Abstract:
Systems and techniques for parallel battery balancing are described. A battery assembly comprises a first battery interface and a second battery interface; the first battery interface may connect to a first battery exhibiting a first voltage profile and the second battery interface may connect to a second battery exhibiting a second voltage profile. The battery assembly further comprises a current flow control mechanism to direct current flow to, from, and between the first battery and the second battery, with current directed to each battery being adapted so as to be compatible with the voltage profile of the battery.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates generally to linkage of multiple battery cells. More particularly, the invention relates to improved systems and techniques for balancing battery cells connected in parallel. 
       BACKGROUND 
       [0002]    With the introduction of portable wireless devices that have substantial capabilities and are heavily used, more attention has been paid to the potential benefits provided by longer-lasting, more powerful and versatile batteries and battery assemblies. One approach to achieving such improved batteries and battery assemblies is to use multiple battery cells. 
       SUMMARY 
       [0003]    In one embodiment of the invention, an apparatus comprises a first battery interface, a second battery interface connected in parallel to the first battery interface, and energy storage between the first battery interface and the second battery interface. The apparatus further comprises a current flow control mechanism for controlling current flow to at least one of the first battery interface, the second battery interface, and the energy storage, wherein the at least one of the switching mechanism and the energy storage are configured to provide a voltage adapted to a battery connected to the battery interface to which the current flow is directed, wherein a battery connected to the first battery interface exhibits a different voltage than does a battery connected to the second battery interface. 
         [0004]    In another embodiment of the invention, a mobile device comprises a first battery interface and a second battery interface connected in parallel to the first battery interface. The mobile device further comprises a current flow control mechanism for controlling current flow to at least one of the first battery interface and the second battery interface, wherein controlling current flow to and from the at least one of the first battery interface and the second battery interface is based at least in part on comparison between a voltage at the interface and a reference voltage value, wherein controlling the current flow comprises adjusting current flowing to the first battery interface so as to be compatible with a voltage profile exhibited at the first battery interface and adjusting current flowing to the second battery interface so as to be compatible with a voltage profile exhibited at the second battery interface. 
         [0005]    In another embodiment of the invention, a method comprises, for each of a first battery interface and a second battery interface connected in parallel in a battery assembly, comparing a voltage against a reference value and, based on the comparison between the voltage and the reference value, controlling current flow to and from each battery interface based on a comparison of the voltage and the reference value. Controlling the current flow comprises adjusting the current flowing to the second battery interface so as to be compatible with a voltage profile exhibited at the first battery interface and adjusting the current flowing to the first battery interface so as to be compatible with a voltage profile exhibited at the second battery interface. 
         [0006]    In another embodiment of the invention, a method comprises, for each of a first battery and a second battery connected in parallel in a battery assembly, comparing a battery voltage against a reference value and, based on the comparison between the battery voltage and the reference value, controlling current flow to and from each battery based on a comparison of the battery voltage and the reference value. Controlling the current flow comprises adjusting the current flowing to the second battery so as to be compatible with a voltage profile of the first battery and adjusting the current flowing to the first battery so as to be compatible with a voltage profile of the second battery. 
         [0007]    In another embodiment of the invention, an apparatus comprises means for comparing a battery voltage against a reference value for each of a first and a second battery interface connected in parallel in a battery assembly and means for controlling current flow to and from each battery interface based on a comparison of a battery voltage and the reference value. Controlling the current flow comprises adjusting the current flowing to the first battery interface so as to be compatible with a voltage profile exhibited at the second battery interface and adjusting the current flowing to the second battery interface so as to be compatible with a voltage profile exhibited at the first battery interface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  illustrates a battery assembly according to an embodiment of the present invention; 
           [0009]      FIG. 2  illustrates a state transition diagram according to an embodiment of the present invention; 
           [0010]      FIGS. 3-5  illustrate battery assemblies according to an embodiment of the present invention; and 
           [0011]      FIG. 6  illustrates a process according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Embodiments of the present invention recognize that one approach to achieving a desired battery capacity and other characteristics has been the connection of multiple cells in parallel. With a parallel connection, an assembly of cells performs similarly to a single cell with an equivalent total electrode area, but the use of an assembly provides for flexibility in physically arranging the cells and also avoids the use of a larger cell which might be more costly to manufacture, and therefore to purchase, than an equivalent group of cells. 
