AC Drive troubles

I have a 5HP AC drive and motor that was installed in place of a 3 HP DC drive system about a year ago as part of a complete controls upgrade. It is an A/B 160 series drive (V/Hz) with 2 parallel dynamic brakes. It occasionally (1 to 10 times per day) faults on high bus voltage. The DBs are only rated to handle 5% duty cycle together. They get warm, but not blistering hot. Also, the perforamce of this part of the machine isn't where I'd like it to be.

In my application the drive is in decel about 25-35% of the time. It controls a cutter carriage that travels about fourteen feet back and forth. It makes a complete cut and return cycle 12 times per minute. It doesn't change directions as quickly as the old DC drive did. Luckily, the rest of the machine performs so much better that the bean counters are still very happy with the project overall.

We're getting ready to perform the same upgrade on another machine, but before we proceed, I'd like to cure this nuiscance problem. We are looking at a 7.5 HP Powerflex40 drive with sensorless vector. The PF40 has a built in IGBT for dynamic braking, but the standard a/b brake, again, is only rated for 5% duty cycle. The 160 drive also has a built in transistor for braking. I will contact our drive tech support to find out if I can choose a third party brake to get the duty cycle closer to what we need.

1. Will sensorless vector improve the drive's ability to decel and change directions

2. Will a vector drive need less dynamic braking duty cycle?

2. Is it true that a larger horsepower drive will allow better decel due to it's larger bus capacity or does it's current limit make that extra HP useless?

Thanks
Paul C.

Just a quick thought, but how much more would it be to add the AB chopper module. that would improve the decel/regen and bleed off the high bus voltage.

I would also look into a servo motor.

I agree with RussB, look into a servo. www.emersonct.com

Emerson has an awsome line up of servos as well as AC drives.

RussB: We are too cheap to spend the money on a servo if an AC drive will do. I just want to get the right drive for the application and give it another try. We have 5 more machines to upgrade. All the controls work flawlesly except this one drive.

LJBMatt: We already have the dynamic braking...it works, but is limited in its ability (5% duty cycle).

OkiePC said:

RussB: We are too cheap to spend the money on a servo if an AC drive will do.

Click to expand...

I understand, there are many companies who would rather spend several hundred dollars each month to pay some one to reset a motor or sort some parts than to spend a couple thousand dollars one time to prevent this.
Some call this job security, others call it waste. I guess that our economy depends on both.

Paul-

I think you are looking at this from the right direction, IMHO. I don't think it's a technology type issue, just a choice of platform. The AB 160 is pretty low performance. I wouldn't use it for a whole lot more than spinning fans or running a conveyor at constant speed.
As a general answer to your vector question, any time you can get better control of the motor flux it's a good thing. This assumes, of course, that you actually get the better control you are looking for by going sensorless vector. It should, since the AB 160 didn't give you ANY control of motor flux. On paper, the PF40 in sensorless vector mode should give you better performance on accel and decel. I haven't used the PF40 before so I can't make any performance claims. But on paper it will be better.

However, decel energy is decel energy. I wouldn't expect the PF40 to give you any better energy dissipation than the AB 160. That is simply a function of the chopper IGBT and the resistors you use. You don't have to buy the AB braking resistors. Just stay within their required resistance range and you are good to go. If you want to double or triple the resistor wattage, feel free. Also, try to stay on the low end of the resistance range as this will allow faster bus voltage relief when the chopper starts going. I usually go with Milwaukee Resistor for these resistors but there are quite a few manufacturers out there that can help.

Another thing I never checked on is whether you can add external bus capacitance to the PF40 and, if so, how much. They do provide access to both sides of the bus at the terminal strip. A correctly sized cap or two might also take care of your problem.

Keith

I would love to try an Emerson servo. I've heard only good things about them...but...we are supposed to use only A/B products, which is fine for PLCs. I'm just not impressed with any of their other stuff. I'll check the costs and see if we can swing it. I'd like to hear an opinion from DickDV (<--I think that's right). He seems to be the drives guru on this site.

