WO2005076025A1

WO2005076025A1 - Monitoring capacity of a rechargeable battery

Info

Publication number: WO2005076025A1
Application number: PCT/EP2005/050593
Authority: WO
Inventors: Stuart Vant
Original assignee: Sendo International Limited
Priority date: 2004-02-10
Filing date: 2005-02-10
Publication date: 2005-08-18
Also published as: GB0402878D0; GB2411055B; GB2411055A

Abstract

A method of determining a level of charge remaining on a re-chargeable battery that is operably coupled to a mobile phone. The method comprises the steps of measuring a level of battery charge of the re-chargeable battery, calculating a rate of change of the level of battery charge; and determining a level of charge remaining on a re-chargeable battery by subtracting or adding the calculated rate of change level from a previously determined level of charge remaining on the re-chargeable battery. A wireless communication unit and is also described. This provides a significant improvement in accuracy, as knowing accurate charge remaining in a battery allows a user to know how much talk time or gaming time remains available in the phone. Furthermore, it also provides an ability to compensate for temperature or load within the phone.

Description

MONITORING CAPACITY OF A RECHARGEABLE BATTERY

Field of the Invention

This invention relates to a method of monitoring a capacity of a battery. The invention is applicable to, but not limited to, measurement of a remaining usable charge capacity of a Li-Ion battery, for example of a mobile phone that is operating under highly varying load conditions .

Background of the Invention

The focus of many mobile phones in today' s high technology marketplace is to make them increasingly portable, lighter and more sophisticated, with longer battery life. In order to make these devices portable, it is necessary to design them to be battery-operated. There are currently two favoured approaches to the battery powering of portable devices :

(i) Enable the portable device to be powered by standard off-the-shelf batteries such as ^ΛΑA' or AAA' batteries; or (ii) Enable the portable device to be powered by re-chargeable batteries, that can be re-charged in situ, or that can be temporarily disconnected from the portable device and placed in a battery charger to effect a re- charge operation of the battery.

In the field of mobile phones, the latter option is invariably selected, due to the phone's need to be portable and the requirement to continuously use circuitry within the phone in order to receive or transmit audio calls, short message service (SMS) text messages, video messages, etc. at anytime. Furthermore, in the context of mobile phones, it is desirable to present to the user of the phone an indication as to the level of charge that remains in the phone, so that the user can determine whether or not to re-charge the phone . In this regard, the phone requires circuitry and associated software to determine a level of remaining, usable battery charge.

Referring first to FIG. 1, a known circuit 100 for determining a charge level of a battery is illustrated. Typically, it is assumed that a battery/cell 105 provides an ideal perfect voltage supply. The battery voltage can be measured by voltmeter 120, by monitoring the current 115 passing through a load 125. Unfortunately, in the context of mobile phones, a particular problem arises with highly varying loads, which cause rapid voltage changes on the battery output due to the inherent internal impedance (i.e. internal resistance 110) of the battery cell 105. This means that measuring the cell voltage alone, say to estimate a remaining usable capacity of the battery, is not accurate. In effect, this inaccuracy results from the fact that the deviations in voltage due to current change are larger than those deviations that would be caused by a relatively small change in remaining capacity.

However, a practical battery module/device has various internal resistances such as connections, tracks, lossy components, (primarily the battery cell's internal impedance) , etc. These internal resistances of the battery are greatly affected by many factors, such as temperature and varying load (due to circuits and devices in the portable device using the battery), etc. These may be modelled as serially coupled internal resistance (s) 110, which is known to cause the supplied voltage to vary, thereby exhibiting a ^xnoise' effect.

In existing mobile phones, such as those compliant with the Global System for Mobile (GSM) communications standard, the accuracy of the charge measurement process is generally deemed acceptable. This is primarily due to the fact that the load variation in such phones is relatively small. Thus, the noise level generated by the switching on/off of components and circuits is manageable. To compensate for such internally generated noise, an average value of the charge measured over a short time period is taken. The relationship of charge versus time, together with the effect of noise on any measurement is illustrated in the graph 200 of FIG. 2, which shows voltage 210 versus time 220. Here, the voltage 240 supplied by the battery is varying, i.e. it is noisy. Effectively, the voltage varies between a higher charge curve 235 and a lower charge curve 230.

