Figures: Figure 1A provides a schematic illustration of a battery pack system comprising a battery management system; Figure Ai provides an illustration of the output voltage generated by the battery pack system of Figure IA; Figure 2 illustrates the generation of an output voltage which approximates a sinusoidal output voltage: Figure 2A shows connection of a first battery module, Figure 2B shows connection of a second battery module, and Figure 2C shows connection of a third battery module; Figure 3 provides a schematic illustration of an alternative)attery management system to that shown in Figure 1; Figure 4 illustrates a three-phase system for output of a three phase voltage signal; Figure 5 illustrates an example use of the battery management system described herein in a photovoltaic energy system; and Figure 6 is a flowchart illustrating an example method of operating the battery management system described herein.

Detailed Description

With reference to Figure IA, a battery pack system 100 comprising a battery pack 102 having a plurality of battery modules and a battery management system is described.

As used herein, a "battery pacic comprises a plurality N of battery modules 104, where N is greater than 1 (optionally there are 12 battery modules arranged to form a "string", where a battery pack can be i string, i.e. N=12, or 2 strings, i.e. N-24, but any suitable number of modules 104 may be provided depending on the application for the battery pack). Each "battery module" comprises one or more battery cells. Optionally, each battery module comprises 4 battery cells, 2 arranged in series and 2 arranged in parallel, but other arrangements can be envisaged.

The battery management system comprises means for measuring, for each battery module 104, one or more parameters indicative of a performance of the battery module 104. These parameter(s) can be used to control connection and disconnection of the battery module, providing an active balancing of the battery modules. 'This active balancing can be quicker and cheaper than other techniques, and is also more dynamic, reflecting changes in battery cell condition over time. It is also more efficient than passive balancing techniques, In paifficular, by connecting and disconnecting battery modules based on one or more indicators of their performance, limitations with different battery module capacities may be overcome. For example, when discharging a battery or operating in an output voltage supply mode, the best performing module is the one with the highest capacity/voltage (the measured voltage can provide an indication of the health of the cell), and the worst performing is the one with the lowest capacity/voltag,e. Without balancing, the battery pack would be effectively depleted when the lowest capacity module was depleted; however, by controlling which modules are connected and in what order, higher performing modules can be used first, and used for longer, extending the useful lifetime of the battery pack. This can also lead to balancing of the system over time. Similarly, when operating in a charge mode of operation, the module with the lowest voltage (worst cell health) may be connected first in order that it can be if) charged for longer; this removes the need to bleed off higher performing modules so that charging can continue until all cells are fully charged (as is done in passive balancing techniques).

The parameter(s) indicative of a performance of the battery module can comprise a /5 state of health (SOH) of the battery module, and/or a voltage across each battery module, and/or a capacity of the battery IWhl or efficiency (energy / weight unit [Wh/kg] or energy / volume unit [Wh/m3]). The means for measuring one or more parameters indicative of a performance of the battery module (not shown) therefore can comprise means for measuring the state of health of the battery module and/or means for measuring a voltage across the batten/ module 104, or for measuring any suitable parameter. In some examples, the means for measuring a voltage across the battery module can comprise a voltage sensor on each battery-cell within the module, or one or more sensors otherwise configured to sense voltage across the entire battery module. This approach allows to constantly monitor the voltage, or any other parameter indicative of a performance of the battery module, and therefore to dynamically adjust the selection of which modules are to be connected or disconnected.

The state of health of each individual battery module in the pack can be determined based on its state of charge (SoC) measurement, which provides a measurement of the 3o ratio of its remaining charge to its capacity (SOC indicates the short term capability of the battery). SoC measurements use factors such as voltage, integrated charge and discharge currents, and temperature to determine the charge remaining in the battery module. The state of health can be measured using a dedicated precision single--chip or multi-chip, for example. However, in some implementations the measurement of state y of health can be slower than measuring the voltage. Measuring the voltage across each -8 -battery module tc:4 may therefore provide a quick and reliable indicator of each battery modules' performance and allow for real-time active balancing.

