Abstract:
An energy storage system for an automotive vehicle includes a plurality of energy storage units electrically connected in series and a plurality of bi-directional energy converters each having first and second sides. Each of the first sides is electrically connected with one of the plurality of energy storage units. The system also includes another energy storage unit. The second sides of the plurality of bi-directional energy converters are electrically connected in parallel with the another energy storage unit. Each of the bi-directional energy converters is capable of transferring energy between the first and second sides.

Description:
BACKGROUND 
     Electrical power systems may be used to electrically power automotive vehicles. Certain techniques for balancing storage cells of electrical power systems are known. As an example, U.S. Pat. No. 6,984,961 to Kadouchi et al. discloses a battery assembly system that includes a plurality of storage batteries connected in series, a voltage detector for detecting voltages generated in the storage batteries and a current detector for detecting a current flowing in the plurality of storage batteries. The battery assembly system also includes a state-of-charge (SoC) calculator for calculating the SoC of the storage batteries based on the detected voltages and current, and a charging/discharging unit for charging or discharging at least one of the plurality of storage batteries so as to equalize the SoC of the storage batteries calculated by the SoC calculator. 
     As another example, U.S. Pat. No. 6,882,129 to Boskovitch et al. discloses a battery pack for a battery-powered vehicle. The battery pack comprises battery modules coupled in series. The battery modules are configured to provide power to the battery-powered vehicle. Each of the battery modules has a SoC. The battery pack also comprises battery control modules (BCMs) that are coupled to the battery modules. Each of the battery modules is coupled to one of the BCMs and each of the BCMs is configured to monitor a battery module parameter. The battery pack further comprises a battery control interface module (BCIM) coupled to each of the BCMs. The BCIM is configured to receive the battery module parameter from each of the BCMs and independently adjust the SoC of each of the battery modules based on the battery module parameter. 
     As yet another example, U.S. Pat. No. 6,583,602 to Imai et al. discloses a lower battery block that feeds low-voltage power to a low-voltage load. At least one higher battery block is connected in series with the lower battery block and cooperates with the lower battery block to feed high-voltage power to a high-voltage load. The lower battery block and higher battery block each include cells. A DC/DC converter transmits power from the higher battery block to the lower battery block. A controller detects (i) an electric parameter of the lower battery block that relates to an average per-cell voltage in the lower battery block and (ii) an electric parameter of the higher battery block that relates to an average per-cell voltage in the higher battery block. The controller controls the DC/DC converter in response to the detected electric parameters to equalize the average per-cell voltage in the lower battery block and the average per-cell voltage in the higher battery block. 
     SUMMARY 
     An energy storage system for an automotive vehicle includes a plurality of energy storage units electrically connected in series and a plurality of bi-directional energy converters each having first and second sides. Each of the first sides is electrically connected with one of the plurality of energy storage units. The system also includes another energy storage unit. The second sides of the plurality of bi-directional energy converters are electrically connected in parallel with the another energy storage unit. Each of the bi-directional energy converters is capable of transferring energy between the first and second sides. 
     An automotive vehicle includes an electric machine, a plurality of batteries electrically connected in series and electrically connected with the electric machine, and a plurality of bi-directional DC/DC power converters each having first and second sides. Each of the first sides is electrically connected with one of the plurality of batteries. The vehicle also includes an electrical load and another battery electrically connected with the electrical load. The second sides of the plurality of bi-directional DC/DC power converters are electrically connected in parallel with the another battery. Each of the bi-directional DC/DC power converters is capable of transferring energy between the first and second sides. 
     An energy storage system for an automotive vehicle includes a battery pack including a plurality of energy storage cells and a plurality of bi-directional DC/DC power converters each having first and second sides and capable of transferring energy between the first and second sides. Each of the first sides is electrically connected with one of the plurality of energy storage cells, and the second sides are electrically connected in parallel. The system also includes a controller configured to balance the battery pack by passing energy between at least two of the plurality of energy storage cells via at least one of the plurality of bi-directional DC/DC power converters. 
