Revolutionizing Connectivity: Crafting the Future of Vehicle Networks
How Wireless Mesh Networks Enhance Battery Management Systems
Greg Zimmer from Linear Technology explains how incorporating a wireless mesh network into battery management systems (BMS) can boost reliability.
Why Lithium-Ion Batteries Need Care
Lithium-ion batteries must be carefully managed to ensure they work well over time. They shouldn’t be charged to their maximum or allowed to deplete completely. Over time, each cell’s capacity dwindles and varies, requiring constant monitoring to keep the cells within a safe state of charge (SoC).
The Challenge of High-Voltage Battery Systems
High-power applications like electric vehicles require tens or even hundreds of battery cells, often generating voltages of 1kV or more. Managing these cells involves:
– Operating at very high voltages
– Rejecting common mode voltage effects
– Measuring and controlling each cell individually
– Communicating each cell’s data to a central point
These battery systems must meet stringent conditions, such as operating amidst electrical noise and fluctuations in temperature. The goal is to extend the battery’s life and reliability while reducing costs, size, and weight.
How Advances in ICs Helped
Improvements in battery cell monitoring integrated circuits (ICs) have led to better performance and reliability for today’s batteries. Wireless BMS, in particular, can further enhance safety and efficiency by eliminating the need for wired connections.
Adopting Modular Battery Packs
For vehicles, batteries are often split into smaller packs and spread throughout the vehicle’s available space. Typically, each module contains 10 to 24 cells and can be reconfigured to suit different vehicle designs. This modular setup simplifies maintenance and warranty issues, making it the foundation for larger battery stacks.
To handle these distributed packs amid the high electromagnetic interference common in electric vehicles, a reliable communications system is essential. Currently, isolated Can bus and isolated SPI methods are popular solutions for connecting these modules.
Comparing Can Bus and SPI
The Can bus is well-established in automotive applications but needs extra components like a transceiver, microprocessor, and isolator, increasing costs and board space.
Alternatively, the isolated SPI interface uses two wires and a simple transformer, offering high resistance to RF noise. This allows modules to be connected in a daisy-chain over long distances, achieving data rates up to 1Mbit/s.
Moving to Wireless BMS
A wireless BMS replaces traditional cabeling with wireless connections. For example, BMW demonstrated the first wireless BMS in their i3 concept car, which used a wireless mesh network to connect battery modules. This setup eliminates the problems of wired connections, offering improved reliability, lower costs, and less complexity.
As automakers strive to convince consumers that electric and hybrid vehicles are safe and reliable, the adoption of wireless BMS could be a game-changer.
