ECN Forum Forums General Topics of the Trade General Discussion Area Electronic load control (for wind turbine etc)

Taking a step back and looking at figuring the RPM on the turbine. On my commute this morning I wondered about the possibilty of attaching a bycycle speedometer/odometer. The good style of these just count the number of times a magnet passes a sensor, the magnet is attached to the wheel. This seems to be the easiest and cheapest method of creating pulses representing the RPM. But you may have a solution to this portion already.

http://www.pwrx.com/

Michael,
Powerex is just one mfg. of power mosfets and IGBTs Whether you use IGBT's or mosfets, you still need to isolate the signal from, and reference the drive to the emitter or source. This link will probably provide some useful info for you. Our driver boards use an Agilent driver chip but I don't remember it's #. I'm starting to feel like you are much more system minded than a circuit nerd so perhaps you shouldn't get to the component level. This thread probably belongs in the theory area when we aren't talking about off the shelf systems.
Joe

Thanks, Joe,
No, I am more the circuitry nerd. That's what I do, but not with power electronics.
However, I reckon the application is not so complicated. Max power of 5kW approx. And I reckon there can be quite a simple and cheap solution. Forget the input, imagine trying to control a heater, using pwm, and using a 400VDC input. Make that work and the rest will fall into place. Can use a micro and bring some intelligence into the control.
Hoping someone who has already experience with the chopping/power switching in this area could put me on the right track.
Michael.

Well, I would forget the micro and worry about the basics. What about control power? Is there an AC source that you plan on using for that? If so, the split, isolated supply is mostly a function of using a transformer with good isolation. If not, you need to strap a switching supply that can handle the entire output range, to the turbine output. That would probably mandate a minimum speed at which your system would work.

From a safety standpoint, it wouldn't be prudent to reference all of your supplies to the emitter or source of your switch unless it was at or near earth potential.
Joe

Before looking at a very complex controller, I'd strongly suggest looking to simplify matters.

What are you using as a generator? If you had an unregulated DC generator, then its output voltage would change with turbine speed, and the power delivered to an uncontrolled resistive load would vary as the square of the turbine speed. Such a system would not stall the turbine, because as the turbine speed dropped, the load would naturally shed. But it might not provide enough load to protect the system during high speed operations.

If you use something with a variable field such as an alternator, then you could control your system by adjusting field current. Simply tie the field current to the pre-rectified frequency, so that if the turbine spins too quickly the field will increase, increasing the output voltage, and pushing more power through the resistors. The field current control could be via a small digital circuit, or even an analog frequency controlled circuit. This would eliminate all the high power semiconductors.

Finally, you could eliminate electronics all together. Use the turbine to run a hydraulic pump, and run the hydraulic fluid through an impedance in the water tank. This would probably have load characteristics that match the turbine quite nicely, and run without any sort of regulation.

-Jon

Hi Jon,
Thanks for the post. Some very interesting ideas, especially the hydraulics idea. That is what is needed, some thinking outside the box - pardon the cliche. I wonder has anyone tried this?
Michael.

Another idea outside the box. Use the wind turbine to power an electrolyser and use the hydroxy or browns gas to heat your home. Excess gas could be used to run a generator.

Splitting water into its constituent components, hydrogen and oxygen or HHO or Browns gas, electrically only uses a fraction of the power that you can generate recombining them thermally in say, an engine that drives a generator.

For example an electrolyser that can generate enough HHO to run a cars engine only uses about 20% of the output of the cars alternator.

Also the exhaust is cleaner than the air going in.

Google browns gas, HHO, water car, joe cell, electrolyser etc.

Call your patent attorney, you have just invented the perpetual motion machine.
In reality it takes more energy to free hydrogen from water than you get back when you recombine it because of losses along the way.

Greg,
Thanks for that very useful intervention. I should have twigged the energy creation bit in Simon's proposal, but my mind is/was a little fuzzy.
Michael.

Another idea: connect your turbine to a small battery bank, with your load coming off the bank. You can use a simple DC voltage switch & contactor to cycle the load on and off; the batteries will dampen any large fluctuations due to wind gusts or brief drops in speed, the load equipment will run at its design current and voltage, and the DC voltage switch will prevent the batteries from being overly charged or discharged.