Virtual Cell SOC Estimation for LFP Battery Packs

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Solution Overview

Problem

Estimating the state of charge (SOC) of Lithium Iron Phosphate (LFP) battery cells with relatively flat open circuit voltage (OCV-SOC) curves is challenging due to their similarity with Nickel Cobalt Manganese (NCM) cells, leading to inaccurate SOC estimation.

Innovation Solution

A battery monitoring system utilizing a virtual cell model defined relative to NCM cells with pronounced OCV-SOC curves, combined with a physical cell model, to generate accurate SOC estimates for LFP cells, incorporating a virtual cell model for definitive outputs and a physical model for indefinitive outputs, and employing a Kalman filter for real-time correction.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a virtual cell model defined relative to NCM cells with pronounced OCV-SOC curves is used, then SOC estimation accuracy is improved, but device complexity increases due to requiring both virtual and physical cell models

Engineering Contradiction:

ImproveSOC estimation accuracyVSAvoidsystem complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent creates a virtual cell model that copies the characteristics of NCM cells with pronounced OCV-SOC curves, allowing the system to benefit from the better voltage-SOC relationship without physically installing NCM cells. This virtual copy enables accurate SOC estimation while maintaining the actual LFP battery pack configuration.

Inventive Principle:

Principle #26Copying

Solution Approach 2:

The virtual cell model acts as an intermediary between the physical LFP battery cells and the SOC estimation algorithm. It transforms the flat OCV-SOC characteristics of LFP cells into the more distinguishable voltage patterns of NCM cells, enabling more accurate SOC determination without directly modifying the physical battery chemistry.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If LFP battery cells are used due to strong thermal stability, then reliability is improved, but SOC measurement precision deteriorates due to flat OCV-SOC curves

Engineering Contradiction:

Improvethermal stabilityVSAvoidSOC estimation accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent changes the voltage-SOC parameter relationship by introducing a virtual cell model with different electrochemical characteristics. Instead of working directly with the flat LFP OCV-SOC curve, the system transforms the measurements through a virtual model that exhibits a more pronounced voltage-SOC relationship, enabling better SOC resolution while keeping the reliable LFP chemistry intact.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS20250208214A1Virtual sensing cell state of charge estimation for battery pack

Publication Date: 2025.06.26 GM GLOBAL TECHNOLOGY OPERATIONS LLC

AI summary

A battery monitoring system for a battery pack of an electric vehicle. The battery monitoring system may include a virtual cell model configured for generating a definitive output based on a current through the battery pack and a definitive equivalent circuit model (ECM) for a virtual cell and a physical cell model configured for generating an indefinitive output based on the current and an indefinitive ECM for the battery pack. The battery monitoring system may include an SOC transformation module configured for generating a battery SOC for the battery pack based at least in part on the definitive and indefinitive outputs.