Battery SOH Estimation Using SOC Change Ratios Across Unit Cells
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Solution Overview
Problem
Existing battery diagnostic technologies face challenges in calculating the state-of-health (SOH) of each unit cell in an assembled battery efficiently, as equipping all unit cells with temperature and impedance sensors increases cost and size.
Innovation Solution
A battery diagnostic apparatus calculates the SOH of each unit cell by using a detection unit in at least one unit cell, acquiring parameters for degradation diagnosis, and employing a calculation method that multiplies the change amount ratio of state-of-charge of a reference unit cell by its SOH to determine the SOH of other cells, even without direct parameter acquisition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If temperature and impedance sensors are equipped in all unit cells for degradation diagnosis, then measurement precision of SOH is improved, but device complexity and cost increase
Solution Approach 1:
The patent segments the battery system into monitored unit cells (with sensors) and unmonitored unit cells (without sensors). The monitored cells serve as reference points, while the unmonitored cells have their SOH estimated through calculation based on the monitored cells' data and the electrical connections between cells, thereby reducing the total number of sensors required
Solution Approach 2:
The patent introduces an intermediary calculation mechanism that uses the electrical connection relationships between unit cells as a mediator to transfer SOH information from monitored cells to unmonitored cells. This allows SOH estimation for cells without direct sensor measurement by leveraging the electrical coupling and state-of-charge change relationships
2Reliability
If temperature and impedance sensors are equipped in all unit cells, then reliability of degradation diagnosis is improved, but manufacturing cost increases
Solution Approach 1:
The patent divides the unit cells into monitored and unmonitored groups, applying sensors only to the monitored segment. This segmentation reduces manufacturing costs while maintaining diagnostic reliability through the calculated SOH values for unmonitored cells based on their electrical relationships with monitored cells
Solution Approach 2:
The patent creates a virtual copy of the SOH information from monitored unit cells and applies it to unmonitored unit cells through calculation. Instead of physically installing sensors in every cell, the system replicates the diagnostic capability computationally by using the measured data from fewer cells to infer the state of all cells
3Device complexity
If sensors are installed in only one unit cell, then device complexity is reduced, but measurement precision of all unit cells deteriorates
Solution Approach 1:
The patent makes the single monitored unit cell serve a universal function for the entire battery pack. The data from one monitored cell is used to calculate SOH for all other unmonitored cells by leveraging the electrical connection relationships and state-of-charge changes, allowing one sensor setup to provide diagnostic information for the entire system
Solution Approach 2:
The patent uses the electrical connection relationships and state-of-charge change ratios as intermediaries to transfer the diagnostic information from the single monitored cell to all unmonitored cells. This intermediary mechanism preserves measurement precision despite having sensors in only one cell
Data Source
AI summary
A battery system includes an assembled battery including unit cells and a detection unit provided in at least one unit cell. A battery diagnostic apparatus calculates a state-of-health based on a parameter for degradation diagnosis detected by the detection unit for at least one unit cell, and calculates a change amount of a state-of-charge caused by energization, for the unit cells. When a unit cell of which the state-of-health is calculated is a first unit cell and a unit cell of which the state-of-health is not calculated is a second unit cell, the battery diagnostic apparatus calculates, as the state-of-health of the second unit cell, a value obtained by multiplying a change amount ratio that is a ratio of the change amount of the state-of-charge of the first unit cell to the change amount of the state-of-charge of the second unit cell by the state-of-health of the first unit cell.