Patent Publication Number: US-11035902-B2

Title: Advanced fuel gauge

Description:
RELATED APPLICATIONS 
     The present disclosure claims priority to U.S. Provisional Application 62/570,572, entitled “Advanced Fuel Gauge,” filed on Oct. 10, 2017, which is herein incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present invention are related to battery management technology and, specifically, to an advanced fuel gauge. 
     DISCUSSION OF RELATED ART 
     Mobile devices, for example smart phones, tablets, wearable devices and other devices are increasingly dependent on battery systems for functionality. Monitoring and maintenance of these battery systems becomes increasingly more important as the dependencies on these devices increases. These monitoring processes include monitoring battery charge, battery temperature, and other parameters during use, charging, and determination of the quality of the battery system. In many such systems, battery characterization is a large component of the battery management process. 
     Traditionally, battery characterization is conducted to determine the optimized equivalent resistance (Req), which is an input to the voltage fuel gauge algorithm to calculate battery Open Circuit Voltage (OCV), at characterized temperatures based on the battery&#39;s dynamic response. Simulation is then used to determine the optimized Equivalent Resistance (Req) at each characterized temperature. The resistance Req across temperature is calculated from piece-wise linear or an exponential function of temperature. 
     However, there are various problems with this approach. Actual battery equivalent resistance is a function of battery remaining capacity under the same battery temperature. Further, actual battery equivalent resistance is a function of load current under the same battery temperature. Battery to battery variation causes error between characterized battery versus actual battery characteristics. This difference causes large OCV error, especially at cold temperatures. The resistance Req calculated using a piece-wise linear function creates additional error at non-characterized temperatures. 
     Further, this open loop implementation does not take into effect battery aging. As the battery ages, the equivalent resistance often increases across all temperatures. However, such adjustments to the equivalent resistance with battery age is often not considered during the equivalent resistance calculations. 
     Therefore, there is a need to develop better characterization techniques for battery management systems. 
     SUMMARY 
     In accordance with aspects of the present invention, a method of providing a fuel gauge is provided. The method includes measuring a battery current through and a battery voltage across a battery; determining an equivalent resistance from the current and the voltage using a multiplier K; determining an open circuit voltage based, in part, on the equivalent resistance; determining a state-of-charge based on the open circuit voltage; and adjusting the multiplier K based on the current and the state-of-charge. 
     A fuel gauge according to some embodiments includes a voltage analog-to-digital converter coupled to a battery and configured to provide a battery voltage; a current analog-to-digital converter coupled to the battery and configured to provide a battery current; a divider coupled to receive the battery voltage and the battery current and configured to produce a resistance; a multiplier coupled to produce an equivalent resistance by multiplying the resistance by a multiplier value K; an adaptive loop that produces the multiplier value K; a table lookup coupled to provide a capacitance based on an open-circuit voltage; a summer that takes a difference between the battery voltage and the open-circuit voltage; and an engine that produces a new open-circuit voltage based on the open-circuit voltage, the capacitance, and the difference. 
     These and other embodiments are further discussed below with respect to the following figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an example of an optimized equivalent resistance versus temperature for some batteries. 
         FIG. 2  illustrates a conventional system for calculating open-circuit voltage (OCV). 
         FIG. 3  illustrates a calculation of OCV based on a calculation of R eq  according to some embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, specific details are set forth describing some embodiments of the present invention. It will be apparent, however, to one skilled in the art that some embodiments may be practiced without some or all of these specific details. The specific embodiments disclosed herein are meant to be illustrative but not limiting. One skilled in the art may realize other elements that, although not specifically described here, are within the scope and the spirit of this disclosure. 
     This description and the accompanying drawings that illustrate inventive aspects and embodiments should not be taken as limiting—the claims define the protected invention. Various changes may be made without departing from the spirit and scope of this description and the claims. In some instances, well-known structures and techniques have not been shown or described in detail in order not to obscure the invention. 
     Elements and their associated aspects that are described in detail with reference to one embodiment may, whenever practical, be included in other embodiments in which they are not specifically shown or described. For example, if an element is described in detail with reference to one embodiment and is not described with reference to a second embodiment, the element may nevertheless be claimed as included in the second embodiment. 
     Traditionally, battery characterization was conducted to determine the optimized equivalent resistance (R eq ) at characterized temperatures based on a battery&#39;s dynamic response.  FIG. 1  illustrates an example graph  100  of R eq  versus temperature that may be used in a conventional calculation of R eq . The battery has been characterized at 3 temperatures (0° C., 20° C., and 40° C. in  FIG. 1 ). A simulation can be used to determine the optimized R eq  at each characterized temperature. The value of R eq  across the temperature range can be calculated from a piece-wise linear or an exponential function of temperature based on the data provided in  FIG. 1 . 
     As discussed above, such an approach to this method of determining the equivalent resistance has several difficulties. The actual battery resistance is a function of battery remaining capacity under the same battery temperature. The actual battery resistance is also a function of load current at the same battery temperature. Further, variation between batteries causes errors between the characterized battery and performance of any individual actual battery. These differences can cause large open circuit voltage (OCV) errors, especially at cold temperatures. Further, calculating the equivalent resistance using a piece-wise linear function creates additional error at non-characterized temperatures, especially temperatures outside of the range where data is actually acquired. An additional error comes from failing to account for the effects of battery aging in these open-loop implementations. As discussed above, as the battery ages, the equivalent resistance of the battery increases across all temperatures. 
       FIG. 2  illustrates a diagram  200  of a conventional calculation of OCV of a battery  202  using a conventional calculation of R eq  as described above. In diagram  200 , the calculation of R eq  is performed in REQ  214 , which receives a measured temperature T from temperature block  210  and battery characterization data for battery  202  from battery characterization block  212 . As discussed above, the value of R eq  can be calculated according to the temperature curves as illustrated in  FIG. 1  above. Battery characterization data from battery characterization block  212  can include the data illustrated in  FIG. 1 . As discussed above, the value Req calculated in block  214  can be calculated from a linear or exponential function of temperature based on the characterization data. As discussed above, a piecewise-linear or exponential fitting of the characterization data of battery  202  stored in battery characterization  212  can provide the value of R eq  determined by REQ  214 . 
     Also illustrated in  FIG. 2 , engine  216  also receives a capacitance C from block  218 . Block  218  receives an OCV output that is generated by engine block  216  and, based on battery characterization from characterization block  212 , provides a state-of-charge (SOC) and an equivalent capacitance of battery  202  based on the value of the OCV output from engine  216 . 
     As is further illustrated, the voltage of the battery is sampled by an analog-to-digital converter (ADC)  204  to provide a digitized voltage V B  representing the voltage output of battery  202 . The previous calculation of the OCV from engine  216 , OCV OLD  is stored in block  206 . In summer  208 , the difference between the stored value OCV OLD  and battery voltage V B  (OCV OLD −V B ) is also input into engine  216 . 
     Consequently, as is illustrated in  FIG. 2 , engine  216  receives the value of the equivalent resistance R eq  from REQ block  214 , the capacitance C from block  218 , and the voltage difference (OCV OLD −V B ) from summer  208  and produces an updated OCV, OCV new . Engine  216  may produce the new OCV according to the following formula: 
                 OCV   new     =       OCV   old     +       (       V   B     -     OCV   old       )     *     (     1   -     e     (       -   t         R   eq     *   C       )         )           ,         
where t is the time measured from the age of the current value of OCV produced by engine  216 .
 
