Total 3-phase AC current metric is ambiguous

[tiyash-basu-frequenz]

What happened?

Per-phase AC currents can be aggregated in two different ways:
a. scalar addition
b. vector addition

The results of these two additions can differ. E.g., if the current on each phase is 16A, then the scalar sum would be 42A, but the vector sum would be 0A (assuming the phases are exactly 120 degrees apart).

The total 3-phase current metric in the AC message is ambiguous, because does not specify whether it was calculated using scalar addition or vector addition. If still used, this could lead to errors in client applications.

What did you expect instead?

The total 3-phase current should be removed from AC metrics. If aggregating the current values in the three phases is required, clients can do it themselves, based upon their respective use-cases.

Affected version(s)

v0.10.x (version:0.10.x)

Affected part(s)

Protocol buffer definition (part:protobuf)

Extra information

No response

[tiyash-basu-frequenz]

What we can do as an intermediate solution is to

• always provide a scalar sum of the 3-phase currents from the API service
• and guarantee it in the API specs by documenting the above wherever required, e.g., here and here.