WO2019097235A2

WO2019097235A2 - Method and apparatus

Info

Publication number: WO2019097235A2
Application number: PCT/GB2018/053310
Authority: WO
Inventors: Stephen Irish; Robin Shaw
Original assignee: Hyperdrive Innovation Limited
Priority date: 2017-11-15
Filing date: 2018-11-15
Publication date: 2019-05-23
Also published as: GB2568663B; WO2019097235A3; GB201718882D0; GB2568663A

Abstract

Disclosed herein is an apparatus comprising a signal interface for obtaining: a temperature signal indicative of temperature of at least one cell of a battery; an energy signal indicative of energy stored in the at least one cell; and a signal indicative of an internal resistance of the at least one cell. The apparatus also comprises a characteristic determiner configured to determine a relation between temperature, an indicator of the internal resistance, and stored energy to characterise the at least one cell, and a data store for storing data indicating the relation.

Description

Method and Apparatus

Field of Invention

The present invention relates to methods and apparatus, and more particularly to batteries and to battery control methods and control electronics, and still more particularly to methods and apparatus enabling the reuse of batteries and battery cells.

Background

There is an increasing use of alternative and renewable energy sources, and a need to provide resilience and continuity in power supply networks. In contrast to conventional electricity generation such energy sources may exhibit large fluctuations in the available power. There is therefore a need to provide energy storage facilities - perhaps in the form of large arrays of batteries, to enable electrical energy to be stored at times of peak supply when demand is low. This stored energy can then be provided to consumers at times when demand outstrips generation capacity. As will be appreciated - very large numbers of very high capacity rechargeable batteries are required if such a facility is to have any practical effect on wholesale energy supply capacity.

In addition, hybrid and electric vehicles are becoming increasingly prevalent. The performance characteristics of the batteries used in such vehicles is a key consideration. High energy density and reliability are needed. As with the stationary energy storage applications explained above, demand for vehicle batteries is only likely to increase. Estimates suggest by 2020 more than 7% of the global transportation market will be electric or hybrid vehicles. These two factors alone mean that very large numbers of rechargeable batteries are being manufactured. This creates its own problems in terms of demand for natural resources, and the very significant manufacturing cost. Indeed, the cost of disassembly, recycling, and disposal of such batteries when they reach the end of their useful life is itself very costly.

Summary

Aspects of the disclosure aim to address, at least in part, the above described technical problems. In particular they aim to enable the reuse of batteries - to provide batteries with a second life as it were.

Embodiments of the disclosure may do this by providing a metric of battery performance that can be obtained by monitoring those batteries in use - e.g. during charging or discharging. Significantly, such monitoring may be performed by a battery management system, also known as a BMS .

Metrics of the performance of a battery cell module may be based on any indication of the condition of the cell module such as an indication of the internal resistance or capacity of the battery cell module. Such indications may be provided in a number of ways, for example one indication is the differential capacity, dQ/dV of the cell module. Another such indication is differential voltage, dV/dQ. The differential capacity may be defined as the rate of change of state of charge of a cell module with cell module voltage. The differential voltage, dV/dQ, may be defined as the rate of change of voltage with state of charge.

Data to characterise a battery cell module may be derived from the variation of such indications (e.g. differential capacity, differential voltage, internal resistance) as a function of temperature, and/or as a function of stored energy in the cell module (e.g. as a function of parameters such as open circuit cell module voltage and its state of charge) .

In an aspect there is provided an apparatus comprising: a signal interface for obtaining (i) an energy signal indicative of energy stored in at least one cell module of a battery; and (ii) an indication of the internal resistance or capacity of the at least one cell module associated with the energy stored in the at least one cell module. This may provide data characterising the cell module, for example in the form of a relation between energy stored in the at least one cell module and the indication of its internal resistance.

The signal interface may also be configured to obtain a temperature signal indicative of temperature of at least one cell module of the battery. The data characterising the cell module may thus comprise data indicating a temperature range associated with the energy level-internal resistance or capacity relation. The data characterising the cell module may comprise a set of such relations each associated with a different temperature range .

In an aspect there is provided an apparatus comprising: a signal interface for obtaining (i) a temperature signal indicative of temperature of at least one cell module of a battery; and (ii) an indication of the internal resistance or capacity of the at least one cell module associated with the energy stored in the at least one cell module. This may provide data characterising the cell module, for example in the form of a relation between temperature of the at least one cell module and the indication of its internal resistance. The signal interface may also be configured to obtain an energy signal indicative of energy stored in at least one cell module of a battery. The data characterising the cell module may thus comprise data indicating a range of energy levels associated with the temperature-internal resistance relation. The data characterising the cell module may comprise a set of such temperature-internal resistance or capacity relations each associated with a different energy level range. The energy signal may comprise a cell module voltage signal, such as the cell module's open circuit voltage and/or a cell module state of charge signal.

In an aspect there is provided an apparatus comprising: a signal interface for obtaining (i) a temperature signal indicative of temperature of at least one cell module of a battery (ii) an energy signal indicative of energy stored in the at least one cell module; and (iii) an indication of the internal resistance or capacity of the at least one cell module.

This can provide a set of tuples, each tuple comprising temperature data, corresponding energy level data, and indication of the internal resistance obtained at the temperature and energy level indicated in that tuple.

The apparatus may also comprise a characteristic determiner configured to determine a relation between temperature, stored energy, and the indication of the internal resistance or capacity to characterise the at least one cell module. The cell module may thus be characterised by data based on this relation between temperature, stored energy, and the indication of internal resistance .

The apparatus may also comprise a data store for storing data characterising the at least one cell module. This relation may define the expected value of the indication of internal resistance or capacity for a range of temperatures and/or a range of energy levels (e.g. a range of cell voltages, or a range of states of charge) . The range of temperatures may span the safe working temperatures of the cell module.

To determine this relation, the characteristic determiner may be configured to fit a model to the data obtained from the at least one cell module for each of the corresponding temperatures and energy levels. The model may comprise an analytic or numerical model of an expected variation of the indication as a function of temperature and energy stored by the battery.

The characteristic determiner may be configured to update the relation in the event that a selected number of samples (e.g. TZV tuples) deviate from this fitted model by more than a threshold deviation. This threshold deviation may be based on the spread of the data values about the model, and may be based on the error in the fit, for example it may be based on a confidence interval or other measure of the expected variance. The characteristic determiner may comprise a recursive estimator configured to update the fit of the model in response to data values obtained from the battery. One example of a recursive estimator is the so- called Kalman filter. Other recursive estimators may also be used.

