Inductor selection for VFD filter appplication
Inductor selection for VFD filter appplication
(OP)
Hi guys,
We had some problems with voltage reflections discussed in thread237-300370: VFD spikes in multiple motor installation
We had two cases, 7 fans in parallel for which we selected a commercial sinus+common mode filter, and just one fan, for which we don´t have the space for that filter and there is no commercial solution for such low power (about 0,7A 220V 60Hz).
For this latter case I did some tests with a compact custom-made LC filter, made with PCB components for power supplies.
After looking for some alternatives I have some doubts about the inductor ratings:
- About the PCB inductor used in prototype, I don´t see any info about voltage ratings in the datasheet, apart from being used for "power supply" applications ¿what do you think?. Current rating is 0,9A DC (AC no idea, but probably more).
- I checked some commercial 3phase inductors (2,5A minimun) and seems to be of two types, for "line" or "motor", but not any clue in the datasheets about the real difference between them.
I am a little worried about voltage and thermal ratings of PCB inductor, but can´t use a "big" 3phase inductor without modifying quite a lot the existing cabinet.
I adjoint info about the inductors and some waveforms of the working filter prototype (including voltage over inductor and current).
It gets a quite nice sinus (or sine
) at the output.
Good weekend
We had some problems with voltage reflections discussed in thread237-300370: VFD spikes in multiple motor installation
We had two cases, 7 fans in parallel for which we selected a commercial sinus+common mode filter, and just one fan, for which we don´t have the space for that filter and there is no commercial solution for such low power (about 0,7A 220V 60Hz).
For this latter case I did some tests with a compact custom-made LC filter, made with PCB components for power supplies.
After looking for some alternatives I have some doubts about the inductor ratings:
- About the PCB inductor used in prototype, I don´t see any info about voltage ratings in the datasheet, apart from being used for "power supply" applications ¿what do you think?. Current rating is 0,9A DC (AC no idea, but probably more).
- I checked some commercial 3phase inductors (2,5A minimun) and seems to be of two types, for "line" or "motor", but not any clue in the datasheets about the real difference between them.
I am a little worried about voltage and thermal ratings of PCB inductor, but can´t use a "big" 3phase inductor without modifying quite a lot the existing cabinet.
I adjoint info about the inductors and some waveforms of the working filter prototype (including voltage over inductor and current).
It gets a quite nice sinus (or sine
Good weekend





RE: Inductor selection for VFD filter appplication
Neil
RE: Inductor selection for VFD filter appplication
Switching is 18kHz, about capacitor it is used 1.5uF prolypopylene type rated for 850Vdc. Current is about 0,8A peak, 18KHz, and checking with rated load depending on cap losses in datasheet should be fine.
What it puzzled me a little was the quite clear parameters in the capacitors datasheet to select and size them, and the not-so-clear parameters for selecting the inductor in relation with voltage/Tª ratings.
About the 3phase motor side inductor, may be the switching freq. rating related specially with thermal capacity of the core?
Regards
RE: Inductor selection for VFD filter appplication
Neil
RE: Inductor selection for VFD filter appplication
RE: Inductor selection for VFD filter appplication
RE: Inductor selection for VFD filter appplication
VFD can be configured in 18,12,6 and 3 kHz pole switching freq.
Line voltage really is that freq.x2 so inductors are working with 36,24,12,6 kHz pulses.
If freq. is low, current consumption by the filter itself rises (L impedance reduction is stronger that C increase) and the VFD trips at start if set up with 3kHz. I am not very confident in permanent mode with 6kHz, so probably the safer point would be at least 12kHz (24kHz pulses line to line).
I got confirmation by Murata that the PCB inductor used is not suitable for that voltage levels, due to realibility issues with voltage stress over the first coil turns (however there is no problem with frequency, I think that they use insulated powder iron core)
So I am quite lost now, I will let you know if advance in some way....
RE: Inductor selection for VFD filter appplication
Neil