About VVVFD

ya Of course I agreed & thanx for ur reply & valuable comment*............... there is also Step up Cycloconverters.....these converters provide thier output frequency greater than input frequency............. another thing i want to get clarify is "what is the necessity of using Rectifier & Inverter combination????????????" I want to know the basic funda behind that arrangement............... *Note: I had not used any kind of short forms in this thread............

The "necessity" comes from the fact that you cannot accomplish the necessary high speed switching of the transistors on AC; they can only do that with DC. But we do not transmit DC, we transmit AC. So you must rectify the AC source to DC, filter it, then re-create the variable voltage / variable frequency PWM waveform output to the motor.

Do you actually understand how a variable speed drive works? (It basically chops up the DC voltage and creates a three phase ac voltage).

Have a look on Wikipedia or the internet regarding basic VSD operation principles for more information.

Jack:

You are absolutely right in what you have said. There is, of course, another advantage of that type of system: you can provide three phase current from a single phase source with the VFD. And, the three phase current produced is very clean and reliable. Just an observation.