SOC ESTIMATION DEVICE FOR SECONDARY BATTERY

• US 20170010327A1
• Filed: 11/28/2014
• Published: 01/12/2017
• Est. Priority Date: 02/25/2014
• Status: Active Application

• Current Assignee: Mitsubishi Electric Corporation
• Original Assignee: Mitsubishi Electric Corporation
• Inventors: NISHIGUCHI, Hiroto, FUKUMOTO, Hisatoshi, YAMAGUCHI, Shingo
• Granted Patent: US 10,254,346 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: G01R 31/3835 involving only voltage measurements
• 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: G01R 31/44 Testing lamps
• CPC Class Codes: H02J 7/0048 Detection of remaining charge capacity or state of charge [SOC]
• CPC Class Codes: H02J 7/005 Detection of state of health [SOH]

Abstract

A State of Charge (SOC) estimation device for a secondary battery in which a correlation curve indicating a relationship between an SOC and Open Circuit Voltage (OCV) differs between a charging process and discharging process. The SOC estimation device estimates the SOC based on a relational formula in which as actually measured OCV increases, weights are assigned to the correlation curve indicating the relationship between the SOC and OCV in the discharging process, and as actually measured OCV decreases, weights are assigned to the correlation curve indicating the relationship between the SOC and OCV in the charging process. With the SOC estimation device, when the correlation curve indicating the relationship between the SOC and OCV differs between the charging and discharging processes, not only when the secondary battery is being used but also when use is started after use of the secondary battery is stopped, SOC can be accurately estimated.

Claims

1. An State of Charge (SOC) estimation device for a secondary battery in which a correlation curve indicating a relationship between an SOC and an Open Circuit Voltage (OCV) differs between a charging process and a discharging process,

wherein the SOC estimation device comprises a means for estimating the SOC based on a relational formula in which as actually measured OCV is increased, weights are assigned to the correlation curve indicating the relationship between the SOC and the OCV in the discharging process, and as actually measured OCV is decreased, weights are assigned to the correlation curve indicating the relationship between the SOC and the OCV in the charging process, and

wherein in the means for estimating the SOC, an OCV at which a difference Δ

Q in a charge amount Q at the same OCV is maximized, in a correlation curve indicating a relationship between the OCV and the charge amount Q in the charging process and the discharging process, is a threshold OCV, and the means estimates the SOC based on a relational formula in which as the actually measured OCV becomes smaller than the threshold OCV, weights are assigned to the correlation curve indicating the relationship between the SOC and the OCV in the charging process, and as the actually measured OCV becomes greater than the threshold OCV, weights are assigned to the correlation curve indicating the relationship between the SOC and the OCV in the discharging process.

3. The SOC estimation device for a secondary battery according to claim 1,

wherein when the actually measured OCV is less than the threshold OCV, the relational formula is the following formula:

SOC_c=β

/2×

SOC_d+(1−

β

/2)×

SOC_c

where SOC_e is an estimated SOC, SOC_d is an SOC calculated by introducing the actually measured OCV into the correlation curve indicating the relationship between the SOC and the OCV in the discharging process, SOC_c is an SOC calculated by introducing the actually measured OCV into the correlation curve indicating the relationship between the SOC and the OCV in the charging process and β

is a value derived from a maximum value Δ

Q_max of a difference Δ

Q/Δ

Q in the charge amount Q at the actually measured OCV in the correlation curve indicating the relationship between the OCV and the charge amount Q in the charging process and the discharging process and is a weight coefficient which has a value of 0 to 1 and when the actually measured OCV is greater than the threshold OCV, the relational formula is the following formula;

SOC_e=β

/2×

SOC_c+(1−

β

/2)×

SOC_d

where SOC_e, SOC_c, SOC_d and β

are as defined above.

4. The SOC estimation device for a secondary battery according to claim 1,

wherein the correlation curve indicating the relationship between the SOC and the OCV is determined, in advance, for each State of Health (SOH), and as the correlation curve used for the assignment of weights, a correlation curve corresponding to a calculated SOH is selected.

