Wind turbine boost converter

       We have a small off grid system at home and I had just completed building a small wind turbine a few months ago. It has generated a bit of power but not as much as the PV panels.

       In our location, we do get the occasional strong winds. But most of the time, it is a gentle breeze. This is enough to spin the turbine but not enough to reach cutin speed so the turbine is mostly doing nothing but spin.

       The boost circuit described here allows me to get a bit of power even when the turbine is spinning at a good RPM but is still well below cutin speed. It works by running a boost converter so we can get an output (albeit only a few watts) even at very low winds. A few watts doesn't sound much but if the turbine spends a lot of time below cutin speed, it still adds up. And with a small off grid system, every bit of power counts!

Complete schematic.

Click here for full resolution.

       The circuit is simple. Two comparators (LM393) are used so that the oscillator works in a predetermined voltage window of the generator output. The oscillator (LM555) is wired as an astable multivibrator acting as a fixed modulation oscillator. This then drives the output stage of a boost converter. No regulation is needed as the battery bank will keep the voltage to the correct level. The inductor is critical, I used an output inductor from a CFL ballast. It has a rather high DC resistance which limits the current drawn at high input voltages. This allows the wind turbine to transition from charging through the boost converter to going direct drive via an external blocking diode.

       In the prototype, the oscillator will run at 55kHz when the voltage of the wind turbine generator is between 5.8V to 11.8V with a battery voltage of 12V. Do note that the threshold voltages will change with different battery voltages. This was done intentionally to minimize the voltage difference between the point where the oscillator stops running and the generator blocking diode (not shown) starts to conduct. The blocking diode is usually connected between the generator and battery. Anode at generator +, cathode at battery +.

       In the schematic, Pad1 is the generator + output, Pad2 is generator and battery negative tied together. Pad3 is the battery + terminal. DO NOT run the circuit without a load/battery connected. The output voltage will reach a high value and will result to an exploding output capacitor!!!

Views of the completed module. Control circuitry on top perf board.

Power circuitry on bottom perf board.

Scavenged inductor from electronic CFL ballast.

Test rig.

Module on panavise and clipped to the system.

       I tried making another inductor (smaller, low profile) but it did not have the right characteristics. I presume that the circuit requires high inductance and a bit of series DC resistance. With the scavenged inductor, at about 6V input, the oscillator starts running and we get about 200mA going into the battery. At around 10V, it gets to about 750mA.
With my self wound inductor, the low DC resistance resulted to the circuit pulling so much current from the generator even at only around 8V which resulted to the turbine not speeding up so that the circuit could cut off and the blocking diode start to conduct.

Page created and copyright R.Quan ©02 Dec 2014.