Hi everyone

I'm trying to exert a controlled load into an electric motor with another motor (having first motor spin at a lower speed than second motor, exerting a torque).
Both are connected through a shaft, and we're measuring speed and torque at the shaft.
Motor #1 has a torque control based on speed commands (by speed command differences exerting acceleration, going into Torque = Inertia*Acceleration equation, passing through a PI controller).
Motor #2 has a speed based control.

When Motor #1 tries to exert torque to Motor #2 lowering its speed (spinning at a lower speed than Motor #2), Motor #2 sees this speed decrement and exerts torque to try to bring back the Motor to its commanded speed.
This is driving the control very unstable and unable to keep a controlled torque, due to this interaction.

Has anyone experienced something similar, where you would try to control torque to a motor, but due to the control being speed based, both motors enter a control loop interaction?

Any torque control schemes you would recommend, based on speed commands? (We can modify Motor #1 torque control algorithm and tune it/change programming, but not Motor #2)

Please let me know your thoughts or any question/comment.

Thank you very much : )

 

MiguelS...
Welcome to Control.com!
Are both motors coupled to the same shaft, that is, connected in tandem, but electrically powered Direct-On-Line (DOL)?
If so, then I can tell you that you will have a problem, but it is easily corrected even if the motors are unequal in size!
Regards, Phil Corso

 

MiguelS,
I'm having trouble in understanding your need.
Are you developing a Drive for Motor speed control and you are using 2 motors coupled back to back as your test setup ?
If yes, then your torque should be in opposite direction of the speed control so that it will act as load to the speed control loop, where you can test different scenarios and loads. What will be your targeted Load change and expected control action ? Any graphical inputs will be good. Till then consider loop tuning by playing with Kp & Ki.
A picture of your setup and actual application would give more insight, where we can recommend better ways to handle it.