SW Efficiency/ PWM Angle Adjustment [RE-wrenches]

[Joel Davidson]

Hello Xantrex people. Are you listening? It was this kind of dialogue between old
Trace and field techs that created the SW-series. Is Xantrex ready for another great
leap forward or is Xantrex just going to milk the profit out of Trace's past
acheivements and be blown away by someone else's better inverter?

"Mr. Sharkey" wrote:

>         Thanks to everyone who contacted me off-list to say " *Some of us* still
> like you". I've been wrong before, I'll probably be wrong again. All I ask
> is that If I'm going to be corrected publicly, it's done with some respect
> so that I can learn from it.
>
>         Onward: No, I doubt that much on the DC side of an inverter would change
> the power factor. I do have some concern that the level of power the
> inverter is handling could affect the PF. An inverter optimized for one
> level of power might be off by a little or a lot, depending on how much the
> power level changes. Maybe not?
>
>         Virtually all grid-tied inverter systems are going to see a reactance
> difference with the utility line, and it will be inductive. In
> transformer-to-transformer connected circuits, maximum power transfer takes
> place when the impedances of the two devices are matched. In (for example)
> an SW inverter setup, there are the three series-connected AC transformers,
> capable of, what?, 2,000 to 5,000 volt amps (roughly), connected to a
> utility step-down transformer of (?) 500,000 VA ? Can you spell mismatch?
> Again, it's inductive, not capacitive, as there are very few utility loads
> that are capacitively reactive. This gives us an interesting angle, as it
> could (should) be possible to correct the PF *outside* the inverter cabinet
> by adding capacitors to the AC line. How many capacitors of what size? That
> can be calculated, but the math is way beyond me. I tend to do things
> empirically. Throw that $10,000 test instrument on the line and begin
> adding caps until the PF reaches unity (assuming that you have that many,
> it might take A LOT of caps).
>
>         OK, fine, now the PF is 100%, but what happens when the air conditioner
> (table saw/TV set/refrigerator/water heater/whatever) comes on? The
> inductance of the AC line changes, and the required value of capacitance
> changes with it. Add or subtract some more caps. Changes in the AC line
> brought on by neighborhood load changes, utility switching, TOU loads, etc.
> could whack out the PF correction even more.
>
>         What's needed is a *dynamic* method of adjusting the PF inside the
> inverter. The Trace SW obviously has this capability in a static mode. How
> about making it dynamic? The inverter senses PF, and self-corrects for the
> difference. A MPPT inverter, always at unity PF. Cool! As far as the
> inverter (and the utility) are concerned, backfed current is always in
> phase, a pure resistive load  (uh, supply).
>
>         As a first step, and because we now know he has the equipment, maybe Bill
> can use his AC analyzer to check the PF correction of an SW at each of the
> available PWM Angle settings and report back to us. This could at least
> give us some idea of the range of this adjustment. Of course, the reading
> would be for *his* inverter, AC line and power level. Even more interesting
> to try it on a variety of systems and see what the typical PF of an
> installed system is.
>
>         set mode = lurk
>
>         -S
>
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