Author Topic: Buck converter for small wind turbine project  (Read 51191 times)

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joestue

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Re: Buck converter for small wind turbine project
« Reply #66 on: March 19, 2012, 12:22:44 AM »
the problem isn't that your circuit is built wrong, but that between every node you have an inductor formed by the wires you've used to connect everything together.

As you discovered earlier, the boot strap capacitor won't get charged if there isn't anything to pull the mosfet down to ground.
this will occur when you connect a battery across the output, if the capacitor gets depleted then you can't turn the mosfet on.
this is another reason why you should use a half bridge design, also known as a synchronous buck.
of course, you can connect a resistor and diode to the highside power supply, and place a 12volt zenar across the cap. but that's just one more milliamp of wasted power.
the zenar is needed of course to prevent overvoltage.

as far as what the bootstrap is referenced to, do a Google image search for 'highside bootstrap' and read the datasheet for the driver you have.
there should be no confusion about how to hook the circuit up.
« Last Edit: March 19, 2012, 12:26:05 AM by joestue »
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GoVertical

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Re: Buck converter for small wind turbine project
« Reply #67 on: March 19, 2012, 06:13:31 AM »
Hi, I found a article that covers design trade off for switch mode battery charger. It will a few days to review the material. I will post results when available.

http://www.ti.com/lit/ml/slyp089/slyp089.pdf
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GoVertical

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Re: Buck converter for small wind turbine project
« Reply #68 on: March 20, 2012, 05:34:42 PM »
Hi, new test circuit based of information received and suggestions. Basically it is the same circuit as before with a blocking diode added at the plus battery terminal and a voltage pump for the bootstrap capacitor. Vg - Vs > Vthreshold , 20 - 12 = 8volts.
If it works the mosfet's can be paralleled and the control circuits can be duplicated for increased current output.
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GoVertical

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Re: Buck converter for small wind turbine project
« Reply #69 on: March 23, 2012, 06:30:40 AM »
Hi, I was able to find all the needed parts to make all the required connections to interface the circuit to a 12 volt battery. I am using to bench power supplies, one to power IC's and the other for Vin.

I had just a LED and 22kohm resistor from the mosfet Vs to ground and the mosfet was turning on and off.

With a capacitor at the output of the circuit no current would flow into the battery.  I removed the capacitor and I was able to measure 0.14 amps flowing into the battery.

I had attached a variable resistor to the 555 to be able to test different duty cycle, I adjusted the variable resistor to low and the 555 fried, so I have to purchase some replacements before I can continue testing. I will post more test results after I replace the 555. 
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GoVertical

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Re: Buck converter for small wind turbine project
« Reply #70 on: April 03, 2012, 12:30:00 AM »
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:
http://www.youtube.com/watch?v=3H5DQQ-dYfI&feature=youtu.be


The circuit using the IR2117 only triggers the mosfet when the PMA provides a input voltage.
Video using IR2117, bottom waveform is mosfet Vs:
http://www.youtube.com/watch?v=B3dLzZZ5jKQ&feature=relmfu
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GoVertical

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Re: Buck converter for small wind turbine project
« Reply #71 on: April 07, 2012, 09:14:33 PM »
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.
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GoVertical

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Re: Buck converter for small wind turbine project
« Reply #72 on: April 22, 2012, 04:02:59 PM »
Hi, I am posting all projects updates in the diary section. Thank you for all the help I received.
http://www.fieldlines.com/index.php/topic,143852.msg1005048.html#new
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