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8/2/2019 Basics of Drives
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AC Drives
AC Drives Basics
Copyright 2005 Rockwell Automation, Inc. All rights reserved28th June2005 1
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AC Drives
How Does A Motor Work?
1. Current flowing through aconductor
2. The direction of the current
flow
3. Pass a conductor through a
magnetic field
Basic Rules:
Magnetic flux around the conductor
Polarity of the magnet
A voltage or current flow
Basic Concept
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AC Drives
Stator Magnetic Field
Rotor Field Created by Induced
Current Flow in Rotor Conductors
N S
Elastic Nature of MagneticLines of Force Rotor
Torque Generated in a motor
N S
F
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AC Drives
Workhorse of modern Industry
Found in virtually every phase of Manufacturing
O
ne of the Most Common Forms of rotating power
in the World
Consists of two sets of electromagnets One set ,the stator,housed in motor Frame and other rotor, free to rotate and
supported by bearings and motor end bells.
Squirrel Cage Induction Motor
Rotor
Fan BladesRotor BarEnd Rings
StatorPerforated Lamination disks stacked together and throughcareful die casting process Aluminum or Cu Brass Alloyis filled in the channels and then End rings are formed.
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AC Drives
Operational Issues
1. To Change the speed
2. Starting Current - Very High
3. Power Factor - Poor at light load
4.Protection - additional Equipments Required
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AC Drives
Frequency Drives
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AC Drives
AC Technology Current Source Inverter
Variable Voltage Inverter
PWM Inverters
V/Hz Inverters High Performance Vector Drive Preferred over CSI & VVI
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AC Drives
Diode rectifier converts AC line voltage to fixed voltage DC.
DC voltage is filtered to reduce current ripple from rectification.
Inverter changes fixed voltage DC to adjustable PWM AC voltage.
Diode rectifier converts AC line voltage to fixed voltage DC.
DC voltage is filtered to reduce current ripple from rectification.
Inverter changes fixed voltage DC to adjustable PWM AC voltage.
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AC Drives
Encoder
Actual Drive System
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AC Drives
PWM INVERTER
Fixed DC Bus
DiodeRectifier
AC Input
L InverterC+
Benefits Constant input P.F. Wide speed range High efficiency (97 - 98%) Ride through options Open circuit protection
Common bus regeneration Smooth low speed operation Vector control performance (optional)
Limitations Extra hardware for regeneration to line Motor noise (solved with IGBTs) Possible Cable length limitations (with IGBTs)
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AC Drives
Rectifier Section -Conversion From AC to DC
Positive Diodes
Negative Diodes
1
4
3
6
5
2
5&6
6&1
1&2
2&3
3&4
4&5
5&6
| One 360Cycle of Power |
| |
| |
| |
| |
60
| |
| |
| || |
| |
3 phase AC input tothe converter
DC output
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AC Drives
To FilterSection
Precharging Arrangement - in low Rated Drives
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AC Drives
Precharging Arrangement - in High Rated Drives
To FilterSection
Driver
Board
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AC Drives
Rectified
DC outputOV
Filtered
DC output
Filter Section - Smoothing of Rippled DC
Vdc
Vdc = 1.35VL- L
Idc =(1.1 X 746 X Drive HP)/ Vdc
CRectifiedInput FilteredOutput
DC Bus (+)
DC Bus(-)
OV
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AC Drives
Inverter Section Conversion From DC to ACPositive DC Bus Line
Negative DC Bus Line
Filtered DC
Input
PWM Output
IGBT fired in a sequence to produce a PWM output
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AC Drives
IGBT Insulated or Isolated Gate Bipolar TransistorIGBT combines the positive attributes of BJTs and MOSFETs.BJTs have lower conduction losses in the on-state, especially in devices withlarger blocking voltages, but have longer switching times, especially at turn-off while.
MOSFETs can be turned on and off much faster, but their on-state conduction losses arelarger, especially in devices rated for higher blocking voltages.
IGBTs have lower on-state voltage drop with high blocking voltage capabilities in addition to
fast switching speeds.
(+) Collector
(+) Base
(-) Emitter
NPN IGBT
(-) Base
(-) Collector
(+) Emitter
PNP IGBT
(+) Base
(+) Collector
(-) Emitter
NPN IGBT
(-) Base
(-) Collector
(+) Emitter
PNP IGBT
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AC Drives
Higher Switching (Carrier) Frequencies than Bipolar Transistors
Lower Motor Noise Lower Motor Heating
Drive Size Reduction
High Input Impedance
Reduces Base Driver Power Consumption
Reduces Base Driver Board Size
IGBT Advantages
Bi-Polar
IGBT
IGBT Insulated or Isolated Gate Bipolar Transistor
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AC Drives
PWM WAVEFORMS
0
0
Voltage(Line to Neutral)
Current(Line)
The PWM waveform actually is a Square wave DC voltage. This voltage is applieddirectly to the AC motor terminals.
