Patent Publication Number: US-10766368-B2

Title: Dual function battery system and method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/013,392, entitled “DUAL FUNCTION ENERGY STORAGE SYSTEM AND METHOD,” filed Aug. 29, 2013, which issued on Oct. 23, 2018 as U.S. Pat. No. 10,106,038, which claims benefit of U.S. Provisional Patent Application Ser. No.: 61/746,818, entitled “DUAL FUNCTION BATTERY SYSTEM DESIGN,” filed Dec. 28, 2012, and of U.S. Provisional Patent Application Ser. No.: 61/800,103, entitled “DUAL FUNCTION BATTERY SYSTEM DESIGN,” filed on Mar. 15, 2013, each of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     The present disclosure relates generally to the field of batteries and battery modules. More specifically, the present disclosure relates to battery cells that may be used in vehicular contexts, as well as other energy storage/expending applications. 
     This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     A vehicle that uses one or more battery systems for supporting propulsion, start stop, and/or regenerative braking functions can be referred to as an xEV, where the term “xEV” is defined herein to include all of the below described electrical vehicles, or any variations or combinations thereof. 
     A “start-stop vehicle” is defined as a vehicle that can disable the combustion engine when the vehicle is stopped and utilize a battery (energy storage) system to continue powering electrical consumers onboard the vehicle, including the entertainment system, navigation, lights, or other electronics, as well as to restart the engine when propulsion is desired. A lack of brake regeneration or electrical propulsion distinguishes a “start-stop vehicle” from other forms of xEVs. 
     As will be appreciated by those skilled in the art, hybrid electric vehicles (HEVs) combine an internal combustion engine (ICE) propulsion system and a battery-powered electric propulsion system, such as 48 volt, 130 volt, or 300 volt systems. The term HEV may include any variation of a hybrid electric vehicle, in which features such as brake regeneration, electrical propulsion, and stop-start are included. 
     A specific type of xEV is a micro-hybrid electric vehicle (“mHEV or “micro-HEV”). Micro-HEV vehicles typically operate at low voltage, which is defined to be under 60V. Micro-HEV vehicles typically provide start stop, and distinguish themselves from “start-stop vehicles” through their use of brake regeneration. The brake regeneration power can typically range from 2 kW to 12 kW at peak, although other values can occur as well. A Micro-HEV vehicle can also provide some degree of electrical propulsion to the vehicle. If available, the amount of propulsion will not typically be sufficient to provide full motive force to the vehicle. 
     Full hybrid electric vehicles (FHEVs) and Mild hybrid electric vehicles (Mild-HEVs) may provide motive and other electrical power to the vehicle using one or more electric motors, using only an ICE, or using both. FHEVs are typically high-voltage (&gt;60V), and are usually between 200V and 400V. Mild-HEVs typically operate between 60V and 200V. Depending on the size of the vehicle, a Mild-HEV can provide between 10-20 kW of brake regeneration or propulsion, while a FHEV provides 15-100 kW. The Mild-HEV system may also apply some level of power assist, during acceleration for example, to supplement the ICE, while the FHEV can often use the electrical motor as the sole source of propulsion for short periods, and in general uses the electrical motor as a more significant source of propulsion than does a Mild-HEV. 
     In addition, a plug-in electric vehicle (PEV) is any vehicle that can be charged from an external source of electricity, such as wall sockets, and the energy stored in the rechargeable battery packs drives or contributes to drive the wheels. PEVs are a subcategory of xEV that include all-electric or battery electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), and electric vehicle conversions of hybrid electric vehicles and conventional ICE vehicles. BEVs are driven entirely by electric power and lack an internal combustion engine. PHEVs have an internal combustion engine and a source of electric motive power, with the electric motive power capable of providing all or nearly all of the vehicle&#39;s propulsion needs. PHEVs can utilize one or more of a pure electric mode (“EV mode”), a pure internal combustion mode, and a hybrid mode. 
     xEVs as described above may provide a number of advantages as compared to more traditional gas-powered vehicles using only ICEs and traditional electrical systems, which are typically 12 volt systems powered by a lead acid battery. For example, xEVs may produce fewer undesirable emission products and may exhibit greater fuel efficiency as compared to traditional vehicles and, in some cases, such xEVs may eliminate the use of gasoline entirely, as is the case of certain types of BEVs. 
     As xEV technology continues to evolve, there is a need to provide improved power sources (e.g., battery systems or modules) for such vehicles. For example, it is desirable to increase the distance that such vehicles may travel without the need to recharge the batteries. Additionally, it may also be desirable to improve the performance of such batteries and to reduce the cost associated with the battery systems. 
     Conventional xEVs have been found to be functionally limited by their electric energy systems that supply power to their electric motor/generator and vehicle accessories. Typically, an electric motor is powered by an energy source that needs to store energy suitable for high-power discharges as well as for electric demands generated by various driving conditions. 
     Moreover, in conventional xEVs two or more different stored power distribution networks are required with different voltage levels to provide stored power to different power consuming loads of the vehicle. A typical Mild-HEV or FHEV usually contains a dual battery system. Unfortunately, the use of two batteries significantly adds to the complexity and cost of the hybrid vehicles. 
     Therefore, there is a need for a battery system that can handle the requirement for different voltage levels of an energy storage system without including a plurality of batteries. 
     SUMMARY 
     Disclosed herein is a dual function energy storage system and method for micro, mild, and full hybrid electric vehicles. 
     In one aspect, an energy storage system for a vehicle includes an energy storage unit having a plurality of energy storage modules connected in series, a plurality of sensing units for sensing state of charges of the plurality of energy storage modules, a pair of primary voltage terminals, wherein the series connected plurality of energy storage modules is connectable across the pair of primary voltage terminals to supply energy storage power at a first voltage level to support primary electrical functions of the vehicle, a pair of secondary voltage terminals, and an energy storage management system and a controller. The controller is configured to select a first subset of the plurality of energy storage modules to connect across the pair of secondary voltage terminals to supply energy storage power at a second voltage level, which is lower that the first voltage level, to support secondary electrical functions of the vehicle. Based on a sensed state provided by the plurality of sensing units, the controller determines whether the first subset of the plurality of energy storage modules should be disconnected from the pair of secondary voltage terminals and a second subset of the plurality of energy storage modules connected across the pair of secondary voltage terminals to continue supporting the secondary electrical functions of the vehicle. 
