Basics of Drives

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


AC Drives


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AC Drives

Phase A

Phase B

Phase C

1 3 5

4 6 2

Powering the Motor


AC Drives


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AC Drives

Phase A

Phase B

Phase C

1 3 5

4 6 2

Powering the Motor


AC Drives


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AC Drives

Phase A

Phase B

Phase C

1 3 5

4 6 2

Powering the Motor


AC Drives


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AC Drives

Phase A

Phase B

Phase C

1 3 5

4 6 2

Powering the Motor


AC Drives


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AC Drives

Phase A

Phase B

Phase C

1 3 5

4 6 2

Powering the Motor


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


120 X 30

RPM = ----------- = 900

4


120 X 60

RPM = ----------- = 1800

4


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


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 !


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


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


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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Basics of Drives

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