Powerflex 7000 Ethernet communication

[GlennM]

I have a contractor at my water plant installing 3 brand new Powerflex 7000 VFD's for my High Service pumps. I would like to control these via ethernet with a SLC 5/05. Is this possible? I have been scouring the interwebs and have come up with nothing. If someone can point be to some documentation, that would be great, especially addressing the drive. Thanks

 

[joseph_e2]

The SLC 5/xx and MicroLogix PLCs can't add drives to their I/O tree the same way that the Logix 5k based controllers can. You can control the drive with explicit messaging, but it gets cumbersome. My colleague at my last place sent a changing speed reference to a Powerflex 525 from a MicroLogix 1400 with MSG instructions. I don't recall all the details, but he had to send multiple messages to affect a speed change and if anything went wrong (and the PLC couldn't always tell when it went wrong), you had to re-send the whole sequence. Also, upon power cycling the system, you had to know to re-send the speed reference or it would "start" but stay at 0Hz until it received another speed reference.
All that to say: yes, it's *probably* possible. Yes, it can be a royal pain to keep it reliable. It will also depend on what you mean by "control via Ethernet". If you just mean adjusting the speed, you're probably fine. With the reliability issues we saw with the MSG-ing, I would probably not use MSG instructions to control the start/stop function. Or at least use a hard wired STOP control that the PLC controls via a relay while allowing the RUN to be a MSG. If that's possible with those drives.

 

[Ken Roach]

I have very strongly recommended against this sort of workaround for many years, ever since a water treatment plant customer roped me into supporting their control architecture mistake. I get kinda mad about it every time it comes up.

Yes, you can in theory control A-B VFDs with message instructions from an SLC-5/05. I recommend strongly against it.

In your application, the drives aren't frequently starting and stopping, and PowerFlex 7000 is the sort of big hardware where running two or three wires for a discrete control input isn't going to break the budget.

So I very strongly recommend that you set up the drive for discrete start/stop control from the SLC-5/05's ordinary I/O, and send it Speed Reference commands and read diagnostic data with MSG instructions.

The simplest way to do that with an SLC-5/05 is to set up the drive to run at Preset Speed 1, then write to that parameter.

Your SLC-5/05 is going to need to have firmware with "Dual Stack" capability; if it was built within the past 15 years it should have that. If it's a "Series C" hardware and has the "10/100" sticker by the Ethernet port it definitely does.

 

[Ken Roach]

Because the PowerFlex 7000 is a big and expensive drive, I very strongly recommend that users get advice from Rockwell and/or their integrator on how to connect it to their control system.

A quick read of the User Manual says that the Preset Speed 1 parameter is:

Preset Speed 1 [Preset Speed 1] 
Linear Number: 33 
Default Value: 30.0 Hz 
Minimum Value: 0.5 Hz
Maximum Value: 75.0 Hz 
Access Level: Advanced 
Read/Write: Read/Write

The linear number and the 20-COMM-E user manual suggest that you would write two 16-bit Words to SLC-style address N150:66 to set a value for Parameter 33.

The units are probably 1/10 Hz, so the value "500" would set the parameter to 50.0 Hz.

Again, I do not recommend trying to use the N41/N42 data table emulation of the Assembly Object read and write to control the drive.

 

[GlennM]

I have a CompactLogix now that is tasked with VFD communication, and have purchased a Studio 5000 subscription. I am doing preliminary programming prior to drive start-up. Are these drives momentary start or maintained? To which element do I send the speed signal too? I have several messages sent to my Rockwell rep but still havent heard back.

 

[Robb B]

I recently setup an SLC 5/05 series C to communicate with ABB ACS880 VFD's using EEM instructions. I am only reading values from the drive to display to the operators, no controls. The EEM instructions aren't terribly bad to configure, though they do eat up memory fast at 58 words per instruction. If you configure the instructions and data tables correctly, you could, in theory, have very good control over the drive. I also would not recommend this however, as the wrong bits in the wrong words will cause unknown issues and make troubleshooting extremely difficult. Stick to hardwired I/O for controlling the VFD.

 

[mylespetro]

Are these drives momentary start or maintained

That can typically be changed using parameters, usually you can select between 2-wire control (maintained) and 3-wire control (momentary).