Apparatus which implements the present disclosure may be provided by battery management systems such as those which may be integrated into batteries and configured to equalise (balance) the energy in the cells of the battery - e.g. to achieve the same cell voltage or state of charge across the cells. Such battery management systems typically comprise a so-called analogue front end or other analogue to digital converter which may be used to sense the voltage across each of the battery cells. The data describing the relation (the variation of internal resistance or capacity as a function of temperature and energy level) may be used to determine whether to gang a set of batteries together. For example, a group of batteries to be used together may be selected based on the relation data of each of those batteries. For example, all the batteries of the group may be chosen so that their TZV characteristics match to within a selected tolerance.

The relation data need not be stored by the battery itself. For example, each battery (or each cell or cell module) may carry an identifier such as a serial number, barcode, QR code or RFID tag. Relation data for each of a set of batteries may be stored on a communications device such as a server configured to provide the relation data of a particular battery in response to a request comprising the identifier of that battery.

An aspect of the disclosure provides a battery powered device comprising a signal interface for obtaining:

a temperature signal indicative of temperature of at least one cell module of a battery arranged to power the device;

an energy signal indicative of energy stored in the at least one cell module; and

an impedance signal indicative of an internal resistance or capacity of the at least one cell module; and,

a characteristic determiner configured to determine a relation between temperature, the indication of internal resistance or capacity, and stored energy to characterise the at least one cell module. Obtaining the temperature signal is optional - the relation may assume a constant temperature (or range of temperatures) .

The battery powered device may also comprise a data obtainer for obtaining an identifier of a battery arranged to power the device, and a controller configured to provide output data indicating an association between the identifier and the relation. The battery powered device may be configured to store the relation in a data store carried by the battery associated with said identifier. It may also be configured to provide the output data for transmission to a second device - for example over a network, such as a wide area network (e.g. such as a telecommunications network or other type of computer network) .

Accordingly, an aspect of the disclosure also provides a battery comprising a data store for storing relation data indicating a relation between temperature, internal resistance or capacity, and energy stored in the battery. Such a battery may also comprise a signal interface for providing monitoring signals to an external controller, and a data interface for receiving relation data from the external controller. The signal interface may comprise one monitoring channel for each cell module of the battery. Each such monitoring channel may be associated with identifier data, identifying the corresponding cell module. The data store may be configured to store relation data for each cell module and may also store the corresponding identifier data.

A controller may be configured to update the relation based on monitoring of operation of the battery. This monitoring may be performed by an external device, such as a battery powered device or energy storage device in which the battery is to be used. For example, a controller carried by such a device may be configured to monitor the internal resistance or capacity of at least one battery cell module, the temperature of the at least one cell module, and the energy stored in the cell module.

Whether it is carried by a device in which the battery is used, or by the battery itself, the controller may be configured to update the relation by fitting a model of internal resistance or capacity to a plurality of tuples each comprising temperature, energy level, and a corresponding internal resistance or capacity. Such a controller can then write the updated relation data to a data store carried by the battery and/or by an external device .

It will be appreciated in the context of the present disclosure that the methods and apparatus described herein may relate to batteries in which a cell module comprises a single cell, or in which each cell module comprises a number of individual cells electrically connected together in series and/or parallel. For example, some of the cell modules described herein comprise four cells arranged in two parallel strings each of two cells in series. These cells may be encapsulated together in the same casing to make up a module. The casing may be liquid tight and may be gas tight. A temperature sensor may be carried by the module to sense its temperature.

Brief Description of Drawings

Embodiments of the disclosure will now be described in detail with reference to the accompanying drawings, in which:

Figure 1 is a diagram of a battery comprising an apparatus for characterising the battery;

Figure 2 is a diagram of a battery management system configured to provide an apparatus such as that illustrated in Figure 1;

Figure 3 is a diagram of an apparatus comprising a battery; and

Figure 4 is a diagram of an battery connected to a charger. In the drawings like reference numerals are used to indicate like elements .

Specific Description

Figure 1 shows a battery 1 comprising an apparatus 2 for characterising the battery 1. This apparatus 2 obtains energy level, and internal resistance or capacity data describing operation of each cell module of the battery. It then determines, based on this data, a relation energy level on the one hand, and the internal resistance or capacity data on the other. It may also take account of temperature as described below. The relation may be determined by fitting a model of the internal resistance or capacity data to the values obtained by monitoring its variation with energy level (and optionally also temperature).

As explained below, the data describing this relation can be used to determine whether or not to use cell modules together - e.g. if they are to be re-used when the battery is replaced.

In addition to the apparatus 2, the battery 1 shown in Figure 1 may also comprise a plurality of cell modules 5, 7, 9, 11, 13, 15, connected together in series between two terminals 19, 21. The apparatus 2 for characterising the battery 1 comprises a signal interface 23, a characteristic determiner 25, and a data store 27. It may also comprise a data interface 29 for the input and/or output of data to an external resource.

The signal interface 23 is connected to each cell module 5-15 of the battery, and to the characteristic determiner 25. The characteristic determiner 25 is connected to the data store 27, and to the data interface 29. The signal interface 23 may comprise a set of input channels. Each of these channels can be configured to obtain an analogue signal from a corresponding one of the cell modules, and to provide digital data indicating the analogue signal level to the characteristic determiner. The analogue signal provided to each channel may comprise one of: a temperature signal from a temperature sensor carried by a cell module; a cell voltage signal (or other energy level) indicating energy stored in a cell module, and a signal indicating the current flowing through a cell module.

The signal interface may comprise an ADC. The signal interface can therefore be configured to obtain a set of cell voltage signals, each signal indicating the cell voltage of a corresponding cell module of the battery. It can also be configured to obtain a temperature signal, indicating a temperature of the battery, and a signal indicating the current flowing through each cell module. Where the cells in a cell module are arranged in series, the current flowing through those cells may be identical - e.g. it may be provided by a single signal .

It will also be appreciated that one or more of these signals may be provided to the characteristic determiner in digital form (e.g. via the data interface) . For example, a cell module energy level signal may be provided as digital data indicating state of charge of the cell module.

