SECONDARY BATTERY DEGRADATION DETERMINATION METHOD AND SECONDARY BATTERY DEGRADATION DETERMINATION DEVICE

• US 20150355288A1
• Filed: 08/18/2015
• Published: 12/10/2015
• Est. Priority Date: 02/19/2013
• Status: Active Grant

• Current Assignee: Furukawa Automotive Systems Incorporated (Furukawa Electric Company Limited), Furukawa Electric Company Limited
• Original Assignee: Furukawa Automotive Systems Incorporated (Furukawa Electric Company Limited), Furukawa Electric Company Limited
• Inventors: YOKOYAMA, Koichi, SATO, Etsuzo
• Granted Patent: US 10,386,420 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01R 31/389 Measuring internal impedance, internal conductance or related variables
• CPC Class Codes: G01R 31/392 Determining battery ageing or deterioration, e.g. state of health
• CPC Class Codes: H01M 10/4285 Testing apparatus
• CPC Class Codes: H02J 2310/40 The network being an on-board power network, i.e. within a vehicle
• CPC Class Codes: H02J 7/0048 Detection of remaining charge capacity or state of charge [SOC]
• CPC Class Codes: H02J 7/14 for charging batteries from dynamo-electric generators driven at varying speed, e.g. on vehicle
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

Provided are a secondary battery degradation determination method and a secondary battery degradation determination device which can detect degradation of a secondary battery in advance even before an engine starts. When it is determined in Step S1 that a vehicle is in a stop state, a stable-state open-circuit voltage OCV is measured in Step S2 and internal resistance R1 is calculated in Steps S3 and S4. On the other hand, when it is determined in Step S1 that a starter 21 is operated, a maximum discharge current value Inew is measured in Step S5 and a maximum discharge current value Is is updated in Steps S6 and S7. In Step S14, a minimum voltage Vs is calculated. In Step S15, the stable-state open-circuit voltage OCV and the minimum voltage Vs are compared with predetermined threshold values to perform the degradation determination of a secondary battery 10.

Claims

1. A secondary battery degradation determination method comprising:

a driving state determination step of determining a driving state of a vehicle provided with a secondary battery on the basis of a current value of the secondary battery;

an open-circuit voltage measurement step of measuring an open-circuit voltage OCV of the secondary battery;

an internal resistance calculation step of detecting a current and a voltage between terminals while the secondary battery is being discharged and calculating internal resistance R1 of the secondary battery;

a maximum current detection step of, when a predetermined load provided in the vehicle is operated with a discharge current equal to or greater than a predetermined value, detecting a maximum discharge current value Inew which is a maximum value of the discharge current;

a maximum current update step of comparing the detected maximum discharge current value Inew with a stored maximum discharge current value Is, updating the maximum discharge current value Is to the larger of the two maximum discharge current values, and storing the updated maximum discharge current value;

a temperature detection step of detecting a temperature of the secondary battery;

a state-of-charge estimation step of estimating a state of charge of the secondary battery;

an internal resistance correction step of correcting the internal resistance R1 to internal resistance R1c at a predetermined reference temperature, on the basis of the state of charge estimated in the state-of-charge estimation step and the temperature detected in the temperature detection step, using a table or a relational expression which is made in advance to indicate a relation between the internal resistance and the state of charge and temperature of the secondary battery;

a minimum voltage calculation step of calculating a minimum voltage Vs of the secondary battery when the load is operated based on the following expression;

Vs=OCV−

R1c×

Is

using the open-circuit voltage OCV, the corrected internal resistance R1c, and the maximum discharge current value Is; and

a degradation determination step of determining that the secondary battery has degraded when the open-circuit voltage OCV is equal to or greater than a first threshold value and the minimum voltage Vs is less than a second threshold value.

2. The secondary battery degradation determination method according to claim 1,

wherein in the internal resistance calculation step, the secondary battery is discharged in a predetermined discharge pattern, a current and a voltage between the terminals are detected while the secondary battery is discharged in the predetermined discharge pattern, and the internal resistance R1 of the secondary battery is calculated;

when the vehicle is determined to be in a stop state in the driving state determination step, the open-circuit voltage measurement step and the internal resistance calculation step are performed;

when the load is determined to be operated in the driving state determination step, the maximum current detection step and the maximum current update step are performed; and

when the degradation determination of the secondary battery is performed, the temperature detection step, the state-of-charge estimation step, the internal resistance correction step, the minimum voltage calculation step, and the degradation determination step are performed.

3. The secondary battery degradation determination method according to claim 2,

wherein the predetermined discharge pattern is a substantially square wave including a predetermined discharge frequency of a discharge current when the load is operated.

4. The secondary battery degradation determination method according to claim 2,

wherein the internal resistance calculation step is performed in a predetermined cycle or in response to a predetermined execution request when the vehicle is in the stop state.

5. The secondary battery degradation determination method according to claim 3,

wherein the internal resistance calculation step is performed in a predetermined cycle or in response to a predetermined execution request when the vehicle is in the stop state.

