Dynamic Reference Time Adjustment for SOC Estimation Error Reduction
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Solution Overview
Problem
Conventional methods for estimating the state of charge (SOC) of electric storage devices face challenges in accuracy due to fixed reference times, leading to increased estimation errors and reduced frequency of SOC calculations, as longer reference times result in less frequent estimations and shorter times lead to larger errors.
Innovation Solution
A state of charge estimation device with a controller and memory that dynamically adjusts the reference time based on total estimation errors, updating the reference time and recalculating the SOC estimation error to improve accuracy, and using a method that calculates the total error by adding first and second estimation errors or updating the tolerance for terminal voltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a relatively long period is set for the reference time, then the SOC estimation error is reduced, but the number of times of SOC estimation during charge/discharge decreases
Solution Approach 1:
The patent applies dynamics by making the reference time variable rather than constant. The reference time is dynamically adjusted based on the elapsed time since charge/discharge cessation and the measured terminal voltage. This allows the system to optimize between accuracy and estimation frequency by adapting the reference time to current battery conditions, thereby resolving the contradiction between reducing estimation error and maintaining frequent estimation updates.
2Productivity
If a relatively short period is set for the reference time, then the number of times of SOC estimation increases, but the SOC estimation error becomes larger
Solution Approach 1:
The patent applies parameter changes by modifying the reference time parameter based on battery state conditions. Instead of using a fixed reference time, the system adjusts the reference time parameter according to the elapsed time since charge/discharge stopped and the terminal voltage characteristics. This parameter adaptation enables the system to achieve both frequent estimations and high accuracy by selecting appropriate reference time values for different operational states.
3Measurement precision
If the reference time is extended to reduce estimation error, then the period in which SOC estimation is not performed is prolonged, but the responsiveness to charge/discharge state changes decreases
Solution Approach 1:
The patent resolves this contradiction through dynamic adjustment of the reference time based on real-time battery conditions. By monitoring the elapsed time since charge/discharge cessation and the terminal voltage, the system dynamically selects the reference time to balance accuracy requirements with responsiveness needs. This dynamic approach ensures that the system responds timely to state changes while maintaining accurate estimations.
Data Source
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AI summary
A battery pack (60) is configured to repeatedly estimate an SOC of a cell (14) that alternately enters a charge/discharge state and a non-charge/discharge state alternately by a current accumulation method and an open circuit voltage (OCV) method. To estimate the SOC of the cell (14) by the OCV method, an error ΔC in the previous SOC estimation by the OCV method is read out of a memory (S22) and an error ΔC in the previous SOC estimation by the current accumulation method is read out of the memory (S24). A total error ΔCS is calculated from the errors ΔC read out of the memory (S26). The reference time KT is set using the total error ΔCS and the SOC is estimated using the set reference time KT.