Battery SOH Determination Using Temperature-SOC Impedance Correction
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Solution Overview
Problem
Existing methods for determining the State Of Function (SOF) and State Of Health (SOH) of batteries, particularly in vehicles, face challenges due to variations in temperature and State Of Charge (SOC), leading to inaccurate calculations of internal impedance and resistance, which complicates the determination of battery health and functionality.
Innovation Solution
A method using a correlative equation with coefficients as functions of temperature and SOC, expressed in polynomial, exponential, or reciprocal functions, to estimate response voltage and determine SOF or SOH by measuring internal impedance or resistance, allowing for high-accuracy corrections and calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If internal impedance or internal resistance is used as an index to determine SOF or SOH, then the determination can be performed, but the accuracy deteriorates because the values are affected by temperature and SOC variations
Solution Approach 1:
The patent applies parameter changes by expressing the correlative function coefficients as functions of temperature and SOC. Specifically, the coefficients a and b in the response voltage equation are defined as functions of temperature T and SOC, allowing the correlative function to dynamically adapt to varying operating conditions. This resolves the contradiction by enabling accurate SOF/SOH determination across different temperature and SOC levels without requiring separate calibration for each condition.
2Measurement precision
If the correlative function coefficients are made constant, then the calculation is simple, but the measurement precision deteriorates due to inability to account for temperature and SOC variations
Solution Approach 1:
The patent changes the parameters of the correlative function by making the coefficients a and b dependent on temperature and SOC rather than constant values. This allows the function to maintain high accuracy across varying conditions while using a unified mathematical framework, balancing complexity and precision.
Solution Approach 2:
The patent performs preliminary action by pre-defining the functional relationships between coefficients and temperature/SOC before actual measurement. The correlative function is prepared in advance with coefficients that can be calculated from temperature and SOC measurements, eliminating the need for complex real-time adjustments during battery operation.
3Measurement precision
If temperature correction is performed using conventional methods, then some accuracy improvement is achieved, but the calculation complexity increases significantly
Solution Approach 1:
The patent merges the temperature correction function with the SOC correction function into a unified correlative function. By combining both corrections into a single equation structure where coefficients depend on both temperature and SOC, the patent reduces the overall complexity compared to performing separate correction steps while achieving comprehensive accuracy improvement.
Data Source
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AI summary
Coefficients A and B are calculated from the measured temperature and the measured state of charge. Next, a response voltage Vc is calculated by substituting the measured internal impedance X into a response-voltage correlation equation. Besides, by comparing the response voltage Vc with a predetermined threshold V0, if Vc is bigger than or equal to V0, the battery is determined as normal. By substituting the measured values of internal impedance, temperature, and SOC into the internal impedance calculation formula, a final internal impedance calculation formula is determined by calculating the value of C by an iterating operation. Next, in the case of determining SOH of a battery, by substituting a standard temperature and a standard SOC into the final internal impedance calculation formula, the internal impedance to determine the SOH is calculated. By comparing the internal impedance with SOH determination threshold, the SOH of the battery is determined.