Rockwell Automation 1557 MEDIUM VOLTAGE AC DRIVE - Manual (Page 236)

9-36 COMMISSIONING
1557-UM050F-EN-P – June 2013
Tuning the Flux Regulator
The tuning of the flux regulator for a synchronous machine is determined by four parameters:
1. Flxreg bandwidth in "P Flux Control"
2. L magnetizing in "P Motor Model"
3. T rotor in "P Motor Model"
4. Lmd in “P Motor Model”
"Flxreg bandwidth" should be set to the default value for almost all applications. "L magnetizing", “Lmd”, and "T
rotor" are usually unknown and must be measured. Although these motor parameters change with different
operating conditions, the variations do not significantly affect the operation of the flux regulator.
The other aspect of flux control is the variation of motor flux with speed. This is determined by two parameters in
the "P Flux Control" group:
1. Base speed
2. Flux command base speed
In most applications, the motor runs at constant flux below rated speed and constant voltage above rated speed.
The motor flux is normally set to 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 autotuning 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.
Flux Regulator Autotuning
Note: If a position encoder is fitted to the motor, the flux regulator autotuning is performed with the encoder
feedback turned off because it is assumed that the encoder has not been aligned with the rotor axis yet. Since
less starting torque is produced with the encoder feedback off, this test should be performed with reduced load.
The encoder offset measurement is also most accurate with no load on the motor.
The flux regulator is tuned with the motor running at constant speed using the following procedure:
1.
Ensure that the analog reference for the field current has been set up as described previously, and that
parameter “L total leakage” has been set to the correct value.
2.
Set parameter "Autotune select" in "P Autotune" to 6.
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.
4.
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. When the measurement is complete, the drive performs a normal
stop.
Parameter "Autotune Lm" is set to the measured magnetizing inductance and parameter "Autotune select" is set to
zero. Parameter "Flux Command Base Speed" in "P 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.