If, as has been the predominant case with mobile phones employing Li-Ion batteries to date, this noise level is small, an indication of the battery charge can be averaged from the higher and lower curves 230, 235, as illustrated in the flowchart 300 of FIG. 3. Here, the process for determining a remaining battery charge of a cell starts in step 305, with the battery cell voltage being read in step 310. In some instances, it is possible to compensate for a known load condition associated with the phone, such as the radio transmit power load or backlight operation, in step 315. The compensated voltage value is then averaged, for example using a rolling average filter, as shown in step 320.

The approximate battery cell charge is then presented to the user of the phone, typically as a number of ^Λfilled- in' charge bars within the phone's display. In this manner, the user of the portable device is able to ascertain roughly whether the device's battery is fully charged or partially charged or in need of a re-charge operation.

However, the new generation of mobile phone's, often termed S artphones, employ many more power-hungry components and circuits . Due to the wide variety of features and complex circuitry involved in these mobile phones, the components and circuits are constantly being turned on/off to conserve battery power. In particular, more power hungry elements, such as microprocessors that run Operating Systems (OSs) , are being used. Thus, the inventor of the present invention has both recognised and appreciated that the ^λnoise' levels associated with measuring a battery voltage level have increased significantly, so much so that the averaging technique illustrated above is accurate to only 15-25% and is therefore now unacceptable .

A need therefore exists for apparatus and an improved process for determining a remaining usable charge of a battery, wherein the abovementioned disadvantages may be alleviated.

Statement of Invention In accordance with a first aspect of the present invention, there is provided a method of determining a level of charge remaining on a re-chargeable battery, as claimed in Claim 1.

In accordance with a second aspect of the present invention, there is provided a wireless communication unit, as claimed in Claim 9.

In accordance with a third aspect of the present invention, there is provided a wireless communication unit, as claimed in Claim 10.

Further features of the present invention are as claimed in the dependent claims .

In summary, the preferred embodiment of the present invention proposes, inter-alia, a method of determining a usable capacity of a re-chargeable battery, such as a Li- Ion battery. The method comprises measuring a level of battery charge of the re-chargeable battery and calculating a rate of change of the level of battery charge. A level of charge remaining on the re-chargeable battery is then determined by subtracting or adding the calculated rate of change level from a previously determined level of charge remaining on the re-chargeable battery.

Preferably, the steps of calculating a rate of change of the level of battery charge and determining a level of charge remaining on a re-chargeable battery are performed in mAh, by integrating the measured level of battery charge over time to identify a loss in a level of charge remaining on a re-chargeable battery. Notably, the step of measuring a level of battery charge is performed within the re-chargeable battery module, which has been adapted to comprise measurement circuitry. In addition, the re-chargeable battery module also comprises a memory element to store charge data specific to that particular re-chargeable battery module.

Brief Description of the Drawings

FIG. 1 illustrates a schematic block diagram representation of a known mechanism for measuring a mobile phone's battery cell voltage level;

FIG. 2 shows a graph illustrating a known general relationship of a mobile phone's battery voltage versus time; and

FIG. 3 illustrates a flowchart of a known mechanism for determining a mobile phone's battery charge.

Exemplary embodiments of the present invention will now be described, with reference to the accompanying drawings, in which:

FIG. 4 illustrates a block diagram of a wireless communication unit adapted in accordance with the preferred embodiment of the present invention;

FIG. 5 illustrates a signal flow diagram of a mapping algorithm between an ideal scenario and a real-world scenario relating to determining a battery charge level, according to the preferred embodiment of the present invention; FIG. 6 illustrates a circuit topology of a mechanism for measuring a voltage level, according to the preferred embodiment of the present invention;

FIG. 7 shows a graph illustrating threshold levels applied to a battery charge determination process, according to the preferred embodiment of the present invention;

FIG. 8 shows a flow chart illustrating a start-up method of monitoring a battery charge level, according to the preferred embodiment of the present invention; and

FIG. 9 shows a flow chart illustrating a method of compensating for inaccuracies in a process of determining a battery charge level, according to the preferred embodiment of the present invention.

