Torque pre-control MCTRL-M-ADD (MADD) in case of speed control, what must be considered?

Question:
What has to be considered in configuration 'speed control' when the input MCTRL-M-ADD is used (additional torque setpoint)?

Answer:
A torque pre-control (e. g. for compensation of frictional forces) can be added in case of 'speed control' via the function block input MCTRL-M-ADD. Please make sure that the selected value for MCTRL-M-ADD does not exceed the torque limits:

• In practice: (MCTRL-LO-M-LIM)  <  (MCTRL-M-ADD)  <  (MCTRL-HI-M-LIM)
• In theory:    (MCTRL-LO-M-LIM)  <  (MCTRL-M-ADD) - friction torque  <  (MCTRL-HI-M-LIM)

When the torque limits are exceeded the drive can accelerate, if necessary until the speed limit / the machine's speed monitoring (NMAX = C0596) is reached! In this case mechanical forces and the machine's load act speed limiting.

Function of torque limit in the function block MCTRL in case of speed control:

• The limitations MCTRL-HI-M-LIM and MCTRL-LO-M-LIM act - as presented in the function block MCTRL (see manual) - behind the summation point from speed controller output and MCTRL-M-ADD.
• Additionally the limitation acts directly at the speed controller output (not presented).
• Generally a too high torque pre-control (MCTRL-M-ADD) is compensated by the speed control-loop, as the speed controller makes sure that the set speed is kept. Compensation by the speed controller is, however, only possible up to the torque limits. If the torque limits area |MCTRL-M-ADD| > |MCTRL-HI/LO-M-LIM| is exceeded, the drive can accelerate strongly.

In applications, which need a torque pre-control (MCTRL-M-ADD) in addition to the speed control with torque limitation, this pre-control should be limited to the torque limits area (MCTRL-HI/LO-M-LIM) by a corresponding function block switching in order to ensure save operation, e. g.:

• Application of function block LIM (in case of constant torque control MCTRL-HI/LO-M-LIM) or
• Switching off the torque pre-control to a fixed, smaller value per ASWx, when the speed controller output has reached the torque limit (MCTRL-MMAX = High).

The described behaviour of the MCTRL applies to all variants of the 9300 drive controller (Servo PLC and 9300 Vector/Hoist frequency inverter, duty type 'Vector control').

URL for linking this AKB article: https://www.lenze.com/en-de/go/akb/20030097/1/