Trending Powerflex Parameters

Hi. I'd like to know if it's possible to trend the DC Bus parameter of a Powerflex 700, series B. I can see the start/stop, etc. parameters in the RSLogix 5000 program (via a 1756-CNB ControlNet module), but I'm not seeing anything resembling the DC Bus parameter.

The reason I'm asking is that recently we've been having an Overvoltage fault on the drive. We were seeing a high bus voltage (760V-780V) on this drive, even after lowering the incoming voltage, (which helped some). The motor being driven is constantly changing speed (average 44fpm) to maintain tension on the sheet and we suspected regeneration. We installed braking resistors, but that didn't seem to help. The other night we were browsing through the parameters and found one called "Regen Power Lmt", or something to that effect (Param 153, I think). The manual explained that this is the amount of regenerative power to be sent to the DC Bus, and that if we had a braking resistor, it was supposed to be set at maximum (_50 to 0%). It was set to the factory default of -50%, and we changed it to 0%. The minute we did, the DC Bus voltage dropped to 650V, which is where it's supposed to be. So now, we'd like to have the capability to trend the DC Bus parameter for future reference.

Any possibility this can be done? If you need more info, it might have to wait until I get to work tonight. Thanks for any help,

John Wolfe
Corinth, Texas

As a general rule, High DC Bus Fault occurring during motor operation is almost always regen. If it occurs when the system is idle, it is almost always a power supply disturbance.

Regen during motor operation can be the obvious decel and braking conditions but it can also be due to the speed loop tuning being so tight as to be unstable. If that is the case, you may not even see any decel but the instability generates regen energy anyway. This would only occur on Sensorless Vector or Flux Vector systems since a simple V/Hz drive would not have any speed loop tuning.

DickDV said:

Regen during motor operation can be the obvious decel and braking conditions but it can also be due to the speed loop tuning being so tight as to be unstable. If that is the case, you may not even see any decel but the instability generates regen energy anyway. This would only occur on Sensorless Vector or Flux Vector systems since a simple V/Hz drive would not have any speed loop tuning.

Click to expand...

Ding! Ding! Ding! Another "golden nugget" alert from DickDV.

Thank you

Please excuse my lack of knowledge as drives are new to me. That said...

This particular drive's "Motor Cntl Sel" parameter is set to FVC which allowed parameter 153, Regen Power Limit to be set. It didn't show up in the drives set to Sensorless Vector and as far as I know, we don't have any drives set to Flux.

I have the manual on my computer and I searched for "Speed Loop Tuning", but I didn't see it. Is that a factor of several different parameters? Either/or, how would I go about checking that?

I can speak to the initial question, about how to trend the DC Bus Voltage using ControlNet and RSLogix 5000.

PowerFlex 700/B drives with 20-COMM-C interfaces use I/O connections that by default include only the Command/Reference words and Status/Feedback words.

You can configure and enable "DataLinks" that expand the I/O connection to include several monitoring and control parameters.

Because the PowerFlex 700/B uses 32-bit values for DataLinks, you can configure 4 of them each for Input and Output. The smaller PowerFlex 70 and older 1336+/+II drives had 16-bit values for DataLinks so you could configure 8.

These parameters are easiest to set up in RSLogix 5000 v16, where you just select the DataLinks from a list and RSLogix sets up the related enable and selection parameters for you.

In RSLogix 5000 v15, you configure the number of DataLinks in the I/O connection in the "General" tab of the I/O connection. You then use DriveExecutive (standalone or embedded) or the HIM module to Enable the Datalink(s) you selected, choose their inclusion in the I/O connection, and set the parameters they point to.

Which version of RSLogix 5000 are you using ? Can you post the *.ACD file and the DriveExecutive *.DNO file (if using v15 or earlier) ?

I would guess that FVC in the Motor Control Sel parameter would stand for Flux Vector Control. That would be encoder feedback if I understant AB's terminology correctly.

That would also mean that speed loop tuning required. Look for parameters that are named Proportional Gain, Integral Gain or Time, and Differential Gain or Time. If you don't know just what these mean or what they do, it would be a good time to call a factory tech for on-site help.

Ken & DickDV,

Thanks for the help, but I think I'm getting in over my head on this one. An AB rep is going to be called in on Monday. Since he'll probably come in during the day and my shift doesn't come until 11pm, I don't know how much info I'll be able to get, but maybe I can get him to write me a detailed report or something.

Thanks again,

John Wolfe
Corinth, Texas