Secondary battery capacity measurement system and secondary battery capacity measurement method

Patent metadata

Field	Value
Publication number	US-10126369-B2
Application number	US-201514829743-A
Country	US
Kind code	B2
Filing date	Aug 19, 2015
Priority date	Sep 1, 2014
Publication date	Nov 13, 2018
Grant date	Nov 13, 2018

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 system comprising at least one memory configured to store computer program code and at least one processor configured to access the at least one memory and operate according to the computer program code, the computer program code including:
a data convertor code configured to cause at least one of the at least one processor to determine a partial derivative characteristic curve of a capacity-to-voltage derivative over voltage from actually measured values of voltage and current in a partial region of a normal operating region of a secondary battery;
State of Charge (SOC) estimation code configured to cause at least one of the at least one processor to compute a difference between the partial derivative characteristic curve and a reference derivative curve that is derived from a positive material of a positive electrode of the secondary battery and a negative material of a negative electrode of the secondary battery and that indicates 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 of the secondary battery using a minimum of actually measured data; and
maximum capacity code configured to cause at least one of the at least one processor to estimate a maximum value of capacity of the secondary battery that is deteriorated, from the partial derivative characteristic curve and the reference derivative curve.

2. The system according to claim 1 ,
wherein the reference derivative curve is given by a separating curve complex of a first characteristic derivative curve that is derived from the positive material of the positive electrode of the secondary battery and a second characteristic derivative curve that is derived from the negative material of the negative electrode of the secondary battery.

3. The 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 system according to claim 1 ;
wherein each of the partial derivative characteristic curve and the reference derivative curve is a pair of first and second curves,
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
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 system according to claim 1 , wherein the computer program code further includes:
a reference derivative curve reconstruction code configured to cause at least one of the at least one processor to, when the maximum capacity computer corrects the reference derivative curve, perform fitting between the partial derivative characteristic curve and the reference derivative curve and correct 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 code is configured to cause at least one of the at least one processor to estimate the maximum capacity using the corrected reference derivative curve.

6. The system according to claim 4 ,
wherein the SOC computer code includes SOC computation ability determination code configured to cause at least one of the at least one processor to:
determine 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, and
in response to the maximum value being less than the first threshold, the SOC estimation code causes at least one of the at least one processor to estimate the SOC.

7. The system according to claim 6 ,
wherein, in response to the returning SOC corresponding to a returning point of the immediately previous charging/discharging being included in the partial derivative characteristic curve, the SOC computation ability determination code causes the at least one of the at least one processor to determine 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
in response to the SOC threshold deing included in the partial derivative characteristic curve, the SOC estimation code causes at least one of the at least one processor to estimate the SOC.

8. The system according to claim 6 ,
wherein the SOC computation ability determination code causes the at least one of the at least one processor to determine 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, and
in response to the difference exceeding the second threshold, the SOC estimation code causes at least one of the at least one processor to estimate the SOC.

9. The system according claim 4 ,
wherein the maximum capacity code includes maximum capacity computation ability determination code configured to cause at least one of the at least one processor to:
determine 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, and
in response to the maximum value exceeding the first threshold, the maximum capacity code causes at least one of the at least one processor to estimate the maximum capacity.

10. The system according to claim 9 ;
in response to the returning SOC corresponding to a returning point of the immediately previous charging/discharging being included in the partial derivative characteristic curve, the maximum capacity computation ability determination code configured to cause at least one of the at least one processor to:
determine 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
in response to the SOC threshold being included in the partial derivative characteristic curve, the maximum capacity code causes at least one of the at least one processor to estimate the maximum capacity.

11. The system according to claim 9 ,
wherein the maximum capacity computation ability determination code is configured to cause at least one of the at least one processor to:
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, and
in response to the difference exceeding the third threshold, the maximum capacity code causes at least one of the at least one processor to estimate the maximum capacity.

12. The system according to claim 1 , wherein the computer program code further includes:
averaging code configured to cause at least one of the at least one pro

Assignees

• Yokogawa Electric Corp

Inventors

• Torai Soichiro
• Nakagomi Masaru

Classifications

• G01R31/3842 Primary

  combining voltage and current measurements · CPC title

• G01R31/3648

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

• 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

• G01R31/389 Primary

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

• G01R31/382

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