The price of lithium batteries is becoming more and more affordable, and the energy density is getting higher and higher, which can drive hybrid electric vehicles (HEV) and electric vehicles (EV) for longer distances. With these improvements, automotive design engineers can now turn their attention to further improving efficiency by reducing the size and weight of the battery management system (BMS).
For background information on the battery management system, see “Introduction to the HEV/EV Battery Management System.”
The traditional wired BMS architecture uses a wire harness based on a daisy chain configuration to connect the battery pack, which is complicated in manufacturing processes, requires frequent maintenance, and is difficult to repair.
The development of wireless BMS technology is expected to solve the above-mentioned problems. This technology uses a wireless chipset to work in conjunction with a battery monitor to transmit voltage and temperature data from each battery cell to the main microcontroller in the system. The inherent reduction in the number of cables and wiring harnesses required reduces vehicle weight and saves costs.
Figure 1 shows an example of a wireless BMS architecture.
Figure 1: TI’s wireless BMS architecture
If you are exploring the feasibility of converting to a wireless BMS architecture, please consider the following three key questions:
1. Is it reliable?
Although wireless communication has replaced cables in various applications, a key point to consider is the reliability of wireless links and networks. You can use the packet error rate and the probability of successfully sending a message between the sender and receiver to quantify reliability. This probability should be 99.999%, and the packet error rate is 10-6.
2. Is the wireless BMS safe for passengers, mechanics and property?
The wireless BMS should accurately monitor the situation and respond quickly, reliably and safely when a dangerous event is detected, in order to reduce the danger or damage. Ideally, the system should meet the requirements of automotive safety integrity level D, which is the highest functional safety goal defined by the International Organization for Standardization 26262 Road Vehicle Standard.
3. Is it safe?
If someone tries to tamper with the vehicle’s battery system, will the wireless BMS work? Look for systems that use encryption accelerators and other security-driven tools with key exchange and refresh mechanisms, message integrity checks, and debugging security to provide encrypted messages.
Additional questions! Which function is better, wired or wireless BMS?
This is a tricky question, because either wired or wireless BMS may be suitable for your design, depending on your vehicle architecture and design goals. Table 1 compares the main differences between wired and wireless systems.
Table 1: Comparison of Wired BMS and Wireless BMS
Although the wired battery management system is time-tested, true and reliable, and will not be eliminated soon; however, wireless BMS is the future development trend. According to Strategy Analytics forecasts, there will be 36 million electric vehicles on the road by 2026, and wireless BMS provides promising ways to improve the efficiency and reliability of vehicles-these advantages attract OEMs and consumers.