US-12618916-B2 - Method and device for estimating an internal resistance of a battery cell

US12618916B2US 12618916 B2US12618916 B2US 12618916B2US-12618916-B2

Abstract

Technologies and techniques for estimating an internal resistance of a battery cell. A voltage and a current are detected at the battery cell. A detected voltage differential is determined by differentiating the detected voltage using a filter, and a modelled voltage differential is determined from the detected current and an actual internal resistance estimation value is determined by differentiating using a filter. A correction factor is determined from the detected voltage differential and the modelled voltage differential, and a new actual internal resistance estimation value is estimated from the determined correction factor and the previous actual internal resistance estimation value, and the new actual internal resistance estimation value is provided as estimated internal resistance of the battery cell. A device configured for estimating an internal resistance of a battery cell is further disclosed.

Inventors

Jiri VALTR
Marian Vlcek
Adam Hrazdira
Stefan Aust

Assignees

VOLKSWAGEN AKTIENGESELLSCHAFT

Dates

Publication Date: 20260505
Application Date: 20220310
Priority Date: 20210520

Claims (19)

1 . A device for estimating an internal resistance of a battery cell, comprising: interfaces configured to receive a voltage detected at the battery cell and a current detected at the battery cell; and a control device comprising at least one filter, and operatively coupled to the interfaces, the control device being configured to: determine a detected voltage differential by differentiating the detected voltage using a filter; determine a modeled voltage differential from the detected current and a present internal resistance estimated value by differentiation, wherein the modeled voltage differential represents a differential voltage across the battery cell derived from the detected current and the present internal resistance estimated value; determine a correction factor from the detected voltage differential and the modeled voltage differential; estimate a new present internal resistance estimated value from the determined correction factor and the previous present internal resistance estimated value; and provide the new present internal resistance estimated value as an estimated internal resistance of the battery cell.
2 . The device according to claim 1 , wherein the at least one filer is configured as antisymmetric filters having a finite impulse response.
3 . The device according to claim 1 , wherein, determining the correction factor comprises performing an estimation using at least one estimation filter.
4 . The device according to claim 3 , wherein the at least one estimation filter comprises a Kalman filter.
5 . The device according to claim 1 , wherein the control device is configured to: compare at least one of the voltage differentials to a predefined threshold value; and provide the new present internal resistance estimated value as an estimated internal resistance of the battery cell when a value of one of the voltage differentials reaches or exceeds the predefined threshold value.
6 . The device according to claim 1 , wherein the control device is configured to: determine a power flow direction and a current direction; and determine a charging internal resistance estimated value and/or a discharging internal resistance estimated value as a function of the determined current direction; and provide the charging internal resistance estimated value and/or the discharging internal resistance as power flow direction-dependent internal resistances of the battery cell.
7 . A method for estimating an internal resistance of a vehicle battery cell, comprising: detecting a voltage at the battery cell; detecting a current at the battery cell; determining, via at least one filter, a detected voltage differential by differentiating the detected voltage using a filter; determining, via the at least one filter, a modeled voltage differential from the detected current and a present internal resistance estimated value by differentiation, wherein the modeled voltage differential represents a differential voltage across the battery cell derived from the detected current and the present internal resistance estimated value; determining, via a control device, a correction factor from the detected voltage differential and the modeled voltage differential; and estimating, via the control device, a new present internal resistance estimated value from the determined correction factor and the previous present internal resistance estimated value; and providing the new present internal resistance estimated value as an estimated internal resistance of the battery cell.
8 . The method according to claim 7 , wherein the at least one filer is configured as antisymmetric filters having a finite impulse response.
9 . The method according to claim 7 , wherein, determining the correction factor comprises performing an estimation using at least one estimation filter.
10 . The method according to claim 9 , wherein the at least one estimation filter comprises a Kalman filter.
11 . The method according to claim 7 , further comprising: comparing at least one of the voltage differentials to a predefined threshold value; and providing the new present internal resistance estimated value as an estimated internal resistance of the battery cell when a value of one of the voltage differentials reaches or exceeds the predefined threshold value.
12 . The method according to claim 7 , further comprising: determining a power flow direction and a current direction; and determining a charging internal resistance estimated value and/or a discharging internal resistance estimated value as a function of the determined current direction; and providing the charging internal resistance estimated value and/or the discharging internal resistance as power flow direction-dependent internal resistances of the battery cell.
13 . The method according to claim 7 , wherein providing the new present internal resistance estimated value comprises providing the new present internal resistance estimated value to a vehicle comprising one of a motor vehicle, a rail vehicle, a watercraft, an aircraft or a space craft.
14 . A vehicle, comprising: a device for estimating an internal resistance of a battery cell, wherein the device comprises interfaces configured to receive a voltage detected at the battery cell and a current detected at the battery cell, and a control device comprising at least one filter, and operatively coupled to the interfaces, the control device being configured to: determine a detected voltage differential by differentiating the detected voltage using a filter; determine a modeled voltage differential from the detected current and a present internal resistance estimated value by differentiation, wherein the modeled voltage differential represents a differential voltage across the battery cell derived from the detected current and the present internal resistance estimated value; determine a correction factor from the detected voltage differential and the modeled voltage differential; estimate a new present internal resistance estimated value from the determined correction factor and the previous present internal resistance estimated value; and provide the new present internal resistance estimated value as an estimated internal resistance of the battery cell.
15 . The vehicle according to claim 14 , wherein the at least one filer is configured as antisymmetric filters having a finite impulse response.
16 . The vehicle according to claim 14 , wherein, determining the correction factor comprises performing an estimation using at least one estimation filter.
17 . The vehicle according to claim 16 , wherein the at least one estimation filter comprises a Kalman filter.
18 . The vehicle according to claim 14 , wherein the control device is configured to: compare at least one of the voltage differentials to a predefined threshold value; and provide the new present internal resistance estimated value as an estimated internal resistance of the battery cell when a value of one of the voltage differentials reaches or exceeds the predefined threshold value.
19 . The vehicle according to claim 14 , wherein the control device is configured to: determine a power flow direction and a current direction; and determine a charging internal resistance estimated value and/or a discharging internal resistance estimated value as a function of the determined current direction; and provide the charging internal resistance estimated value and/or the discharging internal resistance as power flow direction-dependent internal resistances of the battery cell.

