How to maintain a stable voltage on a Wind Turbine for Inverter
You first have to rectify your variable frequency AC to DC, then use an inverter which turns DC into the AC of the grid. There are inverters in the market which include the rectifier.

There is an alternative solution which involves a rotor-fed asynchronous machine. The idea is to feed the difference AC frequency to the rotor so the stator frequency keeps being in phase with the grid. That way, the inverter doesn't have to pass all the power the turbine delivers. It was somewhat popular 20 years ago, when big inverters had been incredibly expensive.