[RE-wrenches] AC Coupling Standard?

Thu Dec 1 16:21:07 PST 2022

This raises a new question. Can the newer grid forming and grid following
inverters be configured to have a tighter Freq/Watt response?
We've run into a situation where some electronic loads behave erratically
when the frequency goes to 62 Hz.

Eric Smiley
Project Manager, North Island

E:  eric at vecoop.ca
T:  1-888-386-0116 ext 702 (toll free)
C:  250-703-6004
W:  viridianenergy.ca

On Thu., Dec. 1, 2022, 16:07 MD Electric & Solar via RE-wrenches, <
re-wrenches at lists.re-wrenches.org> wrote:

> And this is why we LOVE the RE-wrenches list. This is a question that all
> of us have had.  Always good questions and answers! Thanks All!
>
> On Thu, Dec 1, 2022 at 9:39 AM Jeff Clearwater via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
>> Wow. Now THAT was an education. So appreciate you Harry for taking the
>> time to answer so thoroughly!  It’ll take me a few to digest and come back
>> with any follow ups.  And so appreciate SMA for paving the way!
>>
>> Sent from my iPhone
>>
>> On Dec 1, 2022, at 10:56 AM, Harry Mahon <Michael.Mahon at sma-america.com>
>> wrote:
>>
>> 
>>
>> Jeff – THAT is a bunch of loaded questions! My thoughts..
>>
>>
>>
>> Let’s start at the end.  NO, SMA did not create any “standard”.  Sunny
>> Islands have been utilizing FSPC (now commonly called Frequency Watt
>> control) for more than 15 years, and someone decided that the window of
>> frequency to control Sunny Boy PV output would be 61-62Hz for 60Hz nominal
>> SIs. Others on the list may have personal knowledge of the actual decision
>> making process (Sam?); that is before my time at SMA.
>>
>>
>>
>> The SI FSPC was only used in off-grid or micro-grid mode (no utility grid
>> present) when the SI was free to set AC grid frequency where it wanted. If
>> the SI & SB were set up in grid-tied battery backup mode (where the Sunny
>> Boy normally operated in grid-tied mode with no FSPC operational, 60.5 Hz
>> seen as “bad grid (0 W output)” according to “old” UL 1741 testing), the SI
>> would dynamically, via communications signal, change the SB into offgrid
>> mode with “Freq-Watt” enabled, operating from 61Hz (no curtailment of
>> output) to 62Hz (0 W output from SB). SB was kept in off-grid mode as long
>> as SI was forming microgrid, and when the grid came back, the SB would be
>> put back into grid-tied mode when the SI closed the connection to the grid
>> 5 min later.
>>
>>
>>
>> This required two sets of operating parameters in the Sunny Boy and a
>> method to switch between the two as Freq-Watt was not required for any grid
>> interactive inverters in US until around 2017. Ensuring a normally grid
>> tied inverter can recognize an external signal to switch to microgrid mode
>> with new operating parameters is challenging, especially if AC coupling
>> equipment from different manufacturers.
>>
>>
>>
>> But now some utilities want Freq-Watt operation in grid-interactive
>> inverters, so it is conceptually possible to set Freq-Watt on the
>> grid-interactive inverters, and have this function work BOTH in grid-tied
>> and microgrid mode without needing any signal/mode/parameter change if the
>> grid is lost.
>>
>>
>>
>> I believe pre-SA versions of UL 1741 had testing for grid-interactive
>> inverters to support Freq-Watt (and this would be when grid-tied) but this
>> function was not enabled. UL 1741 SA definitely tested inverters to ensure
>> they supported this function.
>>
>>
>>
>> Buuuutttttt, it depends on which Source Requirement Document (SRD) the
>> UTILITY (HECO, CA ISOs like PG&E, SCE and SDG&E, and those in ISO NE
>> territory) decides to implement whether or not the Freq-Watt function is
>> enabled when connecting to their grid AND what setpoints determine the
>> operation (e.g. what freq the ramp starts at and how fast power goes down
>> with increased frequency).
>>
>>
>>
>> So, there is not currently any “standard” for implementing this for
>> grid-interactive inverters. Has anyone on this list activated Freq-Watt on
>> an inverter where the utility does not require it (with the utility’s
>> blessing of course)?
>>
>>
>>
>> Even with all the noise around the impending requirement of UL 1741 SB, I
>> don’t think utilities will require Freq-Watt be enabled until PV
>> penetration is noticeable. And then they still can choose their own
>> setpoints.
>>
>>
>>
>> I think it will remain the discretion of manufacturers how their
>> equipment operates in microgrid mode, but without a standard set of
>> parameters for Freq-Watt operation required for grid-tied operation I don’t
>> see any “common standard” for microgrid Freq-Watt settings.
>>
>>
>> Michael Mahon
>> Senior Technical Trainer, Solar Academy
>> *SMA America*
>>
>>
>>
>> *From:* RE-wrenches <re-wrenches-bounces at lists.re-wrenches.org> *On
>> Behalf Of *Jeff Clearwater via RE-wrenches
>> *Sent:* Thursday, December 1, 2022 7:33 AM
>> *To:* RE-wrenches <re-wrenches at lists.re-wrenches.org>
>> *Cc:* Jeff Clearwater <jeffc at villagepowerdesign.com>
>> *Subject:* [RE-wrenches] AC Coupling Standard?
>>
>>
>>
>> Hey Esteemed Wrenchies,
>>
>> Does anyone know if manufacturer's are using any common standard for AC
>> Coupling frequency shift algorithms?
>>
>> Is it part of any UL standard?  Seems like since it's a battery charge
>> control issue it needs some rigor?  Are manufacturer's just copying each
>> other?  Did SMA's Sunny Island/Sunny Boy set that standard?
>>
>> Curious!
>>
>> Best
>>
>> Jeff C.
>>
>>
>> ~~~~~~~~~~~
>>
>> Jeff Clearwater
>>
>> [image: image001.jpg]
>> linkedin
>> <https://eur02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.linkedin.com%2Fin%2Fjeff-clearwater-0622a312%2F&data=05%7C01%7Cmichael.mahon%40sma-america.com%7C8f0d4c8e8680464d8cef08dad3a8f455%7Ca059b96c28294d1188374cc1ff84735d%7C0%7C0%7C638055019880086703%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=UM00SXQzUP5oPx%2BLXWUkeV8gazAMvdTTQg%2Be9I7Nf9I%3D&reserved=0>
>> www.villagepowerdesign.com
>> <https://eur02.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.villagepowerdesign.com%2F&data=05%7C01%7Cmichael.mahon%40sma-america.com%7C8f0d4c8e8680464d8cef08dad3a8f455%7Ca059b96c28294d1188374cc1ff84735d%7C0%7C0%7C638055019880086703%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=bzCqYDN9FBD9mXT4fSDUEGP6KYc2bMnEr8gDvE%2BMDO0%3D&reserved=0>
>> cell - 413-559-9763
>> ~~~~~~~~~~~~~~~~~~~~~~~
>>
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>
> --
> Michael D Nelson
> MD Electric & Solar Inc.
> Office: 707-412-3181
> Cell: 707-684-0064
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