Wind turbine control

techstudent

Lately I have been doing some reading on homemade wind turbines which by themselves produce 5 phase 'wild' AC (possibly up to 600 volts) meaning the frequency and amplitude vary according to the wind. The way to link them to the grid is via a micro controller. What I am wondering is how this works, how 'wild' AC is 'tamed' and put in sync with household AC. Can it be done without first rectifying to DC then inverted back to AC?

The other thing the micro controller does is maximizes the power from the windmill. A dead short in the lines from the windmill will essentially lock on the brakes making it very difficult to turn (thus it will not produce much power) and an open circuit can let it run at very high rpms producing dangerous voltage and damage to the turbine. So it is the micro controllers job to adjust the load accordingly to maximize efficiency.

My other question is if it running light bulbs or hot water elements is 'wild' AC ok?

I am in the researching step right now I may build one within the next few years. But if anyone has any thoughts/experiences or comments in these matters I figured it may be a fun project for using a STAMP2 I guess basically what I am looking for is just a general ideas/discussion of how to do these things..

Thanks

Philldapill

techstudent, I could be wrong, but I think "wild AC" is just a catch phrase for "non-uniform frequency/amplitude AC". Wild AC DOES sound cooler, I'll give it that. [noparse]:)[/noparse]

I don't think there is anyway to directly convert the wild AC to regular 60Hz(or 50Hz), 120V AC. I think the best, and only, way to do it, is to rectify it and turn it to DC. With this DC, charge a battery bank, and have a grid-tie inverter which would take the DC and turn it into AC for the grid.

As for the microcontroller, yes, you would need one to control the DC-AC conversion, but it's not easy... Also, it is VERY difficult to maximize the power output from a wind turbine. Solar panels are fairly easy because the output from those is fairly constant. Turbines, on the other hand, spin at different speeds... if you increase the load on them, they might stall, causing output to drop... they are just sooo dynamic.

Using the AC to run a lightbulb or water heater is OK, ---IF--- you can make sure the voltage isn't too high. If it's too high, it could burn out the light bulb element or heating element.

As for the STAMP2, this would be a PERFECT opportunity to switch over to a Propeller. STAMPs are great, but Propellers are a piece of sillicon magic - and easy to use!

kwinn

Techstudent, Phil is correct. The following info is based on the one and only wind turbine I have seen, so there may be other approaches as well.

The "wild AC" coming from the wind turbine is of varying voltage and frequency, both of which are dependent on how fast the turbine is turning (which in turn depends on wind speed). The AC is rectified and regulated by a switching regulator to charge batteries. The switching regulator is controlled by a micro to extract the maximum possible power from the wind turbine.

On the output side there is a second inverter that draws power from the battery and converts it to a frequency and voltage to match the power line it is connected to, or to produce the desired frequency/voltage for the application (normally 50/60Hz 120/240V). There is also circuitry and software on the system to prevent over charging the battery, and to prevent the battery discharging at too high a rate, or to a level that will damage the battery.

While controlling the speed and maximizing the output of a wind turbine is more difficult than dealing with a solar cell it can be done. Over the normal range of wind speeds the battery charging inverter can measure the voltage and current from the turbine to calculate the wattage and increase or decrease the current drawn to maximize the power extracted.

If you draw no current the turbine will be turning at maximum speed and producing the maximum voltage, but extracts 0 Watts.
As you increase the current the extracted power increases, but the speed of the turbine and the voltage out decreases.
At some point the decrease in the voltage will outweigh the increase in current and the power extracted will start to decrease.

By measuring the current, voltage, and rpm of the wind turbine the micro controlling the charging inverter can keep the circuit operating in the area at or very near where the maximum power is extracted from the wind turbine.

I also agree with Phil that the propeller would be an excellent choice for controlling the entire system. A dedicated cog for each inverter and 6 cogs left for other functions.

Tesla

There are some new tech's out there for converting AC to AC without a bus. It might be above your price range or willingness to design on. It is called a cycloconverter. Honda uses it in a new generator to reduce size and weight and give clean waveform. Yaskawa electric is working on one just for this kind of scenario. They call it a matrix converter(uses a matrix of IGBT's)

Philldapill

Tesla, that's very intersting. In the Honda version, are there mechanical parts involved? Got any more info on the subjet?

Tesla

The honda generator just uses a high frequancy generator to cut the size of that part down. Letting the motor spin to a high rpm with a PMSM on it then without using an inverter ,like the 2000i or 1000i generators do , it does AC to AC conversion.

