System and method for rebalancing a battery during vehicle operation

Abstract

A system and method for rebalancing a battery in a vehicle during vehicle operation, the battery including a plurality of modules, is provided. The method may include determining when an automatic rebalance mode start condition is satisfied, modifying a target state of charge for the battery at least in part in response to the start condition being satisfied such that the target state of charge is raised from a standard operating value to a rebalance value, operating the vehicle with the target state of charge at the rebalance value, determining when an automatic rebalance mode end condition or an interrupt condition is satisfied, and modifying the target state of charge in response to the automatic rebalance mode end condition or the interrupt condition being satisfied such that the target state of charge is lowered from the rebalance value to the standard operating value.

1 . A method for rebalancing a battery in a vehicle during vehicle operation, the battery including a plurality of modules, the method comprising: 
 determining when an automatic rebalance mode start condition is satisfied;    modifying a target state of charge for the battery at least in part in response to the start condition being satisfied, such that the target state of charge is raised from a standard operating value to a rebalance value;    operating the vehicle with the target state of charge at the rebalance value;    determining when an automatic rebalance mode end condition or an interrupt condition is satisfied; and    modifying the target state of charge in response to the automatic rebalance mode end condition or the interrupt condition being satisfied, such that the target state of charge is lowered from the rebalance value to the standard operating value.    
   
   
       2 . The method of  claim 1  further comprising: 
 determining a throughput for the battery after it is determined that the automatic rebalance mode end condition is satisfied;    determining a state of charge for each of the modules when the vehicle is operating with the target state of charge at the standard operating value;    determining a maximum state of charge from the determined state of charge for each of the modules; and    determining a minimum state of charge from the determined state of charge for each of the modules, and    wherein the automatic rebalance mode start condition is satisfied when at least one of a difference between the maximum state of charge and the minimum state of charge is greater than or equal to a predetermined upper delta limit and the throughput is greater than or equal to a predetermined minimum throughput value.    
   
   
       3 . The method of  claim 2  wherein the predetermined upper delta limit is substantially 10% and the predetermined minimum throughput value is substantially 1800 Amp Hours.  
   
   
       4 . The method of  claim 1  further comprising: 
 determining a discharge power for the battery, and    wherein the automatic rebalance mode start condition is satisfied when the battery discharge power is less than or equal to a predetermined lower discharge limit.    
   
   
       5 . The method of  claim 1  wherein the automatic rebalance mode start condition is satisfied by a command from a diagnostic device.  
   
   
       6 . The method of  claim 1  further comprising determining when a pre-condition is satisfied, wherein the pre-condition is satisfied when the vehicle is operating in a cruise control mode, and the step of modifying a target state of charge for the battery such that the target state of charge is raised from a standard operating value to a rebalance value is performed in response to both the pre-condition and the start condition being satisfied.  
   
   
       7 . The method of  claim 6  wherein the pre-condition is satisfied when the vehicle is operating in a cruise control mode for a predetermined duration.  
   
   
       8 . The method of  claim 6  further comprising: 
 determining a speed of the vehicle, and    wherein the pre-condition is satisfied when the vehicle is operating in a cruise control mode, the speed is greater than or equal to a predetermined minimum cruise speed, and the speed is less than or equal to a predetermined maximum cruise speed.    
   
   
       9 . The method of  claim 6  further comprising: 
 determining a speed of the vehicle, and    wherein the pre-condition is satisfied when the vehicle is operating in a cruise control mode for a predetermined duration, the speed is greater than or equal to a predetermined minimum cruise speed, and the speed is less than or equal to a predetermined maximum cruise speed.    
   
   
       10 . The method of  claim 1 , each of the modules comprising one or more cells, the method further comprising: 
 determining a cell temperature for one or more of the cells of the battery, and    wherein the interrupt condition is satisfied when the cell temperature for one or more cells of the battery is greater than a predetermined maximum cell temperature or less than a predetermined minimum cell temperature.    
   
