Abstract:
A vehicle includes a battery charger system arranged to charge a traction battery. The battery charger system receives current from a power distribution system remote from the vehicle and outputs the current to the traction battery at a series of magnitudes to characterize a charge efficiency profile of the battery charger and power distribution systems. The battery charger system then charges the traction battery according to the charge efficiency profile.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to processes, methods, algorithms and systems for charging automotive vehicle batteries. 
       BACKGROUND 
       [0002]    An alternatively powered vehicle such as a battery electric vehicle, plug-in hybrid electric vehicle, etc. typically includes a power storage unit (e.g., traction battery) used to store energy for moving the vehicle. Energy stored by this power storage unit may be replenished by electrically connecting a charging system associated with the power storage unit with a power distribution circuit remote from the vehicle (e.g., plugging in the vehicle). The cost to charge the power storage unit may depend on the time of day during which charging is performed and the efficiency of the charging operation. 
       SUMMARY 
       [0003]    A vehicle may include a traction battery and a battery charger system. The battery charger system may receive current from a power distribution system remote from the vehicle, output the current to the traction battery at a series of magnitudes to characterize a charge efficiency profile of the battery charger and power distribution systems, and charge the traction battery based on the charge efficiency profile. 
         [0004]    A battery charger system may include a controller arrangement that receives energy from a power distribution circuit defined by wiring connecting a power source remote from a vehicle and the controller arrangement and that outputs a charge current at a magnitude that depends on a resistance of the wiring. 
         [0005]    A battery charger system may receive current from a power distribution system remote from the vehicle, output the current to a traction battery at a series of magnitudes to characterize a charge efficiency profile of the battery charger and power distribution systems, and charge the traction battery based on the charge efficiency profile. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a block diagram of an alternatively powered vehicle. 
           [0007]      FIG. 2  is a flowchart illustrating an algorithm for charging a vehicle battery. 
           [0008]      FIG. 3  is a plot of charge current versus charge operation efficiency. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    Embodiments of the present disclosure are described herein; however, it is to be understood that the disclosed embodiments are merely examples and other embodiments may take various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures may be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, may be desired for particular applications or implementations. 
         [0010]    A charger of an electrified vehicle has a peak efficiency when transferring energy from an external source to the battery. This peak efficiency may vary depending on the design of the charger but is typically about 90%. The charger, however, is only one of the subsystems enabled during charge. Other vehicle subsystems, such as cooling subsystems, etc., may shift the peak efficiency higher or lower depending on the specific design. Additionally, the electrical supply system providing power to the vehicle has losses that impact peak efficiency. Performing the charge operation at or near the system peak efficiency may minimize the cost associated with charging the battery. 
         [0011]    Referring to  FIG. 1 , an automotive vehicle  10  may include a battery charger system  12 , traction battery  14 , and auxiliary battery  16 . The vehicle  10  may further include an electric machine  18 , transmission  20 , and wheels  22 . The battery charger system  12  is electrically connected with the traction and auxiliary batteries  14 ,  16  (as indicated by thin line). The traction battery  14  is further electrically connected with electric machine  18  (as indicated by thin line). The transmission  20  is mechanically connected with electric machine  18  and wheels  22 . Other vehicle arrangements, such as a plug-in hybrid electric vehicle, etc., are also contemplated. 
         [0012]    The battery charger system  12  may be electrically connected with a power grid/plant  24  via a fuse box/power meter  26  (as indicated by thin line). That is, the vehicle  10  may be plugged in to a wall outlet (not shown) of a residential or commercial building. The power cord and associated wiring electrically connecting the battery charger system  12  to the wall outlet and the wiring electrically connecting the wall outlet and fuse box  26  is represented by a line  28 , neutral  30 , and ground  32 . Hence, electrical energy from the power grid  24  may pass through the fuse box  26  and to the battery charger system  12 . 
         [0013]    The battery charger system  12  may charge either or both of the traction and auxiliary batteries  14 ,  16 . In the example of  FIG. 1 , the battery charger system  12  has a high voltage output  34  electrically connected with the traction battery  14  and a low voltage output  36  electrically connected with the auxiliary battery  16 . The battery charger system  12 , in other examples however, may charge only the traction battery  14 . A plug-in hybrid electric vehicle, for example, may include a battery charger system with a high voltage output electrically connected with a traction battery, and a combustion engine arranged to drive an alternator electrically connected with an auxiliary battery. 
         [0014]    The electric machine  18  is arranged to receive electrical energy from the traction battery  14  and convert this electrical energy to mechanical energy. This mechanical energy is used to drive the transmission  20  and wheels  22  to move the vehicle  10 . The transmission  20 , in other examples, may also be driven by a combustion engine, fuel cell, etc. 
         [0015]    The net efficiency, η charge , of the systems/subsystems affecting the charge operation may be given by 
         [0000]    
       
