State-of-charge estimating device of secondary battery

• US 20070029973A1
• Filed: 07/16/2006
• Published: 02/08/2007
• Est. Priority Date: 07/19/2005
• Status: Active Grant

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd.
• Inventors: Ashizawa, Hiroyuki, Nakamura, Hideo, Asai, Hisafumi
• Granted Patent: US 7,352,156 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: G01R 31/374 with means for correcting the measurement for temperature or ageing
• CPC Class Codes: G01R 31/3828 using current integration

Abstract

A state-of-charge (SOC) estimating device and method for a secondary battery that estimates the SOC of the battery with high precision when variation takes place in the parameters of the battery model, even if the input current is constant. A first SOC estimating part estimates the open-circuit voltage by estimating the battery parameters en bloc using an adaptive digital filter computing treatment from the measurement values of the current and the terminal voltage and computes a first estimated SOC of the secondary battery from the open-circuit voltage and a predetermined relationship between the open-circuit voltage and the SOC. A second SOC estimating part computes a second estimated SOC by means of current-integration. State-of-charge estimated value-selecting part selects the second SOC value as when the current is constant and otherwise selects the first SOC value.

Claims

1. A state-of-charge estimating device for estimating a state-of-charge of a secondary battery connected to a load, comprising:

a current detecting device for detecting a current I of the secondary battery;

a terminal voltage detecting device for detecting a terminal voltage V of the secondary battery; and

a controller receiving input from the current detecting device and the terminal voltage detecting device, the controller including;

an open-circuit voltage estimating part operable to perform an adaptive digital filter computing treatment to estimate at least one battery parameter in a battery model

$V=\frac{B<br><br>\left(s\right)}{A<br><br>\left(s\right)}·<br><br>I+\frac{1}{A<br><br>\left(s\right)}·<br><br>V_O<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{en}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{bloc}$

based on the current I and terminal voltage V of the secondary battery and the battery model

$V=\frac{B<br><br>\left(s\right)}{A<br><br>\left(s\right)}·<br><br>I+\frac{1}{A<br><br>\left(s\right)}·<br><br>V_O,$

and operable to estimate an estimated open-circuit voltage V_O of the secondary battery, wherein A(s) and B(s) are polynomials of Laplace operator s;

a first state-of-charge estimating part operable to estimate a first state-of-charge value based on the estimated open-circuit voltage V_O of the secondary battery and a previously derived relationship between an open-circuit voltage and a state-of-charge of the secondary battery;

a second state-of-charge estimating part operable to estimate a second state-of-charge value using a method capable of estimating the state-of-charge even if the current I is constant while one or more of the at least one battery parameter varies; and

a state-of-charge estimated value-selecting part operable to select the second state-of-charge value as the state-of-charge when the current I is constant and otherwise to select the first state-of-charge value as the state-of-charge.

2. The state-of-charge estimating device according to claim 1 wherein the second state-of-charge estimating part is operable to estimate the second state-of-charge value using the method wherein the method excludes the estimated open-circuit voltage V_O that is estimated by the open-circuit voltage estimating part.

3. The state-of-charge estimating device according to claim 1 wherein the second state-of-charge estimating part is further operable to estimate the second state-of-charge value based on at least one of the current I detected by the current detecting device and the terminal voltage V detected by the terminal voltage detecting device before performing the adaptive digital filter computing treatment.

4. The state-of-charge estimating device according to claim 1 wherein the state-of-charge estimated value-selecting part is further operable to determine that the current I is constant when a variation rate of the current I over time is continuously lower than a prescribed variation rate over a prescribed time.

5. The state-of-charge estimating device according to claim 4 wherein the state-of-charge estimated value-selecting part is further operable to select the second state-of-charge value only when the variation rate of the current I is smaller than the prescribed variation rate and an absolute value of the current is larger than a prescribed value continuously for the prescribed time, and otherwise is operable to select the first state-of-charge.

6. The state-of-charge estimating device according to claim 1 wherein the state-of-charge estimated value-selecting part is further operable to determine the current I is constant when a change width of the current I is continuously smaller than a prescribed change width over a prescribed time.

7. The state-of-charge estimating device described in claim 6 wherein the state-of-charge estimated value-selecting part is further operable to select the second state-of-charge value only when the change width of the current I is smaller than the prescribed change width and an absolute value of the current I is larger than a prescribed value continuously for the prescribed time, and otherwise is operable to select the first state-of-charge value.

