SW Efficiency/ PWM Angle Adjustment [RE-wrenches]

[Bill Brooks]

Sharkey,

I apologize for coming across too strong last night. I had been working in
the field all day troubleshooting systems and was pissed off with the
mistakes I found and was little on edge when I got your message. It appeared
that you were questioning my assessment of the situation and it appears that
you still are not convinced. I have seen the very same phenomenon with every
grid-tied, battery-based, ETL-listed SW unit made. This prompted Trace to
fix this problem in their UL-listed version. It has nothing to do with
variations in the utility system. It was simply a software mistake.

Mistakes happen.

Bill.


> -----Original Message-----
> From: Mr. Sharkey [mailto:sharkey at eugeneweb.com]
> Sent: Thursday, September 06, 2001 7:56 PM
> To: RE-wrenches at topica.com
> Subject: Re : SW Efficiency/ PWM Angle Adjustment [RE-wrenches]
>
>
>
> 	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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>
>
>
>

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