Micro Inverters and Frequency Shift Power Control

[agarg]

Folks

AFAIK, the micro inverters require a grid or a battery-backup grid to produce power. If grid fails, the micro inverters will shut down even if they have plenty of sun light for energy production.

When the Micro inverters are connected to the utility grid, it assumes that their is an infinite energy sink, in which they dump all their energy.

However, when the micro inverters are connected to a transfer switch where the energy is serving the load, and then storing the balance into battery. However, what it produces and stores in the battery is limited by the charging capability of ESS.

In a case, where the combiner box out put is 6KW, the load is 2KW, and the ESS can transfer 3KW to battery, it has 1KW of spare to send to the grid. When there is a grid outage, this energy has no where to go.

What I have learned is when there is a grid outage, the battery based nano-grid uses a frequency shift to control the power output of upstream PV inverters. My SMA Sunnyboy storage does that too and, I am sensing that my NEP micro inverters BDM-800 may not be responding to that frequency shift.

I am unable to get a good knowledgeable response NEP and my web search has not yielded any help either.

Does anyone have any pointers on what might I be doing wrong?

Much appreciate.



PS: SMA Sunnyboy Storage documents have following explained as attached.

 

[zanydroid]

Unfortunately this is highly dependent on the behavior of the specific micro inverters/GT inverter you are AC coupling in. So if you can’t find NEP specific info out there, you are in for a lot of digging. At least Sunny Storage should be a good implementation with many users

As a starting point, your NEP are supposed to be using a California grid profile. Rule 21 for your POCO will specify what the FW settings ought to be. You may be able to see the settings in your NEP UI, and it’s quite likely you can be effective at escalating with the support at NEP until you figure out how to set and validate grid profile settings.

You could also look at the threads covering other combinations of grid forming and grid tied inverters, and see what all grid profiles and settings are used. More for understanding the debugging flow and what kind of info to try to find.

I believe some people have shared on those threads how they monitored the behavior of the FW in detail. Probably people with oscilloscopes so they can see the frequency shift, voltage, net power, and AC cut off time. Probably you would set up the scope to trigger on grid down (that you inject manually), and then capture 30 seconds from there.

 

[Ampster]

What I have learned is when there is a grid outage, the battery based nano-grid uses a frequency shift to control the power output of upstream PV inverters. My SMA Sunnyboy storage does that too and, I am sensing that my NEP micro inverters BDM-800 may not be responding to that frequency shift.

The thing that I have learned is that the UL standard is the important thing that determines how they respond. They should be UL1741SA compliant or they probably would not be on the CEC site. It may even require the lates UL1741SB. What that means is that they should be modulating power based on frequency. The key is to have enough load on the grid forming inverter so it will keep the frequency at around 60 Hz. Do you have any way to tell the frequency? When my micros were not responding I saw that my SolArk was putting out 61.5 Hz when I did a grid down test.

 

[Hedges]

Use a DMM that displays frequency. Clamp an ammeter around wire from GT PV inverter.
Connect a few switchable loads. I use a bunch of electric radiators with 600/900/1500W switch settings.
This lets you draw full power, then watch frequency shift at battery tops off and battery inverter begins to raise frequency.

You may have functionality not enabled. I've done this with a few modes of TriPower, some ramping down and some just disconnecting when frequency too high.

 

[zanydroid]

You may have functionality not enabled. I've done this with a few modes of TriPower, some ramping down and some just disconnecting when frequency too high.

Probably the first two steps are confirming grid profile on the microinverters and diving the relevant AC coupling config on the Sunny Boy.

(Before busting out any tools)

 

[agarg]

Rule 21 for your POCO will specify what the FW settings ought to be. You may be able to see the settings in your NEP UI, and it’s quite likely you can be effective at escalating with the support at NEP until you figure out how to set and validate grid profile settings.

The NEP gateway that talks to micro inverters does not have any data exposed other than module level production and aggregated production and a canvas on which one can arrange the module to make them look like how they appear on the roof. I did open the port 22 with ssh and its behind a user/password and there might be stuff there.

Probably you would set up the scope to trigger on grid down (that you inject manually), and then capture 30 seconds from there.

Could be a good clue.

They should be UL1741SA compliant or they probably would not be on the CEC site. It may even require the lates UL1741SB.

BDM-800 is on the California list (it may even be a hoymiles under the skin). And it is globally certified for UL1741, SAA, TUV, VDE-AR-N
4105, VDE 0126, TOR Erzeuger Typ A and is claimed to be IEEE 1547 compliant. From what I read, UL 1741 (short for UL 1741 SA and Rule 21 require enhanced anti-island testing to ensure PV systems disconnect when required. As active grid support functions from other PV systems may impede the ability of an inverter to detect an island situation, and thereby not disconnect from the grid. "QUOTE: voltage and frequency ride through and ramp rate control testing ensure PV systems act in a predictable fashion as the grid experiences fluctuations to its operational thresholds. For example, during a departure from standard grid frequency, it is not desirable to have larger amounts of PV systems disconnect from the grid as this would further complicate the frequency problem. Similarly, ramp rate control allows grid operators the ability to balance thermal generation output against PV output while maintaining grid stability. END QUOTE".

So, it does appear that somewhere they have grid profile data that is hidden from average consumer.

You may have functionality not enabled.

This is what I am suspecting too. Manufacturers can make it easy by posting such details in the resources section but I do suspect I can find it out after a little bit of digging.

Probably the first two steps are confirming grid profile on the microinverters and diving the relevant AC coupling config on the Sunny Boy.

This my plan for tomorrow. Sonnyboy PV input is rated for 50 amps @ 240V input from the AC inverters. It can pump 25 amps into the battery. In the afternoon, I noticed that Sonnyboy tripped its own micro-grid and also dropped power to critical load panel. I suspect it did not know where to send extra energy. I was off grid since I do not have permission from PGE to interconnect at PCC.

 

[Ampster]

I was off grid since I do not have permission from PGE to interconnect at PCC.

It does give you a chance to debug the system for the occasional power outages we have in our area.

 

[zanydroid]

So, it does appear that somewhere they have grid profile data that is hidden from average consumer.

I thought it is standard for installer/operator to have access to grid profile. Since different grids have different settings.

 

[Ampster]

I thought it is standard for installer/operator to have access to grid profile.

I thought I used to have access to my Enphase grid profile but now can't find it. I may call support. Worse case I take the online class if that is what is now required.

 

[agarg]

I take the online class

Is it publicly available for anyone?

 

[Ampster]

Is it publicly available for anyone?

I don't know. Currently not a high priority for me..I still have several options to optimize my grid down AC coupling.

 

[kundip]

I thought I used to have access to my Enphase grid profile but now can't find it. I may call support. Worse case I take the online class if that is what is now required.

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