Grid-Tied AC microinverter

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jwax
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Grid-Tied AC microinverter

Post by jwax » Fri Sep 23, 2016 11:09 am

These devices have a unique feature- they must first see 120 VAC, 60 Hz on their output, before they switch on and contribute power to that AC line.
The purpose is to disable the output of a solar module in the event the grid goes down. If the inverter did not shut down, it would be supplying AC to a "dead" grid, causing a nasty safety issue for those working on the "dead" line.
In order to defeat this shut-down device for an application, I need to generate the grid voltage separately, to fool the inverter into working as if it is feeding a grid.

Looking for ideas on a small cheap 120 VAC sine wave, 60 Hz generator from a 12 volt battery. Not sure how much power this oscillator need supply, perhaps half amp @ 120 VAC?

I have tried off the shelf plug in the cigarette lighter inverters, but their trashy 120 VAC output does not fool the microinverter into turning on. The micro is looking for clean grid quality AC.

Ideas?

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haklesup
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Re: Grid-Tied AC microinverter

Post by haklesup » Fri Sep 23, 2016 1:11 pm

I'm guessing you are using this off grid and want it to act like a regular inverter also that you are not using this near any AC outlets and need to generate the AC from a DC source, perhaps the solar panel itself.

That's a hardware hack I don't understand all the safety risks but it seems all you need is a capacitor in series with the inverter and a good pure sine (not modified sine) to trick it. Maybe the guts from an old UPS with a dead battery will work. Not only does the inverter provide shutdown but it would also need this signal to synchronize the phase of the AC output with the grid. The grid AC may actually be used indirectly to fire the SCRs in the micro inverter to keep it in synch, if that were the case, min signal compliance would be essential

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dacflyer
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Re: Grid-Tied AC microinverter

Post by dacflyer » Fri Sep 23, 2016 2:40 pm

i hope your using this for pure off grid use..
but you may try using a PURE sine wave inverter.. some of the PURE sine wave inverters are actually making better power than the power companies.. but with a micro inverter, not sure how well it will do with regulating..any large fluctuation in voltage and the inverter will disconnect itself for a period of time til it tries to reestablish a connection.
the inverter is grid tied for a reason...and i am not sure you can trick it with a non grid power source.

sauerwald
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Re: Grid-Tied AC microinverter

Post by sauerwald » Fri Sep 23, 2016 4:07 pm

I'd generate a 12V AC sine wave probably with a phase shift oscillator, and then drive the secondary of a transformer intended to be a 12V out transformer, and collect my 110V AC sine wave from the primary.

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jwax
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Re: Grid-Tied AC microinverter

Post by jwax » Fri Sep 23, 2016 6:37 pm

Yes, definitely an off-grid situation. If you're wondering why not use an off-the-shelf Walmart or Harbor Freight inverter, the solar panels I have output 30-40 volts DC, and those inverters do not handle those voltages. A microinverter, however, is made for that input range.
Good ideas folks, and welcome and thanks to sauerwald! I will be trying the oscillator/transformer concept!

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