The battery management system further comprises a plurality of module (or module level) switches 106, each of which is configured to electrically connect or disconnect a respective one of the plurality of battery modules 104 from the electrical circuit of the battery management system. Since each individual battery module 104 can be connected or disconnected via its respective module switch:1.06, the battery management system described herein allows for selective connection or disconnection of each battery module104. This can improve performance of the battery pack, by accommodating and compensating for differences in the capacity of battery modules he pack.

In particular, the battery management system comprises a con troller-108 configured, in an output voltage supply mode of operation, to control each module switch 106 to electrically connect or disconnect the respective battery modules 104. The controller 108 can control the module switches 106 via switching signals no, which can be transmitted by suitable electrical connections (not shown) between the controller sob and the module switches 106. The controller is configured to control each module switch to electrically connect or disconnect one or more of the plurality of battery modules 104 in an order dependent on the measured parameters indicative of a performance of each battery module.

The controller 108 is configured to control the module switches 106 to generate an output voltage V, wherein the controlling is based on the parameters (such as state of health or voltage) measured for each of the plurality of battery modules 104 and a target output voltage signal V1. In some examples, a DC output may be produced by the battery management system, but in other examples an AC output may be produced.

3o In order to produce an AC output directly, without intermediate electronics (or with reduced or minimised inter mediate electronics), the battery management system further comprises a polarity control switch having two switches Sr, 82, the polarity control switch configured to change a polarity of the output voltage V. The controller 108 is configured to control the polarity switches Si, 82 via control signals 112-1, 112-2, y where the controlling of the polarity control switch is based on the target output voltage signal VI. In this way, the controller can control the module switches 106 and the -9 -polarity switches Si, 52 (which together form a switching assembly, controlled by the controller 108) to approximate a sinusoidal output voltage V (i.e. to produce a substantially sinusoidal output voltage).

By producing an AC output directly, fewer electronics or components may be required to generate the output (as compared to implementations which may approximate a rectified sine wave, for example). Therefore, producing an AC output can be simpler and quicker than other approaches which do not generate the negative part of the output directly. A more efficient approach to providing a substantially sinusoidal output signal may therefore be provided by the approach described herein. In some implementations, the approach described herein may produce one or more harmonics of the substantially sinusoidal output, but any such harmonics can be reduced or supressed by filtering the output signal.

i This approximated sinusoidal output voltage V is illustrated in Figure 18. Battery modules are connected and disconnected via module switches 106 in order to provide the desired voltage level or amplitude (discussed in more detail with reference to Figure 2), and the polarity switches Si, 52 are controlled to change the polarity of the output voltage (the polarity switches Si, S2 of Figure IA are reproduced in Figure 113 to illustrate the position of said switches at different stages of the sinusoidal output). As can be seen in Figure IB, when switch Si is in an upper position and switch S2 is in a lower position, a positive output voltage is provided. In contrast, when switch Si is in a lower position and switch S2 is in an upper position, a negative output voltage is provided. However, the positions of the polarity switches Si, 52, and the corresponding polarity of the output voltage, will be specific to the switching circuitry of a particular application, and are provided here for example only.

With reference to Figure LA, the battery management system may further comprise a filter 114 configured to receive the output voltage, optionally the approximated sinusoidal output voltage, and generate a filtered output voltage for supply to a load, A transformer n6 may additionally or alternatively be provided to step up (or down) the output voltage (whether filtered or unfiltered) before the voltage is supplied to the load. The transformer n6 may transform the voltage before filter n4 is applied, after the filter n4 is applied, or in the absence of filter n4.

-10 -With reference to Figure 2 (Figures 2A, 2B, 2C), generation of an output voltage VI is described. The parts of the electrical circuit of the battery pack system through which current flows is shown in bold.

