Cell System Mixed Voltage SOC Estimation
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Solution Overview
Problem
Existing battery pack systems inaccurately estimate the state of charge (SOC) due to inherent differences in degradation characteristics between main constituent batteries and capacity detection batteries, leading to potential overcharging or premature charging termination.
Innovation Solution
A cell system comprising a first cell unit with batteries exhibiting small voltage changes and a second cell unit with batteries showing large voltage changes, combined with a mixed voltage detection device to accurately estimate SOC, and a capacity estimation device using a correlation map to determine the state of charge and capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a battery B exhibiting large voltage change is connected in series for capacity detection, then the SOC estimation capability is improved, but the measurement precision deteriorates due to degradation deviation between battery B and batteries A
Solution Approach 1:
The patent introduces a third battery (battery C) with intermediate voltage characteristics as a mediator between the main batteries A and the detection battery B. This intermediate battery serves as a reference that degrades at a rate closer to batteries A, allowing for more accurate SOC estimation by comparing voltages in a way that compensates for degradation effects.
Solution Approach 2:
The patent changes the voltage characteristics parameter of the detection system by selecting a battery C with specific voltage properties that are intermediate between batteries A and battery B. This parameter selection allows the system to maintain good SOC estimation capability while reducing the deviation caused by degradation.
2Difficulty of detecting and measuring
If battery B with large voltage change is used for detection, then the detectability of SOC is improved, but the device complexity increases due to needing multiple different battery types
Solution Approach 1:
The patent segments the detection function by assigning different roles to different batteries: batteries A for power delivery, battery C as an intermediate reference for degradation compensation, and battery B for voltage-based SOC detection. This segmentation allows each component to be optimized for its specific function while working together in a coordinated system.
Solution Approach 2:
Battery C serves multiple functions: it acts as both a power-contributing battery like batteries A and as a reference battery for degradation compensation. This multi-functionality reduces the need for separate dedicated reference batteries, simplifying the overall system configuration.
Data Source
AI summary
A proposed cell system 100 has a simple second cell unit 20 (for instance, a unit cell (second cell 21)) electrically connected in series to a first cell unit 10 (battery pack) that constitutes a main power source. The state of charge (SOC) of the first cell unit 10 is detected on the basis of a mixed voltage (V3) of first cells 11 included in the first cell unit 10 and the second cell 21.