Description of Preferred Embodiments

For the purposes of the foregoing description, the terms voltage and charge in relation to a battery are understood to be synonymous and interchangeable.

Referring first to FIG. 4, there is shown a block diagram of part of a communication unit 400, adapted to support the inventive concepts of the preferred embodiments of the present invention. The communication unit 400, in the context of the preferred embodiment of the invention, is a mobile phone. As such, the communication unit 400 contains an antenna 402 preferably coupled to a duplex filter or antenna switch 404 that provides isolation between receive and transmit chains within the wireless communication unit 400. The receiver chain, as known in the art, includes receiver front-end circuitry 406 (effectively providing reception, filtering and intermediate or baseband frequency conversion) . The front-end circuit is serially coupled to a signal processing and/or microprocessor controller function 408.^" The signal processing and/or microprocessor controller function 408 is often realised by a digital signal processor (DSP) and controls operations of, and communication between, elements within the communication unit 400. An output from the signal processing and/or microprocessor controller function 408 is provided to a suitable output device 410, such as a display or a loudspeaker.

The signal processing and/or micro-processor controller function 408 is also coupled to a memory device 416 that stores operating regimes, such as decoding/encoding functions and the like and may be realised in a variety of technologies such as a volatile random access memory (RAM) , non-volatile read only memory (ROM) , flash memory or any combination of these. A timer 418 is typically coupled to the signal processing and/or microprocessor controller function 408 to control the timing of operations (transmission or reception of time-dependent signals) within the communication unit 400.

As regards the transmit chain, this essentially includes an input device 420, such as a microphone and/or keypad, coupled in series through transmitter/modulation circuitry 422 and a power amplifier 424 to the antenna 402. The transmitter/ modulation circuitry 422 and the power amplifier 424 are operationally responsive to the signal processing and/or microprocessor controller function 408.

In accordance with the preferred embodiment of the present invention, the signal processing and/or microprocessor controller function 408 is operably coupled to a battery cell 426 of the communication unit 400. Notably, the battery 426 has been adapted to comprise its battery charge measurement circuit 428, for example a coulomb counter integrated circuit (IC) . Preferably, the Coulomb measuring device is in the form of a fine-accuracy ammeter. The signal processor 408 is configured to continuously read the current flow to/from the battery 426 over time.

Furthermore, the battery device 426 has been further adapted in that it comprises an accompanying memory element 432, such as RAM, to store battery charge data. In this manner, the battery 426 maintains battery charge data even when it has been disconnected from the phone 400. Therefore, when the battery 426 is re-connected to the phone 400, the phone 400 is able to obtain charge and/or discharge information from the memory element 432 of the battery 426.

The signal processor 408 first converts measured charge change values (since the last reading) received from the battery charge/discharge measurement circuit 428 into standard units (i.e. mAh) . The amount of charge measured entering the battery is then multiplied by, say, 0.99', to compensate for the charge efficiency of the Li-Ion chemistry (i.e. only 99% of the charge entering a Li-Ion battery during a charge cycle is actually stored and usable during a discharge) . The signal processor then sums (or subtracts if energy is being dissipated) the charge efficiency compensated charge value with the discharge value (measured in the same way as the charge value) to obtain a total charge change value. This yields a real-time representation of the remaining usable battery capacity. This representation is uncompensated with respect to effects of temperature and current draw on the battery.

This means that any deviation in temperature that affects the usable capacity of the battery will not be represented by this value. Preferably, these calculations yield three values : (i) The estimated total pack capacity (TC) ; (ii) The estimated remaining capacity of the pack (or estimated charge position (ECP) ) ; and (iii) The last charge position (LCP) , which is a reference value used to update the counters within the pack IC.

