Rockwell Automation 20D PowerFlex 700S AC Drives with Phase II Control Reference Manual - Manual (Page 127)

Rockwell Automation Publication PFLEX-RM003E-EN-E - January 2011 127
Detailed Drive Operation Chapter 1
original speed. Conversely, when the load is removed, the rotor speed increases
momentarily until slip compensation declines to zero.
The amount of slip added to the speed command is displayed in parameter 107
[Slip RPM Meter].
Slip compensation also affects the dynamic speed accuracy (ability to maintain
speed during “shock” loading). The effect of slip compensation during transient
operation is illustrated in
Figure 22 below. Initially, the motor is operating at
some speed and no load. At some time later, an impact load is applied to the
motor and the rotor speed decreases as a function of load and inertia. And finally,
the impact load is removed and the rotor speed increases momentarily until the
slip compensation is reduced based on the applied load.
When slip compensation is enabled, the dynamic speed accuracy is dependent on
the filtering applied to the torque current. The filtering delays the speed response
of the motor/drive to the impact load and reduces the dynamic speed accuracy.
Reducing the amount of filtering applied to the torque current can increase the
dynamic speed accuracy of the system.
However, minimizing the amount of filtering can result in an unstable motor/
drive. The user can adjust parameter 99 [Slip Comp Gain] to decrease or increase
the filtering applied to the torque current and improve the system performance.
For parameter 99 a higher value decreases filtering and a lower value increases
filtering.
Figure 22 - Rotor Speed Response Due to Impact Load and Slip Compensation Gain
Speed Control, Speed
Mode, Speed Regulation See Speed/Position Feedback on page 128 section for information about
feedback devices and speed regulation with and without a speed feedback device.
See the Speed PI Regulator on page 152 section for information about the speed
regulator.
See the Torque Reference on page 193 section for information about choosing
the output of the speed regulator as the reference to the torque loop.