Rockwell Automation 20G PowerFlex 750-Series AC Drives - Manual (Page 205)

Rockwell Automation Publication 750-RM002B-EN-P - September 2013 205
Motor Control Chapter 4
3. The motor inertia and load inertia in kilogram-meters2, or lb•ft
2
.
4. The gear ratio, if a gear is present between the motor and load, GR.
5. Review the Speed, Torque Power profile of the application.
Equations used for calculating Dynamic Braking values use the following
variables.
ω
(t) = The motor shaft speed in Radians/second, or
N
(t)
= The motor shaft speed in Revolutions Per Minute, or RPM
T
(t)
= The motor shaft torque in Newton-meters, 1.01 lb•ft - 1.355818N•m
P
(t)
= The motor shaft power in Watts, 1.0HP = 746 Watts
-P
b
= The motor shaft peak regenerative power in Watts
Step 1 – Determine the Total Inertia
J
T
= J
m
+ GR
2
x J
L
J
T
= Total inertia reflected to the motor shaft, kilogram-meters
2
, kg•m
2
, or
pound-feet
2
, lb•ft
2
J
m
= Motor inertia, kilogram-meters2, kg•m
2
, or pound-feet2, lb•ft
2
GR = The gear ratio for any gear between motor and load, dimentionless
J
L
= Load inertia, kilogram-meters2, kg•m
2
, or pound-feet2, lb•ft
2
– 1 lb•ft
2
=
0.04214011 kg•m
2
Step 2 – Calculate the Peak Braking Power
J
T
= Total inertia reflected to the motor shaft, kg•m
2
ω
= rated angular rotational speed,
N = Rated motor speed, RPM
ωRad s ⁄
2
πN
60
----------RPM =
P
b
J
T
ω 2 ×
t
3
t
2
–
----------------- =
Rad s
⁄
2
πN
60
---------- =