Referring now to FIG. 5, a circuit 500 for determining a charge level of a battery is illustrated, according to the preferred embodiments of the present invention. The battery charge determination circuit is divided into two regions, a first region 560 located within the battery housing (say, battery module 426 of FIG. 4) and a second region 565 located within the phone housing. Again, it is assumed that an ideal battery cell 505 can be realised in practice by assuming a serially coupled internal resistance 510. Furthermore, in the context of mobile phones, it is assumed that impedance 525 is a highly varying load, which causes rapid voltage changes on the output of the battery. In accordance with the preferred embodiment of the present invention, a serial sense resistance 550 is introduced into the battery circuit 560, in order that a voltage V^"ι can be determined by voltmeter 555 from the current passing through the sense resistance 550. Notably, the voltmeter 555 is preferably an integrated circuit (IC) and is configured with fine accuracy to measure mA (or less) through sense resistance 550. The voltmeter 555 is also configured to integrate measured values over time to result in an accurate digital current-time output .

Thereafter, the accurate digital current-time output is input to an algorithm, to enable the mobile phone's signal processor (say signal processor 408 of FIG. 4) to accurately identify the individual battery' s charge loss and thereby determine the remaining battery charge based on the measured charge loss.

Preferably the phone comprises its own voltmeter V₂ 520, which is used to determine the end of a charging and/or discharging cycle.

Referring now to FIG. 6, an overview of the mapping algorithm 600 is illustrated, as applied by the signal processor. In effect, the inventive concepts of the present invention propose that a signal processor located within the phone switches between ideal charge values, as calculated by the algorithm 615 (i.e. signal processor 408 within the mobile phone 400 of FIG. 4), and real world measured values 605, as measured by the Coulomb counting measuring device, say device 428 of FIG. 4. In this manner, the signal processor 408 then applies a scaling and shifting factor (maps) to the uncompensated values (TC, ECP and LCP) , based upon the temperature, as described later. This is preferably achieved using a multi-step linear algorithm.

In effect, whatever compensation (temperature, load, etc.) is applied by the algorithm in step 610, a reverse uncompensation' factor is applied in the opposite direction. In this manner, ideal or real-world values are continuously interchanged and updated between the ideal-world domain and the measured-world domain to ensure that both domains remain accurate.

Referring now to FIG. 7, a graph 700 illustrates a preferred mechanism of how the mapping algorithm is applied, to compensate for such factors as temperature and load variations . The relationship of charge (voltage) 710 versus temperature 720 is illustrated for the charge contained in the battery. The higher curve indicate the total charge capacity (TC) 770 that is contained in the battery, whereas the lower curve indicates a charge cut-off associated with the battery. A battery is identified as being fully charged when it reaches the TC level 770 and of need of re-charging when the measured charge falls to the cut-off level 730. As shown, the charge level 710 varies as a function of temperature 720.

The battery charge level is illustrated with two values : an estimated charge position (ECP)/ level 760 and a last measured charge position (LCP)/ level 740. Notably, there is fixed offset 750 between the ECP 760 and the LCP 740 for each charge sample measured. Referring now to FIG. 8, a flow chart 800 illustrates a method of initialising a mobile phone in a process to determine a usable battery charge level, in accordance with a preferred embodiment of the present invention.

The process commences with the battery pack data being read by the mobile phone from a flash memory contained in the battery pack, as shown in step 805. A determination is then made, in step 810, as to whether the battery pack is a new pack. If the battery pack is not a new pack, in step 810, all of the charge values are read from the phone pack data, and these are used as initial values. A sanity check of the phone pack values is preferably performed in step 855 and a determination made as to whether there has been a battery pack failure for example the coulomb counting IC (428 of FIG. 4) reports erroneous values. If there has not been a battery pack failure in step 860, the process moves on to the flowchart of FIG. 9.

