GB2537432A

GB2537432A - Battery monitor and monitoring method

Info

Publication number: GB2537432A
Application number: GB1511128.9A
Authority: GB
Inventors: Ball Robert; Tucker Mark
Original assignee: Tata Motors European Technical Centre PLC; Tata Motors Ltd
Current assignee: Tata Motors European Technical Centre PLC; Tata Motors Ltd
Priority date: 2015-04-15
Filing date: 2015-06-24
Publication date: 2016-10-19
Anticipated expiration: 2035-06-24
Also published as: WO2016166713A3; GB2537432B; GB201511128D0; WO2016166713A2

Abstract

A system 10 for monitoring a plurality of cells 12 in at least one battery 14. The system comprises a means for obtaining a first measurement of a cell parameter for each of a plurality of cells in a battery. This parameter can be voltage or temperature. The system then ranks the plurality of cells in dependence upon the first measurement of the parameter to obtain a first ranking value for each of the cells. These first ranking values may be stored in a memory 34. The system can be used to measure the cell parameters during use of the battery. The invention also includes a method for monitoring a plurality of cells in at least one battery and a computer programme 72 that when executed performs the described method. The system is used in a vehicle.

Description

BATTERY MONITOR AND MONITORING METHOD

TECHNICAL FIELD

The present disclosure relates to a battery monitor and monitoring method and particularly, but not exclusively to a system and a method for monitoring a plurality of cells in at least one battery. Aspects of the invention relate to a system, to a battery management system, to a vehicle, to a method and to a computer program.

BACKGROUND

Conventional battery management systems typically use a direct comparison of the individual cell voltages within a battery to identify cell balance and/or the State of Health of cells. For example, a conventional battery management system may use a direct comparison to determine the relative energy contained within individual cells at any moment in time (balance) and/or the maximum energy capacity and/or the electrical resistance of an individual cell (State of Health).

However, in conventional systems this is usually done under specific operating conditions, for example end-of-charge, and cannot be done while the battery is in use. This provides an instantaneous assessment of cell balance rather than a long term assessment.

It is an aim of the present invention to address disadvantages associated with the prior art.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide a system, a battery management system, a vehicle, a method and a computer program as claimed in the appended claims.

According to an aspect of the invention, there is provided a system for monitoring a plurality of cells in at least one battery, the system comprising: means for obtaining a first measurement of a parameter at a first time t1 for each of a plurality of cells in a battery; means for ranking the plurality of cells in dependence upon the first measurement of the parameter to obtain a first ranking value for each of the cells; and means for causing storage of the first ranking values. This allows, for example, for in use monitoring of the plurality of cells.

The parameter may be one or cell voltage and cell temperature.

The plurality of cells may comprise more than two cells.

The means for obtaining the first measurement may comprise means for measuring the parameter for the plurality of cells at the time The system may be for measuring the parameter during use of the battery.

The means for obtaining the first measurement may comprise means for retrieving the measurements of the parameter from at least one memory.

The means for ranking the plurality of cells may comprise means for ranking the cells from the highest value of the parameter to lowest value of the parameter or from lowest value of the parameter to highest value of the parameter.

The system may comprise means for obtaining a plurality of measurements of the parameter at a plurality of times ti to tn for each of the plurality of cells; means for ranking the plurality of cells in dependence upon the plurality of measurements of the parameter taken at each of the times 11 to tn to obtain a ranking value for each of the cells at the times ti to tn; and means for causing storage of the plurality of ranking values.

The system may comprise means for aggregating the ranking values to determine the number of times each cell has achieved each ranking value and means for causing storage of the aggregated ranking values.

The system may comprise analysis means for analysing at least a portion of the aggregated ranking values to perform a diagnostic.

The analysing may comprise applying at least one statistical operator to the aggregated ranking values.

The diagnostic may comprise determining the relative balance and/or the state of health of at least one of the plurality of cells.

A skew distribution in the aggregated ranking values may be indicative of relative cell imbalance.

A bimodal distribution in aggregated ranking values of cell voltage may be indicative of poor state of cell health The system may comprise means for performing at least one action in dependence upon the determined relative balance and/or state of health.

The analysis means may comprise means for comparing at least a portion of the aggregated ranking values with predetermined cell ranking data.

