PID motor control vs ramping up/down to a set-point - is one better for motor?
PID motor control vs ramping up/down to a set-point - is one better for motor?
(OP)
Just wondering - for health/lifespan of motor - is controlling motor through a PID that only makes slight changes better than controlling by ramping up and down between 2 set points?
Currently the motor changes between 500 and 1300 RPM via ramp up/down with VFD about 6 times per hour to maintain a system set point. Its a 2HP 3500 RPM AC motor
Currently the motor changes between 500 and 1300 RPM via ramp up/down with VFD about 6 times per hour to maintain a system set point. Its a 2HP 3500 RPM AC motor





RE: PID motor control vs ramping up/down to a set-point - is one better for motor?
RE: PID motor control vs ramping up/down to a set-point - is one better for motor?
What is the application?
GG
"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)
RE: PID motor control vs ramping up/down to a set-point - is one better for motor?
If the VFD were to ramp too fast (or step) and create very large slip values, you would have surges in current similar to DOL starting, which could be problematic over time.
Curt Wilson
Omron Delta Tau
RE: PID motor control vs ramping up/down to a set-point - is one better for motor?
Not to worry wrt surge currents with a VFD, as the inherent current limiting feature of the VFD will always override any setpoint changes (ie to protect the drive from overcurrent).
GG
"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)
RE: PID motor control vs ramping up/down to a set-point - is one better for motor?
RE: PID motor control vs ramping up/down to a set-point - is one better for motor?
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: PID motor control vs ramping up/down to a set-point - is one better for motor?
500 RPM on a 3500 RPM motor needs supplementary cooling or severe de-rating.
What is the nature of the process?
What is the load profile?
What is the controlled variable? Flow? Pressure? Level? Temperature? Something else?
If you want a better answer, you have to provide better information.
Bill
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"Why not the best?"
Jimmy Carter
RE: PID motor control vs ramping up/down to a set-point - is one better for motor?
If the implementation of PID control results in the motor speed varying slowly between about 900 RPM and 1100 RPM, then PID control may be a better choice.
Consider changing to an 1200 RPM base motor, or changing the drive ratio so as to run the 3600 Base motor much faster.
DON'T RUN A 3500 RPM MOTOR AT 500 RPM. IT WILL NOT BE COOLED PROPERLY.
TEFC MOTOR ARE PARTICULARLY AT RISK.
Bill
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"Why not the best?"
Jimmy Carter
RE: PID motor control vs ramping up/down to a set-point - is one better for motor?
Also, if there is no issue now then running at a constant speed somewhere between those 2 speeds instead should not be an issue either.
So, do the PID loop if it makes the process better.