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derrick thomas avatar image
derrick thomas asked

Clarification on ESS behavior when running generator

I'm having a bit of an issue so I'm looking for a little clarification on what is supposed to happen when running a backup generator on an ESS system. I have parallel mp2 24/3000 2x120. I understand that ESS uses frequency shifting to control feed in and so on and so forth. When running a little Honda 2k inverter generator for backup everything works as expected, stable voltage and frequency, batteries charging. When running my 7.5k Kubota the frequency constantly moves up and down between about 56 and 65 which causes the generator output to fluctuate, voltage is not steady (bounces between about 110 and 135) and causes the DC output (inverter charger output) to fluctuate up and down about 50 amps or so. I have grid code set to "other" with lom disabled. (Yes I have anti islanding protection) Weak ac input is not selected. when I disable ESS and run the 7.5k Genny it is absolutely stable voltage and frequency all the way up to full rated output so I don't believe it's a problem with the generator, but maybe just an issue with the way ESS works with this particular generator. When running a backup generator "generator" is selected as the input source.

I'm assuming that there is no way to temporarily disable ESS while running a generator, other than removing the assistant?

Is this expected behavior? Meaning... wouldn't it be desirable to disable ESS while a generator is running anyway? Or at least disable frequency shifting while running so the multi only synchronizes to the incoming ac rather than trying to push/pull the frequency back to the generator?

I'm still learning so go easy on me. I'm a pretty quick study though.

ESSGenerator
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Alexandra avatar image Alexandra ♦ commented ·
@derrick thomas

You generator does not have a stable way of regulating itself. Which will be the main issue.

When working with generators the impedence is different to that of the grid. So does behave differently. You have LOM disabled that disabled the push back to 'grid'.

Try enabling the weak AC, but also lower your input current limit.

The other way is to increase grid set point a bit as well. But do one at a time to see which one works to help your generator stabilise.

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derrick thomas avatar image derrick thomas Alexandra ♦ commented ·

By grid setpoint I assume you are referring to feedin setpoint? I have feedin disabled.

And I'm assuming that the Honda 2k doesn't have this issue because it regulates frequency as well, whereas the Kubota frequency is only dependant upon engine rpm?

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derrick thomas avatar image derrick thomas Alexandra ♦ commented ·
I've done some more testing and watching closely while on generator. It does seem that the issue is being caused by the multi and not the generator. As I closely monitor things I can see that the multi slightly raises the frequency resulting in a drop in input current (I can also hear the generator load decrease at the same time) the generator frequency remains stable and the fluctuations in input current and resulting DC charge output amps is directly correlating to the frequency changes from the multi. This frequency shift last only milliseconds and this cycle repeats consistently at about 3 to 4 second intervals. This only occurs with ESS enabled. Without ESS there is no fluctuation in input/output current. All feedin settings are disabled and there are no pv inverters, only mppt.
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1 Answer
multiplusinus avatar image
multiplusinus answered ·

ESS "tugs" at the grid by varying the frequency up and down. It does this varying the frequency slightly, which could explain what you are seeing. And the reason that ESS does this is to try to figure out if the connection is really the grid, in which case the shift wouldn't result in any input changes, or some other source like a generator.

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