There are different ways in which an indication of the internal resistance or capacity of a cell module can be obtained. For example, for an individual cell, the cell voltage may be defined as :

VCELL⁼VQC+ IRlNT Where: V_CELL is the total voltage across the cell, I is the current flowing through the cell module, and R_INT is the internal resistance of the cell module. The open circuit voltage of the cell module may be obtained by measuring the voltage when the current through the cell module is zero and then, before the state of charge of the cell module has changed, measuring the cell module voltage as a function of current (e.g. across a range of currents) . The internal resistance of the cell module can thus be determined.

As another possibility, the differential voltage dV/dQ of the cell module can be determined. In the event that a current I is drawn from (or provided to) the battery for a time dT, the change in charge associated with that current can be defined as IdT. The change in cell module voltage (e.g. open circuit cell module voltage), dV, associated with that delivered charge, IdT can thus be determined.

Other methods of obtaining an indication of internal resistance may also be used. For example, a "point cloud" can be obtained by continuous monitoring of each cell module. This point cloud may comprise a plurality of measurements of cell module voltage, cell module current, cell module temperature, and the time at which the respective data values were obtained. These can be used to infer open circuit cell module voltages and an indication of internal resistance or capacity as a function of temperatures (examples of such indications include differential voltage dV/dQ and differential capacity dV/dQ) .

The characteristic determiner 25 stores data defining a model of the indication of internal resistance or capacity of the cell modules 5-15 as a function of temperature and energy level of those cell modules 5-15. The characteristic determiner 25 is configured to obtain, from the signal interface 23, a plurality of sets of data samples. Each set of samples comprises an indication of internal resistance, and values of temperature, and energy level which correspond to that indication of internal resistance. These sets of data samples may each be provided as a tuple to be stored in the data store 27, and/or they may be provided to an external device via the data interface 29.

The characteristic determiner 25 is configured to fit the model of internal resistance to these samples. This may be done by selecting parameters of the model to reduce a merit function, such as a sum of squares of error merit function. This selection may be performed by any appropriate fitting procedure. The characteristic determiner 25 is also configured to provide data based on this fitting procedure to the data store 27. This data defines a relation between temperature, energy level and impedance (e.g. by reference to the model) for each of the cell modules . Fitting the model provides an estimate of the relation between temperature voltage and impedance - TZV. It may also provide an indication of an expected spread of data values (TZV) about the fitted model. For example this may be in the form of an estimate of the error in the fit, or a confidence interval, or some other measure of the variance of the data. If such an estimate is provided, the characteristic determiner 25 may be configured to compare collected data values with this estimate to identify outliers, and to repeat the fitting procedure in the event that more than a selected number of data values lie outside a selected range of the fitted model.

In operation, as the battery 1 delivers current to a load to be powered, or receives charging current from a charging device, the characteristic determiner 25 obtains data indicating the temperature, energy level, and internal resistance of the cell modules. Samples are typically collected at a range of energy level values, e.g. to span a complete charge-discharge cycle with at least a minimum number of sample points over the cycle. The characteristic determiner may be configured to collect a sample in response to the energy level crossing a particular threshold, or falling within a selected range. Once a sufficient number of samples have been collected for a particular cell module 5-15, the characteristic determiner 25 fits the model to the samples to estimate the parameters of the model for that particular cell module. The characteristic determiner 25 then stores the parameter values obtained by this fitting into the data store 27 with data identifying the relevant cell module.

Once the model has been fitted to the data, the characteristic determiner 25 may continue to collect samples via the signal interface 23, and may repeat the fitting procedure at selected intervals. For example, the fitting procedure may be repeated in response to a selected condition - such as the energy level or temperature being within a selected range, or the TZV data differing from the fitted model by more than some selected tolerance, as explained above.

This can enable the relation data which characterises the battery to be kept up-to-date. When the battery 1 is removed from the device in which it is being used (such as an electric vehicle or stationary energy storage unit), there may be a desire to reuse the battery 1, cell modules, or individual cells. In this eventuality, the relation data may be read from the data store 27 and used to determine whether reuse of the battery is appropriate. For example, given a large number of such batteries, the relation data can be read from each, and the batteries, cell modules, or cells, can be grouped to be used together, or to be used for particular applications, based on their relation data.

The temperature signal described with reference to Figure 1 may be provided by a single temperature sensor - for example it may be used as an indication of the temperature of the battery as a whole. It will be appreciated in the context of the present disclosure that the temperature of each cell of the battery may be inferred from this, or from one or more temperature sensors carried by the battery at selected locations. For example, one or more cells may carry temperature sensors arranged to provide temperature signals to the interface.

The battery 1 illustrated in Figure 1 may comprise a battery management system configured to balance the cells 5-15 of the battery (e.g. to ensure that the cells are charged to the same degree) . Such a battery management system may provide the signal interface 23, and may comprise a controller coupled to control a set of voltage controlled impedances, VCIs (such as FETs) . Each of these VCIs may be connected in parallel with a corresponding one of the cells 5-15. Accordingly, by switching on the VCI, the BMS can dissipate charge from the corresponding cell to balance the cells (e.g. equalise the voltages on the cells). Other types of battery management system, BMS, may be used. Such a BMS may comprise data processing logic, and some memory. These aspects of the BMS can be configured to provide a characteristic determiner and data store as described with reference to Figure 1.

Whatever type of BMS is used, it may comprise a communications interface, adapted to communicate with other similar communications interfaces. For example, this may use a communications bus, connected between the devices which need to communicate on that bus. A variety of different protocols may be used. One example of such a protocol is the CANBUS, or controller area network bus, protocol. A number of variants of this protocol exist - and any of these variants may be used. It will also be appreciated in the context of the present disclosure that, even where a BMS is not present, a battery such as that described with reference to Figure 1 may include such a communications interface, which can provide the data interface described above.

The BMS may comprise a so-called "analogue front end". This may comprise one or more voltage inputs, and one or more voltage outputs. In some examples, the analogue front end of the BMS may provide the signal interface 23 of the apparatus described herein .

Figure 2 shows one example of a battery comprising a battery management system configured to provide an apparatus such as that described with reference to Figure 1.

