[RE-wrenches] AC Coupling Standard?

MD Electric & Solar mdelectricsolar at gmail.com
Thu Dec 1 16:07:27 PST 2022


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]
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-- 
Michael D Nelson
MD Electric & Solar Inc.
Office: 707-412-3181
Cell: 707-684-0064
www.mdelectricsolar.com
www.facebook.com/mdelectricandsolar
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