Battery Cell Balancing for Internal Short-Circuit Detection
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Solution Overview
Problem
Existing energy storage systems, such as lithium ion batteries, face challenges in accurately determining abnormal discharge due to internal short-circuits, which are not effectively addressed by current balancer circuit techniques, particularly in deciding a suitable reference value for identifying such events.
Innovation Solution
An energy storage apparatus with a balancer circuit and management unit that compares balancer discharge electricity amounts among cells to determine abnormal discharge, using a reference value calculated from irregularities in both balancer discharge and self-discharge electricity amounts, allowing for precise identification of internal short-circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed reference value is used to determine abnormal discharge, then the determination process is simple, but the accuracy of detecting internal short-circuits deteriorates due to variations in balancer discharge and self-discharge characteristics
Solution Approach 1:
The system performs preliminary measurement of balancer discharge electricity amounts and self-discharge electricity amounts before determining the reference value. The management unit accumulates measurement values over a predetermined period, calculates averages, and establishes the reference value based on these preliminary data, thereby improving detection accuracy without excessive complexity
Solution Approach 2:
The system continuously monitors balancer discharge electricity amounts and self-discharge electricity amounts, compares them against the established reference value, and adjusts the reference value dynamically based on the accumulated measurement data. This feedback mechanism maintains high detection accuracy while adapting to varying operating conditions
2Stability of the object's composition
If the balancer circuit discharges electricity from cells with high voltage to balance the pack, then voltage differences between cells are reduced, but cells with abnormal discharge are less likely to be discharged by the balancer circuit, making detection more difficult
Solution Approach 1:
The management unit acts as an intermediary that independently measures and compares balancer discharge electricity amounts with self-discharge electricity amounts for each cell. By introducing this intermediate measurement and comparison layer, the system can detect abnormal discharge in cells even when those cells are not actively being discharged by the balancer circuit, thus resolving the conflict between maintaining voltage balance and enabling detection
Data Source
AI summary
An energy storage apparatus 1 includes: energy storage cells 30A; a balancer circuit 38; and a management unit 37. The management unit 37 performs: decreasing a difference in voltage or a difference in residual electricity amount between the energy storage cells 30A by making the energy storage cell 30A having a relatively high voltage or a relatively high residual electricity amount discharge electricity using the balancer circuit 38; determining whether or not an abnormal discharge is generated in a specific energy storage cell 30A by comparing a difference between a balancer discharge electricity amount of the specific energy storage cell 30A, which has a smallest balancer discharge electricity amount among balancer discharge electricity amounts discharged using the balancer circuit 38 within a predetermined period, and a balancer discharge electricity amount of another energy storage cell 30A with a reference value; and deciding the reference value based on at least one of an irregularity in the balancer discharge electricity amounts of the energy storage cells 30A in the predetermined period and an irregularity in self-discharge electricity amounts of the energy storage cells 30A in the predetermined period.