Automotive

What’s next in BMS? Safer, more affordable electric vehicles

15th September 2022
Sam Holland

As automakers consider new EV battery chemistries, battery management systems (BMS) with advanced semiconductor technologies are more critical than ever. This article from Texas Instruments' staff discusses.

As electric vehicles (EVs) grow in popularity, advanced battery management systems (BMS) are helping overcome some of the most critical barriers to widespread adoption: driving range, safety, performance, reliability and cost. And semiconductors are the heart of these systems.

“Semiconductor technology is a much bigger part of EVs than it is of internal combustion vehicles," said Sam Wong, who leads a team at our company that develops products for EV battery monitoring. “Our chips can bring huge benefits at a fraction of the cost of a battery pack."

According to a recent BloombergNEF report, EVs account for less than 5% of the passenger vehicle market globally. They’re gaining market share quickly, though, with most major automakers promising to move to a primarily EV lineup over the next five 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, driving automotive innovation forward with 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 leading-edge battery technology.

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 a more efficient alternative.

But 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. However, 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’s right at the limit of what modern semiconductor technology can deliver," said Mark Ng, a BMS system manager at our company.

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. Because manufacturers have to err on the side of underestimating range – to avoid drivers getting surprised by dying batteries in the middle of a highway – vehicles often report remaining driving ranges that are 25% shorter than what’s actually available.

That’s where our cutting-edge technology comes into play. By leveraging our high-precision battery monitors, automakers can indicate a more accurate driving range. 

“Instead of telling you there are 200 miles left when you actually have 250 miles, with our chip the car might tell you that you have 230 miles left," Mark said. “The BMS has essentially extended your range by 30 miles, with the same charge on the same batteries."

That 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. If one cell is discharging faster than others, it can reach near-depletion even though the rest of the pack still has power.

But getting too close to depletion can permanently damage a cell so it can’t hold a charge, rendering an entire group of cells permanently unusable. During charging, the concern is a cell that reaches capacity sooner than others. That risks overcharging the cell and may create a dangerous overheating situation.

Thanks to their accuracy, our battery monitors can spot early indications that a cell is at risk of over-depletion or overcharging and then disconnect the cell to avoid over-discharging or bleed off excess charge so that the entire pack of cells remains balanced during driving and charging. The devices also watch for rising battery temperature, which is another sign of overcharging or other problems.

“The BMS provides an elaborate monitoring network to sense the voltage, current and temperature of each cell," Sam said. “That way, we can cut a battery off from the system, or adjust the current going in or out of it."

The BMS provides redundancy by enlisting two independent sensors to measure voltage, flagging the system if there’s 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 electric vehicles. 

Flexibility for innovation

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. Our 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 carmakers choose to use, saving them research and development costs, software development costs and time.

“When you’re a manufacturer dealing with multiple chemistries and configurations, having a variety of battery monitoring device options in the same product family is paramount," Mark said. “This ability to scale across platforms decreases the cost of individual EVs and brings cars to market faster.”

More BMS innovations are coming. Our company is pushing the boundaries of voltage accuracy and is integrating more control capabilities into each chip to unlock the true potential of car manufacturers. In addition, at TI, research is being done 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," Sam said. “We want to make sure our BMS products can offer the flexibility to get the most out of any of them."

A passion to create a better world

Helping carmakers make electric vehicles safer and more affordable is just one way our innovators are living our company’s passion to create a better world by making electronics more affordable through semiconductors. Each generation of innovation builds upon the last to make technology smaller, more efficient, more reliable and more affordable. We think of this as Engineering Progress. It’s what we do and have been doing for decades.

For more information on energy storage innovation, Electronic Specifier's sister publication, IoT Insider, covers the latest in tech. Plus, you can find more engineering news at ES's LinkedIn page here!

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