Multiplus disconnects under frequency deviation

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egsust asked May 7, '19

Multiplus disconnects under frequency deviation

Hi,

I have an off-grid installation with 3 single-phase multiplus in parallel connected to a battery. The frequency of the isolated system can vary depending on the connection and disconnection of different loads on the system (weak grid). The problem is that depending on the rate of change of frequency the multiplus disconnects. I have noticed that if the frequency deviation is faster than approx. 0.1Hz per second (even if it is from 50Hz to 49.7) the multiplus disconnects. For slower changes the multiplus has no problem.

Is there any option which will allow the multiplus to remain connected even if the frequency deviation is not slow as long as the frequency remains within the stipulated limits? I have configured the system for a weak grid and disabled LOM, not sure if there is any other settings that could help?

Thanks.

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wkirby ♦♦ commented · May 07, 2019 at 11:38 AM

First you said it's off-grid, but then you talk about weak grid. So it's a bit confusing. Please could you clarify if the system is connected to the grid or not?
Do you have PV connected on the AC-OUT side?

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egsust wkirby ♦♦ commented · May 07, 2019 at 11:54 AM

With off-grid I mean that it is an isolated grid, not connected to the national grid. With weak grid I mean that the sources providing energy to the isolated microgrid (not connected to the national grid) are weak and therefore under load changes the frequency can deviate faster than typically happens in a large interconnected grid.

There is no PV or loads connected on the AC-OUT side, the converter purpose is only to interconnect the battery with the microgrid.

Thanks.

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Modifications Space

Node Red Space

Answer 1 · 2019-05-07T13:13:42Z

Paul B answered · May 07, 2019 at 01:13 PM

you could try turning off UPS, don't know if this will help as it just cause a slower change over to inverter.

otherwise as far as I know there is no other frequ adjustments settings.

anyway I would think that the inverter would have to be able to match the external powers frequency shift and if it cant move fast enough it would then disconnect,

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egsust commented · May 07, 2019 at 01:44 PM

Thanks for this, I forgot to add to my comment that UPS is also disabled on my configuration.

Yes, so I'm interested in knowing if this is a limit in the controller of the device which can/cannot be tuned for higher deviation rates or this is caused by a LOM protection which is still enabled somehow? From my understanding, I think that LOM protection is typically carried out by means of a rate of change of frequency setting or a vector shift. Both of these will be clearly affected in this case and could be causing the disconnection?

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