Speed Control of single phase AC induction motor - Possible options?

Hi all,

So I'm working on a project titled "Controlling the speed of a single phase induction motor".

Supply to motor is a 230V,50Hz single phaseAC.

While researching on the internet I came across this one circuit that proposes a model that uses A microcontroller and a triac circuit and a zero crossing detector circuit to "adjust the speed".

Now I also read elsewhere on this website that a single phase induction motor can only be controlled by changing it's frequency - voltage changes...

Speed Control of single phase AC induction motor - Possible options?