AC coupling - light flicker

Discussion about adding energy storage to grid-dependent inverters using OutBack Power technology
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sjsamuel
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Joined: Thu May 28, 2020 9:30 pm

AC coupling - light flicker

Post by sjsamuel »

Well, I’m super excited as I finally, after a lot of work, time and money, have my system up and running. Thanks to everyone here that has helped with my many questions so far.
Well, now the journey to get everything working smoothly starts, and I ran into my first significant issue that has me stumped. Here is my system in a nutshell: 2 Radian 8048a’s powered by a lithium battery bank and Grid Tied. PV is an Enphase IQ7 system that is AC coupled to the Radians.

Turned of the Grid yesterday and had a big grin on my face as my inverters didn’t miss a beat and powered the house without any delay. I left the PV on, and it too continued to function now operating on the local grid created by the Radians as it should. As my load requirements dropped however, I noticed a very apparent flicker in all my lights, LED and incandescent(yes I still have a couple :eek:). If I increased the load by turning in the dryer or something the flicker gets better, but still there. Finally in an attempt to trouble shoot, I turned of PV and the flicker is gone. I’m assuming there is some interaction between the Radians output and the PV output..is it a phasing issue? What can I do to sort this out?

Oh and the Radian Battery Charger is off and still not difference

Thanks for the help in advance!

Samuel
raysun
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My RE system: Flexpower Two: (2) FXR3048A-01, (2) FM80, MATE3s, FlexNetDC
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Re: AC coupling - light flicker

Post by raysun »

I'm an all DC off-grid guy, so am speaking from no experience, but I'd think phase sync between AC coupled busses would be out-of-phase on occasion, on purpose.

One common method to modulate current admittance is to shift frequency. I believe it the method Outback uses. How nimbly the string inverters respond, or don't, may lead to interference waveforms in AC OUT.

I'm not saying that's your issue, but I'd think it might.
billw22
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My RE system: 5.7K solar system with Solaredge inverter. Heat pump water heater.
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Re: AC coupling - light flicker

Post by billw22 »

Well, I’m super excited as I finally, after a lot of work, time and money, have my system up and running. Thanks to everyone here that has helped with my many questions so far.
Well, now the journey to get everything working smoothly starts, and I ran into my first significant issue that has me stumped. Here is my system in a nutshell: 2 Radian 8048a’s powered by a lithium battery bank and Grid Tied. PV is an Enphase IQ7 system that is AC coupled to the Radians.

Turned of the Grid yesterday and had a big grin on my face as my inverters didn’t miss a beat and powered the house without any delay. I left the PV on, and it too continued to function now operating on the local grid created by the Radians as it should. As my load requirements dropped however, I noticed a very apparent flicker in all my lights, LED and incandescent(yes I still have a couple :eek:). If I increased the load by turning in the dryer or something the flicker gets better, but still there. Finally in an attempt to trouble shoot, I turned of PV and the flicker is gone. I’m assuming there is some interaction between the Radians output and the PV output..is it a phasing issue? What can I do to sort this out?

Oh and the Radian Battery Charger is off and still not difference

Thanks for the help in advance!

Samuel
great
I'm new here and it would be nice if you share some other threads that you've started
so that I know where to start on my own system
yay
clarkef
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My RE system: Radian 8048A w/PV GSLC
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Location: South Central KY

Re: AC coupling - light flicker

Post by clarkef »

Click on his username. You can see posts he has made that way.
billw22 wrote: Thu Dec 31, 2020 8:19 am great
I'm new here and it would be nice if you share some other threads that you've started
so that I know where to start on my own system
jnh
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My RE system: GVFX-3524, FM-80+FM-60, ~4.9kW PV in mixed panels on movable platforms, 415 Ah AGMs @ 24V, 80Ah @ 12V, Hub4, Mate, FNDC, Brultech GEM 32-ch AC datalogger, Midnite E-Panel, homebrew DC-DC crossfeed to 12V system, Honda EU-1000i, AIMS CON120AC1224DC charger
Location: St. Augustine, FL, US

Re: AC coupling - light flicker

Post by jnh »

If this is still happening, do your flickering lights have dimmers on them?

Almost all of mine do, and I get occasional flickering of a few LED lights when operating in gridtie mode (selling power back), but only at certain combinations of dimmer setting (toward the low end brings it out more), load wattage behind the dimmer, inverter output power, and other random factor(s) I can't quite identify, possibly other household loads running and/or what the exact grid voltage happens to be at that moment. This does not happen when running in off-grid/standalone mode, but I have a DC-coupled system with only one inverter in operation, the Outback GVFX, which has a completely different regulation mode for off-grid operation, with no need for anti-islanding then, whereas with AC-coupling your Enphase's are always "selling", either to your grid or to the Radian and its battery bank.

I suspect the flicker effect has something to do with anti-islanding safety checks required of all grid-tie inverters, whereby they're supposed to detect an unlikely condition where your neighborhood has become isolated from the grid, but load from those neighbor(s) still connected to, or upstream from, your utility transformer just happens to exactly match what your inverter is producing. Because that would create an unsafe condition for utility crews trying to repair downed lines, or anyone coming in contact with one, the inverter are supposed to recognize it and stop exporting power within a short period of time. Exactly how this is done probably varies between manufacturers, but most likely use some kind of perturb-and-observe method, where they deliberately introduce some small anomaly into the AC waveform, then watch how "stiff" the load's response to that is. e.g. trying to pull the AC line slightly off-phase would have nearly zero effect when fighting the entire grid, but might "succeed" under a balanced-island scenario, which the inverter would then take as a sign that something is wrong and it needs to shut down.

I don't know how they're able to distinguish an intentional and safe AC-coupled micro-grid from an accidental neighborhood island, though. Am I understanding correctly that the flickering only happens for you when you're *not* grid-connected?

Common triac-based dimmers, because of how they work (chopping away part of each AC half-cycle, each switching action based on a voltage threshold) cause lights behind them to be much more sensitive than usual to any line disturbances. Even with no inverter in operation, there are small disturbances at specific times on my local grid (almost 10 minutes past the top of the hour, but not every hour), perhaps related to large industrial loads switching or power plant dispatching, which normally escape notice but become subtly visible when a dimmer is adjusted just right. One particular AC induction-motor fan also modulates its humming sound slightly then, but no other such motors do. I should try to capture these clockwork disturbances (along with suspected inverter-generated ones) on a scope sometimes...
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