Hi,
As others have pointed out, you need a variable frequency drive to power the motor.
Luckily, if you have the same voltage input power available (at say 50 or 60Hz) you can get away with an H bridge drive with no output or input transformer. This would mean an input rectifier and filter, H bridge made from appropriate transistors, and a control circuit to allow variation of the voltage AND frequency simultaneously. To get the variable voltage you cut back the pattern to get lower voltages, and to get the frequency variation you simply vary the local oscillator frequency. The 'pattern' here is usually a pseudo sine pattern which doesnt bother the motor like a square wave might, although you may get away with a square wave where the full output is always a cut back pattern if i remember right it is set to cut the 3rd harmonic. All you do then is make this pulse shorter (PWM). If it doesnt work then you'll have to go to the more complex sine pattern. It will still be PWM but of a more complex nature.
If your input and output are not the same but the output is lower, then you can still do it that way. But if the output has to be higher than the input voltage, then you need a transformer on the input to step up the main power to a higher peak level before rectification.
I should caution you though this isnt a beginners project.