I posted a WhitePaper from the company Yaskawa about the future of AC motor tech and at the last 1/4 of the paper they talk about matrix converters being used in wind power generation because of the ability to convert AC to AC and not have the wear and tear of bus capacitors, so inherently more reliable( no pesky electrolytic capacitors)

Tesla

http://www.hondapowerequipment.com/products/models.aspx?page=models&section=P2GG&category=cyclo

that is the link to thee honda generator. I dont think they go into much detail about the tech, but i was lucky enought to get to work hand in hand with Yaskawa electric for 3 years. They hands down lead the technology market when it come to anything AC motor wise.

I think the White paper i posted is here in the sandbox forum under a post called "Pulse on AC motor tech" If you have the time read the whole thing.....really interesting ideas. I got the PDF from my rep. He was always keeping my in the loop.

Beau Schwabe

I don't know if this is put into practice much, but I remember reading somewhere where a guy used the mains to 'excite' the field coil of a modified alternator (instead of straight DC which is typically used). This way, as the alternator rotated, the output AC voltage was always in-phase with the mains AC and the problem became a function of regulating the voltage proportional to alternators speed. I'm not sure exactly how he did that unless he could govern the speed of the windmill itself, but that seems a bit counter intuitive.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

kwinn

Beau, must be the same article I read a while back. Essentially the frequency applied to the field coil was the difference between the power line and the frequency that would have been produced by the alternator if DC had been applied to the field coil.

Beau Schwabe

kwinn,

I think though that the alternator was setup more like a DC motor being used as a generator... instead of permanent magnets, the mains supplied the field coil. This way the Output voltage produced the same frequency as the mains and allowed the output to "grid-tie" easier back into the system if you wanted that option.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Tesla

Wouldnt that just turn it into a motor? what keep power from flowing back into the windmill?

Beau Schwabe

Tesla,

"Wouldn’t that just turn it into a motor?" - Well yeah it would be and it is exactly that. Think about this.... if you have a DC motor connected to a system and you spin the motor faster than the system would be able to spin it on it's own, then the motor acts like a generator and you end up putting power back into the system. In a sense this is the same as being grid-tied only it's DC. With DC all you would need is a diode to block or prevent the system form flowing back into the motor, and for AC there's probably a few other things that need to happen, but it's still essentially the same sort of balancing act. If the controller senses that the output is not adequate, then the output is isolated from the mains, otherwise, with some load regulation, the output is fed back into the mains.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Tesla

So there would always have to be wind or you would waste power spinning the grid tied windmill?

Someone have a link to that paper?

My last boss was a renewable energy nut so we both we come up with crazy ideas. One way you could do good things with a windmill is use a PMSM to produce "wild ac" then drop it across a heating element for hot water storage.

One thing to think of is the storage capacity of water. Better then batteries. I made a system the ran water thru a heat exchanger on my wood burning stove so i could store heat to heat the house after one fire. Then to make it store even more energy if you use something that phase changes(i used paraffin wax melting point of about 150) you can store over 13kw of energy in a 55 gallon(80 deg F to 155deg F) drum if 50% of the volume is a phase change material stored in plastic container or bags within the water. With just a few insulated plastic drums you could store a lot of energy for cheap. As long as you live somewhere you could use thermal energy.

Beau Schwabe

Tesla,

"So there would always have to be wind or you would waste power spinning the grid tied windmill?" - No, this is where the controller would sense the difference and isolate the generated power or lack there of from the mains.

That paper was at least 15 years old, I'm not sure where I'd start looking.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

kwinn

Beau, I am fairly certain that if you used the power line AC to energize the field coil the resulting output frequency would be the sum of the line frequency and the frequency the alternator would have produced with DC excitation. It would be an interesting experiment to try if you had a car alternator and could bypass the diodes.

Tesla

Ah. I get it Beau. I thought that it was controler-less.

Thanks.

Beau Schwabe

The term 'alternator' is confusing.. What I had read was basically how someone had converted an alternator into an induction motor in a way that it no longer functioned as an alternator.· It seems as though after doing a bit of further reading that the "Induction Generator" method is actually a common practice.· A very simple controller (an "Amp-meter" (ammeter)·even) with a set threshold would be all·that's needed to engage or disengage the output power from the grid.· ... even a speed sensor on the wind turbines shaft would be enough.· If·it's·greater than or equal to the speed of the normal induction motors speed·running off of the mains, then the controller engages power to the induction motor which at this point would start functioning as a generator.·· "The controller ... It's so simple, even a BS1 could do it" ····
·
Search ... "Induction Generators"·
http://en.wikipedia.org/wiki/Induction_generator
·
Here is another article that basically re-iterates what I was trying to explain in an earlier post.
http://sci.tech-archive.net/Archive/sci.electronics.basics/2006-07/msg00061.html
·
·

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 4/7/2009 3:38:59 AM GMT

Gadgetman

Just one question...

