Method for determining a parameter of at least one accumulator of a battery

1. A computer-implemented method for determining a parameter of at least one accumulator of a battery, the computer implemented method comprising the steps:

conducting a series of voltage and current measurements (Un; In) on the terminals of said at least one accumulator;

calculating, using a microprocessor, a plurality of values of the parameter depending on the voltage and current measurements (Un; In);

determining, using the microprocessor, a value of the parameter as the average of the calculated values of the parameter and an associated standard deviation;

determining, using the microprocessor, an absolute uncertainty on the value of the parameter as the product of the standard deviation and of a Student coefficient related to the number of calculated values of the parameter and to a selected probability;

determining, using the microprocessor, a relative uncertainty on the value of the parameter, the relative uncertainty corresponding to a ratio between the absolute uncertainty and a value of the parameter determined as the average of the calculated values of the parameter;

if the relative uncertainty is less than or equal to a predetermined accuracy threshold, validating the value of the parameter.

2. The computer-implemented method for determining a parameter according to claim 1 , wherein said parameter is a resistance of at least one accumulator of a battery, the computer-implemented method comprising the steps:

measuring a current (I) delivered by said at least one accumulator;

measuring a first voltage (U1) on the terminals of said at least one accumulator when the current is substantially equal to a predetermined value (I=I1);

detecting a current pulse;

conducting the plurality of voltage and current measurements (Un; In) of said at least one accumulator during said pulse;

calculating a plurality of resistance values of said at least one accumulator from the first voltage and from the plurality of voltage and current measurements (Rn=|U1−Un|/|I1−In|);

determining a resistance value (R) as the average of the calculated resistance values

(

R

_

=

1

n

⁢

∑

i

=

1

n

⁢

R

i

)

and an associated standard deviation (s m );

determining an absolute uncertainty on the value of the resistance (ΔR) as the product of the standard deviation and of a Student coefficient (t (vp) ) related to the number of calculated resistance values and to a selected probability (ΔR=s m t (vp) );

determining a relative uncertainty on the value of the resistance (ΔR/R);

if the relative uncertainty is less than or equal to a predetermined accuracy threshold (ΔR/R<S), validating the resistance value (R) of said at least one accumulator.

3. The computer-implemented method for determining a parameter according to claim 2 , wherein the detection of a current pulse comprises the steps:

determining a first time interval (Δt1) between a current value equal to the predetermined value and a pulse current value;

determining a second time interval (Δt2) during which the current corresponds to a pulse current;

if the first time interval is less than a first threshold (Δt1<T1) and if the second time interval is greater than a second threshold (Δt2>T2), carrying out the voltage and current measurements (Un; In).

4. The computer-implemented method for determining a parameter according to claim 3 , wherein the detection of a current pulse further comprises the step of determining whether the pulse current remains in a stability interval (ΔI) during the second time interval (Δt2).

5. The computer-implemented method for determining a parameter according to claim 3 , wherein the first time threshold (T1), the second time threshold (T2) and the current threshold (Imin) are adjusted according to the temperature of the battery.

6. The computer-implemented method for determining the resistance according to claim 2 , wherein the predetermined value (I=I1) of the current for conducting the first voltage measurement (U1) is substantially equal to zero.

7. The computer-implemented method for determining a parameter according to claim 1 , wherein said parameter is a stage-of-charge value of at least one accumulator of a battery, the computer-implemented method comprising the steps:

conducting the plurality of voltage and current measurements (Un; In) on the terminals of said at least one accumulator when the current is substantially equal to a predetermined value (I=I1);

calculating a plurality of state-of-charge values (SOCn) from the plurality of voltage and current measurements (Un; In);

determining a state-of-charge value (SOC) as the average of the plurality of calculated state-of-charge values

(

SOC

_

=

1

n

⁢

∑

i

=

1

n

⁢

SOC

i

)

and an associated standard deviation (s m );

determining an absolute uncertainty on the state-of-charge value (ΔSOC) as the product of the standard deviation and of a Student coefficient (t (vp) ) related to the number of calculated state-of-charge values and to a selected probability (ΔSOC=s m t (vp) );

determining a relative uncertainty on the state-of-charge value (ΔSOC/SOC);

if the relative uncertainty is less than or equal to a predetermined accuracy threshold (ΔSOC/SOC<S), validating the state-of-charge value (SOC).

