Abstract:
An automotive vehicle may include a plurality of solar cells electrically connected to form a solar panel array having a minimum output voltage at a specified standard solar irradiance. The vehicle may also include a battery pack having an output voltage at least equal to the minimum output voltage of the array and configured to provide energy for moving the vehicle. The vehicle may further include a controller configured to selectively electrically connect the array and battery pack to trickle charge the battery pack.

Description:
BACKGROUND 
     Alternatively powered vehicles such as hybrid electric vehicles, plug-in hybrid electric vehicles and battery electric vehicles may use an electric machine to convert energy stored in a high-voltage battery to motive power. For hybrid electric vehicles, the high-voltage battery may store energy converted by an internal combustion engine or captured from regenerative braking events. The high-voltage battery of plug-in hybrid electric vehicles may additionally store energy received from a utility grid. Likewise, the high-voltage battery of battery electric vehicles may store energy received from a utility grid. 
     Certain of the above energy sources may have a cost associated with them. An internal combustion engine of a hybrid electric vehicle, for example, may burn gasoline to convert energy for storage by the high-voltage battery. This gasoline, of course, must be purchased. Utility grids likewise charge for the electric power they supply. The energy captured from regenerative braking events, in contrast, does not have such a direct cost. In a sense, it is free energy. It may thus be desirable to charge a high-voltage battery of an alternatively powered vehicle with energy that does not impose a direct cost on the driver. 
     SUMMARY 
     An automotive vehicle may include a traction battery having an output voltage at a target state of charge and a solar panel array having an output voltage, if exposed to a specified standard solar irradiance, at least equal to the output voltage of the traction battery at the target state of charge. Other arrangements and configurations are also described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an embodiment of a power system of an alternatively powered vehicle. 
         FIG. 2  is a schematic diagram of the solar panel array of  FIG. 1 . 
         FIG. 3  is a schematic diagram of the power system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Solar energy may be captured via solar cells and used to charge a high-voltage battery of and alternatively powered vehicle. Typically, solar cells having a low voltage output are arranged in a strategic location on a vehicle&#39;s exterior. The solar cells are electrically connected with a DC/DC boost converter that boosts the voltage output by the solar cells to a level near that of the high-voltage battery to be charged. A high-voltage bus electrically connects the DC/DC boost converter and high-voltage battery. 
     DC/DC boost converters may be inefficient. Substantial portions of the energy captured via the solar cells may thus be lost as heat during the boosting process. Relatively speaking, solar cells may only capture small amounts of energy. Losses of this energy during the boosting process may make charging the high-voltage battery with solar energy impractical. 
     The electrical connection of a high-voltage battery of an alternatively powered vehicle and an electric machine may be facilitated by a set of contactors (main contactors). That is, these contactors may be closed to establish the electrical connection. Main contactors are typically sized to handle, relatively speaking, large amounts of current (e.g., 100+A). 
     Typically, solar cells of an alternatively powered vehicle are electrically connected with the vehicle&#39;s high-voltage battery via the main contactors. Because of the main contactors&#39; size, a substantial amount of energy (e.g., 12 W holding/steady state, 240 W peak) may be required to close the main contactors relative to the amount of energy captured via the solar cells. So much so, that it may make charging the high-voltage battery with solar energy impractical. 
     Certain embodiments disclosed herein may provide a solar panel array that may be electrically connected with a high-voltage battery. The solar panel array&#39;s output voltage may be such that a DC/DC boost converter may not be needed to boost the solar panel array&#39;s output in order to trickle charge the high-voltage battery. As an example, an array may have an output voltage of at least 200 V at a standard solar irradiance of 1000 W/m 2 . Hence, less energy may be lost as heat in such configurations relative to those including a DC/DC boost converter. 
