METHOD AND APPARATUS FOR DETERMINING A CHARGE STATE

Described are methods and devices by which a charge state of a battery can be determined. The determination is made in various embodiments by substantially separating a load, and detecting voltages associated with the battery, and by including adjustments based on operating conditions of the battery.

DETAILED DESCRIPTION

At least one embodiment provides methods and apparatuses which enable determining a state of charge of a battery in a short time with sufficient accuracy.

Exemplary embodiments are described in greater detail with reference to the figures. The invention is not limited to the specifically described embodiments but can be suitably modified and altered. Individual features and feature combinations of one embodiment can be customized with features and feature combinations of other one or more embodiments, unless this is expressly excluded.

Before the following embodiments with reference to the figures are explained in detail, it should be noted that matching elements are provided in the figures with matching or similar reference numerals. In some cases, the description of such matching or similar reference numerals will not repeated. In addition, the figures are not necessarily shown to scale, since their focus is on the illustration and explanation of basic principles.

The method described and the operations or events shown are not necessarily executed in the order shown, but in other embodiments, other orders and/or concurrently performing various operations or events are possible.

In various embodiments, a stationary value of a terminal voltage is approximately determined by the terminal voltage of a battery immediately after the beginning of low load current condition, i.e. a load current below a threshold value. In particular, prior to reaching a steady state, the approximate value of the terminal voltage may be measured one or more times to aid in determining a charge state of the battery.

In one embodiment, a charge state of the battery may be determined based on the basis of correction of the battery operating conditions, such as information on previous loading and/or unloading, for example, based on charging current and/or voltage across the battery during charging and/or discharge status or information on a temperature, a degree of aging, heat transfer, or heat generation of the battery. It should be noted that in the context of one more embodiments, a charging current can be negative or positive depending on whether the battery is charged or discharged by the charging current. Therefore, the concept of charging current may include currents that charge the battery as well as currents that drain the battery.

FIG. 1illustrates a device100according to an embodiment. In particular, the illustrated embodiment includes various elements that enable determining a charge at the battery. The device100includes a first detecting device101, with which a charging current of a battery can be detected, and as already explained, a charging current can be positive or negative, depending on whether the battery is charging or discharging. For detecting the charging current, the first detecting device101can be coupled to a battery using ports102and103.

In addition, for detecting a voltage of the battery, such as a terminal voltage, the device100includes a second detecting device104. For detecting the voltage of the battery, the second detecting device104may be coupled the battery using terminals105and106.

The implementation illustrated inFIG. 1further includes an evaluation device107. The evaluation device107is arranged to determine a charge state of a battery that is coupled to the device100. In one example, the evaluation device107may determine that the battery is in a charging state or discharging state when an absolute value of a charging current is at or above a first predetermined threshold value.

During a charging or discharging state of a battery, the evaluation device107may store information obtained by at least one of the first detecting device101and the second detecting device104. For example, the evaluation device107may store the value or values of a charging current obtained by the first detecting device101. In addition, the evaluation device107may store the value or values of a voltage associated with a battery coupled to the second detecting device104.

In one example, the evaluation device107may determine that the battery is in a low current state, e.g. a load coupled to the battery is drawing minimal or no current, when a current detected by the first detecting device101is below a second predetermined threshold value that is less than or equal to the first predetermined threshold value.

In one example, typical values for the first predetermined threshold value and the second predetermined threshold value may reside in the range of 1/20 C and 1/30 C, where C represents a capacity rating for a given battery. For example, 1.9 Ah battery is concluded to be rated at 1 C and 1.9 A. A battery may be considered to be in a low current mode when the battery is not supplying significant current to a device coupled to the battery, such as a load. Such a low current mode of a battery may be considered a steady state period or a standby state. In one example, the evaluation device107may ascertain the charge state of the battery based on one or more terminal voltages detected by the second detecting device104. The second detecting device104generally is to detect the one or more terminal voltages before it voltage on a terminal of the battery reaches a steady state. Furthermore, the evaluation device107may ascertain the charge state of the battery based one or more current values supplied by the first detecting device101. The first detecting device101generally used to detect the one or more current values associated with the battery before the battery reaches a low current mode. Information obtained from the first detecting device101and the second detecting device104may be used by the device100to ascertain a charging state of the battery. Furthermore, such information obtained by the device100may be used to augment stored history data that indicates a charging state of a battery over a period of time. Such historical data may be stored by the device100, or by another storage medium.