It can be seen in Figure 2A that at. a first point in time 0 only one battery module, 104 1, of the plurality of battery modules 104 is electrically connected and contributing to the output voltage V. The rest of the battery modules 104-2 to 104-N are disconnected (the circuit shown in bold flows around the modules, rather than through them, due to the position of the module switches 106). This battery module 104-1 which is connected first is the module of the plurality of modules 104 with the highest voltage measured across it (or the best state of health). Since there is only one battery module connected, the output voltage generated is VI, which corresponds to the voltage across the module 104-1.

i With reference to Figure 2B, at a next point in time (ti, both the first battery module 104-1 and a second' econd battery module 104-2 having a next highest voltage measured across it (or second best state of health) are electrically connected and contributing to the output voltage V. The rest of the battery modules are disconnected (the circuit shown in bold flows through modules 104-1 and 104-2, but around the other modules due to the position of the module switches 106). Module 104-2 is connected next by the controller 108 because the voltage measured across 104-2 is less than that across 104-1, but greater than any of the other modules of the plurality of modules 104. The output voltage at time t, is thus equal to VI. (the contribution from module 104-1) + V2 (the contribution from module 104-2). V2 is less than Vi. since the capacity of module 104-2 is less than the capacity of module 104-1.

With reference to Figure 2C, at a next point in time (t3), the first battery module 104-1 the second battery module 104-2, and module-m.4-N having a third highest voltage measured across it (or third best state of health) are electrically connected via module switches 106 and contributing to the output voltage V. In other words, the voltage measured across 104-N is less than that across 104-1 and 104-2, but greater than any of the other modules of the plurality of modules 104 (such as 104-(N-1), for example). The output voltage at time t3 is thus equal to Vi (the contribution from module 104-1) 4-172 (the contribution. from module 104-2) VN (the contribution from module 104-N).

y STN is less than. VIL or V2, since the capacity of module 104-N is less than the capacity of either of modules 104-1 or 104-2. The modules are thus sequentially connected in a descending order of performance (as indicated by the voltage measured across them, or the state of health, or any other suitable parameter).

This process is repeated until the value of the output voltage is approximate, or substantially equal to, a maximum value of the target output voltage. For example, when the target output voltage is a sinusoidal output voltage, more and more cells 104 are connected via module switches 106 until the output voltage is approximately equal to an amplitude of the target output voltage, at which point the controller 108 acts to sequentially disconnect the battery modules in an ascending order of performance. It should be noted that the order of battery module, connection and disconnection may be different, depending on how the state of health of each battery has evolved during the cycle. Once a 'cycle' has been completed in this way, the controller:1.08 can control the polarity control switches Si, S2 in order to change a polarity of the output voltage, and then repeat the process.

The module switches 10b are controlled based on a switching time in order to approximate the target output signal (or target waveform). in some examples, the switching time can be based on the time period T of the target, waveform or output signal and the number of battery modules. For example, if there are 12 modules and a ionis waveform, the switching time can be approximately-m/12ms, and can be the same for each battery module, in other examples, the target waveform can be approximated as closely as possible and the switching is determined based on the voltage measured across each battery module 104. For example, for a sinusoidal waveform with a time period T, the switching time for the module switch of module 104-1 could be calculated as T* arcsin(cri / Vitotal), and the switching time for the module switch of module 104-2 could be calculated as T " arcsint( %1 + 172) Nttotal), where Vetotal is the total voltage across all of the battery modules 104. These switching time values could be stored in a took up table accessible by controller 108, and/or can be dynamically updated based on changes in the respective modules capacities over time. Any other suitable method of determining switching times can be used, in order to approximate the target output signal or waveform. The polarity control switch can be controlled based on the time period T of the target output signal.

Through controlling both the plurality of module switches 106 and the polarity control switch (switching assembly) when generating the output voltage, the controller can approximate a sinusoidal output voltage. Moreover, by selecting the modules with the best performance or capacity (those with the best state of health or highest voltage measured across it), higher capacity battery modules 104 are used more frequently than lower capacity ones, and/or for longer. This can improve performance of the system overall, as well as making better use of battery capabilities. A more efficient battery, management may therefore be provided, since the system is limited by the weakest module.

