Battery Internal Resistance Estimation Across Depth of Discharge
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Solution Overview
Problem
Existing methods for estimating direct current internal resistance of batteries, such as IEC 61690, are not accurate when the battery is in use and are affected by the depth of discharge, leading to inconsistent and unreliable resistance readings.
Innovation Solution
A method that defines a depth of discharge detection interval with first and second threshold values, periodically measures discharge current and voltage, calculates the depth of discharge, and uses an open-circuit voltage curve or lookup table to estimate the direct current internal resistance by accumulating voltage differences across the detection interval.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the IEC 61690 two-stage discharge method is used to estimate direct current internal resistance, then the estimation process can be completed with simple voltage and current measurements, but the estimated resistance values vary significantly at different depths of discharge, reducing measurement accuracy
Solution Approach 1:
The patent divides the discharge process into multiple small time intervals (dt) rather than using two discrete stages. By segmenting the continuous discharge process into numerous incremental measurements, the method captures the dynamic behavior of internal resistance across different depths of discharge, allowing for more precise characterization while maintaining operational simplicity through automated incremental sampling.
Solution Approach 2:
The patent transitions from the static two-stage discharge method to a dynamic continuous measurement approach. By performing measurements throughout the entire discharge process and calculating instantaneous internal resistance values at each time point, the method adapts to changing battery conditions and provides accurate resistance estimation regardless of depth of discharge, resolving the contradiction between operational simplicity and measurement precision.
2Reliability
If the IEC 61690 method is applied during actual battery operation, then real-time resistance estimation is achieved, but the required two-stage discharge protocol cannot be executed, making the method inapplicable
Solution Approach 1:
The patent performs preliminary characterization of the open-circuit voltage curve across the full range of depths of discharge before actual operation. This pre-established voltage curve serves as a reference for calculating internal resistance during real-time operation without requiring disruptive two-stage discharge protocols, enabling reliable resistance estimation during normal battery usage while maintaining operational continuity.
Solution Approach 2:
The patent enables continuous internal resistance monitoring throughout the battery discharge process rather than interrupting operation for discrete measurements. By continuously measuring voltage and current at each time interval during normal discharge and applying the established calculation method, the system maintains both reliability through real-time monitoring and ease of operation by avoiding protocol interruptions.
3Loss of information
If multiple measurements are taken at different depths of discharge using IEC 61690, then comprehensive resistance data is obtained, but the results show inconsistent resistance values, indicating measurement unreliability
Solution Approach 1:
The patent acknowledges that internal resistance is dynamic and varies with depth of discharge rather than treating it as a static parameter. By measuring and calculating resistance at multiple time intervals throughout discharge and presenting the progression of resistance values, the method provides both comprehensive information about resistance behavior and reliable data for each specific operating condition, resolving the apparent contradiction through proper characterization of dynamic behavior.
Solution Approach 2:
The patent establishes a preliminary open-circuit voltage curve that serves as a reference for accurate resistance calculation at each depth of discharge. This pre-characterization enables consistent and reliable resistance measurements across the entire discharge range by providing accurate expected voltage values against which actual measurements can be compared, eliminating the inconsistency problem while maintaining complete information about resistance variation.
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
This method provides a more accurate estimation of direct current internal resistance across varying depths of discharge, improving the reliability of battery performance assessment during actual usage.
Implementation Method 1
A battery's internal resistance refers to a resistance to a current passing through the inside of a battery
Implementation Method 2
The less the direct current internal resistance of the battery is, the less the voltage drop inside the battery will be when it outputs the current
Data Source
AI summary
The invention presents a method for estimating a direct current internal resistance of a battery, which defines a depth of discharge detection interval including a first threshold and a second threshold. When the battery is discharging, a currently battery voltage are periodically measured, a currently depth of discharge is calculated, and an open-circuit voltage is queried. The currently battery voltage is subtracted from the open-circuit voltage to obtain a voltage difference. The voltage difference is continuously accumulated to obtain a currently accumulated voltage difference. The currently depth of discharge reaches the first threshold or the second threshold, the currently accumulated voltage difference is a first accumulated voltage difference or a second accumulated voltage difference. A difference value between the first accumulated voltage difference and the second accumulated voltage difference is divided by a discharging amount in the depth of discharge detection interval to obtain the direct current internal resistance.