Why do you want to tie it to the grid?

Unless you can get the timing and voltage very, very, very accurate, no power company will allow you to connect it to their grid.

If it's 'just' to power some appliances at home, why not take them off the grid and hook it to the AC from the wind generator(assuming that you can keep it within normal tolerances, which is much easier than synching with the grid)?

If it's for general 'lighting use' at home, why not go for a 12V DC 'grid' at home?
(A lot of other things can also be run off 12V)

Just wondering...

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Beau Schwabe

Gadgetman,
·
"Why do you want to tie it to the grid?" - Cheaper design cost and better power·transfer efficiency.
·
"Unless you can get the timing and voltage very, very, very accurate..."·- An induction generator would by design take care of all that.·
·
"...no power company will allow you to connect it to their grid." -·Correct, a·grid-tie unit of any kind would need to be certified and inspected by your local power provider before you bring it on-line.
·
"If it's 'just' to power some appliances at home, why not take them off the grid and hook it to the AC from the wind generator (assuming that you can keep it within normal tolerances, which is much easier than synching with the grid)?" - That would be fine·if the AC output were compatible with your appliances and the power output was consistent.· Unfortunately wind is an uncontrolled variable.· So there needs to be some kind of conversion to "normalize" the energy and it is·through this·conversion process·you loose·efficiency.
·
"If it's for general 'lighting use' at home, why not go for a 12V DC 'grid' at home? (A lot of other things can also be run off 12V)" - You could, but you have much more IR drop at 12V verses 120V (or higher)
·
Example:
·
Say you are running a 12V 20Watt lamp 50 feet from your power source using typical 10 gauge wire.· The load, the lamp is putting on the wire is about 1.7 Amps.· 10 gauge wire has a resistance of about 1 Ohm per 1000 feet, so at 100 feet (Remember there and back at 50ft) you have about
0.1 Ohms·... or a voltage loss of about .17V
·
This may not seem like much, but this is only one light and at a fairly light load, at a reasonably short distance.
·
The same scenario at 120V 20Watt lamp 50 feet from the power source using 10 gauge wire, the load would only be 170mA or a 0.017 volt loss.
·


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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Philldapill

A great thing about high voltage is, as Beau wrote about, is the low IR drop in your wire. If you have a 12VDC generator, and you have a load that is pulling 10A, you are losing 10W right off the bat from the wire itself, Chances are, with various connection points, you may have more than 0.1ohms resistance. A better solution, is to have a higher voltage generator, bring that high voltage into a high-efficiency buck converter, and step it down to a nominal 12VDC. Many buck converters can achieve efficiency of 95% and higher.

With the low voltage scheme, you are automatically losing about 1/12th of your power from the generator. Even if you lose 5%(1/20th) of the power through the buck converter, you are still coming out ahead.

Even better about high voltage --AC--, is that you can run it through your lines at high voltage, then near your batteries, run it through a transformer and step it down, then rectify it. No buck converter needed, and you still save alot of energy.

All this talk about wind energy and energy conversion is making me want to build another. [noparse]:)[/noparse]

kwinn

Beau et all, Pretty much every "generator" the utility companies have on the power grid is in reality an alternator. As to the frequency of the AC, the utilities actually count the number of cycles to maintain a 60Hz average over the long term. No idea exactly how they maintain it, or the length of the period they average over.

Keeping all those alternators in lock step is not really that big a problem. If one of the alternators tries to go faster than the rest it is actually going to be trying to drive all the rest on the grid as motors. Alternately, if it tries to go slower, it becomes a motor that is driven by the grid.

Avoiding losses from high currents is the reason the high tension lines run at 660,000 volts, and some may even run at higher voltages. I recall reading about plans to go over a million volts but I am not sure if that was ever done.

Unless you are planning a large installation to sell power to the utilities it would not make sense to connect to the grid. The utilities would only pay about one tenth of what they charge for a kilowatt, so it makes much more sense to use what you produce. This would be particularly true if you are paying a surcharge for "peak demand time" power That would be the best time to use your generated/stored power.

Philldapill

A little off topic, but many power companies are talking of switching to VERY high voltage DC. The power generation would be HV AC, then rectified, sent along the power lines as DC, then converted back to AC at the receiving ends. This is to reduce any loses due to power factor, plus the grid doesn't have to be synched this way - just the same voltage.

Gadgetman

Actually, some power lines are DC and have always been that.

http://en.wikipedia.org/wiki/High-voltage_direct_current

So, if a power company is just now talking about it, it just means they're a century behind the rest of the world...

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randyaz

Nikola Tesla had it right all along.