Secondary battery capacity measurement system and secondary battery capacity measurement method

Patent metadata

Field	Value
Publication number	US-2016061908-A1
Application number	US-201514829743-A
Country	US
Kind code	A1
Filing date	Aug 19, 2015
Priority date	Sep 1, 2014
Publication date	Mar 3, 2016
Grant date	—

Abstract

A secondary battery capacity measurement system includes a data convertor, an SOC computer, and a maximum capacity computer. The data convertor determines a partial derivative characteristic curve of a capacity-to-voltage derivative over voltage, the partial derivative characteristic curve indicating a characteristic of a capacity-to-voltage derivative, from a set of historical data of time-sequentially-measured values of voltage and current. The SOC computer computes a difference between the partial derivative characteristic curve and a reference derivative curve indicating a reference characteristic of the capacity-to-voltage derivative, and fits the partial derivative characteristic curve to the reference derivative curve by reducing the difference to estimate an SOC. The maximum capacity computer estimates a maximum value of capacity, from the partial derivative characteristic curve and the reference derivative curve. The reference derivative curve is given by a complex of first and second characteristic derivative curves respectively derived from positive and negative electrode materials.

First claim

What is claimed is:

1 . A secondary battery capacity measurement system comprising:
a data convertor configured to determine a partial derivative characteristic curve of a capacity-to-voltage derivative over voltage, the partial derivative characteristic curve indicating a characteristic of a capacity-to-voltage derivative, from a set of historical data of time-sequentially-measured values of voltage and current; an SOC computer configured to compute a difference between the partial derivative characteristic curve and a reference derivative curve indicating a reference characteristic of the capacity-to-voltage derivative, and configured to fit the partial derivative characteristic curve to the reference derivative curve by reducing the difference to estimate an SOC; and a maximum capacity computer configured to estimate a maximum value of capacity, from the partial derivative characteristic curve and the reference derivative curve, wherein the reference derivative curve is given by a complex of first and second characteristic derivative curves, the first characteristic derivative curve is derived from a positive material of a battery positive electrode, and the second characteristic derivative curve is derived from a negative material of a battery negative electrode.

2 . The secondary battery capacity measurement system according to claim 1 ,
wherein the reference derivative curve is given by a separating curve complex of the first and second characteristic derivative curves.

3 . The secondary battery capacity measurement system according to claim 2 ,
wherein the first and second characteristic derivative curves are approximated with first and second functions which include first and second characteristic parameters of phase transition of the positive material and the negative material, respectively; and the curves of the first and second functions are adjustable by the first and second characteristic parameters, respectively.

4 . The secondary battery capacity measurement system according to claim 1 ;
wherein each of the partial derivative characteristic curves and the reference derivative curve is a pair of first and second curves, wherein the first curve representing a first relationship of correspondence between the voltage V in the battery and a value dQ/dV obtained by differentiating the capacity Q by taking a change d/dV in the voltage as a differential operator, and wherein the second curve representing a second relationship of correspondence between the capacity Q in the battery and a value dV/dQ obtained by differentiating the voltage value V by taking a change d/dQ in the capacity as a differential operator.

5 . The secondary battery capacity measurement system according to claim 1 ; further comprising:
a reference derivative curve reconstructor that, when the maximum capacity computer corrects the reference derivative curve, performs fitting between the partial derivative characteristic curve and the reference derivative curve and that corrects the reference derivative curve by adjusting the characteristic derivative curves derived from the positive electrode and the negative electrode so as to correspond the fitted shape of the partial derivative characteristic curve, wherein the maximum capacity computer estimates the maximum capacity using the corrected reference derivative curve.

6 . The secondary battery capacity measurement system according to claim 4 ,
wherein the SOC computer has an SOC computation ability determiner that determines whether or not the maximum value of the value dQ/dV in the partial derivative characteristic curve of the first relationship of correspondence is less than a first threshold set beforehand, and wherein, if the SOC computation ability determiner determines that the maximum value of the value dQ/dV in the partial derivative characteristic curve of the first relationship of correspondence is less than the first threshold set beforehand, the SOC computer estimates the SOC.

7 . The secondary battery capacity measurement system according to claim 6 ,
wherein, if the returning SOC corresponding to a returning point of the immediately previous charging/discharging is included in the partial derivative characteristic curve, the SOC computation ability determiner determines whether or not the SOC threshold, based on the peak of the reference derivative curve because of the phase transition of the electrode material of the battery, is included in the partial derivative characteristic curve, and if the judgment is that the SOC threshold is included in the partial derivative characteristic curve, the SOC computer estimates the SOC.

8 . The secondary battery capacity measurement system according to claim 6 ,
wherein the SOC computation ability determiner determines whether or not difference between the maximum value and the minimum value of the value dV/dQ in the partial derivative characteristic curve of the second relationship of correspondence exceeds a second threshold set beforehand, and wherein, if the SOC computation ability determiner determines that the difference between the maximum value and the minimum value of the value dV/dQ in the partial derivative characteristic curve of the second relationship of correspondence exceeds the second threshold set beforehand, the SOC computer estimates the SOC.

9 . The secondary battery capacity measurement system according claim 4 ,
wherein the maximum capacity computer has a maximum capacity computation ability determiner that determines whether or not the maximum value of the value dQ/dV in the partial derivative characteristic curve of the first relationship of correspondence exceeds the first threshold set beforehand, and wherein, if the maximum capacity computation ability determiner determines that the maximum value of the value dQ/dV in the partial derivative characteristic curve of the first relationship of correspondence exceeds the first threshold set beforehand, the maximum capacity computer estimates the maximum capacity.

10 . The secondary battery capacity measurement system according to claim 9 ;
wherein, if the returning SOC corresponding to a returning point of the immediately previous charging/discharging is included in the partial derivative characteristic curve, the maximum capacity computation ability determiner determines whether or not the SOC threshold, based on the peak of the reference derivative curve because of the phase transition of the electrode material of the battery, is included in the partial derivative characteristic curve, and if the judgment is that the SOC threshold is included in the partial derivative characteristic curve, the maximum capacity computer estimates the maximum capacity.

11 . The secondary battery capacity measurement system according to claim 9 ,
wherein the maximum capacity computation ability determiner determines whether or not difference between the maximum value and the minimum value of the value dV/dQ in the partial derivative characteristic curve of the second relationship of correspondence exceeds a third threshold set beforehand, and wherein, if the maximum capacity computation ability determiner determines that the difference between the maximum value and the minimum value of the value dV/dQ in the partial derivative characteristic curve of the second relationship of correspondence exceeds the third threshold set beforehand, the maximum capacity computer estimates the maximum capacity Q max .

12 . The secondary battery capacity measurement system according to claim 1 , further comprising:
an averaging processor that performs piecewise or moving averaging processing in a prescribed

Assignees

• Yokogawa Electric Corp

Inventors

• Torai Soichiro
• Nakagomi Masaru

Classifications

• H01M2010/4271

  Battery management systems including electronic circuits, e.g. control of current or voltage to keep battery in healthy state, cell balancing · CPC title

• G01R31/382

  Arrangements for monitoring battery or accumulator variables, e.g. SoC · CPC title

• G01R31/3842 Primary

  combining voltage and current measurements · CPC title

• G01R31/3648

  comprising digital calculation means, e.g. for performing an algorithm · CPC title

• G01R31/389 Primary

  Measuring internal impedance, internal conductance or related variables · CPC title