Passive Equalization for Lithium Iron Phosphate Battery Packs
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Lithium iron phosphate battery packs experience performance reduction and shortened service life due to uneven State of Charge (SoC) among cells, leading to inconsistent capacity attenuation and unequalization.
Innovation Solution
A passive equalization method and system that determines an accurate voltage range for querying SoC, calculates equalizing capacity and discharge time for each cell, and applies passive equalization based on these calculations, using a system with a storage module, collection module, judgment module, acquisition module, and equalization module, including an energy consumption circuit with a discharge equalizing resistor and switching device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If passive equalization is performed based on approximate SoC values, then equalization can be executed quickly, but the accuracy of SoC measurement deteriorates leading to incorrect equalization decisions
Solution Approach 1:
The patent performs preliminary action by allowing the battery pack to rest in a quiescent state before equalization, during which open circuit voltages are measured to determine accurate SoC values. This preliminary SoC determination enables subsequent equalization to be executed accurately without compromising speed, as the accurate baseline values are already established before the equalization process begins.
Solution Approach 2:
The patent segments the equalization process into two distinct phases: (1) a quiescent measurement phase where accurate SoC values are determined from open circuit voltages, and (2) an active equalization execution phase where discharge currents are applied. This segmentation allows each phase to optimize for its specific purpose - accuracy during measurement and speed during execution - thereby resolving the contradiction between measurement precision and productivity.
2Device complexity
If equalization is performed at any time without separation of judgment and execution, then system complexity is reduced, but reliability of equalization decisions deteriorates due to inaccurate SoC assessment
Solution Approach 1:
The patent divides the equalization control system into separate judgment and execution modules. The judgment module determines whether equalization is needed based on accurate SoC comparisons, while the execution module implements the equalization discharge. This functional segmentation enhances reliability by ensuring accurate decision-making is separated from the actual equalization action, allowing each module to be optimized for its specific function.
Solution Approach 2:
The patent introduces an intermediary mechanism - the quiescent state measurement process - that mediates between the need for simple system structure and reliable equalization decisions. By requiring a brief quiescent period for accurate voltage measurement before triggering equalization, the system ensures reliable decision-making without adding complex continuous monitoring infrastructure, thus balancing simplicity and reliability.
3Loss of time
If continuous monitoring and immediate equalization execution are implemented, then equalization timeliness is improved, but energy consumption increases due to frequent measurements and operations
Solution Approach 1:
The patent implements periodic action by monitoring battery voltages at regular intervals and triggering equalization only when specific conditions are met (voltage difference exceeds threshold during quiescent state). This periodic monitoring approach reduces energy consumption compared to continuous monitoring, while still maintaining timely equalization response by checking at sufficient intervals and acting immediately when unequalization is detected.
Solution Approach 2:
The patent changes the monitoring parameter from continuous current measurement to open circuit voltage measurement during quiescent states. This parameter change reduces energy consumption because voltage measurement requires minimal current draw, yet still provides accurate SoC information for timely equalization decisions when the battery is not under load, effectively balancing response time and energy usage.
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
Improves the performance and extends the service life of lithium iron phosphate battery packs by ensuring accurate SoC difference-based equalization, allowing judgment and execution to be separated and performed at any time, thus enhancing reliability and preventing overdischarge damage.
Implementation Method 1
calculating equalizing discharge current of each cell according to a passive equalization principle, and calculating equalizing discharge time of each cell according to the equalizing capacity and the equalizing discharge current of each cell; and subjecting the lithium iron phosphate battery pack to passive equalization based on the equalizing discharge time of each cell
Data Source
AI summary
The invention discloses a passive equalization method for a lithium iron phosphate battery pack, comprising: determining a voltage range in which a State of Charge can be accurately queried for a cell in the battery pack, and determining a corresponding relation between a voltage at which a State of Charge can be accurately queried and the State of Charge; collecting an open circuit voltage of each cell in a quiescent state; judging whether the open circuit voltage is within the voltage range in which a State of Charge can be accurately queried; if the open circuit voltage is within the voltage range in which a State of Charge can be accurately queried, acquiring the State of Charge of the cell corresponding to the open circuit voltage according to the open circuit voltage and the corresponding relation between a voltage at which a State of Charge can be accurately queried and the State of Charge, and determining equalizing capacity of each cell according to the State of Charge of each cell; calculating equalizing discharge current of each cell according to a passive equalization principle, and calculating equalizing discharge time of each cell according to the equalizing capacity and the equalizing discharge current of each cell; and subjecting the battery pack to passive equalization based on the equalizing discharge time of each cell.