How does MPPT work?
 

How does an MPPT controller work? What I mean is, how does it figure out the maximum power point? Does it monitor voltage and amperage output from the generator and keep messing with the dc-dc input and output? Kinda curious if anyone understands the logic of these controllers.

I'm thinking about a project I have and would like to do something similar, but its more of a wind power project where I have an alternator so I can control the field strength to get a desired output. Obviously it'll have to compensate for different wind speeds, and maintain voltage high enough to charge the battery pack. I know traditional voltage regulators do this job, but I will be modifying things to work at higher voltages, so I'll either have to modify or recreate the voltage regulator.

MPPT uses a table that has volts vs amps. When the wind turbine reaches a specific voltage, it matches the amps in the table. So the table controls amps and volts going out. The volts and amps are then compaired to the battery voltage and amps and the state of charge.

Usually the turbine manufacturer will be able to give you the info you need to program the charge controller. You will probably need a large resistor to burn the excess power when your batteries are full. That will keep the turbine from over speeding.

If you are considering making your own you will need to input your own table. I've done this by testing the alternator. Spin the alternator to 10 rpm, record volts and amps then go to 20, 30,40, etc.

There are ways to control the output by controlling the input amps, but it's generally not done on small wind turbines.

There's much more to setting up a home made wind turbine than using solar.

A few websites specialize in this.
Anothpower.com
Otherpower.com
TheBackshed.com
WINDSUN.com (NAWS)

There are literally a bazillion ways to implement a wind MPPT controller. The main two factors to consider are raw generating capacity and type of generator. A permanent magnet generator is going to use a totally different controller than a multiphase alternator. A 300 watt generator needs a much smaller controller than a 1500 watt unit. A grid-connected rig needs a different output circuit than a rig that will charge a battery bank. The devil is in the details, so to speak.

Luckily, this is not brand new technology. There are lots of manufactured units on the market, as well as kits that can be purchased. The r&d work has been done, as well as reliability trials and experimentation/optimization. Regardless of whether you plan on a custom scratch build or assembling something out of key components, there is an abundance of information on the subject on the web. All you have to do is surf and read.

It's about matching the impedance. All a MPPT controller does is vary its effective input impedance to try to get the most power out. The correct algorithm depends on the characteristics of the source.

For my senior design project, I actually tried implementing MPPT for a stationary bicycle generator. I managed to get it to where it worked pretty well when I used it, but goes unstable when my classmates tried to use it. Probably because the MPPT algorithm was expecting the peak in the "low RPM, high torque" region when (for example) Sarah is more like "high RPM, low torque"...