I should do this with a AVR microcontroller circuit
The motor speed will follow frequency pretty close- slippage that is related to load You have to vary voltage directly to frequency or it will use too much current at low speeds and won't have torque at higher speeds. Variable frequency drives do this automatically, that is why they cost so much.
You may buy 1 Phase Frequency Inverter. Will work well with your motor.
Using one of the 16 bit timers/counters, TCNT1 or TCNT3. If you put it into Fast PWM mode it's really easy to do.
