Grid Forming Inverters

[Joondeka]

You have to have something to control the generator, if the inverter you choose can control a generator then you use that, if not then you need to add another controller which adds complication.

Few post earlier, some guys said, inverters convert DC to AC or vice versa, but Gen is produced AC voltage and connected to AC bus.
So can we use inverter for it?

 

[kommando]

Read the Sunny Island manual I added the link too, it does exactly that when you connect the Gen to AC2, AC2 takes the Grid or Generator, AC1 takes PV in and puts out to connected Loads.

 

[Joondeka]

Read the Sunny Island manual I added the link too, it does exactly that when you connect the Gen to AC2, AC2 takes the Grid or Generator, AC1 takes PV in and puts out to connected Loads.

Yes. I see.

How the battery can be charged? Is Sunny Island bidirectional inverter?

 

[kommando]

Is Sunny Island bidirectional inverter?

Yes, very sophisticated for its age, modern versions of the SI and alternatives work better feature wise but the old ones are built to last and do.

 

[Joondeka]

Yes, very sophisticated for its age, modern versions of the SI and alternatives work better feature wise but the old ones are built to last and do.

It seems this inverter uses internal grid-forming method to control the voltage and frequency, and all energy resources follow the voltage/frequency produced by inverter. Am I correct?

Another scenario is during off-grid situation, this inverter get a voltage/frequency sample of one of the units (like generator or battery) and the rest of units follow the voltage and frequency (grid-following).

Which one is rational for this inverter?

 

[billvon]

Another scenario is during off-grid situation, this inverter get a voltage/frequency sample of one of the units (like generator or battery) and the rest of units follow the voltage and frequency (grid-following).

OK there's a danger here that you're skirting with.

It is possible to AC-couple some solar systems, where everything inside the house connects to one AC bus. The main inverter supplies the AC power and the smaller microinverters (on the panels themselves) connect to that AC power and dump their power into it. The inverter must be designed for this, and the design/microinverters must be chosen so that they play well together. An example is frequency power control, where the inverter increases the frequency if the batteries are almost fully charged, so the microinverters know to back off.

The danger is that someone can hear that and think "great idea! I can get a small/cheap inverter and 'fool' my microinverters into turning on! I'll get free power during the day with almost no $$$." This does not work, since small/cheap inverters cannot handle the output of all those microinverters.

Another danger is that you try this with a generator, which cannot handle such inputs. Several people have destroyed their generators this way,

 

[kommando]

It seems this inverter uses internal grid-forming method to control the voltage and frequency, and all energy resources follow the voltage/frequency produced by inverter. Am I correct?

Yes, but it fails as soon as one generator does not respond to the frequency shift, I have yet to see any micro inverters that respond to frequency shift.

 

[Joondeka]

OK there's a danger here that you're skirting with.

It is possible to AC-couple some solar systems, where everything inside the house connects to one AC bus. The main inverter supplies the AC power and the smaller microinverters (on the panels themselves) connect to that AC power and dump their power into it. The inverter must be designed for this, and the design/microinverters must be chosen so that they play well together. An example is frequency power control, where the inverter increases the frequency if the batteries are almost fully charged, so the microinverters know to back off.

The danger is that someone can hear that and think "great idea! I can get a small/cheap inverter and 'fool' my microinverters into turning on! I'll get free power during the day with almost no $$$." This does not work, since small/cheap inverters cannot handle the output of all those microinverters.

Another danger is that you try this with a generator, which cannot handle such inputs. Several people have destroyed their generators this way,

What's your suggested architecture?
My microgrid consists of BESS, PV, generator, and AC load. The situation is off-grid.

 

[Joondeka]

Yes, but it fails as soon as one generator does not respond to the frequency shift, I have yet to see any micro inverters that respond to frequency shift.

Yes, but it fails as soon as one generator does not respond to the frequency shift, I have yet to see any micro inverters that respond to frequency shift.

Do you mean BESS should be a grid-forming unit and the rest of the units should be grid-following?

 

[kommando]

I have 2 Sunny Island's, 1 is master 2nd is slave. Master creates the grid, slave follows and copies, the PV Inverters latch onto the SI grid react to the frequency shifting the SI's produce.

 

[Joondeka]

I have 2 Sunny Island's, 1 is master 2nd is slave. Master creates the grid, slave follows and copies, the PV Inverters latch onto the SI grid react to the frequency shifting the SI's produce.

You don't have any charger/controller for BESS?

 

[kommando]

The SI's have closed loop with JK BMS via canbus, as the battery approaches 100% the BMS tells the SI's to limit charging amps and the SI's in turn limit the PV production to meet the lower charging amps.