Difference between VVF and VFD

[Fatima Ali]

What is the difference between VFD and VVVF drive used for controlling the speed of Induction motors ?
While studying about different speed drives ,i came across these two terms . One of the two is Variable frequency Drive ( VFD) and the other is Variable Voltage ,Variable Frequency ( VVVF) .
Are they two terminologies for a single concept or two different concepts ?

 

[FvM]

I don't believe that VVVF is a commonly used technical term. But by nature of the motor characteristic, a VFD must have a variable voltage. In so far, VVVF is an unusual synonym for VFD. VFDs can implement different f/V characteristics, linear characteristic is mostly used for standard applications.

 

[Fatima Ali]

dear Fvm ,do you know how can i vary the frequency and voltage of inverter output using a microcontroller ?

 

[chuckey]

Most VFDs have analogue inputs for their remote control panel, just simulate these voltages. i.e. speed 0 -100% = 0 ->10V, set by a pot on the remote control panel, just feed in the voltage instead of the pot derived voltage. As has been said the output "voltage" follows the frequency. You would have to extensively modify a VFD to make it change the voltage without changing its frequency.
Frank

 

[Fatima Ali]

How can i change the frequency of the output of inverter using pwm in microcontroller ? Since VFd is frequency changer than how can pwm changes output signal's frequency using pwm ??Kindly tell me its concept ??
Frank[/QUOTE]

 

[chuckey]

see :- https://en.wikipedia.org/wiki/Pulse-width_modulation
Frank

 

[kappa_am]

you have to pay attention that in field weakening area (reference speed beyond nominal speed) you are just allotted to increase frequency so you haven,t constant V/f. I am not sure but I think VFD is controlling an IM by VVVF beyond its nominal speed. however, generally I'm in FvM side
and about microcontroller, implement a sinusoidal wave using lookup table and pick-up value using a prescaled timer and generated interrupt. prescalling is depend on your points on sine wave and desired frequency.

Good luck

 

[FvM]

Field weakening is of course an option for VFD operation. I don't see why we would use a different name for the device related to this operation mode, at least it's not a common technical term.

Regarding the questions in post #3 and #5, it's not clear to me if the OP is asking about designing a VFD or controlling an existing VFD through a communication channel. The available variants of motor operation are basically the same but the method is different. I presume that the operation of industry standard VFD can be widely parameterized, e.g. for the applied V/f characteristic.