Battery State of Charge Estimation Using Voltage Models
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for estimating the state of charge (SOC) of batteries in portable electronic devices are inadequate as they rely on battery current, which is not always readily available or reliable, and do not effectively account for charging and discharging processes.
Innovation Solution
A method that utilizes battery voltage (VBAT) to build models by observing standard charging and discharging processes, generating membership functions between VBAT and open circuit voltage (OCV) and SOC differences, and applying an optimized gain to estimate SOC, using a system comprising a weighting fuzzifier, dSOC/dV fuzzifier, multiplier, optimizer, and OCV lookup table.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If battery current monitoring is used for SOC estimation, then the estimation can be performed, but the method becomes unreliable when battery current is not readily available
Solution Approach 1:
The patent introduces battery voltage as an intermediary parameter to estimate SOC when direct current measurement is unavailable. The method uses voltage-based models (OCV-SOC relationships, dV/dt analysis) as mediators to infer SOC state without requiring direct access to battery current, thereby resolving the contradiction between reliability and ease of operation.
2Ease of manufacture
If simple voltage-based SOC estimation is used, then the method is easy to implement, but the accuracy is insufficient across various charging and discharging conditions
Solution Approach 1:
The patent applies dynamic modeling approaches that adapt to different operating conditions. The system uses multiple voltage-based models (static OCV-SOC for relaxed states, dynamic dV/dt and d2V/dt2 models for charging/discharging) that are selectively applied based on the current state, maintaining simplicity while improving accuracy across varying conditions through conditional model selection.
Solution Approach 2:
The method changes the parameters used for SOC estimation based on operating conditions. It transitions between different voltage parameters (OCV, dV/dt, d2V/dt2) and applies condition-specific models, allowing the system to maintain high accuracy across different charging and discharging rates while keeping the implementation straightforward through parameter-based model selection.
3Measurement precision
If multiple battery models and complex calculations are used to improve SOC accuracy, then the estimation precision improves, but the computational complexity increases
Solution Approach 1:
The patent segments the SOC estimation process into distinct computational modules: OCV-SOC relationship modeling, dV/dt calculation, d2V/dt2 calculation, and condition-based model selection. Each module performs a specific function with manageable complexity, and the overall system achieves high accuracy through the coordinated operation of these segmented components rather than through a single complex algorithm.
Data Source
AI summary
The invention relates to a method for estimating the state of charge (SOC) of a battery when battery is in the at least states of: charging, discharging, and relaxing. The invention makes use of the battery voltage (VBAT) instead of the battery current. In order to build models in the method, we use standard charging and discharging processes to collect battery information.