Method and system for determining the capacity of a battery

• US 20020130637A1
• Filed: 02/12/2002
• Published: 09/19/2002
• Est. Priority Date: 02/13/2001
• Status: Active Grant

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Schoch, Eberhard
• Granted Patent: US 6,515,454 B2
• Time in Patent Office: Days
• US Class Current: 320/132
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: H01M 10/06 Lead-acid accumulators semi-lead accumulators H01M10/20
• CPC Class Codes: H01M 10/42 Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells H01M10/60 takes precedence
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A method for estimating the capacity of a battery, including the following steps: estimation of a steady-state voltage U_R, an internal resistance R_I, and an internal voltage drop U_K of the battery, caused by a density difference in the battery acid; initialization of a model describing the battery in order to estimate the capacity, using estimated values U_R, R_I and U_K; stimulation of the initialized model with predefined load current characteristic I_Batt,stim, in particular a simulated load current characteristic of a consumer in operative connection with the battery, in order to obtain a voltage response U_Batt,pred of the model, representing the battery voltage given the predefined load current characteristic; comparison of the voltage response U_Batt,pred of the model with a predefinable, minimal battery voltage U_Batt,limit, and estimation of the capacity of the battery by comparing U_Batt,pred and U_batt,limit.

Claims

1. A method for estimating a capacity of a battery, comprising:

estimating a steady-state voltage, an internal resistance, and an internal voltage drop of the battery caused by a density difference in a battery acid;

initializing a model describing the battery in order to estimate the capacity in accordance with estimated values of the steady-state voltage, the internal resistance, and the internal voltage drop of the battery;

stimulating the initialized model with a predefined load current characteristic in order to obtain a voltage response of the initialized model, representing a battery voltage, given the predefined load current characteristic; and

estimating the capacity of the battery by comparing the voltage response of the initialized model with a predefinable minimal battery voltage.

2. The method according to claim 1, wherein:

the predefined load current characteristic includes a simulated load current characteristic of a consumer in operative connection with the battery.

3. The method according to claim 1, further comprising:

determining the steady-state voltage, the internal resistance, and the internal voltage drop of the battery by a monitoring device that produces the estimated values for the steady-state voltage, the internal resistance, and the internal voltage drop of the battery on the basis of at least one of a measured battery voltage, a measured battery temperature, and a measured battery current in accordance with the initialized model describing the battery.

4. The method according to claim 3, wherein:

the monitoring device includes a Kalman filter.

5. The method according to claim 1, wherein:

in the comparison of the voltage response with the predefinable minimal battery voltage, a minimal value over time of the voltage response is used.

6. The method according to claim 5, further comprising:

determining the capacity of the battery in accordance with a formula;

SOH=(min(U_Batt,pred(t))−

U_Batt,limit)/(U_Batt,norm−

U_Batt,limit)

wherein min(U_Batt,pred(t)) is the minimal value over time of the voltage response, U_Batt,limit is the predefinable minimal battery voltage, and U_Batt,norm is a terminal voltage occurring at room temperature in response to a loading of a new, fully charged and balanced battery with a particular consumer.

7. The method according to claim 1, further comprising:

determining a load state of the battery on the basis of the estimated value for the steady-state voltage.

8. A system for estimating a capacity of a battery, comprising:

a predictor for estimating a battery voltage occurring given a particular load current characteristic, in which a steady-state voltage, an internal resistance an internal voltage drop caused by a density difference in a battery acid, and a particular load current characteristic are able to be supplied as input variables to a model used by the predictor to represent the battery, wherein;

an estimated battery voltage is obtained from the model as a response representing an estimation of the battery voltage with respect to the particular load current characteristic, and

the estimated battery voltage is compared to a limiting voltage in order to estimate the capacity of the battery.

9. The system according to claim 8, wherein:

the battery includes a motor vehicle starter battery.

10. The system according to claim 8, further comprising:

a monitoring device for estimating the steady-state voltage, the internal resistance and the internal voltage drop caused by the density difference in the battery acid.

11. The system according to claim 10, wherein:

the monitoring device includes a Kalman filter.