         [0013]    For assemblies consisting of multiple instances of the same cell, or of cells with the same characteristics, such connections are easily accomplished. However, the contemplated uses of electrical and electronic devices continue to increase, and the importance of supplying sufficient power associated with these uses also increases. Many usage scenarios have been contemplated in which a device might benefit from the parallel use of multiple cells, including the parallel use of multiple cells having different characteristics. 
         [0014]    One or more embodiments of the present invention recognize that while parallel connection of batteries of the same technology or chemistry is widely known and used, the use of different technologies or chemistries frequently presents voltage imbalances that impair or prevent successful use in a parallel connection. Embodiments of the invention further recognize that the benefits that may be afforded through parallel connection of cell having different chemistries or technologies. For example, one cell may provide higher power and another cell may provide higher energy, and a parallel connection of such cells would provide a combination of the maximized total power and maximized total energy of the cells. Other benefits may be achieved, such as providing a voltage matched to the high energy cell and to a chipset of the device. Embodiments of the present invention provide mechanisms to achieve these and other benefits by transferring charge between cells connected in parallel, and also recognize that the usefulness of such mechanisms is not limited to the use of different battery chemistries or technologies. For example, parallel connection using charge transfer mechanisms may provide a “hot swap” feature. Such a “hot swap feature provides the ability to remove and replace a discharged or partially discharged battery of a parallel connected battery package without powering down a device, because power is provided by a different battery of the package while the discharged battery is being removed and replaced. A user may, for example, benefit from the “hot swap” feature for example when making a call, listening to music or watching a video, or any time he or she wished to replace a battery without interrupting the use of a device being powered by the battery. 
         [0015]    Therefore, in one or more embodiments, the invention provides for mechanisms to transfer charge between cells, allowing cells having differing characteristics to be discharged and charged in parallel. One or more embodiments of the invention provide for a bidirectional buck/boost converter. In exemplary implementations, multiple cells may be configured so that peak power is provided by a stronger, higher rate cell or set of cells, while the load is connected. A predefined pulse width in a switch mode power supply may provide predetermined coupling between cells to maintain both at an optimized charge level. Charge levels may, for example, be optimized so that a higher power cell is maintained in full charge until a higher energy batter has been mostly discharged. In another exemplary implementation, coupling may be predetermined so that two different discharging voltage curves are followed to maintain equal charge levels at different voltages. 
         [0016]      FIG. 1  illustrates a simplified block diagram of a battery assembly  100  comprising a switch mode power supply (SMPS)  101  according to an embodiment of the present invention. The SMPS  101  comprises a charger  102 , a discharger  104 , and a sensing and control element  106 . The SMPS  101  connects to a device interface  108  of an electronic device, which may, for example, be a wireless communication device. The wireless communication device&#39;s battery assembly  100  may be charged with a device charger. The device charger may be a USB charger, a wireless charger, conventional AC adapter charger, or a solar charger, as an example. The device charger may be coupled or otherwise connected to the device interface  108  to provide charge to the battery assembly  100 . The sensing and control element  106  controls the operations of the charger  102  and discharger  104  depending on the relative voltages of a first battery  110 , connected to a first battery interface  111  and a second battery  112 , connected to a second battery interface  113 , as well as the direction of current flow between the SMPS  101  and the device interface  108 . For example, the first battery may be a slower charging, higher capacity battery, and the second battery may be a faster charging, lower capacity battery. 
         [0017]    Values taken into account in controlling the direction of charge and discharge are: 
         [0018]    V p : Voltage at the first battery  110   
         [0019]    V s : Voltage at the second battery  112   
         [0020]    V stop : Target voltage, below which charging of first battery stops 
         [0021]    V pmin : Minimum voltage at first battery  110   
         [0022]    V smin : Minimum voltage at second battery  112   
         [0023]    I c : Current flow between assembly  100  and device interface  108   
         [0024]    The battery assembly  100  operates in one or more of a number of different modes depending on the absolute and relative values of various voltages, currents, voltage parameters, and current parameters such as those listed above. 