The big advantage to using an AC drive aside from low cost is future replacement. I can run anybody's AC motor with anyone's AC drive. If the current drive becomes obsolete, I'll just get another. No expensive cables and motors to replace. In addition, the motor we're using now is also used in about 60 other places in my department, so stocking a spare is no problem.

Thanks again...

OkiePC said:

The big advantage to using an AC drive aside from low cost is future replacement. I can run anybody's AC motor with anyone's AC drive. If the current drive becomes obsolete, I'll just get another. No expensive cables and motors to replace. In addition, the motor we're using now is also used in about 60 other places in my department, so stocking a spare is no problem.
Thanks again...

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I do not want to start an argument, but if designed and maintained properly, these components will outlive the rest of the machine. The MTBF of a GE Fanuc servo motor is about 35 years, Amplifier and controller, slightly less. This capital equipment will have been fully depreciated long before this.

RussB said:

I do not want to start an argument, but if designed and maintained properly, these components will outlive the rest of the machine. The MTBF of a GE Fanuc servo motor is about 35 years, Amplifier and controller, slightly less. This capital equipment will have been fully depreciated long before this.

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That part about if maintained properly is a big IF in my plant. We are simply not manned well enough to do much more than breakdown fire-fighting type maintenance. You don't have to convince me that a servo would be a better performer. I agree. But, I am a realist, and I have never seen a servo system that lasted a fraction of its advertised MTBF without requiring troubleshooting and emergency maintenance. If we use a non-A/B product, that means new software, cables, and most of all training. Downtime is very expensive here. Yes, we are losing a few seconds per day because the operator has to reset the existing drive (remotely), but when a technician has to work on a servo drive in the middle of the night it could be down for hours. And, it's been so reliable that the poor guy can't remember any of his training. That's when our downstream processes actually suffer, and that's when it really costs us. I believe that simpler is better. It gives us versatility and efficiency.

Someone please answer my original questions and I'll decide which route to take.

1. Will sensorless vector improve the drive's ability to decel and change directions?

2. Will a vector drive need less dynamic braking duty cycle?

3. Is it true that a larger horsepower drive will allow better decel due to it's larger bus capacity or does it's current limit make that extra HP useless?

From post #7:

I think you are looking at this from the right direction, IMHO. I don't think it's a technology type issue, just a choice of platform. The AB 160 is pretty low performance. I wouldn't use it for a whole lot more than spinning fans or running a conveyor at constant speed.
As a general answer to your vector question, any time you can get better control of the motor flux it's a good thing. This assumes, of course, that you actually get the better control you are looking for by going sensorless vector. It should, since the AB 160 didn't give you ANY control of motor flux. On paper, the PF40 in sensorless vector mode should give you better performance on accel and decel. I haven't used the PF40 before so I can't make any performance claims. But on paper it will be better.

However, decel energy is decel energy. I wouldn't expect the PF40 to give you any better energy dissipation than the AB 160. That is simply a function of the chopper IGBT and the resistors you use. You don't have to buy the AB braking resistors. Just stay within their required resistance range and you are good to go. If you want to double or triple the resistor wattage, feel free. Also, try to stay on the low end of the resistance range as this will allow faster bus voltage relief when the chopper starts going. I usually go with Milwaukee Resistor for these resistors but there are quite a few manufacturers out there that can help.

Click to expand...

So, to paraphrase, assuming you are not current limited, the sensorles vector drive will provide better accel/decel performance than the V/H drive. No it will not have inherently better energy dissipation capability.

As for your question about larger HP drives and bus capacity, I believe this is only true if you step up in drive frame size. I think all the drive ratings in a given frame size in the PF family have the same bus capacitance.
Keith

Thanks Keith...I somehow missed your post #7. I will check into the Milwaukee resistors. I guess I'm gonna have to try one to find out how well it will work. I'll post the results in a few weeks.

did you chek the line voltag? is there a line choke for this drive?
it may be a line voltag transiant coming from the maine bus or other device on the net. [sory for my poor english] hope this will be helpfool for you.

OkiePC, the chopper module is different from the dynamic brake kits. it can handle a higher duty cycle. i used chopper modules on stamping presses to handle all the excess energy.

Look here for another solution:


http://www.revcon.de/E/english.htm

Regards,

Ed