However, if there has been a battery pack failure in step 860, or the battery pack is a new pack, in step 810, the power mode of the phone is stabilized, as shown in step 815. A battery voltage is then read in step 820 and this voltage converted to a charge capacity value by the signal processor of the phone in step 825. The calculated charge capacity value is then stored as the ECP value within the battery in step 830. Counters used in the timing calculations are then zeroed in step 835 and the last charge position (LCP) made equal to the estimated charge position (ECP) in step 840. The total charge data is then read from the battery pack in step 845 thereby completing the initialisation phase. The charge data is included by the manufacturer in the battery pack to provide a rough estimate of the battery pack capacity.

The process described in the flowchart 800 of FIG. 8 is preferably used to obtain the most accurate data/ starting point for the battery pack. This data is either accurate data calculated by the algorithm and recorded from a time prior to the battery being previously disconnected from the phone, or it is calculated from voltage and stored manufacturer data.

Referring now to FIG. 9, a flowchart 900 illustrates a method of determining and representing a usable battery charge capacity, in accordance with a preferred embodiment of the present invention. The process commences, in step 905, with a compensated charge value and then applies uncompensation for, say, temperature, load etc., to convert it into an ideal-world value. The IC's charge/discharge state counters are then read in step 910. A charge efficiency compensation value, e.g. the 99% value relating to a Li-Ion battery from step 920, is then applied to the charge counter values to convert them into a mAh value, in step 915. A skilled artisan will appreciate that such compensation values can be applied in any 'currency' and that mAh is the preferred option.

The ECP value stored in the battery memory is then updated based on the measured and converted LCP values, as shown in step 925. If the ECP value is then identified as being outside of a battery's range, i.e. it is identified as being fully charged or below the cut-off level, the TC (and possibly the ECP) value is corrected in step 930. Thus, if the ECP value is less than ^Λ0' it is corrected to ^λ0' or if the ECP value is determined as being higher than the TC value, it is corrected to the TC value. The values are then compensated for again, in step 935. The counters are then checked, zeroed and the LCP value is updated to match the ECP value, if necessary, as shown in step 940.

It is envisaged that the process described in FIG. 9 is implemented by the phone as often as required, say, once per minute to reflect an anticipated change in the temperature, load, etc. When related to a charging or discharging cycle, values for TC or ECP may be adapted, for example following a complete charge cycle, the TC value may be set to 100% or at the end of a complete discharge cycle the ECP value may be set to 0' . The counters in the IC represent the difference between LCP and ECP. The use of LCP allows the counters in the IC to be controlled to prevent them from overflowing without affecting the value of ECP .

As the inventive concepts of the present invention propose to identify and represent remaining chargeable capacity to the user in a real-time manner, the process effectively compensates for ageing of components. Thus, as the values are continuously measured and compensated for, ageing of the battery is no longer a significant issue. Furthermore, the inventive concepts described herein are envisaged to be particularly beneficial to high-tier mobile phones or other similar devices using Li-Ion technology batteries. Compared to existing mobile phone battery voltage measuring techniques the inventive concepts allow a much more accurate representation of the remaining usable battery capacity to be determined and reported to the user. The inventor of the present invention has determined that the aforementioned process is accurate to within +1% of the true remaining charge value, as compared to the current 'averaging' techniques that are only accurate to within +15-25%.

It is envisaged that the inventive concepts are applicable to any battery-powered mobile phone or radio device where the battery undergoes large temperature and/or load variation and would therefore benefit from temperature and/or load compensation.

Furthermore, it is within the contemplation of the invention that the aforementioned inventive concepts may be applied to any battery and not limited to Li-Ion batteries. A skilled artisan will appreciate that the start-up process may need adapting, dependent upon the particular type of battery used and/or the associated battery application. In addition, it is envisaged that the charge determination circuitry may use any current measuring device or circuit, and is not limited to the circuitry or components illustrated in FIG. 6.

