how do you slow down a speed control wind turbine

[kf]

How does one slow down the speed of a wind turbine to follow the maximum power point? I have modelled one and the speed is controlled but now that I think of it I dont actually know what the lads n lassies actually do on site to slow one down. I get that the blade pitch can be controlled and that of course that would just have actuators to turn the blades. But what do they do for speed control? just use break pads to slow it down? Can you use the generator to slow resist torque/speed? or even can one use the generator to speed up the wind turbine if it travels too slow. My model didnt need to go into that detail so I just have the torque being influenced to show that the power varies as the speed or blade pitch varies.

[ewmon]

In controlling blade pitch, the blades won't spin faster than the pitch allows, so it could control the turbine speed. You'd want be able to feather the blades and lock the turbine drive shaft if you want to work on various equipment. If you can rotate the blades to a negative pitch, it can bring the drive shaft to a halt with aerodynamic braking alone. Depending on the generation equipment, it might work in reverse as a motor, and a motor might be useful for checking bearings or alignment, bringing a blade into position for maintenance, etc.

[kf]

In controlling blade pitch, the blades won't spin faster than the pitch allows, so it could control the turbine speed. You'd want be able to feather the blades and lock the turbine drive shaft if you want to work on various equipment. If you can rotate the blades to a negative pitch, it can bring the drive shaft to a halt with aerodynamic braking alone. Depending on the generation equipment, it might work in reverse as a motor, and a motor might be useful for checking bearings or alignment, bringing a blade into position for maintenance, etc.

 

Well basically I have a program that just uses an equation to calculate the Coefficient of Power. And I can change the blade pitch as a value in the program and I can change the speed.

I've read lots of ways of doing speed control, blade control or using both speed and blade control to get the best power achievable foe a given wind speed. The model actually works and that's all fine. I just dont get how in practice how one achives speed control when the blades are fixed. Basically when I google what I am doing, I get websites that dont go into detail because they are for novices, they just specify that you can control speed or pitch or both, and then I get papers that dont explain at all because they target audience of the papers is other engineers. So while I get how one could change the pitch to influence the speed, I dont know what they do for speed control. I have heard its done on the generator side but I have no idea what ideas are out there. is there a breaking mechanism they can use with brake pads? or can you adjust things on a generator so that it resists some of the torque coming from the rotor?

[Schrödinger's hat]

I dont know what they do for speed control. I have heard its done on the generator side but I have no idea what ideas are out there. is there a breaking mechanism they can use with brake pads? or can you adjust things on a generator so that it resists some of the torque coming from the rotor?

 

The only ways to control the speed are to change the pitch, or change the load on the shaft.

One way of doing this is with a brake of some kind. This is wasteful in terms of energy, but can be necessary to stop the turbine from falling apart in high winds.

The other is to change the load produced by the generator. This is highly dependant on how your generator works.

If it's a DC generator, putting a lower resistance electrical load on it will increase the current and increase the force required to turn it (requires some kind of controller/voltage conversion depending on what you're using it for).

Another option might be to use a gearbox of some kind.

I don't really have much domain specific knowledge in this regard. If you explain a bit more about how things are set-up (what kind of generator/stator, how it's controlled, what it's powering etc), I may be able to help further.

[Joatmon]

The only ways to control the speed are to change the pitch, or change the load on the shaft.

 

 

Although not done in practice another theoretical way would be to lessen the effect of the wind with some sort of shield. This could have holes of varying size and be as high as the turbine blades (to keep a balanced load on the blades). For maintenance purposes the holes could be completely closed and, as the structure would be high enough, a roof (possibly sliding) could be incorporated. I imagine a circular structure with diameter large enough to allow movement of the turbine as wind direction changes. Perhaps in light wind conditions the whole structure could sink into the ground. Absolutely a trip down "imagination lane" as I'm sure cost and practical considerations would rule it out! Still, perhaps a forum such as this should be the place to float ideas.

Edited March 7, 2012 by Joatmon

[zorro]

The speed of a wind turbine is controlled by the offset tail at tail angle reductions the blade turning the blade into the wind.

 

 

 

[Enthalpy]

You get the maximum efficiency only for one blade pitch, so only generator loading could keep the turbine at maximum efficiency. This is done by the conversion electronics.

 

At the paleo-windturbine-era, when generators were coupled to the power grid without electronics hence had to be synchronized with the frequency, blade pitch had this function. Now it's used to protect the turbine from overspeed in a gale. No need for a huge shield.

 

One Spanish company varies the pith individually without one rotor turn to reduce vibrations and pitch moment.

 

Some older but sound designs had a fixed pitch and a small tiltable area at the tip of the blades, which served as an aerodynamic brake. Very efficient, because braking the rotor lets it stall, which reduces the lift a lot. Essentially, a turbine running normally catches as much force and power as a complete disk (costing less material) but when stalled, it catches as little as non-lifting blades.