System and method for monitoring a state of health of a battery system

Abstract

Systems and methods for monitoring a state of health of a battery are disclosed. The state of health of the battery may be determined based on an internal resistance of the battery. The state of health of the battery may be determined based on a measured terminal voltage of the battery, a measured current of the battery, a temperature of the battery, and a state-of-charge of the battery.

1 . A method for monitoring a battery connected to a load, the method comprising:
 determining with at least one electronic controller an internal resistance of the battery; and   determining with the at least one electronic controller a state-of-health (SOH) of the battery based on the determined internal resistance of the battery.   
     
     
         2 . The method of  claim 1 , further comprising the steps of:
 measuring a voltage of the battery;   measuring a temperature of the battery; and   measuring a current of the battery, wherein the internal resistance of the battery is based on the measured voltage, the measured temperature, and the measured current.   
     
     
         3 . The method of any one of the preceding claims, further comprising the step of determining with the at least one electronic controller a state-of-charge (SOC) of the battery, wherein the internal resistance of the battery is based on the determined state-of-charge (SOC). 
     
     
         4 . The method of  claim 3 , further comprising the steps of:
 determining an electromotive force of the battery with the at least one electronic controller;   determining a first voltage drop of the battery due to polarization of the battery with the at least one electronic controller; and   determining a second voltage drop of the battery due to hysteresis of the battery with the at least one electronic controller, wherein the internal resistance of the battery is based on the determined electromotive force of the battery, the determined first voltage drop of the battery, and the second voltage drop of the battery.   
     
     
         5 . The method of  claim 4 , wherein the at least one electronic controller determines the electromotive force of the battery, the first voltage drop of the battery, and the second voltage drop of the battery based on the determined state-of-charge (SOC). 
     
     
         6 . The method of  claim 4 , wherein the at least one electronic controller determines the electromotive force of the battery, the first voltage drop of the battery, and the second voltage drop of the battery based on the determined state-of-charge (SOC) and the measured temperature of the battery. 
     
     
         7 . The method of  claim 6 , wherein the at least one electronic controller determines the internal resistance of the battery by subtracting the electromotive force of the battery, the first voltage drop of the battery, and the second voltage drop of the battery from the measured voltage of the battery and dividing by the measured current. 
     
     
         8 . The method of  claim 1 , wherein the step of determining with the at least one electronic controller the internal resistance of the battery includes the step of determining an average internal resistance of the battery. 
     
     
         9 . The method of  claim 8 , wherein the state-of-health (SOH) of the battery is based on the determined average internal resistance of the battery. 
     
     
         10 . The method of  claim 9 , further comprising the steps of:
 determining with the at least one electronic controller an average state-of-charge (SOC) of the battery; and   determining with the at least one electronic controller an average temperature of the battery, wherein the state-of-health (SOH) of the battery is further based on the determined average state-of-charge (SOC) of the battery and on the determined average temperature of the battery.   
     
     
         11 . The method of  claim 8 , wherein the at least one electronic controller measures a set of values of the battery at a plurality of spaced apart intervals, the set of values including a measured voltage of the battery, a measured temperature of the battery; and a measured current of the battery. 
     
     
         12 . The method of  claim 11 , wherein the at least one electronic controller for each set of values determines a state-of-charge (SOC) of the battery. 
     
     
         13 . The method of  claim 12 , wherein the at least one electronic controller for each set of values determines an electromotive force of the battery, a first voltage drop of the battery due to polarization of the battery, and a second voltage drop of the battery due to hysteresis of the battery. 
     
     
         14 . The method of  claim 13 , wherein the average internal resistance is determined by the at least one electronic controller by the following relationship: 
       
         
           
             
               
                 
                   ( 
                   
                     R 
                     I 
                   
                   ) 
                 
                 AV 
               
               = 
               
                 
                   
                     ∑ 
                     
                       N 
                       = 
                       2 
                     
                     
                       N 
                       STOP 
                     
                   
                    
                   
                      
                     
                       Δ 
                        
                       
                           
                       
                        
                       
                         V 
                         N 
                       
                     
                      
                   
                 
                 
                   
                     ∑ 
                     
                       N 
                       = 
                       2 
                     
                     
                       N 
                       STOP 
                     
                   
                    
                   
                      
                     
                       Δ 
                        
                       
                           
                       
                        
                       
                         I 
                         N 
                       
                     
                      
                   
                 
               
             
           
         
       
       wherein ΔV N =((V T ) N −((EMF) N +(V P ) N +(h) N ))−((V T ) N-1 −((EMF) N-1 +(V P ) N-1 +(h) N-1 )) and ΔI N =(I N −I N-1 ), wherein (R I ) AV  is the determined average internal resistance, I is the measured current of the battery, V T  is the measured voltage of the battery, EMF is the determined electromotive force of the battery, V P  is determined first voltage drop of the battery due to polarization of the battery, h is the determined a second voltage drop of the battery due to hysteresis of the battery, and N is an interval identifier of the set of values. 
     
     
         15 . The method of  claim 14 , further comprising the steps of:
 determining with the at least one electronic controller an average state-of-charge (SOC) of the battery; and   determining with the at least one electronic controller an average temperature of the battery, wherein the state-of-health (SOH) of the battery is further based on the determined average state-of-charge (SOC) of the battery and on the determined average temperature of the battery.   
     
     
         16 . The method of  claim 12 , wherein the at least one electronic controller clears the set of values from a memory if a condition of the battery is not satisfied. 
     
     
         17 . The method of  claim 16 , wherein the condition of the battery is one of:
 the determined state-of-charge (SOC) is not within a first range;   the measured temperature is not within a second range;   a product of the measured current from a current interval and a preceding interval is less than zero;   a difference of the measured current from a current interval and a preceding interval is greater than a first threshold;   a maximum change in the determined state-of-charge (SOC) is greater than a second threshold; and   a maximum change in the measured temperature is greater than a third threshold.   
     
     
         18 . A system for monitoring a battery connected to a load, the system comprising:
 at least one measurement element configured for measuring a terminal voltage of the battery and a current of the battery; and   means for determining a state of health (SOH) of the battery.   
     
     
         19 . The system of  claim 18 , wherein the means for determining a state-of-health (SOH) of the battery includes at least one electronic controller which determines the state-of-health (SOH) of the battery based on a determined internal resistance of the battery, the measured terminal voltage of the battery, and the measured current of the battery. 
     
     
         20 . The system of  claim 19 , wherein the at least one electronic controller determines a state-of-charge (SOC) of the battery, wherein the internal resistance of the battery is based on the determined state-of-charge (SOC).