Battery Equivalent Circuit Parameter Estimation for Accurate SOC

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Solution Overview

Problem

Existing battery management systems fail to accurately estimate the state of charge (SOC) due to inaccuracies in current sensors and external noise, and the parameters of equivalent circuit models do not fully reflect changes in electrochemical properties caused by manufacturing deviations or repeated charging/discharging.

Innovation Solution

A method and system for periodically updating the parameters of an equivalent circuit model using recursive least square algorithms, based on measured terminal voltages and currents within a sliding time window, to accurately model dynamic battery characteristics and prevent overcharge/overdischarge.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If ampere counting is used to estimate SOC, then the estimation is simple to implement, but the accuracy deteriorates over time due to current sensor precision limits and external noise

Engineering Contradiction:

Improvesimplicity of SOC estimationVSAvoidaccuracy of SOC estimation

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The patent introduces an equivalent circuit model as an intermediary between the current sensor measurement and the SOC estimation. This model includes voltage sources, resistors, and capacitors that represent the battery's electrochemical behavior. The model acts as a mediator that processes the current measurements through physical laws (Ohm's law, capacitor charge-discharge relationships) to produce more accurate SOC estimates, thereby resolving the contradiction between simplicity and accuracy.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent implements a feedback mechanism where the estimated SOC and terminal voltage from the equivalent circuit model are continuously compared with actual measurements. The discrepancies (errors) are used to update and refine the model parameters (resistance values, capacitance values) in real-time. This feedback loop compensates for accumulated errors in ampere counting and adapts to changing battery conditions, maintaining high accuracy over time.

Inventive Principle:

Principle #23Feedback

2Device complexity

If fixed parameter values from parameter map are used in equivalent circuit model, then the model structure is simple, but the model fails to reflect changes in battery electrochemical properties due to manufacturing deviations or repeated charging/discharging

Engineering Contradiction:

Improvesimplicity of model parameter managementVSAvoidability to reflect battery degradation

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The patent transforms the equivalent circuit model from a static structure with fixed parameters to a dynamic model where parameters (resistance values R1-R4, capacitance values C1-C2) are continuously updated based on real-time battery measurements. The model adapts its parameters in response to changing battery conditions such as temperature, charge/discharge rates, and degradation states, enabling it to reflect actual battery behavior throughout its lifecycle.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent implements continuous parameter estimation and updating of the equivalent circuit model parameters (resistances R1-R4 and capacitances C1-C2) based on real-time measurements of terminal voltage and current. The parameters are adjusted to reflect changes in battery electrochemical properties caused by manufacturing variations, aging, and repeated charging/discharging cycles, thereby maintaining model accuracy throughout the battery's operational life.

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If EKF is used to improve SOC estimation accuracy, then the accuracy is improved, but the computational complexity increases due to periodic parameter updates

Engineering Contradiction:

Improveaccuracy of SOC estimationVSAvoidcomputational complexity of parameter updates

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent segments the equivalent circuit model into distinct electrical components (voltage sources, resistors, capacitors) with separate parameters (R1-R4, C1-C2). This segmentation allows for independent estimation and updating of each parameter based on specific measurement characteristics. The segmented structure simplifies the computational burden compared to updating all parameters simultaneously, as each parameter can be optimized using targeted calculation methods.

Inventive Principle:

Principle #1Segmentation

Data Source

PatentEP3674726B1Method for estimating parameter of equivalent circuit model for battery, and battery management system

Publication Date: 2024.11.06 LG ENERGY SOLUTION LTD

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AI summary

Disclosed is a method and a battery management system for estimating the parameters of an equivalent circuit model for a battery. The equivalent circuit model includes a first resistor, a second resistor connected in series to the first resistor and a capacitor connected in parallel to the second resistor. The method according to an embodiment of the present disclosure individually estimates the resistance of the first resistor and the resistance of the second resistor based on a first number of terminal voltages and a first number of currents measured in a sequential order at each time step in a sliding time window having a predefined size, and stores data indicating the estimated results in the memory.