The predetermined cell ranking data may be from at least one of simulations and measurements of a plurality of cells in a battery having a known problem.

According to another aspect of the invention, there is provided a battery management system as described in the preceding paragraphs.

According to yet another aspect of the invention, there is provided a vehicle comprising a battery management system as described in the preceding paragraph or a system as described in the preceding paragraphs.

According to a further aspect of the invention, there is provided a method for monitoring a plurality of cells in at least one battery, the method comprising: obtaining a first measurement of a parameter at a first time t1 for each of a plurality of cells in a battery; ranking the plurality of cells in dependence upon the first measurement of the parameter to obtain a first ranking value for each of the cells; and causing storage of the first ranking values. This allows, for example, for monitoring of the plurality of cells with small data storage requirements.

According to a still further aspect of the inventlon, there is provided an apparatus comprising means for performing the method as described in the preceding paragraph.

According to still another aspect of the invention, there is provided a computer program comprising instructions that, when executed by a processor, cause a system to perform at least: obtaining a first measurement of a parameter at a first time t1 for each of a plurality of cells in a battery; ranking the plurality of cells in dependence upon the first measurement of the parameter to obtain a first ranking value for each of the cells; and causing storage of the first ranking values. This allows, for example, in use monitoring of the plurality of cells.

According to yet another aspect of the invention there is provided a system for monitoring a plurality of cells in at least one battery, the system comprising an electronic processor and an electronic memory device coupled to the electronic processor and having instructions stored therein, the processor being configured to access the memory device a execute the instructions stored therein such that it is operable to: obtain a first measurement of a parameter at a first time t1 for each of a plurality of cells in a battery; rank the plurality of cells in dependence upon the first measurement of the parameter to obtain a first ranking value for each of the cells; and cause storage of the first ranking values. This allows, for example, monitoring of the plurality of cells with small data storage requirements.

According to a further aspect of the invention, there is provided a system for monitoring a plurality of interconnected electrical storage cells, the system comprising: means for obtaining a first measurement of a parameter at a first time t1 for each of the plurality of cells; means for ranking the plurality of cells in dependence upon the first measurement of the parameter to obtain a first ranking value for each of the cells; and means for causing storage of the first ranking values. This allows, for example, in use monitoring of the plurality of cells.

According to a yet further aspect of the invention, there is provided a system for monitoring a plurality of cells in at least one battery, the system comprising: means for obtaining a first measurement of a parameter at a first time t1 for each of a plurality of cells in a battery; 4 means for ranking the plurality of cells in dependence upon the first measurement of the parameter to obtain a first ranking value for each of the cells; and means for causing storage of the first ranking values, wherein the plurality of cells comprises more than two cells. This allows, for example, in use monitoring of the plurality of cells.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig 1 illustrates an example of a system; Fig 2 illustrates an example of a system; Fig 3 illustrates an example of a method Fig 4 illustrates an example of a method; and Fig 5 illustrates an example of aggregated ranking values.

DETAILED DESCRIPTION

Examples of the present disclosure relate to monitoring a battery or a part of a battery. For example, some examples relate to monitoring a rechargeable battery in a vehicle such as an electric vehicle (EV) or a hybrid electric vehicle (HEV).

In examples, a system may monitor the relative value of a parameter, such as voltage, for a plurality of electrochemical cells in a battery. The system may analyse the relative values of the parameter of each of the cells at a number of points in time to perform a diagnostic of the battery.

For example, a system may rank voltage measurements of the plurality of cells of the battery at a number of points in time and aggregate the ranking values for each of the cells to allow a determination of the relative balance and/or a state of health of one or more of the cells.

A technical effect of at least some examples of the disclosure is that a battery may be monitored while in use and not, for example, just at end of charge.

Another technical effect of at least some examples of the disclosure is that a small amount of data is stored in the analysis, for example cell ranking values rather than absolute cell voltages.

Additionally or alternatively some examples provide for the ability to determine the state of health of one or more cells of the battery independent of influences such as temperature variations, state of charge of the cells and so on.

Another technical effect is that examples provide for a better resolution in monitoring a parameter of cells of a battery such as cell voltage.

