04Dec 2020

When it comes to electric vehicles, there is an understanding that the battery is a fundamental component to the vehicle’s utility. Yet, there is also a false expectation that the battery can deliver all what drivers expect from an EV.  Often underestimated is the role of battery management systems (BMS) in delivering critical performance and safety, in particular, extended driving range, very fast charging, long warranties and utmost safety. I will explore this topic in more detail in a series of blogs. 

In this first part, let’s define what battery management is and does. BMS historically included the electronics (hardware) that measure voltage, current and temperature, protect the battery from current or voltage spikes, and distribute charge evenly across different cells (called cell balancing). There is a basic layer of software that computes how much charge is stored in the battery.

Generally, these are electrical systems with very little intelligence related to the chemical operation of the lithium-ion battery. There are many suppliers of such basic BMS systems, spanning smaller companies to incumbent automotive Tier-1 and Tier-2 suppliers, and some of the battery manufacturers. Most electric vehicles on the road, whether you own a Tesla, a Nissan Leaf, a BMW i3, have one of these basic BMS on board.

Future EVs demand far more performance than what present BMS are providing. Specifically:

  1. Very fast charging: Newer EVs must be able to fully charge the battery in under 20 minutes without degrading the battery. This is strictly the role of more intelligent BMS.  If you try to fast charge your EV today at a DC-fast-charging-station, you likely will not do much better than 35 minutes. The vehicle’s manufacturer will also throttle your charge if you try to DC-fast-charge too many times in a row — in order to preserve the battery’s health. An intelligent BMS should be able to lift such restrictions!
  1. Maximum driving range: Car manufacturers reduce the available charge from the battery (and the driving range) in order to guarantee the battery’s longevity. It is one of the key tradeoffs between available charge capacity, fast charging, and battery longevity (hence warranty). This, again, is the role of a more intelligent BMS.
  1. Extended battery warranty: EVs have traditionally offered 100,000 miles of warranty. But, if you look closely, the fine print warrants that only 70% of the original driving range remains after 100,000 miles. So if your EV has a nominal driving range of 300 miles, the warranty covers you only if the driving range drops below 210 miles after 100,000 miles. Not ok! Yes, you guessed it, it’s the BMS function.

Fast charging, maximum driving range, and battery warranty form a triangle of tradeoffs. An EV maker must balance these three conflicting parameters. If they add more fast charging, then they must sacrifice warranty or driving range….and vice versa. This game of whack-a-mole makes today’s EVs fall short of market expectations. Next-generation of EVs must include intelligent BMS that are able to break this limitation. The technology exists.

The intelligent BMS diagnoses the battery in real time, assesses the likely degradation mechanisms and the battery’s health at that moment in time, then dynamically makes the necessary adjustments to optimize the operation of the battery. It is “computation” meets “chemistry.” 

In part 2, I will cover the suppliers of BMS and their integration into the EV.

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