Figure 2 shows a battery 1 comprising a plurality of cell modules 5', 7', 9', 15' connected together in series between a positive terminal 19, and a negative terminal 21. The battery 1 also comprises a battery management system 2 also referred to as a BMS. The BMS 2 comprises a battery fuel gauge 46, a controller 48, a CANBUS interface 50, a temperature sensing analogue to digital converter (ADC) 52, and an analogue front end 44. The analogue front end 44 is connected to the controller 48.

The controller 48 is also connected to the CANBUS interface 50, and to the temperature sensing ADC 52. The temperature ADC 52 is connected to the temperature sensors 31-37 of each of the cell modules 5' -15'. The battery 2 also comprises a set of FETs 60, 62, 64, 66 and discharge resistances. One FET 60-66 and one discharge resistance is connected in parallel with each cell module 5 ' -15 ' .

The analogue front end 44 provides an analogue to digital and digital to analogue converter (ADC/DAC) for the battery management system 2. Accordingly it comprises a plurality of voltage sensing terminals for obtaining analogue voltage signals from each of the cell modules 5' -15' (each indicating the voltage across a corresponding one of the cell modules) .

The analogue front end 44 may comprise a set of voltage outputs, each operable to provide a controllable voltage signal. The voltage sensing terminals of the analogue front end 44 are connected for sensing the voltage across each of the cell modules 5' -15' of the battery. Its voltage outputs are connected to the gate terminals of each of the FETs. The analogue front end 44 is also configured to provide cell voltage data, based on the voltage signals from each of the cell modules 5' -15' to the controller 48. The analogue front end may also be configured to obtain internal resistance signals indicating the internal resistance of each of the cell modules 5' -15' and to provide these to the controller.

The battery fuel gauge 46 is connected to a current sensor to sense current flowing between the cells and the terminals, and is connected to the controller 48. The battery fuel gauge 46 is configured to determine a state of charge of the battery 2 based on measuring the flow of current into and out from the battery 2.

The CANBUS interface 50 is adapted to communicate, via a controller area network, with other CANBUS enabled devices coupled to such a network.

The controller 48 is configured to obtain cell module voltage data from the analogue front end 44, and to obtain cell module temperature data from the temperature ADC 52. The controller 48 is also configured to control the FETs 60-66 via the analogue front end 44 based on the cell module voltage data to balance the cell modules 5'-15' - e.g. so that the voltage across each of the cell modules is equal across the cells. The controller 48 is also configured with a model of the internal resistance of the cell modules 5' -15' as a function of temperature and energy level of those cell modules 5'-15'. The model can be carried by the selection of parameters to enable the model to be fitted to observed data. The controller 48 is configured to obtain, using the analogue front end 44 a plurality of sets of data samples. Each set of samples comprises an energy level signal for each cell module 5'-15'. This energy level signal may comprise the voltage across each of the cell modules. As will be appreciated in the context of the present disclosure, because the modules may be balanced, this energy level signal may comprise a single voltage. It may also be based on an indication of state of charge obtained from the battery fuel gauge 46. For example the state of charge may be used alone, or the voltage of the cell module and the state of charge of the battery may be used in combination to provide an indication of energy level.

Whatever the nature of the measurements used to provide the data, the controller 48 is configured to obtain sets of data samples which provide: (i) a value of internal resistance, and the values of (ii) temperature, and (ill) energy level which correspond to that internal resistance value. These sets of data samples may each be stored in a data store carried by the battery and/or they may be provided to an external device via the CANBUS interface 50.

The controller 48 is configured to fit the model to these samples. This may be done by selecting the parameters of the model to reduce a merit function, such as a sum of squares of error between the data and the model. This selection may be performed by any appropriate fitting procedure. The controller 48 can thus provide data defining the relation between internal resistance, energy level and temperature that it has determined from this fitting procedure to the data store 27. This relation data may comprise the parameter values which define the best fit of the model to the data. It may also comprise a parameter indicating an expected spread of data about the fit, for example an indication of the variance of the data about the fit, such as a confidence interval. The controller 48 may be configured so that, in the event that more than a selected number of data values differ from the fitted model by more than the expected spread, the fitting procedure is to be repeated.

Figure 3 shows a device comprising a battery 101, a controller 200, and an electrical load 202 connected to be powered by the battery 101.

The battery 101 comprises at least one cell module 104, a signal interface 112, and a data store 116. It also carries an identifier 118 which may comprise a machine readable marker. The signal interface 112 is connected to the cell module 104 the voltage across the cell module 104, and current through the cell module 104. The signal interface 112 may also be arranged for sensing the temperature of the cell module 104.

The controller 200 is connected to the signal interface 112, and to the data store 116, and is arranged for obtaining identifying data from the identifier 118.

The signal interface 112 is configured to sense a voltage level signal indicating the voltage across the cell module, and the current through the cell module. The signal interface is also configured to provide these signals to an output, which in the example illustrated in Figure 3, is connected to the controller 200 carried by the device. This may enable the controller to determine (i) the open circuit voltage of the cell module, or some other indication of energy level in the cell module and (ii) an impedance signal indicating the internal resistance of the cell module.

The controller carried by the device is configured to determine a relation between energy level, and internal resistance based on the signals provided by the battery to the controller. For example, this may provide the functionality of a characteristic determiner such as those explained elsewhere herein. It may also use sensed temperature signals and fit a model which takes account of temperature variations.

A separate relation may be determined for each cell module carried by the battery. This relation may comprise the TZV characteristic of the cell module. The controller is also configured to write data indicating this relation to the data store carried by the battery. It may also be configured to send that relation data, and the identifying data, to a second device. The data may be sent over a network, such as a wide area network (e.g. such as a telecommunications network or other type of computer network) .

In operation, when the battery is installed into the device, the controller reads the identifier and stores the identifier data. As the battery is used to provide electrical power to/from the load, the controller monitors the temperature of the cell module (s), and the voltage across those modules, and the current through them. This monitored data may be used to determine an indication of their internal resistance. The controller may thus store a series of samples of temperature, voltage, current and internal resistance. A time stamp may be associated with each of these samples to enable temporal characteristics of the data to be determined. As explained elsewhere herein, temperature monitoring is optional. The controller may thus provide an association between the identifier and the relation data for the cell modules of the battery. The relation data may be written, by the controller, into a data store carried by the battery. It will also be appreciated in the context of the present disclosure that the device illustrated in Figure 3, and other devices which use battery energy storage, may be configured to communicate over a network such as a wide area communication network like the internet. Accordingly, the relation data may be provided for transmission to a second device over the wide area communications network. For example it may be provided for transmission to a remote server.

