Battery SOC Estimation via Voltage Change Rate Correction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing battery state of charge (SOC) estimation methods, such as ampere-hour integration and open-circuit voltage methods, suffer from inaccuracies due to measurement errors and variations in voltage curves caused by temperature and charging rate, leading to unreliable long-term SOC accuracy.
Innovation Solution
A method that calculates a corrected state of charge by determining voltage change rates and using multi-level voltage change rate thresholds, along with temperature and charging rate correlations, to improve SOC estimation accuracy, particularly on the high-side of charging, by filtering voltage fluctuations and ensuring the battery is in a constant-current charging state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ampere-hour integration method is used for SOC estimation, then SOC can be calculated based on current measurement, but measurement accuracy errors and initial SOC errors cause calculation results to have errors that accumulate over time, leading to poor long-term SOC accuracy
Solution Approach 1:
The patent combines multiple SOC estimation methods (ampere-hour integration, open-circuit voltage, and voltage change rate methods) into a unified system that selects and switches between methods based on battery operating conditions. This merging allows the system to leverage the strengths of each method while mitigating their individual weaknesses, particularly preventing error accumulation in long-term operation by periodically using voltage-based correction methods.
Solution Approach 2:
The patent dynamically changes estimation parameters based on battery state. It monitors voltage change rates and switches between different estimation approaches depending on whether the battery is in constant-current charging, constant-voltage charging, or idle states. This parameter adaptation ensures accurate SOC estimation across different operating conditions while maintaining long-term accuracy.
2Measurement precision
If open-circuit voltage method is used for SOC estimation, then SOC can be determined from voltage measurement, but voltage curves vary under different temperatures and C-rates, resulting in low SOC accuracy
Solution Approach 1:
The patent implements dynamic adaptation of the voltage-SOC relationship based on real-time temperature and charging rate conditions. Instead of using a fixed voltage-SOC curve, the system adjusts the curve selection or parameters according to current temperature and C-rate, ensuring accurate SOC estimation across varying operating conditions. This dynamic approach resolves the contradiction between measurement precision and adaptability.
3Measurement precision
If multi-level voltage change rate thresholds and correction mechanisms are implemented, then SOC accuracy is improved, but calculation complexity increases
Solution Approach 1:
The patent segments the charging process into distinct phases (constant-current, constant-voltage, transition) and applies different estimation strategies to each phase. By dividing the overall SOC estimation task into manageable segments corresponding to different operating conditions, the system achieves high accuracy without requiring complex calculations across all conditions simultaneously. This segmentation reduces overall system complexity while maintaining precision.
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
The present invention relates to a method for determining a state of charge of a battery, including: (a) acquiring a state of charge of the battery at a current sampling time point tn; (b) acquiring a voltage Vn, a temperature Tn, and a charging rate Cn of the battery at the current sampling time point tn, and a voltage Vi of the battery at a sampling time point ti, and calculating a voltage difference Vn-Vi between the voltage Vn and the voltage Vi, where the sampling time point ti is a time point at which a state of charge of the battery is acquired within a preset time period before the sampling time point tn; (c) when the voltage difference Vn-Vi is greater than or equal to a preset voltage threshold, calculating a voltage change rate based on the voltage difference Vn-Vi and a time difference tn-ti between the sampling time point tn and the sampling time point ti; and (d) when the voltage change rate is greater than or equal to a preset voltage change rate threshold for the first time, acquiring a corrected state of charge of the battery as an actual state of charge of the battery based on correspondences between corrected states of charge, and the preset voltage change rate threshold, temperatures, and charging rates of the battery based on the temperature Tn and the charging rate Cn of the battery at the sampling time point tn.