Synchronizing solar,wind, and grid 2

[eeprom]

Hello,
I'm trying to figure out how to tie solar panels and a wind turbine to a building with batteries, but also have these wired so that they are providing power whenever possible. They will provide power if the utility grid is active or not.

My concern is synchronization. If the grid is active, an inverter can synchronize with the grid. But what happens when (1) the grid is off, and (2) if the grid turns back on while the wind and solar are active. How will the synchronization happen? Clearly I am trying to avoid an out of phase closing.

Thanks

 

[FacEngrPE]

Searching

https://duckduckgo.com/?t=lm&q=Hybrid+Inverters+manual&ia=web

pulls up some manuals, one of which contained the panel diagram below.

This Hybrid Inverter (probably most) is designed to sit between the grid and the user, all of the power flows through the inverter, unless the inverter is bypassed (bypass mode). The inverters probably can not be paralleled unless specifically designed for that operating mode.

The inverter controller manages the grid connection, and the battery charging.

 

[xnuke]

You need a sync check before connecting the inverter in parallel with the grid.
If both the grid and the inverter are running at the same frequency but out of phase, the sync check may hang for a long time before drifting into sync.

Distributed energy inverters and battery power converters provide the sync check internally - they sense the AC voltage, frequency, and phase on both sides of their AC contactor and they modulate their output to match the line side before closing. That's why they won't return to operation in grid-following mode unless they see an AC source on the line side of their AC contactor. There's usually a delay built into their reconnection to ensure the grid is stable - many manufacturers use a default of five minutes, but it can go as high as ten minutes, so there's plenty of time to sync. However, the sync can happen very fast once they decide to do it; it just takes a few cycles since all they have to do is modulate the switching.

The hybrid inverters linked above look like they're for home systems with low power and low voltage requirements. I was happy to learn about them, so thanks to those of you who pointed them out. I even saw some that say they can take inputs from solar, wind, and batteries, so that's nice. I tend to design the controls for higher power and voltage microgrids for commercial and industrial facilities and campuses, so I didn't know these existed.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[FreddyNurk]

This is relatively straightforward in certain configurations now, but there's still a few caveats, and it's subject to how big the system and load is.
As an example, SMA has components that are capable of being configured to run in either grid-connect or islanded with solar and batteries, they even have manuals that detail the configuration, although that's at domestic load size.
All AC coupled, and the battery inverter is capable enough to regulate the solar inverter's output.

Otherwise xnuke's suggestion of looking at a microgrid controller and getting someone who understands these systems is an excellent suggestion. This (perhaps not with wind as gusting causes unexpected behaviour that doesn't happen with solar) has been done often enough that there's generally an OEM who's worked out the details by now. The architecture (e.g. DC coupled solar plus batteries versus DC batteries and AC coupled solar) might not look like exactly what you expect at first glance though.

EDMS Australia

 

[wcaseyharman]

My utility company has already done this twice.
The original, which was just four battery containers that I was involved with had a dual mode inverter. It was connected in a constant current grid following mode, and had to shutdown and start up in grid forming mode to island a small town. My company did a relatively small microgrid which auto-detected loss of utility power, isolated part of the distribution system and started the battery in island mode.

The new one is a small microgrid with four customers, solar and a battery. I am not quite sure how it works as far as operating in grid forming or grid following modes, I’ll have to ask. I wasn’t involved at all.

Theoretically I believe a grid forming inverter should act very similarly as a synchronous machine. To protect the inverters, like a synchronous machine, you will want to install sync check on the intertie breaker relays to prevent inadvertent out of phase closure with possible damage. If you don’t want to drop and pick you’ll need to install an auto synchronizing device, which can be packaged in a number of different products including common microgrid controller platforms like the SEL RTAC.

Let me know if you need more information.