V/f Constant control for single phase induction motor?
The RMS value of the fundamental should be 220 volts at 50 Hz and 4.4 V/Hz for operation below 50 Hz. With V/f control of 3-phase motors, the V/f is "boosted" above the constant value at frequencies below 10 Hz or so to prevent reduced torque capability at low frequencies. The boost is needed because the voltage drop in the winding becomes more significant as the frequency is reduced. With a single-phase motor, there is not much that can be done about reduced torque capability at low frequencies because it is mostly due to reduced current and/or reduced phase shift in the auxiliary winding current. The motor will only be suitable to drive a fan or centrifugal pump. It will not have enough torque to drive a load that requires very much torque to start or operate at a low speed.

The motor needs to be a shaded-pole or permanent-split-capacitor (PSC) type motor. A capacitor-start motor will not tolerate continuous current in the auxiliary winding circuit.

The PWM scheme should be designed to minimize the lower order harmonics. The modulation needs to provide constant V/Hz of the fundamental component. Perhaps another answer will provide more detail on that or you can find detailed information at a more tutorial type of web site.


  i boosted voltage upto 380V for Inverter.


If that is the DC input voltage to the inverter section, that seems adequate.


  otherwise i have to use (1.414*220/50)=6.2


No. The V/Hz is based on RMS voltage, not peak.