FIG. 2illustrates a device or apparatus10that includes a battery11. The battery11may be a rechargeable lithium battery, or other type of battery. The device10may determine a charge state of the battery11. The device10may include electrical components or other such elements that are at least partially powered or enabled by the battery11. That is, the battery11may supply electrical current to the electrical components associated with the device10. For example, the device10may be a mobile device, such as a mobile telephone, a navigation device, or a laptop computer. However, the device10is not limited as such. For example, the device10may also be a vehicle that includes a battery, or otherwise a stationary device that includes a battery. The battery11may be a single cell battery or a multi-cell battery, with the cells of the battery are connected in parallel or series. Furthermore, the battery11may be comprised of electrochemical cells. However, it is to be understood that the battery11is not so limited.

In one implementation, the battery11supplies power (e.g., current and voltage) to a load12. The load12may comprise multiple electrical elements and components. The multiple electronic elements and components of the load12may enable the device10to function for desired purpose. For example, in one implementation, the load12may comprise circuitry that at least partially enables a mobile phone to receive and transmit wireless signals.

The load12may be coupled to a switch13. The switch13may be implemented with one or more transistors, such as field effect transistors or bipolar electrical elements. The switch13is designed to decouple and coupled the load12to the battery11. This may be desirable when the electrical components associated with the load12are not required for use by the device10. In another example, the switch13is not required. For example, the electrical components associated with the load12may be configured to enter a standby state in order to reduce the discharge state of the battery11. In another implementation, the switch13may be designed to limit the current drawn by the load12in order to achieve a reduced power or standby state of the device10. In another implementation the battery11may be removed from the device10and placed in an optional external device for charging.

Two connectors19may be associated with the device10. The connectors19enable an external power source to be coupled to the device10. This external power source may supply a voltage that charges the battery11.

The embodiment illustrated inFIG. 2also includes a flowmeter14, such as a current measuring device. The flowmeter14is capable to detect a current flowing from the battery11. Furthermore, the flowmeter14is capable of detecting a current flowing to the battery11. The indicated currents may be associated with the connectors19. In one example, the flowmeter14is the first detecting device101illustrated inFIG. 1. A voltage measuring device16may be coupled in parallel with the battery11. The voltage measuring device16is capable of measuring the voltage applied across the battery100. The voltage applied across the battery100may be considered a terminal voltage. In one embodiment, the voltage measuring device16is the second detecting device104illustrated inFIG. 1. In one example, the voltage measuring device16may perform the voltage measurements when the switch13is in an open state. Alternatively, the voltage measuring device16may perform voltage measurements when the load is in a low current state or otherwise in a standby sleep state. Furthermore, in one implementation, a temperature sensor15may be provided. The temperature sensor15may be used to measure a temperature of the battery11. The use of a temperature sensor15is optional. Furthermore, the use of the flowmeter14is also optional. Furthermore, the temperature sensor15may be used to estimate and ambient temperature associated with the battery11. For example, the temperature sensor15, in combination with other elements of the device10, may estimate the ambient temperature associated with the battery11based on the temperature of the battery11.

In one implementation, the combination of the flowmeter14, the voltage measuring device16and the temperature sensor15provide information related to the operating conditions of the battery11. For example, one or more of the foregoing devices may provide information related to the charging and discharging (e.g. for voltage and current) of the battery11and information related to the operating temperature of the battery11.

The flowmeter14, the voltage measuring device16and the temperature sensor15may be coupled to an evaluation device17. The evaluation device17is at least capable of receiving a plurality of voltage values from the voltage measuring unit16. Advantageously, the evaluation device17may receive one or more voltage values from the voltage unit16before a voltage across the battery11reaches a steady-state. In other words, the one or more voltage levels may be obtained by the voltage measuring unit16during a period of time that the load12transitions to a low current state where the low power state. The detected one or more voltage levels may be used to determine a current charge state to the battery11. The accuracy of the determined current charge state to the battery11may be enhanced from information obtained from at least one of the flowmeter14and the temperature sensor15. Further details and examples of such evaluation are discussed in greater detail hereinafter. The result of the analysis may be displayed to a user of the device10, for example, optically or acoustically by way of an output18.