     While example embodiments in accordance with the invention are illustrated and disclosed, such disclosure should not be construed to limit the invention. It is anticipated that various modifications and alternative designs may be made without departing from the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an automotive vehicle power system according to an embodiment of the invention. 
         FIG. 2  is a schematic diagram of a DC/DC converter of  FIG. 1 . 
         FIG. 3  is a block diagram of an automotive vehicle power system according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIG. 1 , an electrical power system  10  for an automotive vehicle  12  may include a plurality of high-voltage, e.g., 300 V, storage cells  14 , at least one low-voltage, e.g., 12 V, storage cell  16 , a plurality of bi-directional DC/DC power converters  18  and a uni-directional DC/DC power converter  20  (having a turn ratio of, for example, 300:12). In the embodiment of  FIG. 1 , the storage cells  14  are Lithium-Ion batteries and the storage cell  16  is a lead-acid battery. Other storage cells, however, may be used. 
     The low-voltage storage cell  16  is electrically connected with a low-voltage load  22 , such as an ignition system. As apparent to those of ordinary skill, electrical power from the storage cell  16  may be supplied to the load  22  as necessary. 
     The plurality of storage cells  14  are electrically connected in series and form a high-voltage battery pack  24 . The battery pack  24  is electrically connected with the uni-directional DC/DC converter  20  and a high-voltage load  26 . The DC/DC converter  20  is also electrically connected with the low-voltage storage cell  16 . Electrical power from the battery pack  24  may be supplied to the DC/DC converter  20 . The DC/DC converter  20  may step down this high-voltage power to low-voltage power. This low-voltage power may be supplied to the storage cell  16  to, for example, charge the storage cell  16 . As apparent to those of ordinary skill, electrical power from the battery pack  24  may also be supplied to the high-voltage load  26 , such as an electric machine. The electric machine may be used to provide motive power for the vehicle  12 . 
     Each of the plurality of bi-directional DC/DC power converters  18  are electrically connected with one of the plurality of high-voltage storage cells  14  and the low-voltage storage cell  16 . As discussed in more detail below, each of the power converters  18  may pass electrical power between one of the high-voltage storage cells  14 /the high-voltage battery pack  24  and the low-voltage storage cell  16 . 
     Referring now to  FIG. 2 , each of the bi-directional DC/DC power converters  18  may include a pair of bi-directional rectifiers/inverters  28 ,  30 , a pair of coils  32 ,  34  and a capacitor  36 . The capacitor  36  may smooth the input/output of electrical current from/to the power converter  18 . 
     In the embodiment of  FIG. 2 , the bi-directional rectifier/inverter  28  comprises a MOSFET bridge, e.g., a 4-transistor controlled bridge, and is electrically connected with the coil  32 . The bi-directional rectifier/inverter  30  also comprises a MOSFET bridge and is electrically connected with the coil  34 . Any suitable transistor, however, (such as an IGBT) may be used. 
     The coils  32 ,  34  of  FIG. 1  have a 3.6:12 turn ratio and form a high frequency isolation transformer  38 . The turn ratio may be determined by the nominal voltages of the cells  14 ,  16 : the high-voltage storage cells  14  may each have a nominal voltage of 3.6 V and the low-voltage storage cell  16  may have a nominal voltage of 12 V. As apparent to those of ordinary skill, the isolation transformer  38  electrically isolates the high-voltage battery back  24  from the low-voltage storage cell  16 . Of course, the power converters  18  may have any suitable configuration. 
     Referring again to  FIG. 1 , the electrical power system  10  further includes a controller  40 . The controller  40  is in communication and/or electrically connected with each of the plurality of high-voltage storage cells  14  and each of the bi-directional DC/DC power converters  18 . 
     The controller  40  may determine information related to a condition of each of the storage cells  14 . For example, the controller  40  may read temperature, voltage and current information associated with each of the storage cells  14  from appropriate sensors (not shown) operatively arranged to sense such parameters of the storage cells  14 . The controller  40  may further determine a state-of-charge of each of the storage cells  14  based on the condition of each of the storage cells  14 . The controller  40  may use this information to balance the storage cells  14  of the battery pack  24 . 