It will be understood that the performance of each battery module 104 as described herein may be limited by the worst performing battery cell within the module.

ur Nevertheless, by performing module level switching, more efficient use of the batteries may be made than with previous approaches which do not switch at the level of individual modules. In some implementations of the battery management system, battery module switches may be replaced by battery cell switches, and battery modules with battery cells, allowing individual cells to be connected or disconnected in the same way as the modules are in the description above (i.e. based on parameters indicative of the performance of each cell).

The output supply mode of operation described above can be reversed during a charging mode of operation, in which an input voltage signal is provided, and received by controller 108. In the charge mode of operation, the controller io8 is configured to control each module switch 106 to electrically connect or disconnect the respective battery module 104. The controlling is based on the parameter measured for each of the plurality of battery modules (such as voltage or state of health), and the input voltage signal. For example, the controller 108 is configured to first connect a battery module 104 having a lowest measured voltage (or worst state of health), and then connect one or more further battery modules in an ascending order of measured voltage (or in ascending order of state of health), with the highest performing module connected last. This can improve the charging performance of battery modules, particularly second life battery modules. In examples where the input voltage signal is a sinusoidal input signal, the controller 108 can be further configured to control the polarity switch based on the input voltage signal during the charge cycle. Charging can continue until every module has reached a threshold voltage (a minimum state of charge), whereupon the input current can be reduced and a cycle of continuously connecting the lowest voltage cells and disconnecting the highest voltage cells y performed until the desired (or maximum) state of charge is reached.

With reference to Figure 3, there is shown two strings of battery modules 104, each string arranged with opposite polarity. Each string may comprise any suitable number of battery modules 104, though preferably each string has the same number of modules 104. In the specific example shown in Figure 3, Were are five modules 104 arranged to produce the positive part of an AC signal, and five modules 104 arranged to produce the negative part of the AC signal. In other words, each of the two strings of battery modules 104 produces a signal with a different polarity. The strings can be switched between in order to output a voltage of the desired (or target) polarity.

iv In particular, with reference to Figure 3 a plurality of module switches 106 (not shown) are provided to control output from the one or more battery modules 104 by selectively connecting or disconnecting individual ones of the respective modules 104 (as was discussed above with respect to Figures i and 2). Therefore, the controller can produce a controllable output voltage, V, from each of the strings. However, a different form of polarity control switch is provided for this group of battery management system examples than that illustrated in Figure i. In particular, by providing two strings with opposite polarities, the polarity control switch can be controlled by controller 108 to open or close switches Si, S2, thereby connecting or disconnecting an entire string from the circuit and switching the polarity of the output voltage, V. In this way, the polarity of the output voltage can be controlled or changed by the controller switching between the two strings, allowing generation of an output voltage which approximates a sinusoidal voltage.

With reference to Figure 4, a three-phase system can be provided which incorporates the battery management system. The three phase system comprises three different battery packs. In some examples, each battery pack is associated with a separate battery management system. One battery management system can be the master, and the other battery management systems can operate as staves, the slave battery management systems configured to introduce the desired phase delay. In other 3o examples, there is one battery management system configured to control the three battery packs. For example, the one or more battery management systems can operate to delay the output from each of the battery packs by an appropriate phase delay, in order to provide a phase offset between the output voltage of each of the three battery packs (for example, Phi = 10 degrees, Ph2 = 130 degrees, Ph3 = 250 degrees). In some y examples the output from one battery pack may not be phase delayed (such that phase delay Phi -0 degrees, for example, and Ph2 == 120 degrees, Ph3 = 240 degrees). In -14 -some implementations an RLC circuit may be added to help reduce or suppress harmonics in the output signal.

