Limiting the speed of an induction generator
You can control the turbine by controlling the electrical load on the generator if you have a system that can receive power from the turbine generator and deliver power to the load at any required rate. That type of system is used for existing wind-turbine induction generators. With a grid-tie inverter, there is no limit to the level of power that can be delivered to the grid. With an off-grid system, a dump load dissipates power in excess of the power required for loads.

To deliver power to a grid, a grid-tie inverter is required. For isolated loads, the induction-generator output can be rectified and furnished to the load through a DC regulator or converter. AC power could be delivered through an inverter that is not grid-tie capable.

Limits to the braking torque available would be mostly related to induction-generator, controller and dump load sizing. For something like a wind turbine, auxiliary mechanical systems may be required to "feather the prop" or bypass fluid flow.