Salient White Elephant

April 3, 2009

Closed Loop Direct Drive for Highly Scalable Horizontal Axis Wind Turbine

Closed Loop Direct Drive for Highly Scalable Horizontal Axis Wind Turbine

This drive system has sensors in the turbine blade that measure how much each blade is bent by lift and other forces. The shrouds that house direct drive generator windings are moved in the upwind or downwind direction in order to properly position them for the approaching turbine blade. What kinds of sensors might provide the proper information to the closed loop control system that adjusts the position of the generator windings? I don’t know. Strain gauges embedded into the blade spars that communicate with the controller via a radio link? A cylindrical cavity inside the blades that runs in the longitudinal direction and that has a laser at one end and a mirror at the other?

Another idea would give the turbine blade a permanent magnet that can protrude (longitudinally) from the blade tip. With this design, the shroud that houses the generator windings move to a location that is completely outside of the rotor disk (i.e. the swept area). As a blade approaches the windings, its magnet is pushed out of the blade tip. Once it passes the generator windings, the magnet is retracted so that it doesn’t create drag during the rest of the blade’s trip around the rotor disk.

Well it’s a couple of days after I wrote this, and re-reading it, it seems like a pretty stupid idea. I guess I just keep thinking about how once the turbines starting getting really big (1 megawatt or so), then the really sexy power electronics came onto the scene. Making this blog has proven to me that wind turbine innovation is likely to come from integrating other already well-known technologies, like power electronics. They didn’t invent power electronics for wind turbines, but once the machines got big enough to justify the cost of integrating these well understood devices and circuits, the addition of them provided much improved performance, and probably cut the cost of energy as well. So I’m just thinking that closed loop control technology might be one of the next things. Like for example, suppose it’s difficult to manufacture a giant ring generator and still maintain the tight tolerances required for good performance (given temperature changes, etc). Then maybe strain gauges of other sensors could be added, and a closed loop control system could adjust the radius of the rotor or stator at various angular positions… kind of like the way you turn the little nut-like things on a bicycle wheel to make it perfectly round and so that it won’t wobble side to side. So instead of trying to make the perfect ring generator, you just let the control system continually adjust the various tolerances based on sensor readings taken every minute or so. One thing’s for sure… pretty much every wind turbine configuration that can be thought of has already been thought of over all these centuries. So I wish I was in a position to look at how other technologies might be integrated in order to lower the cost of wind electricity… but I’m just not in a position like that. (Another thought that comes to mind is self-health checks… like they have in avionics systems… they have raised the detection of equipment failure or underperformance or abnormal performance to a high art form.)

Magnets In Rotating Shroud

Magnets In Rotating Shroud
This design is applied to the Highly Scalable Horizontal Axis Wind Turbine. I would put the rotating shroud on the other side of the nacelle, away from the blades, but that would require the mechanical power to go through the shaft, and I was trying to avoid that. I wonder if you could just have a rotating shroud with no magnets in it, and wedge its trailing edge between two tires and directly drive an off the shelf generator?

Rotating Shroud Drives Tires

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