- Is your induction motor a split-phase asynchronous motor with a main windings and a starter windings?
- If it is a split-phase than is it a Capacitor start motor or Permanent-split capacitor motor?
Check the the differences here:http://en.wikipedia.org/wiki/AC_motor#Single-phase_induction_motor
- Sometimes 3 phase (3x230V) motors are used in single phase configuration, e.g. I know such a type of washing machine motor. It has 6 windings instead of 4.
1. Capacitor start motor is not suitable for changing the speed.
2. Permanent-split capacitor motor.
Phase control maybe works if you drive the starter winding serial with the capacitor directly from the mains and control the main windings only with a tirac. But is it not a proper solution only works with constant loads. The speed stability is very poor without feedback.
VFD works, but not directly. You have to remove the capacitor, and drive the main and starter windings with 90 degree difference. The voltage on the main windings has to be proportional with the speed (220V at nominal speed). The voltage on the starter windings has to be also proportional to the speed but higher with a factor about 1.2-1.4. (e.g: 1.3*220V at nominal speed.)
3. 3 phase motor in single phase configuration
It is the best with VFD. You just need to remove the capacitor, and use the 3 terminal as a 3 phase motor with standard VFD.
- What is the nominal speed of your motor. About 1440 1/min ?
Your desired speed is only a small fraction of the nominal. It means that the power of the motor will be also a small fraction of the nominal. (VFD can provide constant monument, in that case the power is proportional to the speed, in case of phase control it is even worse.)
You need also external cooling fan.
It is much better if you use gears, and drive the motor near to the nominal speed.
You get much higher monument and the power is also near to the nominal.