Method for determining the capacity of a battery cell

• US 9,575,130 B2
• Filed: 10/06/2014
• Issued: 02/21/2017
• Est. Priority Date: 10/24/2013
• Status: Active Grant

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Rueger, Michael, Boehm, Andre
• Primary Examiner(s): COSIMANO, EDWARD R
• Application Number:
  US15/031,783
• Publication Number:
  US 20160245872A1
• Time in Patent Office: 869 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: G01D 21/00 Measuring or testing not otherwise provided for
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: G01R 31/382 Arrangements for monitoring battery or accumulator variables, e.g. SoC
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements
• CPC Class Codes: G01R 31/392 Determining battery ageing or deterioration, e.g. state of health
• CPC Class Codes: G06F 17/40 Data acquisition and logging for input to computer G06F3/00
• CPC Class Codes: G16Z 99/00 Subject matter not provided for in other main groups of this subclass
• CPC Class Codes: H01M 10/48 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 Class Codes: Y02E 60/10 Energy storage using batteries

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 SOC₁, SOC₂ 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 SOC₁, SOC₂, 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 SOC₁, SOC₂, 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.

Claims

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 SOC₁, SOC₂ 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 SOC₁, SOC₂,

d) determining, by the battery management system (2), a total measurement error

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

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

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

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 SOC₁, SOC₂.

7. The method as claimed in claim 1, characterized in that the states of charge SOC₁, SOC₂ 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 Δ

SOC₁, Δ

SOC₂ of the states of charge SOC₁, SOC₂ 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 SOC₁, SOC₂ is determined on the basis of the formula:

9. The method as claimed in claim 1, characterized in that the beginning and the end of the measurement time period in each case adjoin a relaxation time period of the battery cell.

10. A non-transitory computer readable medium having a computer program which when executed on a programmable computer device:

a) determines a total battery cell current I_tot from the measured battery cell current I,

b) determines states of charge SOC₁, SOC₂ 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) determines 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 SOC₁, SOC₂,

d) determines a total measurement error

11. A battery management system (2) comprising

a) a unit (4) for determining a battery cell current I,

b) a unit (6) for determining an open circuit voltage U_OCV1, U_OCV2 of a battery cell,

c) a unit (8) for determining a total battery cell current I_tot from the measured battery cell current I,

d) a unit (12) for determining states of charge SOC₁, SOC₂ at the beginning and end of the measurement time period on the basis of the measured open circuit voltages U_OCV1, U_OCV2,

e) a unit (16) for determining an estimated value of the capacity Q_est on the basis of the total battery cell current I_tot and a difference between the determined states of charge SOC₁, SOC₂,

f) a unit (18) for determining a total measurement error

12. The battery management system (2) as claimed in claim 11, wherein the battery management system (2) is used in a motor vehicle.