WEG VFD Issues, 400hp motor, and chipper disk

[Jasondelane]

We are running a high inertia load on a WEG CFW11 VFD.

The motor is 400HP, 60hz, 508 FLA(from memory), 598RPM.

The issue we're having is that the high inertia load is causing DC Bus Overvolts when the chipper is loaded and then unloaded.

The installers had the VFD setup on V/Hz mode. I changed it to Sensorless Vector and did a rotate tune. It seems to accelerate better now but I don't think that helped the issue with overvolts.

I also adjusted the Maximum negative torque value from the default 150% to 4%. This seems to have had the greatest improvement.

I noticed when the chipper is running unloaded it always runs -4% torque for some reason. You would think this would slow the chipper down but that seems to be the "idle adjustment" the VFD is making to maintain 600RPM.

The accel is 60 Sec, Decel is 360 Seconds. The VFD runs -4% torque during the decel also.

When I check the last fault snapshot it's usually around 470 amps (unloaded amps are around 280), 680 DC bus volts.

What are some other settings I can adjust to properly run this setup?

 

[Gene Bond]

You might try turning negative torque limit to 0, but be careful to watch for motor speed. Some drives will run away, and overspeed. Be ready to hit the e-stop!

Also, increasing current Proportional gain and decreasing the Current Integral gain can help with some drives.

I'm only slightly familiar with WEG drives, but it appears to be a decent drive, and MAY be able to handle the high inertia without a DB resistor. Some can, some can't...

 

[thingstodo]

I don't have WEG experience. Rockwell, Siemens and Mitsubishi all have settings for 'bus voltage' control. I don't know what they do, exactly. But you select PWM first, or Voltage first ... it's a selector.

I have had problems with speed regulation on high inertia fans. When I run them at 60 Hz, I've had to set the maximum running speed to about 65 Hz so that they don't trip on overspeed when the load drops and the torque needs to compensate.

It doesn't appear to hurt anything to have the maximum speed higher than what you are running your load. But it makes a difference to the drive control system.

 

[Gene Bond]

I don't have WEG experience. Rockwell, Siemens and Mitsubishi all have settings for 'bus voltage' control. I don't know what they do, exactly. But you select PWM first, or Voltage first ... it's a selector.

I have had problems with speed regulation on high inertia fans. When I run them at 60 Hz, I've had to set the maximum running speed to about 65 Hz so that they don't trip on overspeed when the load drops and the torque needs to compensate.

It doesn't appear to hurt anything to have the maximum speed higher than what you are running your load. But it makes a difference to the drive control system.

Fuji/GE has a similar setting. The default Max set speed is 60hz, and the default max freq is 70hz. That could be too high for some loads.

 

[jraef]

The OV on a load change is the result of set speed being lower than the actual speed. So under load, the slip is high because the actual rotor speed is being kept LOWER than the commanded speed by the load. So when the load goes away, the drive has not been told to change speed, but the motor actually speeds up. This is what "Slip Compensation" is for. That drive has this feature (P0138) but the factory default setting is Zero. Try increasing it.