Siemens SINAMICS PERFECT HARMONY GH180 Function Manual page 328

Advanced Operating Functions
8.23 Conveyor Applications
tension between sections of the belt. This is done by means of an external PLC to provide
required load balancing among all motors.
Since an IM uses slip (difference between rotor mechanical speed and stator electrical speed) to
provide torque, it can be magnetized in the normal manner for IMs. Once magnetized, then a
state machine will apply a rotational current vector with the magnitude determined by an
external current command and the rotational speed controlled through an external speed
command. All ramping of both speed and current must be done within the PLC, thus requiring
fast communication register access to allow for smooth operation.
This algorithm provides the means to coordinate the drives and motors along the conveyor, but
the PLC accomplishes synchronization. Further, the state transitions, to a large extent, are
controlled through handshaking signals between the PLC and the NXGPro+ control.
Slip compensation is applied during the open-loop HST mode by utilizing the current command
to calculate the slip. Once magnetized, the motor is spinning, and the flux vector is locked on by
the PLL, the current feedback is decomposed into the d-q components. Slip is then calculated
as normal for IM OLVC control mode.
Because they are controlled externally, ramps for current and frequency are bypassed entirely
until completion of the state machine.
At the completion of the state machine, the drive smoothly transitions into the speed loop
(integrator preset); and, the speed command is generated from the fast access speed demand
(ramp is preset to actual motor speed). The current command is replaced by the output of the
speed regulator, and the external current signal is used as a dynamic torque current limit. By
using the current signal command as the dynamic torque limit, torque current signal controls
the output of the drive directly, provided that the speed regulator remains in saturation.
The HST mode state machine remains at the initialized state until the drive magnetizes the motor
and enters the Run drive state. It then begins the transitions through the state machine. The
sequence is depicted in the figure PLC Directed High Starting Torque Mode Timing Diagram.
Note: NXGPro+ Diagrams wll be updated in a later software release.
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NXGPro+ Control Manual
Operating Manual, A5E50491925A