Secondary Battery Control System with Electrochemical Boundary Conditions
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Solution Overview
Problem
Existing control systems for secondary batteries in hybrid vehicles face challenges in accurately estimating the internal state, leading to inefficiencies in charge/discharge control, particularly due to boundary conditions that do not accurately reflect actual battery behavior, resulting in potential overcharge or overdischarge and reduced battery life.
Innovation Solution
A control system that includes a battery state estimating unit, a battery information generating unit, and a load control unit, utilizing a battery model with appropriately set boundary conditions to dynamically estimate the internal state of the secondary battery, preventing overcharge and overdischarge by quantizing drive power based on electrochemical balanced states rather than concentration differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If boundary conditions for diffusion equation are set based on concentration difference, then material transportation can be analyzed, but the analysis precision deteriorates when battery is sufficiently relaxed because artificially processing must be performed on calculation algorithm
Solution Approach 1:
The patent changes the boundary condition parameter from concentration difference to reaction current. Specifically, the boundary condition is set such that the flux of material at the interface is proportional to the reaction current rather than the concentration gradient, which eliminates the need for artificial processing when the battery is relaxed and current flows naturally in the model
Solution Approach 2:
The patent substitutes the traditional concentration-difference-driven diffusion model with a reaction-current-driven model. This replacement eliminates the contradiction by using reaction current as the driving force for material transportation analysis, which naturally accounts for both charged and relaxed states without requiring artificial calculation adjustments
2Reliability
If boundary conditions are set based on concentration difference, then diffusion analysis can be performed, but reliability deteriorates because arbitrariness occurs in analysis of internal state
Solution Approach 1:
The patent introduces feedback by using reaction current as the boundary condition parameter. The reaction current, which is directly measurable and physically meaningful, provides a reliable feedback mechanism that eliminates arbitrariness in the analysis. The boundary condition is formulated as flux being proportional to reaction current, creating a physically grounded and reliable model
Solution Approach 2:
The patent changes the measurement parameter from concentration difference (which requires artificial processing and introduces arbitrariness) to reaction current (which is directly measurable and eliminates arbitrariness). This parameter substitution improves reliability by grounding the model in physically measurable quantities
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the precision of internal state estimation and charge/discharge control, maximizing battery performance while preventing local deterioration and thermal runaway, thereby extending the battery's lifespan and ensuring reliable operation.
Implementation Method 1
analyze an electrochemical reaction at an interface between an electrode (active material) and an ion conductor
Implementation Method 2
analyze a material transportation (diffusion phenomenon) inside the electrode and the ion conductor
Data Source
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Figure 3~4
Figure 5
AI summary
A battery model unit (60) includes an electrode reaction model unit (61) based on the Butler_Volmer equation, an electrolyte lithium concentration distribution model unit (62) analyzing a lithium ion concentration distribution in an electrolyte solution by a diffusion equation, an active material lithium concentration distribution model unit (63) analyzing an ion concentration distribution in a solid state of an active material by a diffusion equation, a current/potential distribution model unit (64) for obtaining a potential distribution according to the charge conservation law, a thermal diffusion model unit (65) and a boundary condition setting unit (66). The boundary condition setting unit (66) sets a boundary condition at an electrode interface such that a reacting weight at the electrode interface is not determined by a difference in material concentration between positions but a deviation from an electrochemically balanced state causes a change with time in lithium concentration at the interface and thus a (time-based) drive power for material transportation. Thereby, an appropriate charge/discharge control can be performed based on the battery model having the appropriately set battery condition.