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Battery Management Systems Influenced by Vehicle Design and the Grid

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【Summary】As electric vehicles flourish, battery management systems must take both vehicle design and the nation's electric grid into consideration.

Mia Bevacqua    Sep 08, 2017 11:05 AM PT
Battery Management Systems Influenced by Vehicle Design and the Grid

Electric vehicles used to be as rare as a silver half dollar. Now, EVs have proliferated to the point that even Walgreens has a charging station. As more electric vehicles hit the road, companies will need to consider both vehicle design and the nation's electrical grid when creating battery management systems. 

What is a battery management system?

Most Electric vehicles use Lithium-ion batteries. These battery packs are constructed from multiple modules connected in series. The modules contain individual battery cells. The battery management system (BMS) is tasked with monitoring the battery cells health and operation. 

Typically, the mastermind of the BMS is a dedicated electronic control unit (ECU). Using inputs from various sensors, the ECU determines battery cell performance. 

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Vehicle design considerations

Proper battery management is critical, not just for battery longevity, but also for vehicle safety. EV batteries are several hundred volts and pose a threat if not properly maintained. In addition, a battery that is over or undercharged can affect vehicle operation. It also has the potential to start a fire. A BMS must be able to take a corrective action, such as shutting down a module, if such a problem occurs. 

Battery management systems aren't just responsible for monitoring cell health. They also control other aspects of the battery operation that affect vehicle safety and performance. For example, BSMs may aid in battery isolation for safety concerns. They may also adjust battery management for various driving conditions (i.e. during heavy acceleration). 

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Electrical grid considerations

A growing number of EVs could pose challenges to the nation's electrical grid. The need to Feed vehicles a large amount of current could require costly infrastructure upgrades. In addition, bumping up output to meet EV demands may lead to excess power being wasted during off-peak hours.  

Powerelectronics.com points out one potential solution: smart chargers. These devices regulate their demand based on grid load and the vehicle needs. Smart charger use is complicated by the fact the charger must draw lower current during times of peak grid demand. For this to work, a BMS must send information regarding battery state-of-charge to the charging device. Otherwise the battery night not charge properly.

For consumers to get the most out of their EVs, there must be two types of charging stations: residential and public. Residential charge stations can be of the variable grid, slow charge variety. Fast charge public stations allow for longer trips and cure EV range anxiety. On the other hand, slower charge public stations can be used to encourage people to use (and spend money at) nearby facilities.

For improved efficiency, the charging stations could also be networked. Allowing the chargers to communicate, could optimize performance and reduce stress on the grid. 

Tying it all together

To maximize EV charging, standards must be put into place. The first EV charging standard is SAE J1772, which defines the electrical connectors used in charging. Another standard, IEC 62196, covers the various charging modes and connector configurations. 

Charging stations from Tesla and other manufacturers are already available. These units work together with the vehicle BMS to charge the EV. Even so, If the number of EVs continues to grow, a system that is quicker and more efficient will be needed. 

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