Hello Everyone,
I am looking for a controller, or circuit and ideas for a controller for a Wind turbine for heating purposes. I.e it would take the available energy from the turbine and heat water. Therefore it would have to match the load to match the turbine's output. Perhaps using PWM.
I would like to experiment with 3-5kW, and high voltage (~200V) DC. I imagine this might give the simplest overall solution.

at 200 volts DC you are are looking a commercial grade material. Have you checked with the turbine's maker?

Simple 230V AC electric resistance heating elements would work with 200V DC, I'd think- output would always match the input. Of course, at that level of power, you may be better off using an inverter (feeding a small battery bank) to feed a conventional heat pump for the higher efficiency. Might be easiest just to buy an off-the-shelf electric generating wind turbine to reduce electric costs vice trying to do something fancy.

You mention PWM. What are you thinking in this regard? I just want to know exactly what you are trying to do. PWM is consistant with the use of VFD's. How would you incorporate a VFD in this application? VFD's convert ac to a dc bus, then via the IGBT's it is outputed in a simulated signwave that is ac. So it's ac in and ac out.

In DC alternative energy applications PWM's are often used to control the charge rates on batteries. I have not heard of the use suggested, but it does not mean that it is not possible.

Sounds to me like it is an engineering problem as it is unusual and should be taken to an engineer willing to take it on as a project, but that will involve a good deal of money. Or in otherwords, off teh shelf I have not heard of something that will work, unless I did not understand what you are trying to say.

At any windspeed, there is certain amount of energy available. You cannot apply this to just any load, otherwise it would just stall the turbine. Therefore the idea is to try and match the load to the turbine's output. PWM could operate like a switch, switching on and off the load, e.g. a heating element. If done at the right duty cycle, it should be possible to make it work. And I dont think it should require any very fancy electronics - perhaps power Mosfets?
I was hoping someone would already have done something similar and be able to share experiences.
And the turbine output could perhaps be much higher volts - 400-600V.
I am aware of a simpler scheme that switches in and out loads depending on the turbine rpm. But I was hoping for something better...

I was giving this some thought and, given the ability, controlling the pitch of the turbine blades would probably be my choice. Otherwise, I guess I would use an f to v conversion and op amp to feed a PWM ckt. I have a bunch of half-blown, 1200V, 400A, dual IGBTs in the lab so they would be my freebie choice of a switch.

My flow would be: F-V to translate turbine speed to voltage. I would use a tach or encoder to drive a charge pump. Next, run it through an amp to level shift and set my gain. I imagine that there is some minimum desired turbine speed > zero rpm. My PWM could be as simple as a 555 ckt. Finally, isolate and send +-10V, give or take, PWM gate drive to the IGBT. So what do you want to build after lunch???<G>
Joe

Joe,
You are on the right track. I do have the first part of the circuit...can use an lM2917. That will give us a voltage proportional to the rpm
But what about the second part - controlling the load via pwm and using your IGBT's. Do you have any circuitry? What PWM frequency should I use.
All info greatly appreciated,
Michael.

Michael,
It wouldn't seem to be too critical since you're switching DC and not trying to construct a sine wave, worry about harmonic content, prevent inverter switching overlap and desats, Etc. I would think you would find a compromise based on ripple amplitude and noise considerations. I would definitely use an RC snubber across the IGBT. Two 555s or a 556 could be used for an astable MV feeding a PWM stage by way of the control voltage pin. There are several one-shot chips that you could use also. Building the driver from scratch would be the biggest hassle because of the need to include the isolated dual power supply referenced to the IGBT emitter. Now if I were playing with this in our lab, I would just use one of our half-blown dual driver boards to feed the half-blown IGBT. I would just need to provide a +12 Volt source and a TTL level drive signal. Of course, my technical curiosity and interest in your challenge couldn't justify my actually rigging up these things in our lab.

Am I right in thinking that there are times that you would wish to gate this thing totally on or off? What about load side regulation?
Joe

Joe,
in answer to your last question first, yes, it would probably be good to be able to gate the load fully on (act like a brake on the turbine) or off, total disconnect from load.
Please name some IGBT's and I can look them up and see how they might be driven - I have no experience of them.
What about using power Mosfets? Would they be an option do you think?
Michael.

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.