Battery State of Health Estimation via Minimum Cell Voltage
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Solution Overview
Problem
Existing methods for estimating the service capacity and state of health of battery systems in new energy vehicles are inaccurate, particularly due to errors in determining internal resistance and cycle numbers, which are influenced by temperature and charge-discharge rates, and are not practical for hybrid power systems.
Innovation Solution
A method and device that estimate the service capacity and state of health of a battery system by determining the initial and final state of charge of the minimum battery cell using the open-circuit voltage method, calculating the charging capacity, and applying these values to determine the service capacity and state of health of both the minimum battery cell and the entire system, while accounting for temperature and inactive duration to ensure accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the state of health of a battery is determined based on internal resistance, then the determination can be performed during operation, but the measurement precision is poor due to influence of temperature and charge-discharge rate
Solution Approach 1:
The patent applies preliminary action by requiring the battery to undergo a rest period (typically 5-30 minutes) after charging before measurement. This preliminary waiting period allows the battery voltage to stabilize and internal resistance to settle, eliminating the influence of transient effects from charging operations. The method performs state of health determination only after this preliminary action, ensuring accurate measurements while still enabling operation-based assessment.
2Device complexity
If the state of health is determined based on cycle number, then the method is simple to implement, but the reliability is poor due to errors in accumulating cycle numbers and simulation test conditions
Solution Approach 1:
The patent replaces the mechanical counting method (cycle number accumulation) with an electrochemical measurement method. Instead of tracking discrete cycle events and subtracting from a baseline, the invention directly measures the battery's electrochemical state through voltage and current measurements during a standardized charge-discharge test. This substitution eliminates accumulation errors and the need for complex baseline management while maintaining operational simplicity.
3Device complexity
If the service capacity of battery cells is estimated without considering the minimum battery cell, then the calculation is simpler, but the measurement precision is poor because it does not reflect the actual battery system capacity
Solution Approach 1:
The patent applies local quality by focusing the service capacity estimation on the minimum battery cell (the cell with the lowest capacity or highest degradation) rather than treating all cells uniformly. The method identifies which cell is the bottleneck and performs detailed voltage measurements and capacity calculations specifically for that cell. This localized approach accurately reflects the actual system capacity limitation while maintaining reasonable calculation complexity.
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 approach provides an accurate estimation of the service capacity and state of health of battery systems, overcoming the inaccuracies of previous methods and effectively reflecting the degree of battery attenuation, thereby improving battery management and performance.
Implementation Method 1
an initial state of charge of the minimum battery cell, in the battery system being charged, is determined. Once the battery system is fully charged, a final state of charge of the minimum battery cell, at the end of charging, is determined
Data Source
Figure 1
AI summary
A method and a device for estimating a service capacity and a state of health of a minimum battery cell and a battery system is provided. The method for estimating the state of health includes: when a battery system is power-on, determining an initial state of charge of a minimum battery cell in the battery system being charged; after the battery system is fully charged, determining a state of charge of the minimum battery cell at the end of charging, and calculating to obtain a charging capacity of the minimum battery cell; and performing a computation to obtain a service capacity of the minimum battery cell, a service capacity of the battery system and a state of health of the battery system. The method can effectively solve a problem of inaccurate estimations of a service capacity of a minimum battery cell of a vehicle battery, a service capacity of a battery system and a state of health of the battery system.