     As discussed above, there a number of problems with the conventional approach as illustrated in  FIGS. 1 and 2  and discussed above. In particular, actual battery resistance is not a function of temperature along, but is also a function of remaining battery capacity, load current, and battery age. Further, there are significant differences between batteries. These differences and other factors can cause large open-circuit voltage (OCV) error, especially at colder temperatures. Additionally, the value R eq  calculated using a piece-wise linear function creates additional error, especially for temperatures that lie outside of the range that has been specifically characterized. 
       FIG. 3  illustrates a calculation of the OCV of battery  302  according to embodiments of the present invention. As is illustrated in  FIG. 3 , the battery current from battery  302  is measured as well as the voltage across battery  302 . Measuring battery current allows a much more accurate way to calculate the equivalent resistance across temperature, load, and aging conditions for battery  302 . 
     There are several advantages to this approach. For example, the calculated open-circuit-voltage (OCV) and state-of-charge (SOC) using this method is much more accurate across temperature, load, SOC % level, and battery age conditions. Further, the resulting fuel gauge no longer uses temperature information to determine OCV and SOC, which eliminates the need for battery characterization if the battery chemistry is known. The OCV/SOC table is based on the battery chemistry rather than characterization of the battery. Further, since the absolute full capacity (AbsFullCap) is related to the ratio of the change in charge to the change in the state of charge (ΔQ/ΔSOC), having a more accurate OCV and SOC determination will result in a more accurate tracking of the battery&#39;s full capacity. As a result, embodiments of the present invention result in the first non-temperature dependent fuel gauge in the industry that is more accurate than the conventional fuel gauges such as that illustrated in  FIG. 2 . 
       FIG. 3  illustrates a system  300  that results in calculation of OCV according to some embodiments of the present invention. As illustrated in  FIG. 3 , engine  320  operates similarly to engine  216  and receives a capacitance from OCV/SOC table  332 , the difference (OCV OLD −V B ) calculated in summer  310 , and the value of equivalent resistance R eq . As is illustrated in  FIG. 3 , the value of OCV OLD  in block  308  is the stored value of the output OCV NEW  from engine  320 , which is stored in block  308 . The battery voltage V B  is the sampled voltage of battery  302  from ADC  304 . OCV/SOC table  332  receives data from battery characterization  330 , which includes chemistry based data for battery  302  that relates the OCV to the capacitance C and the state-of-charge (SOC). As discussed above, the new value for OCV can be given by 
     
