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### Author Topic: Buck converter for small wind turbine project  (Read 8034 times)

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#### Burnit0017

• Guest
##### Buck converter for small wind turbine project
« on: February 11, 2012, 06:54:02 AM »
Greetings, I have fabricated a VAWT (Vertical Axis Wind Turbine). I have also fabricated a PMA ( Permanent Magnet Alternator). I have road tested the system and it will produce 9 amps at 40 MPH wind speed using a 12 volt deep cell battery as a load.

I recently learned that by adding a MPPT to the system I can increase the output at lower wind speeds. I am starting with just a basic Buck converter to start and if I can get the circuit operational a micro controller will be added at a later time.

I am trying to use a 555 timer as a oscillator to drive a IR2117 high side gate driver that will turn the MOSFET on and off of the Buck circuit.

I am searching for away to integrate a voltage comparator that will turn off the 555 timer when  Vin is less than the battery voltage.

I have only tested the 555 timer. Is there away to turn the 555 timer on and off using a Cmos output?

What makes the circuit difficult is Vs (Source) of the MOSFET is tied to + 12 volts of the battery.   The IR2117 has a boot strap circuit and Vcc is +12 volts from the battery.

This is a first attempt and comments are welcome.
« Last Edit: February 11, 2012, 06:57:21 AM by Burnit0017 »

#### kam

• Hero Member
• Posts: 1849
##### Re: Buck converter for small wind turbine project
« Reply #1 on: February 11, 2012, 10:05:45 AM »
I am running a short experiment with different LED drivers, from simplest to most complex. This "most complex" will finally be a buck/boost converter. My experience so far is very limited to those SMPSs unfortunately. But i'm waiting parts and staff to start experimenting with them.

What i can certainly tell, is that the topology you want to use is wrong. A buck converter will always have output voltage less than the input, a boost is the opposite, and a buck/boost is the one that you wanna build. This converter has always fixed output (for you 12V) regardless if the input is less or more than 12V. Since you don't have a big experience to these systems, i suggest you follow a tested recipe: There are chips doing exactly this... Integrated systems that they only need an external capacitor/diode/inductor to operate.

http://www.maxim-ic.com/products/power/dc_dc_switchers/

#### Burnit0017

• Guest
##### Re: Buck converter for small wind turbine project
« Reply #2 on: February 11, 2012, 17:15:54 PM »

Hi, here is a video example of a MPPT used with a PMA. It demonstrates why a MPPT is useful. A MPPT without the micro controller is just a buck converter.

Thank you for buck boost links.

Because I have no experience with this type of circuit and I am trying to start with just a basic buck converter with a 5 amp max output.

The circuit requirements are :
1. use a comparator to enable a oscillator when Vin is > the battery voltage.
2. the oscillator will enable the IR2117 to turn the MOSFET on and off.
3. when Vin is < the battery voltage the comparator will turn off the buck converter.
4. when the buck converter is off the input capacitor will charge until Vin is > the battery voltage and the cycle will start over.

http://www.usna.edu/EE/ee320/Supplements/dcdc5_driver.pdf

#### kam

• Hero Member
• Posts: 1849
##### Re: Buck converter for small wind turbine project
« Reply #3 on: February 11, 2012, 21:46:53 PM »
i'm afraid i can only provide you with speculations, since i must first learn my lesson :/ I will read the pdf and study it.

i did not knew that MMPT is that important for wind turbines...

#### Burnit0017

• Guest
##### Re: Buck converter for small wind turbine project
« Reply #4 on: February 11, 2012, 22:44:23 PM »
Hi, speculation is good. The video does a very good job showing the problem with wind turbine PMA’s and illustrates the solution to the problem using a MPPT controller.

They have been using MPPT with solar panels and are now starting to apply them to wind turbines. The technology is also very similar to motor control and regenerative braking used in EV’s.

I am just trying to get the MOSFET to turn on and off with the source connected to +12 volts. I think the boot strap with the IR2117 will solve the problem but I am not sure. I have all the parts for the circuit and it will take a few days to wire it up and test. I will post results when available, thanks for the help.
« Last Edit: February 13, 2012, 04:42:53 AM by Burnit0017 »

#### kam

• Hero Member
• Posts: 1849
##### Re: Buck converter for small wind turbine project
« Reply #5 on: February 12, 2012, 09:36:40 AM »
i found an interesting pdf for this (see attachments). From a quick read, i do not think that it is going to be that simple. The IR2117 will work for you as a MOSFET driver.
Looking forward to see your results.