     In another aspect, a computer-implemented method for performing dual functions of an energy storage system in a vehicle includes providing stored electrical power for supporting primary electrical functions of the vehicle during a key-on state at a pair of primary voltage terminals of the energy storage system having a plurality of energy storage modules connected in series across the pair of primary voltage terminals, detecting when the vehicle has been turned off, and providing stored electrical power from a reduced number of the plurality of energy storage modules for supporting secondary electrical functions of the vehicle, thereby operating key-off loads of the vehicle at a pair of secondary terminals by connecting the reduced number of the plurality of energy storage modules across the pair of secondary terminals. 
     In yet another aspect, a computing system includes at least one processing unit and at least one memory unit storing instructions that are operable, when executed by the at least one processing unit, to cause the at least one processing unit to perform the above-introduced method. 
     These as well as other aspects, advantages, and alternatives will become apparent to those of ordinary skill in the art by reading the following detailed description, with reference where appropriate to the accompanying drawings. Further, it should be understood that the disclosure provided in this summary section and elsewhere in this document is intended to discuss the embodiments by way of example only and not by way of limitation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  is a perspective view of a vehicle (an xEV) having a battery system contributing all or a portion of the power for the vehicle, in accordance with an embodiment of the present approach; 
         FIG. 2  is a cutaway schematic view of the xEV embodiment of  FIG. 1  in the form of a hybrid electric vehicle (HEV), in accordance with an embodiment of the present approach; 
         FIG. 3  is a cutaway schematic view of an embodiment of the xEV of  FIG. 1  in the form of a micro-hybrid electric vehicle (Micro-HEV), in accordance with an embodiment of the present approach; 
         FIG. 4  is a schematic view of the Micro-HEV embodiment of  FIG. 3  illustrating power distribution throughout the Micro-HEV, in accordance with an embodiment of the present approach; 
         FIG. 5  is a block diagram illustrating an energy storage system (ESS) and components of the hybrid vehicle that are coupled to the ESS; 
         FIG. 6  is a schematic diagram illustrating an exemplary embodiment of a driving cycle as performed by a micro or mild hybrid electrical vehicle; 
         FIG. 7  is a schematic diagram illustrating an exemplary embodiment of an energy storage system including a plurality of storage modules and a battery management system; 
         FIG. 8  is a schematic diagram of a particular embodiment of the energy storage system of  FIG. 5  that provides power at 53V at a primary pair of voltage terminals and at 13V at a secondary pair of voltage terminals; 
         FIG. 9  is a schematic diagram of another particular embodiment of the energy storage system of  FIG. 5  that provides power at 48V at the primary pair of voltage terminals and at 12V at the secondary pair of voltage terminals; 
         FIG. 10  is a functional block diagram of the battery management system; 
         FIG. 11  is a flow chart of an operational process/method that illustrates a dual function of the energy storage system; 
         FIG. 12  is a block diagram illustrating components of a battery management system; and 
         FIG. 13  is a schematic diagram illustrating a conceptual partial view of an example computer program product. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying figures, which form a part hereof. In the figures, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, figures, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein. 
     As discussed above, there are several different types of xEVs. Although some vehicle manufacturers, such as Tesla, produce only xEVs and, thus, can design the vehicle from scratch as an xEV, most vehicle manufacturers produce primarily traditional ICEs. Thus, when one of these manufacturers also desires to produce an xEV, it often utilizes one of its traditional vehicle platforms as a starting point. As can be appreciated, when a vehicle has been initially designed to use a traditional electrical system powered by a single lead acid battery and to utilize only an ICE for motive power, converting such a vehicle into its HEV version can pose many packaging problems. For example, a FHEV uses not only these traditional components, but one or more electric motors must be added along with other associated components. As another example, a Micro-HEV also uses not only these traditional components, but a higher voltage battery (e.g., a 48V lithium ion battery module) must be placed in the vehicle to supplement or replace the 12V lead acid battery along with other components such as a belt integrated starter-generator, sometimes referred to as a belt alternator starter (BAS) as described in further detail below. Hence, if a battery system can be designed to reduce such packaging problems, it would make the conversion of a traditional vehicle platform into an xEV less costly and more efficient. As used herein, the BAS is not intended to be limited to a belt-driven alternator starter, as other types of drives could be used. 
     The battery systems described herein may be used to provide power to a number of different types of xEVs as well as other energy storage applications (e.g., electrical grid power storage systems). Such battery systems may include one or more battery modules, each battery module having a number of battery cells (e.g., lithium ion electrochemical cells) arranged to provide particular voltages and/or currents useful to power, for example, one or more components of an xEV. Presently disclosed embodiments include lithium ion battery modules that are capable of providing more than one voltage. In particular, certain disclosed battery systems may provide a first voltage (e.g., 12V), for example, to power ignition of a combustion engine using a traditional starter motor and/or support conventional 12V accessory loads, and may provide a second voltage (e.g., 48V), for example, to power a BAS and to power one or more vehicle accessories when the combustion engine is not running, for use in a micro-hybrid system for example. Indeed, in certain embodiments, not only may a single battery system provide two voltages (e.g., 12V and 48V), but it can provide them from a package having a form factor equivalent to a traditional lead acid 12V battery, thus making packaging and conversion of a traditional vehicle to a Micro-HEV simpler, less costly and more efficient. 
     Present embodiments also include physical battery module features, assembly components, manufacturing and assembling techniques, and so forth, that facilitate providing disclosed battery modules and systems that have a desired form factor (e.g., dimensions corresponding to a traditional lead acid battery). Further, as set forth in detail below, the disclosed battery module embodiments include a number of heat transfer devices (e.g., heat sinks, liquid-cooling blocks, heat transfer foams, phase change materials (PCMs), and so forth) that may be used to passively or actively maintain one or more temperatures of the battery module during operation. 
