TDMA CAN Bus Node Synchronization for Battery Management
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Solution Overview
Problem
Existing battery management systems for electric and hybrid vehicles face complexity and challenges in monitoring and controlling multiple battery cells, particularly in preventing overtemperature, overvoltage, undervoltage, and other conditions that can damage battery cells or packs, especially when disparities occur among cells or packs due to self-discharge differences.
Innovation Solution
A deterministic method and circuit for transmitting data over a CAN bus using a Time Division Multiple Access (TDMA) protocol, where each node is assigned a unique ID to determine its transmission time slot, ensuring that nodes do not transmit simultaneously, and a central monitoring unit can adjust power supply and orchestrate battery cell balancing based on voltage information to prevent damage and compensate for disparities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a communication bus is used to connect multiple battery management systems, then system complexity is reduced, but data transmission reliability deteriorates due to simultaneous transmissions causing collisions
Solution Approach 1:
The system performs preliminary synchronization of time bases among all battery management units before data transmission. Each unit adjusts its local time base to match a reference time base, ensuring that transmission time slots are pre-coordinated and no simultaneous transmissions occur, thus preventing data collisions while maintaining communication efficiency
Solution Approach 2:
The system implements periodic time-slot-based transmission where each battery management unit is assigned specific time slots for data transmission. By dividing the communication channel into periodic time slots and assigning them to different units based on their identifiers, the system eliminates simultaneous transmissions while maintaining regular communication rhythm
2Quantity of substance
If the number of battery cells is increased, then power capacity is improved, but monitoring and control complexity increases
Solution Approach 1:
The battery system is segmented into multiple independent battery management units, each responsible for monitoring a specific subset of battery cells. Each unit has its own identifier and is assigned specific time slots for communication, allowing the system to scale to hundreds of cells while maintaining manageable complexity through distributed monitoring architecture
Solution Approach 2:
Each battery management unit is designed as a universal module capable of monitoring multiple battery cells and participating in the same communication network. The units use identical hardware and software architectures with unique identifiers, allowing standardized deployment across the entire battery system regardless of the total number of cells
3Power
If battery cells are connected in series to increase voltage, then power delivery is improved, but voltage disparities among cells increase leading to damage risks
Solution Approach 1:
The system continuously monitors voltage levels of individual battery cells through the communication network. Each battery management unit reports its cell voltage data to the central controller, which uses this feedback information to identify cells with abnormal voltage levels and adjust charging/discharging strategies to prevent overvoltage or undervoltage conditions
Solution Approach 2:
The system dynamically adjusts power distribution and cell balancing strategies based on real-time voltage measurements. When voltage disparities are detected among series-connected cells, the controller modifies current allocation to equalize cell voltages, preventing damage while maintaining optimal power delivery from the battery pack
Data Source
AI summary
A circuit can include a CAN bus and multiple nodes. The multiple nodes can reboot at the same time so that a Time 0 is set at boot for each node. Each node can store an ID node and determine from its ID node one time slot of a plurality of periodic time slots starting from Time 0 in which to transmit on the CAN bus. Each node can transmit messages on the CAN bus in its determined time slot subsequent to Time 0.