FIG. 3illustrates a device20in accordance with an embodiment. Similar to the device10, the device20may be a mobile device that receives power at least partly from the battery11. The elements of the device20that have the same reference as those associated with the device10will not be described again in detail. But as is shown, the device10also includes at least the load12, the temperature sensor15, an output18, the switch13, and the connectors19. Some or more these elements may be omitted.

The embodiment illustrated inFIG. 3further includes a resistor24coupled in series with the battery11. In general, the resistor24is sized small. For example, the resistor24may be 1 ohm or less. The resistor24may be coupled to an evaluation device27. The evaluation device27may include an analog-to-digital converter211that is coupled to the resistor24. The analog-to-digital converter211is functional to convert a voltage drop across the resistor24to a digital value. The voltage drop across the resistor24is representative of a charging applied or discharged from the battery11. A further analog-to-digital converter29is provided. The analog-to-digital converter29is functional to convert a terminal voltage seen at the terminals of the battery11to a digital value.

Furthermore, a voltage level output from the temperature sensor15is provided to an analog-to-digital converter210. The provided voltage level from the temperature15represents a temperature of the battery11. The digital values provided by the analog-to-digital converters211,29and210are provided to a computing device212. As an alternative to the analog-to-digital converters211,29and210, a single analog-to-digital converter may be provided that accomplishes the functionality provided by the analog-to-digital converters211,29and210.

The digital information received by the computing device212may be used individually or collectively to determine a charge state of the battery11. This determined charge state may be output to the output device18. In one implementation, the computing device212may be a microcontroller, a programmable gate array, such as a field programmable gate array, a digital signal processor, or other suitable device. In one implementation, the information provided by the analog-to-digital converters211,29and210and received from the resistor24, battery11and temperature sensor15provide information related to a charge state of the battery11substantially at the time that the load12is transitioning to a low current state but before the terminal voltage associated with the battery11reaches a steady-state.

FIG. 4illustrates a method in flow diagram form according to one embodiment. The method illustrated may be implemented by one or more of the devices illustrated inFIGS. 1-3. Furthermore, the method may be implemented by a device that includes a processor coupled to a tangible storage medium. The tangible storage media may include computer implemented instructions that, when executed by the processor, perform the method illustrated inFIG. 4.

At act400, a battery is evaluated to determine if it is in a charging or discharging state. For example, a battery may be evaluated to determine if the current is being drawn there from or a current is being delivered thereto. In one particular example, a charging or discharging state of the battery may be determined by comparing a current associated with the battery to a first predetermined threshold.

At act401, the battery is evaluated to determine if a charging or discharging voltage is being applied to the battery. In addition, the current associated with the battery may be ascertained. The foregoing information may be used to determine if the battery is in a charging or discharging state.

At act402, a low current state is detected. A low current state may be detected by determining that a current (e.g., a charging current) associated with the battery is below a second predetermined threshold. In one particular embodiment, the second predetermined threshold is less than or equal to the first predetermined threshold. In one particular embodiment, the load current state is indicative of a load associated with the battery being in a standby state, a low power state, or disabled.

At act403, during a low current state, or otherwise while the load associated or connected with the battery is in a standby state, in low power state or disabled, a terminal voltage (i.e., a voltage across the battery) is detected. Detection of the terminal voltage may occur over a time span and prior to a voltage across the battery reaching a steady-state.

At act404, a charge state to the battery is determined. The art state to the battery is determined based on some or all of the information gathered during acts401and403. For example, the charge state of the battery may be determined based on a voltage and/or current associated with battery and determined at act401. Furthermore, the charge state to the battery may be determined based on the detected voltage across the battery. In particular, the charge state of the battery may be determined based on the detected voltage across the battery while the load associated or connected with the battery is in a standby state, in low power state or disabled.

