# how to Regulate the DC output of wind turbine

Discussion in 'The Projects Forum' started by mawais15, May 2, 2011.

1. ### mawais15 Thread Starter New Member

May 2, 2011
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hey guyz!

i am building a windturbine with a permanent magnet generator. The problem is that the wind speeds in our area are very fluctuating, so i expect a greater variation of output voltage. Please tell me how is it possible to regulate the output voltage over the range of DC-AC invertor..?

kind regards

2. ### #12 Expert

Nov 30, 2010
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A battery is the way I'd do it. A battery converts however much energy you are producing into chemical energy at a fairly steady voltage. That is much easier to regulate that trying to build something that can cope with the huge variations you will get from the turbine.

3. ### wayneh Expert

Sep 9, 2010
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There are complex answers (buck-boost power transformer) but the battery is the common and simple solution. It can absorb wide swings in power output as CURRENT variation while holding VOLTAGE more or less constant. The problem with the battery-only solution comes on windy days when your battery is already charged. You cannot pump large currents through it without risking damage. There are all sorts of contraptions to cut out the mechanical connections or divert the excess power to heaters or what-not. But as long as your battery is in near-steady-state, neither discharging too far nor being overcharged, it'll do a great job.

4. ### russpatterson Member

Feb 1, 2010
351
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What voltage range do you expect from your wind powered generator?

@Wayneh, with the battery solution, do you expect to lose power when the generator is producing a high voltage but it collapses due to the battery voltage? Does the maximum power point tracking trick done with solar panels apply here?

5. ### wayneh Expert

Sep 9, 2010
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Not sure I fully understand the question, but peak power will be realized when the impedance of the source (alternator) matches the impedance of the load. I've recently learned that for solar panels, that impedance is fairly high and thus the peak power occurs at ~90% of peak voltage. Drawing more current to get more power will only serve to drop the voltage so much that power falls off.

For a well-designed permanent-magnet-alternator, as so often used in wind turbines, the internal impedance of the alternator should be quite low. This means that peak power can be realized at high current and relatively low voltage.

For instance I've collected data on alternator that produces 31v at a particular rpm, when unloaded. Adding progressively larger (resistive) loads until the power into the load peaks, I see that the voltage has dropped to ~11v, or about 35% of the peak. Lower resistance loads will draw increasingly more current, but voltage falls and total power to the load falls off rapidly. And, power lost to heat in the alternator coil increases.

russpatterson likes this.

Dec 26, 2010
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There is potentially a lurking "nasty" in the output current-voltage characteristic. The alternator may be nice and low-impedance if driven at constant speed, but the windmill will tend to slow down as the generator torque demand increases. This won't happen straight away, due to the inertia of the system. I see a potential for the windmill being slowed down below the most efficient speed unless some measure is taken to prevent it. There may also be a risk of hunting, depending what other delays might exist.

I can see the problem, but not the solution as control is not my strong subject. Perhaps an independent wind speed measure might be useful? Presumably this particular "wheel" has had to be invented before though: maybe somebody more knowledgeable can comment?

Edit: The battery solution at least should not be unstable.

Last edited: May 3, 2011
7. ### wayneh Expert

Sep 9, 2010
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Given all the variables, I can't see how the answer to optimization is anything other than testing and characterizing a particular windmill/generator design. At various wind speeds, draw varying amounts of electrical load while allowing it to achieve "steady state" at any set of conditions. Plot the data and optimize.

8. ### russpatterson Member

Feb 1, 2010
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So bucking the voltage down to closer match the battery voltage will not render any efficiency increase over just letting the voltage collapse?

9. ### wayneh Expert

Sep 9, 2010
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It depends, but IMHO it's unlikely that you would gain from bucking down UNLESS the alternator was wound with too fine a gauge of wire, giving it lots of voltage but not much current capability. Pulling current out at 13v could be far below the optimal peak, and most of the coil's power is going into heating itself. So yes, if it's making 80v, you might be better off bucking it down.

Folks that try to use automotive alternators end up with the opposite problem, too little voltage and "too much" current capacity. They're meant to spin much faster than a wind turbine.

Dec 26, 2010
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I don't think anybody has said that conversion would not help, only that it may not be simple to apply. Beginning with a data-gathering exercise seems like a sound approach. The results should give a better idea of what optimisation may be possible.

11. ### mawais15 Thread Starter New Member

May 2, 2011
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i was planning to use an automobile induction generator with a belt and pulley system to give enough rpm to the generator. one of my friend suggested me to use a DC-DC convertor to regulate the voltage output.

if i would use battery, then there is no problem at all but i don't want to use battery because of some issues. Thats why i am looking for an alternative to get a fairly regulated voltage from turbine to be directly fed in the invertor.

12. ### mawais15 Thread Starter New Member

May 2, 2011
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I guess it'll be 0-24 V. Not sure coz i've not tested the thing so far

13. ### mawais15 Thread Starter New Member

May 2, 2011
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battery iz a solution but its not included in my project :-s

14. ### wayneh Expert

Sep 9, 2010
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Is that just an alternator? You may be better off to stay in the AC domain and never convert to intermediate DC. For one thing, you'll avoid the inevitable power loss in diode rectification. There are ways to convert one AC voltage to another. Obviously a transformer works for a single input voltage, and there is a thing called a Variac for manually adjusting the ratio. You need something fancier.

15. ### mawais15 Thread Starter New Member

May 2, 2011
6
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you're right but there is no other way i have. talking about the variable transformer, it would be difficult for one to automatically adjust it setting accordingly with input voltage.

16. ### wayneh Expert

Sep 9, 2010
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Difficult, yes. You're asking for the holy grail of wind power - a device that accepts any input signal and converts it to 120v, 60 Hz. That's not simple, and I'm not aware of any general solution.

17. ### mawais15 Thread Starter New Member

May 2, 2011
6
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i've started to figure out that its outa reach