   
       11 . The method of  claim 1 , each of the modules comprising one or more cells, the method further comprising: 
 determining a cell temperature for each of two or more of the cells of the battery, and    wherein the interrupt condition is satisfied when a difference between a first cell temperature and a second cell temperature is greater than or equal to a predetermined temperature delta value.    
   
   
       12 . The method of  claim 1  wherein the interrupt condition is satisfied when the step of operating the vehicle with the target state of charge at the rebalance value is performed for a predetermined maximum time.  
   
   
       13 . The method of  claim 1  further comprising: 
 determining a throughput for the battery when the vehicle is operating with the target state of charge at the rebalance value, and    wherein the end condition is satisfied when the throughput is greater than or equal to a predetermined maximum throughput value.    
   
   
       14 . The method of  claim 1  further comprising: 
 determining a state of charge for each of the modules when the vehicle is operating with the target state of charge at the rebalance value;    determining a maximum state of charge from the determined state of charge for each of the modules; and    determining a minimum state of charge from the determined state of charge for each of the modules, and    wherein the end condition is satisfied when a difference between the maximum state of charge and the minimum state of charge is less than or equal to a predetermined lower delta limit.    
   
   
       15 . The method of  claim 1  further comprising: 
 initiating a plurality of battery pulses when the vehicle is operating with the target state of charge at the rebalance value, wherein each battery pulse comprises the steps of charging the battery to a predetermined charge pulse value and subsequently discharging the battery to at least one of a predetermined discharge pulse value and a zero pulse value.    
   
   
       16 . The method of  claim 1  wherein the rebalance value is substantially 80%.  
   
   
       17 . The method of  claim 1  wherein the target state of charge is raised from the standard operating value to the rebalance value using a non-step function.  
   
   
       18 . The method of  claim 1  wherein the target state of charge is lowered from the rebalance value to the standard operating value using a non-step function in response to the end condition being satisfied.  
   
   
       19 . The method of  claim 1  further comprising: 
 generating maximum and minimum standard state of charge limits corresponding to the standard operating value; and    generating maximum and minimum rebalance state of charge limits corresponding to the rebalance value, and    wherein a difference between the rebalance value and the standard operating value is substantially equal to a difference between the minimum rebalance state of charge limit and the minimum standard state of charge limit, and a difference between the maximum standard state of charge limit and the standard operating value is greater than a difference between the maximum rebalance state of charge limit and the rebalance value.    
   
   
       20 . A system for rebalancing a battery in a vehicle during vehicle operation, the system comprising: 
 a battery having a plurality of modules, wherein each of the modules includes one or more cells; and    a controller in electronic communication with the battery for determining when an automatic rebalance mode start condition is satisfied, modifying a target state of charge for the battery at least in part in response to the start condition being satisfied such that the target state of charge is raised from a standard operating value to a rebalance value, determining when an automatic rebalance mode end condition or an interrupt condition is satisfied, and modifying the target state of charge in response to the end condition or the interrupt condition being satisfied such that the target state of charge is lowered from the rebalance value to the standard operating value.    
   
   
       21 . The system of  claim 20  further comprising: 
 a cruise control actuator for placing the vehicle in a cruise control mode; and    a vehicle speed sensor for determining a speed of the vehicle, and    wherein the controller determines when a pre-condition is satisfied and modifies a target state of charge for the battery in response to both the pre-condition and the start condition being satisfied such that the target state of charge is raised from a standard operating value to a rebalance value, the pre-condition being satisfied when the vehicle is operating in the cruise control mode for a predetermined duration, the speed is greater than or equal to a predetermined minimum cruise speed, and the speed is less than or equal to a predetermined maximum cruise speed.    
   
   
       22 . The system of  claim 20  wherein the controller initiates a plurality of battery pulses when the vehicle is operating with the target state of charge at the rebalance value, and each battery pulse comprises charging the battery to a predetermined charge pulse value and subsequently discharging the battery to at least one of a predetermined discharge pulse value and a zero pulse value.  
   
   
       23 . The method of  claim 1  wherein the automatic rebalance mode start condition is satisfied when the vehicle is operating in a cruise control mode.