Limit HP from Torque AI and RPM PID Output

[cstep7263]

Hello,
I have a motor that we are sending a RPM Speed Output from 0-100% to the VFD. However, the Motor HP needs to be limited to 6000 HP and the max rating of the motor is 8000. I have a Torque analog reading from the VFD Coming into my PLC used to calculate HP. How do I limit the HP with only a RPM Speed Output? Do I read the actual HP and if it is over the max, increase Speed Setpoint? This is tricky because that seems elementary doing it this way. Do I use PID to increase and decrease the Speed Setpoint based off of the HP over Limit?

 

[Peter Nachtwey]

Hello,
How do I limit the HP with only a RPM Speed Output

You can't. You need to know the torque too. Can't that be read from the drive?

? Do I read the actual HP and if it is over the max, increase Speed Setpoint? This is tricky because that seems elementary doing it this way. Do I use PID to increase and decrease the Speed Setpoint based off of the HP over Limit?

You should use two PIDs with a low select. Basically the motor will use the lessor of the speed or hp.

 

[cstep7263]

You can't. You need to know the torque too. Can't that be read from the drive?


You should use two PIDs with a low select. Basically the motor will use the lessor of the speed or hp.

We are receiving the Torque from the drive. The problem is Speed Setpoint is sent to another PLC controlled by a company that is driving the VFD. They are not using HP PID, only Speed.

 

[Rob...]

A VFD controlling a 6000HP motor will without doubt offer torque/current control. It's not exactly an "off the shelf" component