Method of estimating state of charge of secondary cell, state-of-charge estimation device, cell pack, electronic apparatus, and electric vehicle

• US 9,581,650 B2
• Filed: 05/21/2013
• Issued: 02/28/2017
• Est. Priority Date: 05/28/2012
• Status: Active Grant

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Hotta, Shin
• Primary Examiner(s): Badii, Behrang
• Assistant Examiner(s): ALSOMIRI, MAJDI A
• Application Number:
  US13/898,864
• Publication Number:
  US 20130317697A1
• Time in Patent Office: 1,379 Days
• Field of Search: 701/34.4, 702/63, 320/132, 324/426, 324/433
• US Class Current: 1/1
• CPC Class Codes: B60L 2240/545 Temperature
• CPC Class Codes: B60L 2240/547 Voltage
• CPC Class Codes: B60L 2240/549 Current
• CPC Class Codes: B60L 2260/44 by parameter estimation
• CPC Class Codes: B60L 58/12 responding to state of charge [SoC]
• 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 31/382 Arrangements for monitoring battery or accumulator variables, e.g. SoC
• CPC Class Codes: G01R 31/3842 combining voltage and current measurements
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries

Abstract

A method of estimating a state of charge of a secondary cell includes: calculating a value of (∂E_emf/∂T) in advance on the assumption that E_emf is an electromotive force of the secondary cell and T is a temperature of the secondary cell; and calculating the state of charge based on at least a value of (∂E_emf/∂T) for which a value of the state of charge is set as a variable, a temperature measurement value of the secondary cell, and a current measurement value of the secondary cell.

Claims

1. A method, comprising:

in a state-of-charge estimation device configured to estimate a state of charge of a secondary cell;

measuring a temperature of the secondary cell using a temperature measurement device;

calculating a value of to be stored in a storage unit, where E_emf is an electromotive force of the secondary cell and T is the temperature of the secondary cell; and

calculating the state of charge based on at least the stored value of ∂

E_emf/∂

T for which a value of the state of charge is set as a variable, a value of the measured temperature of the secondary cell, and a current measurement value of the secondary cell.

2. The method according to claim 1, wherein the state of charge is calculated based on an internal resistance value of the secondary cell.

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

calculating the state of charge at time t₁ based on a state of charge at time t₀ and the current measurement value of the secondary cell from time t₀ to time t₁;

calculating an actual measurement temperature increase amount Δ

T_real based on the temperature measurement value of the secondary cell from time t₀ to time t₁;

calculating a temperature increase amount Δ

T_calc of the secondary cell from time t₀ to time t₁ based on the value of ∂

_emf/∂

T for which the value of the state of charge is set as the variable; and

correcting the state of charge at time t₀ such that an absolute value Δ

T_diff=|Δ

T_real−

Δ

T_calc|, which is a difference between the actual measurement temperature increase amount Δ

T_real and the calculated temperature increase amount Δ

T_calc of the secondary cell from time t₀ to time t₁ becomes a second value in the event the absolute value Δ

T_diff exceeds a first value,

wherein the second value is less than the first value.

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

for a temperature change of the secondary cell is equal to or less than a temperature measurement limit of the temperature measurement device and an open voltage change of the secondary cell is equal to or less than a voltage measurement limit of a voltage measurement device;

measuring an open voltage of the secondary cell by the voltage measurement device;

measuring the temperature of the secondary cell by the temperature measurement device; and

calculating the value of ∂

E_emf/∂

T based on the measured open voltage and the measured temperature.

5. The method according to claim 4, wherein the voltage measurement limit of the voltage measurement device is 1×

10<sup>−

6</sup> volts and the temperature measurement limit of the temperature measurement device is 1×

10<sup>−

2</sup>°

C.

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

measuring, in a state that is lacking a diffusion reaction of lithium ions, an open voltage of the secondary cell by a voltage measurement device, and the temperature of the secondary cell by the temperature measurement device; and

calculating the value of ∂

E_emf/∂

T based on the measured open voltage and the measured temperature,

wherein the secondary cell includes a lithium-ion secondary cell.