With reference to Figure 5, a photovoltaic energy system 500 is provided, comprising the battery pack system 100 and one or more photovoltaic cells 510. The battery management system can control the charging of the one or more battery packs 102 from the input voltage received from the photovoltaic cells, and the discharge of the one or more battery packs 102 / supply of an output voltage V to an external load, such as load 520. Load 520 may be the power grid, or any other suitable load. The battery pack system may also be installed in one or more electric vehicles, for example, where charging the battery modules 10,1. can be via the input voltage received from regenerative braking, or an external power source, for example.

With reference to Figure 6, a method 600 for operating a battery management system in an output voltage supply mode to generate an output voltage V is described.

At step 602, the method comprising measuring, for each of a plurality of battery modifies, each battery module comprising one or more battery cells, a parameter indicative of a performance of the battery module. The parameter indicative of a performance can be a state of health of a battery module, a voltage measured across the battery module, and/or any other suitable parameter. This step 602 may be performed continuously or substantially continuously in order to monitor changes in the parameter, or at any suitable interval. For example, substantially continuous sampling with a sampling rate of ims may be used. Step 602 may also be performed as often as required during method 600, at any suitable point in the method.

At step 604, the method comprises controlling each module switch of a plurality of module switches, each module switch configured to electrically connect or disconnect a respective one of the plurality of battery modules, to electrically connect or disconnect 3o the respective battery module to generate the output voltage, The controlling is based on the parameters measured for each of the plurality of battery modules and a target output voltage signal (for the battery management system to generate). By selectively controlling the connection of battery modules through selective operation of the plurality of module switches, differing states of health between the battery modules can y be better accounted and compensated for. This can be of particular importance when using second life batteries, which may all be of different capacities.

Step 604 optionally comprises at step 608 electrically connecting (in turn) one or more battery' modules in a sequence corresponding to a descending order of the parameter indicative of the performance of the module, in order to connect the best performing module first and then to subsequently connect the next best performing, and so on. in some examples, the parameter indicative of a performance of the battery module comprises a voltage across the battery module. in such instances, controlling each module switch comprises first electrically connecting a battery module of the plurality of battery modules having a highest measured voltage. The next battery module to be connected is the battery module having a second highest measured voltage, and so on, in a descending order of measured voltage.

This selective, turn by turn, connecting can continue until the output voltage approximates a maximum of the target output voltage (peak amplitude of the target is sinusoidal output voltage, for example). Once the output voltage is approximate to the maximum of the target output voltage, method step 604 optionally further comprises, at step 610, electrically disconnecting the connected battery modules in an ascending order of measured voltage.

At step 606, the method comprises controlling, based on the target output voltage signal, a polarity control switch configured to change a polarity of the output voltage, whereupon the method can return to step 604. By controlling both individual module switches and the polarity control switch, the method can facilitate the generation of an output voltage which approximates a sinusoidal voltage, or is substantially sinusoidal. Step 604 (optionally including steps 608 and 610) can therefore be repeated to generate a 'negative' part of the output voltage signal, at which point step 606 can be repeated to again change the polarity and the 'positive' part of the output voltage signal generated, and so on.

It is noted that the system and method can easily be adjusted to approximate other waveforms than a sinusoidal waveform. For example, a triangle or sawtooth waveform may be approximated in a similar way.

It is noted herein that while the above describes various examples of the battery management system and battery pack system, these descriptions should not be viewed in a limiting sense. Rather, there are several variations and modifications which may be -16 -made without departing from the scope of the present invention as defined in the appended claims. Clair

