Transcript Step 2

Sizing Dynamic Brake
Resistors
and Chopper Modules
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
Dynamic Brake Module Circuit
+ DC Bus
Fuse
Bus Caps
FW D
D y n a m ic
B ra k e
R e s is to r
To
V o lta g e
D iv id e r
V o lta g e
D iv id e r
To
V o lta g e
C o n tro l
To
V o lta g e
D iv id e r
S ig n a l
Com m on
Chopper
T ra n s is to r
C ro w b a r
SCR
FW D
To
V o lta g e
C o n tro l
V o lta g e
D iv id e r
C h o p p e r T ra n s is to r
V o lta g e C o n tro l
Bus Caps
To
V o lta g e
C o n tro l
Fuse
To
C ro w b a r
SCR
G a te
- DC Bus
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
Using a Dynamic Brake or Chopper
• In general, the motor power rating, speed, torque, and details of
the regenerative duty cycle need to be known.
• Generally, a dynamic brake can be used whenever regenerative
energy is dissipated on an occasional or periodic basis.
• If the drive will consistently be regenerating, serious consideration
should be given to returning the power to the AC utility.
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
Gather the Information First
•
•
•
•
•
The nameplate power rating of the motor in watts, kilowatts, or horsepower.
The nameplate speed rating of the motor in rpm, or rps.
The motor inertia and load inertia in kilogram-meters2, or lb-ft2.
The gear ratio, if a gear is present between the motor and load, GR.
The motor shaft speed, torque, and power profile of the drive application.
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
Example Speed, Torque, and Power Profile
 (t)
0
t1
t2 t 3
t4
t1
t2 t 3
t4
t
t1+ t 4
t
t1+ t 4
t
t1+ t 4
t
T(t)
0
t
P(t)
t
0
t1
t2 t 3
t4
-Pb
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
How to Choose a Dynamic Brake / Chopper
• Calculate the total inertia of the system
• Calculate the peak regenerative power you need to dissipate.
– This will determine the maximum allowable resistance value of the DB
resistor.
• Calculate the average power dissipation
– This will determine the average power dissipation capacity needed in the
DB resistor.
• Third, check to see that the peak temperature of the dynamic
braking resistor does not exceed its capacity.
– Plot the Average Load and Peak Load on the curve in the sizing guide. This
is necessary only on the dynamic brake modules!
• Dynamic brake modules should only be used on drives 75HP and
smaller.
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
How to Size A Dynamic
Brake Module
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
Step 1 - Total Inertia
JT  Jm  GR xJ L
2
JT = total inertia reflected to the motor shaft, kilogram-meters2 (kg-m2) or pound-feet2 (lb-ft2)
Jm = motor inertia, kilogram-meters2 (kg-m2) or pound-feet2 (lb-ft2)
GR = the gear ratio for any gear between the motor and load, dimensionless.
JL = load inertia, kilogram-meters2 (kg-m2) or pound-feet2 (lb-ft2)
Note: 1.0lb-ft2 = 0.04214011 kg-m2
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
2:1 = 0.5
Step 2 - Peak Regenerative Power
J T x b  b   o 
Pb 
t3  t 2
JT = total inertia reflected to the motor shaft, kg-m2
b = max angular rotational speed, Rad/s = 2pNb/60
o = angular rotational speed, less than rated speed (can be zero) Rad/s
Nb = maximum application speed in RPM
t3-t2 = total time of deceleration from b to o, seconds
Pb = peak braking power, watts
Note: 1.0 HP = 746 watts
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
Step 3 - Maximum DB Resistor Value
2
Vd
Rdb1 
Pb
Resistor tolerances could
be built in here. +/- 10%
Vd = the value of DC Bus voltage that the chopper module regulates at. This value will be
375VDC or 750VDC or 937.5VDC
Pb = peak braking power calculated in step 2
Rdb1 = the maximum allowable value for the dynamic brake resistor
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
Step 4 - Choose the Correct DB Module
• KA005 - 28 ohms, 666 watts
• KA010 - 13.2 ohms, 1650 watts
• KA050 - 10.5 ohms, 7000 watts
• KB005 - 108 ohms, 1500 watts
• KB010 - 52.7 ohms, 2063 watts
• KB050 - 10.5 ohms, 7000 watts
• KC005 - 108 ohms, 1500 watts
• KC010 - 52.7 ohms, 2063 watts
• KC050 - 15.8 ohms, 8000 watts
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
Step 5 - Estimate the Average Power
(t3  t2 ) Pb
Pav 
x
t4
2
 b   o 