It will be understood that the apparatus and improved process for determining a remaining usable charge of a battery, as described above, provides at least the following advantages : (i) It provides a significant improvement in accuracy, as knowing an accurate charge level remaining in a battery allows a user to know how much talk time or gaming time remains available in the phone; (ii) It provides an ability to compensate for temperature in the phone; (iii) It reduces the ability to fraudulently copy phones, due to the increased complexity of the battery; (iv) The remaining charge data is more accurate, as the charge level is stored within the battery itself; and (v) No filtering or compensation of a coulomb counting algorithm is required, as the phone is initialised in a known state upon switch on, where it takes a charge reading from the attached battery.

Whilst the specific and preferred implementations of the embodiments of the present invention are described above, it is clear that variations and modifications of such inventive concepts could be readily applied by one skilled in the art.

Thus, an improved apparatus and process for determining a remaining usable charge of a battery has been described, wherein the aforementioned disadvantages associated with prior art arrangements have been substantially alleviated.

Claims

1. A method (900) of determining a level of charge remaining on a re-chargeable battery that is operably coupled to a mobile phone comprises the step of: measuring (910) a level of battery charge of the re-chargeable battery; wherein the method is characterised by the steps of: calculating (915) a rate of change of the level of battery charge; determining (925) a level of charge remaining on the re-chargeable battery by subtracting or adding the calculated rate of change level from a previously determined level of charge remaining on the re-chargeable battery; and applying and dynamically adjusting one or more threshold levels that indicate a level of charge remaining on a re-chargeable battery.

2. A method (900) of determining a level of charge remaining on a re-chargeable battery according to Claim 1, wherein the steps of calculating (915) a rate of change of the level of battery charge and determining (925) a level of charge remaining on a re-chargeable battery are performed in mAh.

3. A method (900) of determining a level of charge remaining on a re-chargeable battery according to Claim 1 or Claim 2, wherein the step of calculating (915) comprises integrating the measured level of battery charge over time to identify a loss or gain in a level of charge remaining on the re-chargeable battery.

4. A method (900) of determining a level of charge remaining on a re-chargeable battery according to any preceding Claim, wherein the step of measuring (910) is performed within a rechargeable battery housing.

5. A method (900) of determining a level of charge remaining on a re-chargeable battery according to any preceding Claim, wherein the previously determined level of charge is obtained by the step of: reading charge data from the re-chargeable battery.

6. A method (900) of determining a level of charge remaining on a re-chargeable battery according to any preceding Claim, wherein the method is further characterised by the initial steps of: reading charge data from the re-chargeable battery following a battery pack failure (860) , or identifying that a battery pack is a new battery pack; and converting the read level of charge to a charge capacity value (825) .

7. A method (900) of determining a level of charge remaining on a re-chargeable battery according to any preceding Claim, wherein the method is further characterised by the step of: applying a charge efficiency compensation factor to the step of calculating a rate of change of the level of battery charge.

8. A method (900) of determining a level of charge remaining on a re-chargeable battery according to any preceding Claim, wherein the the step of applying and dynamically adjusting threshold levels is arranged to provide a more accurate representation to a user of the mobile phone.

9. A wireless communication unit (400) comprising a re-chargeable battery adapted to perform the steps according to any of the preceding Claims .

10. A wireless communication unit (400) comprising a re-chargeable battery (426) and a coulomb measuring function operably coupled to a processor in the wireless communication unit (400) to integrate battery charge data of the re-chargeable battery (426) over time, the wireless communication unit (400) characterised in that the processor applies one or more threshold levels to determine whether a charging process is complete or required and dynamically adjusts one or more threshold levels that indicate a level of charge remaining on the re-chargeable battery.

11. A wireless communication unit (400) according to Claim 10 further characterised in that the coulomb measuring function comprises a voltmeter.

12. A wireless communication unit (400) according to any of preceding Claims 10 to 11 further characterised in that the re-chargeable battery is a Li-Ion battery.

13. A wireless communication unit (400) according to any of preceding Claims 10 to 12 further characterised in that the memory element stores battery charge measurements and/or rate of change of battery charge measurements .