     Certain embodiments disclosed herein may provide an electrical infrastructure to electrically connect a solar panel array with a high-voltage battery. This electrical infrastructure may require less energy to establish the electrical connection between the array and battery as compared with arrangements where main contactors are closed to establish the connection. A separate (smaller) set of switches/contactors/relays, as an example, may be closed to electrically connect the array and battery. More energy, as a result, may be used to charge the battery. 
     Referring to  FIG. 1 , an alternatively powered vehicle  10  may include a high voltage traction battery  12  (e.g., 200+V at 70% SOC), electric machine  14  (e.g., motor, generator, inventers, etc.), contactors  16  (main contactors), traction battery control module (TBCM)  18  and other powertrain components  20  (e.g., engine, transmission, etc.) The traction battery  12  and electric machine  14  are electrically connected with the contactors  16 . When appropriately closed by the TBCM  18  as discussed below, the contactors  16  permit energy to flow between the traction battery  12  and electric machine  14 . 
     The electric machine  14  and powertrain components  20  are mechanically connected. As such, the electric machine  14  may convert electrical energy from the traction battery  12  to mechanical energy for the powertrain components  20  and visa versa. 
     The vehicle  10  may further include a high voltage solar panel array  22 , output terminals  23  ( FIG. 3 ), solar panel array activation system  24 , multiple power point tracker (MPPT)  26 , and solar cell controller (SCC)  28 . The solar panel array  22 , MPPT  26  and SCC  28  are electrically connected with the output terminals  23 . The SCC  28  may be a separate controller or integrated within a vehicle system controller, hybrid control module unit, or powertrain control module, etc. As discussed in more detail below, the activation system  24  and MPPT  26 , under the control of the SCC  28 , permit energy from the solar panel array  22  to charge the traction battery  12  without having to close any of the contactors  16 . Of course, other arrangements are also possible. 
     In the embodiment of  FIG. 1 , the solar panel array  22  includes a plurality of relatively small (e.g., 50 mm×120 mm) solar cells  30   n  ( 30   a ,  30   b , etc.) electrically connected in series. Each of the cells  30   n  has an effective V cell  (e.g., of about 0.5 V at a standard solar irradiance of 1000 W/m2) and low current (e.g., 150 mA—note that current depends on cell area) output. The cells  30   n  are of sufficient number such that their collective output, at a standard solar irradiance of 1000 W/m2, is, for example, at least equal to the voltage of the traction battery  16  at 70% SOC (e.g., 200 V). This arrangement permits the solar panel array  22  to be directly electrically connected to the traction battery  12  (whether or not a MPPT is used). 
     The MPPT  26  of  FIG. 1  may be used to operate the solar panel array  22  at its peak efficiency in any suitable known fashion. In the embodiment of  FIG. 1  for example, the MPPT  26  is a high efficiency DC/DC buck converter that may extract maximum power from the solar panel array  22 . Other suitable/known MPPT configurations, however, are also possible. 
     The number, n, of cells  30   n  may be determined based on the following equation 
                   n   =         N   HVBatCells     ⁡     (       V     HVBatCEllOCV   @   HiSOC       +     Δ   ⁢           ⁢     V     HVBatCellOCV   @   HiSOC           )         V   i               (   1   )               
where N HVBatCells  is the number of battery cells in the traction battery  12 , V HVBatCellOCV@HiSOC  is the traction battery individual cell open circuit voltage at a high (or target) SOC (e.g., a SOC around 70% and an open circuit voltage at that SOC around 1.7 V), ΔV HVBatCellOCV@HiSOC  is the traction battery individual cell extra voltage rise when a low amount of charge current is passed through the individual battery cell, V i  is the individual solar cell open circuit voltage at a standard solar irradiance of 1000 W/m 2 , and i can be written as follows
 
