View Full Version : Frequency converter for a small compressor

02-07-2013, 11:07 PM
I am trying to control a small compressor by an off-the-shelf standard Frequency Converter -FC- (which I heard that it is not advised, but I don't know why). And the compressor makes too much noise and FC draws too much current which I assume is a sign that something is teribly wrong.

Has anybody know why does a compressor work well with its own FC but not with a standard off-the-shelf FC? is it the carrier frequency? or something about not so smooth FC output ?

Cheers to all

04-07-2013, 08:14 PM
Hi unver
the main reason this is not advised to do is the lubrication system,
at low speed you will not have sufficent gas velocity to move the oil in the circuit,
i hope you are trying to control a 3 phase comp ,
all the new vrf systems have a special system for oil recovery and return, same goes for vfd screw comps that have protections and oil traps to ensure good lubrication ,
the magnetic comps like turbocor have no problem working with a vsd at any speed .
it is hard to understand what exactly you are trying to do ,what carrier comp and vsd are you reffering to?
good luck

05-07-2013, 06:02 AM
It has been done before and a simple trick to solve the oil problem is to go conservative on the minimum frequency and add a timer to do a ramp up to full speed every once in a while.

There's also the issue of the run capacitor not giving the proper phase shift at lower frequencies. The Shannon Liu quadrature drive algorithm also actively supplies the start winding to get around that problem, but I'm not aware of any VFD with that feature.