SOC Estimation Device Voltage Range Control
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Solution Overview
Problem
The SOC estimation accuracy for lithium ion batteries is reduced due to the flat SOC-voltage characteristics, leading to significant SOC fluctuations with small voltage variations within the flat area.
Innovation Solution
A state of charge (SOC) estimation device that includes a first estimation unit to estimate a reference SOC value based on battery voltage and a second estimation unit to estimate the SOC value using the reference value and the integrated battery current. The battery voltage is controlled within specific ranges to improve estimation accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If SOC estimation is performed based on voltage and SOC-voltage characteristics, then the estimation process is simple, but the estimation accuracy is reduced due to flat voltage-SOC characteristics
Solution Approach 1:
The patent combines voltage-based estimation (first estimation unit) and current integration-based estimation (second estimation unit) into a hybrid SOC estimation system. The voltage method provides simplicity while the current integration method compensates for accuracy losses in the flat voltage-SOC region, achieving both simplicity and accuracy through merging two complementary approaches.
Solution Approach 2:
The patent introduces an intermediary calibration process where the battery is charged and discharged to specific voltage ranges to establish accurate reference values. This intermediary calibration step enables the system to compensate for the flat voltage-SOC characteristics without requiring continuous complex measurements during normal operation.
2Adaptability or versatility
If the battery operates within the flat voltage area, then the battery can be charged and discharged flexibly, but the SOC fluctuates greatly with small voltage variations
Solution Approach 1:
The patent implements feedback through continuous monitoring of voltage and current, using the second estimation unit to track SOC changes via current integration. This feedback mechanism detects SOC fluctuations caused by voltage variations in the flat region and compensates by referencing the more stable current-based estimation, maintaining measurement stability while preserving charge-discharge flexibility.
Solution Approach 2:
The patent changes the estimation parameter from voltage-based to current-based when operating in the flat voltage-SOC region. By switching to current integration for SOC estimation during flat area operation, the system maintains measurement stability while allowing flexible charge-discharge operations within the flat voltage range.
3Measurement precision
If the voltage control range is expanded to include specific ranges outside the first range, then the reference value estimation can be performed, but the battery may experience unintended overcharge or overdischarge
Solution Approach 1:
The patent performs preliminary calibration actions by charging and discharging the battery to specific voltage ranges before normal operation. This preliminary action establishes accurate reference values for SOC estimation. During normal operation, the system then references these pre-established values to maintain accuracy without requiring the battery to operate in potentially unsafe voltage ranges.
Solution Approach 2:
The patent dynamically adjusts the voltage control range based on the operational state. The system allows voltage to vary within a first range during normal operation for flexibility, but temporarily expands to a second range only when needed for reference value estimation. This dynamic adjustment ensures accurate estimation while preventing unintended overcharge or overdischarge through controlled, temporary expansion of the voltage range.
Data Source
AI summary
In SOC estimation device, the first estimation unit 36 estimates a reference value of SOC of the battery based on the voltage of the chargeable/dischargeable battery (auxiliary battery). The second estimation unit 38 estimates the estimated value of SOC of the battery based on the estimated reference value and the integrated value of the current of the battery. When the first estimation unit is not performing the process of estimating the reference value, the voltage of the battery is controlled within the first range. When the first estimation unit is executing the process of estimating the reference value, the voltage of the battery is controlled within the second range, and the second range includes a specific range outside the first range. The first estimation unit estimates the reference value based on the voltage of the battery when the value falls within the specific range.