Apologies for the lack of detail around the question as I don't posses a lot of background on the subject.

My question is - is it possible for windmills to control speed of the blades and power output by adjusting the load/resistance of the generator.

I understand that power generating windmills adjust their blade pitch to control speed. They also have a gearbox that can adjust the amount of power being generated.

For example in extreme winds the generator would provide more resistance but and create more power per rotation than it would in low winds.

I appreciate any comments.

 

I'm not sure the size your thinking of ... you can explore this idea by buying a small brushless motor and a prop , many are sold for people who want to make drones , but you can operate it in reverse , in a very strong wind and use it to generate power ...

you have three wires coming out of the motor/generator ... when the wind is blowing and the prop is spinning fast there will be a voltage generated across any two of the wires . as soon as you draw electrical power , this will cause the blades to slow down ... the more power you draw the more the speed slows , so you can adjust the speed easily by adjusting the load even in extreme winds (for small generators)...

The reason this is not done in large commercial generators is this would put extreme loads on the supporting tower , generate too much heat in the generator ... It could be done theoretically if you built a stronger tower and a larger generator .. it's just economics ... more sensible to use gears and adjust the pitch.

 

Thanks for the info Oz. This is very helpful.

As far as scale goes, I am leaning more towards large industrial projects, specifically compressed air energy storage generation.

What you are describing with the windmills being under extreme load makes perfect sense. In CAES the joules-thomson effect could help cool the turbo-expander and generator, and it might be make more economic sense to build stronger units.

When you say that you can slow down as soon as you draw electrical power how could you control that if you are trying to feed into the grid?

**This is all theoretical and I am not planning on connecting anything to the grid**

 

As far as scale goes, I am leaning more towards large industrial projects, specifically compressed air energy storage generation.

You do realize that compressed air is one of the highest cost items in industry don't you. It seems like generating power by using it would be good and cheap, but the reality is different.

 

Would anyone be able to elaborate on possible ways to modify the load/impedance of a generator that is supplying electricity to the grid? Ideally it would help the generator fall into its most efficient range.

 

Small adjustments in the voltage would increase / decrease the load when grid tied. I presume this is how grid tied solar panel inverters work.

Bob

 

Would anyone be able to elaborate on possible ways to modify the load/impedance of a generator that is supplying electricity to the grid? Ideally it would help the generator fall into its most efficient range.

Usually the grid is modeled as a infinite current source and sink for power so the generator would be controlled as a current source optimizing current output. In a perfect world the grid-tie inverter (current source) voltage output would be exactly the same as the grid voltage at any instant as the grid is usually modeled as a infinitely stiff voltage source with perfect conductors but that's usually not the case so they cheat (just slightly higher than the utility voltage with a line isolation inductor for the voltage) a little to prevent power feedback.

So the most practical way for small wind systems without direct grid synchronous control systems to optimize power to the grid is to generate a filtered DC voltage that can be connected into a MPPT grid-tie converter. The expected generator output voltage at normal wind speeds should match the grid-tie inverters input voltage best efficiency voltage range. The grid-tie inverter will then optimize the load on the wind generator to supply the maximum current to the grid.

 

That helps. Thanks nsaspook. So if you wanted to control the load/impedance of the generator you would have to modify they current you are sending to the grid? Is there a grid-tie inverter capable of doing that?

 

That helps. Thanks nsaspook. So if you wanted to control the load/impedance of the generator you would have to modify they current you are sending to the grid? Is there a grid-tie inverter capable of doing that?

There are adjustable power grid-tie inverters with programmable current and voltage limits but they are mainly designed for solar. With wind power you will need a dump load function to control speed in high wind situations if you limit grid power. For US applications an inverter designed for split-phase power is required for proper control of both 'hot' wire currents in respect to neutral because they are often unbalanced in residential service.

There are also some that have a grid-zero function to reduce power to close to actual on-site usage. This would require a battery or storage bank.
http://www.outbackpower.com/downloads/documents/appnotes/gridzero_app_note.pdf