Rockwell Automation 20G PowerFlex 750-Series AC Drives - Manual (Page 223)

Rockwell Automation Publication 750-RM002B-EN-P - September 2013 223
Motor Control Chapter 4
Where is inertia adaption applied?
• Any system with an inertia ratio greater than 3:1 that is plagued by gear
noise or resonance that can’t achieve desired performance by ordinary
tuning. (Inertia ratio is the ratio of system inertia to motor inertia.)
• Most high performance tracking or electronic line shaft systems.
• Most geared systems requiring higher bandwidths and stiffness.
What could be a disadvantage when using inertia adaption?
• It can generate a shrill noise with rigid couplings that lack lost motion or
sufficient compliance. Do not use inertia adaption in such cases.
• It can produce a low level sound emanating from the motor. This is merely
the inertia adaption in action and the sound does not affect performance
nor does it harm the motor.
Inertia Compensation Inertia Compensation is active only in PowerFlex 755 drive and in Flux Vector
(FV) motor control modes selected by P35 [Motor Ctrl Mode].
During speed changes, a certain level of torque to respond is required due to load
inertia. That level of torque is above the torque used to run at constant speed.
Inertia compensation attempts to predict the motor torque required to accelerate
and decelerate an inertial load. The Inertia compensation function calculates a
feed forward torque signal based on proportional acceleration or deceleration
rate of change of speed input and total inertia, also known as the derivative of
speed with respect to time. Then that P699 [Inertia Comp Out] signal torque
can be fed forward into the torque control, becoming an available input to the
P313 [Actv SpTqPs Mode] selector to be summed with P660 [SReg Output]
making for smoother accelerations and decelerations, especially with high inertia
loads.
• Parameter 695 [Inertia CompMode] enables the Inertia Compensation
and selects possible velocity reference input sources of motor speed as
follows:
• “Disabled” (0) – Inertia compensation function is disabled. P699 [Inertia
Comp Out] is zero so the motor torque reference is not affected.
76
696
697
699
695
700
698
d
dt
596
0
d
dt
0
1
2
3
595
Inertia Comp
Inertia CompMode
Disabled
Int Ramp Ref
Filtered Spd Ref
Ext Ramped Ref
Speed Rate Ref
Inertia Dec Gain
Inertia Acc Gain
Total Inertia
Inertia
Comp
LPF
Inert Comp
LPFBW
Inertia Comp
Out
Torque Feed
Forward To
Torque Control