2. (canceled)

5. An SOC estimation device for a secondary battery in which a correlation curve indicating a relationship between an SOC and an OCV differs between a charging process and a discharging process,

wherein the SOC estimation device comprises a means for estimating the SOC based on a relational formula in which as an SOC calculated from a charge amount obtained by summing a charging current and a discharging current of the secondary battery is increased, weights are assigned to the correlation curve indicating the relationship between the SOC and the OCV in the discharging process and as the SOC calculated from the charge amount obtained by summing the charging current and the discharging current of the secondary battery is decreased, weights are assigned to the correlation curve indicating the relationship between the SOC and the OCV in the charging process,

wherein in the means for estimating the SOC, an SOC in which a difference AOCV in the OCV at the same SOC is maximized, in the correlation curve indicating the relationship between the SOC and the OCV in the charging process and the discharging process, is a threshold SOC, and the means estimates the SOC based on a relational formula in which as the SOC calculated from the charge amount obtained by summing the charging current and the discharging current of the secondary battery becomes smaller than the threshold SOC, weights are assigned to the correlation curve indicating the relationship between the SOC and the OCV in the charging process and as the SOC calculated from the charge amount obtained by summing the charging current and the discharging current of the secondary battery becomes greater than the threshold SOC, weights are assigned to the correlation curve indicating the relationship between the SOC and the OCV in the discharging process.

7. The SOC estimation device for a secondary battery according to claim 5,

wherein when the calculated SOC is less than the threshold SOC, a synthesized OCV is calculated by the following formula:

OCV_m=γ

/2×

OCV_d+(1−

γ

/2)×

OCV_c

where OCV_m is the OCV synthesized in the calculated SOC, OCV_d is an OCV calculated by introducing the calculated SOC into the correlation curve indicating the relationship between the SOC and the OCV in the discharging process, OCV_c is an OCV calculated by introducing the calculated SOC into the correlation curve indicating the relationship between the SOC and the OCV in the charging process and γ

is a value derived from a maximum value Δ

OCV_max of a difference Δ

OCV/Δ

OCV in the OCV at the calculated SOC in the correlation curve indicating the relationship between the SOC and the OCV in the charging process and the discharging process and which is a weight coefficient having a value of 0 to 1 and when the calculated SOC is more than the threshold SOC, the synthesized OCV is calculated by the following formula;

OCV_m=γ

/2×

OCV_c+(1−

γ

y/2)×

OCV_d

where OCV_m, OCV_c, OCV_d and γ

are defined above,

a relational formula indicating a relationship between the synthesized OCV and the calculated SOC is determined in advance and

the SOC is estimated by introducing an actually measured OCV into the relational formula.

8. The SOC estimation device for a secondary battery according to claim 5,

wherein the correlation curve indicating the relationship between the SOC and the OCV is determined in advance for each SOH, and as the correlation curve used for the assignment of weights, a correlation curve corresponding to a calculated SOH is selected.

6. (canceled)

9. A method for estimating an State of Charge (SOC) of a secondary battery in which a correlation curve indicating a relationship between an SOC and an Open Circuit Voltage (OCV) differs between a charging process and a discharging process,

wherein the method comprises a step for estimating the SOC based on a relational formula in which as actually measured OCV is increased, weights are assigned to the correlation curve indicating the relationship between the SOC and the OCV in the discharging process, and as actually measured OCV is decreased, weights are assigned to the correlation curve indicating the relationship between the SOC and the OCV in the charging process, and

wherein in the step for estimating the SOC, an OCV at which a difference □

Q in a charge amount Q at the same OCV is maximized, in a correlation curve indicating a relationship between the OCV and the charge amount Q in the charging process and the discharging process, is a threshold OCV, and the step estimates the SOC based on a relational formula in which as the actually measured OCV becomes smaller than the threshold OCV, weights are assigned to the correlation curve indicating the relationship between the SOC and the OCV in the charging process, and as the actually measured OCV becomes greater than the threshold OCV, weights are assigned to the correlation curve indicating the relationship between the SOC and the OCV in the discharging process.