       
         
           
             
               
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     In accordance with embodiments of the present invention, a current ADC  306  provides a digitization of the current from battery  302 , resulting in a digitized indication of the battery current I B . The battery current I B  from current ADC  306  and the difference (OCB−V B ) are input to divider  314 . Divider  314  calculates a resistance by calculating R=(OCV−V B )/I B . The value of R calculated by divider  314  is then multiplied by a value K in amplifier  316  to provide the value of equivalent resistance of battery  302  R eq , R eq =K((OCV−V B )/I B ). The value of R eq  is stored in REQ block  318  and provided to engine  320 . 
     The value of K used in amplifier  316  is adaptively adjusted. As is illustrated in  FIG. 3 , the battery current I B  is integrated in block  312 , which provides a coulomb counter, to provide the charge Q that has been drawn from battery  302 . The value of Q is input to divider  322 , which also receives a value for the full charge capacity of battery  302 , Q F , that is stored in FullCap  324 . The value of Q F  stored in FullCap  324  corresponds to the ideal discharge conditions (e.g., room temperature and C/24 load). In divider  322 , the ratio of Q/Q F  is computed. The ratio Q/Q F  represents an absolute value of the state-of-charge of battery  302 , SOC abs . This value is compared with the value of SOC that is obtained from table lookup  332  to form an error, Error=SOC−SOC abs , in adder  328 . The error value ERROR is input to adaptive amplifier  326  where the new value of K is computed as K′=K−β*(Error), where K′ is the adjusted value of the parameter K while K is the old value of K. Consequently, for every timing cycle where current and voltage data is taken from battery  302 , the value of K is adjusted according to the loop gain parameter β. 
     When fuel gauge  300  is initialized, K is initialized to the same value of Design Capacity, which may be an arbitrary initial value that may be close to the ultimate adaptively chosen value. During each battery relax detection (i.e., each data analysis clock cycle), the value of ERROR (SOC−SOC abs ) is calculated. During every relax, K can be updated as: K′=K−Error*β, where β is the selected loop gain. 
     Fuel gauge  300  as illustrated in  FIG. 3  can be implemented as a combination of microprocessors operating algorithms to perform the calculations described above along with circuitry for receiving and processing current and voltage data from battery  302 . Appropriate filtering and analog signal processing techniques may be additionally added prior to implementation of ADCs  304  and  306 . The value of SOC can be provided to a user through a user interface in order to indicate the charging state of battery  302 . Display of the SOC can be implemented through depiction of a dial, bar graph, numerical number, or other fashion to indicate the charge of battery  302 . 
     As is illustrated in  FIG. 3 , a feedback circuit is used to determine the ratio K between the battery current, battery voltage, and the resultant value of R eq . The calculated OCV and SOC using this method is much more accurate across temperature, load, state-of-charge, and battery aging. The fuel gauge no longer uses temperature information to determine OCV and SOC. If the battery chemistry is well known in the OCV/SOC table used by block  332 , even battery characterization can be eliminated. Since the value of AbsFullCap=ΔQ/ΔSOC, having a more accurate OCV and SOC determination will result in a more accurate tracking of the battery&#39;s full capacity. 
     Therefore, embodiments of the current invention determine the equivalent resistance R eq  based on the measured current and voltage through the battery according to a multiplication factor K, which is dynamically updated based on the integrated current, SOC, and other factors. A fuel gauge according to some embodiments will provide an output OCV that is much more accurate than conventional methods across temperature changes, device-to-device variation, different SOC % levels, different battery currents, and battery aging levels. 
     The above detailed description is provided to illustrate specific embodiments of the present invention and is not intended to be limiting. Numerous variations and modifications within the scope of the present invention are possible. The present invention is set forth in the following claims.