Allen-Bradley PowerFlex User Manual

2-6
Step 4 Minimum Power Requirements for the Dynamic Brake
Resistors
It is assumed that the application exhibits a periodic function of
acceleration and deceleration. If (t
3
– t
2
) equals the time in seconds
necessary for deceleration from rated speed to ω
o
speed, and t
4
is the
time in seconds before the process repeats itself, then the average duty
cycle is (t
3
– t
2
)/t
4
. The power as a function of time is a linearly
decreasing function from a value equal to the peak regenerative power to
some lesser value after (t
3
– t
2
) seconds have elapsed. The average power
regenerated over the interval of (t
3
– t
2
) seconds is:
P
av
= Average dynamic brake resister dissipation (watts)
t
3
– t
2
= Deceleration time from ω
b
to ω
o
(seconds)
t
4
= Total cycle time or period of process (seconds)
P
b
= Peak braking power (watts)
ω
b
= Rated angular rotational speed
ω
o
= Angular rotational speed,
less than rated speed down to zero
The Average Power in watts regenerated over the period t
4
is:
Calculate Average Power in watts regenerated over the period t
4
:
Record Average Power in watts regenerated over the period t
4
:
P
av
=
P
b
2
-----
ω
b
ω
o
+()
ω
b
------------------------
×
Rad
s
---------
Rad
s
---------
P
av
t
3
t
2
–()
t
4
------------------
P
b
2
-----
ω
b
ω
o
+()
ω
b
------------------------
=
P
av
oooooo oooooo–()
oooooo[]
-----------------------------------------------
oooooo[]
2
-----------------------
×
oooooo oooooo+()
oooooo[]
-----------------------------------------------
×=

Allen-Bradley PowerFlex Specifications

General

Brand	Allen-Bradley
Model	PowerFlex
Category	DC Drives
Language	English