FIG. 5illustrates a method in flow diagram form according to one embodiment. The method illustrated may be implemented by one or more of the devices illustrated inFIGS. 1-3. Furthermore, the method may be implemented by a device that includes a processor coupled to a tangible storage medium. The tangible storage media may include computer implemented instructions that, when executed by the processor, perform the method illustrated inFIG. 5.

At act30, a charging and/or discharging of the battery, during the charging and/or discharging of the battery, is determined.

At act31, a load coupled to the battery is transitioned to a low current mode. In one example, the battery is disconnected from the load, or portion of the load. The node may be transitioned to a low current mode in order to save power, and/or because the load entered a standby or disabled state.

At act32, the temperature of the battery is detected. Furthermore, at act32, further operational characteristics of the battery may be detected.

At act33, a terminal voltage associated with the battery is detected. Multiple terminal voltages may be detected over a period of time. In one implementation, the one or more terminal voltages associated with the battery are detected during a low current state associated with the load. In another implementation, the one or more terminal voltages associated with the battery are detected while a load is substantially disconnected from the battery. The one or more terminal voltages may be detected, one of the time, over a duration of the predetermined timeframe. That predetermined timeframe may be up to a maximum of 45 minutes, or up to 10 minutes after the battery is separated or otherwise disconnected from the load. Generally, it is beneficial to detect the terminal voltages before the battery reaches a steady-state. This generally occurs approximately 60 minutes after the battery is substantially disconnected (i.e., open circuit) from the load.

At act34, the charge state of the battery is determined based on the one or more voltages sensed in act33. Furthermore, augmenting information, such as the currents detected at act30and the temperature information provided at act32, may be used to improve the fidelity of the determined charge state to the battery.

The method illustrated inFIGS. 4 and 5may be combined together. Furthermore, various acts associated with methods may be omitted or combined together. In one example, the acts of30,32and33may be performed simultaneously and/or continuously.

FIG. 6illustrates graphs that show an influence of a terminal voltage over time. The upper graph of the figure illustrates a cell voltage plotted against time. The upper graph of the figure illustrates a charge or discharge of the battery against time. The battery used for the graphs shown in the figure had a capacity of 1500 mAh. At the beginning of the measurement period, the battery was charged to 50% of its maximum capacity, where 0% represents a full charge to the battery and 100% corresponds to a full discharge of the battery.

At “a” inFIG. 6, the battery is charged to a full level (0% discharge level) followed by a three-hour relaxation to a steady-state. At “b”, the battery is discharged to the 50% discharge point, followed by a three-hour relaxation. The discharge current used is 0.5 C. At “c”, the battery is discharged to the 60% discharge point, followed by a three-hour relaxation. The discharge current used is 0.6 C. At “d”, the battery is charged to the 50% discharge point, followed by a three-hour relaxation. The charge current used is 0.6 C. At “e”, the battery charged to the 40% discharge point, followed by a three-hour relaxation. The charge current used is 0.6 C. At “f”, the battery is discharged to the 50% discharge point, followed by a three-hour relaxation. The discharge current used is 0.6 C. At “g”−“j”, the foregoing applies, but a charge/discharge currents of 0.13 C are used.

As can be seen, in accordance with the charging and discharging steps b, d, f, h and j, for example, the discharge level of each is 50%. The open circuit voltages after three hours, however, differ slightly. This effect is called the hysteresis effect. This influence is not corrected, but the charging state is determined solely on the basis of the open circuit voltage or determined on the basis of voltage measurements approximating the value of the open circuit voltage and corresponding variations in the charge state result. In addition, different types of batteries have different temperatures at different open circuit voltages. These different temperatures may affect various results.

In general, a terminal voltage of a battery may be written as yk, where

wherein OCV (DOD) is dependent on the degree of discharge DOD open circuit voltage, R is an internal resistance of the battery, which causes at a particular charge/discharge current ik a voltage drop, U(T) represents a voltage contribution which T depends on a time constant and for example reflects chemical processes such as diffusion, and hk is a hysteresis term, which is a function of different historical charge/discharge currents.

