Rockwell Automation 7000 PowerFlex Medium Voltage AC Drive (B Frame) Commissioning - ForGe Control - Manual (Page 101)

Rockwell Automation Publication 7000-IN012B-EN-P - June 2014 101
Commissioning the Drive Chapter 4
The other aspect of flux control is the variation of motor flux with speed,
determined by two parameters:
• Base Speed in Flux Control
• FlxCmd RatedLoad in Flux Control
In most applications, the motor runs at constant flux below rated speed and
constant voltage above rated speed. The motor flux normally operates at a level
that provides rated voltage at rated speed and full load. The flux level required to
achieve this is a function of the motor parameters. The flux regulator auto-tuning
determines a value of rotor flux that should provide rated motor voltage at full
load and rated speed, and sets the flux command parameter to this value.
Speed Regulator
Two parameters in the Speed Control group determine the speed regulator
tuning:
• SpdReg Bandwidth
• Total Inertia
Set Parameter SpdReg Bandwidth to a value determined by the requirements of
the application. Total Inertia is usually unknown; measure it separately. The auto-
tuning determines the total inertia by measuring the change in speed that occurs
when a low frequency sinusoidal torque perturbation is applied to the motor.
Load torque does not affect the inertia measurement as long as the drive does not
hit torque limit. Do not disconnect the driven load from the motor, you are
measuring the total inertia of motor and load.
Use the following procedure to auto-tune FluxSpeed Reg (Induction Motor):
1. Ensure that parameters Rated Motor RPM in Motor Ratings and L Total
Leakage in Motor Model have the correct value. Ensure that parameters
Autotune Spd Cmd and Autotune Trq Stp in Autotune use default values.
2. Set the Autotune Select parameter in Autotuning to FluxSpeed Reg.
3. Start the drive. The motor accelerates normally up to the speed specified
by parameter Autotune Spd Cmd. Calculate the motor magnetizing
inductance from the measured current and flux feedback. Set the Autotune
L Magn parameter to this value. Set the flux command 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. Repeat
the process until the magnetizing inductance and flux commands stabilise.
4. After completing the flux regulator tuning, the drive waits for a few
seconds and adds a sinusoidal perturbation specified by parameter
Autotune Trq Stp to the torque command, causing the speed to vary. After
the initial transient has decayed (this usually takes a few seconds), measure
the variation in torque and speed and calculate the Total Inertia. Remove
the torque perturbation, and the drive performs a normal stop.