The power available from wind goes as the cube of the wind speed. This makes it a lot harder to get useful charging in a light wind.
[... snip about voltage multipliers ...]A voltage multiplier will boost the voltage but I think there are better ways to go. A simple flyback booster will boost by a variable amount. In the wind generator case, things are fairly easy for the flyback design. The MOSFET doesn't have to handle a large amount of power.
At low wind speeds, the input voltage to the booster is low. At low wind speeds, the torque is also low so the current you want to take is low as well. This means that the MOSFET only needs to pass a lowish current when it is on.
At higher wind speeds, the voltage is high. The torque and hence the current is also high. In this case, the MOSFETs on time will be short making the power in the MOSFET low.
At very high wind speeds, the boosting isn't needed at all so the MOSFET never turns on.
If you wind your own inductor, you can go a little light on the core. It doesn't matter if the core saturates in the high wind case because the MOSFET isn't going to turn on.
Chances are a very simple controller will do what you want. I suggest a home brew one that does this:
If the drain on the MOSFET is at a lower voltage than the battery, trigger a one shot.
The one shoot turns on the MOSFET for a fixed time in most cases.
A safety circuit consisting of an NPN and a resistor in the source of the MOSFET forces this first one shot to reset if the current goes too high. This circuit only acts in a fault case.
A second oneshot enforces a short delay after the first oneshot. During this delay, the first oneshot is prevented from firing.
This second oneshot prevents the first from firing again during the time it takes to gat the MOSFET actually turned off. It also helps in the very light wind case where the logic given above would turn the MOSFET on for too great of a duty cycle.