Rockwell Automation 7000L PowerFlex Medium Voltage AC Drive (C Frame) - Classic Control - Manual (Page 324)

5-16 Functional Description
7000L-UM300I-EN-P – June 2013 7000 “C” Frame
Motor Model
The function of the motor model block (Figure 5.8) is to determine
the rotor flux position (Flux Angle), flux feedback (Flux Feedback),
applied stator frequency (Stator Freq), slip frequency (Slip
Frequency) and motor operating variables like stator current (I
Stator), stator voltage (V Stator), torque (Torque), power (Motor
Power) and power factor (Mtr Pwr Factor).
The PowerFlex 7000 uses Rotor Flux oriented control to achieve
independent control of motor flux and torque. This is achieved by
synchronizing the machine converter gating to Flux Angle. To
determine the flux feedback, stator frequency and the synchronizing
reference frame the drive uses either the Voltage or the Current
model. For speeds greater than 3Hz, the drive uses the voltage model
(hardware analog flux model) to calculate the Flux from Voltage,
Flux Angle V and Stator Freq V. Below 3Hz, the drive uses the
current model to calculate Flux from Current, Flux Angle C and
Stator Freq C. The current model is based on indirect vector control
and uses the d-q components of stator current along with motor
parameters T Rotor and L Magnetizing. Based on the operating speed
of the drive and the speed feedback mode (Sensorless or Pulse
Tach), a flux select algorithm determines the model to be used.
Motor model also calculates the Slip Frequency which is used in the
calculation of the motor speed (Speed Control) in Sensorless mode
and for determining the rotor flux position in Pulse Tach mode.
The synchronously rotating frame (Flux Angle) is used in
transforming the measured motor currents and voltages into d-q
components. The direct axis components (I
sd
and V
sd
) are in phase
with the rotor flux, while the quadrature axis components (I
sq
and
V
sq
) are displaced 90 degrees from the rotor flux. The stator current
(I Stator) and voltage magnitudes (V Stator) are calculated by taking
the square root of the sum of the squares of the respective d-q
components. The motor Torque is calculated by multiplying the Flux
Feedback and I
sq
with motor torque constant. Torque multiplied by
the motor speed gives the Motor Power. Mtr Power Factor is
determined as the ratio of motor active power and the apparent
power.