Description

The present application claims priority to International Patent Application No. PCT/EP2022/056247 to Valtr et al., filed Mar. 10, 2022, titled “Method And Device For Estimating An Internal Resistance Of A Battery Cell,” which claims priority to German Pat. App. No. DE 10 2021 205 162.6, filed May 20, 2021, to Valtr et al., the contents of each being incorporated by reference in their entirety herein. TECHNICAL FIELD The present disclosure relates to technologies and techniques for estimating an internal resistance of a battery cell. BACKGROUND Battery cells age over time, which adversely affects the operational properties. Aging manifests itself, in particular, in an increase in internal resistance and a decrease in the electrical capacity of the battery cell. By tracking the internal resistance, an aging process of the battery cell can be tracked. However, the internal resistance cannot be measured directly, but can only be estimated via a voltage at the battery cell and a current flowing through the battery cell. Various influencing factors, however, can make such an estimation more difficult: measurement noise, a disparity of the internal resistance during charging and discharging, the RC circuit-like behavior of the battery cell, as well as the fact that an equivalent circuit model typically used during modeling cannot perfectly map the electrochemical processes in the battery. SUMMARY Aspects of the present disclosure are directed to a method and a device for estimating an internal resistance of a battery cell, by way of which the internal resistance of the battery cell can be reliably estimated. Some aspects are disclosed in the subject matter of the independent claims. Other aspects are disclosed in the respective dependent claims, found below. In some examples, a method is disclosed for estimating an internal resistance of a battery cell, comprising the following measures: detecting a voltage at the battery cell; detecting a current at the battery cell; determining a detected voltage differential by differentiating the detected voltage using a filter; determining a modeled voltage differential from the detected current and a present internal resistance estimated value by differentiation using a filter; determining a correction factor from the detected voltage differential and the modeled voltage differential; and estimating a new present internal resistance estimated value from the determined correction factor and the previous present internal resistance estimated value; and providing the new present internal resistance estimated value as an estimated internal resistance of the battery cell. In some examples, a device for estimating an internal resistance of a battery cell is disclosed, comprising: interfaces that are configured to receive a voltage detected at the battery cell and a current detected at the battery cell; and a control device, wherein the control device is configured to determine a detected voltage differential by differentiating the detected voltage using a filter, to determine a modeled voltage differential from the detected current and a present internal resistance estimated value by differentiation using a filter, to determine a correction factor from the detected voltage differential and the modeled voltage differential, and to estimate a new present internal resistance estimated value from the determined correction factor and the previous present internal resistance estimated value, and to provide the new present internal resistance estimated value as an estimated internal resistance of the battery cell. The method and the device make it possible to “teach” the internal resistance of the battery cell, proceeding from a reference value. The teaching may take place based on a differentially determined internal resistance, that is, the internal resistance is determined as a differential internal resistance. Initially, the reference value may correspond to the nominal internal resistance of the battery cell. The reference value may be set at the first present internal resistance estimated value, and is then updated by way of the measures of the method to a new present internal resistance estimated value with each present iteration. The updating may be carried out as follows: A modeled voltage is estimated from the detected current and the present internal resistance estimated value. Differentials are formed in each case from the detected voltage and the modeled voltage using (differentiating) filters by differentiation. This is based on the idea that an internal resistance can be determined and taught particularly well when the voltage (or the current) changes. A correction factor is determined from the ratio of the differentials with respect to one another. A new present internal resistance estimated value is estimated from the determined correction factor and the (previous) present internal resistance estimated value. The new present internal resistance estimated value is provide