Estimation of self discharge rate as a measure of battery health

Patent metadata

Field	Value
Publication number	US-11217833-B1
Application number	US-201916690516-A
Country	US
Kind code	B1
Filing date	Nov 21, 2019
Priority date	Jan 12, 2018
Publication date	Jan 4, 2022
Grant date	Jan 4, 2022

Abstract

Various embodiments of a technique to estimate and monitor a self-discharge rate for use as a measure of battery health are described herein. In some embodiments, the technique includes a system including a processor and a memory coupled with the processor. The memory is configured to provide the processor with instructions that when executed cause the processor to receive a plurality of snapshots obtained by monitoring a battery system in a quiescent state at a plurality of times. Each snapshot includes a plurality of cell state values at one of the plurality of times. The memory is further configured to provide the processor with instructions that when executed cause the processor to estimate a self-discharge indicator using at least one snapshot in the plurality of snapshots, compare the self-discharge indicator to a threshold, and recommend a remedy for the battery system in response to the self-discharge indicator exceeding the threshold.

First claim

What is claimed is:

1. A method comprising:
receiving, by a computer server, a plurality of snapshots, wherein:
the plurality of snapshots are obtained by monitoring a battery system in a quiescent state at a plurality of times, and
each snapshot includes a plurality of cell state values for a plurality of cells within a respective sub-module of the battery system at one of the plurality of times;
determining, by the computer server, a state of charge value associated with each cell in the plurality of cells;
estimating, by the computer server, a self-discharge indicator using the state of charge value associated with each cell in the plurality of cells over at least two of the plurality of snapshots taken at two different times;
comparing, by the computer server, the self-discharge indicator to a threshold, wherein the threshold is based at least in part on a capacity to replace lost charge as indicated by a remaining amount of time in the quiescent state, or a capacity to replace lost charge as indicated by a balancing rate and a balancing duty cycle; and
instructing, by the computer server, a cell of the battery system to charge or balance in response to the self-discharge indicator exceeding the threshold.

2. The method of claim 1 , further comprising:
converting the state of charge value associated with each cell in the plurality of cells into a capacity associated with each cell in the plurality of cells; and
estimating the self-discharge indicator using the state of charge value using the plurality of snapshots including estimate a self-discharge rate by taking a time derivative of the capacity associated with each cell in the plurality of cells over at least two of the plurality of snapshots.

3. The method of claim 1 , wherein:
the battery system includes a plurality of battery sub-modules;
each of the plurality of battery sub-modules includes a plurality of sub-module cells; and
each cell in the plurality of sub-module cells has a cell state value captured in each of the plurality of snapshots; and
the method further comprises:
estimating an adjusted value for each cell in the plurality of sub-module cells, including:
selecting a snapshot from the plurality of snapshots;
selecting a cell for which an adjusted value is being estimated from the plurality of sub-module cells;
identifying a battery sub-module in the plurality of battery sub-modules that includes the selected cell;
obtaining a sub-module value associated with each cell in the plurality of sub-module cells, including the selected cell, from the selected snapshot;
generating a representative sub-module value in response to sub-module values associated with each cell in the plurality of sub-module cells obtained from the selected snapshot; and
estimating the adjusted value for the selected cell using a difference between the representative sub-module value and the sub-module value associated with the selected cell from the selected snapshot; and

identifying which cells are self-discharging in response to the estimated adjusted value for each cell in the plurality of sub-module cells.

4. The method of claim 3 , wherein the adjusted value is at least one of an adjusted self-discharge rate or an adjusted cell state value, and
wherein the sub-module value is at least one of a sub-module self-discharge rate or a sub-module cell state value.

5. The method of claim 1 , wherein:
the battery system includes a plurality of battery sub-modules; and
each of the plurality of battery sub-modules includes a plurality of sub-module cells; and
each cell in the plurality of sub-module cells has a cell state value captured in each of the plurality of snapshots;
each of the cell state values captured in each of the plurality of snapshots for each cell in the plurality of sub-module cells is a voltage associated with each cell in the plurality of sub-module cells, and
the method further comprises:
estimating an adjusted cell state value for each cell in the plurality of sub-module cells including:
selecting a snapshot from the plurality of snapshots;
selecting a cell for which an adjusted state of charge value is being estimated from the plurality of sub-module cells;
identifying a battery sub-module in the plurality of battery sub-modules that includes the selected cell;
obtaining a sub-module voltage associated with each cell in the plurality of sub-module cells, including the selected cell, from the selected snapshot;
converting each of the sub-module voltages associated with each cell in the plurality of sub-module cells into a state of charge value associated with each cell in the plurality of sub-module cells;
generating a representative sub-module state of charge value in response to sub-module state of charge values associated with each cell in the plurality of sub-module cells obtained from the selected snapshot; and
estimating an adjusted state of charge value for the selected cell using a difference between the representative sub-module state of charge value and the sub-module state of charge value associated with the selected cell from the selected snapshot; and

identifying which cells are self-discharging in response to the estimated adjusted state of charge value for each cell in the plurality of sub-module cells.

6. A system comprising a server configured to:
receive a plurality of snapshots, wherein:
the plurality of snapshots are obtained by monitoring a battery system in a quiescent state at a plurality of times, and
each snapshot includes a plurality of cell state values for a plurality of cells within a respective sub-module of the battery system at one of the plurality of times;

determine a state of charge value associated with each cell in the plurality of cells;
estimate a self-discharge indicator using the state of charge value associated with each cell in the plurality of cells over at least two of the plurality of snapshots taken at two different times;
compare the self-discharge indicator to a threshold, wherein the threshold is based at least in part on a capacity to replace lost charge as indicated by a remaining amount of time in the quiescent state, or a capacity to replace lost charge as indicated by a balancing rate and a balancing duty cycle; and
instruct a cell of the battery system to charge or balance in response to the self-discharge indicator exceeding the threshold.

7. The system recited in claim 6 , wherein:
the battery system includes a plurality of battery sub-modules,
each battery sub-module in the plurality of battery sub-modules includes a plurality of sub-module cells, and
the cell of the battery system is a first sub-module cell in a first battery sub-module.

8. The system recited in claim 7 , wherein the server is further configured to:
convert the state of charge value associated with each cell in the plurality of sub-module cells into a capacity associated with each cell in the plurality of sub-module cells; and
estimate the self-discharge indicator using the state of charge value using the plurality of snapshots including estimate a self-discharge rate by taking a time derivative of the capacity associated with each cell in the plurality of sub-module cells over at least two of the plurality of snapshots.

9. The system recited in claim 7 , wherein:
each cell in the plurality of sub-module cells has a cell state value captured in each of the plurality of snapshots; and
the server is further configured to:
estimate an adjusted value for each cell in the plurality of sub-module cells, including:
selecting a snapshot from the plurality of snapshots;
selecting a cell for which an adjusted value is being estimated from the plurality of sub-module cells;
identifyi

Assignees

• Wisk Aero Llc

Inventors

• Hom Lewis Romeo
• Rathi Dhruv

Classifications

• H01M10/48 Primary

  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 title

• H01M10/482 Primary

  for several batteries or cells simultaneously or sequentially · CPC title

• G01R31/3835

  involving only voltage measurements · CPC title

• G01R31/3648

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

• Y02E60/10

  Energy storage using batteries · CPC title