In the event that a replacement battery or additional battery is to be installed into a device, the device may obtain identifier data from the battery (e.g. by reading a machine readable marker carried by the battery) and communicate it to the remote server to obtain relation data for that battery from the server. The device can then determine whether and/or how to operate that new battery.

For example, an aspect of the disclosure provides an apparatus comprising: a controller configured to obtain, for a first battery, first relation data indicating a relation between energy stored in one or more cell modules of the battery and an indication of the internal resistance of those cell modules. This may be obtained by monitoring operation of the battery (perhaps during charging) as explained elsewhere herein. This may also be obtained reading a machine readable marker carried by the battery to identify the cell modules and requesting the relation data from a remote server. However the relation data is obtained, the apparatus may also obtain second relation data indicating the same relation for a second battery. The apparatus may thus provide an output signal indicating compatibility of the first battery and the second battery. This can enable a testing apparatus to identify cell modules which can be used together (e.g. by being connected together into a series/parallel array) .

It may also provide a control signal for enabling or inhibiting operation of at least one of:

(i) the apparatus;

(ii) the first battery; and

(iii) the second battery,

based on a comparison of the first relation data and the second relation data.

Where the apparatus comprises a device powered at least in part by the first battery and the second battery, it can help to ensure that only compatible batteries are used together in such a device .

Figure 4 shows a battery 100 connected to a charger 102 which is in turn connected to a source of AC power 106.

The battery charger 102 comprises an AC to DC converter 108, and a charging controller 110. The AC/DC converter 108 is connected to the charging controller 110 and to the source of AC power. The AC/DC converter 108 is configured to convert AC electrical energy into a DC charging current for charging a battery 100. For this purpose, the AC/DC converter 108 may comprise a passive rectifier circuit (e.g. an arrangement of diodes) to rectify the AC power supply. Other types of AC/DC converter 108 and other types of rectifier can be used. The controller is configured to control the operation of the AC/DC converter 108 so as to select the current and/or voltage of its DC output. The controller is also configured to receive control signs, such as requests for charging current, from a battery 100 to be charged. The charging controller 110 may control the DC output of the AC/DC converter 108 based on these control signals.

The battery 100 shown in Figure 4 comprises at least one cell module 104, a signal interface 112, a battery controller 114, and a data store 116. It may also carry an identifier 118, which may be provided by a machine readable marker such as an alphanumeric code, a barcode, a QR code, an RFID tag, or a readable memory chip .

The signal interface 112 is connected to the cell module 104 for sensing the voltage across the cell module 104, and for sensing the current flowing through the cell module 104. The battery 100 may also comprise a temperature sensor arranged to sense a temperature of the cell module 104. The signal interface 112 may also be connected to such a temperature sensor for obtaining cell module temperature data. The signal interface 112 is also operable to provide data based on these signals to the battery controller 114. For example, the signal interface 112 may comprise an ADC.

The battery controller 114 is coupled to the signal interface 112 for obtaining such cell module voltage data and cell module current data. The controller is also coupled to the data store 116 for recording the sensed data values, and for retrieving previously recorded data in order to characterise the cell module 104. The battery controller 114 is also operable to provide control signals for controlling a battery charger 102. It is configured to determine a charging current requirement of the battery 100 based on the cell module voltage data, and to provide control signals to the charger 102 to obtain the required charging current. It will be appreciated in the context of the present disclosure that the functionality of the battery controller 114 and the signal interface 112 of the battery 100 illustrated in Figure 4 may be provided by a battery management system such as that described above with reference to Figure 2. The battery controller 114 may be configured to charge the cell module 104 in two modes. In the first mode, the battery controller 114 provides control signals to the battery charger 102 to obtain a constant charging current from the charger 102 to the battery 100. The battery controller 114 may sense the cell module voltage during this constant current phase of charging and, when the cell module voltage reaches a threshold level, the battery controller 114 may switch into a second mode in which it provides control signals to the charger 102 to obtain charging current in a constant voltage mode. The battery controller 114 may be configured to obtain cell module current data, cell module voltage data during charging and to store this data in the data store 116 to be used in characterising the cell module 104.

The cell module voltage data and cell module current data may provide an indication of internal resistance or capacity of the cell module (e.g. based on temporal characteristics of that data) . For example, the differential voltage dV/dQ of the cell module 104 can be determined. In the event that a current I is drawn from (or provided to) the battery 100 for a time dT, the change in charge associated with that current can be defined as IdT. The change in cell module voltage (e.g. open circuit cell module voltage), dV, associated with that delivered/drawn charge, IdT can thus be determined. If temperature sensing capability is included, corresponding cell module temperature data may also be obtained and stored.

It will be appreciated in the context of the present disclosure that by monitoring the behaviour of the cell module during charge and discharge, an indication of the internal resistance as a function of energy stored in the cell (and possibly also as a function of temperature) can be provided. Over time, this can provide a "point cloud". This point cloud may comprise a plurality of measurements of cell module voltage, cell module current, cell module temperature, and the time at which the respective data values were obtained. These can be used to infer open circuit cell module voltages and an indication of internal resistance or capacity (e.g. dV/dQ) as a function of temperatures .

It will also be appreciated in the context of the present disclosure that the spread and sampling distribution of such a point cloud may be uneven. For example, lots of data may be available in one range of stored energy or one range of temperatures, but the data may be sparser in other areas. To address this issue, the battery controller 114 may be configured to control charging (and perhaps also discharging) of the battery based on sampling density of data stored in the data store 116. This may enable the battery controller 114 to provide additional data to characterise the cell module in these ranges. For example, the battery controller 114 may be configured to deviate from the simple two-mode charging (constant current mode followed by constant voltage mode) by providing selected variations of the charging current and/or voltage in order to better characterise the cell module. For example, the battery controller 114 may modulate the charging current during the constant current phase. This may be triggered in the event that the battery controller 114 identifies that the energy level of the cell module, or its temperature, corresponds to a range of values in which the sampling density is less than a threshold level.

