January 17, 2021

Wireless Battery Management Extends Driving Range in EVs

6 min read
Texas Instruments (TI) released updates in electric vehicle (EV) battery management systems (BMS) during CES...

Texas Instruments (TI) released updates in electric vehicle (EV) battery management systems (BMS) during CES 2021. Reducing design complexity helps all automotive manufacturers to speed up production, and in this way, wireless battery management systems (wBMS) can be a key element for electric vehicles.

The new SimpleLink 2.4-GHz CC2662R-Q1 wireless microcontroller (MCU) and BQ79616-Q1 battery monitor and balancer enable ASIL D systems, simplifying the wiring of an EV while improving efficiency.

In an interview with EE Times, Karl-Heinz Steinmetz, general manager for Powertrain in Automotive Systems, Ram Vedantham, business line manager for 2.4 GHz Connectivity and Ivo Marocco, director of business development and functional safety for Battery Automotive products, highlighted how the latest solutions improve safety and reduce vehicle weight to extend driving range.

“We are removing a lot of cables and connectors as well as expensive high voltage isolation components such as high voltage capacitors and transformers” said Steinmetz.  He added, “So removing wires, connectors, high voltage isolation parts is something which helps a lot on the overall reliability of the system, but as well on the cost. Obviously, safety is a critical consideration. And the functional safety of battery management systems today is trending from several chemistries. And meeting the functional safety requirements in the battery management system is really key. That’s the reason why we have started into the development of a wireless battery management system.”

“But equally important is how quickly can we isolate the faulty device,” added Vedantham.

Marocco added, “There are so many additional components that may be needed in traditional wired architecture, right to overcome the different limits, with the wireless we can see an advantage there. Of course, there is also an advantage in terms of electromagnetic compatibility (EMI).

“I think another point to mention on the EMI on the wireless side here is in the wireless battery management system, you are communicating inside the Faraday cage with a wireless carrier, instead of the usual way using wireless, where you want to communicate outside. It’s a metal enclosure and we are communicating inside. In this case, the focus is on addressing interference within the metal enclosure and RF propagation with battery packs to get to the best network availability.,” said Vedantham.

More miles, fewer cables
The use of wireless solutions in battery management offers designers the ability to lighten the load of an electric vehicle and thus balance the electrical charge, while meeting the highest standards of functional safety to improve reliability. The battery is the main element of an electric vehicle: more cells provide more charging capacity, which means longer distances to travel before needing a recharge.

Each cell must be monitored to maximize battery performance. Since a typical EV has 100 cells or more, the ability to remove bulky and heavy cables improves system reliability.

TI’s new battery management concept includes a proprietary wireless connectivity protocol and a set of electronic chips for monitoring parameters. The use of wireless eliminates the potential for failure in wiring exposed to vibration, humidity and other problems. This makes access to the batteries themselves for maintenance easier.

Aged EV batteries, once they have reached the end of their useful life in a vehicle, can also be recycled and reused in battery backup units at data centers, or in energy storage units connected to solar or wind power generation plants – where wireless capabilities make monitoring easy.

TI solutions
To speed up development time for automotive manufacturers, TI received functional safety assessment from TÜV SÜD, independently evaluating quantitative and qualitative error detection to achieve Automotive Safety Integrity Level (ASIL) D through its wBMS. The device combines the CC2662R-Q1 wireless MCU for reliable data exchange and the new BQ79616-Q1 battery monitor to monitor cell voltages and temperature as well as diagnose faults in high-voltage systems up to 800 V and beyond. Throughput and low latency protect data from loss or corruption, allowing the use of multiple batteries to send voltage and temperature data to the main MCU with an accuracy of ±2-mV thanks to the built-in A/D converter, and a packet error rate of less than 10-7. Security against attacks is enabled by various tools 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.

Figure 1: CC2662R-Q1 Block Diagram (Source: TI)

“Another point I want to emphasize is the entire software stack, including the drivers as well as the protocols, is compliant to ASPICE automotive software quality,” said Vedantham.

The deterministic protocol offers designers the ability to create a battery module using a single wireless system on a chip with multiple BQ79616-Q1 ICs for different configurations such as 32-, 48- and 64-cell. The system can support up to 100 nodes with a latency of less than 2ms per node.

“From a performance perspective, one of the critical things you want a wireless system to do is emulate or exceed the packet error rate performance or network availability that a wired system can offer. That is data accuracy. We’re basically able to have a latency of less than two milliseconds for the nodes that are closest to the battery control unit. While we are doing all this, we are not compromising the transmission speed that offers high throughput. Time-division multiplexing and frequency hopping ensure that we are able to achieve maximum throughput without wasting transmission time when we are at full capacity. And last but not least, I also want to stress the importance of the network restart feature; very often when you want to start up you want to make sure that the battery systems are working to be ready to go. So we are able to do this in less than 300 milliseconds, with no noticeable impact in terms of latency,” says Vedantham.

The BQ79616-Q1 allows achieving functional safety objectives and maximize the distance per charge in wired and wireless battery management systems. The BQ79616-Q1 offers monitoring for a wide range of battery chemistries, including lithium iron phosphate (LiFePO4). The BQ79616-Q1 has an integrated digital low-pass filter to optimize measurement accuracy. The device offers robust thermal management to cope with the extreme conditions of the electric vehicle while at the same time proving reliable in terms of electromagnetic compatibility and resistance to high-voltage transients and hot-plug events.

“So on each node basically the BQ79616-Q1 plays that critical role of sensing, measuring the voltage on the cells as well as the temperature and then transmits that information to the connectivity chip, which eventually has the role in making that information available to the ECU. We can detect failures on voltage measurement temperature measurements, according to the severity compliance, and that means of course, that there is no need for additional components, there is no need for additional software work from the system integrator to achieve that level of coverage. And when it comes to communication, the device also has achieved a certain level of safety for communication in each standard daisy chain type of architecture. I want to add that for the BQ79616-Q1 family, we have done an extensive job in enabling more intelligence compared to the previous generation to give chances to have much faster diagnostics. Moreover, BMS can be accurate depending on the chemistry that is chosen,” said Marocco.

Figure 2: Simplified System Diagram for BMS (Source: TI)

Time synchronization is of great importance to obtain a good understanding of the state of charge calculation from the point of view of the total battery, this must be synchronized as an example to a current sensor to a voltage tensor at the pack level.

“To understand if the cell is in a healthy condition, the accuracy of the cell voltage measurement, link availability as well as fast communication to the Battery Control Unit (BCU) are important technical parameters. This is where the functional safety aspect comes into play as it allows appropriate measures to be taken in case of a failure,” said  Steinmetz.

TI’s BQ79616-Q1 performs passive cell balancing using switches with two thermal management functions to prevent the die from overheating. One function controls the die temperature and the other controls the thermistor temperature, all managed by the MCU. This helps maximize battery life, optimizing the cost of an EV and the operating time to increase the distance between charges.

 

The post Wireless Battery Management Extends Driving Range in EVs appeared first on EETimes.

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