变频器制动电阻选择和计算方法

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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.
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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.
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Example Speed, Torque, and Power Profile
(t)
0
t1 t2 t3
t4
t1+t4
t
t
T(t)
0
t1 t2 t3
t4 t t1+t4
t
P(t)
t
0
t1 t2 t3
t4
t1+t4
t
-Pb
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How to Choose a Dynamic Brake / Chopper
To V o lta g e D ivid e r
Chopper T ra n s is to 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
FW D
V o lta g e D ivid e r
To V o lta g e C ontrol
• 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.
S ig n a l Com m on
FW D
To V o lta g e C ontrol
V o lta g e D ivid e r
To C row bar
SCR G ate
- DC Bus来自百度文库
Fuse
Bus Caps
C row bar SCR
To V o lta g e C ontrol
Bus Caps
Note: 1.0lb-ft2 = 0.04214011 kg-m2
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Step 2 - Peak Regenerative Power
– 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.
• 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.
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How to Size A Dynamic Brake Module
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Step 1 - Total Inertia
JTJmG2R xJL
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. 2:1 = 0.5 JL = load inertia, kilogram-meters2 (kg-m2) or pound-feet2 (lb-ft2)
Sizing Dynamic Brake Resistors and Chopper Modules
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Dynamic Brake Module Circuit
+ DC Bus
Fuse
To V o lta g e D ivid e r
D yn a m ic B rake
R e s is to r
• 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.