         [0025]    A battery assembly such as the assembly  100  may suitably operate so as to maintain appropriate voltage profiles at the batteries or battery interfaces. A voltage profile may be, for example, a voltage level or a voltage range. A voltage profile may also comprise a voltage curve—that is, a change in voltage level over time. In one or more embodiments of the invention, the assembly operates to allow for compatibility between voltage profiles appearing at the interfaces, suitably by managing current flows between the interfaces  111  and  113 , the charger  102 , and the discharger  104 , so that appropriate voltage levels appear at the interfaces  111  and  113 . Compatibility between voltage profiles includes factors such as voltage levels at interfaces that avoid excessive differences, maintaining levels within an acceptable range over time, avoiding a level at one interface that will cause an excessive charge or discharge rate for a battery at another interface, and similar factors.  FIG. 2  illustrates a diagram  200  showing different operating modes for a battery assembly such as the assembly  100 . In the case of the assembly  100 , the sensing and control element  106  may place the assembly  100  in the correct mode by operating the charger  102  and the discharger  104  to achieve the correct operation for the mode. The operating modes may include a full power off mode  202 , an idle mode  204 , and a discharge mode  206 , as well as a second battery charging mode  208 , a first battery charging mode  210 , and a first and second battery charging mode  212 . The full power off mode  202  is entered in a transition  214  from the idle mode  204 , when V s &lt;V smin . When current is flowing into the battery assembly  100 , that is, when I c &gt;0, the assembly  100  leaves the full power off mode  202  by making a transition  216  to the second battery charging mode. The second battery is a faster charge, lower capacity battery, so its charging may begin first. 
         [0026]    Once the second battery voltage is no longer below the minimum needed for charging the first battery, that is, when V s ≧V stop , the assembly  100  makes a transition  218  to the first battery charging mode  210 . The assembly  100  may transition between charging the first battery and charging the second battery depending on the level of V s  relative to V stop , making the transition back to the second battery charging mode  208  when V s &lt;V stop . 
         [0027]    The second battery charging mode may also be entered in a transition  222  from the idle mode  204 , or a transition  224  from the discharge mode  206 , with each transition occurring when I c &gt;0. On the other hand, if the current begins flowing from the assembly  100  toward the device interface  108 , the assembly  100  will make a transition  226  from the second battery charging mode  208  to the discharge mode  206 , or a transition  228  from the first battery charging mode  210  to the discharge mode  206 . 
         [0028]    If the first battery voltage becomes equal or substantially equal to the second battery voltage, that is, if V p ˜V s , the assembly  100  makes a transition  230  from the first battery charging mode  210  to the both batteries charging mode  212 . If the current begins to flow toward the device interface  108  while the assembly  100  is in the both batteries charging mode  212 , the assembly  100  undergoes a transition  232  to the discharge mode  212 . Changes in modes may be achieved by adjustments of current, such as adjustment of current voltage levels or current directions, as well as rates of current flow. 
         [0029]      FIG. 3  illustrates the assembly  100  in the discharge mode  206 , showing current flow directions within the assembly  100 , that is, from the charger  102  and discharger  104 , and from the assembly  100  to the device interface  108 . Current is flowing to the device interface  108 , so that I c ≦0, and the discharger  102  is directing current from the first battery  110  to the second battery  112 . 
         [0030]      FIG. 4  illustrates a battery assembly  400  according to an embodiment of the present invention, illustrating electronic components that may be used to implement the assembly. The assembly  400  includes a first battery  402  and a second battery  404 , connecting to a device through an interface  405 . The connection between the first battery  402  and the second battery  404  takes the form of a reversible buck/boost converter, storing energy in an inductor  406 , with current control being accomplished using a first transistor  408  controlled by a pulse diode  410 , and a second transistor  412  controlled by a pulse diode  414 . 
