Paralleling inverter generators

[oldsparky52]

I have never seen it done, but I've seen the ads saying you can plug a couple of inverter generators together to double your power. Well, I watched a video on someone doing this and they just plugged the two generators together with some cabling and started one then the other.

So I started wondering how do the two generators sync up so that the sine waves are peaking at the same time? Does anyone know how they do that? .... I assume they do that, would it work if they didn't?

 

[LarryFine]

So I started wondering how do the two generators sync up so that the sine waves are peaking at the same time? Does anyone know how they do that? .... I assume they do that, would it work if they didn't?

Inverter-generators use inverters (like the kind that give you 12ovac from 12vdc) between the generators and the power receptacles, so the (engine controlled) generators themselves don't have to be in sync, only the (electronically controlled) inverter outputs do.

 

[oldsparky52]

Inverter-generators use inverters (like the kind that give you 12ovac from 12vdc) between the generators and the power receptacles, so the (engine controlled) generators themselves don't have to be in sync, only the (electronically controlled) inverter outputs do.

Yea, I got that.

Do you know how they sync up the outputs? Does the 2nd one to start see the 1st one and automatically sync to that peak?

 

[kwired]

I don't know much about what is out there, but would assume a simple approach would be to put the "paralleling cable" connections on the DC side of the inverters. This of course would mean that which ever unit you plugged your AC load into would need to have a larger inverter than the generator's stand alone capacity to be able to get additional power out of it.

If they connect the AC side of inverters together, they would need to have some sort of circuitry built into them to sync them. I don't know exactly how that is done, but don't we have inverters for tying PV or other off grid sources into the grid that would have to do the same thing? I would guess worst case one may need to be set up as a master and additional units set up as slaves and the master is what the rest of them will sync to.

 

[ggunn]

Yea, I got that.

Do you know how they sync up the outputs? Does the 2nd one to start see the 1st one and automatically sync to that peak?

The same way that a bank of grid tied PV inverters synch up with the grid and each other, I'd wager.

 

[kwired]

The same way that a bank of grid tied PV inverters synch up with the grid and each other, I'd wager.

Something has to be the base to sync up to. With grid tied inverters the grid is the base, if you have several inverters that won't put out anything until they have a frequency reference to sync to, you will have no output until you establish a reference. Never used any of these portables with syncing ability, but wouldn't surprise me if there isn't a master and slaves in a typical setup.

 

[ggunn]

Something has to be the base to sync up to. With grid tied inverters the grid is the base, if you have several inverters that won't put out anything until they have a frequency reference to sync to, you will have no output until you establish a reference. Never used any of these portables with syncing ability, but wouldn't surprise me if there isn't a master and slaves in a typical setup.

That would be my guess. That's the way multiple offgrid PV inverters work; one talks, the others listen.

 

[jaggedben]

If the manufacturer puts some very small but unique signal into their sine wave, then each generator can look for that on its AC terminals when it starts up. If it sees nothing, it starts up as master. If it sees the signal, it starts up as slave. (If it sees another non-compatible sign wave, it refuses to start.) Thus whichever starts first becomes the master automatically.

I'm just brainstorming, I don't know if that's how they do it. I'd be curious how UL looks at this, too, and what their standards allow.

 

[oldsparky52]

If it sees nothing, it starts up as master. If it sees the signal, it starts up as slave. (If it sees another non-compatible sign wave, it refuses to start.) Thus whichever starts first becomes the master automatically.

That makes a lot of sense.

 

[ggunn]

That makes a lot of sense.

In the case of multiple Xantrax off grid inverters 8 years or so ago, there was a data connection between the inverters with one of them designated the master and the others as slaves.