 b 
Pav = average dynamic brake resistor dissipation, watts
t3-t2 = elapsed time to decelerate from b speed to o speed, seconds
t4 = total cycle time, seconds
Pb = Peak braking power, watts
b = maximum motor speed, Rad/s
o = a slower motor speed, Rad/s
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
Step 6 - Percent Average Load
Pav
AL 
x100
Pdb
AL = Average Load in percent of Dynamic Brake Resistor
Pav = Average dynamic brake resistor dissipation calculated in step 5, watts
Pdb = Steady state power dissipation capacity of the selected dynamic brake module
Step 7 - Percent Peak Load
Pb
PL 
x100
Pdb
PL = Peak Load in percent of Dynamic Brake Resistor
Pav = Peak braking power calculated in step 2, watts
Pdb = Steady state power dissipation capacity of the selected dynamic brake module
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
Step 8 - Plot AL and PL on Curves
KA, KB, KC Transient Power Capacity
600 600
500
Power, %
400
P d3( t )
300
200
100
107.544393
0
0.5
1
2
3
4
5
6
t
Time, seconds
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
7
8
9
10
10
How to Select a
Chopper Module and
Dynamic Braking
Resistor
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
Step 1 - Total Inertia
JT  Jm  GR xJ L
2
JT = total inertia reflected to the motor shaft, kilogram-meters2 (kg-m2) or pound-feet2 (lb-ft2)
Jm = motor inertia, kilogram-meters2 (kg-m2) or pound-feet2 (lb-ft2)
GR = the gear ratio for any gear between the motor and load, dimensionless.
JL = load inertia, kilogram-meters2 (kg-m2) or pound-feet2 (lb-ft2)
Note: 1.0lb-ft2 = 0.04214011 kg-m2
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
2:1 = 0.5
Step 2 - Peak Regenerative Power
J T x b  b   o 
Pb 
t3  t 2
JT = total inertia reflected to the motor shaft, kg-m2
b = max angular rotational speed, Rad/s = 2pNb/60
o = angular rotational speed, less than rated speed (can be zero) Rad/s
Nb = maximum application speed in RPM
t3-t2 = total time of deceleration from b to o, seconds
Pb = peak braking power, watts
Note: 1.0 HP = 746 watts
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
Step 3 - Maximum DB Resistor Value
2
Vd
Rdb1 
Pb
Resistor tolerances could
be built in here. +/- 10%
Vd = the value of DC Bus voltage that the chopper module regulates at. This value will be
375VDC or 750VDC or 937.5VDC
Pb = peak braking power calculated in step 2
Rdb1 = the maximum allowable value for the dynamic brake resistor
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
Step 4 - Choose the Correct Chopper Module
Vd
I d1 
Rdb1
Id1 = the minimum current flowing through the chopper module transistor
Vd = the value of the DC bus voltage, see step 3
Rdb1 = the maximum allowable value for the dynamic brake resistor
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
Step 5 - Minimum DB Resistor Value
Rdb 2
Vd