For determining the state of charge of a battery, a suitable function may be chosen which is then adjusted to voltage values measured after disconnecting the battery from the load. A possible description of the timing of the terminal voltage Vt (t), where t is time, is

Vinf, a, b and c are parameters that can be determined by fitting the function of equation (2) to the measured voltage values, h1 and h2 are correction terms which, for example, for hysteresis effects, The initialization of the parameters, for example Vinf, a, b and c can, for example, be on the basis of measured currents flowing for example, while the battery is in a state of charging or discharging, and/or in dependence on other functions, such as the age of the battery and/or the impedance of the battery.

The correction values h1 and h2 may be determined based on the measured currents and/or on the basis of measured temperatures, for example, as well. It should be noted that in some embodiments, only a single correction value can be used and/or only some influences and operating conditions of the battery can be considered. For example, correction values for different preceding charging and discharging for a particular type of battery during a calibration phase can be experimentally determined and then be read during operation in dependence on detected charging and discharging currents from a table. The same is true for different temperature values.

In some embodiments, the equation (2) including the correction values can be adjusted to a measured curve and an approximate value for the steady state open circuit voltage is determined from the equation. In other embodiments, the correction values h1 and h2 may be neglected.

The equation without h1 and h2 may be

With this function, as explained above, fitting may be performed similar to as described above with reference to equation (2), in order to determine the parameters Vinf, a, b and c. A value for V(t) can be extrapolated for any times by certain parameters (possibly neglecting h1 and h2) in equation (2). In embodiments, the time t is selected such that it at least approximately corresponds to a steady-state of the battery.

But use of the foregoing equations, as well as the embodiments presented in connection withFIGS. 1-5, determining an open terminal voltage associated with the battery may be quickly determined compared to processes that require that the terminal voltage associated with the battery approach a steady-state before making the open terminal voltage determination.

FIG. 7illustrates a curve50that shows a measured open terminal voltage associated with the battery. Curves52,53define a region which results from a value of the open circuit voltage after three hours plus/minus a threshold value, said threshold value representing a desired accuracy of the determination. The open circuit voltage after three hours is used as an example of a measurement of the open circuit voltage, as after three hours a steady-state value is reached. A curve51shows an estimate of the open circuit voltage after three hours based on use of the foregoing equations, as well as the embodiments presented in connection withFIGS. 1-5.

As can be noted fromFIG. 7, the estimated, in accordance with the implementations described herein, value of the open circuit voltage after a time tpof about eight minutes falls within the area bounded by the lines52and53range, whereas in a pure measurement of the open circuit voltage according to curve50occurs after tm, a time of more than 100 minutes is the case. Thus, using the embodiments described herein, a value for the open circuit voltage of a desired accuracy can be determined much faster than with a pure measure, such as within a period of time tpof 45 minutes or less (e.g. 15 minutes or less, about 8 minutes as presented).

If the open circuit voltage is determined by fitting and neglecting corrections h1 and h2, the state of charge, a discharge degree DOD may then be in accordance

The OCV can be approximately determined by fitting using open circuit voltage, h1, for example, on the basis of charging currents (for charging and/or discharging of the battery) of specific correction value, and h2 is a correction value based on the temperature. The values for the discharge OCV level for various values of, for example, h1 and h2 can be stored in a table. An example of a table in which no temperature effects are taken into account (i.e., h2 is not considered), is illustrated below:

As already explained, the temperature can be considered as an additional correction. For illustration,FIG. 8shows a steady state value of the open circuit voltage OCV as a function of the degree of discharge DOD. InFIG. 8a discharge rate of 1 corresponds to a discharge rate of 100%, with the curves60,61and62showing the relationship for three different temperatures.

The above simulations and graphs are intended to be illustrative, and the exact curves in actual implementations of the illustrated embodiments may deviate from the curves shown depending a particular implementation.

For the purposes of this disclosure and the claims that follow, the terms “coupled” and “connected” have been used to describe how various elements interface. Furthermore, elements and devices described herein may be implemented in hardware or software, or a combination of hardware and software. Such described interfacing of various elements may be either direct or indirect. Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as preferred forms of implementing the claims. The specific features and acts described in this disclosure and variations of these specific features and acts may be implemented separately or may be combined.