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1、Sizing Dynamic Brake Resistors and Chopper ModulesDynamic Brake Module CircuitUsing a Dynamic Brake or ChopperIn 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
2、 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.Gather the Information FirstThe nameplate power rating of the motor in watts,kilowatts,or horsepower.The nameplate speed rating of the motor
3、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.Example Speed,Torque,and Power ProfiletttHow to Choose a Dynamic Brake/ChopperCalcu
4、late the total inertia of the systemCalculate 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.T
5、hird,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.How t
6、o Size A Dynamic Brake ModuleStep 1-Total InertiaJT=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)JL=load inertia,kilogram-meters2(kg-m2)or pound-feet2(lb-ft2)2=0.04214011 kg-m2Step 2-Peak Regener
7、ative PowerJT=total inertia reflected to the motor shaft,kg-m2wb=max angular rotational speed,Rad/s=2pNb/60wo=angular rotational speed,less than rated speed(can be zero)Rad/s Nb=maximum application speed in RPMt3-t2=total time of deceleration from wb to wo,secondsPb=peak braking power,wattsNote:1.0
8、HP=746 wattsStep 3-Maximum DB Resistor ValueVd=the value of DC Bus voltage that the chopper module regulates at.This value will bePb=peak braking power calculated in step 2Rdb1=the maximum allowable value for the dynamic brake resistorResistor tolerances could be built in here.+/-10%Step 4-Choose th
9、e Correct DB ModuleKA005-28 ohms,666 wattsKA010-13.2 ohms,1650 wattsKA050-10.5 ohms,7000 wattsKB005-108 ohms,1500 wattsKB010-52.7 ohms,2063 wattsKB050-10.5 ohms,7000 wattsKC005-108 ohms,1500 wattsKC010-52.7 ohms,2063 wattsKC050-15.8 ohms,8000 wattsStep 5-Estimate the Average PowerPav=average dynamic
10、 brake resistor dissipation,wattst3-t2=elapsed time to decelerate from wb speed to wo speed,secondst4=total cycle time,secondsPb=Peak braking power,wattswb=maximum motor speed,Rad/swo=a slower motor speed,Rad/sStep 6-Percent Average LoadStep 7-Percent Peak LoadAL=Average Load in percent of Dynamic B
11、rake ResistorPav=Average dynamic brake resistor dissipation calculated in step 5,wattsPdb=Steady state power dissipation capacity of the selected dynamic brake modulePL=Peak Load in percent of Dynamic Brake ResistorPav=Peak braking power calculated in step 2,wattsPdb=Steady state power dissipation c
12、apacity of the selected dynamic brake moduleStep 8-Plot AL and PL on CurvesHow to Select a Chopper Module and Dynamic Braking ResistorStep 1-Total InertiaJT=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(
13、lb-ft2)JL=load inertia,kilogram-meters2(kg-m2)or pound-feet2(lb-ft2)2=0.04214011 kg-m2Step 2-Peak Regenerative PowerJT=total inertia reflected to the motor shaft,kg-m2wb=max angular rotational speed,Rad/s=2pNb/60wo=angular rotational speed,less than rated speed(can be zero)Rad/sNb=maximum applicatio
14、n speed in RPM t3-t2=total time of deceleration from wb to wo,secondsPb=peak braking power,wattsNote:1.0 HP=746 wattsStep 3-Maximum DB Resistor ValueVd=the value of DC Bus voltage that the chopper module regulates at.This value will bePb=peak braking power calculated in step 2Rdb1=the maximum allowa
15、ble value for the dynamic brake resistorResistor tolerances could be built in here.+/-10%Step 4-Choose the Correct Chopper ModuleId1=the minimum current flowing through the chopper module transistorVd=the value of the DC bus voltage,see step 3Rdb1=the maximum allowable value for the dynamic brake re
16、sistorStep 5-Minimum DB Resistor ValueStep 6-Choosing DB Resistor ValueRdb2=the minimum value of the dynamic brake resistorVd=the value of the DC bus voltage,see step 3Id2=the value of the current rating for the chopper moduleAbout Duty CycleGiven that a resistor cools off in about 15 minutes,if cyc
17、le time minus the decel time exceeds 900 then using the larger cycle time cant be used for calculating average power.Lets 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?Step 7-Estimat
18、e Resistor WattagePav=average dynamic brake resistor dissipation,wattst3-t2=elapsed time to decelerate from wb speed to wo speed,secondst4=(adjusted)total cycle time,secondsPb=Peak braking power,wattswb=maximum motor speed,Rad/swo=a slower motor speed,Rad/sStep 8 Calculate Watt-SecondsPws=required w
19、att-seconds of the resistort3-t2=elapsed time to decelerate from wb speed to wo speed,secondsPb=Peak braking power,wattsHow to Size a resistor for PowerFlex 70/700Step 1-Total InertiaJT=total inertia reflected to the motor shaft,kilogram-meters2(kg-m2)or pound-feet2(lb-ft2)Jm=motor inertia,kilogram-
20、meters2(kg-m2)or pound-feet2(lb-ft2)JL=load inertia,kilogram-meters2(kg-m2)or pound-feet2(lb-ft2)2=0.04214011 kg-m2Step 2-Peak Regenerative PowerJT=total inertia reflected to the motor shaft,kg-m2wb=max angular rotational speed,Rad/s=2pNb/60wo=angular rotational speed,less than rated speed(can be ze
21、ro)Rad/sNb=maximum application speed in RPM t3-t2=total time of deceleration from wb to wo,secondsPb=peak braking power,wattsNote:1.0 HP=746 wattsStep 3-Maximum DB Resistor ValueVd=the value of DC Bus voltage that utilizes the full capability of the drive.395VDC or 790VDC or 987VDCPb=peak braking po
22、wer calculated in step 2Rdb1=the maximum allowable value for the dynamic brake resistorResistor tolerances are built into the minimum resistances for each individual driveAbout Duty CycleGiven that a resistor cools off in about 15 minutes,if cycle time minus the decel time exceeds 900 then using the
23、 larger cycle time cant be used for calculating average power.Lets 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?Step 7-Estimate Resistor WattagePav=average dynamic brake resistor di
24、ssipation,wattst3-t2=elapsed time to decelerate from wb speed to wo speed,secondst4=(adjusted)total cycle time,secondsPb=Peak braking power,wattswb=maximum motor speed,Rad/swo=a slower motor speed,Rad/sStep 8 Calculate Watt-SecondsPws=required watt-seconds of the resistort3-t2=elapsed time to decelerate from wb speed to wo speed,secondsPb=Peak braking power,wattsMore discussions:Intermittent overhauling loads.Doubling up chopper units.