In operation therefore, when the battery is connected to a charger 102 for charging, the battery controller 114 may provide a charging current request to the charging controller 110. The charging controller 110 then operates the AC/DC converter 108 to provide the requested charging current to the battery. For example, the battery controller 114 may initially request operation in the constant current phase of charging. Whilst operating in this way, the battery controller 114 may provide a charging current request that causes the charging current supplied to the cell module to reduce, perhaps to zero. This may be done in response to a signal obtained from the signal interface 112 (such as a cell module voltage signal, or a temperature signal) indicating that the state of the cell module corresponds to a sampling density of stored data that is less than a threshold.

This reduction in charging current may persist for a first interval. At the start of this interval, the cell module voltage will begin to drop. If the charging current is reduced to zero then, after a relaxation time, the cell module voltage will reflect the open circuit voltage, V_oc, of the cell module. The relaxation time of the cell, from the voltage during charging down towards the open circuit voltage of the cell may be indicative of the internal resistance of the cell - e.g. it may comprise an exponential decay which may be characterised by a time constant (exponent) indicating the internal resistance of the cell module. In some embodiments, the battery controller 114 may be configured to determine an indication of the internal resistance based on this time constant. It will be appreciated in the context of the present disclosure that changing the charging current for the first interval typically comprises changing it with respect to a preceding state. It may for example be held constant during this first interval, e.g. it may be set to zero or some other reference level. It may then be changed back to its preceding state at the end of the first interval.

The battery controller 114 may be configured to determine whether to reduce the charging current as described above based on a sampling density of data characterising the cell module. For example, if the data obtained from the signal interface 112 indicates that sampling density is low in particular range of values of energy level or internal resistance or temperature the battery controller 114 can modulate the charging current as described. This may comprise a first interval during which the charging current is reduced from the constant current level, and a second interval during which it is increased again.

For example it may be increased back to current used prior to the first interval (e.g. to continue the constant current charging). During this second interval, the battery controller 114 obtains further cell module voltage data and further cell module current data. The indication of the internal resistance described above may be based on both the data collected during the first interval and the further r data collected during this second interval.

This can enable an indication of internal resistance to be obtained as described above. It will also be appreciated in the context of the present disclosure that other approaches may be used. For example, the current may be increased for the first interval, or varied in some other way, and the response characteristics of the cell module can be used to determine an indication of its internal resistance. Irrespective of the approach which is to be used to obtain an indication of internal resistance the battery controller 114 obtains cell module voltage data and cell module current data, which it may store into the data store 116. This data can also provide an indication of the energy stored in the cell module (e.g. the open circuit voltage of the cell module) , of the energy data may be obtained from an external source such as a battery fuel gauge.

This data can be used to characterise the cell module - e.g. by determining a relation by fitting a model to the data as described elsewhere herein. For example, the battery controller 114 of the apparatus illustrated in Figure 3 may be configured to provide a characteristic determiner as described elsewhere herein .

Once the cell module has been characterised, the characteristic can be used to determine how to treat that cell module - for example to determine which other cell modules it should be used with, or to determine a measure of its performance, or the likely length of its future useful life.

To obtain such a relation, the apparatus described herein can operate in three possible ways. In the first case, the apparatus may be deployed in an environment in which the cell module temperature may not vary considerably. For example it may be deployed in a temperature controlled apparatus having a thermostat controlled heating/cooling system. In such circumstances, the temperature at which the cell module is operating can be assumed to be constant, or at least known a priori. A relation between the indication of internal resistance and the level of energy stored in the battery can thus be determined by fitting a model (such as a linear model) to the energy level data and the data providing an indication of internal resistance.

In the second case, the temperature of the cell modules may be monitored (e.g. using a temperature sensor) so that a temperature value can be assigned to the energy level data and the data providing an indication of internal resistance. Items of this data can be selected based on the temperature values to provide a subset of the monitored data which corresponds to a particular range of temperatures. This may be used to determine the likely behaviour of the cell module in a particular temperature range of operation . In the third case temperature may be monitored as in the second case, so that a relation can be determined between temperature and energy level on the one hand and, on the other hand, the indication of internal resistance. This may be determined by fitting a two dimensional model (such as a surface) to the data.

In any one of these three cases, a performance characteristic of the cell module may be determined from the monitored data. The performance characteristic may comprise measures such as one or more of the following:

• one or more parameters of the model fitted to the data, such parameters may include the parameters of the fit and/or an estimate of error or confidence interval associated with those parameters;

• the value of the model in a particular range (such as a particular temperature range) ;

• the spread of the indication of internal resistance values in a particular range of energy levels and/or across a particular range of operating temperatures;

• the rate of change with temperature of any one of the foregoing characteristics; and

• the temporal rate of change of any one or more of the foregoing characteristics.

The battery controller 114 may be configured to provide an output signal indicating any one or more of the foregoing. It may also be configured to compare these characteristics with data indicating a range or threshold of such characteristics, and to trigger a warning signal, or to disable the battery and/or the cell module based on the comparison.

These and other aspects of the disclosure may be employed in the controller of a battery, which battery may also comprise a data store 116 for storing relation data indicating a relation between internal resistance, and energy stored in the battery. The relation data may also comprise temperature. The controller may be configured to update the relation based on monitoring of operation of the battery. This monitoring may also be performed by an external device, such as a battery powered device or energy storage device in which the battery is to be used. For example, a controller carried by such a device may be configured to monitor the internal resistance of at least one battery cell, the temperature of the at least one cell, and the energy stored in the cell.

The signal interface of the apparatus described in Figure 1 is described as sensing cell module voltages. However it will be appreciated that energy level may also be indicated by state of charge - for example its capacity to deliver current. Apparatus of the disclosure may be configured to perform coulomb counting or other methods of charge estimation, to provide an estimate of the state of charge of the battery as a whole, or individual cell modules. It will be appreciated in the context of the present disclosure that the energy level may be determined based on cell module voltage, or state of charge, or based on a combination of the two .

The methods and apparatus described herein are of particular utility in relation to Li-Ion cells. However these methods and apparatus may be applied to any appropriate rechargeable electrical energy storage cell for electrical energy storage. It will be appreciated in the context of the present disclosure that each cell may itself comprise a number of smaller cells (e.g. the methods and apparatus may be applied to individual cells, or to modules comprising a plurality of cells) . But, other than in so far as explained above, the internal physical structure of the cells is not generally material to the present disclosure. It will be appreciated in the context of the present disclosure that an indication of the condition of a cell module or battery may be based on either or both of the following:

1. The rate of change of voltage versus stored energy (dV/dQ), and

2. The internal resistance of the cell as a function of its

open circuit voltage (OCV) , and optionally also its

temperature .

