Battery SOC Estimation Using Self-Discharge Balance Control
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Solution Overview
Problem
Existing methods for estimating the state of charge of lithium iron phosphate batteries suffer from inaccuracies due to self-discharge in replacement modules or main circuit batteries, leading to unstable battery system performance.
Innovation Solution
Implement self-discharge detection and balance control on replacement and main circuit batteries, particularly at low (0%–30% SOC) and high (90%–100% SOC) states, using a larger capacity replacement module to correct the state of charge estimation through proportional conversion and energy transfer or consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a replacement module with larger capacity is used to replace the original battery, then the estimation interval of state of charge is enlarged, but self-discharge in the replacement module or main circuit battery causes large error in estimation
Solution Approach 1:
The patent implements a feedback mechanism by continuously monitoring the state of charge of both the replacement module and main circuit battery, comparing their relationship, and performing balance control when deviations occur. This closed-loop feedback ensures that self-discharge errors are detected and corrected, maintaining reliable SOC estimation throughout the extended charge range.
Solution Approach 2:
The replacement module acts as an intermediary with larger capacity that can be independently managed and balanced. By using this intermediate battery module, the system can perform balance control on the replacement module separately from the main circuit battery, preventing self-discharge errors from directly affecting the main battery SOC estimation.
2Measurement precision
If self-discharge detection and balance control are performed frequently, then the accuracy of state of charge estimation is improved, but the complexity of the control system increases
Solution Approach 1:
The patent changes the parameter of SOC estimation from direct measurement to proportional calculation based on the replacement module's SOC. By using the relationship SOC_main = k × SOC_replacement, the system achieves accurate SOC estimation without requiring complex direct measurement circuits for the main battery, thus improving accuracy while controlling system complexity.
3Adaptability or versatility
If the state of charge estimation is expanded to wider intervals including low and high SOC ranges, then the usability of the battery system is improved, but the error from self-discharge increases
Solution Approach 1:
The patent performs preliminary balance control on the replacement module before it is used for SOC estimation of the main battery. By pre-charging or pre-discharging the replacement module to a known state and maintaining its SOC relationship with the main battery, the system ensures accurate SOC estimation across the full charge range including low and high SOC intervals where self-discharge effects are most significant.
Data Source
AI summary
A method and associated device, the method including: obtaining the state of charge of a replacement module, and obtaining the state of charge of a main circuit battery by the state of charge of the replacement module, wherein the replacement module replaces an original battery and the capacity of the replacement module is greater than the original battery, and the original battery is connected in series with the main circuit battery in a lithium iron phosphate battery branch of the battery system; conducting self-discharge detection on the replacement module and the main circuit battery, and carrying out balance control when the replacement module or the main circuit battery has a large self-discharge; and after balance control, determining an updated state of charge of the replacement module, and updating the state of charge of the main circuit battery according to the updated state of charge of the replacement module.