6. The secondary battery degradation determination method according to claim 1,

wherein in the internal resistance calculation step, the internal resistance R1 of the secondary battery is calculated using a load current and a response voltage before and after the load is operated;

when the vehicle is determined to be in a stop state in the driving state determination step, the open-circuit voltage measurement step is performed;

when the load is determined to be operated in the driving state determination step, the internal resistance calculation step, the maximum current detection step, and the maximum current update step are performed; and

when the degradation determination of the secondary battery is performed, the temperature detection step, the state-of-charge estimation step, the internal resistance correction step, the minimum voltage calculation step, and the degradation determination step are performed.

7. The secondary battery degradation determination method according to claim 1,

wherein in the open-circuit voltage measurement step, the voltage between the terminals of the secondary battery is measured in a predetermined cycle from the time when the vehicle is determined to be in the stop state in the driving state determination step and the discharge current from the secondary battery is equal to or less than a predetermined value, the measured voltages between the terminals are approximated with an exponential function having time as a variable when the number of the measured voltages between the terminals reaches a predetermined number, and the open-circuit voltage OCV is estimated using the exponential function.

8. The secondary battery degradation determination method according to claim 1,

wherein in the open-circuit voltage measurement step, the voltage between the terminals of the secondary battery is measured after a predetermined period of time elapses from the time when the vehicle is determined to be in the stop state in the driving state determination step and the discharge current from the secondary battery is equal to or less than a predetermined value and the measured voltage is set to the open-circuit voltage OCV.

9. The secondary battery degradation determination method according to claim 1,

wherein the state of charge includes at least one of the charging rate, stratification, and polarization of the secondary battery.

10. The secondary battery degradation determination method according to claim 1,

wherein in the internal resistance correction step, the internal resistance R1 is corrected to the internal resistance R1c at a temperature that is lower than the reference temperature by a predetermined temperature.

11. The secondary battery degradation determination method according to claim 1,

wherein in the driving state determination step, the driving state of the vehicle is determined further using information of a communication device provided in the vehicle.

12. The secondary battery degradation determination method according to claim 1,

wherein in the degradation determination step the secondary battery is determined to be insufficiently charged when the open-circuit voltage OCV is less than the first threshold value and the minimum voltage Vs is less than the second threshold value.

13. A secondary battery degradation determination device comprising:

a current sensor that detects a current of a secondary battery;

a voltage sensor that detects a voltage between terminals of the secondary battery;

a temperature sensor that detects a temperature of the secondary battery;

a driving state determination means for determining a driving state of a vehicle provided with the secondary battery using a current value input from the current sensor;

an open-circuit voltage measurement means for measuring an open-circuit voltage OCV of the secondary battery;

an internal resistance calculation means for receiving the current and the voltage between the terminals from the current sensor and the voltage sensor while the secondary battery is being discharged and calculating internal resistance R1 of the secondary battery;

a maximum current detection means for, when a predetermined load provided in the vehicle is operated with a discharge current equal to or greater than a predetermined value, receiving the discharge current from the current sensor, and detecting a maximum discharge current value Inew which is a maximum value of the discharge current;

a maximum current update means for comparing the maximum discharge current value Inew detected by the maximum current detection means and a stored maximum discharge current value Is, updating the maximum discharge current value Is to the larger of the two maximum discharge current values, and storing the updated maximum discharge current value;

a state-of-charge estimation means for estimating a state of charge of the secondary battery;

a storage unit that stores a table or a relational expression which is made in advance and indicates a relation between the state of charge and temperature and the internal resistance of the secondary battery;

an internal resistance correction means for reading the table or the relational expression from the storage unit and correcting the internal resistance R1 to internal resistance R1c at a predetermined reference temperature on the basis of the state of charge estimated by the state-of-charge estimation means and the temperature detected by the temperature sensor;

a minimum voltage calculation means for calculating a minimum voltage Vs of the secondary battery when the load is operated based on the following expression;

Vs=OCV−

R1c×

Is

using the open-circuit voltage OCV, the corrected internal resistance R1c, and the maximum discharge current value Is; and

a degradation determination means for determining that the secondary battery has degraded when the open-circuit voltage OCV is equal to or greater than a first threshold value and the minimum voltage Vs is less than a second threshold value.

14. The secondary battery degradation determination device according to claim 13, further comprising:

a discharge means for discharging the secondary battery in a predetermined discharge pattern;

wherein the internal resistance calculation means calculates the internal resistance R1 using a current and a voltage between the terminals when the secondary battery is discharged by the discharge means.

15. The secondary battery degradation determination device according to claim 13,

wherein the internal resistance calculation means calculates the internal resistance R1 of the secondary battery using a load current and a response voltage before and after the load is operated.

16. The secondary battery degradation determination device according to claim 13, further comprising:

a charging control means for controlling the charging of the secondary battery;

wherein the degradation determination means determines that the secondary battery has not been sufficiently charged when the open-circuit voltage OCV is less than the first threshold value and the minimum voltage Vs is less than the second threshold value, and the charging control means shifts a charge-discharge balance target to a charging side.