Battery Pack SOC Estimation for Cells With Voltage Plateaus
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Solution Overview
Problem
Existing methods for estimating the state of charge (SOC) of a battery pack based on voltage values and open circuit voltage (OCV) curves are inaccurate for cells with voltage plateaus, leading to low estimation accuracy.
Innovation Solution
Introduce a first cell without a plateau and a second cell with a plateau, serially connected to determine capacity variation, and use equalization capacities and state of health (SOH) to estimate the SOC of the second cell accurately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If SOC is estimated based on voltage value and SOC-OCV curve, then the estimation method is simple, but the accuracy is low for cells with voltage plateau
Solution Approach 1:
The battery pack is segmented into two distinct cell groups: first cells without voltage plateau and second cells with voltage plateau. Each cell type is estimated separately using different methods, with the first cell serving as a reference to determine capacity variation that is then applied to correct the second cell's SOC estimation.
Solution Approach 2:
The method introduces multiple parameters including capacity variation, equalization capacity, and state of health (SOH) to transform the SOC estimation problem. By calculating capacity variation from the first cell and applying equalization capacity corrections to the second cell, the estimation accuracy is improved without requiring complex hardware modifications.
2Measurement precision
If battery aging is not considered, then the estimation process is simple, but the SOC estimation accuracy deteriorates over time
Solution Approach 1:
The state of health (SOH) of the first cell is determined in advance and used to calculate capacity variation. This preliminary determination of aging characteristics allows the method to compensate for battery degradation over time, maintaining accurate SOC estimation throughout the battery's lifecycle without requiring real-time complex adjustments.
Data Source
AI summary
This application provides a method and device for estimating a SOC of a battery pack, and a battery management system. The battery pack includes a first cell without a plateau and a second cell with a plateau. At least one first cell is serially connected to the second cell. The method includes: determining a capacity variation of the battery pack based on a SOC variation of the first cell in comparison with an initial SOC of the first cell, and based on a nominal capacity of the first cell; obtaining an equalization capacity of the first cell and an equalization capacity of the second cell; and estimating a SOC of the second cell, and determining the SOC of the battery pack based on the SOC of the second cell.