Methods and Systems for Determining the Initial State of Charge (iSoC) and Optimum Charge Cycle(S) and Parameters for a Cell
Disclosed are method and systems for determining the initial state of charge (iSoC) and current state of charge (SoC) for a cell comprising determining a plurality of cell parameters, including current (i), open circuit voltage (OCV), temperature (T) and time to maximum voltage threshold (t cv ) of the cell, determining a plurality of cell iSoC parameters as a function of the plurality of cell parameters; determining an adjusted time to maximum voltage threshold (t′ cv ) of the cell: and determining a corrected iSoC parameter as a function of a predictor-corrector algorithm, the corrected iSoC parameter representing an estimated iSoC of said cell. Also disclosed are methods for determining optimum charge cycle(s) and parameters for the cell based on the corrected iSoC parameter.
1 . A method for determining the initial state of charge (iSoC) of a cell, comprising the steps of:
determining current (i), open circuit voltage (OCV), temperature (T) and base line time to maximum voltage threshold (t cv ) of a cell;
determining a first iSoC parameter as a function of said cell OCV and temperature (T), said first iSoC parameter representing a first estimate of iSoC of said cell;
determining a second iSoC parameter by discharging voltage (V) from said cell at a constant current (I trial ), said second iSoC parameter representing a second estimate of iSoC of said cell;
determining a third iSoC parameter as a function of said time to maximum voltage of said cell (t cv ) and said cell's voltage threshold, said third iSoC parameter representing a third estimate of iSoC of said cell;
determining the lowest iSoC parameter from said first, second and third iSoC parameters;
determining an adjusted time to maximum voltage threshold (t′ cv ) of said cell; and
determining a corrected iSoC parameter as a function of a predictor-corrector algorithm, said corrected iSoC parameter representing an estimated iSoC of said cell.
2 . The method of claim 1 , wherein said cell constant current (I trial ) comprises in the range of C/20 to C/5 mA, where C comprises a milliamp per hour (mAh) rating of said cell.
3 . The method of claim 1 , wherein said cell constant current (I trial ) comprises in the range of C/10-C/5 mA, where C comprises a mAh rating of said cell.
4 . The method of claim 1 , wherein said cell voltage (V) discharging comprises a steady-state voltage discharging.
5 . The method of claim 1 , wherein said cell voltage (V) discharging comprises a random voltage discharging.
6 . The method of claim 1 , wherein said cell voltage (V) discharging comprises a pseudo-random voltage discharging.
7 . The method of claim 1 , wherein said cell voltage (V) discharging is performed at a time duration in the range of 1 millisecond to 600 seconds.
8 . The method of claim 1 , wherein said adjusted time to maximum voltage threshold (t′ cv ) is determined by linearly extrapolating a curve representing time to maximum voltage threshold (t cv ) of said cell.
9 . The method of claim 1 , wherein said predictor-corrector algorithm determines a further adjusted time to maximum voltage threshold (t″ cv ) of said cell and compares said further adjusted time to maximum voltage threshold (t″ cv ) to a plurality of base line time to maximum voltage threshold (t BLCV ) values derived from a plurality of base line iSoC curves for a similar cell to derive said corrected iSoC parameter.
10 . The method of claim 9 , wherein said further adjusted time to maximum voltage threshold (t″ cv ) of said cell is derived according to the following relationship
t″ cv =(1-η)(p)+η(c)
where: p comprises said lowest iSoC parameter of said cell, c comprises said adjusted time to maximum voltage threshold (t′ cv ) of said cell, and η comprises a correction constant.
11 . The method of claim 10 , wherein said correction constant (η) is in the range of 0 to 1.
12 . The method of claim 10 , wherein said correction constant (η) is determined derived according to the following relationship
η=K×(t cv /t″ cv )
where K=2.
13 . The method of claim 12 , wherein said correction constant (η)=1 when K×t cv >t″ cv .
14 . A method for determining a charge cycle of a cell, comprising the steps of:
determining current (i), open circuit voltage (OCV), temperature (T) and time to maximum voltage (t cv ) of a cell;
determining a first initial state of charge (iSoC) parameter as a function of said cell OCV and temperature (T), said first iSoC parameter representing a first estimate of iSoC of said cell;
determining a second iSoC parameter by discharging voltage (V) from said cell at a constant current (I trial ), said second iSoC parameter representing a second estimate of iSoC of said cell;
determining a third iSoC parameter as a function of said time to maximum voltage threshold (t cv ) of said cell and said cell's voltage threshold, said third iSoC parameter representing a third estimate of iSoC of said cell;
determining the lowest iSoC value from said first, second and third iSoC parameters;
determining a corrected iSoC parameter as a function of a predictor-corrector algorithm; and
comparing said corrected iSoC parameter to a predetermined iSoC threshold to determine a first cell charge cycle parameter.
15 . The method of claim 14 , wherein said cell constant current (I trial ) comprises in the range of C/20 to C/5 mA, where C comprises a milliamp per hour (mAh) rating of said cell.
16 . The method of claim 14 , wherein said cell voltage (V) discharging is performed at a time duration in the range of 1 millisecond to 600 seconds.
17 . The method of claim 14 , wherein said adjusted time to maximum voltage threshold (t′ cv ) is determined by linearly extrapolating a curve representing time to maximum voltage threshold (t cv ) of said cell.
18 . The method of claim 14 , wherein said predictor-corrector algorithm determines a further adjusted time to maximum voltage threshold (t″ cv ) of said cell and compares said further adjusted time to maximum voltage (t″ cv ) to a plurality of base line time to maximum voltage threshold (t BLCV ) values derived from a plurality of base line iSoC curves for a similar cell to derive said corrected iSoC parameter.
19 . The method of claim 18 , wherein said further adjusted time to maximum voltage threshold (t″ cv ) of said cell is derived according to the following relationship
t″ cv =(1-η)(p)+η(c)
where: p comprises said lowest iSoC parameter of said cell, c comprises said adjusted time to maximum voltage threshold (t′ cv ) of said cell, and η comprises a correction constant.
20 . The method of claim 19 , wherein said correction constant (η) is in the range of 0 to 1.
21 . The method of claim 19 , wherein said correction constant (η) is determined derived according to the following relationship
η=K×(t cv t″ cv )
where K=2.
22 . The method of claim 21 , wherein said correction constant (η)=1 when K×t′ cv .