Battery SOC Estimation Using Voltage and Pressure
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Solution Overview
Problem
Existing methods for estimating the state of charge (SOC) of secondary batteries using open circuit voltage (OCV) are inaccurate due to variations in correspondence between OCV and SOC during charging and discharging, leading to suboptimal estimation accuracy.
Innovation Solution
A battery system and control method that utilize both open circuit voltage and internal pressure to estimate SOC by obtaining multiple estimated values based on different correspondences for charging and discharging, and select the most accurate value by comparing differences between these estimates, allowing for accurate SOC estimation even when OCV and internal pressure relationships change.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If SOC is estimated using only open circuit voltage and a single correspondence curve, then the estimation method is simple, but the estimation accuracy deteriorates when correspondence varies between charging and discharging
Solution Approach 1:
The patent segments the SOC estimation process by creating separate correspondence curves for charging and discharging phases. Instead of using a single general curve, the system divides the estimation approach into distinct segments (charging-specific and discharging-specific curves) that are selected based on the current operational phase, thereby improving accuracy without significantly increasing overall system complexity.
Solution Approach 2:
The patent implements a dynamic selection mechanism that automatically switches between different correspondence curves based on the real-time charging-discharging state of the battery. This dynamic adaptation allows the system to maintain high estimation accuracy across varying operational conditions by selecting the most appropriate curve for the current phase.
2Measurement precision
If multiple correspondence curves and selection criteria are used to improve SOC estimation accuracy, then estimation precision improves, but device complexity increases
Solution Approach 1:
The patent prepares multiple correspondence curves in advance for both charging and discharging phases, storing them as pre-computed reference data. This preliminary preparation eliminates the need for complex real-time calculations during operation, as the system only needs to select from pre-existing curves based on simple state detection, thereby managing complexity while maintaining accuracy.
Data Source
AI summary
An ECU obtains an OCV and an internal pressure, obtains a first estimated value of an SOC corresponding to the time of charging and a second estimated value of the SOC corresponding to the time of discharging using the obtained OCV and a first correspondence, obtains a third estimated value of an SOC corresponding to the time of charging and a fourth estimated value of the SOC corresponding to the time of discharging using the obtained internal pressure and a second correspondence, estimates the SOC using at least one of the first or the third estimated value when a first difference between the first and the third estimated value is less than a second difference between the second and the fourth estimated value, and estimates the SOC using at least one of the second or the fourth estimated value when the second difference is less than the first difference.