Method for determining the capacity of a battery cell

Patent metadata

Field	Value
Publication number	US-9575130-B2
Application number	US-201415031783-A
Country	US
Kind code	B2
Filing date	Oct 6, 2014
Priority date	Oct 24, 2013
Publication date	Feb 21, 2017
Grant date	Feb 21, 2017

Abstract

The invention relates to a method for determining the capacity of a battery cell. A battery cell current I is measured during a measurement period, and an open terminal voltage U OCV1 ,U OCV2 of the battery cell is measured at the beginning and end of the measuring period. The method has the steps of ascertaining a total battery cell current I ges from the measured battery cell current I, ascertaining charge states SOC 1 , SOC 2 at the beginning and end of the measurement period using the measured open terminal voltage U OCV1 ,U OCV2 , ascertaining an estimated value of the capacity Q est using the total battery cell current I ges and a difference between the charge states SOC 1 , SOC 2 , ascertaining a total measurement error of the estimated value of the capacity Q est from measurement errors of the total battery cell current I ges and the charge states SOC 1 , SOC 2 , and ascertaining a new value of the capacity Q new using a known value of the capacity Q act , the estimated value of the capacity Q, and the total measurement error. The new value of the capacity Q new is in a monotonic relationship with the known value of the capacity Q act and the estimated value of the capacity Q est such that the new value of the capacity Q new is determined more strongly from the estimated value of the capacity Q est in the case of at least one first value of the total measurement error than in the case of at least one second value of the total measurement error, said second value lying above the at least one first value, and the new value of the capacity Q new is determined less strongly from the known value of the capacity Q est in the case of the first value of the value of the total measurement error than in the case of the second value of the total measurement error. The invention further relates to a computer program, a battery management system ( 2 ), and a motor vehicle which are designed to carry out the method.

First claim

The invention claimed is:

1. A method for determining the capacity of a battery cell, wherein a battery cell current I is measured during a measurement time period and an open circuit voltage U OCV1 , U OCV2 of the battery cell is measured at the beginning and end of the measurement time period, the method comprising:
a) determining, by a battery management system ( 2 ), a total battery cell current I tot from the measured battery cell current I,
b) determining, by the battery management system ( 2 ), states of charge SOC 1 , SOC 2 at the beginning and at the end of the measurement time period on the basis of the measured open circuit voltage U OCV1 , U OCV2 ,
c) determining, by the battery management system ( 2 ), an estimated value of the capacity Q est on the basis of the total battery cell current I tot and a difference between the states of charge SOC 1 , SOC 2 ,
d) determining, by the battery management system ( 2 ), a total measurement error

Δ
⁢

⁢
Q

Q

of the estimated value of the capacity Q est from measurement errors of the total battery cell current I tot and the states of charge SOC 1 , SOC 2 ,
e) determining, by the battery management system ( 2 ), a new value of the capacity Q new on the basis of a known value of the capacity Q act , the estimated value of the capacity Q est and the total measurement error

Δ
⁢

⁢
Q

Q

,

wherein the new value of the capacity Q new is in a monotonic relationship with the known value of the capacity Q act and the estimated value of the capacity Q est such that
in the case of at least one first value of the total measurement error

Δ
⁢

⁢
Q

Q

the new value of the capacity Q new is ascertained from the estimated value of the capacity Q est to a greater extent than in the case of at least one second value of the total measurement error

Δ
⁢

⁢
Q

Q

which lies above the at least one first value, and

in the case of the first value of the total measurement error

Δ
⁢

⁢
Q

Q

the new value of the capacity Q new is ascertained from the known value of the capacity Q act to a lesser extent than in the case of the second value of the total measurement error

Δ
⁢

⁢
Q

Q

;

wherein the battery management system ( 2 ) uses the new value of the capacity Qnew to extend the life of the battery cell.

2. The method as claimed in claim 1 , characterized in that the new value of the capacity Q new below a first threshold value ( 29 ) of the total measurement error

Δ
⁢

⁢
Q

Q

is ascertained using the estimated value of the capacity Q est .

3. The method as claimed in claim 1 , characterized in that the new value of the capacity Q new above a second threshold value ( 31 ) of the total measurement error

Δ
⁢

⁢
Q

Q

is ascertained by the known value of the capacity Q act .

4. The method as claimed in claim 1 comprising the following further step:
f) determining a weight factor W, wherein the weight factor W is in a monotonic relationship with the total measurement error

Δ
⁢

⁢
Q

Q

,

and wherein the new value of the capacity Q new is determined in step f) on the basis of the formula:
Q new =Q act +W·Q est −W·Q act .

5. The method as claimed in claim 1 , characterized in that the total battery cell current I tot is determined in step a) by the integration of the measured battery cell current I over the measurement time period.

6. The method as claimed in claim 1 , characterized in that the estimated value of the capacity Q est is determined in step c) on the basis of a quotient of the total battery cell current I tot and a difference between the states of charge SOC 1 , SOC 2 .

7. The method as claimed in claim 1 , characterized in that the states of charge SOC 1 , SOC 2 at the beginning and end of the measurement time period are determined in step b) on the basis of a characteristic curve ( 34 ) of the behavior of the state of charge as a function of the measured open circuit voltage and the measurement errors ΔSOC 1 , ΔSOC 2 of the states of charge SOC 1 , SOC 2 are determined by the linearization of the characteristic curve ( 34 ) from errors of the measured open circuit voltage U OCV1 , U OCV2 .

8. The method as claimed in claim 1 , characterized in that the measurement error of the states of charge SOC 1 , SOC 2 is determined on the basis of the formula:

Δ
⁢

⁢
SOC

=



∂
SOC

∂

U

OCV
⁢

Assignees

• Bosch Gmbh Robert

Inventors

• Rueger Michael
• Boehm Andre

Classifications

• H01M10/48

  Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte (constructional details of current conducting connections for detecting conditions inside cells or batteries, e.g. details of voltage sensing terminals, H01M50/569) · CPC title

• G01R31/3624 Primary

  Physics · mapped topic

• G01R31/3606

  Physics · mapped topic

• G01R31/3651

  Physics · mapped topic

• G01D21/00

  Measuring or testing not otherwise provided for · CPC title