In some embodiments, the shape of the dV/dQ curve as a function of voltage (and optionally also as a function of temperature) may be used to provide an indication of the capacity of the cell. Changes in the shape of this curve (or surface) over time may be used to indicate the changing condition (e.g. "health" of a cell module) .

The differential voltage (dV/dQ) and internal resistance may be calculated in similar ways but over differing timeframes. For example, to calculate differential voltage at a particular point, the measurement may take place over a period long enough to register a reliable change in the voltage measurement. For example, it may take a few minutes of charge for the measured cell voltage to change (e.g. from 3.700V to 3.705V) . It will be appreciated however that this time period may depend on the charge current. On the other hand, the calculation of internal resistance may be made in response to sharp changes in current. Such changes in current may be sufficiently fast that the open circuit voltage of the cell can be deemed to remain constant.

The model used to fit the data in the embodiments described herein may comprise analytic or numerical functions which define how the internal resistance of the cell modules varies as a function of temperature and energy level. Those functions may comprise parameters which can be changed to vary their contribution to the model as a whole (e.g. by shifting, translating, scaling or otherwise varying those functions). The process of fitting may comprise selecting these parameters to achieve a best fit between the data and the model. The best fit may be determined in any appropriate fashion - for example it may be determined by the reduction of a merit function based on the sums of squares of differences between the TZV data, and the model (at a selected set of parameter values) .

If one is included, the data interface of the embodiment illustrated in Figure 1 may comprise an output interface for providing an external device with at least one of: the samples (e.g. TZV tuples), and the parameters of a model, fitted to the samples. It will be appreciated in the context of the present disclosure that the CANBUS interface illustrated in Figure 2 need not be included. It may also be replaced by any appropriate communications interface. The FETs used for balancing the cell modules may be provided by any voltage controlled impedance (VCI) of an appropriate power rating for the cells. The voltage controlled impedances may comprise transistors such as insulated gate bipolar transistors, IGBTs, field effect transistors, FETs, such as junction field effect transistors, JFETS, insulated gate field effect transistors, IGFETS, metal oxide semiconductor field effect transistors, MOSFETs, and any other type of transistor. The VCIs may be operated as switches. Electromechanical switches such as relays may be used. It will also be appreciated that, although Figure 2 shows resistors as separate elements from these VCIs, the resistances used for discharging the cell modules for balancing may be provided by the VCIs themselves.

The fitting procedures described herein may comprise linear regression, or may be based on non-linear merit functions. In some embodiments log-linear fitting is used. The nature of the fitting procedure and/or the merit function employed in any particular instance is selected based on the data model which is to be fitted. Examples of suitable fitting procedures may be found in Numerical Recipes in C; The Art of Scientific Computing; Third Edition Published 2007 by the Press Syndicate of the University of Cambridge, The Pitt Building, Trumpington Street, Cambridge CB2 1RP.

Any feature of any one of the examples disclosed herein may be combined with any selected features of any of the other examples described herein. For example, features of methods may be implemented in suitably configured hardware, and the configuration of the specific hardware described herein may be employed in methods implemented using other hardware.

It will be appreciated from the discussion above that the embodiments shown in the Figures are merely exemplary, and include features which may be generalised, removed or replaced as described herein and as set out in the claims. With reference to the drawings in general, it will be appreciated that schematic functional block diagrams are used to indicate functionality of systems and apparatus described herein. It will be appreciated however that the functionality need not be divided in this way, and should not be taken to imply any particular structure of hardware other than that described and claimed below. The function of one or more of the elements shown in the drawings may be further subdivided, and/or distributed throughout apparatus of the disclosure. In some embodiments the function of one or more elements shown in the drawings may be integrated into a single functional unit.

Aspects of the disclosure provide a battery monitoring apparatus comprising: a temperature sensing interface for obtaining a temperature signal indicative of temperature of at least one cell of a battery; an energy level sensing interface for obtaining an energy signal indicative of energy stored in the at least one cell; an impedance sensing interface for obtaining an impedance signal indicative of an internal resistance of the at least one cell; and, a characteristic determiner configured to determine a relation between temperature, impedance, and energy to characterise the at least one cell. Embodiments described herein provide further refinements of this functionality.

Such functionality, and the other functionality described and claimed herein, may be provided by a general purpose processor, which may be configured to perform a method according to any one of those described herein.

In some examples the controllers, processors, and characteristic determiners described herein may comprise digital logic, such as field programmable gate arrays, FPGA, application specific integrated circuits, ASIC, a digital signal processor, DSP, or by any other appropriate hardware. In some examples, one or more memory elements can store data and/or program instructions used to implement the operations described herein. Embodiments of the disclosure provide tangible, non-transitory storage media comprising program instructions operable to program a processor to perform any one or more of the methods described and/or claimed herein and/or to provide data processing apparatus as described and/or claimed herein. The controllers, processors, and characteristic determiners described herein may comprise an analogue control circuit which provides at least a part of this control functionality. An embodiment provides an analogue control circuit configured to perform any one or more of the methods described herein.

The above embodiments are to be understood as illustrative examples. Further embodiments are envisaged. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claims

1. An apparatus comprising:

a signal interface for obtaining:

a temperature signal indicative of temperature of at least one cell of a battery;

an energy signal indicative of energy stored in the at least one cell; and

a signal indicative of an internal resistance of the at least one cell; and,

a characteristic determiner configured to determine a relation between temperature, an indicator of the internal resistance, and stored energy to characterise the at least one cell ,

and a data store for storing data indicating the relation.

2. The apparatus of claim 1 wherein the relation relates the indicator of internal resistance to temperature and stored energy level over a range of temperatures and a range of stored energy levels .

3. The apparatus of claim 1 or 2 wherein the characteristic determiner is configured to fit a model of the indicator of internal resistance to the internal resistance signals for each of the corresponding temperature and energy signals, wherein the model comprises an expected form of variation of the indicator of internal resistance as a function of temperature and energy stored.

4. The apparatus of claim 3 wherein the characteristic determiner is configured to update the relation in the event that a selected number of energy-temperature-indicator of internal resistance tuples deviate from the relation by more than an expected range.

5. The apparatus of any preceding claim wherein the signal indicative of internal resistance comprises one of differential voltage, differential capacity, and internal resistance.