Remember, even though we have DC voltage applied to the motor, the current
waveform resembles an AC sine wave. and is used to control speed of the ACsquirrel cage induction motor.
AC D i
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AC Drives
TriangleGenerator
Modulation
Generator
Generation of PWM WAVEFORMS
AC D i
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AC Drives
Sine Weighted PWM Pulses
The pulses are then inverted and are applied to the base of the transistor used to fire gateor turn on the power transistors to create the actual PWM output.
AC D i
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AC Drives
Transistor #4
Transistor #1
180 180
During the positive half cycle ofphase A, transistor # 1 is turned
on and off at a frequency
determined by the drive CPU.Transistor # 4 is used during thenegative half cycle. Notice howthe total duration makes up 360
electrical degrees or one full cycleof power.
Transistor #3
Transistor #6
Transistor #5
Transistor #2
180 180
180 180
Phase B & C operate in the sameway that phase A did except thereis a phase shift. Meaning that thephases start at different times. If
you are having troubleunderstanding phase shifts andelectrical degrees, refer to the
rectification module before movingon in this lesson.
Note: the positive half cycle for B starts 120 degrees after the positive half cycle for A phase, C starts 240 degrees after A.
Conduction
AC D i
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AC Drives
Sine Weighted PWM
AC D i
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AC Drives
Powering the Motor
Phase A
Phase B
Phase C
1 3 5
4 6 2
1,5 and 6 Conducting
AC D i
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AC DrivesPowering the Motor
Phase A
Phase B
Phase C
1 3 5
4 6 2
1,2 and 6 Conducting
AC Drives
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AC Drives
Phase A
Phase B
Phase C
1 3 5
4 6 2
Powering the Motor
1,2 and 3 Conducting
AC Drives
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AC Drives
Phase A
Phase B
Phase C
1 3 5
4 6 2
Powering the Motor
2,3 and 4 Conducting
AC Drives
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AC Drives
Phase A
Phase B
Phase C
1 3 5
4 6 2
Powering the Motor
3,4 and 5 Conducting
AC Drives
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AC Drives
Phase A
Phase B
Phase C
1 3 5
4 6 2
Powering the Motor
4,5 and 6 Conducting
AC Drives
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AC Drives
Phase A
Phase B
Phase C
1 3 5
4 6 2
Powering the Motor
1,5 and 6 Conducting
AC Drives
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AC Drives
Most Positve Phase Most Negative Phase "+" IGBT Conducting "-" IGBT Conducting Turn "On" Order
T1
T2T3
T4
T5
T6
T7T8
In summary, fill in the chart below using the diagrams provided. T1 through T8 represent frozen momentsin time, look at the phases along each time to see which one is most positive and negative. Then apply
what you know about the phases to the IGBT bridge and figure out which transistors are conducting.
Positive DC Buss Line
Negative DC Buss Line
Phase APhase BPhase C
Time
Skip
1 3 5
4 6 2
A & C B 1 & 5 6
A B & C1
6 & 2 2
A & B C 1 & 3 2 3
B C & A 3 2 & 4 4
B & C A 3 & 5 4 5
C A & B 5 4 & 6 6
C & A B 5 & 1 6 1A B & C 1 6 & 2 2
Transistor Conduction Order
AC Drives
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AC Drives
AC Motor
How To Change SPEED ??
1. By Changing Number of Poles Very Complicated and costly method,Linear Speed Change not Possible
2. By Changing Frequency of Input supply
AC Drives
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AC Drives
How To Change SPEED ??
RPM =120 x Applied Frequency
Number of Poles per Phase
e.g for a 4 POLE & 50 Hz FREQUENCY
120 X 50
RPM = ----------- = 1500
4
e.g for a 4 POLE & 30 Hz FREQUENCY
120 X 30
RPM = ----------- = 900
4
e.g for a 4 POLE & 60 Hz FREQUENCY
120 X 60
RPM = ----------- = 1800
4
e.g for a 4 POLE & 70 Hz FREQUENCY
120 X 70
RPM = ----------- = 2100
4
I need high speed machine operation
to increase my production ?
I Want to Control speed
and Save energy ?
