Patent Application
20140139230
This Application claims priority benefit of German Patent Application 10 2012 111 086.7, which was filed on Nov. 19, 2012. The entire contents of the German Patent Application are hereby incorporated herein by reference.
The description of the present application relates to methods and apparatuses for determining a charging state of a battery, for example a rechargeable battery, and to devices comprising such methods and apparatuses.
A battery, such as a rechargeable battery or a nonrechargeable battery, may be the power supply of mobile portable devices such as mobile phones, portable computers, and the like. Batteries may also be used to power technical equipment such as vehicles. Batteries, whether rechargeable or nonrechargeable, may also generally be referred to the accumulators. Regardless of the type of battery use in a particular device or apparatus, it is often desirable to know the charging status of the used battery. In particular, it is beneficial to be able to properly ascertain a level charge associated with a given battery, so that the battery may be recharged and/or replaced before an associated device or apparatus fails because a sufficient power is not being provided by the battery.
Conventionally, in particular applications, a charge condition of a battery may be determined by measuring a voltage state of the battery while no load or a minimal load is coupled to the battery. For example, a charge condition of a battery may be determined by measuring a voltage state of the battery while no current or very low current is being drawn from the battery. However, it may be a problem to determine a charge condition of the battery during a normal operation state of the device coupled to the battery. That is, determining a proper charge condition of the battery, as indicated in the foregoing, generally requires a low terminal voltage associated with the battery and/or that no load or a minimal load is coupled to the battery. This is very difficult to achieve while a device coupled to the battery.
The detailed description is described with reference to the accompanying figures. In the figures, the-most digit(s) of a reference number identifies the figure in which the reference number first appears. The use of the same reference number in different instances in the description and the figures may indicate similar or identical items.
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.
In addition, for detecting a voltage of the battery, such as a terminal voltage, the device 100 includes a second detecting device 104. For detecting the voltage of the battery, the second detecting device 104 may be coupled the battery using terminals 105 and 106.
The implementation illustrated in
During a charging or discharging state of a battery, the evaluation device 107 may store information obtained by at least one of the first detecting device 101 and the second detecting device 104. For example, the evaluation device 107 may store the value or values of a charging current obtained by the first detecting device 101. In addition, the evaluation device 107 may store the value or values of a voltage associated with a battery coupled to the second detecting device 104.
In one example, the evaluation device 107 may 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 device 101 is 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 device 107 may ascertain the charge state of the battery based on one or more terminal voltages detected by the second detecting device 104. The second detecting device 104 generally 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 device 107 may ascertain the charge state of the battery based one or more current values supplied by the first detecting device 101. The first detecting device 101 generally 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 device 101 and the second detecting device 104 may be used by the device 100 to ascertain a charging state of the battery. Furthermore, such information obtained by the device 100 may 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 device 100, or by another storage medium.
In one implementation, the battery 11 supplies power (e.g., current and voltage) to a load 12. The load 12 may comprise multiple electrical elements and components. The multiple electronic elements and components of the load 12 may enable the device 10 to function for desired purpose. For example, in one implementation, the load 12 may comprise circuitry that at least partially enables a mobile phone to receive and transmit wireless signals.
The load 12 may be coupled to a switch 13. The switch 13 may be implemented with one or more transistors, such as field effect transistors or bipolar electrical elements. The switch 13 is designed to decouple and coupled the load 12 to the battery 11. This may be desirable when the electrical components associated with the load 12 are not required for use by the device 10. In another example, the switch 13 is not required. For example, the electrical components associated with the load 12 may be configured to enter a standby state in order to reduce the discharge state of the battery 11. In another implementation, the switch 13 may be designed to limit the current drawn by the load 12 in order to achieve a reduced power or standby state of the device 10. In another implementation the battery 11 may be removed from the device 10 and placed in an optional external device for charging.
Two connectors 19 may be associated with the device 10. The connectors 19 enable an external power source to be coupled to the device 10. This external power source may supply a voltage that charges the battery 11.
The embodiment illustrated in
In one implementation, the combination of the flowmeter 14, the voltage measuring device 16 and the temperature sensor 15 provide information related to the operating conditions of the battery 11. 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 battery 11 and information related to the operating temperature of the battery 11.
The flowmeter 14, the voltage measuring device 16 and the temperature sensor 15 may be coupled to an evaluation device 17. The evaluation device 17 is at least capable of receiving a plurality of voltage values from the voltage measuring unit 16. Advantageously, the evaluation device 17 may receive one or more voltage values from the voltage unit 16 before a voltage across the battery 11 reaches a steady-state. In other words, the one or more voltage levels may be obtained by the voltage measuring unit 16 during a period of time that the load 12 transitions 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 battery 11. The accuracy of the determined current charge state to the battery 11 may be enhanced from information obtained from at least one of the flowmeter 14 and the temperature sensor 15. 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 device 10, for example, optically or acoustically by way of an output 18.
The embodiment illustrated in
Furthermore, a voltage level output from the temperature sensor 15 is provided to an analog-to-digital converter 210. The provided voltage level from the temperature 15 represents a temperature of the battery 11. The digital values provided by the analog-to-digital converters 211, 29 and 210 are provided to a computing device 212. As an alternative to the analog-to-digital converters 211, 29 and 210, a single analog-to-digital converter may be provided that accomplishes the functionality provided by the analog-to-digital converters 211, 29 and 210.
The digital information received by the computing device 212 may be used individually or collectively to determine a charge state of the battery 11. This determined charge state may be output to the output device 18. In one implementation, the computing device 212 may 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 converters 211, 29 and 210 and received from the resistor 24, battery 11 and temperature sensor 15 provide information related to a charge state of the battery 11 substantially at the time that the load 12 is transitioning to a low current state but before the terminal voltage associated with the battery 11 reaches a steady-state.
At act 400, 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 act 401, 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 act 402, 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 act 403, 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 act 404, 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 acts 401 and 403. For example, the charge state of the battery may be determined based on a voltage and/or current associated with battery and determined at act 401. 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.
At act 30, a charging and/or discharging of the battery, during the charging and/or discharging of the battery, is determined.
At act 31, 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 act 32, the temperature of the battery is detected. Furthermore, at act 32, further operational characteristics of the battery may be detected.
At act 33, 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 act 34, the charge state of the battery is determined based on the one or more voltages sensed in act 33. Furthermore, augmenting information, such as the currents detected at act 30 and the temperature information provided at act 32, may be used to improve the fidelity of the determined charge state to the battery.
The method illustrated in
At “a” in
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
yk=OCV(DOD)−R·ik−U(T)+hk (1),
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
Vt(t)=Vinf−a·exp(b/t)+tc30 h1+h2. (2)
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
log(Vinf−V(t))=log(a)+(b/t)+c·log(t). (3)
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 with
As can be noted from
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
DOD=f(OCV, h1, h2). (4)
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,
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2012 111 086.7 | Nov 2012 | DE | national |
