Sam Wong, product line manager—battery gauge and monitor products, and Mark Ng, general manager—HEV/EV powertrain, Texas Instruments (TI)
As automakers consider new EV battery chemistries, battery management systems (BMSs) with advanced semiconductor technologies are more critical than ever. Texas Instruments (TI) empowers automakers to design BMS architectures for new and emerging battery chemistries that help make EVs safer and more affordable.
As electric vehicles (EVs) grow in popularity, advanced BMSs are helping overcome some of the most critical barriers to widespread adoption, namely driving range, safety, performance, reliability and cost; and semiconductors are at the heart of these systems. They are a much bigger part of EVs than they are of internal combustion vehicles. TI’s chips can bring huge benefits at a fraction of the cost of a battery pack.
According to a recent BloombergNEF executive summary1, EVs account for less than 5 percent of the passenger vehicle market globally. They are gaining market share quickly, though, as most major automakers are promising to move to a primarily EV lineup over the next 5 to 10 years, pushing toward a greener, more sustainable future.
Advancements in battery technology are a key factor for mainstream consumers. TI is at the forefront of that effort, developing new technologies that enable engineers to work with multiple battery chemistries and configurations. These advancements are already bringing forth improvements in EV price, performance and reliability from both conventional and new battery technologies.
Gaining miles from millivolts
One big opportunity comes from new battery chemistries. Most EVs have been powered by lithium-ion batteries that rely on cobalt, a rare-earth metal in short supply. But now, much of the EV industry is beginning to embrace a cobalt-free alternative battery chemistry, lithium iron phosphate (LFP), which is more plentiful, more sustainable to mine, easy to work with and therefore a much cheaper and more efficient alternative.
However, while iron’s lower cost and relative abundance make LFP a more sustainable choice, the chemistry comes with a drawback. EVs rely on measuring battery voltage drop to assess remaining capacity, which, to the people in the vehicle, means the remaining driving range. Unlike cobalt-based batteries, which drop steadily in voltage as they discharge, the voltage drop in LFP batteries is miniscule, even as they approach full depletion, which makes it challenging to predict.
LFP’s flat discharge rate requires a voltage measurement accuracy that is right at the limit of what modern semiconductor technology can deliver. Conventional BMS devices measure battery voltage to an accuracy of about 5 millivolts; but in LFP batteries, that inaccuracy translates to about a 25 percent uncertainty in driving range. As manufacturers have to err on the side of underestimating range, to avoid drivers being surprised by dying batteries in the middle of a highway, vehicles often report remaining driving ranges that are 25 percent shorter than what’s actually available.
This is where TI’s high-precision BMSs come into play, allowing automakers to indicate a more accurate driving range. Instead of telling the driver there are 200 miles left when they have 250 miles, a car with a TI chip might tell them that they have 230 miles left. The BMS has essentially extended the range by 30 miles, with the same charge on the same batteries. This extra range can be enough to ensure LFP batteries are feasible, giving automakers the confidence to switch to the emerging chemistry and thus making EVs more sustainable and affordable.
Balancing act
In addition to extending a vehicle’s range, accurate monitoring is critical for the safety and durability of each of the nearly 200 cells that go into an EV’s battery pack. During driving, if one cell is discharging faster than the others, it can reach near-depletion, even though the rest of the pack still has power. Getting too close to depletion can permanently damage a cell so it cannot hold a charge, rendering an entire group of cells permanently unusable. Also, during charging, if a cell reaches capacity sooner than the others and overcharges, a dangerous overheating situation can result.
Thanks to their accuracy, TI’s BMSs can spot early indications that a cell is at risk of near-depletion or overcharging and then disconnect the cell to avoid overdischarging or bleed-off excess charge so that the entire pack of cells remains balanced during driving and charging.
The BMS provides an elaborate monitoring network to sense the voltage, current and temperature of each cell. This way, a battery can be cut off from the system, or the current going in or out of it can be adjusted. It provides redundancy by enlisting two independent sensors to measure voltage, flagging the system if there is a mismatch.
Even the task of cutting the battery off from the system comes with its own set of challenges and solutions. Higher battery voltage stack ups, faster charging requirements and more powerful traction motors all create unique challenges for these disconnect systems in terms of power distribution, robustness and safety for the next generation of EVs.
Flexibility for a better world
As manufacturers introduce new battery chemistries, more powerful packs and different configurations of individual cells, many of them are rolling out EV product lines that leverage different combinations of each. TI’s portfolio offers multiple channel options in the same package, pin-to-pin compatibility and the complete reuse of established software. Thus, one of the most important features that our portfolio of devices offers is the ability to work with virtually any battery chemistry or configuration automakers choose to use, saving them R&D costs, software development costs and time.
When you are a manufacturer dealing with multiple chemistries and configurations, having a variety of battery monitoring device options in the same product family is paramount. This ability to scale across platforms decreases the cost of individual EVs and brings cars to market faster.
More BMS innovations are coming. TI is working to further improve voltage accuracy and integrate more control capabilities into each chip to unlock the true potential of automakers. In addition, we are conducting research to help ensure our BMS solutions are optimised to accurately support emerging battery types. There are probably another hundred different battery chemistries that are being looked at in the industry, and we want to make sure our BMS products can offer the flexibility to get the most out of any of them.
Helping automakers make EVs safer and more affordable is just one way TI is helping to create a better world. Each generation of innovation builds upon the last to make technology smaller, more efficient, more reliable and more affordable.
Texas Instruments
Reference[1] McKerracher, C., O’Donovan, A., Albanese, N., Soulopoulos, N., Doherty, D., Boers, M., Fisher, R., Cantor, C., Frith, J., Mi, S., Grant, A., Jinghong, L., Ampofo, K. and Abraham, A. (2021). Electric Vehicle Outlook 2021. [online] BloombergNEF.Available at: https://bit.ly/3FfujvX