So I've been doing some research and so far I've found that squirrel cage induction generators, like in wind turbines for example, can be connected across the grid either with, or without back to back converters for power conditioning.

I've been reading that the SCIG doesn't need power electronics to deliver power at grid frequency, but most of the papers about modeling a SCIG include a back to back convertor between it and the Grid. So my question is, are there two types of connections for a SCIG one with and one without power electronics, and if so whats the advantage vs disadvantage of each?

 

The converters may be to prevent backdriving of the generator when the wind drops.
An induction generator becomes an induction motor if it's not driven above synchronous speed.
So if the wind is not sufficient to maintain that speed, it will start acting as a motor and draw power from the grid to try to maintain the propellor speed.

 

Alright Thank you.
Also any idea on why an induction generator can be connected across the grid directly?
What if the speed of the rotor goes above synchronous speed by a large margian, wouldn't that induce instability to the turbine's operation?
My guess is mechanical braking could be used, but having mechanical brakes engaged for such long times would be expensive and produce a lot of wear on the gearbox and drivetrain?

 

What if the speed of the rotor goes above synchronous speed by a large margian

It can't under normal circumstances.
The faster you attempt to drive the induction generator the more power it will put out, as the slip speed increases.
But at some point the generator will try to put out more power than it's rated and will burn out.

 

My guess is mechanical braking could be used, but having mechanical brakes engaged for such long times would be expensive and produce a lot of wear on the gearbox and drivetrain?

If you're talking full size wind power generators, they change the pitch of the blades as wind speed picks up, to control the prop speed, not brakes