How to convert AC coupled to DC?

Discussion about adding energy storage to grid-dependent inverters using OutBack Power technology
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gregorio
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How to convert AC coupled to DC?

Post by gregorio » Thu Feb 28, 2019 12:49 pm

I started a thread here http://outbackpower.com/forum/viewtopic ... 85&p=62951 but I guess I was not asking the right questions. I understand Outback is no longer supporting AC coupled systems. So, what do I need to do to convert to DC?

Shadow_Storm56
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Re: How to convert AC coupled to DC?

Post by Shadow_Storm56 » Thu Feb 28, 2019 9:57 pm

I guess I won't be using AC coupling in the future at all. You want to take the output of an inverter that takes DC to AC and then take it back to DC?,

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Gwendoly Espe
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Re: How to convert AC coupled to DC?

Post by Gwendoly Espe » Fri Mar 01, 2019 5:08 am

We actually now have a AC Coupling solution. We did a webinar about in February called "Adding Energy Storage for Grid-Tied Inverters" and application note: How To AC Couple Grid Tied Inverters with OutBack Frequency Shifting Inverters. I will check with marketing to see when the webinar will be on our YouTube channel.
Gwendoly Espe
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Alpha Technologies Inc. / OutBack Power Technologies
3767 Alpha Way Bellingham WA 98226 USA
http://www.alpha.com

gregorio
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Re: How to convert AC coupled to DC?

Post by gregorio » Fri Mar 01, 2019 8:27 am

Thanks for the information. It does bring up another question about the generator connection. How is it possible to backfeed on the GEN connection?

pss
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Re: How to convert AC coupled to DC?

Post by pss » Fri Mar 01, 2019 10:05 am

I just got finished reading the application note and have a few questions. The application indicated for this to work, there needs to be a direct connection from the grid tie inverter to the Radian and an output from the Radian to both a main and secondary panel. In my case, the grid tie inverter, main panel and utility meter are located about 100 feet apart from my Radian inverter which supplies a second main panel. A single 120/240V 50A circuit from my main panel feeds into the GSLC and Radian AC input as my grid tie connection. Due to the distance and building, it would be cost prohibitive and an engineering problem to try and run a second circuit from my Grid Tie Inverter directly to my Radian inverter, bypassing the main panel. The only real way to do this would be to remove the circuit from my main panel (currently connected to my Radian) and connect it directly to my grid tie inverter. But then, I have no way to return AC power from my Radian back to my main panel and into the grid when it is up. (ie. the missing second circuit).

So the question becomes, can I simply have the grid tie inverter go through the main panel, then use the existing circuit from the main panel into my GSLC/Radian, using my Radian to serve as my AC source for coupling when the grid is out and also being the AC output too without having to add a second circuit back to my main panel?

Could the current circuit (in the main panel) which is connected to my Radian as the AC input also be connected to the Radian AC output to back feed the main panel when the grid is out if AC Coupling is enabled?

I currently only charge my batteries with PV and don't use a generator except for a prolonged AC outage.

I have tried to illustrate my current configuration in the attached image.
AC Coupling Map 3-1-19.jpg
Proposed Single Circuit AC Coupling
Thoughts please. Thank you.

gregorio
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Re: How to convert AC coupled to DC?

Post by gregorio » Fri Mar 01, 2019 3:13 pm

Looking at your diagram, it looks very standard. When the grid drops, the only AC that is available is on the AC OUT line from the Radian. The GTI is offline at that point.

In my system, one of my GTIs is connected to the AC OUT on my Radian and is controlled by a circuit breaker internal to my load center called a ROCB. It senses power levels and will open when voltage exceeds a certain level. It is not elegant at all. It is like spinning a motor at redline and then instantly having it come to a stop when voltage gets high. It then goes from a dead stop to readline when voltage gets low. At least that is how it is supposed to work. There are other operational issues and this is probably why Outback stopped selling my GSLC with the AC coupling relay. It looks like they have created a more elegant solution with the phase shifting.

I inherited this system with a failed battery bank and the Radian is off/bypassed. The AC OUT and AC IN are directly connected right now. I am trying to find out the right way to bring this back on before I ruin in a very expensive Lithium battery bank. I don't want to blow the whole thing up, either.
Electrical-schematicREV4.jpg

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Re: How to convert AC coupled to DC?

Post by pss » Fri Mar 01, 2019 4:05 pm

Thanks for your reply. You are right about my system and I cannot connect my Grid Tie inverter to the AC out of the Radian because the physical logistics won't allow it. Thus my question of any work a rounds.

gregorio
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Re: How to convert AC coupled to DC?

Post by gregorio » Fri Mar 01, 2019 4:19 pm

The only way to do that is with a manual bypass breaker of some sort so you cannot back feed the inverter or the utility line when the grid is down. You would also need to regulate the AC with a dump/diversion load or automated relay to shut off the GTI when loads are low and batteries are fully charged.

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Re: How to convert AC coupled to DC?

Post by Lewis-H » Thu Jun 04, 2020 9:11 am

Look back at the figure of direct current. The voltage doesn’t change over time; this is one of the defining characteristics of DC. If the voltage isn’t changing, the frequency is effectively zero. So it doesn’t really matter how you define “low frequency”: a frequency of zero is low. Pass DC through an AC-coupled circuit and it will be removed. Pass AC through an AC-coupled circuit and the DC offset will be removed.

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