Buck converter for small wind turbine project

[Burnit0017]

Greetings, I have been working on buck converter that I use with a permanent magnet alternator driven by a vertical axis wind turbine  that can be used to charge a 12 volt battery bank. I have had limit success manually operating the PMA with the buck converter driving a 50 watt 12 volt halogen light.  The buck converter is operating at 10 kHz with a 20 % duty. Without the buck converter the PMA acts like a electric brake the more the RPM is increased and most of the power being produced is lost as heat at the alternator.

When I try to charger a 12 volt battery the mosfets will not turn on. I am currently trying to solve this problem and comments are welcome.     


video of manual operation PMA and buck

[HackedFridgeMagnet]

That circuit hurts my eyes, can you rescan it?

[Burnit0017]

Hi, I have no experience with this type of power circuit and this is a first attempt. I believe there are two methods used to turn on the mosfet in this configuration. I am trying to use a IR2117 gate driver with boot strap capacitor. The circuit does work with a resistive load, but when I try a 12 volt battery as a load the mosfet will not turn on.

I am now trying a isolated power supply for the driver circuit. What is confusing me is the gate voltage needed to turn on the gate and what do use a reference.

I hope the new circuit helps. 

[jahonen]

The problem is that the mosfet gate driver bootstrap capacitor does not charge due to battery presence, switch node is at battery voltage. Switch node must go to ground in order the capacitor to charge. You could do a synchronous regulator, i.e. replace the diode with a mosfet (low-side mosfet pulls the switch-node low) but then there is a risk that if battery voltage rises above set point, the circuit starts to transfer energy from the battery to the source.

On second look, you seem to have a blocking diode in series with the inductor. In that case, just adding a simple pull-down resistor at fet source might solve the problem.

Regards,
Janne

[Burnit0017]

Hi, I have verified that using a isolated power supply for the gate drive circuit will turn the N channel mosfet on and off in a Buck circuit configuration with a 12 volt battery as a load.  I configured the gate drive circuit with a 555 time and used a Schmitz triggered nand gate as a inverter. The 555 timer was configured with a variable 1 meg ohm pot so the duty cycle could be changed. The shorter I set the duty cycle the easier the PMA was able to spin and produced a very high voltage at Vin. Positive current was flowing into the battery. Under manual operation the best I could achieve was 0.7 amps flowing into the battery. The circuit will definitely benefit from using a microcontroller to adjust the duty cycle.  At this time I starting to work on  paralleling the mosfets and adding a microcontroller to the system. Comments welcome   

This is the part I find confusing:

When comparing the waveforms of the two gate driver circuit’s the circuit without the IR2117 triggers the mosfet all the time.
Video without IR2117 in gate driver circuit:
mosfet Vs is top waveform:



The circuit using the IR2117 only triggers the mosfet when the PMA provides a input voltage.
Video using IR2117, bottom waveform is mosfet Vs:




Waveforms in both videos are measured at the same point.

[HackedFridgeMagnet]

Hi
Can I just say your wind turbine looks awesome. Must have been a lot of work, is it modified from a standard design or did you get the plans from somewhere or just invent it yourself.

A couple of things
I would put a fuse on the batteries postitive terminal.
What fet are you using.
Do you need the blocking diode?

What are the voltages( or Waveforms) on the Vin, VB, HO, VS, Com, all with respect to the earth near your vin cap.

Also I would initially disconnect your wind turbine and use a current limited power supply. Until you are sure that your buck circuit is correct.

If you can step back even further I would simulate your circuit in LTSpice, it's well worth the effort, particualarly if you have a lot of tweaking to do, or you risk blowing components.

[Burnit0017]

Hi, I have posted the VAWT project at:
  http://www.fieldlines.com/index.php/topic,143852.0.html

I am using a modified C rotor configuration. The VAWT is a prototype and was built just for testing so I could gather data. The blades can easily be expanded. The greatest improvement to the system will be to add a Buck converter and after that is working, add a microcontroller so a MPPT algorithm can be implemented. I found a reference paper that shows a buck converter using a isolated power supply for the gate driver to drive a N channel mosfet for a battery charging circuit. Chapter 4. page 69

http://etd.ohiolink.edu/view.cgi?acc_num=akron1320692738

I am now using this as a guide. I have ordered the parts and will post results when available. This is a first attempt and comments are always welcome and appreciated. It looks like using a isolated power supply with a opto-coupled gate driver will solve many problems.

What fet are you using.
IRF540

Do you need the blocking diode?
I really do not know.

What are the voltages( or Waveforms) on the Vin, VB, HO, VS, Com, all with respect to the earth near your vin cap.
Vin is based on the PMA's RPM, can be as high as 200 volts at higher RPMs. I am manually operating the PMA during testing and depending on the duty cycle of the control signal I have measured 50 volts at the input. When I use the IR2117 VB is 12v, HO is 12v, VS depends if it connected to a battery and if the mosfet is on or off. Making the common connections is confusing for me.