 i= 1,2 , . . . ,k− 1 ,k,k+ 1 , . . . ,m− 1 ,m,m+ 1 , . . . ,n− 1 ,n   (2)
 
(1) may be re-written as
 
                   n   =         V     HVBatOCV   @   HiSOC       +     Δ   ⁢           ⁢     V     HVBatOCV   @   HiSOC             V   i               (   3   )               
where V HVBatCellOCV@HiSOC  is the traction battery open circuit voltage at a high (or target) SOC (e.g., a SOC around 70% and an open circuit voltage at that SOC around 270 V—assuming that all of the individual battery cells in the traction battery  12  are balanced and at the same SOC), and ΔV HVBatCellOCV@HiSOC  is the traction battery extra voltage rise when a low amount of charge current is passed through the traction battery  12 . Any suitable relation and/or technique, however, may be used to determine the number, n, of cells  30   n  (or any other parameters herein).
 
     Referring to  FIG. 2 , the solar panel array  22  includes n number of individual solar cells  30   n  connected in series to achieve a high voltage output. The output open circuit voltage of the solar panel array  22  is given by 
                     V     s   ⁢           ⁢   _   ⁢           ⁢   ocv       =       ∑     i   =   1     n     ⁢     V   i               (   4   )               
Assuming similar characteristics for each solar cell  30   n , (4) can be re-written as
 
                     V     s   ⁢           ⁢   _   ⁢           ⁢   ocv       =         ∑     i   =   1     n     ⁢     V   i       =     nV   i               (   5   )               
Substituting (3) into (5) results in
 
     
       
         
           
             
               
                 
                   
                     V 
                     
                       s 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       _ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       ocv 
                     
                   
                   = 
                   
                     
                       
                         ∑ 
                         
                           i 
                           = 
                           1 
                         
                         n 
                       
                       ⁢ 
                       
                         V 
                         i 
                       
                     
                     = 
                     
                       
                         nV 
                         i 
                       
                       = 
                       
                         
                           V 
                           
                             HVBatOCV 
                             @ 
                             HiSOC 
                           
                         
                         + 
                         
                           Δ 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             V 
                             
                               HVBatOCV 
                               @ 
                               HiSOC 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     The solar panel array  22 , in the embodiment of  FIG. 2 , also includes Schotky bypass diodes, D 1 , D 2 , . . . , D p , that may be placed every k solar cells to ensure that optimum power can be generated under, for example, cell shading conditions. Hence, cells whose current drops as a result of shading may be bypassed. 
     In order to achieve a desired maximum power output, P s , of the solar panel array  22 , the area of each of the individual solar cells  30   n  may be selected based on P s . That is, P s  of the solar panel array  22  may be used to determine the short circuit current of the solar panel array, I SC , and the short circuit current of the individual cells, I i . I i  may then be used to determine the area of each of the individual solar cells  30   n  as given by 
                     I   sc     =       P   s         V     s   ⁢           ⁢   _   ⁢           ⁢   ocv       -     Δ   ⁢           ⁢     V     s   ⁢           ⁢   _   ⁢           ⁢   ocv                     (   7   )               
where ΔV S     —     OCV  is the voltage below which the current output of the solar panel array  22  is approximately constant or close to I SC .
 
     Because the individual solar cells  30   n  are connected in series, I SC  is the same as I i . Hence (7) can be re-written as follows for the individual solar cells  30   n   
                     I   i     =       I   sc     =         P   s         V     s   ⁢           ⁢   _   ⁢           ⁢   ocv       -     Δ   ⁢           ⁢     V     s   ⁢           ⁢   _   ⁢           ⁢   ocv             =           P   s     /   n         (       V     s   ⁢           ⁢   _   ⁢           ⁢   ocv       -     Δ   ⁢           ⁢     V     s   ⁢           ⁢   _   ⁢           ⁢   ocv           )     n       =       P   i         V   i     =     Δ   ⁢           ⁢     V   i                         (   8   )               
By solving for V i  from (6) and substituting into (8), we find that
 
     
       
         
           
             
               
                 
                   
                     I 
                     i 
                   
                   = 
                   
                     
                       P 
                       i 
                     
                     
                       
                         ( 
                         
                           
                             
                               V 
                               
                                 HVBatOCV 
                                 @ 
                                 HiSOC 
                               
                             
                             + 
                             
                               Δ 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               
                                 V 
                                 
                                   HVBatOCV 
                                   @ 
                                   HiSOC 
                                 
                               
                             
                           
                           n 
                         
                         ) 
                       
