Hybrid LFP-NCM Battery SOC Mapping for Accurate Charge Estimation
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Solution Overview
Problem
Lithium iron phosphate-system batteries present a challenge in state of charge (SOC) estimation due to their exceptionally flat OCV-SOC curve, making accurate SOC estimation impossible with existing methods.
Innovation Solution
A method that combines a lithium iron phosphate-system battery with a nickel cobalt manganese-system battery, dynamically adjusting their SOC intervals to establish a mapping relationship, allowing for accurate SOC estimation of the battery system by using the nickel cobalt manganese-system battery's easily calculable SOC to reflect the overall SOC of the system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lithium iron phosphate-system batteries are used due to their excellent safety performance, then battery safety is improved, but accurate state of charge estimation becomes impossible due to the exceptionally flat OCV-SOC curve
Solution Approach 1:
The patent introduces a nickel cobalt manganese-system battery as an intermediary component within the battery system. This secondary battery type has a steep OCV-SOC curve that provides measurable voltage changes, serving as a mediator to enable accurate SOC estimation for the overall system while the lithium iron phosphate batteries continue to provide safety benefits
Solution Approach 2:
The patent creates a composite battery system by combining lithium iron phosphate-system batteries and nickel cobalt manganese-system batteries in the same battery pack. This composite approach allows the system to simultaneously achieve the safety advantages of LFP batteries and the measurement advantages of NCM batteries, resolving the contradiction between safety and measurability
2Ease of operation
If conventional SOC estimation methods based on OCV calibration are used, then the estimation process is simple, but accurate SOC estimation is impossible for lithium iron phosphate-system batteries due to the flat OCV-SOC curve
Solution Approach 1:
The nickel cobalt manganese-system battery serves as a mediator that enables the use of simple OCV-based estimation methods to achieve accurate results. By incorporating this battery type with a steep OCV-SOC curve, the system regains the voltage sensitivity needed for conventional estimation techniques to work effectively
Solution Approach 2:
The patent changes the electrical parameters of the battery system by adding a battery type with different OCV-SOC characteristics. The NCM battery's steep voltage-SOC relationship transforms the overall system's electrical behavior, enabling accurate SOC estimation through conventional voltage measurement methods
Data Source
AI summary
An SOC estimation method for a battery system includes mapping an upper limit and a lower limit of the state of charge of the second-system battery to a state of charge interval of the battery system, to establish a mapping relationship between the upper limit and the lower limit of the state of charge of the second-system battery and the state of charge interval of the battery system. The method includes calculating the state of charge of the second-system battery and estimating a state of charge of the battery system according to the mapping relationship.