Battery Capacity Estimation With Polarization-Corrected Voltage
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Solution Overview
Problem
Existing battery capacity estimation methods are inaccurate due to polarization effects, particularly concentration overvoltage, which affects the detection of voltage changes and reduces the estimation accuracy of full charge capacity.
Innovation Solution
A battery system that includes a voltage sensor, current sensor, and a control device with units to calculate cumulative current values, concentration overvoltage, and corrected voltages to subtract polarization effects, enabling accurate detection of maximal voltage changes for precise capacity estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage is detected using a voltage measuring circuit during charging and discharging, then the voltage can be measured, but polarization occurs causing deviation in the detected voltage and reducing estimation accuracy of capacity
Solution Approach 1:
The patent introduces an intermediary calculation method that separates the voltage measurement into two components: the actual cell voltage and the polarization voltage. By calculating the polarization voltage through a dedicated circuit that measures voltage at different time points (V1 at t1, V2 at t2) and computing the difference, the system can eliminate the polarization effect from the capacity estimation calculation, thereby achieving accurate measurement without being affected by the harmful polarization factor
Solution Approach 2:
The patent replaces the direct mechanical voltage measurement approach with an electrical calculation approach. Instead of simply measuring voltage directly (which is affected by polarization), the system uses electrical circuits to measure voltage at different time points and calculates the polarization effect through mathematical operations (subtraction and division by time difference), substituting the direct measurement with a calculated correction method
2Measurement precision
If concentration overvoltage is present during charging and discharging, then the voltage change amount can be detected, but the maximal value detection becomes inaccurate due to lag from concentration overvoltage
Solution Approach 1:
The patent applies preliminary action by measuring the voltage at an earlier time point (t1) before the concentration overvoltage reaches its maximum effect. By capturing the voltage at this preliminary moment and comparing it with the voltage at a later time point (t2), the system can identify the true maximal voltage change before the concentration overvoltage causes a time lag that would mask the actual maximum
Solution Approach 2:
The patent implements feedback by continuously monitoring the voltage at multiple time points and using this information to calculate the polarization effect. The system feeds back the voltage measurements (V1 at t1, V2 at t2) into a calculation that determines the polarization voltage, which is then used to correct the capacity estimation. This feedback mechanism allows the system to compensate for the time lag caused by concentration overvoltage
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 system accurately estimates full charge capacity by detecting maximal voltage changes without polarization influence, improving estimation accuracy by reducing detection errors from concentration overvoltage and other resistances.
Implementation Method 1
a voltage sensor configured to detect a battery voltage that is a voltage of the battery
Implementation Method 2
a current sensor configured to detect a charge and discharge current of the battery
Implementation Method 3
Polarization occurs during charging and discharging of the secondary cell. Therefore, the voltage detected by the voltage measuring circuit includes a deviation due to the polarization. In particular, polarization due to a concentration overvoltage occurs with a lag from an increase or decrease in charge and discharge current.
Data Source
AI summary
The full charge capacity is calculated by adding the cumulative current amount from the time of the maximal value detection to the full charge to the reference capacity in which the change amount of the average value of the second corrected voltage is the maximal value. The first corrected voltage is calculated by subtracting the concentration overvoltage from the voltage of the cell. Based on the relationship between the first corrected voltage and the charge and discharge current in the predetermined period, the second corrected voltage, which is the first corrected voltage when the charge and discharge current is zero, is calculated by extrapolation or interpolation. An average value of the second corrected voltages is calculated, and a change amount of the average value is obtained. Then, the maximal value of the change amount is detected, and the full charge capacity is calculated.