Grid tied PV inverter sync and backup sources

[buddy91082]

Looking for articles why grid tied pv inverters need to sync with the utility and what happens to inverter sync when utility is lost and backup sources come on line.

Thanks.
c

 

[shamsdebout]

This may not be what you are looking for but I think it is pertinent:

http://enphase.com/wp-uploads/enphase.com/2011/03/Enphase_White_Paper_DC_Connectors.pdf

I think the Enphase website has some additional information.

 

[jmbelectrical]

(If anyone else can confirm or correct what I'm about to say, I'd really appreciate it!)

The attached Powerpoint presentation partially explains the necessity for synchronization between a grid-tie inverter and the grid. The most elementary reason, however, is that when there is a frequency mismatch between two AC voltage sources connected in parallel, circulating currents result. To borrow a quote from [URL unfurl="true"]http://electronics.stackexchange.com/questions/13042/why-cannot-generators-having-different-frequencies-supply-in-the-same-transmissi[/url]:

Loads notwithstanding, if you just connect a 50Hz source and a 60Hz source together, they will alternate between being in-phase and out-of-phase 10 times per second. So half the time, things would be fine, but the other half the time, the sources would be trying to burn one another out.

What is the "backup source" that you referred to in your original post? Is it your intent to parallel a grid-tie inverter with a generator?