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What is the output voltage of a 3 phase VFD?

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abc_de

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What is output voltage of 3 phase vfd

Hello

I have question regarding VFD. What is output voltage of 3 phase vfd (input 400v).
And what is out voltage for single phase 220v to single phase vfd for PSC motor.

In 3 phase vfd phase angle difference between each phase is 120 degree and in case of single phase vfd for Psc Is 90drgree from each phase.
Thanks
 

Re: What is output voltage of 3 phase vfd

Maximum output voltage of regular 3-phase inverter is equal to input voltage.

I'm not aware of any industrial inverter designed for PSC motor operation. If you design it however, you have to consider the possible different voltage range of capacitor winding. For 90 degree phase and symmetrical output, the available voltage is only 155 volt with 220 volt input.
 
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Re: What is output voltage of 3 phase vfd

I am working on it for running 3ph induction motor input voltage 220v
For 1ph to 3ph my maximum output voltage is 187vac phase to phase i.e 325/√3 my i was expecting 220v.

For psc Motor where phase difference is 90degree my out put voltage U (0degree) V(180degree) W(90degree)
Voltage between U-V=200v
V-W=145v
U-W=145v

Is it right any suggestion
How phase difference casue of voltage difference
 

Re: What is output voltage of 3 phase vfd

For 1ph to 3ph my maximum output voltage is 187vac phase to phase i.e 325/√3 my i was expecting 220v.

Wrong modulation method. This happens if you output only a three phase sine voltage. You need to superimpose a zero sequence (common mode) component to get maximal output voltage with the available DC bus voltage. It's done in any industrial VFD.
 
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Re: What is output voltage of 3 phase vfd

thats good to read. but i do not know about that modulation technique.
can you support me how i can implement it. so that i can utilize maximum dc bus
 

Re: What is output voltage of 3 phase vfd


Code C - [expand]
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int uvw[3];
int a_uvw[3];
int sym;
 
for (i=0;i<3;i++)
  a_uvw[i] = abs(uvw[i]);
if (a_uvw[1] > a_uvw[2])
  if (a_uvw[2] > a_uvw[3])
    symm = uvw[3];
  else
    symm = uvw[2];
else if (a_uvw[1] > a_uvw[3])
    symm = uvw[3];
else
    symm = uvw[1];
symm = symm/2;
for (i=0;i<3;i++)
  uvw[i] += symm;

 

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Re: What is output voltage of 3 phase vfd

i understand little about code but still unable to implement. can you elaborate more
 

Re: What is output voltage of 3 phase vfd

On input, uvw is the three phase sine voltage vector. It's modified by a zero sequence which is half of the smallest instantaneous value to get a centered sine space vector.

centered.PNG
 
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Re: What is output voltage of 3 phase vfd

I think this modulation technique is space vector right.
I am following v/f spwm technique.
What will be output voltage for 220vac.
 

Re: What is output voltage of 3 phase vfd

That makes no difference.
 
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Re: What is output voltage of 3 phase vfd

seems useful still i am to able to understand. i will try and repost

- - - Updated - - -

zero sequence >> what about amplitude of it. i mean modulation index ?
 

Re: What is output voltage of 3 phase vfd

In the narrower sense, space vector modulation is a specific method to generate the three phase voltage system required by an AC motor. More generally, any multi phase sine modulation method creates a space vector.


Forget about terms and just look at the waveform. As stated, it's necessary to superimpose a common mode voltage to the three sine voltages to get maximal voltage swing. That's possible because the phase voltages have their maximum at different times.
 
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Re: What is output voltage of 3 phase vfd

Here's the resulting three phase waveform

balanced sine.PNG
 
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Re: What is output voltage of 3 phase vfd

I worked on it and get some theoretical results. But i have not checked it on hardware anothercenter.png

- - - Updated - - -

centertapped.png

Here is modulation index is .86+.14
 

Re: What is output voltage of 3 phase vfd

There different possible common mode signals with threefold frequency. The shown sine signal should be fine. Strictly viewn, the maxima of the modified output should be at the zeros of the common mode signal. If the modified signal is further increasing, you are loosing output swing. May be a few volts in your diagram.
 
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Re: What is output voltage of 3 phase vfd

Ok...
It means my results are right. How many frequency folds are need for maximum output voltage
 

Re: What is output voltage of 3 phase vfd

I mean what frequency of zero sequence is needed to get maimum output volts.
 

Re: What is output voltage of 3 phase vfd

As designed in your (or my) example, threefold fundamental frequency.
 
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Re: What is output voltage of 3 phase vfd

ok i will check on my hardware within few days and reply. i hope it fulfill my requirement.
 

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