Rockwell Automation 20G PowerFlex 750-Series AC Drives - Manual (Page 244)

244 Rockwell Automation Publication 750-RM002B-EN-P - September 2013
Chapter 4 Motor Control
Notch Filter A notch filter exists in the torque reference loop to reduce mechanical resonance
created by a gear train. P687 [Notch Fltr Freq] sets the center frequency for the 2
pole notch filter, and P688 [Notch Fltr Atten] sets the attenuation of the notch
filter in the vector control torque reference section. Attenuation is the ratio of the
notch filter input signal to its output at the P687 [Notch Fltr Freq]. An
attenuation of 30 means that the notch output is 1/30th of the input at the
specified frequency.
The notch filter is valid only in Flux Vector Motor Control modes (P35).
Figure 25 - Notch Filter Frequency
Example
A mechanical gear train consists of two masses (the motor and the load) and
spring (mechanical coupling between the two loads).
Mechanical Gear Train
The resonant frequency is defined by the following equation:
• Jm is the motor inertia (seconds)
• Jload is the load inertia (seconds)
• Kspring is the coupling spring constant (rad2 / sec)
The following graph shows a two mass system with a resonant frequency of 62
radians/second (9.87 Hz). One Hertz is equal to 2p radians/second.
Gain
0 db
Hz Notch Filter Frequency
Notch Filter K
Kspring
BL Bm
Jm Jload
ResonanceHz Kspring
Jm Jload
+ ( )
Jm Jload
Ч ( )
--------------------------------- Ч =