Battery SOC Estimation via Preconditioning Discharge
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Solution Overview
Problem
Existing methods for determining the state-of-charge (SOC) of batteries, particularly in electric and hybrid electric vehicles, face inaccuracies due to hysteresis effects in open-circuit voltage (OCV) measurements, which can lead to significant estimation errors, especially when the battery is in a charging or discharging state.
Innovation Solution
A method and apparatus that precondition the battery by partial discharging to mitigate hysteresis effects, using a battery management system to track charge/discharge history and apply appropriate SOC-to-OCV correlation tables or mathematical models, thereby reducing estimation errors and expanding accurate SOC characterization ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If OCV is used to estimate SOC using pre-determined tables, then the method is simple and quick, but significant estimation errors occur due to hysteresis effects
Solution Approach 1:
The patent applies preliminary action by performing a pre-conditioning discharge operation before SOC measurement. The battery is discharged to a predetermined SOC level (e.g., 50%) before measuring OCV, which eliminates hysteresis effects and ensures accurate SOC estimation. This preliminary discharge action standardizes the battery state before measurement, resolving the contradiction between measurement accuracy and method complexity.
Solution Approach 2:
The patent changes the battery state parameter by controlling the discharge depth to a predetermined SOC level before measurement. By adjusting the discharge parameter to a specific SOC value, the system transforms the battery into a standardized state that eliminates hysteresis effects, enabling accurate OCV-based SOC estimation without complex correction tables.
2Measurement precision
If pre-conditioning discharge is performed to eliminate hysteresis, then SOC estimation accuracy improves, but additional time and energy are required
Solution Approach 1:
The patent applies partial action by performing a pre-conditioning discharge only to a predetermined SOC level (e.g., 50%) rather than fully discharging the battery. This partial discharge is sufficient to eliminate hysteresis effects while minimizing the time and energy required. The predetermined SOC level is optimized to achieve the minimum necessary discharge to eliminate hysteresis, avoiding excessive action.
3Ease of operation
If OCV measurement is taken during charging or discharging, then the method is simple, but hysteresis effects cause significant SOC estimation errors
Solution Approach 1:
The patent performs a preliminary discharge action to a predetermined SOC level before taking OCV measurements. This preliminary action ensures the battery is in a standardized state free from hysteresis effects, allowing simple OCV-based SOC estimation to become accurate. The preliminary discharge transforms the complex hysteresis problem into a simple accurate measurement process.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed solution improves SOC estimation accuracy, reduces processing and power requirements, and extends the range of SOC values that can be characterized with acceptable accuracy, effectively addressing the hysteresis-induced errors in existing methods.
Implementation Method 1
measuring a voltage of the battery block after the battery block has been decoupled from any external load (with no significant charge being drawn from the battery block) for a period of time
Implementation Method 2
certain battery chemistries may exhibit a large hysteresis where the previous state of the battery (either charging or discharging) has a large effect on the OCV at a given SOC
Data Source
AI summary
A method and apparatus for determining the state-of-charge of a battery. In response to detecting that the battery is in a rest state, a pre-conditioning current is drawn from the battery to affect a correlation between the state-of-charge of the battery and an open-circuit voltage of the battery. Thereafter, the open-circuit voltage of the battery is measured, and used to determine the state-of-charge.