Input Frequency

[Gary]

The input frequency has no effect on the VFD. A VFD just uses the line power as a sort of raw material, from which it creates an entirely new power output voltage and frequency. The input can be almost anything and certainly 50 or 60Hz is well within it's range. 400Hz may be a problem, but unless you want to power it up on the jet going over, you shouldn't worry.

 

Hopefully you have transformers to boost the voltage however, otherwise you will either have to limit your max. speed or oversize your motors.

 

I have been runnig a Automation Direct GS1-22PO VFD for about 20 hours with a 230VAC 3ph 400Hz input. As one might suspect, Automation Direct will not OK this input frequency. An engineer I contacted at Yaskawa felt that either the MOV of the input diodes would be the first to fail in their J7 series drive (almost identical in capacity to the GS1), but wouldn't guess as to whether there would be a quick failure or it would happen over a long term. jraef's quote from another thread says 400Hz "may" be a problem. Since several of the GS1 units have run a few hours with 400Hz on the input, I can surmise that the failure won't happen quickly. I have not found anyway to test the unit other than running the normal operation sequence. I would be possible to set up a simple automated test rig that would allow cycling the drive for long periods of time.

 

I have not found a manufacture that offers a 400Hz input drive. I can not use the Automation Direct drive in production as it is made in China. I didn't find frequency ratings on either MOV's or the diodes used for the rectification. Is the 400Hz really a problem or is it just the fact that these companies haven't tested under those conditions. I don't imagine that there is much of a market for units that are rated at 400Hz.

 

I'm looking at a quantity of 200, so probably most manufactures wouldn't be interested in providing a custom drive anyway.

 

Any ideas on where I should go from here will be appreciated. The rest of the system is all working and the customer is ready to go, but without a drive the project is stalled (no pun intended).

 

Gary

[marke]

Hello Gary

 

Welcome to the forum.

 

jraef is correct in that the VFD just rectifies the incoming supply voltage converting this to a DC voltage and this is then chopped up to create a new three phase output.

 

Within a reasonable frequency range, the drive will not be affected by the frequency of the supply, but there are a few issues to consider.

 

1. As the frequency is increased, the turnoff losses of the input rectifiers will become significant and cause an increase in the heating of the rectifiers. The turn off losses are a function of the turn off characteristics of the rectifiers used.

   Depending on the size of the drives you are considering, it may be possible to replace the rectifiers with high speed rectifiers. 400Hz may not be an issue for the rectifiers used, but this should be investigated.

2. If there are AC line reactors fitted, at 400Hz, there will be a higher voltage drop across the line reactors and this will reduce the DC voltage and therefore reduce the AC output voltage. The value of the line reactors would need to be reduced to give around a 5% voltage drop under load.
3. If there is a DC Bus Choke, this could also be dramatically reduced in size. There may be eddie current problems with the DC Bus choke on 400Hz depending on its design and construction.
4. The DC capacitors will be handling a much higher ripple current frequency. Depending on the ESR of the capacitors at the higher frequencies, there may be increased losses in the capacitor and consequently a reduced life.
5. RFI Filter capacitors on the input of the VFD will have to carry 8 times the current that they would at 50Hz. This may be an issue, but commonly would not be a problem and 230 volts. Verify the AC voltage rating at 400 Hz.

Not to much of a problem!!

 

Best regards,

Mark.

[Gary]

Hello Gary

 

Welcome to the forum.

 

jraef is correct in that the VFD just rectifies the incoming supply voltage converting this to a DC voltage and this is then chopped up to create a new three phase output.

 

Within a reasonable frequency range, the drive will not be affected by the frequency of the supply, but there are a few issues to consider.

 

1. As the frequency is increased, the turnoff losses of the input rectifiers will become significant and cause an increase in the heating of the rectifiers. The turn off losses are a function of the turn off characteristics of the rectifiers used.

   Depending on the size of the drives you are considering, it may be possible to replace the rectifiers with high speed rectifiers. 400Hz may not be an issue for the rectifiers used, but this should be investigated.

2. If there are AC line reactors fitted, at 400Hz, there will be a higher voltage drop across the line reactors and this will reduce the DC voltage and therefore reduce the AC output voltage. The value of the line reactors would need to be reduced to give around a 5% voltage drop under load.
3. If there is a DC Bus Choke, this could also be dramatically reduced in size. There may be eddie current problems with the DC Bus choke on 400Hz depending on its design and construction.
4. The DC capacitors will be handling a much higher ripple current frequency. Depending on the ESR of the capacitors at the higher frequencies, there may be increased losses in the capacitor and consequently a reduced life.
5. RFI Filter capacitors on the input of the VFD will have to carry 8 times the current that they would at 50Hz. This may be an issue, but commonly would not be a problem and 230 volts. Verify the AC voltage rating at 400 Hz.

Not to much of a problem!!

 

Best regards,

Mark.

 

Hi Mark,

 

It looks as if I have been lucky so far (by not seeing any problems). If the drive (or anything else) fails, there is provision for manual operation. That said, I don't want to give the customer a product that has a higher than normal potential for failure.

 

As you may have guessed, I am a ME rather than a EE so this is an interesting (and steep) learing curve. As the saying goes, I probably know just enough about the subject to be dangerous. I appreciate your in-depth analysis of the issues. I have recently (today) been contacted by a field engineer from Yaskawa so now I will be able to speak a little more inteligently about their drives and the possiblity of modifying them.

 

Regards,

Gary

[marke]

Hi Gary

 

I expect that the answer will be to alter the reactors if fitted and leave everything else the same.

 

Best regards,

Mark.

[Gary]

Hi Gary

 

I expect that the answer will be to alter the reactors if fitted and leave everything else the same.

 

Best regards,

Mark.

 

Hi Mark,

 

I was contacted by a Yaskawa field engineer who has had experience with a 400 Hz input to their drives. There are no reactors fitted to the drive I intend to use and the engineer said that they have experienced no problems to date. Their customer required 60 Hz power at a site that only had 400 Hz available, so a drive was an easy (and cost effective) way to provide 60 Hz power. He didn't feel that using the unit for speed regulation would have any additional effect. The only kicker is that Yaskawa will not honor the warranty with the 400 Hz input. My customer doesn't seem to concerned about that so I may finally have a good solution. The Yaskawa drive is about $50 US more than the Factory Automation unit, but again, that doesn't seem to bother the customer.

 

Thanks for your input as it was very helpful to at least appear to know what I was talking about when discussing the matter with the field engineer.

 

Regards,

Gary