Figs 1 and 2 illustrate a system 10 for monitoring a plurality of cells 12 in at least one battery 14, the system 10 comprising: means for obtaining a first measurement of a parameter at a first time t1 for each of a plurality of cells 12 in a battery 14; means for ranking the plurality of cells 12 in dependence upon the first measurement of the parameter to obtain a first ranking value for each of the cells 12 and means for causing storage of the first ranking values.

Fig 3 illustrates a method 300 for monitoring a plurality of cells 12 in at least one battery 14, the method 300 comprising: obtaining a first measurement of a parameter at a first time PI for each of a plurality of cells 12 in a battery 14; ranking the plurality of cells 12 in dependence upon the first measurement of the parameter to obtain a first ranking value for each of the cells 12; and causing storage of the first ranking values.

Fig 1 illustrates an example of a system 10 that may be a chip or a chipset. The system 10 may form part of a battery management system 68 comprised in a vehicle 70 such as the one illustrated in the example of Fig 2.

Implementation of a system 10 may be as control means in the form of controller circuitry.

The system 10 may be implemented in hardware alone, have certain aspects in software including firmware alone or can be a combination of hardware and software (including firmware) As illustrated in Fig 1 the system 10 may be implemented using instructions that enable hardware functionality, for example, by using executable instructions of a computer program 36 in a general-purpose or special-purpose processor 38 that may be stored on a computer readable storage medium (disk, memory etc) to be executed by such a processor 38.

The processor 38 is configured to read from and write to the memory 34. The processor 38 may also comprise an output interface via which data and/or commands are output by the processor 38 and an input interface via which data and/or commands are input to the processor 38.

The memory 34 stores a computer program 36 comprising computer program instructions 72 that controls the operation of the system 10 when loaded into the processor 38. The computer program instructions 72, of the computer program 36, provide the logic and routines that enables the system to perform the methods illustrated in Figs 3 and 4. The processor 38 by reading the memory 34 is able to load and execute the computer program 36.

The system 10 therefore comprises: at least one processor 38; and at least one memory 34 including computer program code the at least one memory 34 and the computer program code configured to, with the at least one processor 38, cause the system 10 at least to perform: obtaining a first measurement of a parameter at a first time ti for each of a plurality of cells in a battery; ranking the plurality of cells in dependence upon the first measurement of the parameter to obtain a first ranking value for each of the cells; and causing storage of the first ranking values.

As illustrated in Fig 1, the computer program 36 may arrive at the system 10 via any suitable delivery mechanism 42. The delivery mechanism 42 may be, for example, a non-transitory computer-readable storage medium, a computer program product, a memory device, a record medium such as a compact disc read-only memory (CD-ROM) or digital versatile disc (DVD), an article of manufacture that tangibly embodies the computer program 36. The delivery mechanism may be a signal configured to reliably transfer the computer program 36. The system 10 may propagate or transmit the computer program 36 as a computer data signal.

Although the memory 34 is illustrated as a single component/circuitry it may be implemented 15 as one or more separate components/circuitry some or all of which may be integrated/removable and/or may provide permanent/semi-permanent/dynamic/cached storage.

Although the processor 38 is illustrated as a single component/circuitry it may be implemented as one or more separate components/circuitry some or all of which may be integrated/removable. The processor 38 may be a single core or multi-core processor.

References to 'computer-readable storage medium', 'computer program product', 'tangibly embodied computer program' etc. or a 'controller', 'computer', 'processor' etc. should be understood to encompass not only computers having different architectures such as single /multi-processor architectures and sequential (Von Neumann)/parallel architectures but also specialized circuits such as field-programmable gate arrays (FPGA), application specific circuits (ASIC), signal processing devices and other processing circuitry. References to computer program, instructions, code etc. should be understood to encompass software for a programmable processor or firmware such as, for example, the programmable content of a hardware device whether instructions for a processor, or configuration settings for a fixed-function device, gate array or programmable logic device etc. The blocks illustrated in the Figs 3 and 4 may represent steps in a method and/or sections of code in the computer program 36. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some blocks to be omitted.

In examples, the system of Fig 1 provides means for obtaining a first measurement of a parameter such as cell voltage 28 or cell temperature 30 (see Fig 2) at a first time t1 for each of a plurality of cells 12 in a battery 14; means for ranking the plurality of cells 12 in dependence upon the first measurement of the parameter to obtain a first ranking value for each of the cells 12; and means for causing storage of the first ranking values, for example in the memory 34.