     With the foregoing in mind,  FIG. 1  is a perspective view of an xEV  10  in the form of an automobile (e.g., a car) having a battery system  20  in accordance with present embodiments for providing all or a portion of the power (e.g., electrical power and/or motive power) for the vehicle  10 , as described above. Although the xEV  10  may be any of the types of xEVs described above, by specific example, the xEV  10  may be a Micro-HEV, including an ICE equipped with a micro-hybrid system which includes a start-stop system that may utilize the battery system (energy storage system (ESS))  20  to power at least one or more accessories (e.g., AC, lights, consoles, etc.), as well as the ignition of the ICE, during start-stop cycles. 
     Further, although the xEV  10  is illustrated as a car in  FIG. 1 , the type of vehicle may differ in other embodiments, all of which are intended to fall within the scope of the present disclosure. For example, the xEV  10  may be representative of a vehicle including a truck, bus, industrial vehicle, motorcycle, recreational vehicle, boat, or any other type of vehicle that may benefit from the use of electric power. Additionally, while the battery system  20  is illustrated in  FIG. 1  as being positioned in the trunk or rear of the vehicle, according to other embodiments, the location of the battery system  20  may differ. For example, the position of the battery system  20  may be selected based on the available space within a vehicle, the desired weight balance of the vehicle, the location of other components used with the battery system  20  (e.g., battery management systems, vents or cooling devices, etc.), and a variety of other considerations. 
       FIG. 2  illustrates a cutaway schematic view of an embodiment of the xEV  10  of  FIG. 1 , provided in the form of an HEV having the battery system  20 , which includes one or more battery modules  22 . In particular, the battery system  20  illustrated in  FIG. 2  is disposed toward the rear of the vehicle  10  proximate a fuel tank  12 . In other embodiments, the battery system  20  may be provided immediately adjacent the fuel tank  12 , provided in a separate compartment in the rear of the vehicle  10  (e.g., a trunk), or provided in another suitable location in the xEV  10 . Further, as illustrated in  FIG. 2 , an ICE  14  may be provided for times when the xEV  10  utilizes gasoline power to propel the vehicle  10 . The vehicle  10  also includes an electric motor  16 , a power split device  17 , and a generator  18  as part of the drive system. 
     The xEV vehicle  10  illustrated in  FIG. 2  may be powered or driven by the battery system  20  alone, by the combustion engine  14  alone, or by both the battery system  20  and the engine  14 . It should be noted that, in other embodiments of the present approach, other types of vehicles and configurations for the vehicle drive system may be utilized, and that the schematic illustration of  FIG. 2  should not be considered to limit the scope of the subject matter described in the present application. According to various embodiments, the size, shape, and location of the battery system  20 , the type of vehicle, the type of xEV technology, and the battery chemistry, among other features, may differ from those shown or described. 
     The battery system  20  may generally include one or more battery modules  22 , each having a plurality of battery cells (e.g., lithium ion electrochemical cells), which are discussed in greater detail below. The battery system  20  may include features or components for connecting the multiple battery modules  22  to each other and/or to other components of the vehicle electrical system. For example, the battery system  20  may include features that are responsible for monitoring and controlling the electrical and thermal performance of the one or more battery modules  22 . 
       FIG. 3  illustrates a cutaway schematic view of another embodiment of the xEV  10  of  FIG. 1 , provided in the form of a Micro-HEV  10  having the battery system  20 . As discussed above, the battery system  20  for use with a micro-hybrid system of an Micro-HEV  10  may include a single battery that provides a first voltage (e.g. 12V) and a second voltage (e.g. 48V) and that is substantially equivalent in size to a traditional 12V lead acid battery used in traditional ICEs. Hence, such a battery system  20  may be placed in a location in the Micro-HEV  10  that would have housed the traditional battery prior to conversion to a Micro-HEV. For example, as illustrated in  FIG. 3 , the Micro-HEV  10  may include the battery system  20 A positioned similarly to a lead-acid battery of a typical combustion-engine vehicle (e.g., under the hood of the vehicle  10 ). By further example, in certain embodiments, the Micro-HEV  10  may include the battery system  20 B positioned near a center of mass of the Micro-HEV  10 , such as below the driver or passenger seat. By still further example, in certain embodiments, the Micro-HEV  10  may include the battery system  20 C positioned below the rear passenger seat or near the trunk of the vehicle. It should be appreciated that, in certain embodiments, positioning a battery system  20  (e.g., battery system  20 B or  20 C) in or about the interior of the vehicle may enable the use of air from the interior of the vehicle to cool the battery system  20  (e.g., using a heat sink or a forced-air cooling design, as set forth in detail below). 
       FIG. 4  is a schematic view of an embodiment of the Micro-HEV  10  of  FIG. 3  having an embodiment of an energy system  21  disposed under the hood of the vehicle  10  and includes battery system  20 . As previously noted and as discussed in detail below, the battery system  20  may further have dimensions comparable to those of a typical lead-acid battery to limit or eliminate modifications to the Micro-HEV  10  design to accommodate the battery system  20 . Further, the battery system  20  illustrated in  FIG. 4  is a three-terminal battery that is capable of providing two different output voltages. For example, a first terminal  24  may provide a ground connection, a second terminal  26  may provide a 12V output, and a third terminal  30  may provide a 48V output. As illustrated, the 48V output of the battery module  22  may be coupled to a BAS  29 , which may be used to start the ICE  33  during start-stop cycle, and the  12  V output of the battery module  22  may be coupled to a traditional ignition system (e.g., starter motor  28 ) to start the ICE  33  during instances when the BAS  29  is not used to do so. It should also be understood that the BAS  29  may also capture energy from a regenerative braking system or the like (not shown) to recharge the battery module  22 . 