AC Drives
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AC Drives
Speed Speed
0 750 1440
Base
1500
Sync
60 RPMSlip
N
Rotor Speed = Synchronous Speed - Slip Speed
Slip
AC Drives
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AC Drives
T = K x x ILine
V
F
2
In an AC motor, torque varies by:
Where : V/F proportional to Motor Flux
I is current drawn by the motor
PLAY WITH V/F RATIO TO GET HIGHER STARTING TORQUE
TORQUE Control
AC Drives
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AC Drives
Why Voltage varies as frequency is changed1). V/F proportionalRated (Motor Rated Flux)
If > Rated (What Happens?)
If < Rated (What Happens?)
2). Impedance/Reactance Issue
XL is dominant above 3-5
hertz
LZ XR
Ss
22+=
Since I =V/Z; If we increase or decrease the applied frequency we must also
increase or decrease the applied voltage accordingly.
fL2X L =
3). To keep the torque Constant as T V/F Ratio
AC Drives
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AC Drives
0
% Currentand
% Torque
Speed (RPM)
Current
200
400
600
500 900 1725 1800RPM
Torque
1750
100
Rated Torque
at rated FLA.
Synchronous
speed
Break down torque
(peak Torque)
Basespeed
Motor Operating Characteristics
Starting torque
(Break over Torque)
Starting Current
No LoadPull UP torque
(DIP Torque)
AC Drives
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AC Drives
400
300
200
100
00 20 40 60 80 100
Percent
Torque
Percent Synchronous Speed
Breakdown Torque
Operating Range
of Variable Frequency
Drives
Torque & Speed Curve without Drive
AC Drives
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AC Drives
% Currentand
% Torque Current Rated Torqueat rated FLA.
Break down torque
(peak Torque)
0
Speed (RPM)
200
500 900
1725
1800RPM
Torque
100
75RPM Slip75RPM Slip
Torque / Speed with drive applied
AC Drives
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AC Drives
0 to Twice Base Speed Operation
Torque
Speed (Multiple of Base)
Base
Peak
Rated
1.25 1.5 1.75 2
1
N2.64
.44
.33.25
CT range CHP
Tpeak =
AC Drives
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C es
Benefits from DrivesEnergy Saving Concept
AC Drives
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Benefits of VFD
Saves subst an t i a l ene rgy cost s ( due to d i rec t speed con t ro l )
I m p roves Process by sm oo th speed con t r o l
Save Ene rgy cost s by r educi ng m ax i m um u t i l i t y dem and
charges
I nc rease Li f e o f m echan i ca l equ i pm en t ( due t o so f t st a r t i ng )
Reduce Moto r s t ress ( l ow er hea t , v i b ra t i on , and t rans ien t
t o rques )
Low er chances o f Sys tem d i sru p t i ons ( by low e r i ng cu r ren t
in r u sh f r om 6 0 0% t o 10 0 -1 5 0% )
Su b st a n t i a l l y b r i n g s d o w n D ow n t i m e & M a in t e n a n ce co st s
AC Drives
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275
150
75
0
0
120
240
360
480
600
%Torque
%Current
150%-260%180%
115%
150%
600%
480%
600%
ACDrive
Full VoltageStarter
ReducedVoltage Starter
Solid State*(SMC)
ABC
C
B
A
* maximum shown,adjustable via digital switches
180%
Flexibility in Starting Current
Lower Investment in DG setsNo Penalty From Electricity Board
Benefits of VFD
AC Drives
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Benefits of VFD
ACCELERATION RANGE
0 15 3060 300
Seconds
Full Voltage
AC Drive (Adjustable)
(Load Dependent)
(Not Adjustable)
Reduced Voltage
Solid State
600
Smooth Start and perfect Control
Acceleration Time =
Where:
WK2 = Moment of inertia (lb-ft 2)
h N = Change in motor RPM
T = Torque required
308 = Constant
WK
2
x hN308 x T
AC Drives
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STOPPING CHOICES
CoastTime
Speed
SoftRampStop
DynamicBraking
DCInjection
Coast Soft Ramp D.B. DC Inj.
AC Drive X X X X X
Solid State X X
R.V. X
F.V. X
Benefits of VFD
AC Drives
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Complete Motor Protection
Complete Protection for motor
Against Over voltage Overload Motor Stalling Short Circuit
Transients Phase Loss I2t Protect ion to Motor
& so on .Just Nam e.
Benefits of VFD
AC Drives
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Drives Save Energy ?