In some examples, the plurality of cells 12 may be comprised in a single module 78 of the battery 14 or may be comprised in a plurality of modules in the battery 14 (see Fig 2).

Furthermore, in some examples the plurality of cells 12 may be comprised in a plurality of batteries 14.

It is described above that the system of Fig 1 may provide means for obtaining a first measurement of a parameter at a first time t1 for each of a plurality of cells 12 and a battery 14. It is to be understood that the measurement of the parameter may not be obtained at the exact same time t1 for each of the plurality of cells 12 in the battery. In some examples, the measurement of the parameter for each of the plurality of cells 12 in the battery 14 may be obtained in a time window of a few microseconds or milliseconds or seconds, however this should still be considered to occur at the first time t1.

Additionally or alternatively it should be noted that when referring to each of a plurality of cells 12 in a battery 14 that the plurality of cells 12 may be a subset of the cells 12 in the battery 14 and may not be all the cells 12 in the battery 14 and/or may not be all the cells 12 in a module 78 (see Fig 2) of a battery 14. In some examples, the plurality of cells 12 may be from a plurality of modules in one or more batteries.

In some examples, the system 10 may provide means for ranking the plurality of cells 12 in dependence upon the first measurement of the parameter to obtain a first ranking value of each of the cells 12 by ranking the plurality of cells from highest value of the parameter to lowest value of the parameter or from lowest value of the parameter to highest value of the parameter.

For example, the system 10 of Fig 1 may provide means for ranking the cell having the highest value of the parameter, such as voltage, in position 1, the second highest value of the parameter in position 2 and so on.

In some examples storage of the first ranking values may be temporary such as storage in a cache, for later use in analysis without long term storage of the ranking values. In other examples, storage of the first ranking values may be permanent/semi-permanent such that the ranking values are stored until they are deliberately removed.

In some examples, the parameter may be measured during use of the battery 14. For example, the system 10 in the example of Fig 1 may comprise means for measuring the parameter for the plurality of cells at the time t1, which may be during use of the battery 14. This may comprise, for example, determining parameter values from data such as voltage values from voltage data.

In other examples, the system 10 illustrated in the example of Fig 1 may provide means for retrieving the measurements of the parameter from at least one memory, such as the memory 34.

Fig 2 illustrates an example of a system 68. In the illustrated example the system 68 is a battery management system 68 for a vehicle 70. The system 68 may be comprised in a vehicle 70.

In the example of Fig 2, the system 68 comprises one or more multiplexers 76, one or more analogue to digital converters 74 and the system 10 illustrated in Fig 1.

In some examples, the system 68 may be comprised in a battery 14 of the vehicle 70. In some examples, the system 68 may be separate from a battery 14 of the vehicle 70.

In the example of Fig 2, the battery management system 68 is comprised in a battery 14. The battery comprises at least one module 78 comprising a plurality of cells 12. In some examples the plurality of cells may comprise more than two cells, for example the plurality of cells may comprise 3, 4, 5, 6 and so on cells.

The battery 14 may be a rechargeable battery that may be charged and discharged repeatedly. For example, the battery 14 may power one or more systems of the vehicle 70 and may be charged by the motion of the vehicle 70.

As illustrated in the example of Fig 2, the elements 12, 76, 74 and 10 are operationally coupled to each other and any number or combination of intervening elements can exist between them (including no intervening elements).

In other examples, the elements 12, 76, 74 and 10 may be operationally coupled to other elements not illustrated in the example of Fig 2.

In the illustrated example, the plurality of cells 12 are interconnected and may comprise any suitable electrical storage cells for use in a battery 14 such as a rechargeable battery. For example, the plurality of cells 12 may comprise a plurality of interconnected electrochemical cells.

The at least one multiplexer 76 is configured to receive a measurement of a parameter from each of the cells 12 in the module 78.

In some examples, a plurality of multiplexers 76 may receive the measurement values from the plurality of cells 12. The parameter may be cell voltage 28 and/or cell temperature 30.

The multiplexer 76 is configured to combine the signals received from the plurality of cells into a single signal. Any suitable multiplexer may be used The one or more analogue to digital converter 74 is configured to receive the multiplexed signal from the at least one multiplexer 76 and to convert the received signal into digital format.

