LFP Battery Active Equalization via Accurate SoC Mapping
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Solution Overview
Problem
Lithium iron phosphate (LFP) battery packs face performance reduction and shortened lifespan due to unequalization of cells caused by deviations in State of Charge (SoC) resulting from manufacturing processes and environmental factors.
Innovation Solution
An active equalization method and system that determines the accurate State of Charge (SoC) for each cell by sampling open circuit voltage and using a corresponding relation to calculate equalized capacities, allowing for targeted equalization processing based on SoC differences within specific voltage ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If cells are connected in series to form a battery pack, then the battery pack can provide higher voltage and energy density, but deviations in State of Charge (SoC) between cells occur due to manufacturing processes and environmental factors, resulting in unequalization
Solution Approach 1:
The system performs preliminary action by determining the voltage range for accurate SoC querying and establishing the correspondence relation between voltage and SoC before actual equalization is needed. This preparation enables accurate SoC determination when equalization is required, preventing unequalization issues before they affect battery performance.
Solution Approach 2:
The system implements feedback by continuously sampling OCV of each cell, comparing it with the stored voltage-SoC correspondence relation, and using the determined SoC values to calculate equalized capacities. This feedback loop enables real-time monitoring and adjustment of cell states to maintain equalization.
2Reliability
If active equalization processing is performed to balance cell SoC, then cell equalization and battery life are improved, but additional control and measurement steps are required to determine accurate SoC
Solution Approach 1:
The system uses voltage range and correspondence relation as intermediaries to bridge the gap between simple voltage measurement and accurate SoC determination. By establishing a mapping between voltage and SoC within specific ranges, the system enables accurate state assessment without requiring complex direct SoC measurement equipment.
Solution Approach 2:
The system replaces complex direct SoC measurement mechanisms with a simpler voltage-based indirect measurement approach. By using OCV sampling and voltage-SoC correspondence relations, the system achieves accurate SoC determination without requiring sophisticated measurement hardware or complex algorithms.
3Measurement precision
If voltage sampling is performed to determine SoC, then equalization control can be achieved, but measurement accuracy is affected by voltage ranges and quiescent state requirements
Solution Approach 1:
The system segments the voltage range into specific intervals where accurate SoC querying is possible. By dividing the overall voltage range into manageable segments with established correspondence relations, the system enables accurate measurements while accounting for the constraints of voltage range dependencies and quiescent state requirements.
Data Source
AI summary
The present application relates to an active equalization method and system of a lithium iron phosphate (LFP) battery pack. The method includes the following steps of: determining, for each cell in the LFP battery pack, a voltage range in which a State of Charge (SoC) can be accurately queried, and determining a corresponding relation between a voltage at which the SoC can be accurately queried and the SoC; sampling an open circuit voltage of each cell in the LFP battery pack in a quiescent state; judging whether the open circuit voltage is within the voltage range in which the SoC can be accurately queried; if the open circuit voltage is within the voltage range in which the SoC can be accurately queried, acquiring the SoC of a cell corresponding to the open circuit voltage according to the open circuit voltage and the corresponding relation between the voltage at which the SoC can be accurately queried and the SoC, and determining an equalized capacity of each cell according to the SoC of each cell; performing active equalization processing on the LFP battery pack based on the equalized capacities of respective cells in the LFP battery pack.