Battery Pack Circuit with Shift Cell for SOC Detection
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Solution Overview
Problem
Conventional methods for detecting the State Of Charge (SOC) and State Of Health (SOH) of batteries with large potential plateau regions, such as LFP-Gr type batteries, face limitations in accuracy due to the flat voltage characteristics, making it difficult to monitor and maintain battery health effectively.
Innovation Solution
A battery pack circuit that includes a standard cell and a shift cell with mirrored capacity coefficient/voltage characteristic curves, allowing for precise detection of SOC and SOH by calculating potential differences and adjusting charge balance using stored characteristic curves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional OCV detection method is used, then SOC can be determined using pre-stored voltage-SOC table, but detection accuracy is limited in potential plateau region where OCV does not change over large area of SOC
Solution Approach 1:
A detection cell is introduced as an intermediary component with different material system characteristics (smaller plateau region) than the normal cells. The detection cell serves as a mediator that provides accurate SOC information through its voltage changes, which are then used to determine the SOC state of the entire battery pack during plateau regions.
Solution Approach 2:
The detection cell is designed with local quality differences - using a different material system (e.g., LiCoO2 positive electrode) compared to the normal LFP-Gr cells. This local differentiation creates distinct voltage characteristics in the detection cell that enable accurate SOC detection, while the normal cells maintain their original performance characteristics.
2Measurement precision
If two types of cells with different material systems are used for accurate SOC detection, then charge depth can be evaluated accurately, but device complexity increases due to need to monitor and reset SOC among multiple cell types
Solution Approach 1:
The SOC detection function is extracted and concentrated into a single detection cell, while the normal cells focus solely on power delivery. This separation simplifies the control system - only the detection cell's voltage needs to be monitored to determine overall pack SOC, eliminating the need to individually monitor and balance multiple cell types during normal operation.
Solution Approach 2:
The detection cell serves multiple functions: it acts as both a functional component contributing to overall pack capacity and as a sensing element for SOC detection. Its voltage characteristics provide universal information about the charge state of the entire battery pack, simplifying the control architecture.
3Ease of manufacture
If conventional battery design is used, then manufacturing is straightforward, but adaptability is limited as it is not easy to perform different design such as increase in capacity or different material systems
Solution Approach 1:
The battery pack is segmented into functionally distinct components: normal cells for power delivery and a separate detection cell for sensing. This segmentation allows independent optimization - normal cells can be produced using standardized processes while the detection cell can be customized with different material systems to provide necessary detection capabilities.
Data Source
AI summary
A battery pack circuit controls the charging and discharging of a battery pack including a first standard cell having a first standard cell capacity coefficient/voltage characteristic curve and a shift cell having a shift cell capacity coefficient/voltage characteristic curve. The shift cell capacity coefficient/voltage characteristic curve mirrors the standard cell capacity coefficient/voltage characteristic curve but is offset from the standard cell capacity coefficient/voltage characteristic curve by a predetermined amount along a reference axis of the shift cell and standard cell capacity coefficient/voltage characteristic curves. A memory stores a potential difference characteristic curve for the standard and shift cells. A processor detects a present potential difference between the standard cell and the shift cell. A processor determines a present capacity coefficient value of the standard cell as a function of the present potential difference detected by the processor and the potential difference characteristic curve.