Grid Power Limitation

[lprosperi]

Hi,

I am using version 6.18

I have a project with 20 MW as Grid Power limitation.

Actual installed AC Power 22.4 MW

Nominal Array PV Power 26.8 MWp

In my model I have both AC losses:

-AC circuit: inverter to injection point

-External transformer

When I run the Simulation, PVsyst generates the hourly output.

These are the max value for each energy field.

EArray: 20451

EOutInv: 20005

E_Grid: 19585

It seems that the 20MW limit is applied to the AC inverter output instead of the grid.

I would expect that the grip power limitation applies to the E_grid field.

Can you please confirm?

Thanks,

Leonardo

[André Mermoud]

You are right, the grid limitation is applied to the PNom(ac) of the inverters in the present time.

The losses after the inverter are not taken into account.

In a first try, I just foresee this for a simple case. This is the easiest way for programming.

However I have to do some improvements and give some further possibilities to this grid limitation for a next version.

- As you propose, the limitation at the injection point: not easy because PVsyst has to perform the calculation twice for each concerned hour. And I'm not sure that the inverters will operate in this way in the reality: this would require a continuous measurement of the injected power, and a return of this information to the inverter software.

- If you have several sub-systems (not in the same orientation) the limitation should indeed be applied to the injection, and will act differently on each sub-array. Again this involves the re-calculation at each concerned hour, and is not simple to include in the simulation.

[rvarieras]

This is an issue also with inverters using a temperature-dependent Pmax: the grid limitation is almost completely ineffective.

Andre - despite the associated complexity of a feedback system, in my experience it is, in fact, how this works in reality. Grid controllers constantly check the combined output of all inverters at the injection point (or at an acceptable proxy point of the electrical circuit) and use it to calculate a power throttling coefficient that is sent out to inverters so that they can move off the maximum power point and reduce output.

Sometimes this is done using just a subgroup of inverters instead of the entire array, if sufficient.

[André Mermoud]

This choice will be available in the next version 6.39, to be released soon.

[S.Faulkner]

Am I right in understanding that in 6.39 when the power limitation is applied at the grid injection point, the loss is still shown as part of the Inverter Loss (over nominal inv. power)?

This combined loss does drop as expected when changing from limitation applied at inverter to limitation applied at grid injection point.

[André Mermoud]

Yes. The management of the grid limitation is indeed performed by the inverter's control circuits (the Power information at the injection level should be an input information for the inverter).

The limitation itself is done by the inverter, and is considered equivalent to a limitation of the nominal power. We didn't define a special loss variable for that.

[jforbess]

I don't find the implementation in 6.39 helpful, because I would expect the limitation at the grid level to take into account any AC ohmic losses or transformer losses, such that if the output of my inverter is 2.2 MW, with STC AC losses of 0.5% and peak transformer losses at 1.0%, resulting in a peak output of 2.167 at the grid, I would like that output limited to 2.0MW.

Currently the inverter is limited, with AC and transformer losses included after the limitation, but plants are often operated with the limitation including consideration of the AC and transformer losses.

[jforbess]

Nevermind, I see my mistake. The injection port limitation needs to be selected, rather than inverter limitation. (I would suggest making the injection port the default, but at least now the feature is there.)

Thanks.