7. The method according to claim 6, wherein the state in which the diffusion reaction of lithium ions does not occur is a state in which a temperature change of the secondary cell is equal to or less than a temperature measurement limit of the temperature measurement device and an open voltage change of the secondary cell is equal to or less than a voltage measurement limit of the voltage measurement device.

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

calculating the state of charge at time t₁ based on the state of charge at time t₀ and the current measurement value of the secondary cell from time t₀ to time t₁;

calculating an actual measurement temperature increase amount based on the temperature measurement value of the secondary cell from time t₀ to time t₁;

calculating a temperature increase amount of the secondary cell from time t₀ to time t₁ based on the value of ∂

E_emf/∂

T; and

correcting the state of charge at time t₀ such that an absolute value, which is a difference between the actual measurement temperature increase amount and the calculated temperature increase amount of the secondary cell from time t₀ to time t₁ becomes a second in the event the absolute value exceeds a first value,

wherein the second value is less than the first value.

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

calculating a state of charge at time t₁ based on a state of charge at time t₀ and a current measurement value of the secondary cell from time t₀ to time t₁; and

correcting the state of charge at time t₀ based on an actual measurement temperature increase amount from time t₀ to time t₁.

10. A state-of-charge estimation device configured to calculate a state of charge of a secondary cell, comprising:

a storage unit configured to store a value of ∂

E_emf/∂

T where E_emf is an electromotive force of the secondary cell and T is a temperature of the secondary cell;

a temperature measurement device configured to measure the temperature of the secondary cell;

a current measurement device configured to measure a current of the secondary cell; and

an arithmetic device configured to calculate the state of charge based on at least the value of ∂

E_emf/∂

T for which a value of the state of charge is set as a variable, a temperature measurement value of the secondary cell, and a current measurement value of the secondary cell.

11. A cell pack, comprising:

a secondary cell; and

a state-of-charge estimation device configured to calculate a state of charge of the secondary cell,

wherein the state-of-charge estimation device includes;

a storage unit configured to store a value of ∂

E_emf/∂

T, wherein E_emf is an electromotive force of the secondary cell and T is a temperature of the secondary cell;

a temperature measurement device configured to measure the temperature of the secondary cell;

a current measurement device configured to measure a current of the secondary cell; and

an arithmetic device configured to calculate the state of charge based on at least the value of ∂

E_emf/∂

T for which a value of the state of charge is set as a variable, a temperature measurement value of the secondary cell, and a current measurement value of the secondary cell.

12. An electronic apparatus, comprising:

a secondary cell; and

a cell pack that includes a state-of-charge estimation device configured to calculate a state of charge of the secondary cell,

wherein the state-of-charge estimation device includes;

a storage unit configured to store a value of ∂

E_emf/∂

T, where E_emf is an electromotive force of the secondary cell and T is a temperature of the secondary cell;

a temperature measurement device configured to measure the temperature of the secondary cell;

a current measurement device configured to measure a current of the secondary cell; and

an arithmetic device configured to calculate the state of charge based on at least the value of ∂

E_emf/∂

T for which a value of the state of charge is set as a variable, a temperature measurement value of the secondary cell, and a current measurement value of the secondary cell.

13. An electric vehicle, comprising:

a secondary cell; and

a cell pack that includes a state-of-charge estimation device configured to calculate a state of charge of the secondary cell,

wherein the state-of-charge estimation device includes;

a storage unit configured to store a value of ∂

E_emf/∂

T, where E_emf is an electromotive force of the secondary cell and T is a temperature of the secondary cell;

a temperature measurement device configured to measure the temperature of the secondary cell;

a current measurement device configured to measure a current of the secondary cell; and

an arithmetic device configured to calculate the state of charge based on at least the value of ∂

E_emf/∂

T for which a value of the state of charge is set as a variable, a temperature measurement value of the secondary cell, and a current measurement value of the secondary cell.