EV Battery SOC Control for Salt Concentration Non-uniformity
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Solution Overview
Problem
High-rate deterioration of secondary batteries in electric vehicles due to non-uniform salt concentration, exacerbated by high-current charging or discharging, is not effectively inhibited by existing control methods, which can lead to premature battery degradation.
Innovation Solution
An electric vehicle system comprising a vehicle drive apparatus, a secondary battery, a current sensor, and an electronic control unit that calculates an evaluation value indicating battery deterioration and adjusts the target remaining capacity and charging/discharging controls to prevent high-rate deterioration by avoiding low SOC ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the control value of SOC is lowered to charge the battery with larger amount of electricity, then the battery resistance is promptly recovered, but the salt concentration in battery cell surface becomes non-uniform and high-rate deterioration is promoted
Solution Approach 1:
The invention changes the SOC control parameter dynamically based on the evaluation value. When the evaluation value is low (indicating low deterioration risk), the SOC is allowed to decrease to enable larger charging amounts. When the evaluation value exceeds the threshold (indicating high deterioration risk), the SOC is constrained to remain above a predetermined value, preventing the battery from operating in the low-SOC range that causes salt concentration non-uniformity and high-rate deterioration.
2Productivity
If high-current charging or discharging is performed, then charging/discharging speed is improved, but salt concentration becomes non-uniform and internal resistance increases
Solution Approach 1:
The invention introduces a feedback mechanism that continuously monitors the evaluation value (calculated from SOC and temperature) and adjusts the charging/discharging control accordingly. When the evaluation value exceeds the threshold, the system reduces the charging/discharging current to prevent salt concentration non-uniformity, while still allowing operation at higher currents when the evaluation value is below the threshold, thus maintaining productivity when safe.
3Adaptability or versatility
If the battery is used in low-SOC range to increase running distance, then vehicle operation flexibility is improved, but expansion and contraction of negative electrode become large and electrolytic solution is pushed out
Solution Approach 1:
The invention makes the SOC control limit dynamic based on real-time battery conditions (SOC and temperature). Instead of using a fixed low SOC threshold that would allow excessive electrolytic solution loss, the system dynamically adjusts the minimum SOC threshold based on the evaluation value. This allows the battery to operate in lower SOC ranges when conditions are favorable (reducing electrolytic solution loss) while still maintaining operational flexibility.
Data Source
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AI summary
A battery (16) is a secondary battery that receives electricity from a vehicle drive apparatus (22) or outputs electricity to the vehicle drive apparatus (22). A current sensor (24) detects an electric current (I) input into the battery (16) or an electric current (I) output from the battery (16). An ECU (26) controls charging and discharging of the battery (16). The ECU (26) calculates, using the detected electric current from the current sensor (24), an evaluation value (ΣD) indicating the degree of deterioration of the battery (16) due to nonuniformity in the salt concentration in the battery (16) caused by charging and discharging. When the evaluation value (ΣD) reaches a prescribed threshold, the ECU (26) executes control of raising a remaining capacity of the battery, e.g. the SOC of the battery (16).