High power buck-boost DC/DC converter for wind generator

[ahto]

Hello All!

I am new here. I know some basics about electronics but it was quite long time ago I made something by myself. At the moment I am interested in small scale wind power. I have built a "small" wind generator where I used permanent magnet DC servo motor as generator. The generator puts out 0..100V and maximum power is about 1 kW.
I would like to know is it visible  to build buck-boost  converter which turns input voltage 5-100V into usable voltage for 12V battery bank loading (about 15-18V)? Any ideas? 

[trippedbreaker]

Hi, I'm new here as well, and an electronics newbie with a little microcontroller background (Atmel AVR) trying to dabble in power electronics.  I don't know how helpful this is, but I'll respond since no one else has. I've got a project that's similar to yours, in that it will require a buck/boost converter.  I've found this document helpful as an introduction:

http://www.jaycar.com.au/images_uploaded/dcdcconv.pdf

The Cuk converter circuit seems especially interesting; like the standard buck/boost circuit it boosts at duty cycle > 0.5, and bucks at < 0.5.  But, it has low ripple inherently, which might be better for your battery (?)

[ante]

Hi ahto & trippedbraker!

Welcome to our forum both of you! ;)

Ahto: Are you sure you want only a 12 Volts battery bank for this? The losses will be big and the current at 1kW will be hard to handle. For what purpose is the 12 Volt battery bank? If you use it to produce 120 or 230 VAC later you could save some energy by using a higher Voltage battery bank.

[ahto]

Hi Ante!
Why 12V. First of all I have allready two 1,4 kW continues (2,8 kW surge)/12V-220V/50Hz modified sine-wave inverters. Second to get some power from wind turbine in low winds (4-5 m/s I can get littlebit over battery bank charching voltage) I have to have as low battery bank voltage as possible.

But I am open to other ideas as well. If you say that it is relativelly easy to build an inverter 3 kW(6 kW surge)/96V....-220V/50 Hz and boost converter I will choose this way.

[ante]

Hi ahto,

About the 12VDC to 220V50Hz inverters: No I will not say that inverters are easy to build, because they are not! At least not in the power range you require. My personal opinion on inverters is that when exceeding 500W you should purchase the inverter. There are no nasty surprises here you get a tested inverter and you get a warranty, also if you search for one you will find nicely prized inverters.
And for the 0 – 100V to 15 – 18V converter, well that just doesn’t exist in my book I am sorry to say. I guess you have to settle for wind speeds which produce enough voltage to charge the batterys. I don’t know (this might be a long shot) if it is possible to add exiter coils to the PM motor to make it put out more voltage at a lower rpm. Perhaps the limitations are in the rotor and not in the field magnets. :P

[awright]

Hi ahto:  You are lucky if you are in a wind regime providing useable winds and have space to put up a turbine.  I'm jealous.

The altermative energy industry has devices called, "Maximum Power Point Tracking Converters," that may help you out.  I don't claim any particular knowledge of their internal design, but the main purpose is to maximize the amound of energy extracted from a wind turbine or solar array so that the maximum amount of water is pumped using an electrical well pump.  If you get Home Power Magazine (and you should, if you are building a wind turbine), you can probably find suppliers in their ads.  You can get all back issues on CDs.

As you probably know, the power curve for a wind turbine generator at any arbitrary wind velocity or solar array at any arbitrary insolation starts at zero useful power for zero volts out (a short circuit that would probably burn out your generator) to maximum power in the mid range of voltage and current to zero power again at open circuit/maximum voltage.  The peak power output point varies over voltage and current as wind velocity or insolation varies.  The MPPT device is supposed to track that point and adjust the current demand to extract the largest amount of total energy over time.  I do not know how it is done internally, but if you find out, let us know.

So, my answer is yes, it is definitely possible, but, regrettably, no, i don't know how.

As an aside, I just received the current online issue of the AWEA Newsletter (American Wind Energy Association) and it had an article analyzing the cost/benefit tradoff with increased tower height.  The incremental benefit relative to cost for increased tower height is HUGE!  So, whatever else you do, invest in the tallest feasible tower for your site.  (The AWEA is a good group also, and while it is largely for the wind industry, each newsletter has a "Small Turbines" article of interest to individuals and home power entheusiasts.  You might want to join them, also.)

Please keep us posted on your progress!

awright