Tech companies are working hard to improve battery-monitoring accuracy in order to ensure that the vehicle’s battery management system is able to work more efficiently and is able to monitor, in real time, the performance of the individual battery cells.
It’s interesting that elegant technology abounds in the latest EV models but in the chassis underneath there remains a complex mass of components supporting its system of batteries.
EVs are packed with battery cells and, as such, currently require extensive multi-cable solutions to connect each cell to a battery management system (BMS) that is able to deliver the efficiency, longevity and performance that’s required.
EV battery packs can stack up to 1000V and beyond to support the demanding loads of the AC motor and can comprise of hundreds of cells stacked together in series. Distributed battery pack systems are able to support high-cell-count packs by connecting multiple high-accuracy battery monitors on separate printed circuit boards called cell sensing units.
However, operating a high voltage battery pack in a vehicle imposes tough conditions - wide operating temperatures and vibration need to be managed while the battery management electronics are expected to maximise operating range, lifetime, safety and reliability.
Each cell, in such a system, is connected via a complex network of cables and wires to enable performance monitoring and has raised issues around cost, size and weight. As a result, there’s been a growing realisation that these cables and wires are proving a significant drag on reliability, maintenance and manufacturing costs.
Another issue arises in that to accommodate the large quantity of cells that are now required for high powered automotive systems, batteries are being distributed throughout the available spaces in the vehicle, which requires a sound communication system.
To address these issues companies are now developing next generation BMS that operate wirelessly, ending the need to use the pounds of wiring found in current solutions.
Texas Instruments has developed a wireless BMS that not only removes the need for bulky wired solutions, but delivers improved EV reliability.
“EVs are packed with battery cells and multi cabling, so in every EV the BMS is an essential component. Each battery cell has to be connected so it can be monitored but, at present, that requires large amounts of heavy duty copper wiring to ensure reliability. So our BMS is wireless,” explains Karl-Heinz Steinmetz, TI’s General Manager of Powertrain in Automotive Systems.
In theory, removing these wires and additional components will reduce both weight and footprint and improve the vehicle’s reliability.
“Battery management systems are currently connected by wire using a daisy-chain configuration - which is widely perceived as safe. But while it provides reliable communications it is complex using a mass of cabling, wires, connectors and isolation components. The mechanical failure of these components is a common source of cable failures and can prove costly to repair. Replacing batteries is also proving to be ‘super’ expensive,” adds Steinmetz.
According to Steinmetz, the crucial advantage of a wireless BMS is that it significantly reduces the total cost of ownership and eliminates the need for maintenance-prone components.
“A wireless BMS reduces the complexity of the design removing connectors and other components. In a wireless scenario there is a direct link from the BMU to each wireless node that improves the reliability of the complete system.”
TI’s solution is intended to empower automakers, helping them to reduce the complexity of their designs, improve reliability and reduce vehicle weight to extend driving range. But not only that as it also helps to reduce assembly costs too.
“Today these devices are wired manually so by going wireless it’s possible to significantly cut manufacturing costs – there are no complex wiring systems and we no longer need a wiring harness, connectors, transformers or capacitors.
“These advancements provide much greater flexibility of design while also lowering the cost, relative to traditional systems. This is a solution that not only combines these technical advantages but does so with ASIL-D compliance.”
Naturally there are concerns with wireless BMS, as they need to be able to monitor accurately in real time. Not only do they need to be accurate but need to transmit data rapidly and with low error rates – made all the more difficult by operating in a hot and noisy environment.
“Monitoring the battery is critical as is measuring the voltage and temperature if you are to guarantee that the maximum energy is being extracted between chargers. This new family of devices ensure that its possible to measure these parameters with great accuracy,” said Ivo Marocco, director of business development and functional safety for Battery Automotive products at TI.
TI’s wireless solution, includes a proprietary wireless protocol, that looks to address these challenges and combines two new chips, the CC266C2R0QI wireless MCU and the BQ79616-Q1 battery monitor and balancer.
The wireless MCU offers dedicated time slots that provide high throughput and low latency to protect data from loss or corruption while enabling multiple battery cells to send voltage and temperature data to the main MCU with, according to TI, a ±2-mV accuracy and a network packet error rate of less than 10-7.
TI’s wireless BMS functional safety concept addresses communication error detection and security. The proprietary protocol via the CC2662R-Q1 wireless MCU has been designed to enable a robust and scalable data exchange between a host system processor and the BQ79616-Q1 battery monitor and balancer.
According to TI, the wireless protocol for BMS via the CC2662R-Q1 is able to offer the industry’s highest network availability of greater than 99.999% and a network restart of 300-ms maximum availability.
“The car chassis acts as a Faraday cage,” explains Ram Vedantham, manager of TI’s 2.4Ghz Business Line,” so, as a consequence, any interference is contained within the systems. Careful design of the protocol, which has combined time-division multiplexing with frequency hopping, means that we’ve been able to eliminate any noise to the maximum extent possible.”
Moving to production
Auto manufacturers will be able to advance to production much faster using this wireless BMS offering. TI is also making available the SimpleLink 2.4-GHz CC2662R-Q1 wireless microcontroller (MCU) evaluation module, software and functional safety enablers such as a safety manual; failure mode and effects analysis (FMEA); as well as diagnostic analysis (FMEDA).
Security is a key requirement when it comes to wireless devices, so to mitigate potential threats TI is making available security enablers such as key exchange and refreshment; unique device authentication; debug security; software IP protection with a joint test action group (JTAG) lock; Advanced Encryption Standard (AES) 128-bit cryptographic acceleration and message integrity checks
Anticipating automakers’ long-term design needs, TI says that its wireless BMS has been designed to be scalable. Automakers will be able to create a battery module using a single wireless system-on-chip that’s connected with multiple BQ79616-Q1 battery monitors making it possible to deliver different configurations such as 32-, 48- and 60-cell systems.
The system is designed to support up to 100 nodes with low latency of less than 2 ms per node and time-synchronized measurements across every node.
The CC2662R-Q1 wireless MCU isolates individual cell monitoring units, eliminating the need for and cost of daisy-chain isolation components, which is the case with existing solutions.
The BQ79616-Q1 battery monitor and balancer is able to offer different channel options in the same package type, providing pin-to-pin compatibility and supporting 100% reuse of the established software and hardware across any platform.
“This move to a wireless BMS solution demonstrates how vehicle designers will be able to remove heavy, expensive, maintenance-prone cabling and improve the reliability and efficiency of EVs worldwide,” explained Steinmetz.
“It provides much greater flexibility to scale designs across production models and by removing all these components there’s plenty of scope for designers to add more intelligence or more battery cells.”