6. The apparatus of any preceding claim wherein the energy signal indicative of energy stored in the at least one cell comprises the cell voltage, for example the open circuit cell voltage .

7. A battery management system configured to balance the energy stored by a plurality of battery cells, the battery management system comprising the apparatus of any preceding claim.

8. The battery management system of claim 7, wherein the energy level comprises voltage level.

9. The battery management system of claim 8 wherein the sensing interface is coupled to sense the voltage across each of the battery cells.

10. The battery management system of claim 7, 8 or 9 wherein the battery management system is configured to control charging or discharging of the battery cells based on the temperature signals .

11. The apparatus of any preceding claim comprising a controller, configured to enable or inhibit ganging of batteries based on the data indicating the relation.

12. A battery comprising the apparatus of any preceding claim.

13. A battery powered device comprising the apparatus of any preceding claim, and a data obtainer for obtaining an identifier of a battery providing power to the device, and a controller configured to provide output data indicating an association between the identifier and the relation for said battery.

14. The battery powered device of claim 13 wherein the controller is configured to store the relation in a data store carried by the battery associated with said identifier.

15. The battery powered device of claim 13 or 14, wherein the controller is configured to provide the output data for transmission to a second device.

16. A battery comprising a data store for storing relation data indicating a relation between temperature, internal resistance, and energy stored in the battery, and a controller configured to update the relation based on monitoring of operation of the battery.

17. The battery of claim 16 wherein the controller is configured to monitor the internal resistance of at least one battery cell, the temperature of the at least one cell, and the energy stored in the cell.

18. The battery of claim 16 or 17 wherein the controller is configured to determine the update by fitting a model of internal resistance to a plurality of tuples each comprising temperature, energy level, and a corresponding internal resistance, wherein the tuples are obtained from monitoring operation of the battery.

19. The battery of claim 16 or 17 wherein the controller is operable to update the relation based on data provided by an external device.

20. An apparatus comprising the battery of claim 16, 17 or 19 and a characteristic determiner configured to determine the relation by fitting a model of internal resistance to a plurality of tuples each comprising temperature, energy level, and a corresponding internal resistance, wherein the tuples are obtained from monitoring operation of the battery.

21. An apparatus comprising:

a controller configured to:

obtain, for a first battery, first relation data indicating a relation between temperature, internal resistance, and energy stored,

obtain second relation data indicating the relation for a second battery; and to

provide a control signal for enabling or inhibiting operation of at least one of:

(iv) the apparatus;

(v) the first battery; and

(vi) the second battery,

based on a comparison of the first relation data and the second relation data.

22. The apparatus of claim 21, wherein the apparatus comprises a device powered at least in part by the first battery and the second battery.

23. An energy storage system comprising the apparatus of claim

21.

24. A method of operating a first battery, the method comprising :

obtaining a first relation between temperature, internal resistance, and energy stored by the first battery;

obtaining a second relation between temperature, internal resistance, and energy stored by a second battery; and determining whether to enable or inhibit operation of the first battery based on comparing the first relation and the second relation.

25. A battery comprising a controller configured to perform the method of claim 24.

26. A computer program product comprising program instructions configured to program a programmable battery controller to perform the method of claim 24.

27. A method of controlling battery charging, the method comprising:

changing the charging current supplied to a battery cell module for a first interval,

obtaining cell module voltage data and cell module current data during the first interval, and

obtaining an indication of the internal resistance of the cell module based on the cell module voltage data and the cell module current data.

28. The method of claim 27 comprising determining a relation between the indication of internal resistance, and stored energy in the cell module to characterise the cell module.

29. The method of claim 28 further comprising obtaining temperature data indicating the cell module temperature during the first interval.

30. The method of claim 29 comprising selecting, based on the cell module temperature data, values of the indication of internal resistance such that the selected values relate to a selected range of cell module temperatures.

31. The method of claim 29 wherein the relation between the indication of internal resistance and stored energy is also based on the cell module temperature data.

32. The method of any of claims 27 to 31 comprising increasing the current for a second interval subsequent to the first interval and obtaining further cell module voltage data and further cell module current data during the second interval, wherein the indication of the internal resistance is further based on the further cell module voltage data and the further cell module current data.

33. The method of claim 32 wherein the reduction in charging current is provided during a constant current charging mode, and in which increasing the current comprises returning to the constant current charging mode.

34. A controller for a battery configured to provide charging requests to a battery charger to control the charge current supplied to the battery during charging, wherein the controller is configured to control the charging current to obtain an indication of the cell module's internal resistance as a function of at least one of temperature and energy level to characterise the cell module.

35. The controller of claim 34, wherein the energy level comprises one of the state of charge and the open circuit voltage of the cell module.

36. The controller of claim 34 or 35, wherein controlling the charging current comprises changing the charging current for a first interval, and obtaining cell module voltage data and cell module current data during the first interval.

37. The controller of claim 34, 35 or 36 configured to determine whether to change the charging current based on a sampling density of data characterising the cell module.

38. The controller of any of claims 34 to 37 wherein the controller is configured to change the charging current during a constant current stage of battery charging.

39. The controller of claim 38, wherein controlling the charging current comprises reducing the charging current to a lower current during the first interval and increasing the charging current during a second interval subsequent to the first interval, and obtaining further cell module voltage data and further cell module current data during the second interval.

40. The controller of claim 39 wherein increasing the current comprises returning the charging current to the current level of the constant current charging stage.

41. The controller of any of claims 34 to 40, wherein controlling the charging current comprises modulating the charging current with a selected time varying signal.

42. The controller of claim 41 wherein obtaining an indication of the cell module's internal resistance as a function of temperature to characterise the cell module comprises determining the effect of the cell module's capacitive and resistive impedance on the time varying signal.

43. The controller of claim 41 or 42 wherein the time varying signal comprises at least one step, for example a Heaviside function, for example a boxcar function.

44. The controller of any of claims 34 to 43 wherein changing the charging current comprises reducing it to zero.

45. The controller of any of claims 34 to 44 wherein the controller is configured to fit a model of the indication of internal resistance as a function of the corresponding energy level, wherein the model comprises an expected variation of the indication as a function stored energy.

46. The controller of any of claims 34 to 45 wherein the indicator of internal resistance comprises one of: the differential voltage of the cell module, the differential capacity of the cell module, and the internal resistance of the cell module.