Rockwell Automation 7000 PowerFlex Medium Voltage AC Drive (B Frame) Commissioning - ForGe Control - Manual (Page 106)

106 Rockwell Automation Publication 7000-IN012B-EN-P - June 2014
Chapter 4 Commissioning the Drive
Calculating Total Inertia
If you cannot measure the system inertia, calculate it (if you know the motor’s
inertial moment motor and load). The value of parameter Total Inertia is the time
required to accelerate the motor and load to rated speed when applying the rated
torque. Use the following formulas for either metric or imperial calculations.
Metric:
, where:
• T
iM
= Total inertia of motor and load in kg•m

• S
M
= Rated speed in rad/s
• P
M
=Power in watts
Imperial:
, where:
• T
iI
= Total inertia of motor and load in lb•ft

• S
I
= Rated speed in rpm
• P
I
=Power in Hp
If there is a gearbox between the motor and load, refer the inertia of the load to
the motor side of the gearbox.
Flux Speed Regulator (Synchronous Motors)
Configuring the Field Current Reference
Use a current-regulated field supply to excite the synchronous motor: either a dc
supply for a slip ring or DC brushless machine, or a three phase ac supply for an
AC brushless machine. The drive provides an analog current reference as an input
to the field supply. The analog current reference has a range of 0...10V, where 0V
corresponds to zero field current and 10V corresponds to maximum field current.
Adjust the scaling of the analog current reference to achieve a linear relationship
between the current reference and the actual field current. Failing to do so may
result in an unstable flux regulator. Adjust the analog output scaling using the
following procedure:
1. Temporarily assign variable Autotune Lmd in Autotuning to the analog
output that controls the field supply (e.g. ACB Port 1).
IMPORTANT Before tuning the FluxSpeed regulator, you must configure the analog output
for the field current reference.
Total inertia (s)
T
iM
S
M

P
M
---------------------- =
Total inertia (s) 6.21 10
7 – 
T
iI
S
I

P
I
-----------------  
 
=