Induction Generator

If you're referring to a grid connected asynchronous generator, the frequency and voltage are both controlled by the grid parameters.

An asynchronous generator cannot act alone, it requires external excitation and, in the case of a grid connected unit such as a wind generator or similar, that excitation comes from the grid, and that grid controls the frequency independent of the rpm of the rotor, the generator has no specific frequency other than that induced by the grid, and provided rotor speed remains greater than the synchronous speed, then it will self synchronise with the grid for both voltage and frequency.

The rotor must be driven at greater than synchronous speed for generation to occur. At synchronous speed no generation happens, and below synchronous speed the device would act like a motor and so disconnection from the grid is normally done in this circumstance.

The synchronous speed is a direct function of the grid frequency and, as the grid is a very much larger pond than the generator, load changes on the generator do not affect output frequency provided its rotor speed remains above synchronous speed.

For self excited induction generators (SEIGs or isolated induction generators), both frequency and voltage can be highly variable and dependent on rotor speed. In these cases an AC-DC-ACc link is normally provided to synchronise the output as required.

You are correct in being concerned with generator frequency which can be affected by rotor speed.

Normally wind generators have either a constant turbine speed control regulation system or the generated output voltage is input into a AC=> DC => AC voltage converter conditioning system that automatically regulates the frequency of the reconstituted waveform before it is output into the grid.

On units with speed regulation the fan blades have a variable pitch control that adjusts the angle of the blade to offset changes in wind speed and may also have additional mechanical braking circuitry.

The breaker that connects the generator to the grid is required to have over-under frequency, over-under voltage, over current, and anti-motoring protection circuitry that will disconnect the wind generator from the grid if the generator output is not within acceptable limits.

Hope this helps clear things up for you but you really need to put some time into researching the many options available on wind generators so that you can make sound informed decisions on the subject.

Is the AC-DC-AC link located on the tower or ground level

Induction generator or synchronous generator, the analogy is, imagine a group of people pulling a large weight, and those people are of different strengths, each has a governor telling them how fast the large weight is moving. Now one of them has a second wind and pulls harder, the result is that the others will see the weight moving faster and they will slow down putting more of the load on the one pulling harder, the system then remains synchronised.

the Frequency output is directly related to the RPM of the prime mover.

In the case of a power plant reducing the RPM of the gas turbine generator sets, they lowered the Hz output from 60Hz to 50Hz.

Their reasoning was, that during the summer (and this was a desert based power plant) that as everyone would have the A/C unit going full blast, a reduction in the Hz will reduce the load on the turbines.

The real effect was to reduce the output of the submersible pumps, that were designed to produce X number of barrels per day at 60Hz. Reducing the frequency, using the Laws of affinity, reduced the gross production per day of the whole oil field.

So yes the RPM of the prime mover has a direct effect of the output frequency, and the inverter used in wind turbines will be tied to the grid to maintain the correct output Hz to match the frequency of the gird. The output Hz will not change regardless of the rpm of the blade RPM.

Induction generator runs on the principle of induction motor with negative slip. It has to be fed from external supply and the frequency of power generated depends on supply frequency but not the RPM of motor