boost converter for low wind situations

[jacquesm]

I would like to ask if the following makes sense and how I should go about it:

I have just changed my windmill from 'star' to 'delta', which has dropped the coil resistance significantly (half of what it was before), but this has of course increased the cut in speed quite a bit.

It seems there is no 'ideal' setting, either you have stellar low wind performance or you get tons of power in high winds, but you can't have both with the same situation.

I know there are 'maximum power point trackers', but they seem to be pretty expensive, and I was wondering if it would be possible to use a simple 'boost' converter to give you decent low wind performance and short it out using a solid state relay or a large fet or so during higher wind situations.

[RP]

I remember several discussions on automatically switching between star and delta.  I did a google search of the site and got this:

http://www.google.com/search?hl=en&ie=ISO-8859-1&q=site%3Afieldlines.com+star+delta+relay

It seems like this would be the best of both worlds.

rp

[jacquesm]

star delta is not an option for me, because I would have to switch that at the top of the tower near the machine (there are only three leads down the tower, and I use sliprings).

[Victor]

Hi Jack,

 The Bergey XL.1 uses a boost conveter up to~17 mph to get MPPT.

 Assuming you are transmiting three phase from the machine to the controller. A slick way to impliment a boost converter is to use  three FETs with their souces connected to B- and the drains connected to the three phase wires and three regular diodes from AC to B+. In nomal operation the FETs remain off and the intrinsic diodes in the FETs and the three regular diodes form a normal three phase bridge. In boost mode the Fets are pulsed  (1khz is likely plenty fast) shorting the  generator as the inductor. Each time the FETs turn off  boost voltage is clamped by the battery. Varying the duty cycle varies the amount of boost.

Make the wind fun!

Victor Creazzi

Aerofire Windpower

www.aerofirewind.com

[jacquesm]

Hey Victor,

that's pretty clever ! Extremely elegant to reuse the fets AND the coils...

is there a patent on that circuit or is that up for grabs ?

[Victor]

I think it would probably fall under the heading of "obvious to anyone skilled in the art" in other words have at it.

Victor

[bob g]

here is another thought i have posed sometime ago.

assuming that the blade set has an optimum speed, based on TSR. so why not..

use some sort of circuit to sample the rpm via frequency, then use this info to..

trigger a SCR or TRIAC circuit to allow a sort of switching power supply scheme to keep the blades at there optimum speed no matter what the wind speed

by varying the pulse width the blades would be able to maintain a larger power band. and the alternator could be built to maximize its output at the higher anticipated wind speeds, yet be able to harvest power in lower windspeeds with shorter pulse duration.

hope the idea is clear, i can see it in my mind but have problems relating it sometimes.

what do you think

bob g

[jacquesm]

yes, that would work

make it a fixed RPM machine, boost below it so it reaches it's design RPM, buck above it to extract more power at a higher voltage and drop it into the battery at a higher current.

that'd be tricky to get it to work accurately, but I don't see why it would not work.

I need to make a testrig with a variable frequency drive of sufficient horse power so we can drive gennys at various defined RPMs for measurements.

That would make stuff like this a lot easier to do

[Victor]

 I'm presently building a buck converter that does exactly that at about 5kw peak.

 It will be implimented on a 22 year old 25' diam. homebuilt  machine that can be seen at: http://www.fieldlines.com/story/2004/10/13/9173/0355

 The blades are half composite (red) and half sailwing (blue and white) my first sails were made by me and not rinkley, sp?. The ones in the picture were sewn professionally, should have done them myself. When the mill is running the sails take on a camber and smooth out so i don't think it matters much, it just looks bad when the mill is not spinning. To me all wind turbines look much better spinning (grin).

 The blades are designed for a low TSR of 4.5 which the sailwings work quite well at. This plus the 25' foot diameter yeald a low rpm hence the cogbelt drive to the radial ferrite alternator (neos were extremely expencive at the time this was constructed (about 20x)

Make the wind fun!

Victor Creazzi

Aerofire Windpower

www.aerofirewind.com