[HackedFridgeMagnet]

Here is a paper about driving Mosfets, it maybe more than you want but I look at it as my reference whenever I think about making a converter.
http://www.ti.com/lit/ml/slup169/slup169.pdf

I think your plan of using the isolated gate drive is sound, there are many ways to acheive this but yours is logically simple.
The isolated ground should obviously be isolated from everything except  the Mosfet source pin.

[Burnit0017]

Hi, thank you, this should help a lot. It is just what I was looking for.
  Here is a video that explains why a buck converter is so important for any wind turbine project:

[HackedFridgeMagnet]

Apparently they take the smart drives out of washing machines at our local tip, they sell pretty quickly.
Also a nice big air cored inductor, interesting.

I think a hysteretic mode buck converter might be more suitable than mppt.

You define the maximum charging current and the minimum charging current.
You measure instantaneous current in the inductor if it is greater than max then turn off, if it is less than min then turn on.
When wind is low the switch would always be on.
It is very simple and minimises switching.
But then again, I know nothing about wind turbines.
I'm still having trouble understanding why the mismatched load doesn't turn. (back emf) I will look into it.

Ok got it now.
Change of opinion, So I dont think the normal hysteretic mode converter will do you much good, as you need to keep the voltage high on the Vin capacitor to minimize rotor losses.

I think MPPT is easier on a solar panel but obviously important on a wind turbine.
So you will need to measure Vin, I, Vbatt and possibly rotor speed, and wind speed.

Definitely an interesting project.

[Burnit0017]

Hi, I am not a Physics major but it does appear to have something to do with reverse EMF. I tried a SPIC converter and I found no real benefit, because the SEPIC has a constant output. With a buck configuration during the off period of the mosfet, it isolates the PMA from the load and allows the PMA to maintain momentum.  I was very skeptical when I first saw the video but after I was basically able to reproduce the results with my project by adding a buck converter, it dramatically reduced the required torque to spin the PMA. Without a buck converter the faster you try to spin the PMA the more it acts like a electric brake.
 
Adding a micro controller is phase two and will have to wait until I have a basic buck converter working as a 12 volt battery charger using the PMA as supply. Your help is greatly appreciated, thank you.   

[DaveW]

I think MPPT is easier on a solar panel but obviously important on a wind turbine.
So you will need to measure Vin, I, Vbatt and possibly rotor speed, and wind speed.

Definitely an interesting project.

You can get away with measuring less than that, we just measured Vin and Vout for a discontinuous boost MPPT, theory & circuit in the video,

[HackedFridgeMagnet]

No worries about helping Burnit0017 hopefully I can actually be some help to you.
One day I would like to do the same, hopefully next year. I was thinking of a traditional propellor type arrangement though. Why did you choose the vertical arrangement?
I really think you need to measure current for the batteries charging management anyway.
When I make mine, one day in the future?, I am going to measure the current being delivered to the battery and the current supplied by the battery to its load, because to accurately know the batteries charge current you need the net of these.
Also you can measure current with a very low loss, just by making your sense resistor very small, then amplifying it, obviously you need an extra op amp for this.

Nice video DaveW, great Lab too I am really jealous. Good luck in the competition.
I couldn't find any results on your Design spark node.

[Burnit0017]

Why did you choose the vertical arrangement?

Hi, the vertical design was chosen because it is easy to fabricate. Material  cost is very low and the fabrication method is very stable and easily scalable to a larger size.

[Burnit0017]

You can get away with measuring less than that, we just measured Vin and Vout for a discontinuous boost MPPT, theory & circuit in the video,

Hi, great video. If you have chance to test your circuit using a permanent magnet alternator, please post the results. I am mainly interested in if it will help prevent turbine stall.   

[Burnit0017]

Greetings, using a isolated power supply and FOD3180 does work. I am using a blocking diode between the inductor output and the plus terminal of the 12 volt battery. The gate driver is triggering a N channel IRF540 in a Buck circuit configuration and is charging the battery, current about 1 amp. Then I replaced the battery with the 50 watt halogen light and the circuit was able to illuminate the light after I adjusted the duty cycle, current max about 4 amps. I was manually operating the PMA. So far this is a very happy day. The next step is to drive the PMA with the drill press to determine how the circuit behaves at a higher RPM.     

Chapter 4. page 69

http://etd.ohiolink.edu/view.cgi?acc_num=akron1320692738

Isolated power supply with FOD3180 gate driver. N channel Buck converter using a IRF540 mosfet. Bottom wave form is gate of mosfet, top wave form is source of mosfet.
Input voltage max about 40 volts. Output current varies depending on duty cycle. Circuit still needs improvement but it is working. Input voltage is from a permanent magnet alternator and is being manually operated.   Comments welcome.