         
           
             
               
                 
                   
                     η 
                     charge 
                   
                   = 
                   
                     
                       P 
                       HVbattery 
                     
                     
                       
                         P 
                         ACline 
                       
                       + 
                       
                         Δ 
                          
                         
                             
                         
                          
                         
                           P 
                           loss_ACline 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where P HVbattery  is the power output by the battery charger system  12  to the traction battery  14 , P ACline , is the power input to the battery charger system  12 , and ΔP loss     —     Annie  is the I 2 R losses in the line  28  and neutral  30 . Put another way (assuming unity power factor), 
         [0000]    
       
         
           
             
               
                 
                   
                     P 
                     HVbattery 
                   
                   = 
                   
                     
                       I 
                       HVbattery 
                     
                     * 
                     
                       V 
                       HVbattery 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
             
               
                 
                   
                     P 
                     acline 
                   
                   = 
                   
                     
                       I 
                       ACline_input 
                     
                     * 
                     
                       V 
                       ACline_input 
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
             
               
                 
                   
                     Δ 
                      
                     
                         
                     
                      
                     
                       P 
                       loss_ACline 
                     
                   
                   = 
                   
                     
                       I 
                       ACline_input 
                       2 
                     
                     * 
                     
                       R 
                       ACline 
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
             
               
                 
                   
                     R 
                     ACline 
                   
                   = 
                   
                     
                       Δ 
                        
                       
                           
                       
                        
                       
                         V 
                         ACline_input 
                       
                     
                     