8. The computer-implemented method for determining a parameter according to claim 7 , further comprising the steps:

determining a first state-of-charge value (SOC1) for a first plurality of voltage and current measurements (U1n; I1n) on the terminals of said at least one accumulator;

determining a second state-of-charge value (SOC2) for a second plurality of voltage and current measurements (U2n; I2n) on the terminals of said at least one accumulator;

calculating the capacity of said at least one accumulator from the first and second state-of-charge values as:

C

=

∫

t

⁢

⁢

1

t

⁢

⁢

2

⁢

I

⁢

ⅆ

t

/

3600

SOC

⁢

⁢

2

-

SOC

⁢

⁢

1

.

9. The computer-implemented method for determining a parameter according to claim 1 , wherein said parameter is a capacity value of at least one accumulator of a battery, computer-implemented method comprising the steps:

determining a first state-of-charge value (SOC1) of said at least one accumulator;

conducting the plurality of voltage and current measurements (Un; In) on the terminals of said at least one accumulator;

calculating a plurality of second state-of-charge values (SOC2n) from the plurality of voltage and current measurements (Un; In);

calculating a plurality of capacity values from the first and second state-of-charge values as:

C

n

=

∫

t

⁢

⁢

1

t

⁢

⁢

2

⁢

I

⁢

ⅆ

t

/

3600

SOC

⁢

⁢

2

n

-

SOC

⁢

⁢

1

;

determining a capacity value (C) as the average of the calculated capacity values

(

C

_

=

1

n

⁢

∑

i

=

1

n

⁢

C

i

)

and an associated standard deviation (s m );

determining an absolute uncertainty on the value of the capacity (ΔC) as the product of the standard deviation and of a Student coefficient (t (vp) ) related to the number of calculated capacity values and to a selected probability (ΔC=s m t (vp) );

determining a relative uncertainty on the value of the capacity (ΔC/C);

if the relative uncertainty is less than or equal to a predetermined accuracy threshold (ΔC/C<S), validating the capacity value (C) of said at least one accumulator.

10. The computer-implemented method for determining a parameter according to claim 8 , wherein the second state-of-charge value(s) (SOC2) is(are) used for calculating the capacity (C) when they differ by at least 10% from the first state-of-charge value (SOC1).

11. The computer-implemented method for determining a parameter according to claim 1 , wherein the Student coefficient is selected for a probability of 99.7%.

12. The computer-implemented method for determining a parameter according to claim 1 , wherein the accuracy threshold (S) is less than or equal to 10%.

13. The computer-implemented method for determining a parameter according to claim 1 , wherein the accuracy threshold (S) is 5%.

14. The computer-implemented method for determining a parameter according to claim 1 , wherein the battery comprises a plurality of accumulators connected in series and/or in parallel and wherein the parameter is determined for each accumulator of the battery, the plurality of voltage and current measurements (Un; In) being conducted on the terminals of each accumulator.

15. The computer-implemented method for determining a parameter according to claim 1 , wherein the battery comprises a plurality of modules connected in series and/or in parallel, each module comprising a plurality of accumulators, and wherein the parameter is determined for each module of the battery, the plurality of voltage and current measurements (Un; In) being conducted on the terminals of each module.

16. The computer-implemented method for determining a parameter according to claim 1 , wherein the parameter is determined for the battery, the plurality of voltage and current measurements (Un; In) being conducted on the terminals of the battery.

17. A computer-implemented method for determining the state of health (SOH) of at least one accumulator of a battery, comprising the steps:

determining a capacity (C) according to claim 8 ;

normalizing the determined capacity value;

determining the state of health (SOH) of said at least one accumulator of the battery as the ratio of the normalized determined capacity over the capacity of said at least one accumulator in the brand-new condition.

18. The computer-implemented method for determining the state of health (SOH) according to claim 17 , wherein the determined resistance (R) or the determined capacity (C) is normalized at 25° C. and at a current corresponding to discharge conditions.

19. An electronic management system for a battery comprising:

means for measuring a current delivered by at least one accumulator of the battery;

means for measuring the voltage on the terminals of said at least one accumulator;

a microprocessor comprising program means for carrying out the steps of claim 1 .

20. A battery comprising a plurality of electrochemical accumulators arranged in modules and/or connected in series and/or in parallel and at least one electronic management system according to claim 19 .

21. A module comprising a plurality of electrochemical accumulators connected in series and/or in parallel and at least one electronic management system according to claim 19 .

22. An electrochemical accumulator and at least one electronic management system according to claim 19 .