Motor and VFD low frequency "jitters"
Motor and VFD low frequency "jitters"
(OP)
I've hit a brick wall with a Baldor 1HP motor and a Delta VFD"E" series drive. For a 460V blower application, I want to run the motor at 10~60 Hz. The motor is rated 10:1, and my PWM is set to 15kHz. When this motor is running between 10 and 15 Hz, it cogs. This cogging is translating mechanically through the equipment, making a not so pleasant noise; the carrier is also bumped down to the 4-8 kHz range. Beyond 15Hz, this thing operates as expected; smooth and quiet.
I've tried swapping between Vector and V/Hz mode, and performing an Autotune. For V/Hz mode, I tried setting my midpoint voltage at 230, and my midpoint F at 35Hz, (plus several other combinations). I've also verified that the drive isn't trying to inject any DC braking at the lower frequencies; I just turned those features off. I can't seem to null this cogging out, or even make a dent in it.
Any insight would be greatly appreciated,
~M
I've tried swapping between Vector and V/Hz mode, and performing an Autotune. For V/Hz mode, I tried setting my midpoint voltage at 230, and my midpoint F at 35Hz, (plus several other combinations). I've also verified that the drive isn't trying to inject any DC braking at the lower frequencies; I just turned those features off. I can't seem to null this cogging out, or even make a dent in it.
Any insight would be greatly appreciated,
~M





RE: Motor and VFD low frequency "jitters"
RE: Motor and VFD low frequency "jitters"
The reason mine resonate appears to stem from the fact that the motor has a set volts/hz ratio. The VFD slams the motor with full voltage at very short bursts wich causes a sudden increase torque on the rotor. At 20% speed the motor is looking for only 20% of the full voltage (which comes in the form of PWM). The PWM signal slams the motor with full input voltage at short bursts which cause a sudden high torque in the machine. Since the machine is rotating so slow, the harmonics of these are audible. Additionally, as each pole passes by the stator pole, the torque on the rotor changes slightly. This is another harmonic influence.
If you can, increase the frequency of your VFD above 15 kHz and it should smooth out the motor. If not, try manipulating your DC braking settings. If that doesn't work perhaps add a choke or saturable core reator?
------------------------------------------------------------------------
If it is broken, fix it. If it isn't broken, I'll soon fix that.
RE: Motor and VFD low frequency "jitters"
Loving your siggy btw...
RE: Motor and VFD low frequency "jitters"
Keith Cress
kcress - http://www.flaminsystems.com
RE: Motor and VFD low frequency "jitters"
I have been told that it is being done in the Toyota Prius, but their inverter is a very special one.
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Motor and VFD low frequency "jitters"
PM motor?
We aren't discussing no stinnking PM motor!!
Or are we?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Motor and VFD low frequency "jitters"
What I've got is a Baldor 1 HP 3 phase induction motor. I don't think field weakening is an option Keith; while this little drive has a lot of bells and whistles, V/Hz manipulation or anything else regarding the power section is pretty limited. I think I'm SOL here.
RE: Motor and VFD low frequency "jitters"
I am as confused as anyone here. Forget it. If you can...
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Motor and VFD low frequency "jitters"
Borrow a good VFD from a friend or a demo unit from a distributor and see if it does the same thing. I'd be willing to be it doesn't.
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: Motor and VFD low frequency "jitters"
Check the following:
#Temperature around the VFD?. You already indicate you are trying to "keep your enclosure's heat load to a minimum" which tells me you could have a small enclosure.
#Try reducing the carrier frequency even lower.
#monitor the current at the low frequency range that is causing the problem. If you see the amps all over the place, it might need a little more volt boost if this is possible.
#Sounds like you have tried a lot of settings. Have you tried doing a factory reset and simply running it from default with no further changes? Might be worth looking at this. Sometimes you can make so many changes in a VFD that you lose track of them.
RE: Motor and VFD low frequency "jitters"
The VFD was on the open bench, with a relatively default parameter set (this was done a few times
Thanks guys for all the feedback.
RE: Motor and VFD low frequency "jitters"
RE: Motor and VFD low frequency "jitters"
Yea, the AB 4M and the Delta "E" series both roll off the same manufacturing line. Power sections are identical, with the only difference being aesthetics and some interfacing options.
RE: Motor and VFD low frequency "jitters"
What does the drives output current read, compared with the rated current for high PWM frequency? If the drive is derating the pulse frequency it sounds like it's reacting to an overload of current or temperature.
The only other cause I can think of for the problem you describe is a missing phase to the motor, but I'm sure you've ruled that out....
Cheers,
Mort
RE: Motor and VFD low frequency "jitters"
It sounds to me like the autotune is not doing an adequate job at lower shaft speeds. Do a manual tune and see if the cogging can be tuned out.
You say the drive doesn't permit manual tuning of the speed loop?!!! Time to buy a good drive, in that case.
RE: Motor and VFD low frequency "jitters"
just a shot in tha dark though.