                       - 
                       
                         Δ 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           V 
                           i 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     (9) is the desired individual solar cell short circuit current which is essentially proportional to the area of the individual solar cells  30   n . (9) can therefore be used to determine the area of each of the individual solar cells  30   n.    
     Referring to  FIG. 3 , the contactors  16  may include negative terminal main contactor  32  (electrically connected with the negative terminal of the traction battery  12 ), positive terminal main contactor  34  (electrically connected with the positive terminal of the traction battery  12 ), pre-charge contactor  36  (electrically connected between the positive terminal of the traction battery  12  and the inverters  14 ), main capacitor  38  (electrically connected across the positive and negative terminals of the traction battery  12 ), and pre-charge resistor  40  (electrically connected between the positive terminal of the traction battery  12  and the inverters  14 ). The contactors  32 ,  34 ,  36  are also electrically connected with/under the control of the TBCM  18 . Other arrangements are, of course, also possible. The pre-charge contactor  36  may instead, for example, be electrically connected between the negative terminal of the traction battery  12  and the inverters  14 , etc. 
     To electrically connect the traction battery  12  with the electric machine  14 , the TBCM  18  first closes the negative terminal main contactor  32  and the pre-charge contactor  36  to charge the main capacitor  38  through the pre-charge resistor  40 . Once the main capacitor  38  is charged, the TBCM  18  closes the positive terminal contactor  34  and opens the pre-charge contactor  36 . As discussed above (and below), a significant amount of energy may be required to close the contactors  32 ,  34 ,  36 . 
     The solar panel activation system  24 , in the embodiment of  FIG. 3 , may include positive terminal switch/contactor/relay  42  (electrically connected with the positive terminal of the traction battery  12 ), negative terminal switch/contactor/relay  44  (electrically connected with the negative terminal of the traction battery  12 ), pre-charge switch/contactor/relay  46  (electrically connected with the positive terminal of the traction battery  12  and the MPPT  26 ), capacitor  48 , diode  50 , and resistor  52  (electrically connected between the positive terminal of the traction battery  12  and the pre-charge contactor  46 ). The relays  42 ,  44 ,  46  are also electrically connected with/under the control of the SCC  28 . The capacitor  48  is electrically connected between the relays  42 ,  44  and therefore may be used for filtering noise spikes. The diode  50  is electrically connected such that current only flows from the solar panel array  22  to the traction battery  12 . 
     The solar panel activation system  24 , in other embodiments, may comprise a single switch. For example, one of the negative and positive terminals of the traction battery  12  may always be connected with the solar panel array  22 . The other of the negative and positive terminals of the traction battery  12  may be connected with the solar panel array  22  via a switch. Other arrangements and configurations including additional switches, capacitors and/or diodes, and/or lacking capacitors and/or diodes are also possible. 
     The relays  42 ,  44 ,  46  may be sized smaller than the contactors  32 ,  34 ,  36  as they handle less current. For example, the relays  42 ,  44 ,  46  may handle current on the order of 0.035 A to 1 A (up to 5 A for example) whereas the contactors  32 ,  34 ,  36  may handle current on the order of 150 A. As a result, approximately 10 mA to 25 mA of current (or 0.12 W to 0.3 W of power (up to 1 W holding power for example)) may be needed to close the relays  42 ,  44 ,  46  whereas 250 mA to 1 A (peak 10 A to 20 A) of current (or 3 W to 12 W (120 W to 240 W peak power)) may be needed to close the contactors  32 ,  34 ,  36 . Such a difference in energy consumption may be significant given that the solar panel array  22  may only collect energy in the range of 5 W to 200 W. 
     To electrically connect the traction battery  12  with the solar panel array  22  (based on driver and/or vehicle inputs), the SCC  28  may first close the relays  44 ,  46  to soft charge the capacitor  38  through the resistor  52 . Once the capacitor  38  is charged, the SCC  28  may then close the relay  42  and open the relay  44 . To disconnect the traction battery  12  with the solar panel array  22 , the SCC  28  may open the relays  42 ,  44 . Other configurations of the solar panel activation system  24  may, of course, result in different strategies for electrically connecting the traction battery  12  with the solar panel array  22 . 
     While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. 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 invention.