SW Efficiency/ PWM Angle Adjustment [RE-wrenches]

[Mr. Sharkey]

	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

- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://www.topica.com/lists/RE-wrenches/

List rules & etiquette: http://www.mrsharkey.com/wrenches/etiquete.htm

Check out participant bios: www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com

==^================================================================
EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9
Or send an email To: RE-wrenches-unsubscribe at topica.com
This email was sent to: michael.welch at homepower.com

T O P I C A -- Register now to manage your mail!
http://www.topica.com/partner/tag02/register
==^================================================================