Rockwell Automation 7000 PowerFlex Medium Voltage AC Drive (B Frame) Commissioning - ForGe Control - Manual (Page 109)

Rockwell Automation Publication 7000-IN012B-EN-P - June 2014 109
Commissioning the Drive Chapter 4
3. Start the drive. The motor accelerates normally up to the speed specified
by parameter Autotune Spd Cmd. The motor magnetizing inductance is
calculated from the magnetizing current reference and the flux feedback
and parameter Autotune Lm is set to this value. The flux command is then
set to a value that should produce rated voltage at rated speed and load.
The resulting change in the flux level may cause the magnetizing
inductance to change. This process is repeated until the magnetizing
inductance and flux command stabilize. If a position encoder is fitted to
the motor, the angle between the measured flux and the encoder zero is
measured and parameter Encoder offset is adjusted to align the encoder
with the motor flux.
The field current reference is then held constant and the response of the flux to
changes in stator magnetizing current is measured by stepping “Ix command” up
and down at regular intervals. The size of the step in the stator current is specified
by parameter Autotune Isd Step. The step response measurement takes about 3
minutes. During this step parameter Lmd, T Rotor, Lm Rated will be calculated.
When the motor speed has settled at the commanded value, a sinusoidal
perturbation specified by parameter Autotune Trq Stp is added to the torque
command, causing the speed to vary. After the initial transient has decayed (this
usually takes a few seconds), the variation in torque and speed are measured and
used to calculate the total inertia. The torque perturbation is then removed and
the drive performs a normal stop.
Parameter FlxCmd RatedLoad in Flux Control is set to a value calculated to
produce rated voltage at rated speed and load. The value of parameters Autotune
T rotor and Autotune Lmd are calculated from the step response data.
If the flux regulator auto-tuning is successful, then parameter Lm Rated in Motor
Model is set equal to Autotune L Magn, parameter T Rotor in Motor Model is set
equal to Autotune T Rotor, and parameter Lmd in Motor Model is set equal to
Autotune Lmd. Parameter Total Inertia (P#63) in Speed Control is set equal to
Autotune Inertia.
If the flux regulator auto-tuning fails, a warning indicates the cause of the failure:
• L Magnetize Low – indicates that the measured value of magnetizing
inductance is less than 1.0 pu. This warning is intended to draw attention
to an unusually low value of magnetizing inductance. The most likely cause
is incorrect scaling of the analog field current reference.
• L Magnetize High – indicates that the measured value of magnetizing
inductance is greater then 15.0 pu. This warning is intended to draw
attention to an unusually high value of magnetizing inductance. The most
likely cause is incorrect scaling of the analog field current reference.
• T Rotor Low – indicates that the calculated value of rotor time constant is
less than 0.2 seconds
• T Rotor High – indicates that the calculated value of rotor time constant is
greater than 5.0 seconds.