What you've built here is a rudimentary boost converter, using the motor inductance as your inductor, and your battery as your output capacitance. The next step up here is to build a controllable device that can implement maximum power point tracking; a buck-boost power topology might be what you're looking for here. Note that MPPT on a wind turbine is more difficult than, say solar, because the rotor speed is another state variable to consider. A naive/greedy algorithm might apply maximum torque to the rotor to extract maximum power for a moment, but this strategy will try to stall the rotor. As power is torque * angular velocity, both terms require consideration.