                       I 
                       
                         ACline_input 
                          
                         _test 
                       
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where I HVbattery  is the charge current provided by the battery charger system  12  to the traction battery  14 , V HVbattery  is the voltage of the traction battery  14 , I ACline     —     input  is the current input to the battery charger system  12 , V ACline     —     input  is the voltage input to the battery charger system  12 , and ΔV ACline     —     input  is the difference in voltage between the line  28  and neutral  30  before and after a constant current, I ACline     —     input     —     test , is drawn by the battery charger system  12 . I ACline     —     input     —     test  can be any reasonable current capable of being drawn by the battery charger system  12 . Hence, R Anine  represents the resistance as seen at the input of the battery charger system  12  from the power grid  24 —the dominant factor being the resistance of the line  28  and neutral  30 . Each of these parameters may be measured via known sensors provided with the battery charger system  12 . For example, the battery charger system  12  may include current and voltage sensors (not shown) operatively arranged with the high voltage output  34 , a current sensor (not shown) operatively arranged with the line  28 , etc. (Equations (2)-(5) may be modified as known in the art to account for power factors other than unity.) 
         [0016]    The efficiency of the battery charger system  12 , as mentioned above, may be affected by other systems/subsystems operable during battery charge. Hence, the battery charger system  12  may evaluate its efficiency within the context of the systems/subsystems to which it is electrically connected according to (1) and select a charge current for the traction battery  14  that maximizes charge efficiency while meeting any other imposed constraints such as charge duration, etc. 
         [0017]    Referring to  FIG. 2 , a charge current for a high-voltage battery may be swept through some predetermined range and electrical system parameters associated therewith may be measured at operation  38 . The battery charger system  12 , for example, may operate to output a series of charge currents for the traction battery  14 . For each charge current, the battery charger system  12  may measure the associated parameters detailed in equations (2)-(5). At operation  40 , system efficiency may be determined as a function of charge current. For example, the battery charger system  12  may determine the efficiency associated with each charge current according to (1) using the parameters measured at operation  38 . Referring to  FIG. 3 , the battery charger system  12  may operate, for a brief time, to output  13  different charge currents to the traction battery  14  to characterize the efficiency profile associated with the charge operation. Any number of test currents/current sweep schemes, however, may be used. System efficiency may then be reported as a function of charge current. 
         [0018]    Referring again to  FIG. 2 , the charge current associated with peak system efficiency may be selected at operation  42 . The battery charger system  12  may identify, for example, the charge current corresponding to the maximum system efficiency. Referring to  FIG. 3 , the optimum charge current has been labeled. That is, the charge current yielding peak system efficiency has been identified. 
         [0019]    Referring again to  FIG. 2 , it is determined whether charging with the identified battery charge current will exceed the available charge time at operation  44 . Assuming, for example, that the charge current identified at operation  42  is 4 A (with an associated system peak efficiency of 90%), a charge rate of 4 A-hrs/hr may result. If the traction battery  14  needs to receive 16 A-hrs of capacity in order to achieve a target state of charge, the associated charge time at the peak efficiency is 4 hours. If, however, the available charge time is 3 hours, the traction battery will not achieve its target state of charge at the expiration of the available charge time. 
         [0020]    Any known/suitable technique may be used to determine the capacity required to raise the state of charge of the battery from a given value to a target value. For example, if the initial state of charge is 50% and the maximum capacity of the battery is 32 A-hrs, then 16 A-hrs is required to raise the state of charge from 50% to a target of 100% assuming the state of charge is proportional to the capacity of the battery. 
         [0021]    Any known/suitable technique may be used to determine the available charge time. A driver of the vehicle  10 , for example, may provide input specifying the available charge time. Alternatively, a fixed available charge time may be set by the manufacturer of the vehicle  10 . Learning algorithms may also be used to estimate the available charge time given usage patterns of the vehicle  10 , etc. 
         [0022]    Returning to operation  44 , if yes, the charge current may be set to meet the available charge time at operation  46 . Referring again to  FIG. 3 , the minimum charge current necessary to charge the traction battery  14  to the target state of charge within the available charge time has been labeled. This minimum current value, in one example, may be found by dividing the A-hrs necessary to achieve the target state of charge by the available charge time. Other methods, however, are also contemplated. Of the charge currents capable of meeting the available charge time, the minimum charge current is the most efficient in this example. Hence, the charge current for the traction battery  14  may be set to the identified minimum value. Values greater than the minimum value may also be selected. Charging at these values, however, will result in a less efficient charge cycle according to this example. In other examples, a charge current greater than the minimum may be the most efficient. 
         [0023]    At operation  48 , the battery is charged with the selected charge current. The battery charger system  12  may, for example, charge the traction battery with the minimum charge current necessary to meet the charge time illustrated in  FIG. 3 . 
         [0024]    Returning to operation  44 , if no, the charge current is kept at the optimum charge current. In these circumstances, the optimum charge current is of sufficient magnitude to raise the state of charge of the traction battery  14  to the target within the time allotted. The algorithm then proceeds to operation  48 . In other examples, operations  44 ,  46  may, of course, be omitted. 
         [0025]    Referring again to  FIG. 1 , not shown is a DC/DC converter, alternator, etc. that during normal vehicle drive operation may provide energy to the auxiliary battery  16  and the electrical subsystems connected therewith. In most charge cases, the auxiliary battery  16  will have already been fully charged by the DC/DC converter and may not require additional energy. If, however, there is a need for the auxiliary battery  16  to be charged, equation (1) may be modified using known techniques to consider power directed to the auxiliary battery  16 . Considering the most common case where the auxiliary battery  16  is near or at full charge, any power being supplied to the auxiliary battery  16  is power used by loads connected therewith. These loads reduce the amount of power available to charge the traction battery  14  and can be thought of as charge system losses. Equation (1) as written considers these losses. 
         [0026]    Conditions may change during charging of the traction battery  14  resulting in a change in the system peak efficiency. Due to these changes, it may be desirable to repeat the algorithm of  FIG. 2  periodically during charging. As the traction battery voltage increases during charge, for example, the AC line voltage, resistance, etc. may change, which may shift the optimal efficiency point. As a result, the casual observer may observe a charge system changing its charge rate as AC line resistance increases if implementing certain of the processes, methods, etc. detailed herein. 
         [0027]    The losses that increase exponentially with power level noticeably impact the ideal lower cost operating point of the system when implemented on a vehicle. The exponential losses within the charger may be small relative to other charger losses. A maximum charge rate based on available power from the AC line may be an acceptable choice for operation. The addition of charge and battery cooling system may add exponentially increasing power losses with increasing charge power levels resulting in a selection of a less than maximum charge rate. With the further addition of the wire I 2 R losses in the line  28  and neutral  30 , there will be an additional reduction in the ideal charge rate. Hence, if a charge system considers wire I 2 R losses when selecting its charge rate, increasing the length (resistance) of the wires will result in the charge system selecting a lower charge rate (assuming there is sufficient charge time to complete the charge operation at the lower charge rate.) 
         [0028]    The processes, methods, or algorithms disclosed herein may be deliverable to/implemented by a processing device, controller, or computer, which may include any existing programmable electronic control unit or dedicated electronic control unit. Similarly, the processes, methods, or algorithms may be stored as data and instructions executable by a controller or computer in many forms including, but not limited to, information permanently stored on non-writable storage media such as ROM devices and information alterably stored on writeable storage media such as floppy disks, magnetic tapes, CDs, RAM devices, and other magnetic and optical media. The processes, methods, or algorithms may also be implemented in a software executable object. Alternatively, the algorithms may be embodied in whole or in part using suitable hardware components, such as Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), state machines, controllers or other hardware components or devices, or a combination of hardware, software and firmware components. 
         [0029]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. For example, the line  28  and neutral  30  were described within the context of a 120 V AC distribution system common to the United States. It is also contemplated, however, that the disclosure herein applies to other AC voltage systems. The words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the disclosure and claims. As previously described, the features of various embodiments may be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments may have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics may be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes may include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.