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.
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.