Battery SOC Alignment for Adding LFP Batteries With SOH Differences
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Solution Overview
Problem
In battery systems with lithium iron phosphate (LFP) batteries, accurately estimating state of charge (SOC) in the voltage plateau section is difficult, leading to repeated unnecessary balancing control when new batteries are added, due to differences in State of Health (SOH) between existing and new batteries.
Innovation Solution
A battery management apparatus and method that calculates a target SOC based on the SOH and initial SOC of both the pre-installed and new batteries, controlling charging and discharging to align their SOC before connecting the new battery, using the equation SOC_target=SOC_bal-K*(100/SOH_old) to minimize SOC differences and prevent unnecessary balancing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If balancing control is performed based on estimated SOC values in LFP batteries, then battery imbalance is addressed, but unnecessary repeated balancing control occurs when new batteries are added due to SOC estimation difficulty in plateau section
Solution Approach 1:
The system performs preliminary SOC adjustment before connecting new batteries by controlling the SOC of existing batteries to match the target SOC (based on new battery's initial SOC). This preliminary action prevents SOC imbalance from occurring in the first place, eliminating the need for subsequent corrective balancing operations and improving system efficiency.
Solution Approach 2:
The system continuously monitors SOC values of all batteries and compares them against the target SOC. When the SOC of existing batteries deviates from the target, the system automatically adjusts charging/discharging operations. This feedback mechanism ensures accurate SOC management while preventing unnecessary balancing operations.
2Ease of operation
If new batteries are connected when existing battery SOC matches new battery shipping SOC, then connection is simplified, but SOC difference and imbalance occur due to SOH differences between existing and new batteries
Solution Approach 1:
The system changes the connection criterion from matching SOC values to matching target SOC values. The target SOC is calculated based on the new battery's initial SOC and the existing battery's SOH characteristics. This parameter change ensures that batteries are connected when their SOC values are appropriately matched considering their health states, preventing future imbalance while maintaining operational simplicity.
3Reliability
If balancing control is performed in plateau section of LFP batteries, then SOC imbalance can be corrected, but SOC estimation accuracy is insufficient leading to incorrect balancing decisions
Solution Approach 1:
The system introduces target SOC as an intermediary reference value for balancing control. Instead of directly comparing estimated SOC values (which are inaccurate in plateau section), the system uses target SOC - calculated from new battery's initial SOC and existing battery's SOH - as the reference. This intermediary approach enables accurate balancing decisions without relying on imprecise SOC estimation in the plateau section.
Data Source
AI summary
According to embodiments of the present invention, a battery management apparatus, located in a battery system allowing for an addition of one or more new batteries, may include at least one processor; and a memory configured to store instructions executed by the at least one processor. Here, the instructions may cause the at least one processor to:in response to the battery system switching to a mode for adding a new battery into the battery system, determine a target state of charge (SOC) which is determined based on the state of health (SOH) of at least one battery and an initial SOC of the new battery, wherein the battery is a pre-installed battery; control charging and discharging of the battery so that the SOC of the battery becomes the target SOC; and terminate the control of charging and discharging when the SOC of the battery reaches the target SOC.