     It should be appreciated that the 48 V and 12 V outputs of the battery module  22  may also be provided to other components of the Micro-HEV  10 . Examples of components that may utilize the 48 V output in accordance with present embodiments include radiator cooling fans, climate control fans, electric power steering systems, active suspension systems, electric air-conditioning systems, auto park systems, cooled seats, electric oil pumps, electric super/turbochargers, electric water pumps, heated seats, heated windscreen/defrosters, and engine ignitions. Examples of components that may utilize the 12 V output in accordance with present embodiments include window lift motors, vanity lights, tire pressure monitoring systems, sunroof motor controls, power seats, alarm systems, infotainment online features, navigation features, lane departure warning systems, electric parking brakes, and external lights. The examples set forth above are not exhaustive and there may be overlap between the listed examples. Indeed, for example, in some embodiments, features listed above as being associated with a 48 V load may utilize the 12 V output instead and vice versa. 
     In the illustrated embodiment, the 48 V output of the battery module  22  may be used to power one or more accessories of the Micro-HEV  10 . For example, as illustrated in  FIG. 4 , the 48 V output of the battery module  22  may be coupled to the heating, ventilation, and air conditioning (HVAC) system  32  (e.g., including compressors, heating coils, fans, pumps, and so forth) of the Micro-HEV  10  to enable the driver to control the temperature of the interior of the Micro-HEV  10  during operation of the vehicle. This is particularly important in a Micro-HEV  10  during idle periods when the ICE  33  is stopped and, thus, not providing any electrical power via engine charging. As also illustrated in  FIG. 4 , the 48 V output of the battery module  22  may be coupled to the vehicle console  34 , which may include entertainment systems (e.g., radio, CD/DVD players, viewing screens, etc.), warning lights and indicators, controls for operating the Micro-HEV  10 , and so forth. Hence, it should be appreciated that the 48 V output may, in certain situations, provide a more efficient voltage at which to operate the accessories of the Micro-HEV  10  (e.g., compared to 12 V), especially when the ICE  33  is stopped (e.g., during start-stop cycles). It should also be appreciated that, in certain embodiments, the 48 V output of the battery module  22  may also be provided to any other suitable components and/or accessories (e.g., lights, switches, door locks, window motors, windshield wipers, and so forth) of the Micro-HEV  10 . 
     Also, the Micro-HEV  10  illustrated in  FIG. 4  includes a vehicle control unit/module (VCM)  36  that may control one or more operational parameters of the various components of the vehicle  10 , and the VCM  36  may include at least one memory and at least one processor programmed to perform such tasks. Like other components of the Micro-HEV  10 , the battery module  22  may be coupled to the VCM  36  via one or more communication lines  38 , such that the VCM  36  may receive input from the battery module  22 , and more specifically, the battery control module (BCM) of the battery module  22  (discussed in detail below). For example, the VCM  36  may receive input from the battery module  22  regarding various parameters, such as state of charge and temperature, and the VCM  36  may use these inputs to determine when to charge and/or discharge the battery module  22 , when to discontinue charging the battery module  22 , when to start and stop the ICE  33  of the Micro-HEV  10 , whether to use the BAS  29  or the starter  28 , and so forth. 
     As stated above, a conventional Mild-HEV, Micro-HEV, or FHEV includes an ESS in which two or more batteries are provided to meet the requirement for different voltage levels to provide stored power to different power consuming loads of the vehicle. For example, one battery may be a typical lead-acid (Pb-acid) battery to manage the key-off load of the vehicle, such as intrusion alarm and the like, or other key-on accessories. The other battery, such as a Ni-metal-hydride battery or Li-ion battery, provides the primary electrical functions, such as power assistance during acceleration, power regeneration during deceleration and the like. Unfortunately, the use of two batteries significantly adds to the complexity and cost of the vehicles. This is partly due to the need for voltage/current/power regulation devices, such as DC-DC converters, in many applications. Also, with regard to the batteries being used to the vehicle&#39;s electrical accessories, such as key-off accessories, there is a risk of deep depletion that can damage the assigned battery. 
     Accordingly, the present disclosure is directed to a single battery system configured to provide both the key-on electrical function of the vehicle, such as power assistance during the vehicle&#39;s acceleration modes, power regeneration during the vehicle&#39;s deceleration modes, and cranking modes, and the key-off electrical functions when the vehicle&#39;s engine is off, such as the vehicle alarm, computing devices, and the like. As will be described in further detail hereafter, in accordance with one embodiment, the single battery system is coupled to an energy storage (battery) management system that selectively couples the single battery to a high voltage supply for the key-on electrical function, and to a low voltage supply for the key-off electrical function. 
     For the purposes of the present disclosure, it should be noted that the energy storage devices, battery modules, and systems illustrated and described herein are particularly directed to applications in providing and/or storing energy in xEV electric vehicles. 
     As discussed above, a micro-hybrid vehicle or a stop-start car may have an ICE that turns off when the vehicle comes to a stop, such as at an intersection. The micro-hybrid vehicle relies on an ESS at times to provide some or all power to a power network which powers the vehicle&#39;s electronics and accessories, such as air conditioning, radio and other electronics operating within the vehicle. In one embodiment, as shown in  FIG. 5 , the power to ESS  100  can be supplied through an integrated starter-generator (ISG)  114  that is configured as a two quadrant alternator connected to the ICE  33 . ISG  114  provides the functions of starting, generating and regenerating. As such, during a regenerative braking event, ISG  114  performs as a power regenerative device by converting the vehicle&#39;s kinetic energy into electrical energy, which is provided to ESS  100 . By providing some or all of the power to a power net which powers the vehicle&#39;s electronics and accessories, and by relying mainly on power from a renewable energy generating device, ESS  100  in a micro-hybrid vehicle can increase the vehicle&#39;s fuel economy. 
     The use of the terms battery, energy storage device, or energy storage systems are all intended to include any type of electrical energy storage devices including lead-acid battery, ultra-capacitor storage capacitors and all other energy storage devices of any type. 
     Now referring to  FIG. 5 , ESS  100  includes a single battery system  102 , and a battery management system  104 . As shown, single battery system  102  is coupled to electrical accessories that includes low voltage loads  105  and high voltage loads  107 , and to ISG  114 . Alternatively, battery management system  104  can be integrated into single battery system  102 . 
