Allen-Bradley LOGIX 5000 Reference Manual page 305

Drives Chapter 2
Its corresponding bode diagram is shown in Diagram B below.
The SOC instruction can be used in a torque or tension regulating application
where a load cell or force transducer is used as feedback and the output of the
regulating scheme operates directly on the torque (current) minor loop of the
drive. In many such applications, the controlled system may be mechanically
under-damped and have a natural frequency which is difficult to stabilize as it
becomes reflected through the feedback device itself.
Using the SOC instruction, PID tuning is simplified because the regulating terms
can be arranged so that you have WLead and ZLead as inputs to the SOC
instruction, rather than Kp, Ki, and Kd values. In this manner, the corner
frequencies of the controller/regulator are easier to adjust and setup against the
real world process. During startup, the natural frequency of the system and the
damping factor can be measured empirically or on-site. Afterward, the parameters
Rockwell Automation Publication 1756-RM006K-EN-P - November 2018 305