     As known in the art, the plurality of storage cells  14  may achieve differing states-of-charge as power is delivered to/removed from the high-voltage battery pack  24 . The bi-directional DC/DC power converters  18  may be used to shuttle power between the storage cells  14  to balance the respective states-of-charge. For example, if one or more of the storage cells  14  has a state-of-charge greater than a target state-of-charge, the controller  40  may command those power converters  18  associated with the one or more storage cells  14  to discharge power to, for example, the low-voltage storage cell  16 , which, in this example, acts as a reservoir. This power may then be re-distributed to the storage cells  14  of the battery pack  24  or may be retained by the storage cell  16 . If one or more of the storage cells  14  has a state-of-charge less than the target state-of-charge, the controller  40  may command those power converters  18  associated with the one or more storage cells to pull power from, for example, the low-voltage storage cell  16  and provide it to the one or more storage cells  14 . Other scenarios are, of course, also possible. 
     Referring now to  FIG. 3 , numbered elements of  FIG. 3  that differ by 100 relative to the numbered elements of  FIG. 1  have similar, although not necessarily identical, descriptions to the numbered elements of  FIG. 1 . An electrical power system  110  for an automotive vehicle  112  includes a plurality of high-voltage storage cells  114 , at least one low-voltage storage cell  116  and a plurality of bi-directional DC/DC power converters  118 . Other configurations, however, are also possible. 
     The low-voltage storage cell  116  is electrically connected with a low-voltage load  122 . 
     The plurality of storage cells  114  are electrically connected in series and form a high-voltage battery pack  124 . The battery pack  124  is electrically connected with a high-voltage load  126 . Electrical power from the battery pack  124  may be supplied to the high-voltage load  126 . 
     Each of the plurality of bi-directional DC/DC power converters  118  are electrically connected with one of the plurality of high-voltage storage cells  114  and the low-voltage storage cell  116 . Each of the power converters  118  may pass electrical power between one of the high-voltage storage cells  114 /the high-voltage battery pack  124  and the low-voltage storage cell  116 . As discussed in more detail below, this may be performed to rebalance the storage cells  114  and/or charge the storage cell  116 . 
     The electrical power system  110  further includes a controller  140 . The controller  140  is in communication and/or electrically connected with each of the plurality of high-voltage storage cells  114  and each of the bi-directional DC/DC power converters  118 . As discussed with reference to the controller  40  illustrated in  FIG. 1 , the controller  140  may further determine a state-of-charge of each of the storage cells  114  based on their condition. The controller  140  may use this information to balance the storage cells  114  of the battery pack  124  by, for example, commanding selected power converters  118  to shuttle power between the storage cells  114  to achieve balance in a manner similar to that described above. 
     The controller  140  may also balance the storage cells  114 , on the fly, while, for example, providing power to the low-voltage storage cell  116 . The controller  140  may, for example, command each of the storage cells  114  to provide a specified amount of power to the storage cell  116 . This specified amount may depend on the state-of-charge of the particular storage cell  114 . For example, while the converters  118  are commanded by the controller  140  to deliver 1.0 A to support a load on the low voltage storage cell  116 , those storage cells  114  having a state-of-charge greater than a target value may have their command adjusted to provide 1.1 A of current for a fixed period of time, while those storage cells  114  having a state-of-charge less than the target value may have their command adjusted to provide 0.9 A of current for the fixed period of time. The fixed period of time may be some portion of the total time current is to be provided to the storage cell  116  to achieve state-of-charge balancing. The controller  140  may thus assess and alter the balance between the storage cells  114  continuously while charging or maintaining the charge on the storage cell  116 . 
     In other embodiments, the low-voltage storage cell  116  may be omitted and the bi-directional DC/DC power converters  118  may be electrically connected with the low-voltage load  122 . The power converters  118  may be sized to handle maximum transient loads presented by the load  122  and thus power from the storage cells  114  may be stepped up and collectively provided to the load  122  via the power converters  118 . Other arrangements and configurations are also possible. 
     While example embodiments in accordance with the invention are illustrated and disclosed, such disclosure should not be construed to limit the invention. It is anticipated that various modifications and alternative designs may be made without departing from the scope of the invention.