In some examples, the system 68 may comprise a plurality of analogue to digital converters 74 configured to receive signals from more or more multiplexers 76.

The analogue to digital converter 74 is configured to output digitized parameter data, such as digitized voltage data and/or digitized temperature data towards the system 10.

In examples, the system 10 may be configured to control the one or more analogue to digital converters 74 and/or the one or more multiplexers 76. This is illustrated in the example of Fig 2 by the double-ended arrows connecting the system 10 and the analogue to digital converter 74 and the analogue to digital converter 74 and the multiplexer 76.

In the example of Fig 2, double-ended arrows are used between each of the elements to indicate that data may flow in any direction in the system 68 and, in some examples, to the one or more modules 78.

However, in some examples data may flow in a single direction from the plurality of cells 12 to the multiplexer 76 to the analogue to digital converter 74 and to the system 10.

In the example of Fig 2, the system 10 may be as described above in relation to the example of Fig 1.

In some examples, the system 10 may comprise means for outputting BO. In examples, the system 10 may perform an analysis of measurements of the parameter obtained from the plurality of cells 12 and may perform at least one action in dependence upon the analysis.

For example, the system 10 may be configured to provide an output using the means for outputting 80 in dependence upon the analysis and/or to adjust the relative balance between the cells 12.

In general, the processor 38 may provide means for controlling operation of the system 10 and/or the system 68 and/or the battery 14 and/or at least part of the vehicle 70.

In some examples, the system 68 and/or the battery 14 may comprise any number of additional elements. In some examples, the system 68 and/or the battery 14 may not comprise one or more elements illustrated in the example of Fig 2.

For example, the one or more multiplexers 76 and/or the one or more analogue to digital converters 74 may be omitted in some examples.

In some examples, the system 10 illustrated in an example of Fig 2 may output data to one or more further systems, such as the system 10 illustrated in the example of Fig 1, for analysis. For example, the system 10 in the example of Fig 2 may output the digitized parameter data for analysis. In some examples, analysis may be shared between the system 10 in the example of Fig 2 and one or more external systems.

Fig 3 illustrates an example of a method 300. The method 300 may be performed by the system 10 of Fig 1 or the system 68 of Fig 2.

That is, in examples the system 10 of Fig 1 or the system 68 of Fig 2 comprises means for performing the method 300.

At block 302 a first measurement of a parameter at a first time t1 for each of a plurality of cells 12 in a battery 14 is obtained. As discussed above, the time t1 may be a time window of a certain duration.

In some examples, the measurement for each of the plurality of cells 12 may be measured at the time t1. For example, see the example of Fig 2.

In other examples, the measurement of the parameter for each of the plurality of cells 12 may be retrieved from at least one memory, such as the memory 34. In some examples, the measurements may be stored in a memory by the system 68 and later retrieved by a system such as the system 10 in Fig 1.

In some examples, the parameter may be cell voltage 28 and/or cell temperature 30.

At block 304, the plurality of cells 12 are ranked in dependence upon the first measurement of the parameter to obtain a first ranking value for each of the cells 12.

For example, the plurality of cells may be ranked from highest value of the parameter to lowest value of the parameter or from lowest value of the parameter to highest value of the parameter.

In examples where there is a tie with regard to parameter value for two or more of the plurality of cells 12 any suitable method for resolving the tie may be used.

At block 306 storage of the first ranking values is caused.

In some examples the storage of the first ranking values may be temporary/transient, such as in one or more cache memories. In other examples, the storage of the first ranking values may be in one or more non-volatile memories for later retrieval. This may be considered permanent storage In some examples, the method 300 may be performed a plurality of times, for example at times t1 to tn. This is indicated in the example of Fig 3 by the dotted line joining block 306 to block 302.

In examples, times t1 to tn may be non-overlapping time windows of certain duration that may or may not be the same duration.

Fig 4 illustrates an example of another method 400. The method 400 may be performed by the system 10 of Fig 1 or the system 68 of Fig 2.

That is, in some examples the system 10 of Fig 1 or the system 68 of Fig 2 may comprise means for performing the method 400.

At block 402 a measurement of a parameter at a time tx for each of a plurality of cells 12 in a battery 14 is obtained. For example at a time t1.

At block 404 the plurality of cells are ranked in dependence upon the measurement of the parameter to obtain a ranking value of each of the cells 12.

