vfd power factor

[daldesign]

We design exercise equipment, some using DC drives and some using AC drives. They are in-house designs. The AC drive is a simple V/F type and exhibits poor PF (0.7 or less) owing to its front-end being a simple bridge rectifier and capacitor design. The supply is 240V 60Hz single-phase. The output is 3-phase 230VAC 10 to 120Hz. The motor is 2hp.
To improve the PF we can add a series inductance either on the AC or DC side of the bridge, but inductors are large and expensive. We could design our own PFC, or we could specify a commercial VFD that has PFC.
Can anyone recommend VFDs of 2 to 3hp that feature PFC?
thanks

 

[dpc]

thread237-207697 - scroll down to the post by Ozmosis.

With internal dc link reactors, typical PWM drive power factor should be 0.9 - 0.95.

 

[jraef]

I am assuming you mean active PFC, because you cannot do passive PFC on VFDs without serious risk of premature failure. To that issue then, there are VFDs that can do active PFC, but they are very expensive and not something typically sold in small HP sizes. It would be far far less expensive for you to just put in an inductor.

But what is your purpose for wanting to improve the pf? If is because of pf penalties, residential users (in the US anyway) don't get penalized for poor pf, so there is no compelling reason to exert effort to correct it. In addition, VFDs have a poor distortion power factor, but the displacement power factor, which is usually the only kind measured by standard utility metering, is actually around .95.

If you are needing to do this because you want to go for an Energy Star rating, I'm not sure the .95pf requirements for SMPS apply to VFDs.


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[daldesign]

Jraef, yes I am thinking about active PFC. But that adds around $50 to the system cost if we design it. While the US does not regulate PF yet, the new Smart Meters seem to have the potential to measure PF, both distortion and displacement.
Right now we measure PF using a California Instruments AC programmable supply, I believe it is summing both flavours of PF. Drives that have no active PFC exhibit poor PF on the California box.
I was curious to know if any commercial drives had built-in active PFC.
I had one large maker of drives tell me that their PF was 0.95- but that must have been based on displacement only.

Energy Star is a possibility- not sure if it applies to our products.

 

[jraef]

To get active PFC in a VFD, it has to have what is called an "Active Front End", often abbreviated as AFE. It's available, but expensive because it is essentially another inverter on the input side. I don't know of anyone doing that on sizes as small as what you need, and I don't know if anyone has dealt with doing it less expensively for a 1 phase input on those small drives yet either. There is no compelling market condition driving the development at this point. AFE drives are used either to mitigate large THD propblems or to provide regenerative braking, neither of which is a big concern on small 1 phase supply VFDs. It is a lot less expensive to do on an SMPS but the power requirements are usually a lot lower, plus there are burgeoning regulations pertaining to SMPS on single phase equipment that is driving the development. You may be right that it's coming, I just don't see anyone addressing it in the VFD industry yet.

We ended up (in our typically tangential manner) discussing this in greater detail this thread, probably worth a read for you. thread237-244890



"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

 

[daldesign]

Thanks Jraef for the info on drive technology. We have enough problems right now, so I won't be starting a boost PFC or AFE anytime soon.