Rockwell Automation 20G PowerFlex 750-Series AC Drives - Manual (Page 212)

212 Rockwell Automation Publication 750-RM002B-EN-P - September 2013
Chapter 4 Motor Control
The Dynamic Brake Resistor power rating in watts that is chosen will be equal to
or greater than the value calculated in Step 7.
Step 8 – Calculate the requires Watt-Seconds (joules) for the resistor
To be sure the resistor’s thermal capabilities are not violated, a calculation to
determine the amount of energy dissipated into the resistor is made. This
determines the amount joules the resistor must be able to absorb.
P
ws
= Required watt - seconds of the resistor
t
3
- t
2
= Elapsed time to decelerate from
ω
b speed to
ω
0 speed, seconds
P
b
= Peak braking power, watts
Internal Brake IGBT for PowerFlex 755 Drives
Sizing Resistors for an internal DB IGBT
Sizing resistors for the internal DB IGBT Uses the same formula's as previous,
and is very similar to the Chopper Module sizing.
Step 1 – Determine the Total Inertia
J
T
= Total inertia reflected to the motor shaft, kilogram-meters2, kg•m
2
, or
pound-feet2, 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, dimensionless
J
L
= load inertia, kilogram-meters2, kg•m
2
, or pound-feet2, lb•ft
2
(1.0 lb•ft
2
=
0.04214011 kg•m
2
)
P
ws
t
3
t
2
– ( )
P
b
2
------ × =
J
T
J
m
GR 2 J
L
Ч + =