At block 406 storage of the ranking values is caused.

In examples, blocks 402, 404 and 406 may be as described above in relation to blocks 302, 304 and 306 of Fig 3.

In the example of Fig 4, at block 408 a check on the value of x is performed. In the illustrated example, a check is performed as to whether x is equal to N where N may be any integer value.

If x is not equal to N the method 400 returns to block 402 and the value of x is incremented by 1.

Accordingly, at block 402 when returned from block 408 for the first occasion a measurement at a time t2 for each of the plurality of cells 12 in the battery 14 would be obtained. If x is equal to N the method moves to block 410.

It is noted that in some examples block 408 may be omitted as in some examples block 402, 404 and 406 may be performed until a certain timer has expired or similar.

In examples block 408 allows the method 400, or at least part of the method 400, to be performed a plurality of times to obtain a plurality of sets of ranking values.

At block 410 the plurality of sets of ranking values obtained via cycling blocks 402, 404 and 406 are aggregated to determine the number of times each cell 12 has achieved each ranking value.

For example, for a cell Cl at block 410 it would be determined the number of times cell Cl has achieved rank 1, rank 2, rank 3... and so on for the plurality of cells 12.

Accordingly, at block 410 aggregated ranking values 50 (see, for example, Fig 5) for each cell 12 are determined. In some examples, the aggregated ranking values 50 may be stored and therefore the method 400 may comprise, in some examples, causing the storage of the aggregated ranking values 50 (not illustrated in the example of Fig 4).

At block 412 at least a portion of the aggregated ranking values is analyzed to perform a diagnostic.

For example, analyzing at least a portion of the aggregated ranking values 50 may comprise applying at least one statistical operator to the aggregated ranking values 50. In some examples the statistical operator may comprise skewness and/or mean and/or mode and/or median and/or split distribution and/or bimodality.

In some examples, analyzing the at least a portion of the aggregated ranking values 50 may comprise comparing at least a portion of the aggregated ranking values 50 with predetermined cell ranking data.

For example, a portion of the aggregated ranking values 50 may be compared with simulated cell data and/or measurements of a plurality of cells 12 in a battery 14 having a known problem.

In examples, any suitable predetermined cell ranking data may be used.

In some examples, the diagnostic may comprise determining the relative balance and/or the state of health of at least one of the plurality of cells 12. For example, the diagnostic may comprise determining that at least one of the plurality of cells 12 is relatively out of balance with the other cells in the plurality of cells 12 and/or that at least one cell of the plurality of cells 12 has deteriorated and/or failed. See, for example, the example of Fig 5.

At block 414 at least one action is performed. This may also be considered to be causing at least one action to be performed. The at least one action may be performed in dependence upon the diagnostic performed in block 412. For example, the at least one action may be performed in dependence upon the determined relative balance and/or state of health of at least one of the plurality of cells 12.

In examples, the at least one action may comprise any suitable action such as causing adjustment of and/or adjusting the relative balance between the plurality of cells 12 and/or providing an output indication of the diagnostic. For example the output indication may be of relative balance and/or state of health of at least one of the plurality of cells 12.

As indicated by the dashed lines returning from blocks 410, 412 and 414 to block 402 the method may repeat from any of these blocks. In some examples, the counter x may be reset to zero when the method repeats from block 410, 412 or 414.

For example, if the method repeats after block 410, the aggregated ranking values may be caused to be stored and/or stored before the method 400 repeats. In such examples, blocks 412 and 414 may not be performed or may be performed at a later time.

Similarly, if the method 400 repeats from block 412 the result of the analysis may be caused to be stored and/or stored before the method 400 repeats. In such examples, block 414 may not be performed or may be performed at a later time.

Fig 5 illustrates an example of aggregated ranking values 50 that are for example determined in the method 400 of Fig 4.

In Fig 5 four examples A, B, C and D are illustrated. The illustrated examples may relate to cells A, B, C and D respectively.

The top-left example of Fig 5 labeled A relates to cell A and illustrates the aggregated ranking values 50 for cell A. In the illustrated example, the aggregated ranking values are illustrated as a histogram showing ranking value on the X axis (BIN) and on the Y axis the frequency that cell A obtained each ranking value.

