Rockwell Automation 1557 MEDIUM VOLTAGE AC DRIVE - Manual (Page 29)

DESCRIPTION OF OPERATION 5-11
1557-UM050F-EN-P –June 2013
Flux Control
The function of the flux control block is to determine the magnetizing current command. The inputs are
flux feedback and stator frequency from the motor model, speed feedback from the speed control block,
and line voltage from the current control block.
Below base speed, the flux command varies linearly with Torque Reference from the value specified by
parameter Flux Command No Load at zero torque to the value specified by parameter Flux Command
Base Speed at rated torque. Above base speed, the drive goes into field weakening and the flux
command decreases with increasing speed. The flux command also decreases when the current
regulator approaches advance limit or retard limit.
The flux reference is determined by adding parameter Flux Reference Step, which is used to demonstrate
the step response of the flux regulator, to the flux command. The flux feedback is subtracted from the
flux reference to determine the flux error, which is the input to the flux regulator. The response of the flux
regulator is determined by parameters Flux Regulator Bandwidth, Magnetizing Inductance, and Rotor
Time Constant. The output of the flux regulator is called Isd Command 1. An open loop estimate of the
magnetizing current called Isd Command 0 is determined by dividing the flux reference by parameter
Magnetizing Inductance. Isd Command 0 and Isd Command 1 are added to produce Isd Command,
which is the magnetizing component of the stator current command.
An estimate of the magnetizing current supplied by the motor filter capacitor is calculated from Isd
Command, stator frequency, and parameters Total Leakage Inductance and Filter Capacitor. The
resulting value is called Icd Command and is subtracted from Isd Command to determine Ix Command,
which is the magnetizing component of the dc link current command. Ix Command becomes negative at
high speed because the motor filter capacitor supplies more magnetizing current than the motor requires.