Variable Voltage Variable Frequency Drive (VVVF)

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abdullahab4

Joined Jan 24, 2018
6
Hello everyone, I am trying to design a three phase VVVF as shown in the schematic attached.
I am using a PWM signal as an input to the gate drivers.

I am struggling to understand how to control the output current/voltage by altering the the input PWM signal. What exactly do I change in the PWM signal to control the output (because it contains varying duty cycles to resemble a sine wave, hence I can't easily change each one of them). What I know is that to control the output frequency, we need to alter the input carrier sawtooth frequency that generates the PWM (not sure if thats correct). But I have no idea how to control the ouput voltage.
Please excuse me for this, but I am a beginner in this.
 

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shortbus

Joined Sep 30, 2009
8,869
Hello everyone, I am trying to design a three phase VVVF as shown in the schematic attached.
I am using a PWM signal as an input to the gate drivers.
Don't they use a higher frequency (carrier wave) sine wave and a comparator circuit to generate the PWM? Used to be a report on the web describing it, but couldn't find it just now.
 

Reloadron

Joined Jan 15, 2015
6,123
Don't they use a higher frequency (carrier wave) sine wave and a comparator circuit to generate the PWM? Used to be a report on the web describing it, but couldn't find it just now.
I have seen it done where a square wave is fed to an integrator resulting in a triangle wave and the triangle wave into a comparator. You set Vref into the comparator resulting in a PWM signal out.

Ron
 
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