Line frequency effect

Hello Bob,

Another question has been in my mind.

What is your concern about changes in frequency on the AC?

Here is the problem. When we have battery backup and solar, when the grid fails the battery will provide power at 60Hz. Except when the battery is full. The battery pack (Power wall) will throttle the solar inverter using frequency. The frequency deviation can go all the way to 66Hz to signal the solar inverter to shut down.
I think there is an issue or there was an issue where PW keeps the frequency at 63Hz when it should just do so for 10 sec.

This is painful because with most UPS, when there is a frequency deviation of more than 3Hz it will use battery power.

As the battery pack gets depleted, the frequency drops and the solar inverter starts providing energy to charge. And then the control is much more smooth, staying withing a Hz or 2 from 60.

I was wondering if you have any provisions for this? I saw a post from Mar 19 about the frequency phase correction. That means it should work as good?

I have not tried that yet… I will later in the year when I have my full setup ready.

Pertinent standard: UL1741SA

The IoTaWatt should have no problem with frequency variation. Unfortunately there is a bug in 02_07_04 where you cannot plot frequency, but it is being recorded accurately and you will be able to revisit it with the next release.

You would think there would be a more sensible way to signal to the inverter that it has no customers.

Doesn’t that mean it has to stay high to keep the inverter off?

What I read is that it really is 60Hz ± 2Hz and that is a “signaling” used in the power grid to disconnect and isolate faults… And it is not so much that they force a change on frequency rather than the change of frequency changes when the load does not match generation.
When the the load is much greater than the generation, the frequency will decrease as the load makes the generators work harder “slowing” them down. Opposite the same…
Equipment can get damaged (motors and generators) when the frequency is beyond this limits.

Basically that picture (from AEE Solar webinar UL-1741-Supplement-A_Webinar)
So the PW should only have to do 63Hz for a few seconds to trip the inverter (which must trip <160ms). and then it could keep 61Hz to keep it off…

What I read about the PW is that it has to work with some old inverters that do not meet UL-1741 and that they trip at 66Hz… I have not tested it lately but I will…
I am glad to know that all the info is corrected and will be saved by IoTaWatt