Report grid connection point's current limit

[tiyash-basu-frequenz]

What's needed?

Every microgrid has a limit on how much current is allowed to flow through the grid connection point. This is generally a static value, dictated by the fuses/circuit breakers placed in the microgrid.

The microgrid API should report this value, so that clients can incorporate it into their decision making mechanisms.

Proposed solution

No response

Use cases

This value can be used by clients to preemptively check if a command does not allow the current at a grid connection point to exceed its fuse's limits.

Alternatives and workarounds

No response

Additional context

No response

[thomas-nicolai-frequenz]

The microgrid API needs to be enhanced to expose the grid connection component as well as the grid fuse limit property. This is needed for the PowerManager and other grid fuse protection layers to work properly. Right now this is needed for preventing the FCR test with multiple batteries to exceed the grid fuse limit.

[tiyash-basu-frequenz]

The API already exposes the grid connection component. It does not however report the fuse limit, as you indicated. This is precisely what this issue will address.

[thomas-nicolai-frequenz]

@sahas-subramanian-frequenz and @leandro-lucarella-frequenz we should extend the SDK so that it already exposed a grid fuse limit for the grid connection even the API doesn't yet expose it as part of the PowerManager. Of course by default it would be NULL as in not available but that would help to have a more stable interface right away.

[leandro-lucarella-frequenz]

Do you see this as metadata at the same level as the location of the microgrid? If so I guess it would make sense to have it as frequenz.sdk.microgrid.grid_max_current (or whatever name we think it's best.

So, this value could be None (unknown) for real in an installation? This is important info for the type system, to know if really None is a possible value or if we should refuse to run without knowing this limit because it is too dangerous.

[thomas-nicolai-frequenz]

Do you see this as metadata at the same level as the location of the microgrid

No the grid fuse limit is a property of the grid connection component. that has nothing to do with the metadata. Its just that the property is not yet exposed but will be soon. But in order to move fast we could have the SDK already provide that property even its not set yet.

[thomas-nicolai-frequenz]

know if really None is a possible value or if we should refuse to run without knowing this limit because it is too dangerous.

if there is no value given None should be fine. Its a good question if the system should run without. At least it should trigger a warning if its not set.

[leandro-lucarella-frequenz]

No the grid fuse limit is a property of the grid connection component.

OK, I'm trying to understand this, but at the microgrid API level there is no explicit "grid connection component", that would be just the root component (meter) in the component graph. Am I correct?

So if this is so, should all meters have now this max_current property?

I think it would be a good idea to also add it to the microgrid API (this repo), specially if it could be null, the microgrid service could just not set it for now and all should be fine and just add it to the API specs should be pretty trivial (once the design is decided).

Then it will much easier to know exactly how to plug it into the SDK, because we would have to think about it depending on where the data comes from (like if it will be just some other meter metric or what).

[tiyash-basu-frequenz]

OK, I'm trying to understand this, but at the microgrid API level there is no explicit "grid connection component", that would be just the root component (meter) in the component graph. Am I correct?

No, there is a grid connection point category. The max current limit will be provided as a metadata of this category.