Autonomous Cell Balancing Circuit for Battery Pack Safety
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Solution Overview
Problem
The complexity and cost of monitoring individual lithium-ion battery cells in large battery packs for hybrid and electric vehicles make existing battery management systems inefficient and prone to overcharging, which reduces battery life.
Innovation Solution
A decentralized battery management system with autonomous cell balancing circuits integrated across each cell group, using a divider and switch circuit to shunt current around overcharged cells, allowing for efficient charge balancing without monitoring every cell individually, and employing analog control to maintain a high State of Charge similar to other chemistries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If individual cell monitoring and control is implemented for each lithium-ion cell, then battery safety and precision are improved, but system complexity and cost increase significantly
Solution Approach 1:
The battery management system is segmented into modular units, each managing a group of cells (e.g., 5-10 cells per unit). Each unit has its own controller that monitors and balances cells within that group, eliminating the need for a single complex controller to manage every cell individually. This segmentation reduces overall system complexity while maintaining safety through distributed monitoring.
Solution Approach 2:
The controller units are designed with multi-functionality, capable of performing monitoring, balancing, and protection functions for multiple cells simultaneously. A single controller unit can manage an arbitrary number of cells within its group, reducing the total number of controllers needed and simplifying the overall architecture while maintaining comprehensive cell-level oversight.
2Measurement precision
If every cell is monitored individually with dedicated monitoring ICs, then measurement precision is improved, but manufacturing cost and complexity increase
Solution Approach 1:
Multiple cell monitoring functions are merged into single controller units. Each controller unit monitors and manages multiple cells within a group, reducing the total number of monitoring ICs required. This merging maintains precise measurement of each cell's voltage while simplifying the manufacturing process and reducing component count, making the system more suitable for mass production.
3Use of energy by moving object
If lithium-ion batteries are used to provide high energy cell output, then energy density is improved, but susceptibility to overcharge damage increases
Solution Approach 1:
The system performs preliminary balancing actions on lithium-ion cells before overcharge conditions develop. By continuously monitoring cell voltages and applying balance currents proactively, the system prevents overcharge damage before it occurs, allowing lithium-ion batteries to operate at high energy densities safely. This preliminary intervention is critical for lithium-ion chemistry which is particularly sensitive to overcharge.
Solution Approach 2:
The battery management system implements continuous feedback monitoring of cell voltages and adjusts balancing currents in real-time. When a cell approaches its maximum safe voltage, the system automatically reduces or stops charging current to that cell, preventing overcharge damage. This feedback mechanism enables safe operation at high energy densities by dynamically adjusting charge parameters based on actual cell states.
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
Enables the balancing of lithium-ion cells in a group or brick, avoiding overcharging damage, while allowing an arbitrary number of cells to be combined with a single output to a battery monitor IC, reducing architecture complexity and costs, and maintaining battery health.
Implementation Method 1
an autonomous cell balancing circuit for each cell that shunts current around the overcharged cell
Data Source
AI summary
Systems and methods for controlling a vehicle having a traction battery with a plurality of cell groups each having a plurality of serially connected battery cells include balancing each cell of each cell group with a corresponding autonomous cell balancing circuit, and coupling a single output associated with each cell group to an associated battery monitoring circuit. An integrated driver and switch circuit adapts the voltage from an associated cell group for powering battery monitoring integrated circuits with a voltage range corresponding to a single cell voltage range to facilitate use of an existing battery monitoring integrated circuit design and subsequent input to a microprocessor-based battery controller. Cell balancing is performed at each cell with a battery monitor circuit associated with each group of cells.