I am working on VDF for Sigle phase induction motor. I just want to compute the total voltage of single-phase induction motor that will need to create from DC link. I am not sure about the calculation. As we need SPWM based inverter for VFD of the Single induction motor. The input of the inverter is DC link voltage. how can I calculate the required voltage for DC link for Single phase induction motor? The voltage rating for induction motor is 220V,
The DC voltage is calculated for the maximum AC voltage you want the converter to output. For a single phase 220VAC the DC would be:
Vdc = sqrt(2) * Vac + x + y + z = 1.41 * 220 + x + y + z = 310.2V + x + y + z
x is the maximum voltage drop of all the components through which the current flows and
y should be added to ensure a low THD of the waveform due to the switching deadtimes and limitations of the controller. Here
z stands for the half voltage ripple of the DC link capacitor. I would let:
x = 10-15V y = 10% * 310 = 31V z = 10%/2 * (310+x+y) = 18V
So total DC voltage you need to get a nice and clean 220VAC sinewave would be:
Vdc = 310.2V + x + y + z= 380V DC.
Of course you should verify
z components for your design, but this is the basic route you should follow.
As another aside, how well did you vet this concept in the first place? There are many different types of single phase motors, only two of them are suitable for use on a VFD; Permanent Split Capacitor (PSC) type and Shaded Pole. Shaded Pole motors can also be controlled with simple voltage control, no need for the complexity of a VFD, so effectively you would only use a VFD is the motor was PSC type. Any other single phase motor type will result in failure of the motor, the VFD or both.
But to answer your question, AC V = DCV/1.41, so if you want 220VAC, the DC V must be at least 310V. But here again are some potential pitfalls. "220V" is not a standard motor design voltage, it is usually 230V, so the DC voltage would need to be 324V minimum. Since you will be doing SPWM, you are going to be in control of the output RMS voltage, so it's best to start out a little high on the DC bus; most VFDs run the DC bus at around 330V.