Id 2
Rdb2 = the minimum value of the dynamic brake resistor
Vd = the value of the DC bus voltage, see step 3
Id2 = the value of the current rating for the chopper module
Step 6 -Choosing DB Resistor Value
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
About Duty Cycle
Given that a resistor cools off in about 15 minutes, if cycle time
minus the decel time exceeds 900 then using the larger cycle time
can’t be used for calculating average power.
 (t)
0
t1
t2 t 3
t4
t1+ t 4
t
T(t)
Let’s say that I decel in 10 seconds every hour. That would be 10 / 3600 or
0.002777 times the peak power. What if I decel in 50 seconds once a day?
Or 60 seconds once a week?
0
t1
t2 t 3
t4
t1+ t 4
t
If t4  t3  t2   900 then t4  900  t3  t2 
P(t)
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
Step 7 - Estimate Resistor Wattage
(t3  t2 ) Pb
Pav 
x
t4
2
 b   o 


 b 
Pav = average dynamic brake resistor dissipation, watts
t3-t2 = elapsed time to decelerate from b speed to o speed, seconds
t4 = (adjusted) total cycle time, seconds
Pb = Peak braking power, watts
b = maximum motor speed, Rad/s
o = a slower motor speed, Rad/s
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
Step 8 – Calculate Watt-Seconds
Pb
Pws  t3  t 2 x
2
Pws = required watt-seconds of the resistor
t3-t2 = elapsed time to decelerate from b speed to o speed, seconds
Pb = Peak braking power, watts
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
How to Size a resistor for PowerFlex 70/700
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
Step 1 - Total Inertia
JT  Jm  GR xJ L
2
JT = total inertia reflected to the motor shaft, kilogram-meters2 (kg-m2) or pound-feet2 (lb-ft2)
Jm = motor inertia, kilogram-meters2 (kg-m2) or pound-feet2 (lb-ft2)
GR = the gear ratio for any gear between the motor and load, dimensionless.
JL = load inertia, kilogram-meters2 (kg-m2) or pound-feet2 (lb-ft2)
Note: 1.0lb-ft2 = 0.04214011 kg-m2
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
2:1 = 0.5
Step 2 - Peak Regenerative Power
J T x b  b   o 
Pb 
t3  t 2
JT = total inertia reflected to the motor shaft, kg-m2
b = max angular rotational speed, Rad/s = 2pNb/60
o = angular rotational speed, less than rated speed (can be zero) Rad/s
Nb = maximum application speed in RPM
t3-t2 = total time of deceleration from b to o, seconds
Pb = peak braking power, watts
Note: 1.0 HP = 746 watts
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
Step 3 - Maximum DB Resistor Value
2
Vd
Rdb1 
Pb
Resistor tolerances are built
into the minimum resistances
for each individual drive
Vd = the value of DC Bus voltage that utilizes the full capability of the drive.
395VDC or 790VDC or 987VDC
Pb = peak braking power calculated in step 2
Rdb1 = the maximum allowable value for the dynamic brake resistor
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
About Duty Cycle
Given that a resistor cools off in about 15 minutes, if cycle time
minus the decel time exceeds 900 then using the larger cycle time
can’t be used for calculating average power.
 (t)
0
t1
t2 t 3
t4
t1+ t 4
t
T(t)
Let’s say that I decel in 10 seconds every hour. That would be 10 / 3600 or
0.002777 times the peak power. What if I decel in 50 seconds once a day?
Or 60 seconds once a week?
0
t1
t2 t 3
t4
t1+ t 4
t
If t4  t3  t2   900 then t4  900  t3  t2 
P(t)
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
Step 7 - Estimate Resistor Wattage
(t3  t2 ) Pb
Pav 
x
t4
2
 b   o 


 b 
Pav = average dynamic brake resistor dissipation, watts
t3-t2 = elapsed time to decelerate from b speed to o speed, seconds
t4 = (adjusted) total cycle time, seconds
Pb = Peak braking power, watts
b = maximum motor speed, Rad/s
o = a slower motor speed, Rad/s
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
Step 8 – Calculate Watt-Seconds
Pb
Pws  t3  t 2 x
2
Pws = required watt-seconds of the resistor
t3-t2 = elapsed time to decelerate from b speed to o speed, seconds
Pb = Peak braking power, watts
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.
More discussions:
Intermittent overhauling loads.
Doubling up chopper units.
Copyright © 2006 Rockwell Automation, Inc. All rights reserved.