State of charge detection device

• US 10,429,444 B2
• Filed: 09/26/2012
• Issued: 10/01/2019
• Est. Priority Date: 01/31/2012
• Status: Active Grant

• Current Assignee: Primearth EV Energy Company Limited (Toyota Motor Corporation)
• Original Assignee: Primearth EV Energy Company Limited (Toyota Motor Corporation)
• Inventors: Koba, Daisuke, Takeda, Sachio, Maegawa, Katsunori, Osaka, Tetsuya
• Primary Examiner(s): Evanisko, Leslie J
• Assistant Examiner(s): Hinze, Leo T
• Application Number:
  US14/343,743
• Publication Number:
  US 20140229130A1
• Time in Patent Office: 2,561 Days
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: G01R 31/382 Arrangements for monitoring battery or accumulator variables, e.g. SoC
• 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 10/48 Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte constructional details of current conducting connections for detecting conditions inside cells or batteries, e.g. details of voltage sensing terminals, H01M50/569
• CPC Class Codes: H02J 7/00716 in response to integrated charge or discharge current
• CPC Class Codes: H02J 7/04 Regulation of charging current or voltage
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

The present invention pertains to the detection of the state of charge of a battery, whereby the complex impedance in the diffusion region of the battery is used. An arithmetic device such as a computer determines the slope of the complex impedance at least two different frequencies in the diffusion region of a rechargeable battery when a straight-line approximation has been made. The state of charge of the rechargeable battery is detected by using the slope that has been determined, and the relationship between the state of charge and slopes that have been stored in advance in a storage means.

Claims

1. A rechargeable battery system, comprising:

a rechargeable battery formed by a nickel-metal hydride battery;

an AC voltage source connected to the rechargeable battery, wherein the AC voltage source is configured to apply AC voltage at least at two frequencies;

an impedance analyzer connected to the rechargeable battery;

a processing unit configured to calculate a slope of a straight line or an approximate straight line which connects together two or more complex impedances of different frequencies in the diffusion region of the battery measured by the impedance analyzer, wherein the diffusion region defines a plot of complex impedances of the battery at frequencies lower than about 10 Hertz; and

a memory that preliminarily stores correlations between a slope and a state of charge, wherein the slope decreases as the state of charge increases,

wherein the processing unit changes a detection method of the state of charge of the battery between when the state of charge is less than or equal to a specific threshold value of 0 to 10% and when the state of charge exceeds the threshold value, such that the processing unit detects and outputs the state of charge of the battery by comparing the calculated slope and the correlations between the slope and the state of charge stored in the memory when the state of charge of the battery is less than or equal to the threshold value and detects and outputs the state of charge of the battery in another method without using the calculated slope; and

recycling the rechargeable battery based on the calculated state of charge.

2. The rechargeable battery system according to claim 1, wherein the processing unit calculates the slope of the straight line or the approximate straight line that connects together the two complex impedances or more of different frequencies by use of a two-dimensional plane which employs a real-axis component and an imaginary-axis component for axes.

3. The rechargeable battery system of claim 1, wherein the diffusion region defines a plot of complex impedances of the battery, which includes a curved portion and a nearly-straight portion, at frequencies lower than a point of inflection of the nearly-straight portion.

4. The rechargeable battery system of claim 1, wherein the correlations include correlations of slope angles in the diffusion region of the complex impedances with respect to the state of charge.

5. A hybrid or electric vehicle, comprising the rechargeable battery system of claim 1.