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The goal is to build a 200 V Lithium-ion battery pack using 21700 cells.

I am trying to make a design decision on lithium-ion battery pack architecture for an electric vehicle and it boiled down to below two options:

Approach 1: 100 V lithium ion module on the left side of the vehicle and another 100 V Lithium ion module on the right side of the vehicle with high voltages wires connecting in series to stack the voltage to 200 V.

Approach 2: A single battery rated for 200 V.

Would like to prefer approach I from dynamics point of view. Barring the vehicle dynamics discussion, is there a concern in terms of battery performance and losses to worry about between "Approach 1" and "Approach 2". Is there an added complexity to think about BMS communication or not really?

Each battery pack will of course consider of lithium ion modules and the overall number of cells in the battery are based on energy sizing requirements of the vehicle.

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Lithium-ion battery pack in series or parallel

Definitely in series. Connecting Li-ion modules or batteries in parallel brings an inordinate amount of headaches.

Approach 1 vs. Approach 2

Certainly Approach 1 is acceptable from an electrical point of view, and, indeed, is quite commonly done in automotive applications.

Is there an added complexity to think about BMS communication or not really?

There is a slight increase in the complexity of the wiring to the cells in the two modules, but nothing of great concern. I recommend a master/slave BMS for the job:

  • A slave in box 1
  • A slave on box 2
  • The master in a convenient location, such as near the current sensor or the contactors.
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approach 3: same as approach 1 but with 200 V modules running in parallel, giving you redundancy if one of the modules develops a fault of some kind.

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    \$\begingroup\$ "200v modules running in parallel" is bad advice as it brings a host of problems. The most obvious is that it requires two BMS that are coordinated, or a BMS that can handle strings in parallel, either of which is expensive. "redundancy if one of the modules develops a fault" BAD idea! it allows one battery to be reconnected without regards of voltage difference. That's how EV fires start. \$\endgroup\$ Nov 26 at 17:31

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