8. The state-of-charge estimating device according to claim 1 wherein the second state-of-charge estimating part is further operable to estimate the second state-of-charge value by integrating the current I detected using the current detecting device.

9. The state-of-charge estimating device according to claim 8 wherein the second state-of-charge estimating part is further operable to estimate a total capacity of the secondary battery, and to estimate the second state-of-charge value by integrating the current I based on the estimated total capacity and a formula

10. The state-of-charge estimating device according to claim 8 wherein the second state-of-charge estimating part is further operable, when the state-of-charge estimated value-selecting part changes from a state of selection of the first state-of-charge value to a state of selection of the second state-of-charge value, to use the first state-of-charge value just before selection of the second state-of-charge value as an initial value and to start integration of the current I.

11. The state-of-charge estimating device according to claim 1 wherein the second state-of-charge estimating part is further operable to detect a correlation relationship between the current I and the terminal voltage V from the current I detected using the current detecting device and the terminal voltage V detected using the terminal voltage detecting device, to estimate the estimated open-circuit voltage V_O of the secondary battery based on the correlation relationship, and to estimate the second state-of-charge value based on the estimated open-circuit voltage V_O.

12. The state-of-charge estimating device according to claim 1 wherein the first state-of-charge estimating part is operable to perform the adaptive digital filter computing treatment based on values for the current I and terminal voltage V obtained by applying a low-pass-filter or band-pass filter treatment on the current I and terminal voltage V;

and wherein the second state-of-charge estimating part is operable to perform filter treatment having equal delay characteristics to those of the low-pass filter or band-pass filter on the second state-of-charge value.

14. The state-of-charge estimating device according to claim 1 wherein an amount of time used by the state-of-charge estimated value-selecting part to select from the first state-of-charge value and the second state-of-charge value decreases when an absolute value of the current I increases.

13. The state-of-charge estimating device according to claim I wherein the state-of-charge estimated value-selecting part is further operable to select the second state-of-charge value when there is no change in the at least one battery parameter estimated using the adaptive digital filter computing treatment or when the at least one battery parameter estimated with the adaptive digital filter computing treatment changes in a direction opposite a predicted trend under conditions wherein the current I is constant and variation in the at least one battery parameter is as predicted, and otherwise is operable to select the first state-of-charge value.

15. The state-of-charge estimating device according to claim I wherein the open-circuit voltage estimating part further comprises a parameter-estimating part operable to use the adaptive digital filter computing treatment to perform en bloc estimation of the at least one battery parameter in modified battery model G_LPF(s)·

A(s)·

s·

V=G_LPF(s)·

{B(s)·

s+h}I wherein G_LPF(s) represents transmission characteristics of a low-pass filter of the adaptive digital filter computing treatment and h represents variable efficiency; and

wherein the open-circuit voltage estimating part is further operable to compute the estimated open-circuit voltage V_O from the current I and terminal voltage V and the at least one battery parameter wherein

16. The state-of-charge estimating device according to claim 15 wherein the second state-of-charge estimating part is operable to estimate the second state-of-charge value using the method wherein the method excludes the estimated open-circuit voltage V_O that is estimated by the open-circuit voltage estimating part.

17. The state-of-charge estimating device according to claim 15 wherein the second state-of-charge estimating part is further operable to estimate the second state-of-charge value based on at least one of the current I detected by the current detecting device and the terminal voltage V detected by the terminal voltage detecting device before performing the adaptive digital filter computing treatment.

18. The state-of-charge estimating device according to claim 15 wherein the second state-of-charge estimating part is further operable to estimate the second state-of-charge value by integrating the current I detected with the current detecting device.

19. The state-of-charge estimating device according to claim 18 wherein the second state-of-charge estimating part is further operable to estimate a total capacity of the secondary battery, and to estimate the second state-of-charge value by integrating the current I based on the estimated total capacity and a formula

20. The state-of-charge estimating device according to claim 18 wherein the second state-of-charge estimating part is further operable, when the state-of-charge estimated value-selecting part changes from a state of selection of the first state-of-charge value to a state of selection of the second state-of-charge value, to use the first state-of-charge value just before selection of the second state-of-charge value as an initial value and to start integration of the current I.