     As shown, ISG  114  is coupled to ICE  33 , and single battery system  102  is connected to receive from ISG  114  electrical energy converted from kinetic energy captured from drive train  35  during regenerative power events, such as when vehicle  10  is decelerating. Regeneration is achieved by heavily generating energy through ISG  114 , this in effect adds a negative torque to ICE  33  through a serpentine belt, slowing ICE  33  and converting this energy into electric power. Further, battery management system  104  is connected to VCM  36 , which is configured to communicate with ISG  114  to request a level of electric power to supply or generate to achieve smooth drivability during braking and acceleration events. VCM  36  also receives other data from multiple other sources, such as an environmental data source (not shown). The data from drive train  35  and the other sources of data obtained by VCM  36  are used by battery management system  104  to perform battery control functions, as described hereafter. 
     Now referring to  FIG. 6 , an exemplary embodiment  300  of a driving cycle  302  as performed by a Mild-HEV or Micro-HEV is shown. Driving cycle  302  includes six operational modes, which are a restart engine mode  304 , an acceleration mode  306 , a cruising mode  308 , a slow-down mode  310 , an engine-off mode  312 , and a stopped vehicle mode  314 . In one embodiment, during slowdown mode  310 , ESS  100  is configured to capture braking energy through regeneration of electrical power to raise the state of charge (SOC) of single battery system  102 . During engine-off mode  312 , ESS  100  is configured to support vehicle accessories, such as interior and exterior lights, infotainment, fans and blowers, and electronics based the current SOCs. During acceleration mode  306 , ESS  100  is configured to provide boosting power using ISG  114 . Though typically, engine-off mode  312  may be inhibited based on climate control demand and battery conditions, because of the regenerating energy captured during a slow-down event (i.e., braking event), ESS  100  is configured to enable activation of electric A/C. 
     Now referring to  FIG. 7 , an exemplary embodiment of dual function single battery system  102  includes a modular energy storage unit  400  connected to primary voltage terminals  404  and  405 . Modular energy storage unit  400  also has a plurality of intermediate taps or outputs that are connected to inputs  406 ,  408 ,  410 ,  412 , and  414  of BMS  104 , which in turn has a pair of outputs connected with a pair of secondary voltage terminals  415  and  416 . 
     Thus, both pairs of terminals  404  and  405 , and  415  and  416  are connected to modular energy storage unit  400 . In one embodiment, the terminals  405  and  416  are positive terminals, and the terminals  404  and  415  are negative terminals. In one embodiment, modular energy storage unit  400  includes three or more substantially identical energy storage modules  418 ,  420 , and  424 , each with at least one and preferably at least a pair of substantially identical cells  430  connected in series. There may also be other cells connected in parallel with cells  430 . All of the modules  418 ,  420 , and  424  are connected to each other and any other more modules that may be provided (as indicated by the broken line  432 ) in series across primary voltage terminals  404  and  405 . 
     In one embodiment, each of energy storage modules  418 ,  420 , and  424 , has at least one of the following characteristics: an equal number of energy storage cells that all produce power at approximately the same voltage; a plurality of energy storage cells connected in series, a plurality of cells connected in parallel; at least one energy storage cell with chemistry of one of (a)NCA, (b) NMC, (c) LiMn2O4; (d) a blend of the chemistries of (a), (b) and (c); cells with cathode material with cell chemistry that is olivine based material; cells with cathode material made of LiFe1-xPO4 in which x is greater or equal to zero and less than or equal to one; and cells with cathode material that is made of olivine material Zx doped LiFePO4, in which x is greater or equal to zero and less than or equal to one. 
     The term module, or battery module, should be understood to mean an energy storage module with one or more electrochemical or electrostatic cells connected in series or parallel combinations of such cells which parallel combinations are connected in series. An energy storage module is also an energy storage device that has opposite electrical poles accessible outside of the device in order that it may be individually switched into and out of service. For instance, an energy storage device that had only one energy storage cell with available poles would be considered a module, while a single cell connected in series with two other cells but without these connections being available for connection with other electrical element would not be considered an energy storage module. While illustrative examples are given below, the total cell count of all the modules within a given dual function energy storage device is flexible and not limited by these examples. 
     The different terminals, primary terminals  404  and  405 , and secondary terminals  415  and  416 , provide power at different voltage levels needed by different loads used when vehicle  10  is in a key-off mode and other loads used when vehicle  10  is in a key-on mode. Primary voltage terminals  404  and  405  are connected to one or more key-on high voltage loads  440  to enable primary voltage terminals  404  and  405  to provide a high voltage power supply needed for the primary functions of vehicle  10 , such as providing power assistance during acceleration, receiving power regeneration during deceleration, providing cranking power, providing motive power and the like. 
     On the other hand, secondary voltage terminals  415  and  416  are connected to one or more key-off low voltage loads  442 , such as an intrusion alarm system, an anti-theft GPS tracking device, a computer and the like, which only need low voltage power supply when the vehicle is in a key-off, non-operating mode. Additionally, or alternatively, secondary voltage terminals  415  and  416  are connected to one or more key-on relatively low voltage loads  444 , of vehicle  10 , such as air conditioning, heating and the like. 
     The voltages of key-off low voltage loads  442  may be in the range of approximately 7-volts to approximately 18-volts, while the voltage required by the high voltage loads may be as high as 660-volts for a heavy duty hybrid application and approximately 36-volts to 54-volts for a micro-hybrid application. 
     The junctions between modules  418  and  420  and between module  424  and whatever module with which it is contiguous, such as module  420  (if there are only three modules), are individually, respectively connected to individual ones of inputs  408 ,  410 , and  412 . In addition, the outer, or end, side of the end module  418 , opposite the interior junction connected to input  408 , is connected to an end, or outer, input  406  of BMS  104 . Likewise, the other outer side of the other end module  424 , opposite the junction connected to input  412 , is connected to another outer input  414  of BMS  104 . Broken line  432  should be understood to represent 1−N modules where N is any integer. Between these N modules there are N−1 junctions and each of these junctions are separately connected with BMS  104 . In one embodiment, modular energy storage unit  400  can include three modules, four modules, or any higher number of modules. Each one of these modules may have the same or different numbers of cells. 
