Grid Forming Inverters

[Joondeka]

Grid-forming inverters should be installed in DC side or AC side?

 

[timselectric]

Grid-forming inverters should be installed in DC side or AC side?

An inverter turns DC power into AC power.
They are installed between the two.

 

[Joondeka]

An inverter turns DC power into AC power.
They are installed between the two.

So we don't have DC/DC or AC/AC inverters?

 

[timselectric]

So we don't have DC/DC or AC/AC inverters?

No those would be converters and transformers.
An "inverter" inverts (reverses) DC current into an alternating flow of current.
DC = direct current
AC = alternating current

 

[RCinFLA]

The difference is just whom is in charge of being AC phase master and who is AC phase following slave.

A battery powered hybrid inverter can switch between being a slave to grid phase or standalone master for off grid AC coupled PV GT inverters.

For hybrid battery powered inverter, when AC input pass-through relay is closed it is a slave. When pass-through relay is open the inverter is its own AC phase master.

 

[wpns]

Yet another interesting article, including analysis of Hawaii grid collapse avoidance using grid-supporting features of grid-scale inverter/battery systems:

Getting the Grid to Net Zero

Grid-forming inverters will take us to 100 percent renewable energy

spectrum.ieee.org

I’m seeing references in the EG4 18Kpv settings that might be response curves you could have programmed in to support the grid but they aren’t relevant to me, as my grid is so poorly managed that my primary focus is getting completely off it.

Is it possible for residential inverters to operate in a grid-support function (I’ll avoid grid forming and following terminology as it just adds confusion)? Or would this be a “virtual power plant” kind of thing that would probably require a middleman to sit between the poco and the homeowner?

Nice to see a scientific analysis of grid stability, I hadn’t considered rotational inertia of the grid-coupled generators as part of the legacy grid stability equation. Emulating that in software securely and reliably will be very important (SCADA attacks anyone?)

 

[Joondeka]

Do we have multi-mode inverter for grid-connection?

I mean an inverter with grid-forming and grid-following mode.

Do you know any brand for these type of inverters?

 

[Joondeka]

My another question is control of microgrid. If these inverters can control the voltage and frequency, why do we need to add another controller for microgrid? The figure below shows a separate controller in addition to the inverters.

 

[Luk88]

My another question is control of microgrid. If these inverters can control the voltage and frequency, why do we need to add another controller for microgrid? The figure below shows a separate controller in addition to the inverters.

View attachment 210244

The controller is what forms your micro grid. It also controls the generation of all sources by increasing/decreasing the frequency slightly to let them know what to do. No doubt others know more on this topic. The only setup I know of like that is one that involves a Victron Multiplus II as a controller and the battery inverter/charger in one. I think the advantage of this is that you need at least one device on this micro grid that can respond to demand/oversupply much quicker than what it takes to measure the frequency of the AC. The Multiplus being the master and having a battery it can use as a source/sink can do that to stabilise the microgrid even if it takes time to spin other sources up or down.

 

[RCinFLA]

Do we have multi-mode inverter for grid-connection?

I mean an inverter with grid-forming and grid-following mode.

Do you know any brand for these type of inverters?

Most hybrid inverter do.

- Pass-through relay open, grid forming.
- Pass-through relay closed, grid following.

Closing pass-through relay is based on first detecting AC voltage present on AC input then aligning inverter's voltage/freq/phase (becoming a slave) before closing pass-through relay.

Some newer systems place the grid disconnect relay external from hybrid inverter, between utility input lines and main panel and allow multiple hybrid inverters and/or PV GT inverters to provide AC feed power directly to main panel. Again, pass-through relay open means grid forming, with one of the units feeding panel being reference master.

Providing power contribution does not mean a source is phase master, although it can help lower micro-grid mastering impedance.

 

[Joondeka]

The controller is what forms your micro grid. It also controls the generation of all sources by increasing/decreasing the frequency slightly to let them know what to do. No doubt others know more on this topic. The only setup I know of like that is one that involves a Victron Multiplus II as a controller and the battery inverter/charger in one. I think the advantage of this is that you need at least one device on this micro grid that can respond to demand/oversupply much quicker than what it takes to measure the frequency of the AC. The Multiplus being the master and having a battery it can use as a source/sink can do that to stabilise the microgrid even if it takes time to spin other sources up or down.

Thanks. We call this controller energy management system (EMS). Right?

Which type of control algorithm/strategy is used for this controller? (i.e., PID, adaptive controller, ...).

If this can be used for both inverter/charger for battery/PV and also for energy management system as a controller, how it can manage the microgrid when the main grid is outage?

 

[Joondeka]

Most hybrid inverter do.

- Pass-through relay open, grid forming.
- Pass-through relay closed, grid following.

Closing pass-through relay is based on first detecting AC voltage present on AC input then aligning inverter's voltage/freq/phase (becoming a slave) before closing pass-through relay.

Some newer systems place the grid disconnect relay external from hybrid inverter, between utility input lines and main panel and allow multiple hybrid inverters and/or PV GT inverters to provide AC feed power directly to main panel. Again, pass-through relay open means grid forming, with one of the units feeding panel being reference master.

Providing power contribution does not mean a source is phase master, although it can help lower micro-grid mastering impedance.

Thanks. It was very informative.
Unit feeding panel means our distributed generation (DG)? Like solar panel or wind turbine?
So, if grid-forming uses one of the units feeding panel for reference, how it can detect this reference is accurate for our target (voltage and frequency)?

 

[Luk88]

Thanks. Which type of control algorithm/strategy is used for this controller? (i.e., PID, adaptive controller, ...)

Unfortunately I have no idea. I doubt the victron Multiplus II manual I read specified it. I seriously considered this setup for myself for a while, only deciding against it based on price.

 

[Joondeka]

Most hybrid inverter do.

- Pass-through relay open, grid forming.
- Pass-through relay closed, grid following.

Closing pass-through relay is based on first detecting AC voltage present on AC input then aligning inverter's voltage/freq/phase (becoming a slave) before closing pass-through relay.

Some newer systems place the grid disconnect relay external from hybrid inverter, between utility input lines and main panel and allow multiple hybrid inverters and/or PV GT inverters to provide AC feed power directly to main panel. Again, pass-through relay open means grid forming, with one of the units feeding panel being reference master.

Providing power contribution does not mean a source is phase master, although it can help lower micro-grid mastering impedance.

If the main grid is outage, what's your suggestion about control strategy to maintain stable voltage and frequency?

 

[houseofancients]

If the main grid is outage, what's your suggestion about control strategy to maintain stable voltage and frequency?

The inverter will take care of that

 

[Joondeka]

The inverter will take care of that

Thanks. But beside the inverters, we need to have separate controller (energy management system) to control and manage the power flow. Like the following picture.

 

[kommando]

Depends upon the inverter used, my SMA Sunny Islands include the controller and use frequency shift to control output of connected PV inverters.

 

[Joondeka]

Depends upon the inverter used, my SMA Sunny Islands include the controller and use frequency shift to control output of connected PV inverters.

So, it works like EMS. Right?
Is the control strategy "droop control" in it?
What's your control strategy when you face with grid outage? This controller can manage it?

 

[kommando]

Early Sunny Islands are for off-grid mainly with the option to use the grid for battery charging instead of a generator or PV. Later ones for Europe can be grid tied. To know more you would be best to read the manual.

 

[Joondeka]

Early Sunny Islands

I couldn't find Early Sunny Islands datasheet. Could you please share the link?