As can be seen from example A in Fig 5 cell A is sometimes the highest ranked cell of the 10 cells and rarely the lowest ranked cell of the 10 cells. However, in the illustrated example, cell A is most often somewhere in the middle of the 10 cells when ranked on a parameter such as cell voltage 28 and/or temperature 30.

Cell A is therefore not showing any particularly strong signs of lack of relative balance with the other cells 12 (when ranked on cell voltage) or any particularly strong indication that cell A is damaged and/or worn and/or has failed (when ranked on cell voltage and/or cell temperature).

In some examples, the performing/causing performance of at least one action in block 414 of method 400 may comprise outputting an indication that a cell, such as cell A in the example of Fig 5, appears to be problem free.

In an idealized battery the histograms for each cell would be flat. However in reality, the histograms for a real, functioning battery may look similar to the example of cell A in Fig 5.

The top-right example of Fig 5 illustrates the histogram for cell B. It can be seen that cell B is often the highest rank and lowest rank cell in respect of cell voltage but is rarely in the middle rankings.

Cell B is therefore displaying a strong bimodal or "twin peaks" shape. This shape strongly suggests that cell B has more resistance in it than the other cells in the plurality of cells 12.

The bimodal shape in the histogram is caused by the voltage drop across the resistance in cell B adding for charging and subtracting for discharging.

Such a profile in a histogram for a cell suggests that there is an issue with the cell and it may be damaged and/or worn and/or has failed. That is, a bimodal distribution may be indicative of a cell in a poor state of health.

In such examples, the performing/causing performance of at least one action at block 414 of method 400 may comprise outputting an indicator that cell B requires attention such as repair or replacement.

In the lower left example of Fig 5 a histogram for cell C is shown.

As can be seen in the example C of Fig 5 cell C is often the highest ranked cell in terms of cell voltage. Cell C in the example of Fig 5 is displaying a skew distribution in terms of cell voltage. This suggests that cell C is out of relative balance with respect to the other cells in the plurality of cells 12.

In such examples, the performing/causing performance of at least one action at block 414 in method 400 may comprise causing an adjustment of the relative balance between the cells 12 and/or outputting at least one notification that cell C may require attention.

Example D in the lower right of Fig 5 is similar to example C but in the case of example D cell D is often the lowest rank based on cell voltage which again displays a skew distribution and suggests that cell D appears out of relative balance with the other cells 12 in the plurality of cells 12.

The performing/causing performance of at least one action 414 in method 400 may be similar for example D as for example C. The examples illustrated in Fig 5 show some possibilities of example profiles that may be obtained when cells have state of health and/or balancing issues.

However, through the use of predetermined cell data, such as data from simulations and/or data from cells having a known issue other cell histogram profiles indicative of many different problems may be obtained and used in the method 400 for the analysis for example.

In addition, the aggregated ranking values may be illustrated using a table with ranking values in the rows and cells in the columns with a shading of each cell used dependent upon the value in the cell. In this way, high values and low values may be easily represented when there is a lot of data.

As used herein 'for' should be considered to also include 'configured or arranged to'. For example 'a system for' should be considered to also include 'a system configured or arranged to'.

Examples of the present disclosure provide a number of advantages. In examples, a diagnostic, such as determining cell balance or state of health, may be performed during use of the battery.

Furthermore, examples of the disclosure provide for long-term assessment of plurality of cells/battery rather than an instantaneous assessment.

Additionally or alternatively the results are aggregated for each cell over time, such as by summing the number of first rank' values, 'second rank' values and so on. The aggregation of the repeated comparisons enables differences between cells in the parameter such as cell voltages to be detected to a finer resolution than otherwise possible due to quantisation errors in the analogue to digital conversion.

Where a structural feature has been described, it may be replaced by means for performing one or more of the functions of the structural feature whether that function or those functions are explicitly or implicitly described The term 'comprise' is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use 'comprise' with an exclusive meaning then it will be made clear in the context by referring to "comprising only one.." or by using "consisting".

In this brief description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term 'example' or for example' or 'may' in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus 'example', 'for example' or 'may' refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all of the instances in the class. It is therefore implicitly disclosed that a features described with reference to one example but not with reference to another example, can where possible be used in that other example but does not necessarily have to be used in that other example.

Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed.