         [0031]      FIG. 5  illustrates a more detailed view of a battery assembly  500  according to an embodiment of the present invention. The battery assembly  500  may suitably be used in a mobile telephone, mobile device or other suitable device coupled or otherwise connected to a device charger or incorporating a device charger. The battery assembly  500  may also be placed in a separate charging station, for example, so that the battery assembly  500  may be charged separately from usage in a device. When the battery assembly  500  is placed in a device, the device draws charge from the battery assembly  500  when no charging current is provided. At other times, an incorporated or separate charger may provide current to charge the battery assembly—for example, when the device is connected to line current or placed in a charging receptacle, or which the battery assembly  500  is separately placed in a charging stand. A device charger may be a USB charger, a wireless charger, conventional AC adapter charger, or a solar charger, as examples. 
         [0032]    The battery assembly  500  comprises a first battery  502  and a second battery  504 , as well as a charger  506  and a discharger  508 . The battery assembly provides switching to allow for the selection of current flow so that under different conditions, the assembly operates in one of a plurality of charge or discharge modes. Depending on the voltage levels of the batteries (which generally depend on charge levels), the first battery may supply the second while the second battery powers the device, the device may enter an idle state, or the device may enter a full power-off state. In the charge modes, the first battery, the second battery, or both, may be charged, depending on the voltage levels of the batteries, compared to one another or to thresholds. 
         [0033]    Switching is performed by transistors  512 ,  514 , and  516 , with control of the transistors  512 ,  514 , and  516  being provided by the sensing device  518 , which senses the presence of a device charger, based on charge current delivered through a conditioner  518 . The sensing device  522  performs input voltage tracking, and the sensing device  524  detects undervoltage of the first battery  502 , so that the battery assembly  500  may continue or cease operation. If the first battery remains at a sufficient voltage level, the second battery  504  may provide power for the device, while the second battery  504  is charged, or its level is maintained, using power from the first battery  502 , but if the first battery  502  can no longer maintain the sufficient voltage level, the assembly  500  may cause the device to enter an idle or power off mode. 
         [0034]      FIG. 6  illustrates a process  600  of battery control according to an embodiment of the present invention. The process  600  may be used, for example, to manage use of a battery assembly comprising a high power battery and a high energy battery connected in parallel, with the high power battery supplying power to a device and the high energy battery providing charge for the high power battery. At step  602 , an assembly comprising a high power battery and a high energy battery is connected to a device. At step  604 , upon detection that current is flowing toward the device interface, connected in parallel, the assembly is placed in a discharge mode, and voltage levels of the first and the second battery are sensed. At step  606 , upon detection that the first battery voltage is at a voltage allowing for charging of the second battery, the battery assembly is controlled so that current flows from the first battery to the second battery, with voltage adjustment between the first and second battery being accomplished by components of the assembly. 
         [0035]    At step  608 , upon detection that the first battery is below a minimum level, current flow to the second battery is stopped and the device is placed in an idle state. At step  610 , upon detection that the second battery is below a minimum level, the device is placed in a full power-off state. 
         [0036]    At step  612 , upon detection that charging current is available, that is, upon detection that current is flowing from a device interface to the battery assembly, the battery assembly is placed in a charging mode and charging current is directed to the second battery. At step  614 , upon detection that the second battery voltage is at a threshold voltage such that charging is not immediately needed, charging current is directed to the first battery. Charging may alternate between the first and the second battery as the voltage of the second battery rises above or falls below the threshold. At step  616 , upon detection that the first battery and second battery voltages are equal, charging current is directed so as to charge both batteries simultaneously. 
         [0037]    While various exemplary embodiments have been described above it should be appreciated that the practice of the invention is not limited to the exemplary embodiments shown and discussed here. Various modifications and adaptations to the foregoing exemplary embodiments of this invention may become apparent to those skilled in the relevant arts in view of the foregoing description. 
         [0038]    Further, some of the various features of the above non-limiting embodiments may be used to advantage without the corresponding use of other described features. 
         [0039]    The foregoing description should therefore be considered as merely illustrative of the principles, teachings and exemplary embodiments of this invention, and not in limitation thereof.