     In one embodiment, BMS  104  is configured to selectively control when, which ones, and how many of modules  418 ,  420 , and  424  are connected with the secondary voltage terminals  415  and  416 . On the other hand, power being supplied to primary voltage terminals  404  and  405  is taken off the end poles, or outer poles, of end modules  418  and  424  such that power to primary voltage terminals  404  and  405  is provided from the entire group of energy storage modules that comprise modular energy storage unit  400 , which includes modules  418 ,  420 , and  424 , and if present, one or more modules that can be identical to or different from the modules  418 ,  420 , and  424  in terms of the number of cells  430 , for example. 
     In one embodiment, when power is being connected to secondary voltage terminals  415  and  416  by BMS  204 , power is taken from at least one but less than all the modules of modular energy storage unit  400  used to provide the high voltage power at primary voltage terminals  404  and  405 . Moreover, power for secondary voltage terminals  415  and  416  can be taken from only one of the modules, such as module  424 . As stated above, the low voltage range is from approximately seven (7) volts (V) to 8V to provide power to key-off voltage loads  442 , such as the vehicle alarm, computer and the like. In accordance with the present disclosure, the precise voltage that may be needed can be adjusted by altering the total number and type of energy storage cells  430  such that, for example, an industry standard of 12V for the secondary voltage level. However, preferably, the capacity of the dual function ESS  100  may range from less than four (4) ampere-hours (Ah), if ultra-capacitors are used for the energy storage devices, to more than 80 Ah, if lead acid batteries are used. 
     The relatively high voltage range that may be obtained also depends upon the type and size of the energy storage devices being used. Nominally, the high voltage range for micro-hybrid system is approximately 36V to 54V. In the case of a heavy duty hybrid application, the voltage provided at primary terminals  404  and  1405  may be as high as 600V. In general, it should be appreciated that the term relatively high voltage simply means a voltage that is relatively higher than the relatively low voltage, and vice versa. Inherently, the voltage provided at primary terminals  404  and  405  from all of the energy storage modules will be higher than the voltage provided by a one energy storage module or provided by number of energy storage modules less than the total number of energy storage modules in modular energy storage unit  400 . 
     Now referring to  FIG. 8 , an embodiment of a particular case of dual function battery system  102  that includes four modules (i.e., N is equal to four), and the high voltage produced from all four modules at primary voltage terminals  404  and  405  is approximately 53V. The various loads  440 ,  442 , and  444  are not shown for purposes of simplicity but the connections to these loads are the same as shown in  FIG. 7 . 
     In this embodiment, each of the four battery modules  518 ,  520 ,  522 , and  524  includes four cells for a total of sixteen cells, each of which produces approximately 3.3V. All the battery modules are preferably based on LiFePO4 chemistry. Primary voltage terminals  404  and  405  supply electrical power at a 53V level to high voltage loads  440 . Such relatively high voltage loads may include an electrical motor to provide electrical boost for the engine of vehicle  10  during acceleration, if vehicle  10  is a hybrid vehicle. Primary voltage terminals  404  and  405  also are connected to be charged by means of electrical regeneration during deceleration. The 53V of power available at primary voltage terminals  404  and  405  can also be used to provide cranking power to turn over and start ICE  33 . 
     Still referring to  FIG. 8 , the low voltage power provided at secondary voltage terminals  415  and  416  can be taken from only a single one of the four modules  518 ,  520 ,  522 , and  524  at a time, such as module  524 . As each of modules  518 ,  520 ,  522 , and  524  produces approximately 3.3 V, and thus approximately 13V is provided at secondary voltage terminals  415  and  416 . This low voltage at these secondary voltage terminals is connected to one or more key-off low voltage loads  442 , one or more key-on voltage loads  444 , or both. 
     Referring now to  FIG. 9 , another exemplary embodiment of dual function battery system  102  is configured with a high voltage of approximately 48V provided at high voltage supply terminals  404  and  405 , and a low voltage of approximately 12V is provided at the low voltage supply terminals  415  and  416 . In one embodiment, a first module  618  includes four identical cells  430 , and each of three other battery modules  620 ,  622 , and  624  includes three identical cells  632  connected in series. Cells  630  may be different from or be the same as cells  632 . In one embodiment, each of these thirteen cells has NCA cathode material with an average cell voltage of approximately 3.65V. Alternatively, the cell chemistry could be NMC, LiMn2O4, or blends of any of the three chemistries. 
     In this exemplary embodiment, module  618  uses four cells  630  to provide power at approximately 14.6V. The other three modules  620 ,  622 , and  624  use their respective three identical cells  632  to produce an average voltage output of approximately 11V. Thus, the supplied low voltage can be provided at approximately 12V with a range between approximately 11V and 15V. Advantageously, unlike the embodiments of  FIGS. 7 and 8 , in this embodiment of  FIG. 9 , the level of low voltage provided can be selectively changed simply by changing between two battery modules of different size and capacity, such as between energy storage module  618  and any one of energy storage modules  620 ,  622 , and  624 . 
     In keeping with one aspect of the disclosure, BMS  104  of all the embodiments of  FIGS. 7, 8, and 9  is configured to monitor the SOC of each of the associated modules and to selectively connect different ones of the modules to secondary voltage terminals  415  and  416  based on the measured SOCs. This is performed so as to prevent any one of the four battery modules, such as modules  618 - 624 , from becoming excessively discharged beyond a preselected minimum. For example, initially when vehicle  10  is shut off, BMS  104  is configured to, for instance, connect battery module  620  to secondary voltage terminals  415  and  416 . 
