"dump load" kind of???

[fcfcfc]

Hi: First take all of these statements as questions. So, all of what I have read so far on how to handle too much power from the gens involve "channeling" the un wanted power to a specified "place". Bottom line though is that you are loading the gen at a higher energy level than you can actually use until you kick in some form of mechanical system to stop the gen from generating that level of power. Now, for the moment lets say that your turbine by passive design would not fly apart no matter how strong the wind was. But, your gen could not handle the power being generated by the turbine if it was loaded by A, what was really being used and B, an extra dump load as well. So here is the question, suppose you have an inverter that can handle Vmax incoming as 500VDC. Is there an electronic circuit that can continue to "sample" the incoming and deliver 500VDC and maintain the max current at that voltage (500) and just let the turbine and gen spin as fast as the extra wind wants to spin it, I.E. the gen does not load electrically more than Vmax times the current at that voltage..??.. The voltage across the gen would of course continue to rise and current fall, BUT the feed to the inverter would hold at 500VDC at the max current level. I hope that doesn't sound too confusing....

Resectioned, missed it before. TW

[commanda]

Frankly, your question is clear as mud. And I think it belongs in the controls section.

Consider a DC-DC converter as an ideal block box. It takes an input voltage (Vin) and an input current (Iin), which gives us an input power (Pin). By the use of pulse width modulation, a switching device (transistor or fet), and an inductor, it converts all of Pin into Pout, at some other voltage and current. A PC power supply is a typical example. It takes an input voltage over some range, maybe 80-264 volts AC, and outputs a number of dc voltages at various currents. The sum of the output voltages times output currents is Pout. This power comes from Pin, which is the input voltage times the input current. So, for a fixed output power, the input current will vary inversely with a changing input voltage to maintain a constant input power. The black box does this by varying the pulse width of the on time of the switching device.

I can't for the life of me work out why you want 500 volts DC output though.

Amanda

[Flux]

Thick mud at that.

Not sure I got the intention but here goes.

The normal reason to continue to load the thing beyond the power you need is to stop the thing flying apart. If you make it part of your criteria that it can't fly apart then it is up to you if you want to keep loading it. It should be perfectly ok on open circuit.

In that case you could regulate the output voltage to any level you want ( 500dc if you so choose) as long as the load you take from that voltage does not require an input too great for the machine to supply without over heating.Not so easy with permanent magnets as with a wound field alternator, but still possible, but don't expect to go out and buy a commercial device, you would need to design and build something, but that should be no problem with your flux concentrators and strange windings. Another uncertainty wouldn't matter.

Flux

[fcfcfc]

Hi Amanda & Flux:

LOL, I thought maybe dirty water but not mud. Its not that complicated. The "To Be VAWT" Will be made to handle winds on an OC. The possible problem is the gen. I am designing it for very high voltage at low rpm (direct drive) and even if I do the phases in two layers so I can switch from series to parallel to half the voltage when things get really moving, there exists the problem of over loading the gen in very strong winds. Some of the typical inverters (grid tie) I have been looking at have a top input VDC in the 500 range. Its not that I need 500 all the time, but if the inverter can not do its own "sampling" of an input over 500 to keep from frying itself, I have to provide a way to do that. A very easy way to solve the whole problem is just to take the perspective that when you get to "magic" high limit under load just OC the input. Let the turbine and gen "do there thing" until they spin down then re load. The problem that bothers me is that you have a turbine with a tremendous energy output going to waste when it could be "tapped" and still have its speed partially regulated. Again, I may have all kinds of problems making this whole thing work, vibrational issues at the higher speeds, will the stator be able to handle the torque put on it when the KW start going into the 3,4,5 range etc and a 100 things I have not thought of. The design goal I was looking for was to be able to load the gen to a high point then as the wind gets stronger just let it spin faster but hold the same load on the gen so as not to overheat it... that's all...

Hope this brings it back to dirty water.....

PS: Off the shelf would be nice....

[Flux]

If you can limit your output to 500v at top turbine speed then you are ok. If that brings you below inverter input volts in lower winds then you have a problem.

Most of the grid tie inverter schemes using HAWTs with furling use a dump limiter to clamp the occasional voltage spike when the furling gets caught out or during inverter synchronising.

With a HAWT you will have far too much energy to shunt clamp so you would need a series voltage limiter to let the generator exceed 500v and hold the inverter safe. This would be another pwm buck controller or similar and very expensive but possible.

Perhaps a crude solution such as adding heaters in series with the input of the inverter above a certain wind speed would be the best option. It would let the inverter keep running and if you could use the heat then you win all ways. You may still have a problem if the inverter came off line for some reason in a high wind.

Flux

[vawtman]

Hi Bill

 Could you go into more detail on the to be vawt?Whats an OC?

Thanks

 GO Packers

[electrondady1]

i agree with your philosophy that the vawt should be strong enough to withstand any wind , open circuit.with out bits flying off.

but to me , living in town, the operating speed is more a matter of public relations.

lately i have been  thinking along the lines that you rig up you devise to turn at an rpm were the neighbours are not afraid. (no matter what the wind speed.)

to do this you simply add more load to the mill.

if the alternator starts to get pushed ,add more alternators.

this could be triggered by voltage levels.

as well , the secondary alternators could be of the electromagnet type .

[fcfcfc]

Hi: OC, short for (O)pen (C)ircuit, letting the gen spin without an electrical load. The only electrical problem is that the wire insulation has to be able to stand up to that voltage without shorting itself and mechanically the gen and turbine have to be able to take the physical stresses. I believe balancing everything will be a challenge in itself, let alone all the other stuff.

[vawtman]

Thanks for clearing that up Bill.

When you stated {on an OC}I was picturing something the vawt was mounted on.

 Have fun with your project.

[fcfcfc]

Hi: I kind of live out in the country so not to many problems with that kind of stuff. The challenges here are just all the electrical ones and the mechanical ones. When you get into the 5 KW range and maybe peak into 7 or 8, the torques are huge. If I remember off the top of my head, one horsepower is about 755 watts, so you are talking 10 HP here at times. That kind of power can shear and bend allot of stuff. For a first wind project it is definitely not small. Once I wind tunnel the turbine allot of these things may solve themselves passively. On my wishful thinking list is that the turbine will increase power up to about 30MPH winds and then start to flatten out.... yea right...LOL...