Low voltage charging and balancing of a high voltage, series-connected string of battery modules

Abstract

Systems and methods for performing low voltage charging of a high voltage, series-connected string of battery modules are disclosed. A battery pack system may include a plurality of battery cells, including one or more groups of battery cells coupled in parallel. A processor may be configured to select a sub-group of battery cells from a group of battery cells for charging separately from other battery cells of the selected group of battery cells. The group of battery cells may be reconfigured to allow charging of the sub-group of battery cells separate from the other battery cells. The sub-group of battery cells may be charged, and then the group of battery cells may be reconfigured to allow operation of the sub-group of battery cells with the other battery cells. During charging, the sub-group of battery cells may be unavailable but other battery cells may continue to discharge.

What is claimed is: 
     
         1 . A method, comprising:
 selecting a sub-group of battery cells from a group of battery cells for charging separately from other battery cells of the group of battery cells;   reconfiguring the group of battery cells to allow charging of the sub-group of battery cells separate from the other battery cells;   charging the sub-group of battery cells; and   reconfiguring the group of battery cells to allow operation of the sub-group of battery cells with the other battery cells.   
     
     
         2 . The method of  claim 1 , wherein the step of charging the sub-group of battery cells comprises charging the sub-group of battery cells with a charge source having a voltage less than a full charge voltage of the group of battery cells. 
     
     
         3 . The method of  claim 2 , wherein, in operation, the group of battery cells has a full charge voltage greater than a voltage used by the charge source to charge the sub-group of battery cells. 
     
     
         4 . The method of  claim 1 , further comprising:
 repeating the steps of selecting a sub-group, reconfiguring the group of battery cells to allow charging, charging the sub-group of battery cells, and reconfiguring the group of battery cells to allow operation, wherein the steps are repeated for a different sub-group of battery cells than the first sub-group of battery cells until each battery cell in the group of battery cells has been charged an equal number of times, wherein each different sub-group of battery cells is comprised of the same number of battery cells as the initially-selected sub-group of battery cells.   
     
     
         5 . The method of  claim 1 , further comprising:
 selecting a second sub-group of battery cells from the group of battery cells for balancing, wherein the second sub-group comprises at least a battery cell having the lowest voltage of any battery cell in the group of battery cells;   reconfiguring the group of battery cells to allow charging of the second sub-group of battery cells separate from the other battery cells;   charging the second sub-group of battery cells; and   reconfiguring the group of battery cells to allow operation of the second sub-group of battery cells with the other battery cells.   
     
     
         6 . The method of  claim 1 , wherein the reconfiguring and charging steps are performed automatically without operator intervention. 
     
     
         7 . The method of  claim 1 , wherein the reconfiguring and charging steps are performed without interrupting a power bus coupled to the group of battery cells. 
     
     
         8 . The method of  claim 1 , wherein the method is performed by a battery management system (BMS) coupled to the group of battery cells. 
     
     
         9 . The method of  claim 1 , wherein the method is performed by a control block within one battery cell of the group of battery cells. 
     
     
         10 . An apparatus, comprising:
 a plurality of battery cells comprising one or more groups of battery cells coupled in parallel;   a processor configured to:
 select a sub-group of battery cells from a group of battery cells for charging separately from other battery cells of the selected group of battery cells; 
 reconfigure the group of battery cells to allow charging of the sub-group of battery cells separate from the other battery cells; and 
 reconfigure the group of battery cells to allow operation of the sub-group of battery cells with the other battery cells after the sub-group of battery cells have been charged; and 
   a power source configured to charge the sub-group of battery cells when the group of battery cells have been reconfigured to allow charging of the sub-group of battery cells separate from the other battery cells.   
     
     
         11 . The apparatus of  claim 10 , further comprising a plurality of string isolators coupled to the processor, wherein each group of battery cells coupled in parallel is coupled to at least one string isolator, and wherein the plurality of string isolators are configured to receive a signal from the processor and, in response to reception of the signal, isolate the group of battery cells from other groups of battery cells to allow reconfiguration and charging of battery cells within the group of battery cells without interrupting a power bus coupled to the group of battery cells. 
     
     
         12 . The apparatus of  claim 11 , wherein a string isolator comprises a diode or an ideal diode circuit. 
     
     
         13 . The apparatus of  claim 10 , wherein the processor is further configured to:
 interrogate each battery cell in the plurality of battery cells;   compare capacities of each parallel-coupled groups of battery cells; and   calculate an amount of charge required to approximately equalize a lowest capacity group with a highest capacity group.   
     
     
         14 . The apparatus of  claim 13 , wherein the processor is further configured to:
 control the plurality of string isolators to isolate the lowest capacity group of battery cells from the other parallel-coupled groups of battery cells; and   coupling the power supply to the lowest capacity group.   
     
     
         15 . The apparatus of  claim 9 , wherein the power source comprises a power source having a voltage less than a full charge voltage of the group of battery cells. 
     
     
         16 . The apparatus of  claim 15 , wherein, in operation, the group of battery cells has a full charge of voltage greater than a voltage used by the power source to charge the sub-group of battery cells.