Claims

A battery management system, comprising; means for measuring, for each of a plurality of battery mod odes, each battery module comprising, one or more battery cells, a parameter indicative of a performance of the battery module; a plurality of module switches, each module switch configured to electrica connect or disconnect a respective one of the plurality of battery modules; a controller configured, in an output voltage supply mode of operation, to control each module switch to electrically connect or disconnect the respective battery module to generate an output voltage, the controlling based on the parameters measured for each of the plurality of battery modules and a target output voltage signal; and a polarity control switch configured to change a polarity of the output voltage, the controller further configured to control the polarity switch based on the target output voltage signal, wherein the plurality of module switches and the polarity control switch form a ing assembly.
2. The battery management system of claim 1, wherein the controller is configured to control the switching assembly to approximate a sinusoidal output voltage.
The battery management of claim 1 or claim 2, wherein the controller is further configured, in a charge mode of operation, to control each module switch to electrically connect or disconnect the respective battery module, the controlling based on the parameter measured for each of the plurality of battery modules and an input voltage signal, and wherein the controller is further configured to control the polarity switch based on the input voltage signal.
The battery management system of any of claims Ito 3, wherein the means measuring a parameter indicative of a performance of the battery module comprises means for measuring a state of health, SOH, of the battery module.
The battery management system of any of claims I to 3, wherein the means for measuring a parameter indicative of a performance of the battery module comprises means for measuring a voltage across the battery module.
6. The battery management system of claim 5, wherein the controller is configured to control each module switch to electrically connect or disconnect one or more of the plurality of battery modules in an order dependent on the voltage measured across each battery module.
7. The battery management system of claim 6, wherein in the output voltage supply mode of operation the controller is configured to first connect a battery module having a highest measured voltage, and then connect one or more further battery modules in a descending order of measured voltage.
8. The battery management system of any preceding claim, further comprising a filter configured to receive the output voltage and generate a filtered output voltage.
9. The battery management system of any preceding claim, further c, impnsirrg a step up transformer.
10. A battery pack system comprising: at least one battery management system of any preceding claim; and at least one battery pack, each battery pack comprising a plurality of battery modules, each battery module comprising one or more battery cells.mm.
The battery pack system of claim 10, wherein the plurality of battery modules are arranged to form a string, wherein the polarity control switch is configured to switch a polarity of the string to change a polarity of the output voltage.
12. The battery pack system of claim 10, wherein the plurality of battery modules are arranged to form two strings, each string having a different polarity, wherein the polarity control switch is configured to switch between the two strings to change a polarity of the output voltage.
13. The battery pack system of any of claims 10 to 12, wherein each battery module comprises four battery cells, t1.1'70 of the battery cells arranged in parallel and two of the battery cells arranged in series.
14. The battery pack system of any of claims to to 13, wherein the one or more battery cells are second life battery cells.
15. A photovoltaic energy system comprising: one or more photovoltaic cells; and the battery pack system of any of claims 10 to 14.
16. An electric vehicle comprising the battery pack system of any of claims to to 14.
17. A method of operating a battery management system o generate an output voltage, the method comprising: measuring, for each of a plurality of battery modules, each battery module comprising one or more battery cells, a parameter indicative of a performance of the battery module; and in an output voltage supply mode of operation: controlling each module switch of a plurality of module switches, each module switch configured to electrically connect or disconnect a respective one of the plurality of battery modules, to electrically connect or disconnect the respective battery module to generate the output voltage, the controlling based on the parameters measured for each of the plurality of battery modules and a. target output voltage signal, and controlling, based on the target output voltage signal, a polarity control switch configured to change a polarity of the output voltage, wherein the plurality of module switches and the polarity control switch form a switching assembly.
18. The method of claim 17, wherein the parameter indicative of a performance of the battery module comprises a voltage across the battery module, and wherein controlling each module switch comprises: electrically connecting a battery module of the plurality of battery modules having a highest measured voltage; subsequently electrically onnecting a battery module having a second highest measured voltage; subsequently electrically connecting one or* more battery modules in a descending order of measured voltage until the output voltage approximates a maximum, of the target output voltage; and once the output voltage is approximate to a maximum of the target output voltage, electrically disconnecting the connected battery modules in an ascending order of measured voltage.u)
19. The method of claim 17 or 18, the method further comprising, in a charge mode of operation: controlling the plurality of module switches to electrical y connect a battery module of the plurality of battery modules having a lowest voltage measured across then battery modules; and subsequently controlling the plurality of module switches to electrically connect one or more further battery modules in an ascending order of measured voltage.