Features described in the preceding description may be used in combinations other than the combinations explicitly described.

Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

CLAIMS1. A system 10 for monitoring a plurality of cells 12 in at least one battery 14, the system 10 comprising: means for obtaining a first measurement of a parameter at a first time t1 for each of a plurality of cells 12 in a battery 14; means for ranking the plurality of cells in dependence upon the first measurement of the parameter to obtain a first ranking value for each of the cells 12; and means for causing storage of the first ranking values.
2. A system 10 as claimed in claim 1, wherein the parameter is one of cell voltage 28 and cell temperature 30.
3. A system 10 as claimed in any preceding claim, wherein the means for obtaining the first measurement comprises means for measuring the parameter for the plurality of cells 12 at the time t1.
4. A system 10 as claimed in any preceding claim, wherein the system 10 is for measuring the parameter during use of the battery 14
5. A system 10 as claimed in claim 1 or 2, wherein the means for obtaining the first measurement comprises means for retrieving the measurements of the parameter from at least one memory 34.
6. A system 10 as claimed in any preceding claim wherein the means for ranking the plurality of cells 12 comprises means for ranking the cells 12 from highest value of the parameter to lowest value of the parameter or from lowest value of the parameter to highest value of the parameter.
7. A system 10 as claimed in any preceding claim, comprising: means for obtaining a plurality of measurements of the parameter at a plurality of times tl to tn for each of the plurality of cells 12; means for ranking the plurality of cells 12 in dependence upon the plurality of measurements of the parameter taken at each of the times t1 to tn to obtain a ranking value for each of the cells 12 at the times t1 to tn; and means for causing storage of the plurality of ranking values.
8. A system 10 as claimed in claim 7, comprising means for aggregating the ranking values to determine the number of times each cell has achieved each ranking value and means for causing storage of the aggregated ranking values 50.
9. A system 10 as claimed in claim 8, comprising analysis means for analysing at least a portion of the aggregated ranking values 50 to perform a diagnostic.
10. A system 10 as claimed in claim 9, wherein analysing comprises applying at least one statistical operator to the aggregated ranking values.
11. A system 10 as claimed in claim 9 or 10, wherein the diagnostic comprises determining the relative balance and/or the state of health of at least one of the plurality of cells.
12. A system 10 as claimed in claim 11, comprising means for performing at least one action in dependence upon the determined relative balance and/or state of health.
13. A system 10 as claimed in claim 9, 10, 11 or 12, wherein the analysis means comprises means for comparing at least a portion of the aggregated ranking values 50 with predetermined cell ranking data.
14. A system as claimed in claim 13, wherein the predetermined cell ranking data is from at least one of simulations and measurements of a plurality of cells in a battery having a known problem.
15. A battery management system 68 comprising a system 10 as claimed in at least one of claims 1 to 14.
16. A vehicle 70 comprising a system 10 as claimed in at least one of claims 1 to 14 or a battery management system 68 as claimed in claim 15.
17. A method for monitoring a plurality of cells 12 in at least one battery 14, the method 5 comprising: obtaining a first measurement of a parameter at a first time t1 for each of a plurality of cells 12 in a battery 14; ranking the plurality of cells 12 in dependence upon the first measurement of the parameter to obtain a first ranking value for each of the cells 12; and causing storage of the first ranking values.
18. A method as claimed in claim 17, wherein the parameter is one of cell voltage 28 and cell temperature 30.
19. A method as claimed in claim 17 or 18, wherein the method is performed during use of the battery 14.
20. A method as claimed in claim 17, 18 or 19, comprising performing the method a plurality of times to obtain a plurality of sets of ranking values.
21. A method as claimed in claim 20, comprising aggregating the plurality of sets of ranking values to determine the number of times each cell has achieved each ranking value.
22. A method as claimed in claim 21, comprising analysing at least a portion of the aggregated ranking values 50 to perform a diagnostic.
23. A method as claimed in claim 22, wherein analysing comprises applying at least one statistical operator to the aggregated rankings.
24. A computer program 36 comprising instructions that, when executed by a processor 38, cause a system to perform the method of at least one of claims 17 to 23.
25. An apparatus comprising means for performing the method as claimed in at least one of claims 17 to 23.
26. A system and/or method for monitoring at least one battery module as described herein with reference to the accompanying drawings.