Static state of charge correction techniques for lithium iron phosphate battery systems
Static state of charge (SOC) correction for a lithium iron phosphate (LFP) battery system of an electrified vehicle includes in response to a power-off of the electrified vehicle, (i) determining an initial SOC of the LFP battery system, (ii) initiating a power-off timer and (iii) initiating a periodic temperature measurement of the LFP battery system, in response to a subsequent power-on of the electrified vehicle, (i) stopping the power-off timer, (ii) determining an average of the periodic temperature measurements of the LFP battery system, and (iii) accessing a calibrated look-up table to determine a self-discharge rate of the LFP battery system based on a value of the power-off timer and the measured temperature of the LFP battery system, and determining a corrected SOC for the LFP battery system by determining an SOC change based on the determined self-discharge rate and subtracting the SOC change from the initial measured SOC.
1 . A static state of charge (SOC) correction method for a lithium iron phosphate (LFP) battery system of an electrified vehicle, the static SOC correction method comprising:
obtaining and storing, by a controller of the electrified vehicle and in a memory accessible by the controller, a calibrated look-up table relating (i) power-off times of the electrified vehicle and temperatures of the LFP battery system to (ii) self-discharge rates of the LFP battery system, wherein the self-discharge rates of the LFP battery system corresponds to periods where an active C-rate discharge of the LFP battery system is not commanded;
detecting, by the controller, a power-off of the electrified vehicle;
in response to detecting the power-off of the electrified vehicle, (i) determining, by the controller, an initial SOC of the LFP battery system, (ii) initiating, by the controller, a power-off timer, and (iii) initiating, by the controller, a periodic temperature measurement of the LFP battery system;
after detecting the power-off of the electrified vehicle, detecting, by the controller, a subsequent power-on of the electrified vehicle;
in response to detecting the subsequent power-on of the electrified vehicle, (i) stopping, by the controller, the power-off timer, (ii) determining, by the controller, an average of the periodic temperature measurements of the LFP battery system to obtain a measured temperature of the LFP battery system, and (iii) accessing, by the controller via the memory, the calibrated look-up table to determine an actual self-discharge rate of the LFP battery system based on a value of the power-off timer and the measured temperature of the LFP battery system; and
determining, by the controller, a corrected SOC for the LFP battery system by determining an SOC change based on the determined actual self-discharge rate and subtracting the SOC change from the initial measured SOC.
2 . The static SOC correction method of claim 1 , further comprising communicating, by the controller and with a display device of a driver interface, to command the display device to display a final SOC for the LFP battery system.
3 . The static SOC correction method of claim 2 , further comprising determining, by the controller, whether the value of the power-off timer exceeds a minimum power-off threshold corresponding to an expected self-discharge of the LFP battery system.
4 . The static SOC correction method of claim 3 , further comprising when the value of the power-off timer does not exceed the minimum power-off threshold, setting, by the controller, the final SOC equal to the initial SOC of the LFP battery system.
5 . The static SOC correction method of claim 3 , further comprising when the value of the power-off timer exceeds the minimum power-off threshold, setting, by the controller, the final SOC equal to the corrected SOC for the LFP battery system.
6 . The static SOC correction method of claim 1 , wherein the calibrated look-up table includes at least two self-discharge rates and the controller is configured to perform linear extrapolation based on the at least two self-discharge rates to determine the self-discharge rate for the LFP battery system.
7 . The static SOC correction method of claim 1 , wherein the LFP battery system is characterized by a voltage flat zone between high and low voltage thresholds, and wherein the voltage flat zone prevents operation of other SOC correction techniques.
8 . The static SOC correction method of claim 1 , wherein the electrified vehicle is an electrified sport utility vehicle (eSUV).
9 . A static state of charge (SOC) correction system for a lithium iron phosphate (LFP) battery system of an electrified vehicle, the static SOC correction system comprising:
a memory configured to store a calibrated look-up table relating (i) power-off times of the electrified vehicle and temperatures of the LFP battery system to (ii) self-discharge rates of the LFP battery system, wherein the self-discharge rates of the LFP battery system corresponds to periods where an active C-rate discharge of the LFP battery system is not commanded; and
a controller configured to access the memory and to:
detect a power-off of the electrified vehicle;
in response to detecting the power-off of the electrified vehicle, (i) determine an initial SOC of the LFP battery system, (ii) initiate a power-off timer, and (iii) initiate a periodic temperature measurement of the LFP battery system;
after detecting the power-off of the electrified vehicle, detect a subsequent power-on of the electrified vehicle;
in response to detecting the subsequent power-on of the electrified vehicle, (i) stop the power-off timer, (ii) determine an average of the periodic temperature measurements of the LFP battery system to obtain a measured temperature of the LFP battery system, and (iii) access the calibrated look-up table to determine an actual self-discharge rate of the LFP battery system based on a value of the power-off timer and the measured temperature of the LFP battery system; and
determine a corrected SOC for the LFP battery system by determining an SOC change based on the determined actual self-discharge rate and subtracting the SOC change from the initial measured SOC.
10 . The static SOC correction system of claim 9 , wherein the controller is further configured to communicate with a display device of a driver interface to command the display device to display a final SOC for the LFP battery system.
11 . The static SOC correction system of claim 10 , wherein the controller is further configured to determine whether the value of the power-off timer exceeds a minimum power-off threshold corresponding to an expected self-discharge of the LFP battery system.
12 . The static SOC correction system of claim 11 , wherein when the value of the power-off timer does not exceed the minimum power-off threshold, the controller is further configured to set the final SOC equal to the initial SOC of the LFP battery system.
13 . The static SOC correction system of claim 11 , wherein when the value of the power-off timer exceeds the minimum power-off threshold, the controller is configured to set the final SOC equal to the corrected SOC for the LFP battery system.
14 . The static SOC correction system of claim 9 , wherein the calibrated look-up table includes at least two self-discharge rates and the controller is configured to perform linear extrapolation based on the at least two self-discharge rates to determine the self-discharge rate for the LFP battery system.
15 . The static SOC correction system of claim 9 , wherein the LFP battery system is characterized by a voltage flat zone between high and low voltage thresholds, and wherein the voltage flat zone prevents operation of other SOC correction techniques.
16 . The static SOC correction system of claim 9 , wherein the electrified vehicle is an electrified sport utility vehicle (eSUV).