Buzzing noise after VFD conversion

[rabler]

@7milesup I also have a Teco L510, and mine is very quiet. One setting that can make more noise is an incorrectly set amperage value. My motors are 6.3 amps, and when I originally set them to 6 mine buzzed as well. I set mine to 6.9 it all went away.

I'd guess more amperage would change the PWM output. Makes me wonder if tuning the DC voltage level could also have some impact that might reduce the noise at the lower amperage setting. Purely academic curiosity here.

 

[woodchucker]

A motor can/will generate noise(s) due to a VFD. I fly large electric RC airplanes and helis and the motors will generate different noises based on the settings. In fact, the "beeps" that comes from the motors during setup and every time you plug the batteries in are coming from the motor, not the VFD (or ESC in that case).

oh, I agree with you. I think mksj either missed that, or was discounting it. I worry that it might not be good for the motor if it vibrates the windings. electro magnetics cause wire fluctuations.. some motors can handle it, some cannot.

 

[7milesup]

Ok, here are 3 videos. I will be curious if you can hear anything at all. When I was doing this my middle daughter came out to the shop to see what was going on. When I turned the mill on she made this face of "what the heck is that!?" She said that the buzzing was very apparent. Unfortunately, my tinnitus has been really bad lately, due to stress. If I am sick or stressed out my hearing issues become prominent.

 

[mksj]

I did indicate that the VFD noise is from the motor. The motor VFD whine is normal in the last video, although a bit louder than I would expect at 16 kHz. If it doesn't bother you, I wouldn't run out and replace the VFD. As I mentioned, higher end VFD's may use different PWM algorithms and/or variable frequencies.

Reducing Audible Noise in VFD Applications

This article gives an overview of audible noise in VFD Applications and provides 4 steps on how to reduce audible noise in the system.

www.kebamerica.com

 

[stupoty]

Is the whine changing in pitch to match the carrier frequency? Especially with an off brand VFD, I'm just wondering if you have something like a bad output transistor that is causing the VFD to ouput a messier signal than it should. If you are, male, over 50 and have tinnitus, I'd be really surprised if you could hear 16kHz. I guess it may be a lower frequency resonance in the motor.

You could be hearing a harmonic of the frequency, as @tq60 said the windings are probably resonating with the carrier frequency.

Stu

 

[7milesup]

So is 16kHz the maximum on most (or all) VFD's? I am now understanding that there is a balance between carrier frequency, noise and possible longevity of the motor.

 

[Dabbler]

The higher the PWM frequency, the more energy is dissipated in the IGBT modules. Never too much of a problem, though. You need to pick a frequency that minimizes that whine, not just for esthetic reasons. as @woodchucker is suggesting, it can be a little harder on the windings to vibrate them at these frequencies.

A reactive output filter (a torroid inductor) on each of the phases can help to minimize these sounds/vibrations. You choose the size based on the running current and maximum current. For Teco L510 I go to Westing house ans specify that my max running amps is 7, and that my typical in use amperage is about 3, and they specified my inductors for me. worked fine.

 

[macardoso]

So is 16kHz the maximum on most (or all) VFD's? I am now understanding that there is a balance between carrier frequency, noise and possible longevity of the motor.

The carrier frequency primarily only affects heating. This is because the IGBT's (transistor outputs from the drive) have extremely low resistance when fully turned ON, but have some significant resistance as they momentarily switch from ON/OFF. Each time the transistor switches, a small pulse of extra heat is dissipated. The more times the transistors switch per second (the carrier frequency) the more heat is generated in the drive output.

A similar phenomenon occurs at the motor due to eddy current breakdown losses, but it plays a lesser effect.

 

[rabler]

You could be hearing a harmonic of the frequency, as @tq60 said the windings are probably resonating with the carrier frequency.

Stu

I believe technically a harmonic is a higher frequency component. Not sure what you'd call a lower frequency, a sub-harmonic? (lol). But that's what I was pointing toward with a "lower frequency resonance".

 

[7milesup]

A reactive output filter (a torroid inductor) on each of the phases can help to minimize these sounds/vibrations. You choose the size based on the running current and maximum current. For Teco L510 I go to Westing house ans specify that my max running amps is 7, and that my typical in use amperage is about 3, and they specified my inductors for me.

Wow, those puppies are expensive.

Edit: Well, they can be expensive but found some for a reasonable price.

RL-01201

3HP, 3% IMP

www.wolfautomation.com

KDRAA28L2

www.wolfautomation.com

@Dabbler So these just mount to the output side of the VFD within my enclosure?

I am at a little bit of a dilemma here. Do I spend some money on a higher end VFD (WEG or TECO for example) with the hope that it solves it, or keep my existing VFD and buy a line reactor and hope that solves the issue. If I go up to 80Hz the noise goes away, I think. I will have to have my daughter check it out later. I'm sure you guys are wondering why I'm worried about this with my tinnitus but it actually seems to make my tinnitus worse with this noise.