#### Burnit0017

• Guest
##### Re: Buck converter for small wind turbine project
« Reply #6 on: February 16, 2012, 22:37:58 PM »
Hi, the IR2117 have arrived and I completed all the high current connections of the buck converter. Using a Zener diode as Vcc to power just the nand gate oscillator I was able to illuminate a LED with a quarter turn of the PMA. Not great results but it is a start.  I have to test the IR2117 with the oscilloscope to determine if HO is oscillating. I wired the test circuit and used a 12 volt halogen light as a test load and spun the PMA manually. The PMA was very easy to spin until the MOSFET turn on, then I was unable to spin the PMA. I believe the MOSFET is not turning off. My concerns are there is a lot energy stored in the input capacitor and I do not want to harm my oscilloscope. Are there any points I should avoid when testing the circuit?? The chassis ground and each channel ground are a the same common point, is there a safe method to use when testing the circuit with the scope? Comments welcome.

#### kam

• Hero Member
• Posts: 1849
##### Re: Buck converter for small wind turbine project
« Reply #7 on: February 16, 2012, 23:59:37 PM »
the energy in the capacitor has a certain voltage which will be delivered. The energy might be gigantic, but if the voltage is small, the current will be small as well - proportional to the resistance of the load. The oscilloscope itself has large input resistance, so if the voltage is small, the current will not harm the input. At 10x probe set you can probably measure directly the 220VAC (with mine this is possible), and the energy in the power lines compared to the capacitor is like the sea and a water-drop. No worries (again IF the voltage is small).

PS: I'm about to announce the openning of a new section in the site, in which everyone will be able to upload the worklog and present their project. Right now it is in the final stages of the Beta testing (the editor). Some people are testing with me the editor - you might have seen new posts from other people instead of me in the site. If you want to start a worklog page in my site, i can make you a beta account and start posting the worklog of this project.

#### Burnit0017

• Guest
##### Re: Buck converter for small wind turbine project
« Reply #8 on: February 17, 2012, 02:56:42 AM »
Hi, can other people input comments and help with suggestions? If so I would like to try it. Thank you.

#### kam

• Hero Member
• Posts: 1849
##### Re: Buck converter for small wind turbine project
« Reply #9 on: February 17, 2012, 17:24:37 PM »
it has the same outlook and functionality like the pages i've been posting the last 3 years. These are the posts from other users:

The Maximite Computer By Ron P
Bench power supply from pc's power supply By Pike
Homemade Soldering Station 2 (AVR) By Herctrap

These projects are already posted in the home page, but i know that they have new staff running in the background and more will be posted soon. Ron has also posted the High Res Cap Meter and curently i am preparing to post a new theory with LED driving and controlling methods. The editor is still in beta version, but it is running like this for some 2 months, so within this month (hopefully) i will announce it for people to make their own accounts and post their projects.

In the meanwhile, i can make you a beta account to run the editor if you want.

#### Burnit0017

• Guest
##### Re: Buck converter for small wind turbine project
« Reply #10 on: February 19, 2012, 06:33:38 AM »
http://www.fairchildsemi.com/an/AN/AN-6076.pdf

A more complete application  data sheet covering the boot strap circuit.

Hi, photo shows input timing signal from 555 timer and output (HO) of  IR2117. The MOSFET is not connected.  I had to connect Vs to ground. Duty cycle is a little greater then 50%.

The application notes says that the logic ground and power ground should not be connected but their diagram shows they are connected, I find this very confusing. I am not sure where to generate Vcc? Comments welcome.

#### Burnit0017

• Guest
##### Re: Buck converter for small wind turbine project
« Reply #11 on: February 19, 2012, 16:01:57 PM »
Hi, I may have found a solution to provide an isolated Vcc. I may not sure if it work, comments welcome. I will post results when available.

#### kam

• Hero Member
• Posts: 1849
##### Re: Buck converter for small wind turbine project
« Reply #12 on: February 20, 2012, 16:30:26 PM »
i know what you mean, and many times this is a problem with electronics. But a decoupling LC filter will work for you. In the last schematic you posted for example, an inductor between the two capacitors will do a great job, many times better than the filter you posted.

#### Burnit0017

• Guest
##### Re: Buck converter for small wind turbine project
« Reply #13 on: February 20, 2012, 18:40:53 PM »

Hi, I reviewed the operation requirements for the IR2117 and I found two main mistakes that I have made. Vcc of the 555 timer and VDR of the IR2117 have to be different values.  The other mistake I found is all the grounds have to be referenced to the negative side of the load. This is a first attempt and I apologize for posting misleading information.
I am making the corrections and I will post results when available.

http://www.usna.edu/EE/ee320/Supplements/dcdc5_driver.pdf

http://web.mit.edu/6.131/www/datasheets/float_drive.pdf

#### roneeron

• Guest
##### Re: Buck converter for small wind turbine project
« Reply #14 on: February 26, 2012, 05:14:12 AM »

Hi, I reviewed the operation requirements for the IR2117  snip

I had nothing but problems with the IR2117. What I found as a superior replacement was the MIC5014. This is a very robust chip and no external charge pump components needed. It will work on the same VDD as the 555.

http://www.micrel.com/page.do?page=/product-info/products/mic5014.shtml

Ron P