     Still referring to  FIG. 9 , in accordance with the present disclosure, when vehicle  10  is first shut off, all four battery modules  618 ,  620 ,  622 , and  624  may have an SOC of approximately sixty percent (60%) of a full, or maximum, charge. As time passes, module  622  is slowly discharged by its connection to a load and the SOC gradually declines. When the SOC has declined to a preselected minimum SOC limit, such as 40% of full SOC, BMS  104  switches out the coupling of first battery module  618  to secondary voltage terminals  415  and  416 , and then switches on the coupling to second battery module  620  to secondary voltage terminals  415  and  416 . When SOC of battery module  620  approaches the preselected SOC minimum (e.g., 40% of full SOC), then BMS  104  switches the coupling from second module  620  to third battery module  622 . Likewise, when the SOC of third battery module  622  decreases to 40%, BMS  104  substitutes the coupling to secondary voltage terminals  415  and  416  to fourth battery module  624  from third battery module  622 . Thus, later, when vehicle  10  is again being operated and single battery system  102  is being charged during a vehicle acceleration process or regenerative process, four battery modules  618 ,  620 ,  622 , and  624  will be automatically balanced with approximately equal charge. 
     Alternatively, cycling from one energy storage module to another for provision of the secondary voltage may be performed more rapidly, such as by switching from one energy storage module to another when the SOC level is approximately 10-30% different between modules. In such case switching from one energy storage module to the next could be performed with a timeframe of seconds to minutes. 
     In a key-off mode, modular energy storage unit  400  over time could become fully depleted, but in accordance with the disclosure, that can be prevented from happening. In one embodiment, when all of the energy storage modules of modular energy storage unit  400  have reached their respective lower limit SOCs (i.e., when almost depleted from a preselected low voltage limit), BMS  104  is configured to cause the disconnection of all the energy storage modules from secondary voltage terminals  415  and  416  and goes into a dead battery mode to prevent full depletion and resultant damage to the energy storage modules. When operation of vehicle  10  resumes, modular energy storage unit  400  will again become charged to a preselected level, normal operation of the dual function single battery system  102 . 
     Referring now to  FIG. 10 , an exemplary embodiment of a block diagram of BMS  104  configured to manage the dual function of single battery system  102  is shown. In accordance with the disclosure, BMS  104  includes a plurality of electronically controllable switches SW 1 , SW 2 , SW 3 , SW 4  SW 5 , SW 6 , SW 7  and SW 8   730 , interconnected with energy storage modules  718 ,  720 ,  722 , and  724  and secondary terminals  415  and  416  to collectively define a switching network. In one embodiment, energy storage modules  718 ,  720 ,  722 , and  724  include sensing units  742 ,  744 ,  746 , and  748 , respectively, which are configured to estimate a SOC of a corresponding energy storage module, or to provide relevant cell condition data to BMS  104  to determine the corresponding SOCs. Moreover, it should be appreciated that the term “switching network” is not intended to be limited to such a network with only eight switches, as needed for modular energy storage unit  400  with only four modules as shown in  FIG. 10 , but will have any suitable number of switches that are needed to individually connect each of the individual energy storage modules to secondary terminals  415  and  416 . Generally, for each one of N modules to be individually connected to secondary terminals  415  and  416 , BMS  204  may need  2 N switches, where N is an integer number. It should be understood that the term “switch” used here is intended to not be limiting but to include any device that is capable of being selectively changed between an electrically conductive state to a nonconductive state, such as a silicon controlled rectifier, a power transistor, a relay switch or any other like device. Although the connections are not shown for purposes of simplicity, all of switches  730  are connected with a controller  750 . 
     In one embodiment, upon detection of a key-off mode, VCM  36  is configured to trigger controller  750  to control switches  730  based on input signals received from sensing units  742 ,  744 ,  746 , and  748  to successively, individually connect energy storage modules  718 ,  720 ,  722 , and  724  to secondary voltage terminals  415  and  417 , as described above. Alternatively, BMS  104  includes a key-off detector configured to detect when the key of vehicle  10  has been turned to a key-off position. 
     As shown, switches SW 1 , SW 2 , SW 4  and SW 6  are connected to the positive poles of the first, second, third and fourth battery modules  718 ,  720 ,  722 , and  724  on one side and to the low voltage positive terminal  415 . Switches SW 3 , SW 5 , SW 7  and SW 8  are connected to the negative poles of the first, second, third and fourth battery modules  718 ,  720 ,  722 , and  724  on one side and to the negative low voltage terminal  416 . These switches may be selectively controlled to selectively, individually, connect each of the four battery modules  718 ,  720 ,  722 , and  724  across the secondary voltage terminals  415  and  415 , one at a time, as discussed above. 
     For instance, when energy stored in first battery module  718  is being supplied to a load, switches SW 1  and SW 3  may be actuated by an activation unit (e.g., controller  750 ) into a conductive on state and all the other switches are deactivated into a nonconductive off state. When it is time to substitute second battery module  720  for first battery module  718 , then switches SW 1  and SW 3  may be turned off, and switches SW 2  and SW 4  may be turned on. 
