Method for estimating state of health of a battery

1. A method for estimating state of health (SOH) of an electric battery, comprising the steps of:

starting a charging cycle of an electric battery with a charge current (I),

measuring a voltage (V) of the electric battery during the charging,

determining a first point in time (t1) at which a minimum slope of the voltage curve (V) during the charging occurs,

determining a second point in time (t2) when the measured voltage (V) of the electric battery equals a maximum charging voltage (V Threshold ),

determining a SOH-interval (t SOH ) between the first point in time (t 1 ) and the second point in time (t 2 ), and

estimating the state of health for the electric battery based on the SOH-interval (t SOH ).

2. The method according to claim 1 , wherein the method further comprises the steps of;

determining a state of charge of the electric battery before starting the charging of the electric battery.

3. The method according to claim 2 , wherein the method further comprises the method step of:

cancelling the method if the state of charge of the battery is above a predefined state of charge threshold.

4. The method according to claim 3 , wherein the state of charge threshold of the battery is between 80 and 20% or 50% or 40% or 30%.

5. The method according to claim 1 , wherein the method further comprises the step of:

saving determined and/or measured and/or estimated data of a charging cycle at a memory.

6. The method according to claim 5 , wherein the method further comprises the step of:

forming historical data for the electric battery.

7. The method according to claim 6 , wherein the method further comprises the step of:

comparing historical data with data from a current charge cycle and/or nominal data, and

estimating the electric battery's state of health dependent on the comparison.

8. The method according to claim 6 , wherein the method further comprises the method step of:

estimating a future state of health of the electric battery dependent on the historical data.

9. The method according to claim 6 , wherein the method further comprises the steps of;

comparing a current estimated state of health value of a charging cycle with the historical data, and

excluding the current estimated state of health value if a difference from the historical data is above a difference threshold value.

10. The method according to claim 1 , wherein the first point in time (t 1 ) is determined through the method step:

determining the maximum value

(

(

Δ

⁢

Q

Δ

⁢

V

)

⁢

max

)

of a ratio between the derivate of charging amount (ΔQ) and derivate of charging voltage (ΔQ) occurs.

11. The method according to claim 1 , wherein the estimating of state of health is done by;

estimating the state of health as a ratio between an actual SOH-interval (t SOH N ) and a nominal SOH-interval (t SOH Nom ).

12. The method according to claim 1 , wherein the method further comprises the method step of:

detecting if the charge current is constant or variable, and;

selecting an estimation strategy for the state of health for the electric battery based thereon.

13. The method according to claim 12 , wherein

if a constant charge current is detected;

selecting a simplified estimation strategy, and thereby

using the time between the first point in time (t1) and the second point in time (t2) as indicative for the SOH-interval (t SOH ), and

if a variable charge current is detected;

selecting a full estimation strategy, and thereby continuously measuring the charge current,

using the charge amount (Q t1,t2 N ) between the first point in time (t 1 ) and the second point in time (t 2 ) as indicative for the SOH-interval (t SOH ).

14. A battery management system for controlling and monitoring an electric battery, wherein the battery management system is adapted to:

start a charging cycle of an electric battery,

measure a voltage (V) of the electric battery during the charging cycle,

determine a first point in time (t 1 ) at which a minimum slope of the voltage curve (V) during the charging cycle occurs,

determine second point (t2) in time when the measured voltage (I) of the battery equals a threshold charging voltage,

determine a SOH-interval (t SOH ) between the first point in time (t 1 ) and the second point in time (t 1 ), and

estimate the state of health for the electric battery based on the SOH-interval-t SOH ) between the first and the second point in time (t 1 , t 2 ).

15. A load, a battery or a charger comprising at least partially the battery management system according to claim 14 .

16. A computer program embodied on a non-transitory computer readable medium and comprising program code means for performing all the steps of the method of claim 1 , when said program is run on a computer.

17. A computer program product comprising program code means stored on a non-transitory computer readable medium for performing all the steps of the method of claim 1 , when said program product is run on a computer.

18. The method according to claim 2 , wherein the method further comprises the step of:

saving determined and/or measured and/or estimated data of a charging cycle at a memory.

19. The method according to claim 3 , wherein the method further comprises the step of:

saving determined and/or measured and/or estimated data of a charging cycle at a memory.

20. The method according to claim 4 , wherein the method further comprises the step of:

saving determined and/or measured and/or estimated data of a charging cycle at a memory.