State-of-Charge Estimation Using Two-Stage Parameter Optimization
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Solution Overview
Problem
Conventional state-of-charge estimation methods for secondary batteries face challenges in accurately determining the convergence value of the adjustment parameter, leading to potential divergence or prolonged calculation times due to unsuitable initial value settings, especially when the voltage profile deviates from assumed ranges.
Innovation Solution
The method involves selecting specific voltage measurement values at strategic timings to calculate initial adjustment parameters, using a voltage characteristic formula with exponential attenuation terms, and iteratively correcting these parameters to minimize errors, thereby stabilizing the open-circuit voltage estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a complicated nonlinear function such as a quartic or more exponential attenuation function is used for approximate calculation of the open-circuit voltage, then the precision of open-circuit voltage approximation is improved, but the calculation complexity and time required for optimizing the adjustment parameter increases
Solution Approach 1:
The patent segments the parameter optimization process into two distinct phases: (1) a rough optimization phase using simplified calculation methods to obtain initial parameter values, and (2) a precise optimization phase using the full complicated nonlinear function with the initial values as starting points. This segmentation reduces the overall calculation complexity while maintaining high precision in the final result.
Solution Approach 2:
The patent performs preliminary optimization using simplified voltage characteristic formulas before applying the complicated nonlinear function. This preliminary action provides good initial values for the adjustment parameters, which significantly reduces the computational burden and convergence time of the subsequent precise optimization phase using the full nonlinear model.
2Device complexity
If conventional voltage characteristic formulas such as polynomial or logarithmic functions are used, then the calculation complexity is reduced, but the precision of open-circuit voltage approximation deteriorates
Solution Approach 1:
The patent merges the advantages of simple and complicated voltage characteristic formulas by combining them in a two-stage optimization process. The simple formulas (polynomial, logarithmic) are used in the first stage for their computational efficiency, while the complicated nonlinear function (quartic or more exponential attenuation) is used in the second stage for its high precision approximation capability. This merging allows the system to achieve both calculation efficiency and measurement precision.
3Ease of operation
If the initial value of the adjustment parameter is set using only the initial voltage measurement value and the voltage measurement value immediately before completion, then the method is simple to implement, but the optimization may diverge or take extremely long time when the voltage profile deviates from assumed ranges
Solution Approach 1:
The patent performs a preliminary rough optimization using simplified voltage characteristic formulas and multiple voltage measurement values before initiating the precise optimization with the complicated nonlinear function. This preliminary action produces more reliable initial values for the adjustment parameters, ensuring that the subsequent optimization process converges reliably even when the voltage profile deviates from assumed ranges.
Solution Approach 2:
The patent introduces an intermediary optimization step using simplified formulas as a bridge between the initial parameter settings and the final precise optimization. This intermediary process acts as a mediator that transforms potentially unreliable initial values into reliable starting points for the final optimization, ensuring convergence reliability while maintaining ease of operation.
Data Source
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AI summary
There is provided a state-of-charge estimation method, a state-of-charge estimation device, and a secondary-battery power system that may quickly and stably determine the convergence value of an adjustment parameter of a voltage characteristic formula that may approximate change over time of an open-circuit voltage of a secondary battery with high precision by appropriately setting the initial value of the adjustment parameter. At step S14, a selected voltage measurement values V1, VMbi ((i = 1 to (n-1)), and VMm are used to calculate an initial value A0i (i = 1 to n) of an adjustment parameter Ai (i = 1 to n). In addition, at step S15, an integer string bi (i = 1 to (n - 1)) and a real number C are used to calculate an initial value B0i (i = 1 to n) of an adjustment parameter Bi (i = 1 to n).