OkiePC
Lifetime Supporting Member
I am putting together a class for our technicians to teach them the basics of AC VFDs and stumbled on some conflicting information that surprised me and I am not sure it is accurate.
It 1st says variable voltage...then says constant voltage...then the picture shows what looks like 4 different voltages, 2 magnitudes on each side of the zero line.
Don't IGBT drives just do PWM with full bus voltage like an SCR drive? With a single voltage level that produces a sinusoidal current?
Thanks in advance, Paul...
EDIT: sorry about the cruddy pic, but you get the idea...
Today's inverters use IGBTs to switch the DC bus on and off at specific intervals. In doing so, the inverter actually creates a variable AC voltage and frequency output. As shown in Fig. 7, the output of the drive doesn't provide an exact replica of the AC input sine waveform. Instead, it provides voltage pulses that are at a constant magnitude.
It 1st says variable voltage...then says constant voltage...then the picture shows what looks like 4 different voltages, 2 magnitudes on each side of the zero line.
Don't IGBT drives just do PWM with full bus voltage like an SCR drive? With a single voltage level that produces a sinusoidal current?
Thanks in advance, Paul...
EDIT: sorry about the cruddy pic, but you get the idea...