     Now referring to  FIG. 11 , a flow chart shows an exemplary embodiment of a computer-implemented method (process), initiated at Step  802 , for managing a dual function of an energy storage device. As stated above, BMS  104  is configured to provide stored electrical energy for operating vehicle  10  at primary energy storage terminals  404  and  405  of single battery system  102 , and for supplying stored electrical energy at secondary energy storage terminals  415  and  416  to low voltage loads during a key off state of vehicle  10 . VCM  36  is configured to monitor the operating mode of vehicle  10 . As such, based on data received from VCM  36 , BMS  104  is configured to determine whether vehicle  10  is in a key-on state, at Step  804 . In the affirmative, BMS  104  is configured to keep primary voltage terminals  404  and  405  connected to one or more key-on high voltage loads  440  to provide a high voltage power supply needed for the primary functions of vehicle  10 , at Step  806 . Otherwise, BMS  104  is configured to determine the SOC of each of the energy storage modules using data collected/sensed by sensors associated with the module cells, at Step  808 . Then, at Step  810 , BMS  104  determines which of the requirement of the low voltage load needs power supply. Upon determination of which of the requirement of the low voltage load (i.e., a key-off accessory load) needs power supply, at Step  812 , BMS  104  selects a first subset (one or more) of the energy storage modules that has a suitable SOC (i.e., an SOC that is above a predetermined low SOC limit) for coupling to secondary voltage terminals  415  and  416  to which the determined low voltage load is connected, at Step  814 . Following this coupling, BMS  104  is configured to track the SOC level of the coupled first subset of energy storage modules, at Step  816 . Then, at Step  818 , BMS  104  determines whether the SOC of the coupled first subset of energy storage modules declines to a level that is near the corresponding low SOC limit. In the negative, BMS  104  keeps on tracking its SOC level, at Step  816 . Otherwise, BMS  104  determines whether there is a second subset (one or more) of energy storage modules that has a suitable SOC to keep providing energy to the determined low voltage load, at Step  820 . In the affirmative, BMS  104  deactivates switches that couple the previously connected first subset of energy storage modules that now has an undesirable SOC level, and activate switches to couple the second subset of energy storage modules to secondary voltage terminals  415  and  416  to which the determined low voltage load is already coupled, at Step  822 . In the negative, BMS  104  goes into a dead battery mode to prevent full depletion and resultant damage to the energy storage modules. Thus, in accordance with this disclosure, BMS  104  is configured to successively connect subsets of the plurality of energy storage modules across secondary voltage terminals  415  and  416 , as each subset, in turn, becomes depleted to a preselected minimum SOC level. That is, BMS  104  establishes a preselected order of succession of connection of the plurality of energy storage modules. 
     Advantageously, with this method, the total energy stored of modular energy storage unit  400  that is used for power at a relatively high voltage when vehicle  10  is being operated in a key-on mode can be used for providing power for accessories needing power at a relatively lower voltage. In the case of using four energy storage modules, the key-off load can be supported four times longer than could be achieved with a single energy storage device being used as a separate accessory battery. 
     The relatively lower voltages that are provided to the pair of secondary voltage terminals, of course, may also be provided to other key-on accessories  444  but in such case there is less need to regularly exchange energy storage modules if modular energy storage unit  400  is recharged during operation by a regenerative power source, such as regenerative braking, etc. The need of another special battery for the accessories and the resultant cost and complexity are eliminated. Further, not one of the energy storage modules becomes depleted faster than any other one and power at the secondary voltage such that when recharged all cells become charged to approximately the same level. 
     It should also be understood that the voltage levels indicated above are merely exemplary and are not intended to be limiting. For instance, in the case of powering only the key off low voltage loads being powered and the key-off low voltage loads being only electronic devices, to increase efficiency the voltage on the pair of secondary terminals may be as low as 5V. Also, while the present disclosure eliminates the need for DC-DC converters, a DC-DC converter could still be connected to the pair of secondary voltage terminals to provide another voltage in addition to the voltage provided by the dual function, energy storage controller provided at the pair of secondary voltage terminals. 
     As shown in  FIG. 12 , the process performed by battery management system  104  includes an SOC module  902 , a switching control module  904 , an energy storage module selection module  906 . Battery management system  104  includes a processing unit  908 , and a memory unit  910  coupled to processing unit  908 . Processing unit  908  can be implemented on a single-chip, multiple chips or multiple electrical components. For example, various architectures can be used including dedicated or embedded processor or microprocessor (μP), single purpose processor, controller or a microcontroller (μC), digital signal processor (DSP), or any combination thereof. In most cases, each of processing unit  908  together with an operating system operates to execute computer code and produce and use data. Memory unit  910  may be of any type of memory now known or later developed including but not limited to volatile memory (such as RAM), non-volatile memory (such as ROM, flash memory, etc.) or any combination thereof, which may store software that can be accessed and executed by processing unit  908 , respectively, for example. 
     In some embodiments, the disclosed method may be implemented as computer program instructions encoded on a computer-readable storage media in a machine-readable format.  FIG. 13  is a schematic illustrating a conceptual partial view of an example computer program product  1000  that includes a computer program for executing a computer process on a computing device, arranged according to at least some embodiments presented herein. In one embodiment, the example computer program product  1000  is provided using a signal bearing medium  1001 . The signal bearing medium  1001  may include one or more programming instructions  1002  that, when executed by a processing unit may provide functionality or portions of the functionality described above with respect to  FIGS. 5-11 . Thus, for example, referring to the embodiment shown in  FIG. 11 , one or more features of blocks  802 - 824 , may be undertaken by one or more instructions associated with the signal bearing medium  1001 . 
     In some examples, signal bearing medium  1001  may encompass a non-transitory computer-readable medium  1003 , such as, but not limited to, a hard disk drive, memory, etc. In some implementations, the signal bearing medium  1001  may encompass a computer recordable medium  1004 , such as, but not limited to, memory, read/write (R/W) CDs, R/W DVDs, etc. In some implementations, signal bearing medium  1001  may encompass a communications medium  1005 , such as, but not limited to, a digital and/or an analog communication medium (e.g., a fiber optic cable, a waveguide, a wired communications link, etc.). 
     As utilized herein, the terms “approximately,” “about,” “substantially,” and similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. It should be understood by those of skill in the art who review this disclosure that these terms are intended to allow a description of certain features described and claimed without restricting the scope of these features to the precise numerical ranges provided. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and claimed are considered to be within the scope of the invention as recited in the appended claims. 
     One or more of the disclosed embodiments, alone or in combination, may provide one or more technical effects useful in the dual functioning of an energy storage system. The technical effects and technical problems in the specification are exemplary and are not limiting. It should be noted that the embodiments described in the specification may have other technical effects and can solve other technical problems. 
     While only certain features and embodiments of the disclosure have been illustrated and described, many modifications and changes may occur to those skilled in the art (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters (e.g., temperatures, pressures, etc.), mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the disclosure. Furthermore, in an effort to provide a concise description of the exemplary embodiments, all features of an actual implementation may not have been described (i.e., those unrelated to the presently contemplated best mode of carrying out the invention, or those unrelated to enabling the claimed invention). It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation specific decisions may be made. Such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure, without undue experimentation.