VFD as a LED light dimmer 4

[goldeneagle272]

Hello All,

Does anyone has any experience using a VFD as a light dimmer? I am a recent graduate and I have just started working at this company not too long ago, my boss wants me to take a ATV12H018M2 (240V Single Phase) and use it as a dimmer. I know there are triac, sine and IGBT dimmers out there in the market but they seem to be either incompatible or expensive.
Anyhow, I have read the manual and since it is meant to be for a motor I don't understand what configuration menu to use for my purpose. I have so many questions. Firstly, I would like to know about the drive outputs u,v,w and GND. How do I connect a 3 wire lamp to these outputs? U-Hot, V or W-Neutral and GND - Ground wire?
Secondly, if I connect drive output to a oscilloscope would I be able to see a PWM signal? I have so many more but I want to start with these two first. I think what he would like me to do is control when it fires or crosses zero. I'm so clueless and the manual seems to be not so helpful either. I would really appreciate if someone could guide me through this. Attached please find the user manual for the VFD I have been using.

Thanks,
GoldenEagle

 

[goldeneagle272]

Is there a relationship between i/p and o/p voltage of a VFD? With the one I have got, for 230V input (single phase), the o/p voltage (three phase) across a line(any) to GND is around 160Vrms where as the voltage between lines is only 20-30Vrms. Is this how it is suppose work (I guess not from Gunnar's post above) so do you guys think my VFD acting up? I have used multimeter for testing.

Thanks

 

[Skogsgurra]

Sorry. Didn't get the time. Turbine explosion nearby got in my way. Will be back later with some measurements.

In the meantime, make sure you understand the difference between RMS voltage, fundamental component and total voltage (including all harmonics). With a good multimeter, you will read all components in the output voltage while the voltage you set via the input setpoint is RMS of fundamental voltage.

And don't forget that it is between lines on the output of the VFD that you shall measure. Not fom line to GND. That was described in an earlier post.

Finally, not so sure that your LED reacts to RMS. Could just as well be AVG. Also, if your LED "ballast" is anything else than a resistor, you may be in for some surprises.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[itsmoked]

Gunnar. The RMS should definitely change with (speed)frequency adjust. I was under the impression goldeneagle272 was talking about the modulation frequency. The "8KHz" mentioned above. Re-reading I could go either way.

goldeneagle272 What exactly are you using for "lights"? Got a link?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[roydm]

If I am not mistaken the VFD will rectify the line Voltage and charge the DC link capacitor to the peak value.
As soon as it starts it will turn on a pair of transistors to apply the full capacitor directly across the load.
For the brief instant in time while the transistors are on I would expect the LED to be very bright.

One way of making LEDs more appear brighter to the human eye is to pulse them at high power/high frequency, the eye is fooled into seeing it as though it was on all the time just as the image on a TV appears to be there when in fact its flickering off and on.
Another example is a movie screen for the split second while one picture is changed for the next the screen is blacked right out by the rotating shutter, your eye can't see that but will notice wheels that appear to rotate backwards.
I thing the numbers in a calculator (I'm talking about the old LED or discharge tube displays) are also flashed in sequence too fast for your eye to see.

 

[LionelHutz]

Details on this LED ligtht would help. If you're applying the VFD output to a rectifier inside this LED light then the DC after the rectifier will be the peak of the PWM modulated output of the VFD. The VFD may be PWM modulating an equivalent 0-60Hz RMS output voltage, but the peak voltage of the VFD output PWM waveform never changes.

 

[goldeneagle272]

Here is the Link

I cannot share more about it since this technology is patent pending, all we use is a current sink (MOSFET and sense resistor) to control each LED stage. LED stage consists of number of LEDs depending up on our requirement, voltage drop and i/p voltage.

As in the frequency control I mentioned above it was just by using the jog dial, with the set output frequency 2kHz - 8kHz.

I was able to control the brightness a little, flickering at low frequency (again jog dial) to constant brightness at high frequency. But, with the restricted range (jog dial)I wasn't able to fully turn up the brightness, I used both 120V and 230V lamps.

 

[KllrWolf]

It looks to me like the frequency you were adjusting was the carrier frequency, not the equivalent line frequency. That would be why you were not getting any change in the output. It is the carrier frequency that also causes the hum you were hearing. Either you have to filter out the carrier frequency or get it above hearing (over 20KHz if I remember right.)

 

[goldeneagle272]

That might be it but I'm not so sure since the manual is not very clear about it. The carrier (switching) frequency range is 2kHz - 8kHz where as for line (or motor frequency) I have to choose either 50 or 60 Hz. So, When I setup the VFD, I have been entering the motor frequency as 60Hz(my lamp is compatible at this frequency).

This is an excerpt from the manual about the jog dial, "the jog dial on the HMI acts as a potentiometer to change the reference value up and down within the limits preset by other parameters (LSP or HSP)." LSP being low speed set at 0Hz and HSP high speed set at 400Hz(max). The adjustment range for a jog dial is 0-100%.

 

[Skogsgurra]

Are you kidding? The switching (carrier) frequency does not have much (next to nothing) to do with the output frequency. Forget about the kHz. You will need to filter the carrier out anyway.
The VFD output is a variable frequency and voltage going from zero Hz up to a few hundred Hz. Just as your excerpt says.

It is fine that your lamp is "compatible" with 60 Hz. Good, good. Sarcasm.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[roydm]

Thanks for the link
I'm still puzzled why you would want to use a VFD to
control LED brightness though.

 

[LionelHutz]

I have not seen a VFD for motor control where you can set the VFD so a pot controls the carrier frequency so I highly doubt that's what the pot was doing.

If you set the VFD for a motor rated frequency of 60Hz with a motor voltage of 240V then the pot should vary the PWM generated V/Hz output from 0V/0Hz to 240V/60Hz.

 

[Skogsgurra]

I got somewhat tired of seeing clueless guys trying to discuss simple matters on EngTips. We have a policy, after all, and that is to avoid hobbyists and hobbyist discussions. Unless there are good reasons not to. This is a compilation of measurements that I made recently. With comments.

http://www.gke.org/pub/files/VFD as a LED driver.pdf

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[LionelHutz]

At this point, you should likely do more reading and learning to understand exactly what's going on. I expect your boss wants you to show that you understand exactly why it won't work, not that you blindly tried some things and failed and then read on the internet that it doesn't work so you gave up.

What do they teach in engineering schools these days? You're doing it all backwards. The first step of this experiment is to investigate the LED SMPS to determine how it will you can dim the lamp. If you can dim the lamp, ou then have to determine if the VFD output will give the SMPS what it wants to be able to dim the lamp. If it's not compatible then determine if there is a way to make it compatible.


You have to learn to read too. The first 2 posts told you to connect between phases on the output of the VFD and that connecting to a SMPS was a dumb thing to do.

 

[SciZee]

Actually, I believe that circuitry goldeneagle272 is testing is linear, not SMPS. But I do agree, he has to learn to read... And Gunnar, thanks for for your insights.

 

[waross]

Thanks Gunnar. I liked that. lps

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

SciZee - it's described as a rectifier feeding some type of circuit which appears to be active. It might be some type of linear current regulator too though. At any rate, it's still described as having a rectifier first, which means the peak voltage from the PWM output gets to the circuit regardless of what lower frequency output the PWM is simulating.

I already posted what should work as the solution.