AC Drives
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Phase A
Phase B
Phase C
PWM VFDPWM VFDAC InputAC Input
PowerPowerAC OutputAC Output
PowerPower
IInput Current is less than Output since Source Voltage is Constannput Current is less than Output since Source Voltage is Constantt
LLower demand on distribution systemower demand on distribution system
PPower Consumption is proportional to motor speedower Consumption is proportional to motor speed
Real & ReactiveReal & Reactive
motor currentmotor current
Real Current OnlyReal Current Only
Energy Saving Concepts
AC Drives
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Auto-Economizer - Extra Saving
Idle Mode Energy Saver
Reduced LoadAutomatically fold back Voltage to reduce motor flux
Energy Saving Concepts
A key in Press Applications - 3-5% Saving
AC Drives
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Energy Savings
High Efficiency (>97% )Improves Power Factor to 0.98Payback within 12 to 24 months for reduced energy consumption
An investment which pays back immediately !
Energy Saving Concepts
AC Drives
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Types of Loads & Energy SavingsVariable Torque (VT)
Constant Torque (CT)
Constant Power (CHP)
Non Motor Applications (NMA)
AC Drives
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HP PRESSURE * FLOW
PRESSURE
SPEEDFLOW
HP SPEED3
SPEED2
Variable Torque
AFFINITY LAW
Power (Speed)3
Torque (Speed)2
AC Drives
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Some Applications PUMPS
Chilled water pumps
Pressure boosting pumps
Cooling tower pumps
Wastewater pumps
Syrup pumps
FANS
Primary Air fans Return fans Cooling tower fans Ventilation fans
Dryer fans
ID / FD Fans
20 % REDUCTION IN SPEED REDUCES 45 % ENERGY CONSUMPTION
AC Drives
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Variable Torque
P2 = P1 X (N2/ N1)3
P2 = 100HP X (1200 / 1440)3P2 = 58HP
Power Saved = P1 P2 = 100-58
= 42HP
20 % REDUCTION IN SPEED REDUCES 45 % ENERGY CONSUMPTION
Multiply this quantity (42HP) by Time of operation and Cost/HP
and get the energy saving on a variable torque applicationsInstantly.
AC Drives
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To reduce the flow from 100% to60% , input power requirementsare reduced from
100 % to 62 %
Variable Inlet Vane ID Fan application
Saves 38%
Variable Torque
AC Drives
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To reduce the flow from 100% to60% , input power requirementsare reduced only from
100 % to 86 %
Outlet Damper
Saves 14%
Variable Torque
ID Fan application
AC DrivesV i bl T
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Reduction of flow from 100% to60% , results into Input power
requirements reduction from
100% to 22%
Variable Speed Drive
EnergySaved
Saves 78% of Energy
ID Fan application
Variable Torque
AC DrivesC t t T
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Power (Speed)
Torque is ConstantP = 2 X X N X T
Constant Torque
AC Drives
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Food processing equipment
Machine toolsConveyor equipment
Packaging machinery
Wood working machinery
Press and stamping
Winder
Some Applications
20 % REDUCTION IN SPEED REDUCES 20 % ENERGY CONSUMPTION
Wagon Tippler
Screw Feeder
Press and stamping
Crane/Hoists - Drive needsa special software
Lifts
Compressors
Etc.
AC Drives
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20 % SPEED REDUCTION SAVES 20 % ENERGY
Constant Torque
P2 = P1 X (N2/ N1)
P2 = 100HP X (1200 / 1440)P2 = 84HP
Power Saved = P1 P2 = 100-84
= 16HP
Multiply this quantity (16HP) by Time of operation and Cost/HP
and get the energy saving on a Constant torque applicationsInstantly.
AC DrivesConstant Power
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Power is Constant
Torque Decreases
Constant Power
Constant Power
ExamplesMixers
Spindles etc..
AC DrivesNon Motor Applications
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Non Motor Applications
Voltage and Fequency controlled separatelyV/F ratio not necessarily maintained
ExamplesResistive Heaters
Power SupplyInduction heatingVibrating Conveyorsetc..
AC DrivesSome of Best Features in our Drive
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Some of Best Features in our Drive Ambient Temperature of50 Degree C.
Flexible performance with ForceTM Feature
Upto 400% maximum torque can be achieved in closed loop
Meets IEEE 519 -1992 Standards
Built in DC Chokes to abate input Current Harmonics with 97.5% Efficiency
Power Devices having PIV of 1700V and Transient Protection of 6KV
Built in Software to control the effect of reflected wave
Built in EMC Filters and common mode core to address noise related issues. Conformity to EMC directives and european Standards.
Excellent Feature of Zero Stacking
PTC input to the Drive
Internal family of communications and HIM modules
7th IGBT Chopper is internally Provided
Offers 150% Overload for 60Seconds & 200% for 3 Seconds.
Complete Output Short Circuit Protection
Compact Size
Safe OffOption to Address Category 3 safe off Clause EN 954-1
AC Drives
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