Battery SOC Estimation Using Reflection Coefficient Correction

Solution Overview

Problem

Existing methods for determining the state of charge (SOC) of batteries using estimated open-circuit voltage (OCV) are prone to errors, especially in regions with small slopes in the SOC-OCV characteristic curve, leading to inaccuracies in SOC estimation.

Innovation Solution

A power storage apparatus with a control circuit that determines an estimated open-circuit voltage after a predetermined time period following charging or discharging, calculates a first estimated SOC, and adjusts it using a reflection coefficient to account for measurement errors, thereby improving accuracy before polarization is fully eliminated.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of time

If SOC is determined using estimated OCV in a region with small slope in SOC-OCV characteristic curve, then SOC estimation can be performed before polarization is eliminated, but the accuracy of SOC estimation decreases due to larger difference between estimated and actual SOC

Engineering Contradiction:

Improvetime for polarization eliminationVSAvoidaccuracy of SOC estimation

Core Design Contradiction:

Loss of timeVSMeasurement precision

Solution Approach 1:

The control circuit performs preliminary actions by determining the reflection coefficient and the difference between first and second estimated SOC values before polarization is fully eliminated. This allows the system to pre-calculate correction parameters that will be applied to obtain the final accurate SOC value, enabling early SOC determination while maintaining accuracy through pre-computed correction factors.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention implements feedback by using the difference between the first estimated SOC (obtained during polarization) and the second estimated SOC (obtained after polarization elimination) to calculate a reflection coefficient. This reflection coefficient is then fed back to correct the SOC determination in future measurements, continuously improving accuracy by learning from the polarization effect's impact on voltage measurements.

Inventive Principle:

Principle #23Feedback

2Measurement precision

If SOC is determined using estimated OCV in a region with large slope in SOC-OCV characteristic curve, then accuracy of SOC estimation is improved, but SOC determination cannot be performed accurately before polarization is eliminated

Engineering Contradiction:

Improveaccuracy of SOC estimationVSAvoidapplicability before polarization elimination

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The invention changes the parameter used for SOC determination from direct OCV-based estimation to a corrected estimation that incorporates the reflection coefficient. By modifying the determination parameter to account for polarization effects, the system can accurately determine SOC in regions with small slopes (where traditional methods fail) while maintaining the accuracy benefits of using appropriate SOC-OCV characteristic curve regions.

Inventive Principle:

Principle #35Parameter changes

3Loss of time

If measurement is performed before polarization is eliminated, then SOC can be determined earlier, but error in measured voltage value causes larger difference between estimated and actual SOC

Engineering Contradiction:

Improvewaiting time for polarization eliminationVSAvoidreliability of SOC measurement

Core Design Contradiction:

Loss of timeVSReliability

Solution Approach 1:

The control circuit performs preliminary actions by determining the reflection coefficient and the difference between first and second estimated SOC values before polarization is fully eliminated. This allows the system to pre-calculate correction parameters that will be applied to obtain the final accurate SOC value, enabling early SOC determination while maintaining accuracy through pre-computed correction factors.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention implements feedback by using the difference between the first estimated SOC (obtained during polarization) and the second estimated SOC (obtained after polarization elimination) to calculate a reflection coefficient. This reflection coefficient is then fed back to correct the SOC determination in future measurements, continuously improving accuracy by learning from the polarization effect's impact on voltage measurements.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS10436850B2Power storage apparatus and controlling method for the same

Publication Date: 2019.10.08 TOYOTA INDUSTRIES CORP

AI summary

A power storage apparatus including a battery and a control circuit controlling charging/discharging of the battery, wherein the control circuit determines, when a predetermined time period that has elapsed after the charging/discharging of the battery was ended is shorter than a polarization elimination time period extending from a time at which the charging/discharging of the battery was ended to a time at which polarization of the battery was judged to have been eliminated, an estimated open-circuit voltage for the battery after the elimination of the polarization of the battery; determines the difference between a first estimated charge state and a charge state determined by a time at which the estimated open-circuit voltage was estimated; and determines a second estimated charge state by summing the state of charge determined by the time at which the estimated open-circuit voltage was estimated and the product of the difference and the reflection coefficient.