21. The state-of-charge estimating device according to claim 15 wherein the second state-of-charge estimating part is further operable to detect a correlation relationship between the current I and the terminal voltage V from the current I detected using the current detecting device and the terminal voltage V detected using the terminal voltage detecting device, to estimate the estimated open-circuit voltage V_O of the secondary battery based on the correlation relationship, and to estimate the second state-of-charge value based on the estimated open-circuit voltage V_O.

22. The state-of-charge estimating device described in claim 15 wherein the first state-of-charge estimating part is operable to perform the adaptive digital filter computing treatment based on values for the current I and terminal voltage V obtained by applying a low-pass-filter or band-pass filter treatment on the current I and terminal voltage V;

and wherein the second state-of-charge estimating part is operable to perform filter treatment having equal delay characteristics to those of the low-pass filter or band-pass filter on the second state-of-charge value.

23. The state-of-charge estimating device described in claim 15 wherein the state-of-charge estimated value-selecting part is further operable to select the second state-of-charge value when there is no change in the at least one battery parameter estimated using the adaptive digital filter computing treatment or when the at least one battery parameter estimated with the adaptive digital filter computing treatment changes in a direction opposite a predicted trend under conditions wherein the current I is constant and variation in the at least one battery parameter is as predicted, and otherwise is operable to select the first state-of-charge value.

24. The state-of-charge estimating device described in claim 15 wherein an amount of time used by the state-of-charge estimated value-selecting part to select from the first state-of-charge value and the second state-of-charge value decreases when an absolute value of the current I increases.

25. A state-of-charge estimating device for estimating a state-of-charge of a secondary battery connected to a load, comprising:

means for detecting a current I through the secondary battery;

means for detecting a terminal voltage V of the secondary battery;

open-circuit voltage estimating means for performing an adaptive digital filter computing treatment to estimate at least one battery parameter in a battery model

$V=\frac{B<br><br>\left(s\right)}{A<br><br>\left(s\right)}·<br><br>I+\frac{1}{A<br><br>\left(s\right)}·<br><br>V_O<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{en}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{bloc}$

based on the current I and terminal voltage V of the secondary battery and the battery model

$V=\frac{B<br><br>\left(s\right)}{A<br><br>\left(s\right)}·<br><br>I+\frac{1}{A<br><br>\left(s\right)}·<br><br>V_O,$

and for estimating an estimated open-circuit voltage V_O of the secondary battery, wherein A(s) and B(s) are polynomials of Laplace operator s; and

state-of-charge estimating means for estimating the state-of-charge based on the estimated open-circuit voltage V_O of the secondary battery and a previously derived relationship between an open-circuit voltage and a state-of-charge of the secondary battery when the current I is not constant and for estimating the state-of-charge using a state-of-charge estimating method that allows estimation of the state-of-charge excluding the open-circuit voltage V_O when the current I is constant.

26. A state-of-charge estimating method for estimating a state-of-charge of a secondary battery connected to a load, comprising:

detecting a current I through the secondary battery;

detecting a terminal voltage V of the secondary battery;

performing an adaptive digital filter computing treatment to estimate at least one battery parameter in a battery model

$V=\frac{B<br><br>\left(s\right)}{A<br><br>\left(s\right)}·<br><br>I+\frac{1}{A<br><br>\left(s\right)}·<br><br>V_O<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{en}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{bloc}$

based on the current I and terminal voltage V of the secondary battery and the battery model

$V=\frac{B<br><br>\left(s\right)}{A<br><br>\left(s\right)}·<br><br>I+\frac{1}{A<br><br>\left(s\right)}·<br><br>V_O,$

and to estimate an estimated open-circuit voltage V_O of the secondary battery, wherein A(s) and B(s) are polynomials of Laplace operator s; and

estimating a first state-of-charge value based on the estimated open-circuit voltage V_O of the secondary battery and a previously derived relationship between an open-circuit voltage and a state-of-charge;

estimating a second state-of-charge value using a method capable of estimating the state-of-charge even if the current I is constant while one or more of the at least one battery parameter varies;

selecting the second state-of-charge value as the state-of-charge when the current I is constant; and

selecting the first state-of-charge value as the state-of-charge when the current I varies.