Rockwell Automation 7000 PowerFlex Medium Voltage AC Drive (B Frame) - Classic Control - Manual (Page 264)

5-10 Functional Description
7000-UM150I-EN-P – June 2013 7000 “B” Frame
Flux Control for Synchronous
Motor
Most of the magnetization for a synchronous motor is supplied by
the rotor field winding, unlike an induction motor where all of the
magnetizing current is supplied through the stator. However, control
of the motor flux through the field current is very slow because of
the large time constant of the dc field winding and the current and
voltage limitations of the field supply. To obtain sufficiently fast
response from the flux regulator the magnetizing current is split into
transient and steady state components, with the steady state
component supplied through the rotor and the transient component
through the stator.
The additions to the flux control required for synchronous machines
are shown in the block diagram (Figure 5.6). The portion of the
motor filter capacitor current supplied by the drive is then added to
determine Ix Command, which is the magnetizing component of the
dc link current command.
Parameter Icd Command Gain (107) determines how the motor filter
capacitor current is split between the motor and the drive. When this
parameter is set to its minimum value of 0.0, all the capacitor current
is supplied by the drive. The line current is higher than the motor
current and the motor operates at approximately unity power factor.
When this parameter is set to its maximum value of 1.0, the motor
supplies all the capacitor current. The line current is less than the
motor current and the motor operates at a lagging power factor with
reduced field current.