As electric vehicles (EVs) have risen to the forefront of consumer tech alongside mobile and wireless products, a new generation of application-specific integrated circuits (ASICs) has quietly arisen in response. Semiconductor companies have made their mark by producing a broad portfolio of products targeting multiple electronic systems in EVs. In an EV, the battery management system (BMS) is a critical system for ensuring vehicle safety, range and reliability, and these systems have seen a new wave of innovation.
Today’s advanced EV BMS designs are going wireless thanks to a suite of new products from some major semiconductor companies. The goal in this shift to wireless BMS technology is about more than keeping up with trends, it’s about making EVs a more competitive and reliable alternative to HEVs and gasoline vehicles. To see why this is occurring and what it means for automotive power systems designers, let’s start by looking at the typical architecture of an EV BMS design.
Architecture and challenges of an EV BMS design
A BMS has a simple architecture composed of a set of battery charge monitors that interface with a host controller unit, typically an MCU or field-programmable gate arrays (FPGAs). More sophisticated diagnostics chips may be added to these systems so that some functions can be offloaded from the host controller. The data captured by the MCU is then sent back to a higher-level ECU in the system over a standard protocol (CANbus).
In this system, cabling has to be run between monitors and each cell in the battery array. With some systems operating with as many as 96 series cells, they require a significant amount of cabling.
If this type of system were to be built about 30 years ago, it would have been very difficult to implement all the required functions into a small package and small chip count. Plenty of discrete logic would be needed to implement the required calculations and control functions, all of which would have to operate in a potentially high voltage, current and heat environment. Today, there are many ASICs available that can be used to implement the required monitoring and control functions, which can then interface with a host controller as shown above. As BMS design typically targets EVs, these newer ASICs may also have some level of AEC or SAE qualification.
What has been missing from these designs is a way to reduce the mass of cables that span throughout the vehicle. The cabling that connects each portion of the system to the host controller, and ultimately the rest of the vehicle, is very bulky and heavy. The availability of more 2.4 GHz-compatible MCUs and FPGAs allows portions of these designs to operate wirelessly.
Advantages of wireless EV BMS designs
A wireless BMS is just like it sounds: the traditional cabling used to connect batteries, monitors, a host controller, peripherals and any external systems are replaced with wireless communications to the greatest extent possible. Wireless BMS designs are short-range RF systems operating in the ISM band (2.4 GHz). The goal is to replace the wired link between batteries, monitors and the control unit with a wireless channel.
Implementing wireless connectivity in these systems provides multiple advantages:
- Fewer cables reduces weight — The cabling and wire harnesses in an EV battery system is heavy and bulky; removing these cables reduces total weight and provides more space for other systems in the battery compartment. This also allows many fittings and connectors to be removed, which also reduces costs.
- Eliminated cable design costs — Cables used in wired BMSs are customized and expensive. Typically, they would need to be redesigned for each model and each year major changes are made to the battery system. Going all-wireless removes these costs as well.
- Modularity — Because a proprietary cable assembly and harnesses are not needed for a wireless BMS, the remaining components and systems can be made highly modular. It now becomes easier for third party vendors to participate in this space.
- Simpler maintenance — Removing cabling also allows the cells to be accessed, inspected and replaced more easily. The same applies to portions of the system itself should it become obsolete or fail.
- Open-source and vendor support — Control and balancing algorithms for BMS designs are well-developed and are available as open-source code.
Challenges and innovation opportunities
As a short range wireless system, a wireless BMS design for an EV faces many of the same challenges as other wireless networked systems. The monitor units and the host controller in the system need to form an initial network during vehicle startup, and they need to do so very quickly. Problems with latency, multipath errors and radiated noise can make operation more difficult. And of course, these systems need to have low power consumption to ensure low temperature during operation and long-term reliability.
Despite the challenges facing wireless BMSs, there is still significant room for innovation to ensure these systems are more reliable. Further reductions in cabling and harness weight can be seen if the output interface was implemented in an IEEE 802.3ch automotive Ethernet, which can further reduce latency and allow a central controller to orchestrate power management throughout a vehicle.
On the embedded software side, a universally accepted wireless BMS protocol would provide many advantages for developers, OEMs, maintenance techs and aftermarket vendors. If a universally accepted wireless BMS protocol can be developed and standardized, vendors can take a plug-and-play approach to design, development and maintenance. There are many other opportunities for innovation in these systems at multiple levels, and board designers will play a central role in ensuring future EV BMS designs are modular, reliable and safe.
